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We designed a prospective, observational study enrolling patients presenting for treatment of acute myeloid leukemia (AML) at 13 institutions to analyze associations between hematopoietic cell transplantation (HCT) and survival, quality of life (QOL), and function in: the entire cohort, those aged ≥65 years, those with high comorbidity burden, intermediate cytogenetic risk, adverse cytogenetic risk, and first complete remission with or without measurable residual disease. Patient were assessed 8 times over 2 years. Time-dependent regression models were used. Among 692 patients that were evaluable, 46% received HCT with a 2-year survival of 58%. In unadjusted models, HCT was associated with reduced risks of mortality most of the subgroups. However, after accounting for covariates associated with increased mortality (age, comorbidity burden, disease risks, frailty, impaired QOL, depression, and impaired function), the associations between HCT and longer survival disappeared in most subgroups. Although function, social life, performance status, and depressive symptoms were better for those selected for HCT, these health advantages were lost after receiving HCT. Recipients and nonrecipients of HCT similarly ranked and expected cure as main goal of therapy, whereas physicians had greater expectations for cure than the former. Accounting for health impairments negates survival benefits from HCT for AML, suggesting that the unadjusted observed benefit is mostly owing to selection of the healthier candidates. Considering patients’ overall expectations of cure but also the QOL burdens of HCT motivate the need for randomized trials to identify the best candidates for HCT. This trial was registered at www.clinicaltrials.gov as #NCT01929408.

We designed a prospective, observational study enrolling patients presenting for treatment of AML at 13 institutions to analyze associations between hematopoietic cell transplantation (HCT) and survival, quality of life (QOL), function and geriatric health, in 6 groups: 1) the entire cohort, 2) ≥65 years old, 3) high comorbidity burden, 4) intermediate cytogenetic-risk, 5) adverse cytogenetic-risk, and 6) first complete remission with or without measurable residual disease. Patient health and preferences were assessed eight times across 2 years. Time-dependent regression models were used. Among 692 evaluable patients, 46% received HCT with 2-year survival of 58%. In unadjusted models, HCT was associated with reduced risks of mortality in the entire group and most of the subgroups. However, after accounting for covariates associated with increased mortality (age, comorbidity-burden, disease risks, frailty, impaired QOL, depression, and impaired function), the associations between HCT and longer survival disappeared in all groups. While function, social life, performance status, and depressive symptoms were better for those selected for HCT compared to those who were not, these health advantages were lost after receiving HCT. Recipients and non-recipients of HCT similarly ranked and expected cure as main goal of therapy, while physicians expected more cure for the formers. Accounting for health impairments negate survival benefits from HCT for AML, suggesting that the unadjusted observed benefit is due mostly to selection of the healthier candidates. Considering patients' overall expectations of cure but also the QOL burdens of HCT motivate the need for randomized trials to identify the best candidates for HCT.

Minimal residual disease (MRD) has become an increasingly prevalent and important entity in multiple myeloma (MM). Despite deepening responses to frontline therapy, roughly 75% of MM patients never become MRD-negative to ≤10(−5), which is concerning because MRD-negative status predicts significantly longer survival. MM is highly heterogeneous, and MRD persistence may reflect survival of isolated single cells and small clusters of treatment-resistant subclones. Virtually all MM clones are exquisitely sensitive to radiation, and the α-emitter astatine-211 ((211)At) deposits prodigious energy within 3 cell diameters, which is ideal for eliminating MRD if effectively targeted. CD38 is a proven MM target, and we conjugated (211)At to an anti-CD38 monoclonal antibody to create an (211)At-CD38 therapy. When examined in a bulky xenograft model of MM, single-dose (211)At-CD38 at 15 to 45 µCi at least doubled median survival of mice relative to untreated controls (P < .003), but no mice achieved complete remission and all died within 75 days. In contrast, in a disseminated disease model designed to reflect low-burden MRD, 3 studies demonstrated that single-dose (211)At-CD38 at 24 to 45 µCi produced sustained remission and long-term survival (>150 days) for 50% to 80% of mice, where all untreated mice died in 20 to 55 days (P < .0001). Treatment toxicities were transient and minimal. These data suggest that (211)At-CD38 offers the potential to eliminate residual MM cell clones in low-disease-burden settings, including MRD. We are optimistic that, in a planned clinical trial, addition of (211)At-CD38 to an autologous stem cell transplant (ASCT) conditioning regimen may improve ASCT outcomes for MM patients.

Less-intensive induction therapies are increasingly used in older patients with acute myeloid leukemia (AML). Using an AML composite model (AML-CM) assigning higher scores to older age, increased comorbidity burdens, and adverse cytogenetic risks, we defined 3 distinct prognostic groups and compared outcomes after less-intensive vs intensive induction therapies in a multicenter retrospective cohort (n = 1292) treated at 6 institutions from 2008 to 2012 and a prospective cohort (n = 695) treated at 13 institutions from 2013 to 2017. Prospective study included impacts of Karnofsky performance status (KPS), quality of life (QOL), and physician perception of cure. In the retrospective cohort, recipients of less-intensive therapies were older and had more comorbidities, more adverse cytogenetics, and worse KPS. Less-intensive therapies were associated with higher risks of mortality in AML-CM scores of 4 to 6, 7 to 9, and ≥10. Results were independent of allogeneic transplantation and similar in those age 70 to 79 years. In the prospective cohort, the 2 groups were similar in baseline QOL, geriatric assessment, and patient outcome preferences. Higher mortality risks were seen after less-intensive therapies. However, in models adjusted for age, physician-assigned KPS, and chance of cure, mortality risks and QOL were similar. Less-intensive therapy recipients had shorter length of hospitalization (LOH). Our study questions the survival and QOL benefits (except LOH) of less-intensive therapies in patients with AML, including those age 70 to 79 years or with high comorbidity burdens. A randomized trial in older/medically infirm patients is required to better assess the value of less-intensive and intensive therapies or their combination. This trial was registered at www.clinicaltrials.gov as #NCT01929408.

Human herpesvirus 6 (HHV-6) species have a unique ability to integrate into chromosomal telomeres. Mendelian inheritance via gametocyte integration results in HHV-6 in every nucleated cell. The epidemiology and clinical effect of inherited chromosomally integrated HHV-6 (iciHHV-6) in hematopoietic cell transplant (HCT) recipients is unclear. We identified 4319 HCT donor-recipient pairs (8638 subjects) who received an allogeneic HCT and had archived pre-HCT peripheral blood mononuclear cell samples. We screened these samples for iciHHV-6 and compared characteristics of HCT recipients and donors with iciHHV-6 with those of recipients and donors without iciHHV-6, respectively. We calculated Kaplan-Meier probability estimates and Cox proportional hazards models for post-HCT outcomes based on recipient and donor iciHHV-6 status. We identified 60 HCT recipients (1.4%) and 40 donors (0.9%) with iciHHV-6; both recipient and donor harbored iciHHV-6 in 13 HCTs. Thus, there were 87 HCTs (2%) in which the recipient, donor, or both harbored iciHHV-6. Acute graft-versus-host disease (GVHD) grades 2-4 was more frequent when recipients or donors had iciHHV-6 (adjusted hazard ratios, 1.7-1.9; P = .004-.001). Cytomegalovirus viremia (any and high-level) was more frequent among recipients with iciHHV-6 (adjusted HRs, 1.7-3.1; P = .001-.040). Inherited ciHHV-6 status did not significantly affect risk for chronic GVHD, hematopoietic cell engraftment, overall mortality, or nonrelapse mortality. Screening for iciHHV-6 could guide donor selection and post-HCT risk stratification and treatment. Further study is needed to replicate these findings and identify potential mechanisms.

Many patients with hematologic malignancies cannot tolerate hematopoietic cell transplantation (HCT), whereas others may not have a compatible human leukocyte antigen-matched donor. To overcome these limitations, we optimized a conditioning regimen employing anti-CD45 radioimmunotherapy (RIT) replacing total body irradiation (TBI) before haploidentical HCT in a murine model. Mice received 200 to 400 μCi (90)Y-anti-CD45 antibody (30F11), with or without fludarabine (5 days starting day -8), with cyclophosphamide (CY; days -2 and +2) for graft-versus-host disease prophylaxis, and 1.5 × 10(7) haploidentical donor bone marrow cells (day 0). Haploidentical bone marrow transplantation (BMT) with 300 μCi (90)Y-anti-CD45 RIT and CY, without TBI or fludarabine, led to mixed chimeras with 81.3 ± 10.6% mean donor origin CD8(+) cells detected 1 month after BMT, and remained stable (85.5 ± 11% mean donor origin CD8(+) cells) 6 months after haploidentical BMT. High chimerism levels were induced across multiple hematopoietic lineages 28 days after haploidentical BMT with 69.3 ± 14.1%, 75.6 ± 20.2%, and 88.5 ± 11.8% CD3(+) T cells, B220(+) B cells, and CD11b(+) myeloid cells, respectively. Fifty percent of SJL leukemia-bearing mice treated with 400 μCi (90)Y-DOTA-30F11, CY, and haploidentical BMT were cured and lived >200 days. Mice treated with 200 μCi (90)Y-DOTA-30F11 had a median overall survival of 73 days, while untreated leukemic mice had a median overall survival of 34 days (P < .001, Mantel-Cox test). RIT-mediated haploidentical BMT without TBI may increase treatment options for aggressive hematologic malignancies.

α-Emitting radionuclides deposit a large amount of energy within a few cell diameters and may be particularly effective for radioimmunotherapy targeting minimal residual disease (MRD). To evaluate this hypothesis, (211)At-labeled 1F5 monoclonal antibody (mAb) (anti-CD20) was studied in both bulky lymphoma tumor xenograft and MRD animal models. Superior treatment responses to (211)At-labeled 1F5 mAb were evident in the MRD setting. Lymphoma xenograft tumor-bearing animals treated with doses of up to 48 µCi of (211)At-labeled anti-CD20 mAb ([(211)At]1F5-B10) experienced modest responses (0% cures but two- to threefold prolongation of survival compared with negative controls). In contrast, 70% of animals in the MRD lymphoma model demonstrated complete eradication of disease when treated with (211)At-B10-1F5 at a radiation dose that was less than one-third (15 µCi) of the highest dose given to xenograft animals. Tumor progression among untreated control animals in both models was uniformly lethal. After 130 days, no significant renal or hepatic toxicity was observed in the cured animals receiving 15 µCi of [(211)At]1F5-B10. These findings suggest that α-emitters are highly efficacious in MRD settings, where isolated cells and small tumor clusters prevail.

This study attempted to characterize causes of treatment failure, identify associated prognostic factors, and develop shorter-term end points for trials testing investigational products or regimens for second-line systemic treatment of chronic graft-versus-host disease (GVHD). The study cohort (312 patients) received second-line systemic treatment of chronic GVHD. The primary end point was failure-free survival (FFS) defined by the absence of third-line treatment, nonrelapse mortality, and recurrent malignancy during second-line treatment. Treatment change was the major cause of treatment failure. FFS was 56% at 6 months after second-line treatment. Lower steroid doses at 6 months correlated with subsequent withdrawal of immunosuppressive treatment. Multivariate analysis showed that high-risk disease at transplantation, lower gastrointestinal involvement at second-line treatment, and severe NIH global score at second-line treatment were associated with increased risks of treatment failure. These three factors were used to define risk groups, and success rates at 6 months were calculated for each risk group either without or with various steroid dose limits at 6 months as an additional criterion of success. These success rates could be used as the basis for a clinically relevant and efficient shorter-term end point in clinical studies that evaluate agents for second-line systemic treatment of chronic GVHD.

Whether the hematopoietic cell transplantation comorbidity index (HCT-CI) can provide prognostic information about development of acute graft-versus-host disease (GVHD) and subsequent mortality is unknown. Five institutions contributed information on 2985 patients given human leukocyte antigen-matched grafts to address this question. Proportional hazards models were used to estimate the hazards of acute GVHD and post-GVHD mortality after adjustment for known risk variables. Higher HCT-CI scores predicted increased risk of grades 3 to 4 acute GVHD (P < .0001 and c-statistic of 0.64), and tests of interaction suggested that this association was consistent among different conditioning intensities, donor types, and stem cell sources. Probabilities of grades 3 to 4 GVHD were 13%, 18%, and 24% for HCT-CI risk groups of 0, 1 to 4, and ≥5. The HCT-CI was statistically significantly associated with mortality rates following diagnosis of grade 2 (hazard ratio [HR] = 1.24; P < .0001) or grades 3 to 4 acute GVHD (HR = 1.19; P < .0001). Patients with HCT-CI scores of ≥3 who developed grades 3 to 4 acute GVHD had a 2.63-fold higher risk of mortality than those with scores of 0 to 2 and did not develop acute GVHD. Thus, pretransplant comorbidities are associated with the development and severity of acute GVHD and with post-GVHD mortality. The HCT-CI could be useful in designing trials for GVHD prevention and could inform expectations for GVHD treatment trials.

The success of HCT is highly dependent on the availability of compatible donors. Depending on ethnicity, fully HLA-matched donors cannot be identified for 25-84% of patients. In an effort to extend the use of HLA-mismatched donors to patients only eligible for NMA HCT, we previously demonstrated that engraftment and long-term survival can be achieved using CSP and MMF immunosuppression after HLA class I antigen-mismatched HCT (Nakamae et al, 2010). Based on this trial, we designed a phase II multi-center trial to assess the efficacy of GVHD prophylaxis with triple immune suppression with CSP, MMF and sirolimus after HLA class I or class II antigen mismatched NMA HCT (fludarabine 90mg/m2 and 2-3 Gy TBI). Patients ineligible for high-dose conditioning with only HLA class I or class II antigen mismatched donors available were eligible for inclusion. The primary objective was to determine whether the incidence of grades 2-4 acute GVHD can be reduced to less than the historical rate of 70% with the triple-immunosuppression. The evaluation was planned to be carried out separately among HLA class I and class II mismatched patients. Secondary objectives included day 100 non-relapse mortality (NRM) and grades 3-4 acute GVHD. CSP was started on day -3 and continued to day +150 and then tapered off by day +180. Sirolimus was started on day -3 through day +180 and then tapered off by day +365. MMF was given thrice daily from days 0 to +30 then twice daily to day +100 and tapered off by day +150. A total of 76 patients were enrolled and received conditioning with fludarabine and TBI followed by infusion of unmodified G-CSF mobilized peripheral blood stem cell (PBSC) grafts. The median age was 63 (21-76) years, and median follow-up of surviving patients was 47 (4-94) months. 51 (67%) and 25 (33%) of patients had HLA class I or II mismatches, respectively. Transplant demographics are summarized in Table 1. Sustained engraftment was observed in all but 1 (1%) patient with myeloproliferative disease who had autologous recovery after transplant. Median number of days with neutrophils < 500 cells/ml and platelets 95% donor) was achieved in 48% and 63% at days +28 and 84, respectively. Outcomes are summarized in Table 2.The cumulative incidence of grade 2-4 acute GVHD at day +100 was 34% in all patients (29% and 48% after HLA class I and class II mismatched, respectively; p=0.09) (Figure 1), with only 3% of patients experiencing grade 3 acute GVHD and no patients experienced grade 4 acute GVHD. NRM at day +100, 2 years and 4 years were 4%, 15% and 17%, respectively (HLA class I vs class II: p=0.58) (Figure 2). The 2- and 4-year cumulative incidences of chronic GVHD were 54% and 57% (HLA class I vs. class II: p=0.11). Relapse incidences at 2 and 4 years were 26% and 31% with no differences between the class I and II mismatched patients (p=0.54) (Figure 2). The cumulative incidences at 2 and 4 years of progression-free survival (PFS) were 59% and 52%, and overall survival (OS) were 68% and 62% with no differences between HLA class I and II mismatches for PFS or OS (p=0.64 and 0.90, respectively) (Figure 2). Compared to historical data from our previous trial using MMF and CSP prophylaxis alone in patients with HLA class I mismatches, the addition of sirolimus to GVHD prophylaxis with CSP/MMF improved outcomes both after HLA class I or class II mismatched HCT (Nakamae et al, 2010). In a comparison of HLA class I mismatches only, day +100 grade 2-4 acute GVHD was reduced from 69% in the historical cohort to 29% in the current trial. The relapse incidences were comparable, while 2-year NRM decreased from 47%, in historical controls, to 16%, and translated into improved OS from 26% to 67% at 2 years in the current study. No difference was observed in the incidence of chronic GVHD. Furthermore, in the current trial, similar results were seen using HLA class II mismatched donors, suggesting that the triple drug immunosuppression could be used with either type of mismatch. The current trial demonstrates that triple drug immunosuppression with CSP, MMF, and sirolimus is safe and effective in reducing both acute GVHD and NRM after NMA HCT with either HLA class I or class II antigen mismatched donors. Disclosures Maloney: Juno Therapeutics: Honoraria, Patents & Royalties: patients pending , Research Funding; Celgene,Kite Pharma: Honoraria, Research Funding; BioLine RX, Gilead,Genentech,Novartis: Honoraria; A2 Biotherapeutics: Honoraria, Other: Stock options . OffLabel Disclosure: In the current study cyclosporine, mycophenolate mofetil and sirolimus are used to prevent graft versus host disease after allogeneic hematopoietic cell transplantation. Fludarabine is used together with total body irradiation as at part of the conditioning prior to allogeneic hematopoietic cell transplantation.

Optimal post-remission therapy for adolescents and young adults (AYAs, 16-39 years) with Ph-negative (Ph-) acute lymphoblastic leukemia (ALL) in first complete remission (CR1) is not well established. We hypothesized that post-remission therapy with a pediatric-inspired regimen would yield superior outcomes to myeloablative allogeneic HCT for AYA patients with Ph- ALL in CR1. We compared overall survival (OS), disease-free survival (DFS), relapse, and non-relapse mortality (NRM) for patients receiving post-remission therapy on CALGB 10403 to a contemporary matched AYA cohort undergoing myeloablative allogeneic HCT in CR1 reported to the CIBMTR (Table). The allogeneic HCT cohort consisted of patients 16-39 years of age with Ph- ALL in CR1 undergoing myeloablative transplant from a matched sibling/relative or unrelated donor using peripheral blood or bone marrow stem cells between 11/2002 and 8/2012 in the United States. Patients receiving post-remission therapy with pediatric-inspired chemotherapy had superior OS (P Figure. Allogeneic HCT (HCT) vs. CALGB 10403 pediatric-inspired chemotherapy (chemo) after CR1: Adjusted (left-truncated) overall survival, disease-free survival, cumulative incidence of relapse, and cumulative incidence of non-relapse mortality. Disclosures Wieduwilt: Daiichi Sankyo: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Amgen, Leadiant, Merck, Servier: Research Funding; Reata Pharmaceuticals: Equity Ownership. Stock:Astellas: Membership on an entity's Board of Directors or advisory committees; Research to Practice: Honoraria; Kite, a Gilead Company: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Daiichi: Membership on an entity's Board of Directors or advisory committees; Agios: Membership on an entity's Board of Directors or advisory committees; UpToDate: Honoraria. Advani:Macrogenics: Research Funding; Abbvie: Research Funding; Pfizer: Honoraria, Research Funding; Amgen: Research Funding; Kite Pharmaceuticals: Consultancy; Glycomimetics: Consultancy, Research Funding. Luger:Ariad: Research Funding; Biosight: Research Funding; Celgene: Research Funding; Cyslacel: Research Funding; Daichi Sankyo: Honoraria; Genetech: Research Funding; Jazz: Honoraria; Kura: Research Funding; Onconova: Research Funding; Pfizer: Honoraria; Seattle Genetics: Research Funding; Agios: Honoraria. Larson:Novartis: Honoraria, Other: Contracts for clinical trials; Agios: Consultancy; Celgene: Consultancy. Tallman:Daiichi-Sankyo: Consultancy, Membership on an entity's Board of Directors or advisory committees; BioLineRx: Consultancy, Membership on an entity's Board of Directors or advisory committees; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Biosight: Research Funding; Nohla: Consultancy, Membership on an entity's Board of Directors or advisory committees; Orsenix: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; ADC Therapeutics: Research Funding; KAHR: Consultancy, Membership on an entity's Board of Directors or advisory committees; Cellerant: Research Funding; Tetraphase: Consultancy, Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees; Delta Fly Pharma: Consultancy, Membership on an entity's Board of Directors or advisory committees; UpToDate: Patents & Royalties; Oncolyze: Consultancy, Membership on an entity's Board of Directors or advisory committees; Rigel: Consultancy, Membership on an entity's Board of Directors or advisory committees. Kebriaei:Kite: Honoraria; Jazz: Consultancy; Amgen: Research Funding; Pfizer: Honoraria. Weisdorf:Pharmacyclics: Consultancy; Incyte: Research Funding; Fate Therapeutics: Consultancy.

Although some data (Scott, JCO 2017) suggest that myeloablative conditioning (MAC) is preferred for allogeneic hematopoietic cell transplantation (HCT) in acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS), these data were not informed by analysis of disease specific risk factors. We analyzed AML and MDS HCT outcomes stratified by the disease risk index (DRI) in order to identify the preferred transplant conditioning intensity (reduced-intensity conditioning [RIC] vs. MAC). In this large CIBMTR registry study we identified 4387 adult patients (age 40-65 years) who received HCT for AML (68%) or MDS (32%) between 2009 and 2015. DRI was stratified as low/ intermediate risk (1539 MAC and 999 RIC) and high/ very high risk (1121 MAC and 728 RIC). Examining the low/ intermediate risk DRI cohort (Table), RIC was associated with lower risk of TRM (HR=0.74, 95% CI 0.62-0.88; p In this large study of HCT for AML or MDS stratified by DRI, RIC was independent predictor of lower TRM, but significantly higher risk of relapse. The MAC was an independent predictor of lower relapse in both low/ intermediate and high/very high DRI groups. However, MAC only resulted in RFS benefit in the low/ intermediate group where the magnitude of impact on relapse was not offset by the higher TRM. In adults with AML or MDS aged 40-65 years, these data support MAC as the preferred conditioning intensity for low/ intermediate risk DRI, whereas MAC does not provide significant benefit in those with high/ very high risk DRI. Safer, yet still potent MAC regimens could benefit this higher risk group. Disclosures Bejanyan: Kiadis Pharma: Other: advisory board. Brunstein:Gamida: Research Funding; Astex: Research Funding; Magenta: Research Funding. Kebriaei:Amgen: Research Funding; Jazz: Consultancy; Pfizer: Honoraria; Kite: Honoraria; Pfizer: Honoraria; Kite: Honoraria. Weisdorf:Fate Therapeutics: Consultancy; Pharmacyclics: Consultancy; Incyte: Research Funding.

Background:Myeloablative allogeneic hematopoietic cell transplantation (HCT) is a common post-remission treatment strategy for medically fit adults with acute myeloid leukemia (AML) in morphologic remission. Several conditioning regimens have been utilized for this purpose, with ongoing controversy regarding the benefit of high-dose total body irradiation (TBI) in this setting. It is also unknown whether the relative value of TBI- versus non-TBI-based myeloablative conditioning differs for patients presenting with measurable residual disease (MRD) at the time of HCT from those in MRDnegremission. These open questions prompted us to compare outcomes among a large cohort of adult AML patients in MRDposand MRDnegremission who had myeloablative allogeneic HCT at our institution. Patients and Methods:We retrospectively studied 387 consecutive adults ≥18 years with AML in first or second morphologic remission (i.e. Results: Fifty-eight of the 387 patients (15%) received high-dose (HD; ≥12 Gy) TBI-based conditioning (HD-TBI/Cy [n=32], HD-TBI/thiotepa/Flu [n=22], HD-TBI±Flu [n=4]). Regimens for the other 329 patients included Bu/Cy [n=160], Bu/Flu [n=72], and treosulfan/Flu±low-dose TBI [n=97]. Patients receiving HD-TBI conditioning were younger (median: 33 [range: 18-58] vs. 51 [18-70] years, p Conclusion:For adults with AML undergoing myeloablative allogeneic HCT in morphologic remission, our analyses found no differences in survival and relapse risks between patients who received HD-TBI and those who received non-HD-TBI containing conditioning. Considering the known late effects of HD-TBI, non HD-TBI regimens should be used preferentially. Figure Disclosures Othus: Celgene: Membership on an entity's Board of Directors or advisory committees; Glycomimetics: Membership on an entity's Board of Directors or advisory committees. Walter:Aptevo Therapeutics: Consultancy, Research Funding; Argenx BVBA: Consultancy; Astellas: Consultancy; BioLineRx: Consultancy; BiVictriX: Consultancy; Boehringer Ingelheim: Consultancy; Boston Biomedical: Consultancy; Kite Pharma: Consultancy; New Link Genetics: Consultancy; Pfizer: Consultancy, Research Funding; Race Oncology: Consultancy; Seattle Genetics: Research Funding; Covagen: Consultancy; Daiichi Sankyo: Consultancy; Agios: Consultancy; Amgen: Consultancy; Amphivena Therapeutics: Consultancy, Equity Ownership; Jazz Pharmaceuticals: Consultancy.

Patients who develop therapy-related myelodysplastic syndromes (t-MDSs) or acute myeloid leukemia (t-AML) following prior chemotherapy or an autologous hematopoietic cell transplant (HCT), have a poor prognosis. An earlier analysis of allogeneic HCT (n=868, 1990-2004) showed 5-year overall survival (OS) and disease free survival (DFS) were 22% and 21% (reference). Furthermore, older age, graft source other than a HLA-matched sibling or HLA well matched unrelated donor (URD), t-AML not in remission or advanced t-MDS, and poor risk cytogenetics were associated with worse outcomes. Modern supportive care and conditioning regimens including reduced intensity (RIC) regimens may have improved outcomes. Therefore we analyzed 1531 HCT for t-AML (n = 772) or t-MDS (n = 759) performed from 2000 to 2014. The median age at transplant was 52 (18-77) for t-AML and 59 (18-74) for t-MDS. Eleven percent of patient with t-AML and 24% of patient with t-MDS had a prior autologous transplant. A myeloablative regimen was used for conditioning in 61% of patients with t-AML and 49% of patients with t-MDS (Table 1). For t-AML, the 5-year non-relapse mortality (NRM) and relapse rates (RR) were 33% (95% confidence interval [CI], 30-36) and 43% (40-47), respectively. For t-MDS, the 5 year TRM and RR were 32% (29-36) and 46% (43-50), respectively. Five year DFS and OS were 24% (21-27) and 25% (22-28), respectively, for patients with t-AML. Five year DFS and OS were 21% (18-24) and 27% (23-31), respectively, for patients with t-MDS. In multivariate analysis, t-AML OS and DFS was worse for: previous autologous transplant, relapsed disease at HCT, intermediate or adverse cytogenetics, partially matched and cord blood grafts, and RIC. For t-MDS: age greater than 60, previous autologous transplant, very high IPSS score, and use of HLA-partially matched unrelated grafts. A significant minority of patients with t-AML and t-MDS can achieve long-term remission with allogeneic HCT, yet risks of both NRM and relapse are still excessive. Relapse is the major cause of treatment failure. Disclosures Metheny: Takeda: Speakers Bureau; Incyte: Speakers Bureau. Weisdorf:Incyte: Research Funding; Fate Therapeutics: Consultancy; Pharmacyclics: Consultancy. Kebriaei:Jazz: Consultancy; Amgen: Research Funding; Pfizer: Honoraria; Kite: Honoraria.

Introduction: AML patients with intermediate or high-risk features often undergo allogeneic hematopoietic cell transplantation (alloHCT) during first complete remission (CR). The 2017 European LeukemiaNet guidelines for AML specify categories of CR: both with and without count recovery (CR vs. CRi) and with and without measurable residual disease (MRD). Previous smaller retrospective studies have suggested poorer survival outcomes after alloHCT for patients with responses less than CR. Methods: Eligible cases were determined using the CIBMTR registry. Each had AML in CR1, was ≥ 18 years, and underwent alloHCT between January 1, 2007 and December 31, 2015. MRD was defined based on the answers to qualitative questions on standard clinical reporting forms that ask if the patient is in either molecular or cytogenetic remission and if disease is detected in marrow by flow cytometry at time of HCT. The primary outcome was overall survival (OS), and secondary outcomes were non-relapse mortality (NRM), relapse and disease-free survival (DFS). The Kaplan-Meier method was used to estimate survival and cumulative incidence function was used to estimate relapse and NRM. Multivariable analysis (MVA) was performed using the Cox proportional hazards model to adjust for patient-, disease-, and transplant-related factors. Adjusted probabilities of DFS and OS, adjusted cumulative incidence curves of NRM and relapse were generated from final Cox regression models stratified on CR vs. CRi and weighted averages of covariate values using pooled sample proportion as weight function. Results: We identified 2492 cases (CR, n=1799; CRi, n=693). The main effect variable (CR vs. CRi) was missing in 262 additional patients; these patients were excluded when univariate analysis confirmed no significant associations, suggesting a random distribution of missing data. Patient characteristics are summarized in Table 1. Compared with patients with CR, patients with CRi were more likely to have a Karnofsky score Conclusions: Analysis of this large CIBMTR cohort demonstrates that survival outcomes differ among AML patients nominally in CR at the time of alloHCT. Patients with CRi and/or MRD have significantly shorter OS after alloHCT compared to those in CR, as well as shorter DFS and higher NRM. Further studies should focus on limiting NRM and reducing relapse to optimize post-alloHCT outcomes for patients with responses less than CR. Disclosures Percival: Pfizer Inc.: Research Funding; Nohla Therapeutics: Research Funding; Genentech: Membership on an entity's Board of Directors or advisory committees. Kebriaei:Jazz: Consultancy; Pfizer: Honoraria; Amgen: Research Funding; Kite: Honoraria. Weisdorf:Fate Therapeutics: Consultancy; Incyte: Research Funding; Pharmacyclics: Consultancy.

This study attempted to characterize causes of treatment failure, identify associated prognostic factors, and develop shorter-term end points for trials testing investigational products or regimens for second-line systemic treatment of chronic graft-versus-host disease (GVHD). The study cohort (312 patients) received second-line systemic treatment of chronic GVHD. The primary end point was failure-free survival (FFS) defined by the absence of third-line treatment, nonrelapse mortality, and recurrent malignancy during second-line treatment. Treatment change was the major cause of treatment failure. FFS was 56% at 6 months after second-line treatment. Lower steroid doses at 6 months correlated with subsequent withdrawal of immunosuppressive treatment. Multivariate analysis showed that high-risk disease at transplantation, lower gastrointestinal involvement at second-line treatment, and severe NIH global score at second-line treatment were associated with increased risks of treatment failure. These three factors were used to define risk groups, and success rates at 6 months were calculated for each risk group either without or with various steroid dose limits at 6 months as an additional criterion of success. These success rates could be used as the basis for a clinically relevant and efficient shorter-term end point in clinical studies that evaluate agents for second-line systemic treatment of chronic GVHD.

Strategies to prevent active infection with certain double-stranded DNA (dsDNA) viruses after allogeneic hematopoietic cell transplantation (HCT) are limited by incomplete understanding of their epidemiology and clinical impact. We retrospectively tested weekly plasma samples from allogeneic HCT recipients at our center from 2007 to 2014. We used quantitative PCR to test for cytomegalovirus, BK polyomavirus, human herpesvirus 6B, HHV-6A, adenovirus, and Epstein-Barr virus between days 0 and 100 post-HCT. We evaluated risk factors for detection of multiple viruses and association of viruses with mortality through day 365 post-HCT with Cox models. Among 404 allogeneic HCT recipients, including 125 cord blood, 125 HLA-mismatched, and 154 HLA-matched HCTs, detection of multiple viruses was common through day 100: 90% had ≥1, 62% had ≥2, 28% had ≥3, and 5% had 4 or 5 viruses. Risk factors for detection of multiple viruses included cord blood or HLA-mismatched HCT, myeloablative conditioning, and acute graft-versus-host disease (P values < .01). Absolute lymphocyte count of

Clonal cytogenetic abnormalities are a major risk factor for relapse after hematopoietic cell transplantation (HCT) for myelodysplastic syndrome (MDS). We determined the impact of the recently established 5-group cytogenetic classification of MDS on outcome after HCT. Results were compared with the impact of the International Prognostic Scoring System (IPSS) 3 cytogenetic risk groups, and the additional effect of a monosomal karyotype was assessed. The study included data on 1007 patients, 1-75 years old (median 45 years), transplanted from related (n = 547) or unrelated (n = 460) donors. Various conditioning regimens were used, and marrow, peripheral blood, or cord blood served as stem cell source. Both IPSS and 5-group cytogenetic risk classifications were significantly associated with post-HCT relapse and mortality, but the 5-group classification discriminated more clearly among the lowest- and highest-risk patients. A monosomal karyotype tended to further increase the rates of relapse and mortality, even after considering the IPSS or 5-group classifications. In addition, the pathologic disease category correlated with both relapse and mortality. Mortality was also impacted by patient age, donor type, conditioning regimen, platelet count, and etiology of MDS. Although mortality declined significantly in recent years, novel strategies are needed to overcome the barrier of high-risk cytogenetics.

Background: There is limited data comparing the outcomes of the two most common (FM or FB) RIC regimens in AML. Previous smaller retrospective studies suggest increased non-relapse mortality (NRM) but decreased relapse with FM based RIC with a variable effect on overall survival as compared to FB. Methods: AML patients aged ≥18 years who had their 1st allo HCT using FM or FB (iv Bu only) RIC between 2001-2015 who had data reported to CIBMTR were studied. Patients with cord blood or identical twin donors, TBI as a part of conditioning, GVHD prophylaxis with T cell depletion/CD34 selection or post HCT Cyclophosphamide were excluded. Primary endpoint was overall survival (OS), and secondary endpoints included non-relapse mortality (NRM), relapse, leukemia free survival (LFS) and acute and chronic GVHD. Cox proportional hazards multivariable regression was used to compare the two RIC regimens while adjusting for significant patient, disease and transplant related factors. Major subgroup analysis included patients in CR pre-HCT. Results: 622 patients received FB and 791 had FM RIC. Median age of the FM group was 59 years, range (18 to 76) and median age of FB group was 61 years, range (18- 77). Compared to FB RIC regimen, FM group had more patients with active disease (36% vs 18%), with mismatched donors (24% vs 15%), with bone marrow grafts (19% vs 9%), HCT before 2005 (29% vs 12%) and without ATG/alemtuzumab (58 % vs 48%); but fewer patients in CR1 (46% vs 62%) and matched sibling donor grafts (21% vs 30%). There was significantly increased NRM in the FM vs FB within 3 mo post HCT (hazard ratio (HR)=3.85 (95% confidence intervals [CI] 2.46-6.03), but not beyond 3 mo FM vs FB , HR= 1.14 (95% CI 0.88-1.47). There was significantly decreased relapse for FM vs FB, (HR=0.65 (0.55-0.76), p Conclusion: The current study of this large CIBMTR AML transplant cohort has showed that in these two most common RIC regimens for allogeneic HCT, long-term survival with FM was similar to FB. While the FM regimen showed higher early NRM, it was associated with lower risks of relapse. Further analysis to evaluate FB and FM regimens in relationship to comorbidities, comprehensive geriatric assessments, and presence of minimal residual disease is warranted to better define the relative efficacy of these two RIC regimens in AML. Disclosures Weisdorf: Pharmacyclics: Consultancy; Seattle Genetics: Consultancy; SL Behring: Consultancy; FATE: Consultancy; Equillium: Consultancy.

Although HCT offers the best potential for cure for patients with high risk leukemia and MDS, the procedure may not be an option for all patients due to the toxicity of the conditioning regimen. Reduced-intensity conditioning (RIC) allo-HCT regimens are associated with lower non-relapse mortality (NRM), but patients receiving these regimens have a higher risk of relapse. Radioimmunotherapy (RIT) can potentially deliver high doses of targeted radiation while minimizing toxicity to normal tissue. When combined with RIC allo-HCT, RIT may improve responses without increasing toxicity associated with myeloablative conditioning. We evaluated the safety and efficacy of yttrium 90 (90Y)-anti-CD45 antibody (MAb; BC8) followed by a standard RIC regimen with fludarabine (Flu) and 2 Gy total body irradiation (TBI) as a means of developing an improved HCT strategy for high-risk acute leukemia or MDS patients. We used CD45 as a target due to its ubiquitous expression on hematopoietic stem cells including the leukemic blasts. We used the high-energy (2.2 MeVmax) beta-emitter 90Y, which has a relatively short half-life (2.7 days) to eliminate targeted malignant cells. This phase I dose-escalation trial (NCT01300572) was designed to estimate the safety, feasibility and maximum tolerated dose (MTD) of 90Y-BC8-DOTA MAb when combined with Flu and 2 Gy TBI followed by HLA‐matched, related or unrelated allo-HCT for patients with high-risk leukemia or MDS. The MTD was defined as the radiation absorbed dose delivered by 90Y-BC8-DOTA MAb associated with a true dose-limiting toxicity (DLT) rate of 25%, where a DLT is defined as Bearman grade III/IV regimen-related toxicity. Doses of 90Y were escalated in increments of 2 Gy depending on the occurrence of DLT. Inclusion required patients to have advanced leukemia or high-risk MDS (defined as primary refractory or relapsed AML/ALL, secondary AML, MDS expressed as RAEB or CMML). To determine the dose of 90Y-BC8-DOTA, patients first underwent a biodistribution step using a trace-labeled infusion of 111Indium (111In)-BC8-DOTA followed by gamma-camera imaging. On pre-HCT day -12, patients received 90Y-BC8-DOTA at a prescribed radiation dose calculated from the trace-labeled 111In-BC8-DOTA biodistribution, followed by Flu (30 mg/m2/day) on days -4 to -2. TBI (2 Gy) was administered on day 0, prior to G-CSF mobilized donor PBSC infusion. GVHD prophylaxis consisted of mycophenolate mofetil and cyclosporine. Fifteen patients, median age of 62 (range 37-76), were treated (10 with advanced AML, 5 with high-risk MDS). At time of HCT, 9 patients had refractory active disease while 6 were in remission with minimal residual disease (Table 1). The patients received 22.8 to 151.2 mCi of 90Y, delivering an average of 10.5 Gy to marrow, 70 Gy to spleen, and 17 Gy to liver. Although a maximum dose of 28 Gy was delivered to the liver, no DLT was observed. Therefore, the MTD could not be estimated. Treatment led to complete remission in 13 patients (87%), 2 patients had persistent disease after HCT. All patients engrafted with a median donor-derived CD3 and CD33 chimerism both 100% by day 28 after HCT. Ten patients (67%) developed grade II-IV acute GVHD (grade II: n=7; III: n=2; IV: n=1). Five patients (33%) developed chronic GVHD. Six patients relapsed, 5 of whom subsequently died due to progression of disease. The median time to relapse among these 6 patients was 59 days (range, 6- 351 days). One patient died from stage IV steroid-refractory GVHD. One patient died in remission from acute renal failure at 7 months after HCT. Eight patients (53%) are surviving with a median follow-up of 1.8 (range, 0.9-5.9) years. Estimated overall survival at one and two years were 66% and 46%, respectively, with progression-free survival estimated to be 46% at each of these time points. The 1-year estimate of relapse was 41% (Fig. 1). The inclusion of 90Y-BC8-DOTA into a RIC allo-HCT regimen is feasible, tolerable and no DLTs were observed. The efficacy of this approach is promising considering the high-risk leukemia/MDS patients with active disease enrolled. Current studies are evaluating the use of an alpha emitter, astatine-211, which is short-lived (t ½ = 7.2 hours) and provides high-energy radiation, conjugated to anti-CD45 MAb BC8 as part of an HCT conditioning regimen for patients with advanced AML, ALL, or high-risk MDS, in place of 90Y with the goal of continuing to improve outcomes using RIT for allo-HCT (NCT03128034). Disclosures Orozco: Actinium Pharmaceuticals: Research Funding. Green:Juno Therapeutics: Patents & Royalties, Research Funding. Gopal:Incyte: Consultancy; Pfizer: Research Funding; Gilead: Consultancy, Research Funding; Teva: Research Funding; Aptevo: Consultancy; Merck: Research Funding; Janssen: Consultancy, Research Funding; Spectrum: Research Funding; Takeda: Research Funding; BMS: Research Funding; Seattle Genetics: Consultancy, Research Funding; Brim: Consultancy; Asana: Consultancy. Pagel:Pharmacyclics, an AbbVie Company: Consultancy; Gilead: Consultancy.

Introduction: Survival rates continue to improve after allogeneic HCT (Gooley et al, NEJM, 2013). Population-based studies also indicate overall improvement in survival of older (60-80 years old) AML patients (pts) (Bower, Blood Cancer Journal, 2016). Yet, only a small minority (6%-8%) of them receive HCT (Medeiros, Ann Hematol. 2015). Given these potentially incongruent findings and the changing face of survival in AML, we designed the first prospective multi-center longitudinal study dating from first presentation of adults with AML to be treated at one of 13 different referral centers that provide both AML treatment and HCT. We compared survival according to whether or not pts received HCT at later time points. Methods: We enrolled 695 pts (Table 1). Data on demographics, AML status, cytogenetic risks per European Leukemia Network (ELN), and response; age; comorbidities per the HCT-comorbidity index (CI); function including activities of daily living (ADL); frailty; geriatric assessment including cognition; QOL including the Functional Assessment of Cancer Therapy-Bone Marrow Transplant Scale (FACT-BMT), Euro-QOL 5-Dimension scale, ENRICHD Social Support Instrument, Social Activity Log, and Patient Health Questionnaire 9-item Depression Scale (PHQ-9) were collected at enrollment and at 1, 3, 6, 9, 12, 18, and 24 months thereafter. We used time-dependent Cox regression analyses to identify baseline and time-dependent risk factors associated with mortality in the overall population. The factors identified as significantly associated with mortality (p Results: Median follow-up was 16.8 months (range 0.1-52.4). In the initial multivariate analyses, the following were identified as significantly associated with an increased risk of mortality (Table 2): HCT-CI scores ≥5 (p Survival after HCT was 58% at 2-years. Initial unadjusted analyses showed significantly lower risks of mortality in association with receiving allogeneic HCT (p=0.0003). These findings were similar in pts with intermediate (p=0.0005) or unfavorable (p However, in the adjusted models, the advantage of HCT in reducing mortality rates was lost both in the overall population (p=0.21, see figure) as well as in the other groups (p>0.54, 0.40, and 0.51, respectively, Table 3). Formal tests of interactions (Table 3) showed no statistically compelling evidence that the association of HCT and mortality varies with respect to the timing of mortality or to the underlying ELN risk. Conclusions: In a prospective observational study, adjusting for key AML-specific and pt-specific variables negated the observed benefit of HCT over non-HCT therapies in reducing mortality rates among AML pts. Our results might reflect 1) improvement in supportive care and non-HCT therapies, 2) a relatively high non-relapse mortality early after HCT and the need for longer follow-up to demonstrate an adjusted benefit of HCT, and 3) the high selectivity of the transplant eligibility process, as we accounted here for variables that are often ignored in "genetic assignment" randomized studies (i.e. comorbidities and function). New randomized trials are needed; however, these trials have to be more inclusive of vulnerable pts and measure pt-specific variables. Trials focusing on reducing burden of comorbidities, frailty and poor function are needed alongside trials to treat AML with or without HCT. Disclosures Gerds: Celgene: Consultancy; Apexx Oncology: Consultancy; CTI Biopharma: Consultancy; Incyte: Consultancy. Shami:JSK Therapeutics: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Baston Biologics Company: Membership on an entity's Board of Directors or advisory committees; Lone Star Biotherapies: Equity Ownership; Pfizer: Consultancy. Rizzieri:Teva: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Jazz: Consultancy, Membership on an entity's Board of Directors or advisory committees; Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Arog: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy; Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Wang:Amgen: Consultancy; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees; Jazz: Speakers Bureau; Novartis: Speakers Bureau; Novartis: Speakers Bureau; Amgen: Consultancy; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Jazz: Speakers Bureau; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees. Faderl:Jazz Pharmaceuticals: Employment, Equity Ownership. Koprivnikar:Alexion: Consultancy, Speakers Bureau; Amgen: Speakers Bureau; Otsuka: Consultancy. Sekeres:Opsona: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Opsona: Membership on an entity's Board of Directors or advisory committees. Becker:GlycoMimetics: Research Funding.

Background: Patients with acute myeloid leukemia (AML) admitted to the ICU have high in-hospital mortality, ranging from 40-70% (Halpern A, JAMA Oncology, 2017, 3; 374 and Thakkar SG, Cancer, 2008, 112; 2233). A model that considers AML-specific as well as ICU-specific variables could be of great value to identify critically ill patients likely to survive beyond hospital discharge and would help providers frame goals of care discussions. The AML Composite Model (AML-CM) was recently developed to predict early as well as late mortality after diagnosis of AML (Sorror ML, JAMA Oncology, 2017, 3:1675). The AML-CM incorporates AML cytogenetic risk, age, and comorbidity burden. It is unknown whether the AML-CM scores calculated at diagnosis of AML could add prognostic value to variables collected at the time of admission to ICU. To this end, we investigated the predictive value of AML-CM scores at diagnosis in addition to other risk factors including traditional ICU markers of illness severity collected from the time of ICU admission for prediction of 90-day mortality in patients with AML. Methods: This is a retrospective study of 218 patients with AML admitted to an ICU at one of two affiliated referral hospitals at any time during or after the initiation of chemotherapy between 2008 and 2017. We used factors from three time points: 1) initial diagnosis: sex, race, and AML-CM; 2) time of ICU admission: age, presence of relapsed or refractory disease, history of hematopoietic stem cell transplant (HCT), presence of neutropenia with ANC Results: The final study population was 217 patients, because one patient was lost to follow-up. The median age at ICU admission was 59 (range 19-83), 58% were male, and 79% were white. Mortality was 52% at 90 days. The median AML-CM was 7 (interquartile range 5-10), with 54% having AML-CM ≥7, and 46% having AML-CM The results of the univariate and multivariable analyses are listed in Table 1. The following variables were independently associated with 90-day mortality in the multivariate analysis: AML-CM ≥ 7 was associated with 3.6 times the odds of dying (95% CI 1.9-6.8, p=0.0001); IMV, 4.8 times the odds of dying (95% CI 2.2-10.5, p The AUC of the multivariable model which combined the 5 variables with statistically significant association on univariate analysis was 0.77. Based on results above, we calculated 90-day mortality rates among patients with 0 (n=39), 1 (n=84), 2 (n=75), and 3-4 (n=19) of the following factors: AML-CM ≥7, history of HCT, relapsed or resistant/refractory disease at ICU admission, and use of IMV (figure 1). Mortality rates at 90 days were 10%, 48%, 68%, and 95%, respectively. Conclusions: We identified 4 risk factors that show promise in predicting 90-day mortality after ICU admission in patients with AML: the AML-CM from time of diagnosis, history of HCT prior to ICU admission, disease status at ICU admission, and use of invasive mechanical ventilation within 24 hours of admission. Collectively, these factors can provide strong rationale to consider futility of ICU care among those with 3-4 risk factors, who represent ~9% of the population and have an extremely high risk of mortality at 90 days. Further, patients with 1-2 risk factors (73% of population) could be good candidates for early palliative care consult coincident with ICU admission given relatively high mortality risk within 90 days. Disclosures Becker: GlycoMimetics: Research Funding.

Introduction: Acute myeloid leukemia (AML) is most frequently diagnosed in older patients (pts), whose median survival is less than 1 year. Allogeneic hematopoietic cell transplantation (HCT) is a potentially curative treatment. However, older pts often have significant comorbidities and other geriatric health problems, and the effect of these on the probability of receiving HCT is unknown. To this end, we designed a prospective, multi-center, longitudinal, observational study dating from first presentation of adult pts with AML to be treated at one of 13 different referral centers that provide both AML treatment and HCT. We examined the effects of different variables (see methods) on the probability to 1) survive long enough to receive HCT and 2) to receive HCT if such survival occurred. Methods: We enrolled 695 pts (Table 1). Data on demographics, AML status, cytogenetic risks per European Leukemia Network (ELN), and response; age; comorbidities per the HCT-comorbidity index (CI); function including instrumental activities of daily living (IADL) and activities of daily living (ADL); frailty including walk test; geriatric assessment (GA) including cognition; Karnofsky performance status (KPS); QOL including the Functional Assessment of Cancer Therapy-Bone Marrow Transplant Scale (FACT-BMT), Euro-QOL 5-Dimension scale (EQ-5D), ENRICHD Social Support Instrument, Social Activity Log, and Patient Health Questionnaire 9-item Depression Scale (PHQ-9) were collected at enrollment and at 1, 3, 6, 9, 12, 18, and 24 months thereafter. High-risk myelodysplastic syndromes (MDS) receiving AML-like therapy were included. We used competing risk Cox regression analyses, treating HCT as the event of interest and death without HCT as a competing risk, with staggered entry (left truncation) at time of consent. Associations between variables were assessed both at enrollment and over time. Results: The overall rate of HCT at 9 months after enrollment was 43% (Figure 1) and 92% of pts who received HCT did so by the 9 month mark. In multivariate analyses, death without HCT (Table 2) was associated with augmented HCT-CI scores ≥5 (HR:2.11, p Among survivors (Table 3), low likelihood to receive HCT was associated with age ≥70 years (HR:0.40, p=0.0001), low ELN risk (HR:0.28, p Conclusions: In a prospective, observational, multi-center study, increasing age, comorbidity burden, ELN risk, low-intensity initial AML induction regimen, depression, and functional dependence increase risks of early mortality without HCT. In those who survived long enough to potentially receive HCT, age up to 69 years and/or multiple comorbidities were not found to be barriers to HCT, likely reflecting the widespread use of reduced-intensity conditioning regimens. However, the independent sharp decline in receipt of HCT in pts aged 70-80 years suggests continued bias, although pts in this age group have been shown to derive similar benefit from HCT as younger pts. Use of objective comorbidity and GA tools rather than age per se to decide on HCT is encouraged. The adverse impact of impairments in psychological health and function on survival and of impairments of cognition, geriatric health, and performance status on receipt of HCT emphasize the need for interventions that target these health limitations in conjunction with AML treatment to improve outcomes. Finally, the benefit of intensive vs. less-intensive induction therapies should be addressed with a randomized trial. Disclosures Gerds: Celgene: Consultancy; Apexx Oncology: Consultancy; Incyte: Consultancy; CTI Biopharma: Consultancy. Shami:Lone Star Biotherapies: Equity Ownership; Baston Biologics Company: Membership on an entity's Board of Directors or advisory committees; JSK Therapeutics: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy. Rizzieri:Arog: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees; Teva: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Jazz: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees. Wang:Novartis: Speakers Bureau; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy; Jazz: Speakers Bureau; Novartis: Speakers Bureau; Amgen: Consultancy; Jazz: Speakers Bureau; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees. Faderl:Jazz Pharmaceuticals: Employment, Equity Ownership. Koprivnikar:Amgen: Speakers Bureau; Otsuka: Consultancy; Alexion: Consultancy, Speakers Bureau. Sekeres:Celgene: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Opsona: Membership on an entity's Board of Directors or advisory committees; Opsona: Membership on an entity's Board of Directors or advisory committees. Becker:GlycoMimetics: Research Funding.

INTRODUCTION: Emerging data indicate myeloid-derived suppressor cells (MDSCs) adversely impact outcomes of patients with a variety of malignancies. However, it is less clear how MDSCs affect acute myeloid leukemia (AML) disease biology or the response of AML patients to treatment. Here, we studied a cohort of people with AML undergoing hematopoietic cell transplantation (HCT) in first complete remission (CR1) to examine the relationship between the monocytic subtype of MDSCs (M-MDSCs), pre-transplant measurable residual disease (MRD) status, and outcome after HCT. PATIENTS AND METHODS: Adults ≥18 years of age were included if they underwent first allogeneic HCT with myeloablative or nonmyeloablative conditioning for AML in CR1 from April 2006 until October 2014. Prospective MRD testing in bone marrow aspirates was performed routinely via 10-color multiparameter flow cytometry (MFC) as part of the pre-transplant work-up. Pre-transplant MFC data were used retrospectively to quantify M-MDSCs as the proportion of monocytes (identified by side scatter properties and CD14 positivity) with low or negative expression of HLA-DR. M-MDSC frequency was then expressed as a percentage of the total number of viable cells in the sample. Available combinations of antigens measured by MFC did not allow for the identification of other MDSC subsets (e.g. granulocytic MDSCs). RESULTS: We identified 349 adults undergoing allogeneic HCT for AML in CR1 for whom pre-transplant MRD testing was performed and for whom follow-up data were available. Of these, 8 had to be excluded because of insufficient MFC events available for identification of M-MDSCs. In the remaining 341 patients, M-MDSC frequency ranged from The median follow-up time after HCT among all survivors was 5.8 (range, 2.0-11.4) years. The time was slightly longer for survivors with lower compared to those with higher M-MDSC frequency (6.1 [range 2.6-11.4] vs. 5.1 [range 2.0-11.3] years; p=0.0076). Stratified by the median M-MDSC frequency, the 3-year estimates of overall survival were similar for patients with lower and higher pre-HCT M-MDSCs (58.2% [95% confidence interval 50.4-65.2%] vs. 57.6% [49.8-64.7%]), as were 3-year estimates for relapse free survival (53.5% [45.7-60.7%] vs. 48.3% [40.6-55.6%]), 3-year estimates of the cumulative incidence of relapse (31.8% [24.9-38.8%] vs. 34.6% [27.6-41.8%]), and 3-year estimates of non-relapse mortality (14.7% [9.9-20.5%] vs. 17.0% [11.8-23.0%]). Analyses restricted to the subset of patients undergoing myeloablative (MA) conditioning or those undergoing MA conditioning in MRDneg remission showed qualitatively similar results. CONCLUSIONS: In the largest study to date examining the role of M-MDSCs in AML, we found no convincing evidence for a prognostic role of these cells for adults undergoing allografting in CR1. Disclosures Walter: Actinium Pharmaceuticals, Inc.: Other: Clinical trial support, Research Funding; Amgen Inc.: Other: Clinical trial support, Research Funding; Amphivena Therapeutics: Consultancy, Equity Ownership, Other: Clinical trial support, Research Funding; Aptevo Therapeutic: Consultancy, Other: Clinical trial support, Research Funding; Covagen AG: Consultancy, Other: Clinical trial support, Research Funding; Seattle Genetics, Inc.: Consultancy, Other: Clinical trial support, Research Funding; Boehringer Ingelheim Pharma GmbH & Co. KG: Consultancy; Pfizer: Consultancy.

Introduction: The preferred post-remission therapy for older patients (pts) with AML remains uncertain. We compared outcomes for older AML pts in CR1 receiving HCT reported to the CIBMTR to older AML pts achieving CR1 on National Clinical Trials Network induction and non-HCT consolidation therapy (CT) trials. Methods: This study focused on pts 60-75 years of age treated between 2004 to 2013. CT pts (n=211) underwent induction and consolidation on Alliance for Clinical Trials in Oncology, ECOG-ACRIN or SWOG clinical trials for initial therapy for newly diagnosed AML; the CIBMTR provided data for HCT pts (n=431). CT patients received at least one cycle of CT on study and were excluded if HCT occurred at any time. Time to event started at CR1 and pts entered at CT or HCT, respectively, using left-truncation to account for differential entry times. Results: For the CT cohort, first consolidation included standard therapy (e.g., cytarabine or a hypomethylating agent) and additional study drug (e.g., bortezomib, dasatinib, sorafenib, and Zosuquidar, gemtuzumab) or tipifarnib alone. Among HCT pts, the donor was a HLA-matched sibling or unrelated donor (URD) in 66% and the others were partially HLA-matched/mismatched URD (10%) or cord blood (24%). HCT pts were younger and more frequently had high-risk AML (high WBC, secondary AML and unfavorable cytogenetics) (Table). The median time from CR1 to HCT and CT was 3.2 and 0.5 months, respectively. Allogeneic HCT showed worse overall survival (OS) (HR=1.52, p=0.02) prior to 9 months and better OS thereafter (HR= 0.53, p Conclusions. Allogeneic HCT led to heightened early risks from TRM, but resulted in superior long-term survival in older AML pts receiving HCT relative to CT by reducing relapse. Efforts to attenuate early TRM after allogeneic HCT may further improve HCT outcomes for older pts. Disclosures Ustun: novartis: Speakers Bureau. Attar:Agios: Employment, Equity Ownership. Larson:Pfizer: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; BristolMyers Squibb: Consultancy, Research Funding; Ariad/Takeda: Consultancy, Research Funding. Roboz:Roche/Genentech: Consultancy; Eisai: Consultancy; Cellectis: Research Funding; Aphivena Therapeutics: Consultancy; Sandoz: Consultancy; Janssen Pharmaceuticals: Consultancy; Otsuka: Consultancy; Jazz Pharmaceuticals: Consultancy; Sandoz: Consultancy; AbbVie: Consultancy; Celltrion: Consultancy; Cellectis: Research Funding; Eisai: Consultancy; Astex Pharmaceuticals: Consultancy; Argenx: Consultancy; Pfizer: Consultancy; Celgene Corporation: Consultancy; Novartis: Consultancy; Jazz Pharmaceuticals: Consultancy; Bayer: Consultancy; Bayer: Consultancy; Roche/Genentech: Consultancy; Orsenix: Consultancy; Astex Pharmaceuticals: Consultancy; Celgene Corporation: Consultancy; Daiichi Sankyo: Consultancy; Pfizer: Consultancy; Janssen Pharmaceuticals: Consultancy; Otsuka: Consultancy; Orsenix: Consultancy; Daiichi Sankyo: Consultancy; Celltrion: Consultancy; Novartis: Consultancy; Aphivena Therapeutics: Consultancy; Argenx: Consultancy; AbbVie: Consultancy. Uy:GlycoMimetics: Consultancy; Curis: Consultancy. Stone:Fujifilm: Consultancy; Ono: Consultancy; Orsenix: Consultancy; Otsuka: Consultancy; Agios: Consultancy, Research Funding; AbbVie: Consultancy; Argenx: Other: Data and Safety Monitoring Board; Celgene: Consultancy, Other: Data and Safety Monitoring Board, Steering Committee; Arog: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Jazz: Consultancy; Astellas: Consultancy; Merck: Consultancy; Pfizer: Consultancy; Sumitomo: Consultancy; Amgen: Consultancy; Cornerstone: Consultancy. Foran:Agios: Research Funding; Xencor, Inc.: Research Funding. Weisdorf:Seattle Genetics: Consultancy; Equillium: Consultancy; FATE: Consultancy; SL Behring: Consultancy; Pharmacyclics: Consultancy.

Introduction Multiple myeloma (MM) is considered incurable but patients achieving minimal-residual disease (MRD) negative status following treatment have significantly better overall and progression-free survival. MM is highly heterogeneous both between and within patients, limiting the curative potential of novel agents targeting specific pathways. However all MM is highly sensitive to radiation. The α-emitter astatine-211 (211At) deposits a very large amount of energy (~100 keV/μm) within a few cell diameters (50-90 μm) resulting in irreparable double strand DNA breaks, making 211At, targeted to MM cells, particularly suited to eliminating MRD. CD38 is expressed on malignant plasma cells regardless of mutational status, and CD38 monoclonal antibodies (mAbs) constitute a proven targeted therapy for MM but do not alone eradicate disease. We proposed that 211At conjugated to an anti-CD38 mAb could effectively eliminate MM MRD, and tested this hypothesis in cellular and murine models. Methods We conjugated the anti-CD38 mAb OKT10 and an isotype matched control mAb, BHV1, to the amine-reactive labeling agent B10-NCS and labeled the final constructs with 211At. To assess in vitro cell binding we incubated each labeled construct with CD38+ cell lines, washed, and then measured cell pellet radioactivity in a gamma counter. To assess cytotoxicity we incubated CD38+ and CD38- cell lines with unlabeled or 211At-labeled OKT10-B10 for 60 hrs, then assayed viability. NOD.Cg-Rag1tm1MomIl2rgtm1Wjl/SzJ (NRG) mice bearing H929luc or OPM-2luc MM xenografts were generated by subcutaneous (SQ) flank injection of 107 cells 7 days prior to treatment. MRD was modeled by intravenous (IV) injection of 2.5 - 5 x 105 cells 5 days prior to treatment. Radioimmunotherapy (RIT) was administered by IV injection of 7.5 - 45 µCi of 211At-OKT10-B10 or 211At-BHV1-B10. For biodistribution studies (n = 5/group) mouse tissues were harvested 24 hrs post RIT and measured in a gamma counter. For therapy studies (n = 8-10/group), all mice received syngeneic bone marrow transplant 3 days post RIT. Disease progression was assessed by tumor dimensions, luminescence imaging and survival. Results 211At-CD38 mAb selectively bound and killed CD38+ but not CD38- MM cells in vitro. In vivo, biodistribution experiments demonstrated that 211At-CD38 RIT delivered 2.4 times more radiation to MM xenografts than did control 211At-BHV1 RIT (p = 0.007), and delivered significantly higher dose to tumor than to healthy tissues including lung (p = 0.04) and kidney (p = 0.015). In murine therapy studies, 211At-CD38 RIT at 15 - 45 µCi at least doubled median survival relative to untreated controls in each of two MM SQ xenograft models (p < 0.003). However, no mice in these models achieved complete remission and all eventually died of disease. In contrast, therapy studies using MRD models showed that 30 µCi 211At-CD38 RIT eliminated detectable disease in 80% of mice at day 21, compared to 20% of mice receiving nontargeted 211At RIT and 0% of untreated mice. At day 130, 50% of the 30 µCi 211At-CD38-RIT mice remained alive and disease-free, while all nontargeted and untreated mice died before day 85 (Fig. 1, survival of 30 µCi > 15 µCi 211At-CD38-RIT [p = 0.016] and all other groups [p < 0.0007]). The impact of therapy on body weight as well as hematopoietic, liver and kidney function was mild and returned to normal within 32 days of treatment. Conclusions The efficacy of CD38 targeted 211At appears to be a function of disease distribution and malignant plasma cell access, as compellingly demonstrated by our models. Bulky tumor geometry reduces mAb penetration. In contrast, the isolated cells and small tumor clusters that define MRD are readily accessible to mAbs, creating optimal conditions for α-emitter cell kill. In an era of highly potent MM therapy, preventing relapse remains frustratingly rare. Our approach is both agnostic to high-risk cytogenetic features and offers the potential to eliminate all residual MM cell clones. These encouraging findings will be explored in a clinical trial of 211At-CD38 RIT. Disclosures Orozco: Actinium Pharmaceuticals: Research Funding. Jones:Juno Therapeutics, a Celgene Company: Employment, Equity Ownership. Till:Mustang Bio: Patents & Royalties, Research Funding. Gopal:Teva: Research Funding; Spectrum: Research Funding; Janssen: Consultancy, Research Funding; BMS: Research Funding; Incyte: Consultancy; Gilead: Consultancy, Research Funding; Seattle Genetics: Consultancy, Research Funding; Brim: Consultancy; Pfizer: Research Funding; Aptevo: Consultancy; Takeda: Research Funding; Merck: Research Funding; Asana: Consultancy. Green:Juno Therapeutics: Patents & Royalties, Research Funding.

Hematopoietic cell transplantation (HCT) can be accomplished with grafts from alternative donors for patients lacking an HLA-matched related or unrelated donor. The optimal choice of an alternative donor stem cell source remains an open question and is influenced by several factors including chronic graft-versus-host disease (cGVHD). Chronic GVHD is a heterogeneous syndrome with major morbidity and adverse effects on quality of life (QoL) among long-term allogeneic HCT survivors. The aim of this study was to analyze the incidence of cGVHD and manifestations associated with severe morbidity and poor functional outcomes among recipients with alternative HCT donors. Methods: This retrospective study included adults who received a first alternative donor HCT for any diagnosis between 2006 and 2015 in Seattle and subsequently developed cGVHD. The alternative grafts included unrelated 4-6/6-HLA-matched single or double cord blood units (UCB), related HLA-haploidentical bone marrow or mobilized blood stem cells with post-transplant cyclophosphamide (R-HAPLO), and mobilized blood cells from unrelated donors with 1-allele mismatching at an HLA-A, B, C or DR locus at any HLA-typing resolution (1-mMUD). Endpoints were cumulative incidence frequencies (CI) of cGVHD and the CI of manifestations associated with severe morbidity (i.e., grade 2 or 3 keratoconjunctivitis sicca, scleroderma-like skin features, grade 2 or 3 myofasciitis, bronchiolitis obliterans, or esophageal stricture requiring dilation) and the CI of functional outcomes (i.e., return to work/school after the diagnosis of cGVHD, discontinuation of systemic immunosuppressive therapy, and change in KPS). We also compared the 2014 NIH overall severity of cGVHD at initial diagnosis, the incidence of new systemic immunosuppression after first-line therapy for cGVHD, non-relapse mortality and overall survival after cGVHD diagnosis. Results: Of 396 alternative donor HCT recipients, 129 developed cGVHD and were included in this study. Chronic GVHD developed in 29 of 163 UCB recipients (3-year CI, 18%), 21 of 88 R-HAPLO recipients (24%) and 79 of 145 1-mMUD recipients (55%) HCT (Fig. 1A). The median follow-up times after onset of cGVHD were 48 (range 4-121) months for UCB, 60 (range Conclusions: Compared to 1-mMUD group, UCB and R-HAPLO HCT recipients were less likely to develop cGVHD. Among those with cGVHD, UCB and R-HAPLO HCT recipients were less likely to develop manifestations of severe morbidity, had less protracted cGVHD (a shorter duration of systemic treatment), and higher likelihood of resuming work or school, suggesting better QoL compared to 1-mMUD HCT recipients. Our results will help better counsel patients about alternative HCT donors. A randomized study (NCT01597778) comparing UCB with R-HAPLO HCT is underway to determine which of these donors may be associated with superior outcomes. Disclosures Lee: Mallinckrodt: Honoraria; Amgen: Other: One-time advisory board member; Bristol-Myers-Squibb: Other: One-time advisory board member; Kadmon: Other: One-time advisory board member. Martin: Pfizer: Consultancy; Procter and Gamble: Equity Ownership; Incyte: Consultancy; Fresenius, Neovii: Research Funding. Cheng: Gilead Sciences, Inc.: Consultancy. Flowers: Pharmacyclics: Consultancy.

Introduction: Novel agents and autologous stem cell transplant (auto-SCT) have resulted in a survival benefit among patients with multiple myeloma (MM), but almost all ultimately relapse. Allogeneic transplant (allo-SCT) provides a tumor-free graft and graft-versus-myeloma (GVM) effect, but myeloablative conditioning regimens are associated with high rates of treatment-related mortality (TRM). In contrast, reduced intensity allo-SCT conditioning regimens are associated with lower TRM, but patients receiving these regimens tend to have a higher risk of relapse. Radioimmunotherapy (RIT) offers the potential to deliver high doses of targeted radiation while minimizing toxicity to normal tissue. When incorporated into reduced intensity allo-SCT, RIT may improve responses without the associated toxicity historically associated with myeloablative conditioning. We studied 90Yttrium conjugated to an IgG1 murine anti-CD45 monoclonal antibody (MAb) (BC8), in conjunction with a reduced intensity-conditioning regimen prior to allogeneic SCT. We used CD45 as a target due to its ubiquitous expression in hematopoietic stem cells. We used the high-energy (2.8 MeVmax) beta-emitter, 90Y to facilitate a bystander crossfire effect and eliminate malignant plasma cells. Methods: This is a single-arm, open label, dose-escalation, phase I trial designed to estimate the safety, feasibility and maximum tolerated dose (MTD) of 90Y-BC8-DOTA MAb when combined with fludarabine (flu) and low dose total body irradiation (TBI) followed by HLA-matched, related or unrelated allo-SCT for patients with high risk MM. Inclusion required patients to have at least one high risk MM-associated disease characteristic at diagnosis (del13 or hypodiploidy by conventional cytogenetics, t(4;14), t(14;16), del 17 by FISH, beta-2 microglobulin >3.5 mcg/mL, LDH >1.5 times upper limit of normal, plasma cell leukemia or progressive disease following primary therapy), and/or disease progression after auto-SCT. To determine the dose of 90Y-BC8-DOTA, patients first underwent a biodistribution step using a trace-labeled infusion of 111Indium-BC8-DOTA followed by gamma camera imaging and bone marrow biopsy. On pre-transplant day -12, patients received 90Y-BC8-DOTA at a dose calculated from the trace-labeled 111Indium-BC8-DOTA biodistribution, followed by Flu (30 mg/m2/day) on days -4 to -2. TBI (2 Gy) was administered on day 0, prior to growth factor mobilized donor peripheral blood stem cell infusion. GVHD prophylaxis consisted of mycophenolate mofetil and cyclosporine initiated on day 0 and day -3, respectively. The MTD was defined as the dose of 90Y-BC8-DOTA MAb associated with a true dose-limiting toxicity (DLT) rate of 25%, where a DLT is defined as Bearman grade III/IV regimen-related toxicity. Doses of 90Y were escalated in increments of 2 Gy depending on the occurrence of DLT. Results: A total of 15 patients were enrolled. Patient characteristics and outcomes are summarized in Table 1. One patient was withdrawn from the study prior to receiving the therapy dose after testing positive for human anti-mouse antibodies. The remaining 14 patients went on to receive 90Y-BC8-DOTA (0.5 mg/kg antibody) at escalating 90Y dose levels of 6 to 32 Gy to the liver, which is the normal critical organ. Six patients (43%) experienced grade 3-4 toxicity, predominantly GI and metabolic/electrolyte disturbances. No DLTs were observed. Because no DLTs were seen, the MTD could not be estimated. All patients achieved platelet and neutrophil engraftment, and 13 patients (93%) were >95% donor in the CD3, CD33 and CD56 compartments at day +28. Estimates of overall and progression-free survival at 2 years were 77% and 78%, respectively (Figure 1). Eleven patients who completed the study regimen are alive at 2.6 months to 4.1 years. Of these, 6 patients are in complete remission, 2 have persistent disease, and 3 have relapsed at 4 months, 6 months, and 3 years post-transplant. Three patients died: 2 due to progressive disease and 1 due to respiratory failure in the setting of liver GVHD. Conclusion: The inclusion of 90Y-BC8-DOTA into a reduced intensity allo-SCT conditioning regimen is feasible and no dose-limiting toxicities have been observed. The efficacy of this regimen is promising compared with historical control rates of conventional allo-SCT for MM and should be explored in a phase II trial. Disclosures Orozco: Actinium Pharmaceuticals: Other: Research Funding to Institution for sponsored Clinical Trials. Gopal: Seattle Genetics: Consultancy, Research Funding. Becker: GlycoMimetics, Inc.: Research Funding. Press: Roche: Honoraria, Research Funding; BMS: Honoraria; Bayer: Consultancy. Bensinger: Janssen: Membership on an entity's Board of Directors or advisory committees.

Purpose A nonmyeloablative (NMA) regimen of fludarabine and 200cGy TBI combined with post-grafting immunosuppression with mycophenolate mofetil (MMF) and a calcineurin inhibitor allows for allogeneic hematopoietic cell transplantation (HCT) from HLA-matched related or unrelated donors in older patients and those with comorbidities affected by myelodysplastic syndrome (MDS) or myeloproliferative neoplasms (MPN). Results of phase I/II studies in patients with chronic myelomonocytic leukemia (CMML) or MDS/MPN have been disappointing, however, due to high incidences of relapse or graft failure (together termed HCT-failure). We hypothesized that escalating the TBI dose may decrease relapse and ensure engraftment. We performed a phase I/II TBI dose-escalation trial and compared the rates of HCT-failure. Methods This was a study conducted at three transplant centers. Patients ages 50-75 or Patients with MDS/MPN could not have received myelosuppressive chemotherapy; patients with CMML who had progressed could have received myelosuppressive chemotherapy before HCT to reduce marrow blasts to less than 5%. Patients were enrolled in groups of 6; dose escalation rules were imposed for HCT failure >20% before day 200 on Arms A and B. Stopping rules were imposed for nonrelapse mortality (NRM) at day 200 of >25% in Arm A and >35% in Arm B. The TBI dose levels were: Level 1: 300cGyLevel 2: 400cGyLevel 3: 450cGy All patients received fludarabine 30/m2/day IV x3 days on days -4 to -2. TBI was administered on day 0 followed by infusion of G-CSF mobilized PBSC from HLA-matched related (n=30) or unrelated (n=47) donors. Post-grafting immunosuppression with MMF and cyclosporine was administered. The primary endpoint was a decrease in the incidence of day200 HCT-failure to Results The study enrolled 77 patients with 36 patients in Arm A and 41 patients in Arm B. Median follow-up is 56.3 months among surviving patients. The primary endpoint (Figure 1) was reached on Arm A at dose level 1 (300cGy TBI) with a cumulative incidence of day200 HCT-failure of 11%. The primary endpoint was not reached in Arm B at dose levels 1 and 2, with dose escalation being triggered at 12 and 5 patients respectively. The endpoint was reached on dose level 3 (450cGy) with a cumulative incidence of day200 HCT-failure of 9%. See Table 2 and Figures 2-5 for OS, PFS, RI and NRM. Cumulative incidence of grades III-IV acute graft-versus-host (aGvHD) by day100 was 17% in Arm A, 12% in Arm B for dose levels 1-2, and 9% in Arm B for dose level 3. Chronic graft-versus-host (cGvHD) cumulative incidence at 1year was 44% in Arm A, 35% in Arm B for dose levels 1-2 and 29% in Arm B for dose level 3. Regarding chimerism analysis, no statistically significant differences were seen among the different arms (Figure 6). Summary and Conclusions In Group A (MPN / low-risk MDS), increasing the TBI dose from 200cGy to 300cGy reduced the day200 HCT-failure rate from 31% in previous trials to 11%. As a result, the OS and PFS was 61% and 58%, respectively, at 2 years. Similarly, for Group B (high-risk MDS / CMML), the day200 HCT-failure rate was reduced from 58% in previous trials to 9% when 450cGy was used. This resulted in an OS and PFS of 37% and 33%, respectively, at 2 years. TBI doses of 300cGy and 400cGy were insufficient to reduce HCT-failure in this high risk group. In conclusion, increasing the TBI dose can lead to a higher success rate in this setting of nonmyeloablative conditioning by reducing both relapse and rejection. Further studies are necessary to decrease nonrelapse mortality, especially among patients affected by high-risk disease. Current trials using targeted radioimmunotherapy are currently being investigated towards this end. Disclosures Flowers: Pharmacyclics: Consultancy. Maloney: Kite Pharmaceuticals: Other: Advisory board; Celgene: Other: Advisory board; Juno Theraapeutics: Other: Advisory board, Patents & Royalties, Research Funding; Roche/Genetech: Other: Advisory board.

A new hematopoietic cell transplantation–specific comorbidity index (HCT-CI) was effective in predicting outcomes among patients with hematologic malignancies who underwent HCT at Fred Hutchinson Cancer Research Center (FHCRC). Here, we compared the performance of the HCT-CI to 2 other indices and then tested its capacity to predict outcomes among 2 cohorts of patients diagnosed with a single disease entity, acute myeloid leukemia in first complete remission, who underwent transplantation at either FHCRC or M. D. Anderson Cancer Center (MDACC). FHCRC patients less frequently had unfavorable cytogenetics (15% versus 36%) and HCT-CI scores of 3 or more (21% versus 58%) compared with MDACC patients. We found that the HCT-CI had higher sensitivity and outcome predictability compared with the other indices among both cohorts. HCT-CI scores of 0, 1 to 2, and 3 or more predicted comparable nonrelapse mortality (NRM) among FHCRC and MDACC patients. In multivariate models, HCT-CI scores were associated with the highest hazard ratios (HRS) for NRM and survival among each cohort. The 2-year survival rates among FHCRC and MDACC patients were 71% versus 56%, respectively. After adjustment for risk factors, including HCT-CI scores, no difference in survival was detected (HR: 0.98, P = .94). The HCT-CI is a sensitive and informative tool for comparing trial results at different institutions. Inclusion of comorbidity data in HCT trials provides valuable, independent information.

We analyzed outcomes after hematopoietic cell transplantation (HCT) in 257 patients, 3 to 72.7 years old (median, 43 y), with secondary myelodysplastic syndrome (MDS) including those with transformation to acute myeloid leukemia (tAML). Conditioning regimens included high-dose total-body irradiation (TBI)/chemotherapy (n = 83); busulfan (BU)/cyclophosphamide (CY) (BUCY, n = 122; with BU targeting [tBUCY], n = 93); fludarabine (Flu) with tBU (FLUtBU; n = 12); Flu plus 200 cGy TBI (n = 26); and miscellaneous regimens (n = 14). Donors were HLA-identical or partially mismatched family members in 135 and unrelated individuals in 122 patients. Five-year relapse-free survival was highest (43%) and nonrelapse mortality lowest (28%) among tBUCY-conditioned patients. Outcomes were compared with results in 339 patients who received transplants for de novo MDS/tAML, and a multivariate analysis failed to show significant differences in outcome between the 2 cohorts. Relapse probability and relapse-free survival correlated significantly with disease stage (P < .001) and karyotype (P < .001). Relapse incidence was lower (P = .003) and relapse-free survival superior (P = .02) with unrelated donor transplants. The data suggest that overall inferior outcome in patients with secondary MDS/tAML was related to the frequency of high-risk cytogenetics. For both cohorts, transplantation outcomes improved over the time interval studied.

We previously reported that the Charlson Comorbidity Index (CCI) was useful for predicting outcomes in patients undergoing allogeneic hematopoietic cell transplantation (HCT). However, the sample size of patients with scores of 1 or more, captured by the CCI, did not exceed 35%. Further, some comorbidities were rarely found among patients who underwent HCT. Therefore, the current study was designed to (1) better define previously identified comorbidities using pretransplant laboratory data, (2) investigate additional HCT-related comorbidities, and (3) establish comorbidity scores that were suited for HCT. Data were collected from 1055 patients, and then randomly divided into training and validation sets. Weights were assigned to individual comorbidities according to their prognostic significance in Cox proportional hazard models. The new index was then validated. The new index proved to be more sensitive than the CCI since it captured 62% of patients with scores more than 0 compared with 12%, respectively. Further, the new index showed better survival prediction than the CCI (likelihood ratio of 23.7 versus 7.1 and c statistics of 0.661 versus 0.561, respectively, P < .001). In conclusion, the new simple index provided valid and reliable scoring of pretransplant comorbidities that predicted nonrelapse mortality and survival. This index will be useful for clinical trials and patient counseling before HCT. (Blood. 2005;106: 2912-2919)

Fifty-six patients, 10 to 66 years of age, with idiopathic myelofibrosis (IMF) or end-stage polycythemia vera or essential thrombocythemia received allogeneic hematopoietic cell transplants from related (n = 36) or unrelated (n = 20) donors. Forty-four patients were prepared with busulfan plus cyclophosphamide and 12 with total body irradiation plus chemotherapy. The source of stem cells was marrow in 33 and peripheral blood in 23 patients. All but 3 patients achieved engraftment. While 50 patients showed complete donor chimerism, 3 patients were found to be mixed chimeras at 26, 48, and 86 months after transplantation, respectively. Two patients died from relapse/progressive disease, and 18 died from other causes. There are 36 patients surviving at 0.5 to 11.6 (median, 2.8) years, for a 3-year Kaplan-Meier estimate of 58% (CI, 43%-73%). Dupriez score, cytogenetic abnormalities, and degree of marrow fibrosis were the most significant risk factors for posttransplantation mortality. Patients conditioned with a regimen of busulfan targeted to plasma levels of 800 to 900 ng/mL plus cyclophosphamide had a higher probability of survival (76% [CI, 62%-91%]) than other patients. Results with unrelated donors were comparable with those with HLA-identical sibling transplants. Thus, allogeneic hematopoietic cell transplantation offers long-term relapse-free survival for patients with myelofibrosis.

A hematopoietic cell transplantation (HCT) approach was developed for elderly or ill patients with hematologic malignancies that employed nonmyeloablative conditioning to avoid common regimen-related toxicities and relied on graft-versus-tumor effects for control of malignancy. Eighty-nine patients, median age 53 years, were given fludarabine (90 mg/m2) and 2 Gy total body irradiation. Marrow (n = 18) or granulocyte colony-stimulating factor (G-CSF)–stimulated peripheral blood mononuclear cells (G-PBMCs; n = 71) were transplanted from unrelated donors matched for human leukocyte antigen A (HLA-A), -B, -C antigens and -DRB1 and -DQB1 alleles. Postgrafting immunosuppression included mycophenolate mofetil and cyclosporine. Donor T-cell chimerism was higher for G-PBMCs compared with marrow recipients. Durable engraftment was observed in 85% of G-PBMCs and 56% of marrow recipients. Cumulative probabilities of grade II, III, and IV acute graft-versus-host disease (GVHD) were 42%, 8%, and 2%, respectively. Nonrelapse mortality at day 100 and at 1 year was 11% and 16%, respectively. One-year overall survivals and progression-free survivals were 52% and 38%, respectively. G-PBMC recipients had improved survival (57% vs 33%) and progression-free survival (44% vs 17%) compared with marrow recipients. HLA-matched unrelated donor HCT after nonmyeloablative conditioning is feasible in patients ineligible for conventional HCT. G-PBMCs conferred higher donor T-cell chimerism, greater durable engraftment, and better progression-free and overall survivals compared with marrow.

The incidence of invasive mold infections has increased during the 1990s among patients undergoing allogeneic hematopoietic stem cell transplantation (HCT) after myeloablative conditioning. In this study, we determined risk factors for invasive mold infection and mold infection-related death among 163 patients undergoing allogeneic HCT with nonmyeloablative conditioning. The cumulative incidence rates of proven or probable invasive fungal infections, invasive mold infections, invasive aspergillosis, and invasive candidiasis during the first year after allogeneic HCT with nonmyeloablative conditioning were 19%, 15%, 14%, and 5%, respectively, which were similar to those after conventional myeloablative HCT. Invasive mold infections occurred late after nonmyeloablative conditioning (median, day 107), with primary risk factors including severe acute graft-versus-host disease (GVHD), chronic extensive GVHD, and cytomegalovirus (CMV) disease. The 1-year survival after diagnosis of mold infections was 32%. High-dose corticosteroid therapy at diagnosis of mold infection was associated with an increased risk for mold infection–related death. Overall, nonrelapse mortality was estimated at 22% (36 patients) after nonmyeloablative conditioning, of which 39% (14 patients) were mold infection-related (9% of the overall mortality). More effective strategies are needed to prevent invasive mold infections, which currently account for a notable proportion of nonrelapse mortality after nonmyeloablative allogeneic HCT.

Two major immunologic barriers, the host-versus-graft (HVG) and graft-versus-host (GVH) reactions, have to be overcome for successful allogeneic hematopoietic cell transplantation. T cells were shown to be primarily involved in these barriers in the major histocompatibility complex identical setting. We hypothesized that selective ablation of T cells using radioimmunotherapy together with postgrafting immunosuppression would suffice to ensure stable allogeneic engraftment. We had described a canine model of nonmyeloablative marrow transplantation in which host immune reactions were impaired by a single dose of 200 cGy total body irradiation (TBI), and both GVH and residual HVG reactions were controlled by postgrafting immunosuppression with mycophenolate mofetil (MMF) and cyclosporine (CSP). Here, we substituted the α-emitter bismuth-213 (213Bi) linked to a monoclonal antibody (mAb) against T-cell receptor (TCR) αβ, using the metal-binding chelate diethylenetriaminepentaacetic acid (DTPA) derivative cyclohexyl–(CHX)-A″, for 200 cGy TBI. Biodistribution studies using a γ-emitting indium-111–labeled anti-TCRαβ mAb showed uptake primarily in blood, marrow, lymph nodes, spleen, and liver. Four dogs were treated with 0.13 to 0.46 mg/kg TCRαβ mAb labeled with 3.7 to 5.6 mCi/kg (137-207 MBq/kg) 213Bi. The treatment was administered in 6 injections on days –3 and –2 followed by transplantation of dog leukocyte antigen-identical marrow on day 0 and postgrafting immunosuppression with MMF/CSP. The therapy was well tolerated except for elevations of transaminases that were transient in all but one of the dogs. No other organ toxicities or signs of graft-versus-host disease were noted. The dogs had prompt allogeneic hematopoietic engraftment and achieved stable mixed donor-host hematopoietic chimerism with donor contributions ranging from 5% to 55% after more than 30 weeks of follow up.

Nonmyeloablative allogeneic hematopoietic stem cell transplantation (HSCT) is increasingly being explored as therapy in patients who are not eligible for conventional myeloablative HSCT. Whether these transplants are associated with reduced risk of transplantation-related infections is unknown. We analyzed the incidence of posttransplantation cytomegalovirus (CMV) infections in 56 consecutive mycophenolate mofetil (MMF) patients with hematologic malignancies who underwent nonmyeloablative HSCT (TBI, 2Gy, day 0; MMF/cyclosporine after transplantation). In addition, 18 of 56 patients received 30 mg/m2/d fludarabine on days −4 to −2. Most donors were HLA matched and related (93%). Each case patient was matched to 2 controls who were treated by conventional HSCT during the same time period (January 1997 through April 2000). Matching criteria included CMV risk group, HSC source, donor type, age, and underlying diseases. No CMV disease occurred in the low (donor and recipient serologically negative) and intermediate (donor serologically positive and recipient negative) CMV risk groups during the first 100 days. Among cases at high risk for CMV (seropositive recipients), trends to less CMV antigenemia (P = .11), viremia (P = .16), and disease (P = .08) compared with controls were observed; all severe manifestations combined (CMV viremia and disease) were significantly reduced among cases (P = .01). However, by day 365, the overall incidence of CMV disease became similar in both groups. The onset of CMV disease was significantly delayed among case patients compared with controls (median, 130 days versus 52 days; P = .02). It was concluded that CMV disease was significantly delayed in nonmyeloablative cases, but that the overall 1-year incidence was similar to myeloablative HSCT patients. Therefore, nonmyeloablative HSCT patients should receive CMV surveillance beyond day 100 and pre-emptive ganciclovir treatment similar to that of myeloablative HSCT patients.

Red blood cell (RBC) and platelet transfusion requirements in patients given nonmyeloablative versus conventional peripheral blood stem cell (PBSC) transplants from HLA-matched siblings were compared. Between December 1997 and March 2000, 40 patients, aged 21 to 67 years (median 51), with hematologic malignancies underwent nonmyeloablative allografts after either 2 Gy total body irradiation alone (n = 30) or 2 Gy total body irradiation preceded by fludarabine 30 mg/m2/d on days −4, −3, and −2 (n = 10). All received postgrafting mycophenolate mofetil and cyclosporine. Controls included 67 concurrent patients, aged 23 to 66 years (median, 46 years), given conventional PBSC transplants following high-dose conditioning and postgrafting methotrexate and cyclosporine. Among patients given nonmyeloablative transplants, 23% required platelet transfusions compared with 100% among patients given conventional grafts (P

Toxicities have limited the use of allogeneic hematopoietic cell transplantation (HCT) to younger, medically fit patients. In a canine HCT model, a combination of postgrafting mycophenolate mofetil (MMF) and cyclosporine (CSP) allowed stable allogeneic engraftment after minimally toxic conditioning with low-dose (200 cGy) total-body irradiation (TBI). These findings, together with the known antitumor effects of donor leukocyte infusions (DLIs), led to the design of this trial. Forty-five patients (median age 56 years) with hematologic malignancies, HLA-identical sibling donors, and relative contraindications to conventional HCT were treated. Immunosuppression involved TBI of 200 cGy before and CSP/MMF after HCT. DLIs were given after HCT for persistent malignancy, mixed chimerism, or both. Regimen toxicities and myelosuppression were mild, allowing 53% of eligible patients to have entirely outpatient transplantations. Nonfatal graft rejection occurred in 20% of patients. Grades II to III acute graft-versus-host disease (GVHD) occurred in 47% of patients with sustained engraftment. With median follow-up of 417 days, survival was 66.7%, nonrelapse mortality 6.7%, and relapse mortality 26.7%. Fifty-three percent of patients with sustained engraftment were in complete remission, including 8 with molecular remissions. This novel allografting approach, based on the use of postgrafting immunosuppression to control graft rejection and GVHD, has dramatically reduced the acute toxicities of allografting. HCT with the induction of potent graft-versus-tumor effects can be performed in previously ineligible patients, largely in an outpatient setting. Future protocol modifications should reduce rejection and GVHD, thereby facilitating studies of allogeneic immunotherapy for a variety of malignancies. (Blood. 2001;97:3390-3400)

Total body irradiation (TBI)-based conditioning regimens are considered the standard of care for patients with acute lymphoblastic leukemia (ALL) undergoing allogeneic hematopoietic cell transplantation (HCT). However, due to concerns regarding acute and long-term toxicities, non-TBI regimens, commonly including busulfan (BU), have been increasingly explored. We performed a retrospective cohort analysis with the hypothesis that there would be equivalence of these two myeloablative approaches by reviewing outcomes for adult patients (pts), aged 18-60 years, undergoing a first, well-matched sibling, related or unrelated donor HCT in CR1 or CR2 reported to the Center for International Blood and Marrow Transplant Research (CIBMTR) from 2005-2014. Eight hundred nineteen pts received TBI (63% 9-12 Gy, 37% ≥13 Gy) combined with etoposide (25%) or cyclophosphamide (Cy) (75%) and 299 pts received intravenous BU combined with a second alkylator Cy (15%) or melphalan (Mel) (13%), or a nucleoside analogue fludarabine (Flu) (41%) or clofarabine (Clo)(30%). The majority of the BU-based pts were treated at the Moffitt or MD Anderson Cancer Center. The BU-based regimens were grouped together for analyses since no significant differences in basic outcomes among the different chemotherapy-only regimens were noted. Patients in the BU-containing group were older but had better performance status, took longer to achieve CR1 and longer to receive HCT; more received peripheral blood than marrow grafts, peri-HCT ATG, pre- and post HCT tyrosine kinase inhibitors ( TKI), and were treated more recently than pts in the TBI-based group (Table 1). With median follow-up of 3.6 years for the BU-based group and 5.3 years for the TBI-based group, adjusted 3 year outcomes showed treatment-related mortality (TRM) BU 19% vs. TBI 25% (p=.04); relapse BU 37% vs. TBI 28% (p=.007); disease-free survival (DFS) Bu 45% vs. TBI 48% (p=.35); and overall survival (OS) BU 57% vs. TBI 53% (p=.35) (Figures A-B). Patients in the BU group had significantly more grade II-IV acute GVHD (47% vs. 40%, p=.025), but marginally less chronic GVHD (49% vs. 55% at 3 years, p=.073). In multivariate analysis, the BU group had a significantly higher rate of acute GVHD after day 50 (RR 1.75, 95% CI 1.19-2.58, p=.004), but marginally less chronic GVHD (RR 0.83, 95% CI 0.68-1.01 p=.059) and higher risk of relapse (RR 1.46, 95% CI 1.15-1.85 p=.002) compared with TBI-based regimens. Despite the observed higher risks of acute GVHD and relapse, BU-based conditioning led to similar TRM, OS, and DFS following HCT for ALL. Table 1 Table 1. Figure Figure. Disclosures Ciurea: Spectrum Pharmaceuticals: Other: Advisory Board; Cyto-Sen Therapeutics: Equity Ownership. Seftel:Otsuka: Research Funding. Pulsipher:Medac: Other: Housing support for conference; Chimerix: Consultancy; Jazz Pharmaceutical: Consultancy; Novartis: Consultancy, Other: Study Steering Committee. Champlin:Ziopharm Oncology: Equity Ownership, Patents & Royalties; Intrexon: Equity Ownership, Patents & Royalties.

A randomized 3-arm Phase II trial involving 208 older or medically infirm patients (pts) with hematological malignancies given unrelated HCT after minimal intensity conditioning demonstrated that adding sirolimus to tacrolimus and MMF resulted in less grades II-IV GVHD, less steroid use, and less CMV reactivation (Hematologica 2014; 99(10); 1624). Based on this trial we designed a Phase III multi-site trial comparing triple therapy with sirolimus/MMF/CSP (Arm2) to the standard immunosuppressive regimen of MMF/CSP (Arm1). The primary objective of the trial was to compare the respective incidences of grades II-IV acute GVHD. Secondary objectives included comparing non-relapse mortality, survival, and progression-free survival. Pts in both Arms received CSP 5 mg/kg bid starting on day -3 through day 96 with a taper through day 150. In the first 28 days after HCT CSP was targeted to 400 and 350ng/ml in Arm1 and Arm2, respectively and 120-360ng/ml after day 28 in both arms. Arm 1: MMF was given daily at 15 mg/kg Q8 hours until day +30, reduced to 15 mg/kg Q12 hours until day 150, then tapered through day 180. Arm 2: MMF was given daily at 15 mg/kg Q8 hours until day +30, reduced to 15 mg/kg Q12 hours until day 40, then discontinued (no taper). In addition to the MMF/CSP, sirolimus was administered starting on day -3 at 2.0 mg/day through day 150 with a target level of 3-12ng/ml, with tapering off by day 180. The target enrollment was 300 pts with a built-in interim analysis for futility. At the time of the interim analysis, 158 pts ineligible for high-dose conditioning had been enrolled (Nov. 2010 to Jan. 2016: Arm1 n=74, Arm2 n=84) Their median age was 62 (range 18-79) yrs. The median HCT comorbidity index (HCT-CI) was 3 (range 0-10). Five pts had 6 previous allogeneic HCT and 32 pts (20%) had 36 previous autologous HCT. All pts were matched for HLA-DRB1 and -DQB1 at the allele level: 8 had single allele mismatches at HLA-A, -B or -C and the remainder (n=150) were fully HLA-matched. Diagnoses included AML (n=64), MDS/MPD (n=30), NHL (n=23), MM (n=13), CLL (n=13), ALL (n=11), HL (n=2), and CML (n=2). Randomization was stratified by transplant center. Unmodified PBSC grafts contained a median of 8.0 ×106 CD34 and 2.9 × 108 CD3 cells/kg. Conditioning consisted of fludarabine 90mg/m2 and 2-3 Gy TBI. Sustained donor engraftment occurred in 99% of pts. The median follow-up of surviving pts was 24 (range, 1-65) months. Table 1 and Figures 1 and 2 summarize results. The day-100 cumulative incidences of grades II-IV acute GVHD were in Arm1: 53%, and Arm2: 25% (p=0.0001) and the grades III-IV acute GVHD were in Arm1: 8%, Arm2: 2% (p=0.04). The 1-year cumulative incidence of chronic extensive GVHD was similar between Arm1: 49%, and Arm2: 48% (p=0.94). The 1-year cumulative incidence of non-relapse mortality was lower in Arm2 (Arm1: 15% and Arm2: 5%; p=0.007), while relapse/progression was similar at 1 year for Arm1: 21%, and Arm2: 19% (p=0.86). The 1-year overall and progression-free survivals for Arm1 vs. Arm2 were: 72% vs. 85% (p=0.03), and 65% vs. 77% (p=0.08); respectively. T-cell (CD3) donor chimerism was lower in Arm 2 on day 28 (median, Arm1 85%; Arm2 80%; p=0.05) with no differences seen in granulocyte (CD33: Arm1 98%, Arm2 95%) or NK cell (CD56: Arm1 96%, Arm2 97%) donor chimerisms. In summary, the interim analysis showed that adding sirolimus to MMF and CSP not only reduced the risks of grades II-IV but also of grades III-IV acute GVHD and of non-relapse mortality without increasing the risk of relapse or progressive malignancy. Based on these findings and the significantly improved survival, the DSMB recommended the trial be closed. This triple immunosuppressive regimen should, therefore, be considered in the future as the standard of care in pts given unrelated donor grafts after minimal intensity conditioning. Disclosures Pulsipher: Novartis: Consultancy, Other: Study Steering Committee; Chimerix: Consultancy; Jazz Pharmaceutical: Consultancy; Medac: Other: Housing support for conference.

Allogeneic hematopoietic cell transplantation (alloHCT) is potentially curative for patients with ALL who achieve complete remission with upfront chemotherapy (CR1). However, the necessity of consolidation chemotherapy remains uncertain in patients with an available donor undergoing alloHCT, even if the goal is to reduce the detectable disease burden prior to alloHCT. We therefore compared clinical outcomes of 524 adult patients with ALL in CR1 who received ≥2 cycles (n=109) vs. 1 cycle (n=93) vs. no (n=322) consolidation chemotherapy prior to myeloabalative alloHCT from 2008-2012. The median follow up of survivors was 59 (6-78) months. All three consolidation groups had similar patient, disease and transplant characteristics, but no consolidation patients were older, took longer to achieve CR1 and less frequently received CNS prophylaxis or maintenance chemotherapy prior to alloHCT. In contrast, fewer with 1 cycle consolidation had prior comorbidities. Time to alloHCT was longer with increasing cycles of consolidation. Only a minority had either cytogenetic or molecular detectable disease in their pre-HCT CR1 assessment; and it was similar in each consolidation cohort. For ≥2 cycles, 1-cycle, no consolidation groups, the adjusted 3-year cumulative incidence of relapse was 20%, 27% and 22% and 1-year transplant-related mortality (TRM) was 16%, 18% and 23%, respectively (all p-values > 0.4). Similarly, adjusted 3-year leukemia-free survival (LFS) was 54%, 48% and 47% (Figure), while overall survival (OS) was 63%, 59% and 54%, respectively (all p-values > 0.3). Consolidation did not influence acute or chronic GVHD risks. Multivariable regression analysis adjusted for recipient age, Karnofsky performance status, time to CR1, graft source, donor type and recipient CMV serostatus, confirmed that consolidation chemotherapy was not prognostic of LFS (RR=1.20, 95% CI 0.86-1.67; p=0.28 for no consolidation; RR=1.18, 95% CI 0.79-1.76; p=0.41 for 1 cycle; ≥2 cycles=reference). Similarly, consolidation was not associated with OS, relapse, TRM or GVHD. We conclude that consolidation chemotherapy does not benefit adult ALL patients with readily available donor who undergo myeloablative alloHCT in CR1. Figure. Figure. Disclosures No relevant conflicts of interest to declare.

Background: Induction therapy for newly diagnosed AML pts can be classified as intensive or non-intensive. Non-intensive therapies are increasingly used in pts aged >65 years due to concerns about their ability to tolerate intensive chemotherapy. However, the relative benefit-risk ratios associated with intensive versus non-intensive therapies in AML pts is likely affected by age, comorbidities, and disease-related characteristics, such as cytogenetic and molecular features. Here, we examine these relationships. Methods: Data from 1295 newly diagnosed AML patients, given induction therapy between 2008 and 2012 at six participating academic centers, were retrospectively collected. We used two previously validated models to define distinct prognostic groups, and within each, compared 2-year mortality rates according to whether pts received intensive or non-intensive therapy. Non-intensive therapy principally included azacitidine, decitabine, or low-dose cytarabine, while intensive therapies primarily included the standard 7+3 regimen or "high-dose" cytarabine combinations with anthracyclines or purine analogs. The first model (Blood 2015; 126:532) was a composite of the prognostic effects of age, comorbidity index, and cytogenetic/genetics risks per European Leukemia Net (ELN) classification. The second (JCO 2011; 29(33): 4417) was a treatment related mortality (TRM) index including 8 pt- and AML-specific risk factors. Results: Age distribution of the pts were ≤49 (23%), 50-59 (20%), 60-69 (33%), and ≥70 (24%) years old. Median follow-up for currently alive pts was 41 (range, 0-99) months. Cytogenetic-molecular risks per ELN classification were favorable (18%), intermediate I and II (39%), or unfavorable (43%). Induction treatments were intensive in 77% and non-intensive in 23% of pts. The proportion of patients receiving non-intensive therapy increased with increasing age (Table 1). Almost all pts (99%) with the lowest composite scores (1-3) received intensive therapies and were therefore omitted from the comparisons with either model. Per the composite model grouping, pts had better survival rates if they received intensive therapy, although the differences were not statistically significant in pts with composite scores ≥10 (Table 2). Pts with TRM scores of 0-4 and ≥5, with a score of 5 corresponding to the median score, statistically significantly benefitted from intensive therapies (Table 2). Among all pts aged 70-79 years old (n=242), 41% received intensive therapy, while 59% received non-intensive therapy. The intensively treated pts in this age range had statistically significantly higher survival rates at 2 years (26% versus 13%, HR: 0.73, 95% CI: 0.54-0.98, P=0.04, Figure). Conclusion: After accounting for underlying prognosis using 2 validated models, we found pts with newly diagnosed AML generally had better survival if they received intensive therapy. This survival benefit was not statistically proven for pts with the highest composite scores (≥10). Early mortality was not increased in older pts given intensive versus non-intensive therapy (Figure), likely due to improvements in supportive care which allowed the greater anti AML effect of intensive therapy to become manifest over time. While we cannot exclude the effects of selection bias, absent a randomized trial our results suggest intensive therapy could be considered for most pts, up to the age of 80 years, regardless of their comorbidity burden. Although results seem better with intensive therapy, less than 50% of patients with composite scores >3 given such therapies were predicted to be alive at 2 years, suggesting the need for randomized clinical trials between novel intensive and non-intensive therapies to achieve better survival. Table 1 Regimen intensity per pt age groups Table 1. Regimen intensity per pt age groups Table 2 Comparisons of hazard ratios (HR) and 2-year rates of survival between intensive and non-intensive initial therapies Table 2. Comparisons of hazard ratios (HR) and 2-year rates of survival between intensive and non-intensive initial therapies Figure. Intensive versus non-intensive therapies among pts aged 70-79 years with AML Figure. Intensive versus non-intensive therapies among pts aged 70-79 years with AML Disclosures Fathi: Bexalata: Other: Advisory Board participation; Celgene: Consultancy, Research Funding; Merck: Other: Advisory Board participation; Agios Pharmaceuticals: Other: Advisory Board participation; Seattle Genetics: Consultancy, Other: Advisory Board participation, Research Funding. Sekeres:Millenium/Takeda: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees. Mukherjee:Novartis: Consultancy, Honoraria, Research Funding; Ariad: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding. Wang:Incyte: Speakers Bureau; Immunogen: Research Funding. Shami:JSK Therapeutics: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Research Funding.

Endothelial dysfunction has been shown to be associated with severe complications and increased NRM after alloSCT. Endothelial risk markers, such as angiopoetin-2 (ANG2) serum levels and thrombomodulin single nucleotide polymorphisms can be used for pre-transplant prediction of endothelium-related complications after alloSCT (Blood 2011;118:1685; J Clin Oncol. The aim of the present study was to develop a tool for prediction of endothelial dysfunction prior to alloSCT that can be easily used in clinical practice. For this purpose, we focused on routine parameters which are used to diagnose transplant-associated thrombotic microangiopathy (TMA), which is an endothelial complication associated with high NRM. Based on the fact that TMA is defined by high creatinine, high lactate dehydrogenase (LDH), low thrombocyte counts, schistocytes, and loss of haptoglobin, we hypothesized that the simplified formula termed 'Endothelial Activation and Stress Index (EASIX)' might be valuable for predicting TMA, NRM and overall survival (OS) after alloSCT. Design: The capacity of pre-transplant EASIX ("EASIX-pre") obtained directly prior to conditioning for alloSCT for predicting TMA was tested retrospectively in 771 consecutive adult patients undergoing alloSCT in Heidelberg between 2001 and 2013 (training cohort) using cause-specific Cox regression analysis. The correlation of EASIX-pre with pre-transplant ANG2 and suppressor of tumorigenicity-2 (ST2) serum levels was assessed by Kruskal-Wallis test / Pearson correlation. The prognostic strength of EASIX-pre for NRM, time to relapse (TTR) and OS was calculated in the training cohort and in three independent validation cohorts (Berlin adults n=386, Seattle adults n=450 and Cincinnati children n=247) by calculating the prediction error (integrated Brier score), concordance index, and calibration index. Different intensities of conditioning (MAC+RIC+non-MAC) as well as all donor types and all degrees of HLA-matching were included. Hazard ratios (HR) were estimated to illustrate the effect of a two-fold change in EASIX-pre. Results: In the training cohort, EASIX-pre was a significant risk factor for TMA in univariable (HR=1.24, p=0.03) and in multivariable models including age, disease score, ATG, donor sex, recipient sex, graft source, diagnosis and statin intake as covariates (HR 1.28, p=0.02). EASIX-pre correlated with pre-transplant serum levels of the endothelium-related markers ANG2 and ST2. Increasing EASIX-pre was significantly associated with increasing NRM (uni: HR 1.22, p Conclusions: The novel and easy to assess EASIX-pre score is a powerful predictor of NRM and overall mortality in adult alloSCT recipients which might be helpful for pre-transplant definition of the individual transplant risk. Disclosures Dreger: Novartis: Consultancy; Janssen: Consultancy; Roche: Consultancy; Novartis: Speakers Bureau; Gilead: Speakers Bureau; Gilead: Consultancy.

Background: Graft rejection is a significant complication following allogeneic hematopoietic cell transplantation (HCT). Heavily transfused patients with nonmalignant blood disorders, such as aplastic anemia, thalassemia major, and sickle cell anemia, had rejection probabilities in the range of 5~60% in earlier transplant series. Since rejections were seen despite the use of HLA-identical donors, rejections were attributed to sensitization to minor non-HLA antigens via transfusions. Systemic intensification of regimens with higher doses of chemotherapy or total body irradiation (TBI) lead to worse outcomes due to regimen-related mortality. In our well-established canine model, following 9.2Gy TBI conditioning, only 1.6% (1/62) of untransfused dogs rejected the marrow grafts from their dog leukocyte antigen (DLA)-identical littermate donors. However, 100% (27/27) of the dogs pretreated with three unirradiated transfusions from their respective DLA-identical marrow donors rejected their grafts. We seek to overcome graft rejection by adding monoclonal antibody (MAb)-based targeted radioimmunotherapy (RIT) with astatine-211 (211At) to conditioning with 9.2 Gy TBI. 211At is an alpha-particle-emitting isotope, which has a short path length (0.06 mm), very high energy, and high cytotoxicity of alpha emissions. These properties and the short half-life (7.2 hours) may reduce early toxicities as well as late effects, such as secondary malignancies. The purpose of this study is to determine the quantity of 211At required to provide durable donor engraftment in DLA-identical HCT when 211At-labeled anti-CD45 MAb is used in combination with TBI to condition transfusion-sensitized dogs. Methods: Five recipients were given three preceding transfusions of 50 mL unirradiated whole blood from their respective DLA-identical marrow donors on days -24, -17, and -10, followed by 211At-labeled anti-CD45 MAb on day -3 and 9.2 Gy TBI and a marrow transplant on day 0. The injected 211At activity ranged between 0.188 and 0.304 mCi/kg body weight labeled on 0.5 mg/kg anti-CD45 MAb. Ten percent of the total dose of anti-CD45 MAb was administered as unlabeled MAb prior to infusion of the radiolabeled MAb in order to prevent nonspecific tissue binding of the radiolabeled MAb. Dogs received marrow containing a mean of 5.1 x 108 (range, 1.3-8.3) total nucleated cells/kg and 2.8 x 106 (range, 0.4-5.5) CD34+cells/kg. Dogs did not receive post-grafting immunosuppression. Results: Results are shown in Figure 1. Granulocyte nadirs (median, 20/µL) and platelet nadirs (median, 4500/µL) occurred at a median time of 5 days and 11 days, respectively. Neutrophil engraftment (>=500/µL, 3 consecutive days) and platelet engraftment (>=20,000/µL, 7 consecutive days, without transfusion) were achieved at a median of 8 (7-9) days and 20 (18-21) days, respectively. Four dogs achieved 100% donor chimerism in mononuclear cells, granulocytes, and CD3+ T-cells. Only one dog rejected the graft on day 14 after transplantation. That dog received the lowest numbers of CD34+ and marrow cell dose (0.35 x 106 CD34+ and 1.3 x 108 total nucleated cells per kg, respectively), which could be one of the reasons for the graft rejection. After a median follow-up time of 60 (21-182) days, no renal toxicity had been observed. One dog was euthanized on day 60 due to liver toxicity (CTCAE grade 4), but there was no evidence of GVHD on histopathological evaluation. Conclusions: The preliminary results are encouraging and show that 211At-labeled anti-CD45 MAb in combination with TBI as conditioning is successful in establishing sustained DLA-identical grafts in 4/5 dogs, especially when compared to previous studies showing that 100% of the dogs (27/27) rejected their grafts when pretreated with three unirradiated transfusions from their marrow donors. We will increase the sample size and then proceed to study canine models of human blood disorders to further determine the optimal dosing of 211At in disease settings. In view of the potential of RIT, 211At-anti-CD45 RIT in conjunction with TBI may serve as a novel promising strategy to overcome graft rejection. Figure 1. Figure 1. Disclosures No relevant conflicts of interest to declare.

Objectives: Low donor chimerism after hematopoietic cell transplantation (HCT) is associated with increased risk of post transplant relapse. Our group has shown that donor lymphocyte infusion (DLI) was ineffective for converting 90% elicited GVT effects (Blood 2004;103:790). To facilitate effectiveness of DLI for patients (pts) with low or declining donor CD3chimerism, a prospective multicenter trial assessing the safety and efficacy of addingpentostatin was developed. Patients and Methods: Pts at risk for rejection after HCTs, defined as low (5%) donor CD3 chimerism and with stable/in remission disease, were included. Pts were excluded if they had evidence of relapse/progression, ongoing grades II-IV acute (a)GVHD, or extensive chronic (ec)GVHD. Between 2003 and 2014, 36 pts were treated on the study; 35 pts received a total of 41 DLIs following a dose of pentostatin, and 1 pt received pentostatin only. Diagnoses included AML (n=13), NHL (n=4), CLL (n=7), CML (n=2), MDS (n=6), MPD (n=2), MM (n=1), NHL and MDS (n=1). Pts received nonmyeloablative (n= 35) or ablative (n=1) conditioning, followed by PBSCs from HLA-matched related (n=17) or unrelated (n=17) donors, or 1-allele mismatched unrelated donor (n=2). Median age at HCT was 58 (34-72) years. DLI was given at a median of 96 (54-339) days after HCT. A dose of pentostatin was given 2 days before infusing 1x107 CD3 cells/kg (n=26), 2x107 CD3 cells/kg (n=1), or 3x107 CD3 cells/kg (n=14). Per protocol, prophylactic immunosuppression (IS) with cyclosporine and MMF was given after DLI to the last 6 pts on study. Results: Median donor CD3chimerism beforepentostatin/DLI was 28 (5-47)%. Efficacy, defined by increases in donor CD3chimerism>10% maintained to day 56 post-DLI, was seen in 16 pts (44.4%) with a median CD3 donorchimerism of 64 (48-100)%. There was a trend for better efficacy among the 21 pts who received first treatment within 100 days after transplant (57%) compared to the 15 pts who received first treatment more than 100 days after HCT (27%) (p=0.07). Six pts received 2nd treatment ofpentostatin/DLI; among them 1 responded. Fifteen pts (12 responders) developedaGVHD after DLI [grade I (n=2), II (n=9), III (n=3), IV (n=1)] at a median of 10 (0-83) days after DLI. One pt developed skinGVHD, grade II, afterpentostatin administration and DLI was aborted. Of the 16 pts who developedaGVHD afterpentostatin/DLI, 3 had a prior history of GVHD after transplant. Thirteen pts developedcGVHD, ofwhom 10 developedecGVHD at a median of 112 (13-347) days after DLI. One pt developedecGVHD with no prioraGVHD. Among the 6 pts who received prophylaxis IS after DLI 1 pt developedaGVHD grade II, and none developedcGVHD. However, only 2 of those 6 pts responded. Seventeen pts developed grade 4cytopenia after DLI; 9 pts developed both neutropenia and thrombocytopenia, 4 pts developed neutropenia, and 4 pts developed thrombocytopenia. Among the 13 patients who developed grade 4 neutropenia, 9 (69%) were non-responders. Median time between DLI and lowest ANC count was 22 (2-100) days, and neutropenia lasted for median of 7 (1-52) days. Twelve pts received platelet transfusions started at median of 33 (1-98) days after DLI. Nineteen pts relapsed at a median of 91 (26-777) days after DLI. Among the 20 non-responders 12 relapsed (60%), compared to 7 of 16 responders (44%) (HR 0.64 (0.3-1.6), p=0.35). Ten of the 17 pts (59%) who developedcytopenia relapsed, 6 ofwhom (60%) were non-responders. Median number of significant infections was 2 (0-10) per pt. Twenty-eight pts died at a median of 522 (67-2028) days after DLI. Causes of death were relapse (n=21), respiratory failure/infections (n=4), grade IV GVHD (n=2), or other causes (n=1). Five of the 16 responders (31%) are alive, all in CR. Six of the 20 non-responders (30%) are alive, only 3 in CR (Figure 1). Summary:Pentostatin/DLI increased donor CD3chimerism in pts after HCT if was given within 100 days after transplant, and it was well tolerated. Response was associated with GVHD. Delayed treatment after HCT and prophylactic IS after DLI were associated with decreased efficacy. There was a trend for higher relapse rate among the non-responders and pts who developed cytopenia, but the differences were not statistically significant. Figure Progression Free Survival after pentostatin/DLI Figure. Progression Free Survival after pentostatin/DLI Disclosures Pulsipher: Novartis: Consultancy, Other: Advisory Board, Steering Committee for Phase II Study; Jazz Pharmaceutical: Consultancy, Other: Advisory Board; Chimerix: Consultancy, Other: Advisory Board ; Medac: Other: Travel support for a study group.

Background: Regimens using post-transplant cyclophosphamide (CY) have been developed to provide potent in vivo T cell depletion for patients undergoing human leukocyte antigen (HLA)-haploidentical hematopoietic cell transplantation (HCT). Luznik, O'Donnell and colleagues (BBMT 2008) reported that when this immune suppression strategy is coupled with non-myeloablative conditioning (fludarabine 150 mg/m2, CY 29 mg/kg, 2 Gy total body irradiation) followed by marrow transplantation, it was well-tolerated with low rates of non-relapse mortality (NRM; 15% at 1 year). However, the 2 year overall survival (OS) and event-free survival were low at 36% and 26%, respectively, due to high relapse rates (51% at 1 year). One explanation could be that while post-HCT CY promoted low rates of acute graft-versus-host disease (GVHD), it also eliminated early T and natural killer (NK) cell clones important for disease surveillance. Based on this hypothesis, we developed a next-generation Phase I/II clinical trial incorporating a boost of donor NK cells on day +7 as an attempt to prevent relapse after transplant. In this study, CY 50 mg/kg as a single dose on day +3 was used for T cell depletion. Methods: Forty patients (pediatric, n=14; adult, n=26) with median age of 45 (range 8-75) years having ALL (n=11), AML (n=9), MDS (n=6), HL (n=6), MM (n=4), NHL (n=3), and CLL (n=1) underwent non-myeloablative transplantation using related, HLA-haploidentical marrow donors on this prospective clinical trial. Patients were high risk due to underlying disease, potential for relapse, and/or risk for transplant-related mortality (TRM). Most patients were heavily pre-treated, with median time from cancer diagnosis to transplant being 2 (0.3 - 12.1) years, including 18 patients having 26 prior HCTs (auto, n=14; allo, n=12). Twenty-five patients (63%) had HCT-CI scores ≥ 3 indicating high risk for TRM. In order to obtain NK cells, non-mobilized peripheral blood mononuclear cells were collected from donors on day +6 using apheresis and stored overnight. NK cells were isolated on day +7 using the Miltenyi CliniMACS system (CD3 depletion followed by CD56 selection) and were administered as a single, fresh infusion that same day without prior culturing or expansion. The Phase I dose-finding study (n=11) enrolled at 2 NK doses [2.5 or 5 x 106/kg +/- 20%, respectively], with extended enrollment at the 2nd dose level for Phase II (n=29) with 83% of patients meeting NK dose parameters. NK cell products had a median log T cell depletion of 5.4 (4.1-7.1), median NK recovery of 54% (33-68%), and median NK purity of 92% (74-99%). Excellent viability (>95%) was seen in all NK products. Results: One patient developed chest pain associated with NK cell infusion; otherwise all other patients tolerated their NK cell infusions well without fevers or other adverse reactions. Full donor chimerism (>95% CD3) was seen in 83% of patients at last follow-up, while 18% and 10% experienced graft rejection or graft failure, respectively. Cumulative incidence of grades 2-3 and grade 3 (no grade 4 seen) acute GVHD occurred in 36% and 8% of patients, respectively, at day +100. Of the 39 evaluable patients, 16% developed chronic extensive GVHD at 1 year. Relapse or progression occurred in 31% of patients by 1 year after HCT. With a median follow-up of 1.5 years (range, 0.1 - 4.9 years), 14 patients have died from relapse/progression (n=11) or infection/VOD (n=3), giving a probability of OS, relapse/progression-free survival (PFS), and NRM at 1 year of 73%, 62%, and 8%, respectively, and 2 year OS and relapse/PFS of 63% and 46%, respectively (Fig 1). Summary: We have demonstrated the safety of infusing donor NK cells early after HCT in a group of heavily-treated patients with high-risk hematological malignancies. In many patients, disease-free survival was possible with the aid of this prophylactic infusion of donor NK cells in combination with allogeneic HCT. These results provide a promising platform to further augment NK cell alloreactivity in the post-HCT setting to prevent relapse and disease progression. Figure 1 Incidence of Overall Survival and Relapse/Progression-Free Survival Figure 1. Incidence of Overall Survival and Relapse/Progression-Free Survival Disclosures Hari: Merck: Research Funding; BMS: Honoraria.

Between 1970 and 1996, 333 patients with severe aplastic anemia underwent HLA-matched related marrow transplant after conditioning with cyclophosphamide (CY). Thirty-five percent of patients transplanted between 1970 and 1976 (group 1), 12% of those transplanted between 1977 and 1981 (group 2), and 9% of patients transplanted between 1982 and 1997 (group 3) had graft rejection. Graft rejection occurred later among group 3 patients (median, 180 days) than among those in groups 1 and 2 (medians, 28 and 47 days, respectively; P < .001 group 3 v 2). In group 3, 92% of rejecting patients underwent a second transplant, compared with 78% and 77% in groups 1 and 2, respectively. Group 1 patients received various conditioning regimens before second transplant, whereas most patients of groups 2 and 3 received CY combined with antithymocyte globulin (ATG). Graft-versus-host disease (GVHD) prophylaxis after second transplant consisted of methotrexate (MTX) for all group 1 and 2 patients, whereas group 3 patients received MTX combined with cyclosporine (CSP). Over the three time periods studied, first graft rejection decreased from 35% to 9%, and the proportion of rejecting patients undergoing second transplants increased from 77% to 92%. The 10-year probability of survival after second transplants increased from 5% to 83%. Multivariate analysis showed MTX/CSP GVHD prophylaxis to be a significant factor accounting for the increase in patient survival after second transplant. © 1998 by The American Society of Hematology.

Primary graft rejection after marrow transplantation occurs more frequently in patients receiving HLA-haploidentical compared with HLA-identical sibling transplants. Both human and experimental animal data suggest that the cells responsible for this phenomenon are either host natural killer (NK) cells, T cells, or both. To investigate the mechanisms of graft rejection, we have developed a canine model of marrow transplantation, which uses DLA-nonidentical unrelated donors in the absence of postgrafting immunosuppression. In this model most animals rejected their marrow grafts after a preparative regimen of 9.2 Gy total body irradiation (TBI). However, engraftment of DLA-nonidentical marrow can be facilitated when the recipients are pretreated with monoclonal antibody (MoAb) S5, which recognizes CD44. In this report, we extended these observations by first cloning the canine CD44 and, next, mapping the epitope recognized by S5, which was located in a region conserved among human and canine CD44 and was distinct from the hyaluronan binding domain. However, in vitro binding of S5 caused a conformational change in CD44, which allowed increased hyaluronan binding. Then, we reexamined the in vivo model of marrow transplantation and compared results with MoAb S5 to those with two other anti-CD44 MoAbs, IM7 and S3. Only MoAb S5 significantly increased the engraftment rate of DLA-nonidentical unrelated marrow, whereas the two other anti-CD44 MoAbs were ineffective. The enhanced in vivo effect was not related to differences in the MoAbs' avidities, since both S5 and IM7 had equivalent binding to CD44, but most likely related to the specific epitope that S5 recognizes. Thus, this study shows that the effect of the anti-CD44 MoAb S5 in facilitating engraftment is epitope specific and if one is to use an anti-CD44 to facilitate engraftment of marrow in humans, one cannot assume that any anti-CD44 would work.

Primary graft rejection after marrow transplantation occurs more frequently in patients receiving HLA-haploidentical compared with HLA-identical sibling transplants. Both human and experimental animal data suggest that the cells responsible for this phenomenon are either host natural killer (NK) cells, T cells, or both. To investigate the mechanisms of graft rejection, we have developed a canine model of marrow transplantation, which uses DLA-nonidentical unrelated donors in the absence of postgrafting immunosuppression. In this model most animals rejected their marrow grafts after a preparative regimen of 9.2 Gy total body irradiation (TBI). However, engraftment of DLA-nonidentical marrow can be facilitated when the recipients are pretreated with monoclonal antibody (MoAb) S5, which recognizes CD44. In this report, we extended these observations by first cloning the canine CD44 and, next, mapping the epitope recognized by S5, which was located in a region conserved among human and canine CD44 and was distinct from the hyaluronan binding domain. However, in vitro binding of S5 caused a conformational change in CD44, which allowed increased hyaluronan binding. Then, we reexamined the in vivo model of marrow transplantation and compared results with MoAb S5 to those with two other anti-CD44 MoAbs, IM7 and S3. Only MoAb S5 significantly increased the engraftment rate of DLA-nonidentical unrelated marrow, whereas the two other anti-CD44 MoAbs were ineffective. The enhanced in vivo effect was not related to differences in the MoAbs' avidities, since both S5 and IM7 had equivalent binding to CD44, but most likely related to the specific epitope that S5 recognizes. Thus, this study shows that the effect of the anti-CD44 MoAb S5 in facilitating engraftment is epitope specific and if one is to use an anti-CD44 to facilitate engraftment of marrow in humans, one cannot assume that any anti-CD44 would work.