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Plasmablastic lymphoma (PBL) is a rare entity, commonly associated with immunosuppressed states such as human immunodeficiency virus (HIV) infection or solid organ transplant. The clinical course is characterized by high relapse rates and a poor prognosis, leading some clinicians to recommend aggressive frontline therapy. However, a specific review of limited stage (LS) PBL patients is not available to evaluate outcomes and justify treatment recommendations. We performed a retrospective review of LS PBL cases to provide insight into this rare disease. Our cohort consisted of 80 stage I or II PBL patients from 13 US academic centers. With a median follow up of 34 months (1-196), the 3-year progression-free survival (PFS) and overall survival (OS) of the entire cohort were 72% (95% CI 62, 83) and 79% (95% CI 70, 89), respectively. The 3-year PFS and OS of patients treated with frontline chemotherapy alone was 65% (95% CI 50, 84) and 71% (95% CI 56, 89), respectively, compared to 85% (95% CI 72, 100) and 96% (95% CI 89, 100), respectively, in patients treated with combined frontline chemotherapy with radiation consolidation. Our data demonstrate favorable outcomes in LS PBL with no improvements in outcome from aggressive frontline treatment including Hyper-CVAD or auto-SCT consolidation. Multivariate regression analysis (MRA) demonstrated improved PFS for patients receiving EPOCH based frontline therapy versus CHOP (HR: 0.23; p = 0.029). Frontline chemotherapy followed by radiation consolidation versus chemotherapy alone appeared to be associated with improved relapse and survival outcomes but did not show statistical significance in MRA.

New therapies are needed for patients with relapsed/refractory (rel/ref) diffuse large B-cell lymphoma (DLBCL) who do not benefit from or are ineligible for stem cell transplant and chimeric antigen receptor therapy. The CD30-targeted, antibody-drug conjugate brentuximab vedotin (BV) and the immunomodulator lenalidomide (Len) have demonstrated promising activity as single agents in this population. We report the results of a phase 1/dose expansion trial evaluating the combination of BV/Len in rel/ref DLBCL. Thirty-seven patients received BV every 21 days, with Len administered continuously for a maximum of 16 cycles. The maximum tolerated dose of the combination was 1.2 mg/kg BV with 20 mg/d Len. BV/Len was well tolerated with a toxicity profile consistent with their use as single agents. Most patients required granulocyte colony-stimulating factor support because of neutropenia. The overall response rate was 57% (95% CI, 39.6-72.5), complete response rate, 35% (95% CI, 20.7-52.6); median duration of response, 13.1 months; median progression-free survival, 10.2 months (95% CI, 5.5-13.7); and median overall survival, 14.3 months (95% CI, 10.2-35.6). Response rates were highest in patients with CD30+ DLBCL (73%), but they did not differ according to cell of origin (P = .96). NK cell expansion and phenotypic changes in CD8+ T-cell subsets in nonresponders were identified by mass cytometry. BV/Len represents a potential treatment option for patients with rel/ref DLBCL. This combination is being further explored in a phase 3 study (registered on https://clinicaltrials.org as NCT04404283). This trial was registered on https://clinicaltrials.gov as NCT02086604.

Background Breast implant–associated anaplastic large cell lymphoma (BIA-ALCL) is a rare malignancy originating from the periprosthetic capsule of a textured, most often macrotextured, breast implant. Identified in women whose indications for breast implants can be either aesthetic or reconstructive, the genomic underpinnings of this disease are only beginning to be elucidated. Objectives The aim of this study was to evaluate the exomes, and in some cases the entire genome, of patients with BIA-ALCL. Specific attention was paid to copy number alterations, chromosomal translocations, and other genomic abnormalities overrepresented in patients with BIA-ALCL. Methods Whole-exome sequencing was performed on 6 patients, and whole-genome sequencing on 3 patients, with the Illumina NovaSeq 6000 sequencer. Data were analyzed with the Illumina DRAGEN Bio-IT Platform and the ChromoSeq pipeline. The Pathseq Genome Analysis Toolkit pipeline was used to detect the presence of microbial genomes in the sequenced samples. Results Two cases with STAT3 mutations and 2 cases with NRAS mutations were noted. A critically deleted 7-Mb region was identified at the 11q22.3 region of chromosome 11, and multiple nonrecurrent chromosomal rearrangements were identified by whole-genome sequencing. Recurrent gene-level rearrangements, however, were not identified. None of the samples showed evidence of potential microbial pathogens. Conclusions Although no recurrent mutations were identified, this study identified mutations in genes not previously reported with BIA-ALCL or other forms of ALCL. Furthermore, not previously reported with BIA-ALCL, 11q22.3 deletions were consistent across whole-genome sequencing cases and present in some exomes. Level of Evidence: 5

Polatuzumab vedotin is an antibody-drug conjugate comprised of an anti-CD79b monoclonal antibody conjugated to monomethyl auristatin (MMAE), a microtubule-disrupting cytotoxin. CD79b is almost exclusively expressed on normal and malignant B-cells, making it an appealing target for novel therapeutics.This article reviews the current literature on polatuzumab vedotin, including its pharmacology, as well as summarizing the results of clinical trials in relapsed/refractory diffuse large B-cell lymphoma (DLBCL) as a single agent and in combination with other chemotherapies and chemoimmunotherapies. The current landscape of approved therapies for relapsed and refractory DLBCL, as well as other promising novel approaches, is discussed.The recent approval of polatuzumab vedotin in combination with bendamustine and rituximab (BR) offers another option to patients with DLBCL who are not eligible for autologous hematopoietic cell transplant or chimeric antigen receptors (CAR)-T cell therapy. In younger patients and those without serious comorbidities, polatuzumab vedotin-BR may serve as bridging therapy to more intensive therapies with reasonable efficacy and tolerability. Polatuzumab vedotin is currently being studied in a randomized trial in the front line setting in combination with rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP).

Breast implant-associated anaplastic large cell lymphoma (BIA-ALCL) is a subtype of T-cell lymphoma with much of its pathogenesis poorly understood. Mutations in the JAK/STAT pathway have been identified in a substantial proportion of cases, as well as copy number aberrations (CNAs). However, a more discrete characterization is vital to identify those with a germline predisposition to develop BIA-ALCL when exposed to a textured implant, and to identify targets for precision anti-BIA-ALCL therapeutics.To determine if there are recurrent gene mutations in BIA-ALCL patients in a cohort at a single institution.Ten patients were included that were diagnosed with BIA-ALCL between April 2015 and May 2020. Whole exome sequencing (WES) was performed on 8 tumor and normal BIA-ALCL samples and whole genome sequencing (WGS) was performed on 3 BIA-ALCL fluid samples. Samples were sequenced on an Illumina NovaSeq 6000. Data was analyzed using the Illumina DRAGEN Bio-IT Platform v3.8 workflow.This study was carried out at Barnes Jewish Hospital/Siteman Cancer Center.Patients were included if they have a pathology proven diagnosis of BIA-ALCL.Incidence and quantification of recurrent mutations in tumor samples of patients with BIA-ALCL evaluated via WES and WGS.Nearly all BIA-ALCLs showed substantial CNAs. Most patients had missense mutations in large genes with predominantly C to T transitions. Two cases had STAT3 mutations, consistent with previously reported data. Whole genome sequencing showed a critically deleted 7Mb region on chromosome 11 at 11q22.3 region in all 3 samples evaluated. This region contains the ATM gene which upon deletion in mouse models has shown an increased number of tumors. Clinically, the overall prognosis of BIA-ALCL was favorable; one patient passed from complications.There are no highly recurrent mutations in BIA-ALCL, however, 11q22.3 deletions were consistent across WGS cases and present in some exomes. Given the small sample size due to the rarity of the disease, genomic evaluation of a larger cohort is necessary to confirm this finding. Financial support for this study was provided by the Aesthetic Surgery Education Research Foundation and Barnes Hospital Foundation.

The malignant Hodgkin and Reed Sternberg (HRS) cells of classical Hodgkin lymphoma (cHL) are scarce in affected lymph nodes, creating a challenge to detect driver somatic mutations. As an alternative to cell purification techniques, we hypothesized that ultra-deep exome sequencing would allow genomic study of HRS cells, thereby streamlining analysis and avoiding technical pitfalls. To test this, 31 cHL tumor/normal pairs were exome sequenced to ∼1000x median depth of coverage. An orthogonal error-corrected sequencing approach verified >95% of the discovered mutations. We identified mutations in genes novel to cHL including: CDH5 and PCDH7; novel mutations in IL4R, and a novel pattern of recurrent mutations in pathways regulating Hippo signaling. This study provides proof-of-principle that ultra-deep exome sequencing can be utilized to identify recurrent mutations in HRS cells, allowing for the analysis for clinically relevant genomic variants in large cohorts of cHL patients.

While most patients with Hodgkin lymphoma (HL) are cured with initial treatment, relapse occurs in approximately 10–30% of cases [1,2]. Additionally, approximately 10% of patients have refractory d...

Current prognostic variables can only partly explain the large outcome heterogeneity in diffuse large B cell lymphoma (DLBCL). We aimed to investigate the utility of systems-level protein and immune repertoire profiling for outcome prognostication in DLBCL.In this retrospective study, we used proximity extension assay technology to quantify 81 immune-related proteins in serum or plasma in 2 independent cohorts in a total 111 DLBCL patients. Protein levels were assessed before and after treatment with rituximab and chemotherapy, and the patients were compared with 19 age- and sex-matched healthy blood donors. In a subset of the patients, we performed a broad mass cytometric characterization of immune cell repertoires in peripheral blood.Patients displayed large deviations in protein profiles compared with healthy controls. Development of a systemic protein deviation (SPD) score provided a 4-protein-based metric that reflected the overall degree of protein deviations compared with age- and sex-matched healthy blood donors. The SPD score identified patients with very poor overall survival in both cohorts and correlated with increased frequencies of peripheral blood PD-1Our results show that a simple metric based on measurement of a small set of serum or plasma proteins can be used to probe systemic immune changes associated with poor survival in DLBCL. This finding warrants further investigation in larger, prospective studies to establish a clinical prognostic biomarker.

For patients with relapsed or refractory classical Hodgkin lymphoma (cHL), salvage chemotherapy followed by consolidation with autologous stem cell transplant (ASCT) remains the standard of care. Even with this aggressive treatment strategy, 5-year progression-free survival is ≤50%, and there remains interest in maintenance strategies to improve long-term disease-free survival. Lenalidomide is an immunomodulatory agent with demonstrated activity in multiple subtypes of lymphoma including cHL, and has also been shown to improve both progression-free and overall survival as maintenance therapy after ASCT in multiple myeloma. This multicenter study evaluated maintenance lenalidomide after ASCT for patients with cHL. Patients were enrolled 60 to 90 days post-transplant and received oral lenalidomide on days 1 to 28 of 28-day cycles for a maximum of 18 cycles. Lenalidomide was started at 15 mg daily and increased to maximum of 25 mg daily if tolerated. The primary objective of this study was to assess the feasibility of this regimen, with a goal30% rate of discontinuation at or before cycle 12 for drug-related reasons. Twenty-seven patients were enrolled and 26 received at least 1 dose of lenalidomide. With a median follow-up of 51.3 months (range, 12.2 to 76.2 months), 23 of 26 patients were alive. Median event-free survival was 9.4 months and median progression-free survival had not been reached, with 17 of 26 patients (65.4%) remaining in remission at last follow-up. Excluding 4 patients who discontinued therapy for progression and 2 who discontinued due to noncompliance, the discontinuation rate at or before cycle 12 was 52%. Treatment was complicated by a high frequency of hematologic adverse events, with 15 patients (58%) experiencing grade 3 to 4 hematologic toxicity and 5 (19%) experiencing grade 4 hematologic toxicity. We conclude that the regimen of maintenance lenalidomide explored in this study is not feasible for patients with cHL immediately following ASCT. An alternative lenalidomide dose or schedule may be better tolerated following ASCT for patients with relapsed or refractory cHL.

Objectives Image-guided tissue sampling in the workup of suspected lymphoma can be performed by core needle biopsy (CNB) or CNB with fine-needle aspiration (FNA). We compared the yield of clinically actionable diagnoses between these methods of tissue sampling. Methods All ultrasound-guided percutaneous peripheral lymph node biopsies from 2010 to 2017 at a single institution were retrospectively reviewed for biopsy type (CNB versus CNB + FNA), prior diagnosis of lymphoma, size of the target lymph node, number of cores, length of core specimens, and pathologic diagnosis. Lymphoma and lymphoid tissue were included; metastatic disease and nonlymphoid tissue were excluded. An oncologist specializing in lymphoma independently determined whether an actionable diagnosis could be made with the pathologic results in the context of the patient's medical record. χ2 analyses and univariable/multivariable logistic regression models were used for statistical analyses. Results Of 578 lymph node biopsies, 306 (53%) had a prior diagnosis of lymphoma; 273 (47%) were CNB, and 305 (53%) were CNB + FNA. There was no significant difference between biopsy types (CNB versus CNB + FNA) in the number of cores (median [25th, 75th percentiles], 3 [3, 4] versus 4 [3, 4]; P = .47) or total length of tissue (4.1 [2.5, 6.1] versus 3.7 [2.3, 6] cm; P = .09). There was no difference in obtaining an actionable diagnosis between biopsy types after controlling for a known history of lymphoma (P = .271) or after controlling for the number of core specimens (P = .826). Conclusions In cases of suspected lymphoma, CNB without FNA was sufficient to obtain an actionable diagnosis.

Ubiquitous expression of CD19 on B cell non-Hodgkin lymphoma identified it as a potential target for immune-based therapies.This article reviews the current literature on anti-CD19 therapies currently in clinical trials including monoclonal antibodies (mAb), antibody targeted cytotoxic drug conjugates (ADC), bispecific antibodies, and chimeric antigen receptor (CAR) modified T cells.Naked anti-CD19 mAbs have shown little clinical benefit in B cell lymphomas. Despite unusual toxicity profiles with many anti-CD19 ADCs slowing development, durable remissions in a substantial minority of patients with refractory aggressive lymphomas should encourage continued efforts in this area. Blinatumomab, an anti-CD19 bispecific T cell engager, has shown impressive responses in relapse/refractory diffuse large B cell lymphoma (DLBCL), but is plagued by neurotoxicity issues and the need for continuous infusion. CD19 targeting CAR-T cell therapies are the most promising, with the potential for curing a third of refractory DLBCL patients. There is still much work to be done to address potentially life-threatening cytokine release syndrome and neurotoxicity, an extended production time precluding patients with rapidly progressive disease, and treatment expense. However, if the promise of CAR-T cell technology is confirmed, this will likely change the approach and prognosis for relapse/refractory aggressive lymphoma.

Background: Although the majority of patients with diffuse large B-cell lymphoma (DLBCL) can be cured with intensive chemotherapy and rituximab, 30-40% of patients will be refractory to or relapse after first line treatment. For these patients, the current standard of care is salvage chemotherapy followed by high-dose chemotherapy and autologous stem cell transplantation (ASCT). Prior studies have largely examined clinical risk factors associated with higher risk of relapse after ASCT; however, there is limited data integrating both pathologic and molecular features. Thus, we aimed to identify high-risk features associated with relapse and survival after ASCT using a combination of clinical, molecular, pathologic, and transplant characteristics. Methods: We retrospectively analyzed the medical records of all adult patients with DLBCL who underwent ASCT at our two institutions from 2010 to 2020. Patients with primary CNS lymphoma, primary mediastinal B-cell lymphoma, or Burkitt lymphoma were excluded. We analyzed demographics, clinical characteristics, cell of origin (COO) by immunohistochemistry (IHC), fluorescence in-situ hybridization (FISH) testing, and treatment/transplant characteristics. The primary endpoints were 3-year progression-free survival (PFS) and overall survival (OS) from ASCT. The Kaplan-Meier method was used to estimate survival with univariate and multivariate Cox proportional hazards regression performed to identify factors associating with PFS and OS, summarized using hazard ratios (HR) with 95% confidence intervals (CI). Results: A total of 235 DLBCL patients underwent ASCT from 2010 to 2020. Median age at ASCT was 61 years (range: 25-75) and 63% were male. At DLBCL diagnosis, 80% had advanced stage disease, 74% had extranodal involvement, 13% had poor performance status, and 65% had elevated lactate dehydrogenase (LDH). 71 patients (30%) had a prior or concurrent indolent lymphoma diagnosis indicating transformed disease. Of the patients with available COO and molecular data, 115 (60%) had germinal center B-cell (GCB) phenotype by IHC, 10 (6%) had a single MYC rearrangement by FISH, and 35 (22%) had MYC plus BCL2 and/or BCL6 rearrangements (DHL/THL). After first-line treatment, 12% remained refractory and 62% later relapsed at a median of 13 months (range: 1-240). Patients received a median of 2 (range: 1-5) lines of treatment pre-ASCT. At time of ASCT, 66% were in complete response (CR) and 32% were in partial response (PR) by standard of care imaging and response criteria. With median follow-up of 5.2 years from time of ASCT, 98 patients (42%) relapsed and 78 (33%) died. 3-year PFS and OS were 58% (95% CI 51-64%) and 74% (95% CI 67-79%), respectively. In univariate analysis, factors associated with worse PFS and worse OS included 3 or more lines of treatment pre-ASCT (p60 at ASCT (HR 1.92, 95% CI 1.06-3.47, p=0.03) (Figure 1C). Stratifying by COO and disease status at transplant, 3-year OS was best in the GCB/CR group (84%, 95% CI 73-90%), while worse but similar in the GCB/non-CR and non-GCB/CR groups (68%, 95% CI 51-80% and 71%, 95% CI 56-83%, respectively) (Figure 1D). The non-GCB/non-CR group had the worst 3-year OS (48%, 95% CI 27-67%). No individual factors beyond CR/non-CR at ASCT were associated with worse 3-year PFS. Notably, DHL/THL patients (77% of whom were in CR at time of ASCT) had similar PFS (p=0.08) and OS (p=0.30) to non-DHL/THL patients, suggesting that response to therapy may be more prognostic than high-risk molecular features alone. Conclusions: This analysis indicated that factors associated with OS after ASCT were disease status at time of transplant and COO, with non-GCB patients not in CR having the poorest outcomes. GCB patients not in CR were still able to be cured by ASCT at a high rate. Molecular rearrangements including DHL/THL were not prognostic, although interpretation may be limited by the modest number of DHL/THL patients. These findings may inform which patients should undergo ASCT, while the highest risk group may be better treated with alternatives including novel targeted agents or chimeric antigen receptor cell therapy. Figure 1 Figure 1. Disclosures Bachanova: FATE: Membership on an entity's Board of Directors or advisory committees, Research Funding; Incyte: Research Funding; KaryoPharma: Membership on an entity's Board of Directors or advisory committees; Gamida Cell: Membership on an entity's Board of Directors or advisory committees, Research Funding. Fehniger: Compass Therapeutics: Research Funding; Affimed: Research Funding; ImmunityBio: Research Funding; Wugen: Consultancy, Current equity holder in publicly-traded company, Patents & Royalties: related to memory like NK cells, Research Funding; OrcaBio: Other; Kiadis: Other; HCW Biologics: Research Funding; Indapta: Other. Weisdorf: Fate Therapeutics: Research Funding; Incyte: Research Funding.

N-cadherin inhibits osteogenic cell differentiation and canonical Wnt/β-catenin signaling in vitro. However, in vivo both conditional Cdh2 ablation and overexpression in osteoblasts lead to low bone mass. We tested the hypothesis that N-cadherin has different effects on osteolineage cells depending upon their differentiation stage. Embryonic conditional osteolineage Cdh2 deletion in mice results in defective growth, low bone mass, and reduced osteoprogenitor number. These abnormalities are prevented by delaying Cdh2 ablation until 1 month of age, thus targeting only committed and mature osteoblasts, suggesting they are the consequence of N-cadherin deficiency in osteoprogenitors. Indeed, diaphyseal trabecularization actually increases when Cdh2 is ablated postnatally. The sclerostin-insensitive Lrp5A214V mutant, associated with high bone mass, does not rescue the growth defect, but it overrides the low bone mass of embryonically Cdh2-deleted mice, suggesting N-cadherin interacts with Wnt signaling to control bone mass. Finally, bone accrual and β-catenin accumulation after administration of an anti-Dkk1 antibody are enhanced in N-cadherin-deficient mice. Thus, although lack of N-cadherin in embryonic and perinatal age is detrimental to bone growth and bone accrual, in adult mice loss of N-cadherin in osteolineage cells favors bone formation. Hence, N-cadherin inhibition may widen the therapeutic window of osteoanabolic agents. © 2017 American Society for Bone and Mineral Research.

Introduction The management of younger fit patients with mantle cell lymphoma (MCL) varies widely with no consensus on an optimal induction therapy. To date, the treatments with the longest progression-free survival incorporate a chemotherapy backbone that includes high dose cytarabine, followed by consolidation with an autologous stem-cell transplantation (ASCT) (Hermine et al. Lancet 2016, Eskelund et al. Br J Haematol 2016). Recent data showed that a regimen of bendamustine/rituximab followed by cytarabine/rituximab achieved high complete response rates with high minimal residual disease (MRD) negativity (Merryman RW et al. Blood Adv 2020). We hypothesized that adding the Bruton tyrosine kinase inhibitor acalabrutinib to the same chemotherapeutic backbone would be safe and increase complete response rates as well as minimal residual disease (MRD) negativity pre-transplant, and potentially improve clinical outcomes. Methods We conducted a single arm, single institution pilot study registered at clinicaltrials.gov (NCT03623373). Patients with untreated MCL, who were between ages 18-70 and were candidates for ASCT, were eligible. Patients received six 28-day cycles of treatment. Cycles 1-3 consisted of bendamustine 90 mg/m2 on days 1 and 2, rituximab 375 mg/m2 on day 1 and acalabrutinib 100mg BID on days 1 through 28. Cycles 4-6 consisted of rituximab 375 mg/m2 on day 1, cytarabine 2 g/m2 (1.5 g/m2 if age>60) q12 hours on days 1 and 2, and acalabrutinib 100mg BID on days 1 through 7 and 22 through 28. Restaging PET/CT and response assessment based on the Lugano classification were obtained following cycles 3 and 6. After cycle 6 patients underwent leukapheresis and stem-cell collection as preparation for ASCT. Blood for MRD status was collected after cycles 2, 4 and 6 and will be evaluated using the ClonoSeq assay (Adaptive Biotechnologies). The primary objective was to determine the stem cell mobilization success rate. Secondary objectives included safety and tolerability, overall response rate (ORR), pre-transplant complete response rate (CR), and the MRD negativity rate during and after completion of therapy. Results The trial enrolled 14 patients from December 2018 to February 2020. One patient withdrew consent prior to start of treatment and another was found to have an undiagnosed adenocarcinoma shortly after starting MCL treatment. Both are excluded from the analysis. The median age was 57 years (range 52-66). 11 patients were males (92%), all patients had an ECOG performance status of 0-1. 11 patients (92%) presented with stage IV disease. The mean MCL International Prognostic Index (MIPI) score was 6.3 (25% high-risk, 42% intermediate-risk and 33% low-risk). Of the 12 patients who began treatment, 9 completed all 6 cycles. Three patients did not complete therapy due to: insurance issues (n = 1), and thrombocytopenia (n = 2) following cycle 5 and 4. The side effect profile showed expected hematologic toxicities with grade 3-4 cytopenias in all patients, mostly during cytarabine cycles. In total, 100% of patients developed grade 3-4 thrombocytopenia and 83% of patients developed grade 3-4 neutropenia. Three episodes of febrile neutropenia were observed. One patient had a grade 3 transaminase increase, and one patient had grade 3 diarrhea. No bleeding events or treatment related deaths occurred. The remainder of the side effects were low grade and the treatment was generally well tolerated. Of the 12 evaluable patients, 10 responded (ORR 83%) with 9 achieving CR (75%). One patient achieved PR prior to being removed from the study due to thrombocytopenia and then achieved CR off study. Two patients experienced PD during induction. With a median follow up of 9 months, no responding patients have relapsed. The median CD34+ stem cell collection was 3.84x106 cells/kg (range 2.77 - 5.9). MRD results will be presented at the meeting. Conclusions This is the first study attempting to combine BTK inhibition with a high dose cytarabine containing regimen. The addition of acalabrutinib to a regimen of bendamustine/rituximab followed by cytarabine/rituximab appears to be safe. The R-ABC combination will be further tested in the recently activated intergroup trial EA4181. Disclosures Bartlett: Autolus: Research Funding; BMS/Celgene: Research Funding; Forty Seven: Research Funding; Immune Design: Research Funding; Janssen: Research Funding; Kite, a Gilead Company: Research Funding; Merck: Research Funding; Millennium: Research Funding; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pharmacyclics: Research Funding; Seattle Genetics: Consultancy, Research Funding; Roche/Genentech: Consultancy, Research Funding; Seattle Genetics: Membership on an entity's Board of Directors or advisory committees, Research Funding; BTG: Consultancy; Acerta: Consultancy; Affimed Therapeutics: Research Funding; ADC Therapeutics: Consultancy. Fehniger:ImmunityBio: Research Funding; HCW Biologics: Research Funding; Kiadis: Consultancy; Nkarta: Consultancy; Indapta: Consultancy; Wugen: Consultancy; Orca Biosystems: Consultancy; Compass Therapeutics: Research Funding. Ghobadi:Amgen: Consultancy, Research Funding; Kite: Consultancy, Research Funding; Bristol Myers Squibb: Consultancy; EUSA: Consultancy; WuGen: Consultancy. Mehta-Shah:Bristol Myers-Squibb: Research Funding; C4 Therapeutics: Consultancy; Celgene: Research Funding; Genetech/Roche: Research Funding; Innate Pharmaceuticals: Research Funding; Kyowa Hakko Kirin: Consultancy; Verastem: Research Funding; Karyopharm Therapeutics: Consultancy; Corvus: Research Funding. Kahl:Celgene Corporation: Consultancy; AstraZeneca Pharmaceuticals LP: Consultancy, Membership on an entity's Board of Directors or advisory committees; Genentech: Consultancy; Pharmacyclics LLC: Consultancy; Roche Laboratories Inc: Consultancy; BeiGene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Acerta: Consultancy, Research Funding; ADC Therapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; AbbVie: Consultancy.

Background: Hodgkin lymphoma (HL) is a rare lymphoma that often affects young people, with a median age of diagnosis of 39. While the 5-year PFS rate for patients after front-line chemotherapy is 94.6%, those who relapse have a 50% to 60% rate of cure (Alinari and Blum, Blood 2016). We recently discovered that increased abdominal visceral fat normalized to subcutaneous fat (rVFA) is associated with poorer outcomes in females, but not males, with diffuse large B-cell lymphoma (DLBCL). (Teja e tal ASH 2018) Interestingly, increased body mass index overall has been found to be associated with favorable prognosis in DLBCL (Carson et al., Journal of Clinical Oncology 2012). The correlation between these findings and elevated fasting blood glucose further supports a relationship between metabolism and prognosis in lymphoma. Since HL patients are generally younger and healthier than DLBCL patients at diagnosis, we sought to determine if rVFA and other metabolic markers had similar prognostic value in relapsed/refractory HL patients. Methods: We conducted a retrospective study of 95 consecutively treated relapsed/refractory HL patients treated at Washington University in St. Louis, who presented with first relapse between 2004 and 2018. We recorded baseline clinical risk factors such as sex, age, BMI, IPI, diabetes status, extranodal sites at relapse, and duration of response to initial therapy. Treatment and response to therapy by PET/CT were also recorded. In 80 patients, pre-treatment CT images were available to determine areas of subcutaneous and visceral fat at the level of the umbilicus. These values were normalized to total fat to calculate rVFA (Nguyen Radiology, 2018). Thresholds for risk stratification and sex differences were obtained using Cutoff Finder (Budczies PLOS One 2012). Data was analyzed with SPSS. Results: Ninety-five patients were eligible for analysis (54M, 41F) and 50 (53%) had refractory disease to initial therapy. (Table 1) The overall response rate to salvage therapy was 77%. There was no significant difference in overall survival (OS) (p = 0.55) or progression-free survival (PFS) (p = 0.49) between males and females in our study. Patients with higher BMI at diagnosis had a trend towards inferior OS and PFS after relapse. Those with BMI Eighty patients had CT images available for rVFA analysis (45M, 35F). Both males and females had a median rVFA of 28%. Patients with rVFA greater than 34% had inferior OS after relapse (HR= 8.85, 95% CI: 2.38-32.93, p Conclusion: In this cohort, elevated rVFA was associated with inferior OS in all patients with relapsed/refractory HL, which is consistent with our findings in DLBCL as well as other solid tumors. Our results also suggest an association between diabetes and HL prognosis. Given the association of increased BMI, rVFA, diabetes and poorer outcomes in our cohort, there may be an association between a patient's metabolism and prognosis in Hodgkin lymphoma. Further studies should be conducted to examine the relationship between metabolism and cancer prognosis in a larger cohort. Disclosures Bartlett: Seattle Genetics: Consultancy, Research Funding; Immune Design: Research Funding; Forty Seven: Research Funding; Millennium: Research Funding; Merck: Research Funding; BTG: Consultancy; Roche/Genentech: Consultancy, Research Funding; BMS/Celgene: Research Funding; Pharmacyclics: Research Funding; Janssen: Research Funding; Acerta: Consultancy; Kite, a Gilead Company: Research Funding; Seattle Genetics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Autolus: Research Funding; ADC Therapeutics: Consultancy; Affimed Therapeutics: Research Funding; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Ippolito:Vital Images, Inc: Research Funding. Mehta-Shah:Karyopharm Therapeutics: Consultancy; C4 Therapeutics: Consultancy; Verastem: Research Funding; Celgene: Research Funding; Genetech/Roche: Research Funding; Corvus: Research Funding; Bristol Myers-Squibb: Research Funding; Kyowa Hakko Kirin: Consultancy; Innate Pharmaceuticals: Research Funding.

BACKGROUND: Central nervous system (CNS) relapse in systemic non-Hodgkin's lymphoma is associated with a guarded prognosis with a median survival of only 2-6 months. However, information regarding CNS relapse is still limited and there is no consensus regarding which clinical or biologic risk factors should be used to identify patients who need prophylaxis and the optimal prophylactic regimen has not yet been established. The CNS-IPI score represents a robust risk model for CNS relapse in patients with diffuse large B cell lymphoma treated with R-CHOP and may potentially serve as a useful benchmark to evaluate the impact of novel treatment approaches. In particular, patients with chromosomal rearrangements of MYC and BCL2 and/or BCL6 genes, as is encountered in double hit (DHL) or triple hit (THL) lymphoma, have been associated with an increased risk for CNS involvement in retrospective series. CNS prophylaxis is typically administered in patients with DHL/THL treated with DA-R-EPOCH due to this perceived heightened risk, but there are limited data to support this approach. METHODS: We conducted a comprehensive multi-institutional retrospective analysis of outcomes of patients with DHL/THL, who received a minimum of 4 cycles of DA-R-EPOCH therapy with or without CNS prophylaxis, namely intrathecal (IT) or high-dose intravenous (IV) methotrexate or cytarabine. Each academic institution provided clinical data to assess the risk of CNS relapse (CNS-IPI) and FISH testing for MYC/BCL2/BCL6 translocations. Outcomes included overall survival (OS), progression-free survival (PFS), CNS relapse-free survival (CNSFS) and time to CNS recurrence which were calculated from time of diagnosis. Fisher's exact test or Chi-square test and Kaplan-Meier method were used to evaluate associations between outcomes and demographics as well as clinical characteristics including administration of CNS prophylaxis and CNS-IPI risk stratification. RESULTS: We collected data on 109 DHL/THL patients across 6 US academic medical centers. Demographic and clinical variables at diagnosis include - Age >60 57.8%(n=63); Male sex 59.6%(n=65); Stage III/IV 78.9%(n=86); ECOG PS >1 12.8%(n=14); CNS-IPI low risk (score 0-1) 11%(n=12), intermediate risk (score 2-3) 57.8%(n=63), high risk (score 4-5) 31.2%(n=34). A total of 95 (87.2%) patients received CNS prophylaxis [IT 81.1%(n=77); IV ± IT 18.9%(n=18)] with a median of 4 doses. Eight patients developed CNS relapse (7.3%) during a median of 25.9 (range 4.0 to 63.2) months of follow up. The patterns of relapse were predominantly leptomeningeal (n=7/8), as shown in Table 1. Estimated incidence was 4.9% at 12 months and 6.1% at 24 months after diagnosis. 5.6% (1/18) of the patients who received IV ±IT CNS prophylaxis developed CNS relapse, whereas the rates of CNS recurrence for patients who received only IT or no CNS prophylaxis were 6.5% and 7.1% respectively. No statistically significant differences in outcomes were found between baseline patient characteristics with respect to whether or not CNS prophylaxis was received, as well as the route of administration of CNS prophylaxis. The rate of CNS relapse was low for patients with low to intermediate compared to high CNS-IPI scores (4.0% vs. 14.7%, p=0.047). Patients with high CNS-IPI scores had reduced CNSFS (2-yr survival: 85.2% vs 97.3%, p=0.08), as well as reduced OS (2-yr survival: 46.5% vs. 87.5%, p CONCLUSIONS: CNS relapse is associated with significantly reduced OS as compared to systemic non-CNS relapse following R-EPOCH treatment in DHL/THL, justifying the need for a rational CNS prophylaxis strategy in these patients. The rate of CNS relapse was significantly lower in patients in the low-intermediate CNS-IPI risk category but it is unclear whether CNS events are reduced by administration of IT CNS prophylaxis due to the relatively small proportion of DHL/THL patients who did not receive any CNS prophylaxis. Furthermore, only 1 of the 18 DHL/THL patients (including 6 patients with high CNS-IPI scores) who received IV ± IT CNS prophylaxis developed CNS relapse, suggesting that this prophylactic strategy, especially in patients with high risk CNS-IPI scores, may be more effective in preventing this devastating clinical event. Disclosures Haverkos: Viracta THerapeutics: Consultancy. Hughes:Acerta Pharma and HOPA: Research Funding; AstraZeneca: Consultancy; Genzyme: Consultancy; Janssen: Consultancy; AbbVie: Consultancy. Grover:Genentech: Research Funding; Tessa: Consultancy. Portell:AbbVie: Research Funding; Amgen: Consultancy; Bayer: Consultancy; TG Therapeutics: Research Funding; Infinity: Research Funding; Roche/Genentech: Consultancy, Research Funding; Xencor: Research Funding; BeiGene: Consultancy, Research Funding; Kite: Consultancy, Research Funding; Acerta/AstraZeneca: Research Funding; Janssen: Consultancy; Pharmacyclics: Consultancy. Voorhees:AstraZeneca: Research Funding. Landsburg:Triphase: Research Funding; Seattle Genetics: Speakers Bureau; Karyopharm: Membership on an entity's Board of Directors or advisory committees; Curis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Morphosys: Membership on an entity's Board of Directors or advisory committees; Takeda: Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees. Kamdar:BMS: Consultancy; Seattle Genetics: Speakers Bureau; Pharmacyclics: Consultancy; AstraZeneca: Consultancy; Celgene: Consultancy; Karyopharm: Consultancy; Abbvie: Consultancy. Kahl:Acerta: Consultancy, Research Funding; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees; BeiGene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Roche Laboratories Inc: Consultancy; Pharmacyclics LLC: Consultancy; Genentech: Consultancy; Celgene Corporation: Consultancy; AstraZeneca Pharmaceuticals LP: Consultancy, Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy; ADC Therapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Hill:Genentech: Consultancy, Honoraria, Research Funding; Abbvie: Consultancy, Honoraria, Research Funding; Pharmacyclics: Consultancy, Honoraria, Research Funding; Beigene: Consultancy, Honoraria, Research Funding; AstraZenica: Consultancy, Honoraria, Research Funding; Kite, a Gilead Company: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria; BMS: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Takeda: Research Funding; Karyopharm: Consultancy, Honoraria, Research Funding.

Background: Plasmablastic lymphoma (PBL) is a rare subtype of Non-Hodgkin Lymphoma with a well-known association with HIV infection. The outcomes of PBL patients are typically described with high relapse rates and poor prognosis. (Loghavi S, J Hematol Oncol. 2015; Morscio J, Am J of Pathol. 2014; Castillo JJ, Clin Lymphoma Myeloma Leuk. 2011; Castillo JJ, Am J Hematol. 2008) There has been a paucity of data suggesting that limited stage disease (Ann Arbor stage I-II) may have a more favorable prognosis. However, due to the rarity of this disease there have been no large-scale reviews to confirm this. Thus, many patients with limited stage disease are subject to the aggressive therapy recommendations based on the poor outcomes of PBL patients as a whole. (Loghavi S, J Hematol Oncol. 2015; NCCN Guidelines, version 2.2020; Al-Malki MM, BBMT. 2014) We attempted to determine the treatment patterns and outcomes of patients with limited stage PBL. Methods: We conducted a multi-center (13 US academic centers) retrospective study of patients with limited stage (Ann Arbor stage I-II) Plasmablastic lymphoma. Determination of limited stage and diagnosis of PBL was determined by the investigators at each individual center. Patients diagnosed between 1/1/1990 and 6/1/2018 were included. Baseline demographic, clinical, laboratory, pathology, and outcomes data were extracted by retrospective chart review. Kaplan Meier was utilized for time to event analysis. Results: Baseline characteristics are included in table 1. A total of 80 patients were identified with limited stage disease. With a median follow up of 34 months the 3-yr Progression free survival (PFS) and overall survival (OS) was 71.9% and 78.7% respectively (Figure 1A and 1B). Patients that received frontline chemotherapy with (n=29) and without RT (n=36) had a 3-yr PFS and OS of 84.6% and 96.2% as compared to 64.5% and 70.8%, respectively (Figure 2A and 2B; Figure 3A and 3B). The Hazard ratio (HR) for PFS and OS for chemo (reference) vs chemo-RT was 0.47 (95% CI 0.18-1.3; P=0.131) and 0.18 (95% CI 0.04-0.84; p=0.029) respectively. The HR for PFS and OS for CHOP (n=14, reference) vs EPOCH (n=33) based regimens was 0.37 (95% CI 0.11-1.2; p=0.106) and 0.36 (95% CI 0.079-1.6; p=0.182) respectively. Patients with stage I/IE disease (n=56) had a 3-yr PFS and OS of 73.1% and 81.2% respectively. Patients with stage II/IIE disease (n=24) had a 3-yr PFS and OS of 69.3% and 73.4% respectively. Patients that received aggressive treatment (n=17) with Hyper-CVAD based regimens and/or Auto-SCT as consolidation had a 3-yr PFS and OS of 63.6% and 72.7% respectively. Patients with concomitant HIV (n=16) had a 3-yr PFS and OS of 80.8% and 77.4% respectively. Seven patients received RT alone and 6 patients had surgical resection alone as frontline therapy; 1 patient received no therapy; 1 patient received HAART therapy only and remains in CR without any other treatment for PBL 29 months after diagnosis. There were 8 deaths (10%) related to PBL, 3 deaths (4%) related to treatment of PBL (2 during frontline chemo and 1 upon relapse with salvage chemo), and 9 deaths (11%) related to other causes. The 3-yr lymphoma free survival (LFS) of the entire cohort, pts receiving chemo alone, and pts receiving chemo-RT (without including treatment related mortality (TRM) as an event) was 89.1%, 85.2%, and 100% respectively. The 3-yr LFS survival of the entire cohort, pts receiving chemo alone, and pts receiving chemo-RT (including TRM as an event) was 85.1%, 80.0%, and 96.2% respectively. Discussion: Here we report the largest review to our knowledge of limited stage PBL. Outcomes appear to be excellent with 3-yr PFS and OS of 71.9% and 78.7% respectively and a 3-yr LFS of 89.1% (85.1% when attributing TRM as an event). There was no obvious benefit to receiving aggressive therapy with H-CVAD based regimens and/or Auto-SCT. Although this is a small, uncontrolled sample size the HR for OS was improved in patients receiving frontline chemo-RT vs chemo alone 0.18 (95% CI 0.04-0.84; p=0.029). However, this did not take into account TRM with or progression while receiving frontline chemotherapy. Patients who were HIV+ had similar PFS and OS outcomes compared to the entire cohort. This retrospective study clearly demonstrates the favorable outcomes in this patient population, especially in those able to receive definitive therapy for their disease. Disclosures Hess: ADC Therapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees; BMS, AstraZeneca: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Patel:Takeda: Consultancy, Research Funding; Precision Biosciences: Research Funding; Nektar: Consultancy, Research Funding; Celgene: Consultancy, Research Funding; Bristol Myers Squibb: Consultancy, Research Funding; Poseida: Research Funding; Cellectis: Research Funding; Oncopeptides: Consultancy; Janssen: Consultancy, Research Funding. Nowakowski:Nanostrings: Research Funding; Seattle Genetics: Consultancy; Curis: Consultancy; Ryvu: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other; Kymera: Consultancy; Denovo: Consultancy; Kite: Consultancy; Celgene/BMS: Consultancy, Research Funding; Roche: Consultancy, Research Funding; MorphoSys: Consultancy, Research Funding. Chavez:Bayer: Consultancy; AbbVie: Consultancy; BeiGene: Speakers Bureau; Morphosys: Consultancy, Speakers Bureau; Merck: Research Funding; AstraZeneca: Speakers Bureau; Celgene: Consultancy; Genentech: Speakers Bureau; Epizyme: Speakers Bureau; Gilead: Consultancy; Novartis: Consultancy; Kite, a Gilead Company: Consultancy, Speakers Bureau; Karyopharm: Consultancy; Verastem: Consultancy; Pfizer: Consultancy. Hill:Beigene: Consultancy, Honoraria, Research Funding; Abbvie: Consultancy, Honoraria, Research Funding; Genentech: Consultancy, Honoraria, Research Funding; Takeda: Research Funding; AstraZenica: Consultancy, Honoraria, Research Funding; Kite, a Gilead Company: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria; BMS: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Pharmacyclics: Consultancy, Honoraria, Research Funding; Karyopharm: Consultancy, Honoraria, Research Funding. Maddocks:Pharmacyclics: Consultancy, Honoraria; Morphosys: Consultancy, Honoraria; Celgene: Consultancy, Honoraria; Seattle Genetics: Consultancy, Honoraria; Karyopharm: Consultancy; ADC Therapeutics, AstraZeneca: Consultancy; BMS: Consultancy, Research Funding. Wagner-Johnston:ADC Therapeutics, Regeneron, CALIB-R, Verastem: Membership on an entity's Board of Directors or advisory committees. Kahl:AstraZeneca Pharmaceuticals LP: Consultancy, Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy; Pharmacyclics LLC: Consultancy; Genentech: Consultancy; Acerta: Consultancy, Research Funding; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene Corporation: Consultancy; ADC Therapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; BeiGene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Roche Laboratories Inc: Consultancy. Alderuccio:ADC Therapeutics: Membership on an entity's Board of Directors or advisory committees; Forma Therapeutics: Other: Family member; Agios Pharmaceuticals: Other: Family member; Oncinfo: Honoraria; Inovio Pharmaceuticals: Other: Family member; Foundation Medicine: Other: Family member; Puma Biotechnology: Other: Family member; OncLive: Honoraria. Lossos:Janssen Biotech: Honoraria; Verastem: Consultancy, Honoraria; Janssen Scientific: Consultancy, Other; Seattle Genetics: Consultancy, Other; Stanford University: Patents & Royalties; NCI: Research Funding. Portell:Bayer: Consultancy; BeiGene: Consultancy, Research Funding; Kite: Consultancy, Research Funding; Acerta/AstraZeneca: Research Funding; Amgen: Consultancy; Janssen: Consultancy; Pharmacyclics: Consultancy; AbbVie: Research Funding; TG Therapeutics: Research Funding; Infinity: Research Funding; Roche/Genentech: Consultancy, Research Funding; Xencor: Research Funding. Landsburg:Celgene: Membership on an entity's Board of Directors or advisory committees; Triphase: Research Funding; Takeda: Research Funding; Curis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Karyopharm: Membership on an entity's Board of Directors or advisory committees; Morphosys: Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Speakers Bureau. Castillo:TG Therapeutics: Research Funding; Beigene: Consultancy, Research Funding; Kymera: Consultancy; Janssen: Consultancy, Research Funding; Abbvie: Research Funding; Pharmacyclics: Consultancy, Research Funding.

Follicular lymphoma (FL) is the most common indolent non-Hodgkin's lymphoma; however, it remains incurable with conventional therapies and is poorly responsive to checkpoint blockade. Additionally, because FL develops so slowly (and often asymptomatically), a major research focus has been to avoid chemotherapy treatments to limit the potential development of treatment-related side effects and the risk of therapy-related second cancers. The mutational processes that lead to lymphomagenesis and progression also produce tumor-specific mutant antigens (TSMAs) that can be targeted by the immune system to control malignancies. Personalized cancer vaccines designed for these TSMAs represent a promising new strategy for treatment of FL. However, the feasibility of this approach and precisely how to optimize effective vaccine design, informed by next-generation sequencing data, are not fully understood. We hypothesize that (tumor/normal) whole-exome sequencing (WES) and (tumor) RNA sequencing (RNA-Seq) can be used to predict patient HLA typing and neoepitopes to engineer personalized cancer vaccines for FL. DNA and RNA from 58 patients' FL biopsies underwent WES and RNA-Seq. pVACtools and MiXCR predicted potential somatic and B-cell clonotype neoantigens, which were filtered to identify high-quality TSMAs. B-cell oligoclonality was determined by comparison to B-cell receptor (BCR) repertoire profiling of healthy individual lymph nodes. RNA-seq data allowed us to identify expressed TSMAs. Complementary in silico analysis based on mRNA-based peptide reconstruction and custom HLA affinity binding predictions were performed. An average of 52 somatic mutations per patient (range: 2-172) were identified. At least one high-quality TSMA was predicted for 57 of 58 patients. Five or more TSMA candidates were identified for 52 (90%) patients with a mean of 17 predicted peptides per patient (range: 0-45). 81% (813/1,004) of the total predicted TSMA peptides arose from missense mutations, 9% (94/1,004) from indels, and 10% (97/1,004) from BCR. 78% (45/58) of patients have both somatic and BCR vaccine candidates, while 21% (12/58) of patients had only somatic vaccine candidates. No fusion genes were identified within the cohort that could have been a source of neoepitope candidates. Predicted TSMAs were identified in multiple genes recurrently mutated in lymphoma (e.g., BCL2). There was a high prediction concordance with the orthogonal BostonGene Vaccine Module V1 pipeline. These preclinical results led to a first-in-human pilot trial of personalized TSMA vaccine combined with anti-PD-1 mAb for rel/ref FL patients (NCT03121677), with one response observed within 4 patients evaluable for response to date. TSMA peptides suitable for cancer vaccines were identified for most FL patients via next-generation sequencing, MiXCR and pVACtools. This preclinical study suggests that FL patients will be candidates for TSMA vaccine clinical trials, and pilot clinical results provide proof of concept for this approach. Citation Format: Cody A. Ramirez, Felix Frenkel, Olga Plotnikova, Vladislav Belousov, Alexander Bagaev, Elena Ocheredko, Susanna Kiwala, Jasreet Hundal, Zachary L. Skidmore, Marcus Watkins, Michelle Becker-Hapak, Thomas B. Mooney, Jason Walker, Catrina Fronick, Robert Fulton, Robert Schreiber, Nancy L. Bartlett, Brad Kahl, Ravshan Ataullakhanov, Malachi Griffith, Obi Griffith, Todd A. Fehniger. Identification of predicted neoantigen vaccine candidates in follicular lymphoma patients [abstract]. In: Proceedings of the AACR Virtual Meeting: Advances in Malignant Lymphoma; 2020 Aug 17-19. Philadelphia (PA): AACR; Blood Cancer Discov 2020;1(3_Suppl):Abstract nr PO-56.

8054 Background: Follicular lymphoma (FL) is incurable with conventional therapies and poorly responsive to immune checkpoint blockade. There is a need for new therapies without long-term complications of chemotherapy and with curative potential. We hypothesize that FL contains tumor-specific mutant antigens (TSMAs) that can be targeted by the immune system by vaccination. Recent reports have highlighted the potential for unique immunoglobulin peptides to elicit immune response in lymphomas. We utilized whole exome sequencing (WES) and RNA sequencing (RNA-Seq) of FL patient samples to infer HLA genotype, and predict TSMAs with the goal of designing a personalized cancer vaccine, supported by recent reports of this approach in solid cancers. Methods: DNA and RNA from 58 patients’ FL biopsies underwent WES and RNA-Seq. pVACtools and MiXCR predicted potential somatic and B-cell clonotype neoantigens, which were filtered to identify high quality TSMAs. B-cell oligoclonality was determined by comparison to B-cell receptor (BCR) repertoire profiling of healthy individual lymph nodes. RNA-seq data allowed us to identify expressed TSMAs. Complementary in silico analysis based on mRNA-based peptide reconstruction and custom HLA affinity binding predictions were performed. Results: An average of 52 somatic mutations per patient (range: 2-172) were identified. At least one high quality TSMA was predicted for 57 of 58 patients. Five or more TSMA candidates were identified for 52 (90%) patients with a mean of 17 predicted peptides per patient (range: 0-45). 81% (813/1,004) of the total predicted TSMA peptides arose from missense mutations, 9% (94/1,004) from indels, and 10% (97/1,004) from BCR. 78% (45/58) of patients have both somatic and BCR vaccine candidates, while 21% (12/58) of patients had only somatic vaccine candidates. Predicted TSMAs were identified in multiple genes recurrently mutated in lymphoma (e.g., BCL2). There was a high prediction concordance with the orthogonal BostonGene Vaccine Module V1 pipeline. These pre-clinical results led to a first-in-human pilot trial of personalized TSMA vaccine combined with anti-PD-1 mAb for rel/ref FL patients (NCT03121677), with one response observed within 4 patients evaluable for response to date. Conclusions: TSMA peptides suitable for cancer vaccines were identified for most FL patients via next-generation sequencing, MiXCR and pVACtools. This pre-clinical study suggests that FL patients will be candidates for TSMA vaccine clinical trials and pilot clinical results provide proof of concept for this approach.

Until recently, advances in classic Hodgkin lymphoma (HL) treatment primarily consisted of minor modifications of highly effective decades-old chemotherapy and radiation approaches. In early-stage disease, excellent outcomes have been reported with fewer cycles of chemotherapy, lower doses, smaller radiation fields and in some circumstances, radiation elimination. In advanced-stage disease, maintaining the dose intensity of standard chemotherapy regimens has resulted in modest improvements in outcomes. During the past decade, the use of early interim positron emission tomography (PET) scans to escalate or de-escalate treatment has been the subject of intense investigation with the goal of maximizing efficacy and minimizing toxicity. Important updates from recent PET-directed trials include; elimination of bleomycin in patients with advanced-stage HL and negative interim PET findings, the benefit of therapy escalation in patients with unfavorable early-stage HL and positive interim PET findings, and the minimal benefit of consolidative radiotherapy in patients with unfavorable early-stage HL and negative interim PET findings. A more nuanced approach to consolidative radiotherapy is required for patients with favorable early-stage disease based on age, disease sites, secondary cancer risk, and cardiovascular disease. Brentuximab vedotin and nivolumab/pembrolizumab have provided promising new options with surprisingly high response rates and modest toxicity for patients with relapsed HL whose disease does not respond to standard treatments. Incorporating these agents into earlier therapy is an area of active investigation for all stages of HL. Although the overall prognosis for HL patients has seen incremental improvement, efforts to optimize treatment with more effective and less toxic approaches continue.

SummaryIn the bone marrow (BM), hematopoietic progenitors (HPs) reside in specific anatomical niches near osteoblasts (Obs), macrophages (MΦs), and other cells forming the BM microenvironment. A connection between immunosurveillance and traffic of HP has been demonstrated, but the regulatory signals that instruct the immune regulation of HP circulation are unknown. We discovered that the BM microenvironment deficiency of p62, an autophagy regulator and signal organizer, results in loss of autophagic repression of macrophage contact-dependent activation of Ob NF-κB signaling. Consequently, Ob p62-deficient mice lose bone, Ob Ccl4 expression, and HP chemotaxis toward Cxcl12, resulting in egress of short-term hematopoietic stem cells and myeloid progenitors. Finally, Ccl4 expression and myeloid progenitor egress are reversed by deficiency of the p62 PB1-binding partner Nbr1. A functional “MΦ-Ob niche” is required for myeloid progenitor/short-term stem cell retention, in which Ob p62 is required to maintain NF-κB signaling repression, osteogenesis, and BM progenitor retention.

Introduction: A positive interim PET scan (PET2) following 2 cycles of ABVD for Hodgkin lymphoma (HL) is associated with a poor prognosis; several studies in advanced stage demonstrate benefit from escalating therapy. Definition of positivity (Deauville 3 (D3) vs Deauville 4/5 (D4/5)), initial treatment and response adaptive decisions may vary among clinicians. Data examining practice patterns in managing positive PET2 scans is lacking. We report practice patterns and outcomes for patients (pts) with positive PET2 results including D3 and D4/5 outcomes. Methods: Adult pts with classical HL and PET2 findings of D3, D4, and D5 after initial therapy between 01/01/2015 and 07/01/2019 were identified. Pts enrolled in clinical studies were excluded. Retrospective demographic, clinical, and treatment data were obtained and described from 14 academic and community sites across North America (NA). Progression-free survival (PFS) and overall survival (OS) were summarized by Kaplan-Meier curves and compared by log-rank test. Results: 166 PET2 positive pts were identified. Clinical characteristics included 54% (89/166) with advanced stage (III/IV) and 46% (77/166) with early stage (IA-IIB) disease. 152 pts (92%) were treated with initial ABVD like therapy and 14 pts (8%) with an alternate regimen (Table 1). After initial treatment, 163 pts demonstrated PET2 scores of D3 (n=33), D4 (n=99) and D5 (n=31). Of the 130 D4/5 pts; 23% (30/130) underwent therapeutic escalation and 77% (100/130) did not escalate. The complete response rate (CR) at end of treatment (EOT) for all D4/5 patients receiving escalation was 37% (11/30) compared to 45% (45/100) without escalation (p=0.43). (Table 2) The 12 month PFS was 54% (38.2-76.3) versus (vs) 69.2% (60.4-79.2) for escalation and no escalation respectively. Of the 66 D4/5 pts with advanced stage disease; 21% (14/66) had therapeutic escalation and 79% (52/66) did not escalate. CR at EOT was noted in 29% (4/14) with escalation vs 31% (16/52) without escalation (p=0.88). (Table 2) The 12 month PFS was 54.2% (32.9-89.3) vs 57.5% (44.9-73.7) for escalation and no escalation respectively. (Figure 1; Log Rank p=0.38). Of the 64 D4/5 pts with early stage disease; 75% (48/64) did not undergo escalation and 25% (16/64) had escalation. CR at EOT was noted in 44% (7/16) with escalation vs 60% (29/48) without escalation (p=0.26). (Table 2) The 12 month PFS was 54.7% (34.5-86.7) vs 80.8% (70.2-92.9) for escalation and no escalation respectively. Of the 33 D3 pts; 52% (17/33) de-escalated with the remainder (16/33) continuing on initial therapy. No D3 pt underwent escalation. In the 12 D3 pts with early stage disease, 50% (6/12) de-escalated. Of the 21 D3 pts with advanced stage disease; 52% (11/21) had de-escalation and 48% (10/21) did not de-escalate. CR at EOT was noted in 71% (12/17) with de-escalation vs 81% (13/16) without de-escalation (p=0.50). (Table 2) Progression was noted in 29% (5/17) of patients who underwent de-escalation compared to 38% (6/16) without de-escalation. The 12 month PFS was 76.5% (85.8-99.6) vs 72.1% (52.2-99.7) for de-escalation and no de-escalation respectively. Conclusion: This is the first study evaluating clinical practice patterns and outcomes of PET adaptive therapy in NA. In this retrospective study, less than a quarter of advanced stage ABVD-treated D4/5 pts had therapy escalation despite prior studies reporting benefit. Our data suggest that outcomes for advanced stage PET positive pts are suboptimal irrespective of therapeutic escalation. In addition, pts with D3 findings represent a heterogeneous population and demonstrate favorable outcomes compared to D4/5 pts. Longer follow up time and further studies with larger numbers of pts are essential for confirming the reported findings. Disclosures Rutherford: Seattle Genetics: Consultancy, Honoraria; Verastem: Consultancy, Honoraria; Karyopharm: Honoraria, Membership on an entity's Board of Directors or advisory committees; AstraZeneca: Consultancy, Honoraria; Celgene: Consultancy, Honoraria; Heron: Consultancy, Honoraria; Janssen Scientific Affairs: Consultancy, Honoraria; Juno Therapeutics Inc: Consultancy, Honoraria. Bartlett:ADC Therapeutics: Consultancy, Research Funding; Affimed: Research Funding; Forty Seven: Research Funding; Celgene: Research Funding; Bristol-Myers Squibb: Research Funding; Genenetech: Research Funding; Gilead: Research Funding; Immune Design: Research Funding; Janssen: Research Funding; Merck: Research Funding; Millenium: Research Funding; Pfizer: Research Funding; Pharmacyclics: Research Funding; Seattle Genetics: Research Funding. Maddocks:Novartis: Research Funding; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees; Merck: Research Funding; BMS: Research Funding; Teva: Membership on an entity's Board of Directors or advisory committees. Feldman:Takeda: Honoraria, Speakers Bureau; Viracta: Research Funding; Trillium: Research Funding; Roche: Research Funding; Portola Pharma: Research Funding; Pfizer: Research Funding; Kyowa Hakko Kirin: Research Funding; Eisai: Research Funding; Corvus: Research Funding; Roche: Research Funding; Cell Medica: Research Funding; Seattle Genetics: Consultancy, Honoraria, Other: Travel expenses, Speakers Bureau; AbbVie: Honoraria, Other: Travel expenses, Speakers Bureau; Pharmacyclics: Honoraria, Other: Travel expenses, Speakers Bureau; Janssen: Honoraria, Speakers Bureau; Kite Pharma: Honoraria, Other: Travel expenses, Speakers Bureau; Bayer: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Research Funding; Celgene: Honoraria, Research Funding, Speakers Bureau. Magarelli:Tevan Oncology: Speakers Bureau. Advani:Merck: Research Funding; Infinity Pharma: Research Funding; Roche/Genentech: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celmed: Consultancy, Membership on an entity's Board of Directors or advisory committees; Kura: Research Funding; Kyowa Kirin Pharmaceutical Developments, Inc.: Consultancy; Millennium: Research Funding; Pharmacyclics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Agensys: Research Funding; Seattle Genetics: Consultancy, Research Funding; Stanford University: Employment, Equity Ownership; Bayer: Consultancy, Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Research Funding; Regeneron: Research Funding; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees; Cell Medica, Ltd: Consultancy; Forty-Seven: Research Funding; Autolus: Consultancy, Membership on an entity's Board of Directors or advisory committees; Gilead Sciences, Inc./Kite Pharma, Inc.: Consultancy, Membership on an entity's Board of Directors or advisory committees; Janssen: Research Funding; AstraZeneca: Consultancy, Membership on an entity's Board of Directors or advisory committees. Stephens:Karyopharm: Research Funding; Gilead: Research Funding; Acerta: Research Funding. Patel:Sunesis: Consultancy; Genentech: Consultancy, Speakers Bureau; Pharmacyclics/Janssen: Consultancy, Speakers Bureau; Celgene: Consultancy, Speakers Bureau; AstraZeneca: Consultancy, Research Funding, Speakers Bureau. Tees:Celgene: Speakers Bureau; Pharmacyclics: Speakers Bureau. Karmali:Gilead/Kite; Juno/Celgene: Consultancy, Speakers Bureau; Takeda, BMS: Other: Research Funding to Institution; Astrazeneca: Speakers Bureau. Cheson:Portola: Research Funding; Kite: Research Funding; Gilead: Research Funding; Symbios: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Trillium: Research Funding; Epizyme: Research Funding; Morphosys: Membership on an entity's Board of Directors or advisory committees; AstraZeneca: Membership on an entity's Board of Directors or advisory committees; Acerta: Consultancy, Research Funding; Genentech: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pharmacyclics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; TG Therapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Bristol Myers Squibb: Research Funding; Seattle Genetics: Research Funding; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Yazdy:Bayer: Honoraria, Speakers Bureau; Octapharma: Consultancy; Genentech: Research Funding; Abbvie: Consultancy. Pagel:AstraZeneca: Consultancy; Gilead Sciences: Consultancy; Pharmacyclics: Consultancy. Ramchandren:Seattle Genetics, Inc.: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Research Funding; Bristol-Myers Squibb: Consultancy, Membership on an entity's Board of Directors or advisory committees; Genentech: Research Funding; Merck: Research Funding; Sandoz-Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pharmacyclics LLC, an Abbvie company: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding.

N-cadherin inhibits osteogenic cell differentiation and canonical Wnt/β-catenin signaling in vitro. However, in vivo both conditional Cdh2 ablation and overexpression in osteoblasts lead to low bone mass. We tested the hypothesis that N-cadherin has different effects on osteolineage cells depending upon their differentiation stage. Embryonic conditional osteolineage Cdh2 deletion in mice results in defective growth, low bone mass and reduced osteoprogenitor number. These abnormalities are prevented by delaying Cdh2 ablation until 1 month of age, thus targeting only committed and mature osteoblasts, suggesting they are the consequence of N-cadherin deficiency in osteoprogenitors. Indeed, diaphyseal trabecularization actually increases when Cdh2 is ablated postnatally. The sclerostin-insensitive Lrp5A214V mutant, associated with high bone mass, does not rescue the growth defect, but it overrides the low bone mass of embryonically Cdh2 deleted mice, suggesting N-cadherin interacts with Wnt signaling to control bone mass. Finally, bone accrual and β-catenin accumulation after administration of an anti-Dkk1 antibody are enhanced in N-cadherin deficient mice. Thus, while lack of N-cadherin in embryonic and perinatal age is detrimental to bone growth and bone accrual, in adult mice loss of N-cadherin in osteolineage cells favors bone formation. Hence, N-cadherin inhibition may widen the therapeutic window of osteoanabolic agents.

The gap junction protein, connexin43 (Cx43) controls both bone formation and osteoclastogenesis via osteoblasts and/or osteocytes. Cx43 has also been proposed to mediate an anti-apoptotic effect of bisphosphonates, potent inhibitors of bone resorption. We studied whether bisphosphonates are effective in protecting mice with a conditional Cx43 gene deletion in osteoblasts and osteocytes (cKO) from the consequences of ovariectomy on bone mass and strength. Ovariectomy resulted in rapid loss of trabecular bone followed by a slight recovery in wild type (WT) mice, and a similar degree of trabecular bone loss, albeit slightly delayed, occurred in cKO mice. Treatment with either risedronate (20 μg/kg) or alendronate (40 μg/kg) prevented ovariectomy-induced bone loss in both genotypes. In basal conditions, bones of cKO mice have larger marrow area, higher endocortical osteoclast number, and lower cortical thickness and strength relative to WT. Ovariectomy increased endocortical osteoclast number in WT but not in cKO mice. Both bisphosphonates prevented these increases in WT mice, and normalized endocortical osteoclast number, cortical thickness and bone strength in cKO mice. Thus, lack of osteoblast/osteocyte Cx43 does not alter bisphosphonate action on bone mass and strength in estrogen deficiency. These results support the notion that one of the main functions of Cx43 in cortical bone is to restrain osteoblast and/or osteocytes from inducing osteoclastogenesis at the endocortical surface.

Cx43 in osteogenic cells controls both arms of the bone-remodeling cycle via direct actions on osteoblast differentiation and function and indirect modulation of osteoclastogenesis. These result in changes remindful of those that occur in skeletal disuse or aging and disclose a far broader function of Cx43 in skeletal biology., Connexin43 (Cx43) has an important role in skeletal homeostasis, and Cx43 gene (Gja1) mutations have been linked to oculodentodigital dysplasia (ODDD), a human disorder characterized by prominent skeletal abnormalities. To determine the function of Cx43 at early steps of osteogenesis and its role in the ODDD skeletal phenotype, we have used the Dermo1 promoter to drive Gja1 ablation or induce an ODDD mutation in the chondro-osteogenic linage. Both Gja1 null and ODDD mutant mice develop age-related osteopenia, primarily due to a progressive enlargement of the medullary cavity and cortical thinning. This phenotype is the consequence of a high bone turnover state, with increased endocortical osteoclast-mediated bone resorption and increased periosteal bone apposition. Increased bone resorption is a noncell autonomous defect, caused by exuberant stimulation of osteoclastogenesis by Cx43-deficient bone marrow stromal cells, via decreased Opg production. The latter is part of a broad defect in osteoblast differentiation and function, which also results in abnormal structural and material properties of bone leading to decreased resistance to mechanical load. Thus Cx43 in osteogenic cells is a critical regulator of both arms of the bone remodeling cycle, its absence causing structural changes remindful of aged or disused bone.

Connexin43 (Cx43) is involved in bone development, but its role in adult bone homeostasis remains unknown. To overcome the postnatal lethality of Cx43 null mutation, we generated mice with selective osteoblast ablation of Cx43, obtained using a Cx43fl allele and a 2.3-kb fragment of the α1(I) collagen promoter to drive Cre in osteoblasts (ColCre). Conditionally osteoblast-deleted ColCre;Cx43–/fl mice show no malformations at birth, but develop low peak bone mass and remain osteopenic with age, exhibiting reduced bone formation and defective osteoblast function. By both radiodensitometry and histology, bone mineral content increased rapidly and progressively in adult Cx43+/fl mice after subcutaneous injection of parathyroid hormone (PTH), an effect significantly attenuated in ColCre;Cx43–/fl mice, with Cx43–/fl exhibiting an intermediate response. Attenuation of PTH anabolic action was associated with failure to increase mineral apposition rate in response to PTH in ColCre;Cx43–/fl, despite an increased osteoblast number, suggesting a functional defect in Cx43-deficient bone-forming cells. In conclusion, lack of Cx43 in osteoblasts leads to suboptimal acquisition of peak bone mass, and hinders the bone anabolic effect of PTH. Cx43 represents a potential target for modulation of bone anabolism.

Yeast Tor1 is dynamically distributed in the cytoplasm and nucleus, and its association with the rDNA promoter is important for 35S rRNA synthesis and cell growth. TOR is the target of the immunosuppressant rapamycin and a key regulator of cell growth. It modulates diverse cellular processes in the cytoplasm and nucleus1,2,3,4,5, including the expression of amino acid transporters, ribosomal RNAs and ribosomal proteins. Despite considerable recent progress, little is known about the spatial and temporal regulation of TOR signalling, particularly that leading into the nucleus. Here we show that Tor1 is dynamically distributed in the cytoplasm and nucleus in yeast. Tor1 nuclear localization is nutrient dependent and rapamycin sensitive: starvation or treatment with rapamycin causes Tor1 to exit from the nucleus. Tor1 nuclear localization is critical for 35S rRNA synthesis, but not for the expression of amino acid transporters and ribosomal protein genes. We show further that Tor1 is associated with 35S ribosomal DNA (rDNA) promoter chromatin in a rapamycin- and starvation-sensitive manner; this association is necessary for 35S rRNA synthesis and cell growth. These results indicate that the spatial regulation of TOR complex 1 (TORC1) might be involved in differential control of its target genes. TOR is known as a classic cytoplasmic kinase that mediates the cytoplasm-to-nucleus signalling by controlling the localization of transcription factors. Our data indicate that TOR might be more intimately involved in gene regulation than previously thought.

Recent advances have established connexin43 (Cx43) as a key regulator of osteoblast function and of bone response to mechanical stimuli. Work by independent laboratories has consistently demonstrated postnatal development of larger than normal cross-section of long bones after conditional ablation of the Cx43 gene, Gja1, selectively in osteoblasts and/or osteocytes. This phenotype is caused by excessive endocortical bone resorption associated with periosteal expansion and cortical thinning. Review of published data suggests that the earlier in the osteogenic lineage is Gja1 deleted, the more severe is the cortical phenotype, implying functional roles of Cx43 at different stages of the osteoblast differentiation program. Such cortical modeling abnormalities resemble the changes occurring in the cortex upon disuse or aging. Indeed, Cx43 deficiency desensitizes endocortical osteoclasts from activation induced by removal of mechanical load, thus preventing medullary area expansion. The action of Cx43 on cancellous bone is controversial. Furthermore, the absence of Cx43 in osteoblasts and osteocytes results in activation of periosteal bone formation at lower strains than in wild-type bones, suggesting that Cx43 deficiency increased cortical sensitivity to mechanical load. Thus, Cx43 modulates cortical bone modeling in homeostatic conditions and in response to mechanical load by restraining both endocortical bone resorption and periosteal bone formation. Cx43 may represent a novel pharmacologic target for improving cortical bone strength through modulation of mechano-responsiveness.

Osteoblasts, osteocytes, and osteoprogenitor cells are interconnected into a functional network by gap junctions formed primarily by connexin43 (Cx43). Over the past two decades, it has become clear that Cx43 is important for the function of osteoblasts and osteocytes. This connexin contributes to the acquisition of peak bone mass and is a major modulator of cortical modeling. We review key data from human and mouse genetics on the skeletal consequences of ablation or mutation of the Cx43 gene (Gja1) and the molecular mechanisms by which Cx43 regulates the differentiation, function, and survival of osteogenic lineage cells. We also discuss putative second messengers that are communicated by Cx43 gap junctions, the role of hemichannels, and the function of Cx43 as a scaffold for signaling molecules. Current knowledge demonstrates that Cx43 is more than a passive channel; rather, it actively participates in the generation and modulation of cellular signals that drive skeletal development and homeostasis.

Canonical Wnt/β-catenin (cWnt) signaling regulates osteoblast proliferation and differentiation to enhance bone formation. We previously reported that osteogenic action of β-catenin is dependent on BMP signaling. Here, we further examined interactions between cWnt and BMP in bone. In osteoprogenitors stimulated with BMP2, β-catenin localizes to the nucleus, physically interacts with Smad4, and is recruited to DNA-binding transcription complexes containing Smad4, R-Smads1/5, and TCF4. Furthermore, Tcf/Lef-dependent transcription, Ccnd1 expression, and proliferation all increase when Smad4, 1, or 5 levels are low, whereas TCF/Lef activities decrease when Smad4 expression is high. The ability of Smad4 to antagonize transcription of Ccnd1 is dependent on DNA-binding activity; Smad4-dependent transcription is not required. In mice, conditional deletion of Smad4 in Osterix+ cells increases mitosis of cells on trabecular bone surfaces as well as in primary osteoblast cultures from adult bone marrow and neonatal calvaria. By contrast, ablation of Smad4 delays differentiation and matrix mineralization by primary osteoblasts in response to Wnt3a, indicating that loss of Smad4 perturbs the balance between proliferation and differentiation in osteoprogenitors. We propose that Smad4 and Tcf/Lef transcription complexes compete for β-catenin, thus restraining Wnt/β-catenin-dependent proliferative signals while favoring the matrix synthesizing activity of osteoblasts.

We have previously shown that the effect of mechanical loading on bone is partly dependent on connexin43 (Cx43). To determine whether Cx43 is also involved in the effect of mechanical unloading, we have used botulinum toxin A (BtxA) to induce reversible muscle paralysis in mice with a conditional deletion of the Cx43 gene in osteoblasts and osteocytes (cKO). BtxA injection in hind limb muscles of wild type (WT) mice resulted in significant muscle atrophy and rapid loss of trabecular bone. Bone loss reached a nadir of about 40% at 3 weeks post-injection, followed by a slow recovery. A similar degree of trabecular bone loss was observed in cKO mice. By contrast, BtxA injection in WT mice significantly increased marrow area and endocortical osteoclast number, and decreased cortical thickness and bone strength. These changes did not occur in cKO mice, whose marrow area is larger, osteoclast number higher, and cortical thickness and bone strength lower relative to WT mice in basal conditions. Changes in cortical structure occurring in WT mice had not recovered 19 weeks after BtxA injection, despite correction of the early osteoclast activation and a modest increase in periosteal bone formation. Thus, BtxA-induced muscle paralysis leads to rapid loss of trabecular bone and to changes in structural and biomechanical properties of cortical bone, neither of which are fully reversed after 19 weeks. Osteoblast/osteocyte Cx43 is involved in the adaptive responses to skeletal unloading selectively in the cortical bone, via modulation of osteoclastogenesis on the endocortical surface.

We have previously shown that targeted expression of a dominant-negative truncated form of N-cadherin (Cdh2) delays acquisition of peak bone mass in mice and retards osteoblast differentiation; whereas deletion of cadherin 11 (Cdh11), another osteoblast cadherin, leads to only modest osteopenia. To determine the specific roles of these two cadherins in the adult skeleton, we generated mice with an osteoblast/osteocyte specific Cdh2 ablation (cKO) and double Cdh2+/−;Cdh11−/− germline mutant mice. Age-dependent osteopenia and smaller diaphyses with decreased bone strength characterize cKO bones. By contrast, Cdh2+/−;Cdh11−/− exhibit severely reduced trabecular bone mass, decreased in vivo bone formation rate, smaller diaphyses and impaired bone strength relative to single Cdh11 null mice. The number of bone marrow immature precursors and osteoprogenitor cells is reduced in both cKO and Cdh2+/−;Cdh11−/− mice, suggesting that N-cadherin is involved in maintenance of the stromal cell precursor pool via the osteoblast. Although Cdh11 is dispensable for postnatal skeletal growth, it favors osteogenesis over adipogenesis. Deletion of either cadherin reduces β-catenin abundance and β-catenin-dependent gene expression, whereas N-cadherin loss disrupts cell-cell adhesion more severely than loss of cadherin 11. Thus, Cdh2 and Cdh11 are crucial regulators of postnatal skeletal growth and bone mass maintenance, serving overlapping, yet distinct, functions in the osteogenic lineage.

MAGP1 is an extracellular matrix protein that, in vertebrates, is a ubiquitous component of fibrillin-rich microfibrils. We previously reported that aged MAGP1-deficient mice (MAGP1Delta) develop lesions that are the consequence of spontaneous bone fracture. We now present a more defined bone phenotype found in MAGP1Delta mice. A longitudinal DEXA study demonstrated age-associated osteopenia in MAGP1Delta animals and muCT confirmed reduced bone mineral density in the trabecular and cortical bone. Further, MAGP1Delta mice have significantly less trabecular bone, the trabecular microarchitecture is more fragmented, and the diaphyseal cross-sectional area is significantly reduced. The remodeling defect seen in MAGP1Delta mice is likely not due to an osteoblast defect, because MAGP1Delta bone marrow stromal cells undergo osteoblastogenesis and form mineralized nodules. In vivo, MAGP1Delta mice exhibit normal osteoblast number, mineralized bone surface, and bone formation rate. Instead, our findings suggest increased bone resorption is responsible for the osteopenia. The number of osteoclasts derived from MAGP1Delta bone marrow macrophage cells is increased relative to the wild type, and osteoclast differentiation markers are expressed at earlier time points in MAGP1Delta cells. In vivo, MAGP1Delta mice have more osteoclasts lining the bone surface. RANKL (receptor activator of NF-kappaB ligand) expression is significantly higher in MAGP1Delta bone, and likely contributes to enhanced osteoclastogenesis. However, bone marrow macrophage cells from MAGP1Delta mice show a higher propensity than do wild-type cells to differentiate to osteoclasts in response to RANKL, suggesting that they are also primed to respond to osteoclast-promoting signals. Together, our findings suggest that MAGP1 is a regulator of bone remodeling, and its absence results in osteopenia associated with an increase in osteoclast number.

Recent reports of long-term bisphosphonate-treated patients developing cortical fractures have raised concerns that such fractures may relate to excessive suppression of bone turnover after prolonged use of these drugs. To evaluate the bone histology of patients presenting with cortical fractures after bisphosphonate therapy, we conducted a retrospective analysis of patients treated at Washington University Bone Health Program presenting with a history of low-energy cortical fractures (femoral shaft, pelvis, rib, metatarsal, and ankle), who had received bisphosphonates for at least two consecutive years and had undergone bone biopsy. Fifteen of 54 patients who underwent bone biopsy between November 2004 and March 2007 met the criteria. Of these, 10 patients had findings of suppressed trabecular bone remodeling, as demonstrated by lack of double tetracycline labels. There were no significant differences in bone density, clinical features, and biochemical features between those with suppressed turnover and the other five subjects with normal remodeling. However, the low-turnover group had received bisphosphonates (primarily alendronate) for a significantly longer duration (6.5 +/- 0.6 vs. 3.9 +/- 0.8 years, P = 0.02). Thus, about two-thirds of patients presenting with cortical fractures while on long-term treatment with bisphosphonates had suppressed turnover. Since the prevalence of such histological findings in nonfracture patients remains unknown, the impact of suppressed bone turnover on the development of cortical fractures cannot be determined. Considering the widespread use of bisphosphonates, it appears that the overall risk of cortical fractures is low. However, there may be a subset of as yet unidentified patients who could be predisposed to this complication.

Oculodentodigital dysplasia (ODDD) is a dominant negatively inherited disorder with variable but characteristic anomalies of the fingers and toes, eyes, face and teeth, which are caused by mutations in the connexin 43 (Cx43) gene. All mutations analyzed so far have a negative influence on the conductance through gap junctional channels and hemichannels, as well as trafficking of Cx43 protein in transfected cells. In this study, we inserted the human Cx43G138R point mutation into the mouse Cx43 gene and generated mice conditionally expressing this mutation. All ODDD phenotypic manifestations observed in humans, including syndactyly and enamel hypoplasia as well as craniofacial, bone and heart anomalies, were also observed with significant penetrance in Cx43G138R mice. When this mutation was specifically expressed in cardiomyocytes, characteristic alterations in the electrocardiogram and spontaneous arrhythmias were recorded. In vitro studies with Cx43G138R-expressing cells revealed loss of the Cx43 P2 phosphorylation state, which was also absent in the mutated hearts. This loss has previously been associated with gap junctional dysfunction and increased cellular ATP release. The Cx43G138R mutated mice show significantly increased arrhythmogeneity ex vivo in Langendorff experiments with explanted hearts and in vivo in particular under hypoxic conditions. Our results suggest that the increased activity of ATP-releasing channels in Cx43G138R mutated cardiomyocytes may further reduce the already decreased gap junctional communication and thus aggravate arrhythmogenesis in the mouse mutant.

Ovariectomy-induced bone loss is accentuated in mice with germline Cdh2 haploinsufficiency, the result of a decreased osteoblastogenesis in the face of normal osteoclast number. Reduced N-cadherin abundance in these mice decreases cell—cell adhesion and alters signaling pathways important for osteoblast commitment and differentiation, thus providing in vivo evidence that N-cadherin—mediated cell—cell interactions are involved in homeostatic responses to increased bone remodeling. Introduction: We have shown that targeted expression of a dominant negative truncated form of N-cadherin (Cdh2) delays acquisition of peak bone mass in mice and retards osteoblast differentiation. We tested the role of this molecule in the skeletal homeostatic response to ovariectomy in mice with germline Cdh2 haploinsufficiency. Materials and Methods: Heterozygous Cdh2 null (Cdh2+/−) and wildtype mice were ovariectomized and followed up to 13 weeks by in vivo radiodensitometric and ex vivo histologic assessment of bone mass and turnover. Cells isolated from wildtype and Cdh2+/− mice were used to determine the alterations in bone cell function produced by partial loss of N-cadherin. Results: Bone mass was not significantly different between Cdh2+/− and wildtype littermates, but on ovariectomy, bone loss in Cdh2+/− mice was initially slower, but with time it became significantly greater than in wildtype mice. This accentuated bone loss was associated with lower osteoblast number and serum osteocalcin levels, with no differences in bone resorption. Although development of calcified nodules was faster in calvaria cells isolated from Cdh2+/− mice relative to Cdh2+/+ cells, bone marrow osteogenic precursors were lower in the former than in the latter genotypes. Cdh2 expression was downregulated with differentiation in wildtype calvaria cells, whereas cadherin-11 abundance remained unchanged. Furthermore, cell—cell adhesion (postconfluence) was decreased among heterozygous calvaria cells, as was cell proliferation (preconfluence), relative to wildtype cells. Finally, the abundance and cellular distribution of β-catenin was minimally decreased in Cdh2+/− cells, whereas mitogen-activated protein kinase (MAPK) signaling was more active in Cdh2 insufficient cells. Conclusions:Cdh2 is involved in the homeostatic bone formation response to ovariectomy, presumably by regulating osteoprogenitors number and differentiation through stabilization of cell—cell adhesion and/or signaling modulation.

Our previous studies identified a role for MZM in the movement of lymphocytes into the splenic white pulp. Here we show that phagocytosis of colloidal carbon by marginal zone macrophages results in a splenic influx of B lymphocytes, and T lymphocytes of memory/activated phenotype, with concomitant upregulation of B Lymphocyte Chemoattractant (BLC, CXCL13) mRNA, a chemokine acting on B and memory/activated T lymphocytes. The recruitment of B cells and activated T cells to the spleen after phagocytic uptake would allow an immune response against blood-borne pathogens to be quickly and effectively mounted by bringing together the two key cell types responsible for generating humoral immunity.

In the bone marrow (BM), hematopoietic stem cells and progenitors (HSC/P) reside in specific anatomical niches. Among these niches, a functional osteoblast (Ob)-macrophage (MΦ) niche has been described where Ob and MΦ (so called "osteomacs") are in direct relationship. A connection between innate immunity surveillance and traffic of hematopoietic stem cells/progenitors (HSC/P) has been demonstrated but the regulatory signals that instruct immune regulation from MΦ and Ob on HSC/P circulation are unknown. The adaptor protein sequestosome 1 (Sqstm1), contains a Phox bemp1 (PB1) domain which regulates signal specificities through PB1-PB1 scaffolding and processes of autophagy. Using microenvironment and osteoblast-specific mice deficient in Sqstm1, we discovered that the deficiency of Sqstm1 results in macrophage contact-dependent activation of Ob IKK/NF-κB, in vitro and in vivo repression of Ccl4 (a CCR5 binding chemokine that has been shown to modulate microenvironment Cxcl12-mediated responses of HSC/P), HSC/P egress and deficient BM homing of wild-type HSC/P. Interestingly, while Ccl4 expression is practically undetectable in wild-type or Sqstm1-/- Ob, primary Ob co-cultured with wild-type BM-derived MΦ strongly upregulate Ccl4 expression, which returns to normal levels upon genetic deletion of Ob Sqstm1. We discovered that MΦ can activate an inflammatory pathway in wild-type Ob which include upregulation of activated focal adhesion kinase (p-FAK), IκB kinase (IKK), nuclear factor (NF)-κB and Ccl4 expression through direct cell-to-cell interaction. Sqstm1-/- Ob cocultured with MΦ strongly upregulated p-IKBα and NF-κB activity, downregulated Ccl4 expression and secretion and repressed osteogenesis. Forced expression of Sqstm1, but not of an oligomerization-deficient mutant, in Sqstm1-/- Ob restored normal levels of p-IKBα, NF-κB activity, Ccl4 expression and osteogenic differentiation, indicating that Sqstm1 dependent Ccl4 expression depends on localization to the autophagosome formation site. Finally, Ob Sqstm1 deficiency results in upregulation of Nbr1, a protein containing a PB1 interacting domain. Combined deficiency of Sqstm1 and Nbr1 rescues all in vivo and in vitro phenotypes of Sqstm1 deficiency related to osteogenesis and HSC/P egression in vivo. Together, this data indicated that Sqstm1 oligomerization and functional repression of its PB1 binding partner Nbr1 are required for Ob dependent Ccl4 production and HSC/P retention, resulting in a functional signaling network affecting at least three cell types. A functional ‘MΦ-Ob niche’ is required for HSC/P retention where Ob Sqstm1 is a negative regulator of MΦ dependent Ob NF-κB activation, Ob differentiation and BM HSC/P traffic to circulation. Disclosures Starczynowski: Celgene: Research Funding. Cancelas:Cerus Co: Research Funding; P2D Inc: Employment; Terumo BCT: Research Funding; Haemonetics Inc: Research Funding; MacoPharma LLC: Research Funding; Therapure Inc.: Consultancy, Research Funding; Biomedical Excellence for Safer Transfusion: Research Funding; New Health Sciences Inc: Consultancy.

The gap junction protein, connexin43 (Cx43) is involved in mechanotransduction in bone. Recent studies using in vivo models of conditional Cx43 gene (Gja1) deletion in the osteogenic linage have generated inconsistent results, with Gja1 ablation resulting in either attenuated or enhanced response to mechanical load, depending upon the skeletal site examined or the type of load applied. To gain further insights on Cx43 and mechanotransduction, we examined bone formation response at both endocortical and periosteal surfaces in 2-month-old mice with conditional Gja1 ablation driven by the Dermo1 promoter (cKO). Relative to wild type (WT) littermates, it requires a larger amount of compressive force to generate the same periosteal strain in cKO mice. Importantly, cKO mice activate periosteal bone formation at a lower strain level than do WT mice, suggesting an increased sensitivity to mechanical load in Cx43 deficiency. Consistently, trabecular bone mass also increases in mutant mice upon load, while it decreases in WT. On the other hand, bone formation actually decreases on the endocortical surface in WT mice upon application of axial mechanical load, and this response is also accentuated in cKO mice. These changes are associated with increase of Cox-2 in both genotypes and further decrease of Sost mRNA in cKO relative to WT bones. Thus, the response of bone forming cells to mechanical load differs between trabecular and cortical components, and remarkably between endocortical and periosteal envelopes. Cx43 deficiency enhances both the periosteal and endocortical response to mechanical load applied as axial compression in growing mice.