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When multiple haploidentical donors are available for transplantation, those of younger generations are generally selected over those of older generations. However, it is unclear who is the optimal donor when selecting candidates from within a generation, such as father versus mother, son versus daughter, or brother versus sister. Although traditionally male donors are favored over female donors, particularly for male recipients, and significant associations of individual HLA mis(matches) on outcomes are being increasingly recognized, the hierarchy of factors for donor selection is indeterminate. To assess whether HLA factors take precedence over non-HLA factors and to isolate the influence of specific characteristics on outcomes, we analyzed 412 patients stratified by donor relationship: child donor (son [n = 202] versus daughter [n = 96]), parent (father [n = 28] versus mother [n = 29]), and sibling (noninherited maternal [NIMA; n = 29] versus paternal [NIPA; n = 28] mismatched). Among siblings, NIMA mismatch was associated with a lower risk of acute graft-versus-host disease (aGVHD); B-leader mismatch was associated with high nonrelapse mortality (NRM), poor progression-free survival, and a trend toward poor overall survival (OS), whereas A-mismatch was associated with lower aGVHD. Among parent donors, the relationship did not impact any outcome; B-leader mismatch was associated with higher NRM and a trend toward poor OS, whereas A-mismatch was associated with lower NRM and improved progression-free survival and OS. Among child donors, no individual HLA mismatch was predictive of any outcome, and daughter donors were not associated with any adverse outcomes in multivariate analyses. Our data suggest that certain HLA factors may be more significant in some cases and should be given priority over simply selecting a donor based on relationship/sex.

Recent compelling evidence showed that innate immune effector cells could recognize allogeneic grafts and prime an adaptive immune response. Signal regulatory protein α (SIRPα) is an immunoglobulin superfamily receptor that is expressed on myeloid cells; the interaction between SIRPα and its ubiquitously expressed ligand CD47 elicits an inhibitory signal that suppresses macrophage phagocytic function. Additional studies showed that donor-recipient mismatch in SIRPα variants might activate monocytic allorecognition, possibly as the result of non-self SIRPα-CD47 interaction. However, the frequency of SIRPα variation and its role in hematopoietic stem cell transplantation (HSCT) remains unexplored. We studied 350 patients with acute myeloid leukemia/myelodysplastic syndrome who underwent HLA-matched related HSCT and found that SIRPα allelic mismatches were present in 39% of transplantation pairs. SIRPα variant mismatch was associated with a significantly higher rate of chronic graft-versus-host disease (GVHD; hazard ratio [HR], 1.5; P = .03), especially de novo chronic GVHD (HR, 2.0; P = .01), after adjusting for other predictors. Those with mismatched SIRPα had a lower relapse rate (HR, 0.6; P = .05) and significantly longer relapse-free survival (RFS; HR, 0.6; P = .04). Notably, the effect of SIRPα variant mismatch on relapse protection was most pronounced early after HSCT and in patients who were not in remission at HSCT (cumulative incidence, 73% vs 54%; HR, 0.5; P = .01). These findings show that SIRPα variant mismatch is associated with HSCT outcomes, possibly owing to innate allorecognition. SIRPα variant matching could provide valuable information for donor selection and risk stratification in HSCT.

Haploidentical donors are increasingly used for patients requiring hematopoietic stem cell transplantation (HSCT). Although several factors have been associated with transplant outcomes, the impact of HLA disparity in haploidentical HSCT (haplo-HSCT) remains unclear. We investigated the impact of HLA disparity quantified by mismatched eplets (ME) load of each HLA locus on the clinical outcome of 278 consecutive haploidentical transplants. Here, we demonstrated that the degree of HLA molecular mismatches, at individual HLA loci, may be relevant to clinical outcome in the haplo-HSCT. A significantly better overall survival was associated with higher ME load from HLA-A (hazard ratio [HR], 0.97; 95% confidence interval [CI], 0.95-0.99; P = .003) and class I loci (HR, 0.99; 95% CI, 0.97-0.99; P = .045) in the host-versus-graft direction. The apparent survival advantage of HLA-A ME was primarily attributed to reduced risk in relapse associated with an increase in HLA-A ME load (subdistribution HR, 0.95; 95% CI, 0.92-0.98; P = .004). Furthermore, we have identified an association between the risk of grade 3-4 acute graft-versus-host disease (GVHD) and a higher ME load at HLA-B and class I loci in graft-versus-host (GVH) direction. Additionally, GVH nonpermissive HLA-DPB1 mismatch defined by T-cell epitope grouping was significantly associated with relapse protection (subdistribution HR, 0.19; 95% CI, 0.06-0.59; P = .004) without a concurrent increase in GVHD. These findings indicate that alloreactivity generated by HLA disparity at certain HLA loci is associated with transplant outcomes, and ME analysis of individual HLA loci might assist donor selection and risk stratification in haplo-HSCT.

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a potentially curative therapy for hematologic malignancies. Alloreactivity after HSCT is known to be mediated by adaptive immune cells expressing rearranging receptors. Recent studies demonstrated that the innate immune system could likewise sense the non-self signals and subsequently enhance the alloimmune response. We recently demonstrated that the donor/recipient mismatch of signal regulatory protein α (SIRPα), an immunoglobulin receptor exclusively expressed on innate cells, is associated with a higher risk of cGVHD and relapse protection in a cohort of acute myeloid leukemia patients who underwent allo-HSCT. Whether these effects also occur in other hematologic malignancies remains unclear. In the present study, we compared outcomes by SIRPα match status in a cohort of 310 patients who received allo-HSCT from an HLA matched-related donor for the treatment of lymphoid malignancies. Multivariable analysis showed that SIRPα mismatch was associated with a significantly higher rate of cGVHD (hazard ratio [HR] 1.8, P= .002), cGVHD requiring systemic immunosuppressive therapy (HR 1.9, P= .005), a lower rate of disease progression (HR 0.5, P= .003) and improved progression-free survival (HR 0.5, P= .001). Notably, the effects of SIRPα mismatch were observed only in the patients who achieved >95% of donor T-cell chimerism. The mismatch in SIRPα is associated with favorable relapse protection and concurrently increased risk of cGVHD in patients who undergo allo-HSCT for lymphoid malignancies, and the optimal donor could be selected based on the finding of the study to mitigate the risk of GVHD and relapse.

HLA-DPB1 mismatches between donor and recipient are commonly seen in allogeneic hematopoietic stem cell transplantation from an unrelated donor. HLA-DPB1 mismatch, conventionally determined by the similarity of the T-cell epitope (TCE), is associated with an increased risk of acute graft-versus-host disease (GVHD) and a decreased risk of disease relapse. We investigated the clinical impact of HLA-DPB1 molecular mismatch quantified by mismatched eplets (ME) and the Predicted Indirectly Recognizable HLA Epitopes Score (PS) in a cohort of 1,514 patients receiving hematopoietic stem cell transplants from unrelated donors matched at HLA-A, -B, -C, -DRB1/3/4/5, and - DQB1 loci. HLA-DPB1 alloimmunity in the graft-versus-host direction, determined by high graft-versus-host ME/PS, was associated with a reduced risk of relapse (hazard ratio [HR]=0.83, P=0.05 for ME) and increased risk of grade 2-4 acute GVHD (HR=1.44, P

We investigated the impact of donor-recipient HLA-DPB1 matching on outcomes of allogeneic hematopoietic stem cell transplantation with in vivo T-cell depletion using antithymocyte globulin (ATG) for patients with hematological malignancies. All donor-recipient pairs had high-resolution typing for HLA-A, HLA-B, HLA-C, HLA-DRB1, HLA-DQB1, HLA-DPB1, and HLA-DRB3/4/5 and were matched at HLA-A, HLA-B, HLA-C, and HLA-DRB1. HLA-DPB1 mismatches were categorized by immunogenicity of the DPB1 matching using the DPB T-cell epitope tool. Of 1004 donor-recipient pairs, 210 (21%) were DPB1 matched, 443 (44%) had permissive mismatches, 184 (18%) had nonpermissive mismatches, in graft-versus-host (GVH) direction, and 167 (17%) had nonpermissive mismatches in host-versus-graft (HVG) direction. Compared with HLA-DPB1 permissive mismatched pairs, nonpermissive GVH mismatched pairs had the highest risk for grade II to IV acute graft-versus-host disease (aGVHD) (hazard ratio [HR], 1.4; P = .01) whereas matched pairs had the lowest risk (HR, 0.5; P < .001). Grade III to IV aGVHD was only increased with HLA-DPB1 nonpermissive GVH mismatched pairs (HR, 2.3; P = .005). The risk for disease progression was lower with any HLA-DPB1 mismatches, permissive or nonpermissive. However, the favorable prognosis of HLA-DPB1 mismatches on disease progression was observed only in peripheral blood stem cell recipients who were in the intermediate-risk group by the Disease Risk Index (HR, 0.4; P = .001) but no other risk groups. Our results suggest avoidance of nonpermissive GVH HLA-DPB1 mismatches for lowering the risk for grade II to IV and III to IV aGVHD. Permissive or nonpermissive HVG HLA-DPB1 mismatches may be preferred over HLA-DPB1 matches in the intermediate-risk patients to decrease the risk for disease progression.

Detection of donor-specific anti-HLA antibodies (DSA) has been associated with graft rejection in all forms of transplantation. The mechanism by which DSA increase the risk of graft failure remains unclear. We hypothesized that complement-binding DSA are associated with engraftment failure in hematopoietic stem cell transplantation (HSCT) and analyzed 122 haploidentical transplant recipients tested prospectively for DSA. Retrospective analysis to detect C1q binding DSA (C1q+DSA) was performed on 22 allosensitized recipients. Twenty-two of 122 patients (18%) had DSA, 19 of which were women (86%). Seven patients with DSA (32%) rejected the graft. Median DSA level at transplant for patients who failed to engraft was 10,055 mean fluorescence intensity (MFI) versus 2065 MFI for those who engrafted (P = .007). Nine patients with DSA were C1q positive in the initial samples with median DSA levels of 15,279 MFI (range, 1554 to 28,615), compared with 7 C1q-negative patients with median DSA levels of 2471 MFI (range, 665 to 12,254) (P = .016). Of 9 patients who were C1q positive in the initial samples, 5 patients remained C1q positive at time of transplant (all with high DSA levels [median, 15,279; range, 6487 to 22,944]) and experienced engraftment failure, whereas 4 patients became C1q negative pretransplant and all engrafted the donor cells (P = .008). In conclusion, patients with high DSA levels (>5000 MFI) and complement-binding DSA antibodies (C1q positive) appear to be at much higher risk of primary graft failure. The presence of C1q+DSA should be assessed in allosensitized patients before HSCT. Reduction of C1q+DSA levels might prevent engraftment failure in HSCT.

Cord blood transplant requires less stringent human leukocyte antigen matching than unrelated donors. In 133 patients with hematologic malignancies who engrafted after double cord blood transplantation with a dominant unit, we studied the effect of high resolution testing at 4 loci (-A, -B, -C, -DRB1) for its impact on 2-year transplant-related mortality. Ten percent of the dominant cord blood units were matched at 7-8/8 alleles using HLA-A, -B, -C, and -DRB1; 25% were matched at 6/8, 40% at 5/8, and 25% at 4/8 or less allele. High resolution typing at 4 loci showed that there was no 2-year transplant-related mortality in 7-8/8 matched patients. Patients with 5-6/8 matched dominant cord blood units had 2-year transplant-related mortality of 39% while patients with 4/8 or less matched units had 60%. Multivariate regression analyses confirmed the independent effect of high resolution typing on the outcome when adjusted for age, diagnosis, CD34(+) cell dose infused, graft manipulation and cord to cord matching. The worst prognostic group included patients aged over 32 years with 4/8 or less matched cord blood units compared with patients who were either younger than 32 years old independent of allele-level matching, or aged over 32 years but with 5-6/8 matched cord blood units (Hazard Ratio 2.2; 95% confidence interval: 1.3-3.7; P

The use of unrelated donors matched in all alleles of HLA-A, -B, -C, and -DRB1 loci has been associated with superior outcomes compared with those having 1 or more mismatches. Recent studies showed increased transplant-related mortality (TRM) with the use of HLA-DPB1 mismatched donors supporting the notion that the ideal volunteer unrelated donor should fully match at HLA-A, -B, -C, and -DRB1 and lack -DPB1 mismatches. The issue of the effect of HLA-DPB1 mismatch on the disease progression rate is still controversial and we aimed to investigate the impact of HLA-DPB1 mismatch in the graft versus host direction on transplant outcomes in patients categorized according to the recently defined disease risk index (DRI) for disease risk classification. Our study cohort included 1,211 transplant patients with hematological malignancies whohave received an hematopoietic stem cell transplant (HSCT) from an unrelated HLA-A, -B, -C,-DRB1 matched donor by high resolution typing (8/8 matched) after 2005 through 2014. The study cohort had a median age of 55 (range, 19-77); the hematopoietic stem cell source was peripheral blood (PB) in 698 and bone marrow (BM) in 513 patients. Disease risk index (DRI) at HSCT was high or very high in 382 (33%), intermediate in 598 (51%), low in 185 (16%) patients. Of the pairs, 1,154 (95%) were matched atHLA-DQB1 and 1,116 (92%) at HLA- DRB3/4/5 by high resolution testing. However, 633 (52%) had mismatch at one of the DPB1 alleles and 208 (17%) had two mismatches. There was association between matching for DPB1and matching for DRB3/4/5 (p=0.002) but not with DQB1. In PB recipients, there was a highly significant decreaseof disease progression in DPB1 mismatched pairs (one and two allele; HR=0.7, p=0.01 and HR=0.6, p=0.01 respectively) as compared tothose pairs with DPB1 matched. The impact of mismatches at one or two alleles were not different on disease progression (HR=1.2, p=0.4). However, the impact of DPB1 mismatch on disease progression was not uniform in different disease risk groups by DRI. Mismatch at DPB1 significantly decreased disease progression only in the intermediate risk group (HR=0.5, p=0.002) but not in low risk and high/very high disease groups by DRI (HR=0.9, p=0.8 and HR=0.7, p=0.1 respectively) (Figure 1a-c). In BM recipients, increasing number of DPB1 incompatibilities decreased disease progression (HR=0.9, p=0.4 and HR=0.6, p=0.1 for 1 and 2 allele mismatches respectively) but did not reach significance. Mismatches at HLA-DQB1 and -DRB3/4/5 had no impact on disease progression in both PB and BM recipients. Pairs with one or two allele-level DPB1 mismatches increased TRM compared with DPB1 matched pairs in PB (HR=1.5, p=0.04 and HR=1.9, p=0.006 respectively) and BM recipients (HR=1.8, p=0.03 and HR=1.9, p=0.05). There was no difference between two and one allele DPB1 mismatched for TRM in PB and BM recipients. Multivariate analyses revealed that the negative impact of DPB1 mismatch on TRM was not uniform in younger or (?) older patients. Interestingly, DPB1 mismatches increased TRM only in younger (aged We next analyzed the impact of DPB1 matching on progression free survival (PFS) and did not observe any impact of DPB1 mismatches on PFS in PB (HR=0.9, p=0.9) and BM (HR=1.12, p=0.6) recipients. Subgroup analyses by DRI to identify a specific risk group that the use of HLA-A, -B, -C and -DRB1 matched but DPB1 mismatched unrelated donor might lead to improved PFS did not reveal any particular risk group in both PB and BM recipients. Thus, in recipients of HLA-A, -B-C and DRB1 allele-level matched unrelated donors a mismatch for DPB1 is associated with a significantlydecreased risk of disease progression with no impact on PFS in intermediate risk group by DRI. Further analysis permissive vs. non-permissive DPB1 mismatches would be warranted. Figure 1. The cumulative incidence of disease progression by DPB1 mismatch and Disease Risk Index in peripheral blood recipients. Figure 1. The cumulative incidence of disease progression by DPB1 mismatch and Disease Risk Index in peripheral blood recipients. Disclosures No relevant conflicts of interest to declare.

Cord blood (CB) as a hematopoietic stem cell source has the advantage of decreased stringency of human leukocyte antigen (HLA) matching requirements. However, recent studies showed better outcomes in single CB transplant (CBT) with improved allele-level matching for 4 HLA loci (-A, -B, -C, and -DRB1). We retrospectively analyzed 146 patients with hematological malignancies who engrafted after dCBT between 2003 through 2013 to compare the prognostic value of the current standard HLA matching criteria (intermediate resolution HLA typing at A and B and allele-level typing at DRB1) versus that of allele level matching at –A, -B, -DRB1 (6/6 allele) and at -A, -B, -C, and -DRB1 (8/8 allele). The effect of HLA match was based on the HLA type of the predominant long term engrafting unit. The primary endpoint was 1-year transplant related mortality (TRM). In this cohort, median age was 43 (range; 1 –73). Disease diagnoses were AML in 56%, ALL in 21%, other hematological malignancies in the rest of the group. Disease status at dCBT was first or second complete remission in 55% and third remission or active disease in 45% of the patients. Conditioning was myeloablative in 62% of the patients consisting of mostly thiotepa, fludarabine and melphalan (86%). Reduced intensity conditioning was given to older and/or frail patients (38%) and consisted of cytoxan, fludarabine and TBI 200 cGy in 64% and melphalan with fludarabine in 36% of the patients. Immunosuppressive were mycophenolate mofetil (MMF) with tacrolimus and all patients received ATG as a part of the conditioning. Per protocol requirements over the years, 63% of the patients had ex-vivo expansion of one of the CB units with mesenchymal-cell coculture and 2% had one of the CB unit fucoylated. Median cell dose infused was 2.2 x 10e7 TNC/kg (range 0.5-291). Of 146 patients, 54% had 4/6, 40% 5/6 and only 6% 6/6 matched CB units by the current standard HLA matching criteria. Patients who had 6/6 matched units have the lowest TRM compared with 4/6 group but this did not reach statistical significance (p=0.2). By 6/6 allele-level matching criteria; 20% of the patients had ≤3/6; 51% 4/6 and 29% were 5-6/6 matched CB units. Per this criteria, patients with 5-6/6 allele-level matched units had lower TRM compared with ≤4/6 allele-level matched unit recipients (HR=0.4, p=0.04). More importantly, of 65 patients with 5-6/6 matched units by standard criteria, 37% were found to have ≤4/6 allele-level matched units that would lead to high TRM. By 8/8 allele-level matching criteria; 26% of the patients had 3-4/8; 39% 5/8, 26% 6/8 and 10% 7-8/8 matched CB units. Based on this criteria, 3 different groups emerged; 7-8/8, 5-6/8, and ≤4/8. Recipients of 7-8/8 allele-level matched units did not experience TRM at one year. Patients with 5-6/8 allele-level matched units also had less TRM compared with ≤4/8 matched recipients (HR=0.5, p=0.02). Among other variables analyzed; including age, disease, disease status, conditioning regimen, CB unit modification, unit TNC dose; only age >30 was a poor risk factor for 1-year TRM (HR=2.5, p=0.03). When we simultaneously accounted for age and 8/8 allele-level matching, we were able to identify 3 distinct risk groups for 1-year TRM (Table and Figure): 1) Low risk; 7-8/8 allele-level matched unit recipients with 1 year TRM of 0%. 2) High risk; age>30 and ≤4/8 allele-level matched CB units with 1-year TRM of 60% 3) Intermediate risk; all remaining patients with TRM of 30%. This risk stratification was independent of TNC cell dose infused. The respective 1-year cumulative incidence of TRM in the low-, high-, and intermediate-risk groups was 0%, 64% and 30% for patients who received TNC dose ≤ median (0.22X10e7); and 0%, 54% and 31% for patients who received TNC dose > median. Abstract 2532. Table 1TRMProgressionOSnHR95%CIpHR95%CIpHR95%CIpHigh risk27RefRefRefIntermediate risk930.40.1-0.70.0041.50.4-4.40.40.50.3-0.80.005Low risk13NE0.0032.30.6-8.50.20.40.1-0.90.04 Figure 1 Figure 1. These results show that, compared with the current standard matching, allele-level matching for HLA -A, -B, -C, and –DR may have a stronger prognostic value as it identifies subgroups of patients likely to have very high or very low rate of TRM after dCBT. We suggest that allele-level matching for 4 HLA loci should be used for the selection of dCB units. Disclosures No relevant conflicts of interest to declare.