Forman, Stephen J.

Background: Ph-like ALL is a high-risk subset of B-lineage ALL that responds poorly to standard chemotherapy regimens. While allogeneic hematopoietic cell transplantation (HCT) is routinely recommended for patients with Ph-like ALL, large multicenter data addressing its role is limited. Here, we conducted a multicenter study to evaluate the role of HCT in adolescent and young adult (AYA) and adult patients (pts) with Ph-like ALL and compare their outcomes to pts with Ph-pos and Ph-neg (non-Ph-like) ALL. Methods: The study included pts (age ≥18) with B-lineage ALL who received HCT in first complete remission (CR1) at 3 academic centers (MD Anderson Cancer Center, City of Hope and Mayo Clinic) between 2006 and 2021. Pts were divided into 3 main subgroups: Ph-like, Ph-pos and Ph-neg ALL. Ph-like ALL cases were identified using cumulative data obtained by targeted RNA sequencing, conventional cytogenetics, FISH studies, whole genome chromosomal microarray and flow cytometry. Measurable residual disease (MRD) prior to HCT was measured using flow cytometry with a sensitivity of 0.01% for Ph-neg and Ph-like ALL, and with a PCR assay for BCR::ABL1 for Ph-pos ALL. MRD-negativity was defined as <0.01%. Predictors of relapse were evaluated in univariate and multivariate analysis using Fine-Gray sub-distribution hazard models considering non-relapse mortality (NRM) as a competing risk. Results: 673 patients were identified, 83 (12.3%) had Ph-like ALL, of which 73% had CRLF2-alterations. The remaining patients were classified either as Ph-pos (N=271, 40.3%) or Ph-neg ALL (N=319, 47.4%). Patients with Ph-like ALL were younger (median age 40 years vs 48 and 46 years for Ph-pos and Ph-neg ALL, respectively, p=0.01), more likely to be of Hispanic ethnicity (69% vs 32% and 48% for Ph-pos and Ph-neg ALL respectively, p<0.001). Patients with Ph-like ALL were also more likely to have induction failure (24% vs 2% and 11% for Ph-pos and Ph-neg ALL, respectively, p=0.001). A summary of pts characteristics for each subgroup can be found in Table 1. The median follow-up was 30, 52 and 48 months for patients with Ph-like, Ph-pos and Ph-neg ALL, respectively. In univariate analysis, 3-yr OS and PFS did not differ significantly (66% and 59% vs 59% and 54%, p=0.1) between patients with Ph-like and Ph-neg ALL, respectively. Similarly, the cumulative incidence of relapse was comparable between patients with Ph-like and Ph-neg ALL (22% vs 20%, respectively, p=0.7). In contrast, the 3-yr OS (75%, p<0.001) and PFS (70%, p=0.001) were significantly higher and relapse rate significantly lower (12%, p=0.003) in pts with Ph-pos ALL compared with Ph-like or Ph-neg ALL (Figure 1). The inferior survival in patients with Ph-like and Ph-neg ALL was likely attributable to higher relapse rates (22% and 20% vs 12%, respectively, p=0.003) compared to Ph-pos ALL. Finally, the 3-yr NRM rate in patients with Ph-like ALL was comparable (20% vs 18% and 23%, respectively, p>0.1) to Ph-pos and Ph-neg ALL. We confirmed that the relapse rate in patients with Ph-like ALL was comparable to the rate in pts with Ph-neg ALL (HR=1.02, 95% CI 0.6-1.8, p=0.9) on multivariate analysis (MVA). Ph-pos ALL was associated with a significantly lower relapse rate compared with Ph-neg ALL (HR=0.4, 95% CI 0.3-0.7, p<0.001). MRD positivity prior to allo-HCT was the only additional significant predictor for relapse on MVA (HR=2.9, 95% CI 1.8-4.7, p<0.001). Conclusions: HCT appears to overcome the poor prognosis of patients with Ph-like ALL. Despite higher induction failure rates, patients with Ph-like ALL undergoing HCT in CR1 had similar outcomes to other Ph-neg ALL subsets. The impact of effective salvage therapy leading to MRD-negativity in CR1 in this group is under investigation and will be reported. Further studies are needed to assess the impact of different Ph-like alterations on HCT outcomes. Outcomes for patients with Ph-pos ALL are significantly better than other groups, likely due to the use of TKIs pre- and post-HCT.

PURPOSE Allogeneic hematopoietic cell transplantation (HCT) is the only potentially curative therapy for myelodysplastic syndromes (MDS), although it is infrequently offered to older patients. The relative benefits of HCT over non-HCT therapy in older patients with higher-risk MDS have not been defined. METHODS We conducted a multicenter biologic assignment trial comparing reduced-intensity HCT to hypomethylating therapy or best supportive care in subjects 50-75 years of age with intermediate-2 or high-risk de novo MDS. The primary outcome was overall survival probability at 3 years. Between January 2014 and November 2018, we enrolled 384 subjects at 34 centers. Subjects were assigned to the Donor or No-Donor arms according to the availability of a matched donor within 90 days of study registration. RESULTS The median follow-up time for surviving subjects was 34.2 months (range: 2.3-38 months) in the Donor arm and 26.9 months (range: 2.4-37.2 months) in the No-Donor arm. In an intention-to-treat analysis, the adjusted overall survival rate at 3 years in the Donor arm was 47.9% (95% CI, 41.3 to 54.1) compared with 26.6% (95% CI, 18.4 to 35.6) in the No-Donor arm ( P = .0001) with an absolute difference of 21.3% (95% CI, 10.2 to 31.8). Leukemia-free survival at 3 years was greater in the Donor arm (35.8%; 95% CI, 29.8 to 41.8) compared with the No-Donor arm (20.6%; 95% CI, 13.3 to 29.1; P = .003). The survival benefit was seen across all subgroups examined. CONCLUSION We observed a significant survival advantage in older subjects with higher-risk MDS who have a matched donor identified and underwent reduced-intensity HCT, when compared with those without a donor. HCT should be included as an integral part of MDS management plans in fit older adults with higher-risk MDS.

Background: Recent advances in the treatment of myelodysplastic syndrome (MDS) have improved patient survival and quality of life (QOL), while reducing transfusion burden. However, allogeneic hematopoietic cell transplantation (HCT), widely used in younger MDS patients, remains the only curative therapy for MDS. While transplantation outcomes among selected older patients with MDS are similar to younger patients with MDS, early transplantation for older patients is infrequently offered since the relative benefits of HCT over non-HCT therapy in have not been well defined in this patient group. We conducted a multi-center, biologic assignment trial in older individuals with high risk MDS to define the benefit of HCT over non-HCT therapy. Methods: The study was a multicenter, biologic assignment trial in subjects aged 50-75 with higher risk de novo MDS (IPSS Intermediate-2 (Int-2) or High) who were candidates for reduced-intensity conditioning (RIC) allogeneic HCT, comparing outcomes of those with a suitable 8/8 HLA-matched donor to those without a donor. The trial was conducted by the Blood and Marrow Transplant Clinical Trials Network (BMT CTN 1102, NCT02016781). Eligible subjects were enrolled prior to a formal donor search, and before or after MDS treatment was initiated. Biological assignment to the Donor or No Donor arm was based on high-resolution HLA typing of eligible family members and a search of the unrelated donor registries. Subjects were initially assigned to the No Donor arm and re-assigned to the Donor arm when a suitable donor was identified. Subjects who died or whose 90-day donor search ended without identifying a suitable donor remained in the No Donor arm. Subjects in the Donor arm were expected to undergo RIC HCT within 6 months of enrollment. Subjects underwent RIC HCT or non-HCT therapy according to institutional standards. The primary analysis compared three-year overall survival (OS) between arms using adjusted survival estimates to account for the potential bias resulting from biological assignment. The sample size was selected to provide at least 80% power to detect a difference of 15% in 3-year OS. Between January 2014 and November 2018, 384 subjects (Donor n=260, No Donor n=124) were enrolled at 34 centers. The study arms were well balanced for age, gender, KPS, IPSS risk, MDS disease duration and responsiveness to hypomethylating therapy (Table). The median follow-up time for surviving patients was 34.2 months (range: 2.3-38 months) in the Donor arm and 26.9 months (range: 2.4-37.2 months) in the No Donor arm. Results: In an intent-to-treat analysis, adjusted OS at 3 years from study enrollment in the Donor arm was 47.9% (95% CI: 41.3%-54.1%) compared with 26.6% (95% CI: 18.4%-35.6%) in the No Donor arm (p=0.0001, absolute difference 21.3%, 95% CI: 10.2%-31.8%)(Figure). A sensitivity analysis excluding subjects assigned to the No Donor arm who died or withdrew prior to the end of the 90-day search window showed no effect on outcome (Adjusted OS: 48.0% vs. 28.1%, p=0.0004). Leukemia-free survival (LFS) at 3 years was greater in the Donor arm (35.8%, 95% CI: 29.8%-41.8%) compared with the No Donor arm (20.6%, 95% CI: 13.3%-29.1%, p=0.003), with no changes in the sensitivity analysis. An OS and LFS benefit was seen across all subgroups tested (Figure). There were no clinically significant differences in QOL between Donor and No Donor arms as measured by the FACT-G, the MOS-SF36 Physical and Mental Component Scores and the EQ-5D utility score at all time points. The overall non-compliance rate for the trial was 26.3%. Reasons for non-compliance included the use of myeloablative conditioning or failure to proceed to RIC transplant in the Donor arm, and the use of alternative donors in the No Donor arm. In an as-treated analysis, comparison of the HCT and No HCT arms demonstrated a significant advantage in 3-year OS (47.4% vs. 16.0%, p<0.0001) and LFS (39.3% vs. 10.9%, p<0.0001) for subjects who underwent HCT. Conclusions: We observed a significant OS advantage in older patients with Int-2 and High IPSS risk de novo MDS who are RIC HCT candidates and have an HLA-matched donor, when compared with those without a donor. The benefit of having a matched donor was seen across subgroups, including those who were of Medicare age (>65) and below. HCT should be offered to all individuals between the ages of 50-75 with Int-2 and High IPSS risk MDS in whom a suitable donor can be identified. Table Disclosures Nakamura: Magenta Therapeutics: Other: Advisory board meeting; Kyowa-Kirin: Other: Support on a meeting presentation; Alexion: Other: Support on a meeting presentation; Merck: Other: advisory board meeting; NapaJen Pharma: Consultancy; Kadmon Corporation: Other: Advisory board meeting; Celgene: Other: Support on seminar; Viracor: Consultancy. Scott:Alexion, Incyte, Novartis, Regeneron: Consultancy; Agios, BMS: Honoraria; BMS, Novartis: Research Funding. Oran:ASTEX: Research Funding; Celgene: Consultancy; Arog Pharmaceuticals: Research Funding. Maziarz:Novartis, Incyte, CRISPR Therapeutics, Artiva Biotherapeutics, and AlloVir: Consultancy; Novartis and Athersys: Other: DSMB participant; Athersys: Patents & Royalties; Incyte, Kite, BMS/Celgene, PACT Pharma, Orca BioSystems, and Omeros: Honoraria; Novartis and Juno: Research Funding. McGuirk:Allo Vir: Consultancy, Honoraria, Research Funding; Gamida Cell: Research Funding; Pluristem Ltd: Research Funding; Bellicum Pharmaceutical: Research Funding; Astellas: Research Funding; Fresenius Biotech: Research Funding; Novartis: Research Funding; Kite Pharmaceuticals: Consultancy, Honoraria, Research Funding, Speakers Bureau; Juno Therapeutics: Consultancy, Honoraria, Research Funding. Sekeres:BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees; Takeda/Millenium: Consultancy, Membership on an entity's Board of Directors or advisory committees. Cutler:Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees; Kadmon: Consultancy, Membership on an entity's Board of Directors or advisory committees; Jazz: Consultancy, Membership on an entity's Board of Directors or advisory committees; Medsenic: Consultancy, Membership on an entity's Board of Directors or advisory committees; Generon: Consultancy, Membership on an entity's Board of Directors or advisory committees; Mesoblast: Consultancy, Membership on an entity's Board of Directors or advisory committees.

Introduction: Standard of care for patients (pts) with relapsed or refractory (RR) Hodgkin lymphoma (HL) is salvage therapy (tx) followed by autologous hematopoietic cell transplantation (HCT). However, most pts with high-risk RR HL will relapse after HCT. The AETHERA study demonstrated that post-HCT consolidation with brentuximab vedotin (BV) in high-risk HL pts improved progression-free survival (PFS) compared to placebo, particularly in pts with 2+ risk factors (Moskowitz, 2018). Pts with prior BV exposure were excluded from AETHERA, and BV is increasingly used prior to HCT in HL. PD1 blockade is effective in pts with RR HL and PD1 monotherapy as post-HCT consolidation in HL resulted in promising 18 mo PFS (Armand, 2019). Combined BV and nivolumab (Nivo) is a safe and effective salvage tx in HL, therefore we conducted a multicenter phase 2 study to evaluate the safety and efficacy of BV-Nivo post-HCT consolidation in high risk RR HL. Methods: After HCT, adult pts with high-risk HL defined as having ≥ 1 of the following modified AETHERA risk factors were eligible: primary refractory HL, relapse < 1 year of completing initial tx, extranodal disease (dz) at relapse, B symptoms (sx) at relapse, requiring > 1 salvage tx, not in CR at HCT. Prior BV or PD1 blockade were allowed if pts were not refractory. Pts underwent HCT according to institutional standards at the 5 centers. Starting between day 30-75 after HCT, pts received 1.8 mg/kg of BV and 3mg/kg nivo q21 days for a planned 8 cycles. If 1 drug was discontinued due to toxicity, the other could be continued. Investigators assessed response and progressive disease (PD) according to the 2014 Lugano classification. The primary endpoint was 18 mo PFS from study tx initiation. Secondary endpoints were overall survival (OS), safety, and the response rate in pts not in complete response (CR) at baseline. Results: 59 pts were enrolled and treated with at least one dose of study tx. Baseline characteristics are listed in Table 1. 18 (31%) pts were primary refractory, 35 (59%) had early relapse, 23 (39%) had extranodal dz and 14 (24%) had B sx at relapse, 15 (25%) received > 1 salvage tx before HCT, and 48 (81%) were in CR at HCT. 21 (36%) had 1 modified AETHERA risk factor, 23 (40%) had 2 and 14 (24%) had 3+ risk factors. The median follow-up time from study tx initiation was 15.7 months (range, 2.8-35.5). Patients initiated BV-nivo a median 54 days from HCT (range, 34-75) and received a median of 8 cycles (range, 1-8). 29 (49%) pts completed all 8 cycles of BV and nivo and 45 (76%) patients completed 8 cycles of one drug. 14 (24%) pts discontinued both BV and nivo early, including 6 for adverse events (AE), 6 pt withdrawals, 1 pt lost to follow-up, and 1 pt death from PJP pneumonia unrelated to study tx. BV was discontinued in 8 (14%) pts - due to grade (gr) 3 peripheral neuropathy (PN) in 2 pts, gr 2 PN in 2 pts, carpal tunnel syndrome in 1 pt, gastrointestinal AEs in 2 pts, and infusion related reaction in 1 pt. Nivo was discontinued in 7 (12%) pts - due to pneumonitis in 2 pts, and colitis, elevated bilirubin, abnormal transaminases, pneumonia with elevated creatinine, and hypotension with fever in 1 pt each. BV was dose reduced to 1.2mg/kg in 11 (19%) pts, 9 pts for PN, and 1 each for neutropenia and arthralgia. The most common AEs related to BV-Nivo consolidation were PN (51%, 3% gr 3), neutropenia (42%, 31% gr 3-4), fatigue (37%), diarrhea (29%, 3% gr 3), nausea (25%, 2% gr 3), arthralgia (24%), AST elevation (24%, 2% gr 3). The most frequent gr 3-4 AEs were neutropenia (31%), pneumonitis (7%), and ALT elevation (5%). Immune-related (ir) AEs requiring systemic corticosteroids occurred in 18 (31%) patients. Most common Gr 2 or higher irAEs included: pneumonitis (12%), AST or ALT elevation (8%), hypothyroidism (5%), and rash (3%). 6 pts were not in CR at baseline after HCT (all PR). 5 pts converted to CR with study tx and 1 pt remained in PR without PD. There were only 2 PFS events, 1 pt with relapse at 15 months and PJP-related death after prophylaxis was self-discontinued. The estimated 18 mo PFS and OS in all patients were 95% and 98%, respectively. The estimated 18 mo PFS in pts with 2+ and 3+ risk factors were 92% and 89%, respectively. Conclusions: Post-HCT consolidation with BV-Nivo in pts with high-risk RR HL is a promising approach, with only 1 relapse observed in our cohort with short follow-up thus far. Post-HCT BV-Nivo was tolerable, though IrAEs were observed more frequently than in the pre-HCT setting and PN and neutropenia were common. Disclosures Herrera: Pharmacyclics: Research Funding; Karyopharm: Consultancy; AstraZeneca: Research Funding; Gilead Sciences: Consultancy, Research Funding; Immune Design: Research Funding; Seattle Genetics: Consultancy, Research Funding; Genentech, Inc./F. Hoffmann-La Roche Ltd: Consultancy, Research Funding; Merck: Consultancy, Research Funding; Bristol Myers Squibb: Consultancy, Other: Travel, Accomodations, Expenses, Research Funding. Nieto:Affimed: Consultancy, Other: Grant Support; Secura Bio: Other: Grant Support; Novartis: Other: Grant Support; Astra Zeneca: Other: Grant Support. Holmberg:Sanofi: Research Funding; Seattle Genetics: Research Funding; Millenium-Takeda: Research Funding; Bristol-Myers Squibb: Research Funding; UpToDate: Patents & Royalties: Royalties; Janssen: Research Funding; Merck: Research Funding. Mei:Sanofi: Consultancy; Morphosys: Membership on an entity's Board of Directors or advisory committees. Chen:Autolus Therapeutics: Current Employment. Rosen:Abbvie: Speakers Bureau; Seattle Genetics: Consultancy; NeoGenomics: Consultancy; Aileron Therapeutics: Consultancy; Novartis: Consultancy; Pebromene: Consultancy; Celgene: Speakers Bureau; paradigm Medical Communications: Speakers Bureau. Kwak:CJ Healthcare: Consultancy; Xeme Biopharma/Theratest: Other: equity; Sellas Life Sciences Grp: Consultancy; Enzychem Life Sciences: Membership on an entity's Board of Directors or advisory committees; Antigenics: Other: equity; InnoLifes, Inc: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pepromene Bio: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celltrion Healthcare: Membership on an entity's Board of Directors or advisory committees; Celltrion, Inc.: Consultancy. Feldman:Portola: Research Funding; Pfizer: Research Funding; Kyowa Kirin: Consultancy, Research Funding; Eisai: Research Funding; Cell Medica: Research Funding; Amgen: Research Funding; Pharmacyclics: Honoraria, Other, Speakers Bureau; Abbvie: Honoraria; Bayer: Consultancy, Honoraria; Trillium: Research Funding; Janssen: Speakers Bureau; Viracta: Research Funding; Rhizen: Research Funding; Corvus: Research Funding; BMS: Consultancy, Honoraria, Research Funding; Kite: Honoraria, Other: Travel expenses, Speakers Bureau; Celgene: Honoraria, Research Funding; Takeda: Honoraria, Other: Travel expenses; Seattle Genetics, Inc.: Consultancy, Honoraria, Other: Travel expenses, Research Funding, Speakers Bureau; AstraZeneca: Consultancy. OffLabel Disclosure: Nivolumab is not FDA-approved for use as consolidation after autologous stem cell transplantation

Acute leukemia is a constellation of rapidly progressing diseases that affect a wide range of patients regardless of age or gender. Traditional treatment options for patients with acute leukemia include chemotherapy and hematopoietic cell transplantation. The advent of cancer immunotherapy has had a significant impact on acute leukemia treatment. Novel immunotherapeutic agents including antibody-drug conjugates, bispecific T cell engagers, and chimeric antigen receptor T cell therapies have efficacy and have recently been approved by the US Food and Drug Administration (FDA) for the treatment of patients with acute leukemia. The Society for Immunotherapy of Cancer (SITC) convened a panel of experts to develop a clinical practice guideline composed of consensus recommendations on immunotherapy for the treatment of acute lymphoblastic leukemia and acute myeloid leukemia.

Background: Studying gene expression and clinical outcome data from 136 clinical trials for patients with cancer (~21,000 patients with 26 cancer types), we found CD25 as one of the strongest predictors of poor clinical outcome in patients with B-cell malignancies, but not in other cancer types. This was unexpected because CD25 is known as one of three chains of the IL2 receptor on T-cells and NK-cells. Interleukin-2 (IL2) functions as essential T-cell growth factor. IL2 signals through b- and g-, but not a-chains (CD25) of its heterotrimeric receptor. CD25-deficiency causes lymphoproliferation and autoimmunity, however, its mechanistic role is unclear. Results: Our experiments based on genetic mouse models and engineered patient-derived B-cell leukemia and lymphoma xenografts revealed that CD25 expressed on B-cells is not an IL2 receptor chain, but in fact binds downstream signaling molecules of the B-cell receptor (BCR). Through these interactions, CD25 mediates negative feedback to BCR signaling in response to antigen-encounter in normal B-cells. Defects in CD25-/-B-cells were not replicated in mice that express CD25 but lack expression of the IL2 cytokine. These findings demonstrate IL2-independent functions of CD25 in B-cells and B-cell derived leukemia and lymphoma. To comprehensively study the interactome of the short cytoplasmic tail of CD25, we performed proximity-dependent biotin identification (BioID). This analysis revealed that the CD25 tail exerts negative feedback control through recruitment of the PKCβ-scaffold RACK1 and the inhibitory phosphatase SHIP1 (see schematic, left). Interestingly, the cytoplasmic tail of CD25 harbors a PKCβ-substrate motif and mutation of a central serine residue (S268) to A268 compromised interactions with PKCβ, its scaffold RACK1 and SHIP1, demonstrating that feedback control was dependent on PKCβ-mediated phosphorylation of CD25-S268. A genetic observation in a family with monogenic autoimmunity confirmed the functional importance of the cytoplasmic CD25-tail motif: a mutation immediately preceding S268 compromised CD25-surface translocation, which was restored by homology-directed repair of the S268. In vitro kinase assay with 62 candidate kinases against recombinant cytoplasmic tail of CD25-S268 or -A268 identified PKCβ as top-ranking kinase hit for CD25-S268 but not CD25-A268. Our genetic studies revealed that PKCβ is required for cell-membrane translocation of CD25, but also transcriptional expression of CD25 via NF-κB activation. Therefore, PKCβ act as critical effector molecule downstream of CD25 to mediate B-cell selection during normal B-cell development and calibrate oncogenic BCR signaling in B-cell tumors. In B-cell malignancies, BCR-dependent survival and proliferation signals are often substituted by oncogenic BCR-mimics (e.g. BCR-ABL1, JAK2, BRAFV600E, LMP2A, CD79B mutations; see schematic, right). Accordingly, we identified CD25 surface-expression as biomarker of oncogenic BCR-signaling and predictor of poor clinical outcomes. CD25-/-B-cell leukemia failed to initiate fatal disease in transplant recipients. Owing to imbalances of oncogenic BCR-signaling and p53-checkpoint activation, CD25-/- B-cell leukemia failed to initiate fatal disease in transplant recipients. In patient-derived xenograft models of drug-resistant B-cell malignancies, treatment with a CD25-specific antibody drug-conjugate (ADCT-301) extended survival of transplant recipients or eradicated disease. These findings identified CD25 as previously unrecognized feedback regulator of oncogenic BCR-signaling and provide a rationale for therapeutic targeting of CD25 in refractory B-cell malignancies. Figure Disclosures Zammarchi: ADC Therapeutics: Employment. Van Berkel:ADC Therapeutics: Research Funding. Melnick:Constellation: Consultancy; Janssen: Research Funding; Epizyme: Consultancy. Luger:Celgene: Research Funding; Cyslacel: Research Funding; Pfizer: Honoraria; Seattle Genetics: Research Funding; Agios: Honoraria; Ariad: Research Funding; Biosight: Research Funding; Kura: Research Funding; Onconova: Research Funding; Genetech: Research Funding; Jazz: Honoraria; Daichi Sankyo: Honoraria. Meffre:AbbVie: Consultancy, Other: Grant. Weinstock:Celgene: Research Funding.

Introduction. Our previous flow cytometry-based comparison of HIV(+) and HIV(-) autologous hematopoietic stem cell transplant (auto-HSCT) recipient immunomes at 56, 180 and 365 days post-transplant to each other and to healthy controls (HCs) showed that both sets of auto-HSCT recipient immunomes approached HCs over time, but retained significant differences. HIV(+), but not HIV(-), auto-AHCT recipients retained pro-inflammatory features consistent with chronic HIV infection. Here, we report the results of a quantitative and functional analysis of immune reconstitution in HIV(+) patients treated with allogeneic hematopoietic stem cell transplant (allo-HSCT), in comparison with HIV(+) auto-HSCT recipients and HCs. Methods. Blood samples were collected for analysis at days 56, 180 and 365 post-transplant from HIV(+) transplant recipients and at 1 time point from HCs. Whole blood analysis was performed by five-color flow cytometry across 100 immune marker combinations. Comparisons were made between HIV(+) allo-HSCT recipients (n=17, acute myeloid leukemia, acute lymphocytic leukemia, myelodysplastic syndrome, Hodgkin and non-Hodgkin lymphoma that received myeloablative or reduced intensity conditioning on the BMT-CTN-0903/AMC-080 trial), HIV(+) auto-HSCT recipients (n=36, aggressive B cell non-Hodgkin lymphoma or Hodgkin lymphoma that received myeloablative conditioning on the BMT-CTN-0803/AMC-071 trial) and 71 HCs. Unsupervised principal component analysis (PCA) examined differences in immune cell proportions, identified by flow cytometry across 100 cell subsets at each time point. Wilcoxon rank-sum tests compared median absolute counts and median proportions of cell subsets. An independent feature importance score analysis (FIS) identified contributions of immune cell populations expressing specific immune marker combinations to the differences between HIV(+) auto-HSCT recipients, HIV(+) allo-HSCT recipients and HCs. Functional responsiveness of HIV(+) allo-HSCT recipients' T cells to stimulation with CD3- and CD28-directed antibodies, NK cells to stimulation with IL-12 and IL-18 and monocytes to stimulation with lipopolysaccharide (LPS) was assessed in a preliminary mass cytometry on peripheral blood mononuclear cells isolated at the same time points (n=2) and compared to HCs (n=2). Results. PCA showed that immunomes of HIV(+) allo-HSCT recipients and HIV(+) auto-HSCT recipients clustered together with each other, but away from HCs at all time points throughout the post-transplant year. FIS identified: 1) 13 cell subsets that defined the difference between HIV(+) allo-HSCT recipients (all visits) and HCs, and 2) 11 immune cell subsets that defined the difference between HIV(+) auto-HSCT recipients (all visits) and HCs; in both of these comparisons, activated CD3+/HLA-DR+ T cells had the greatest impact on the difference between HIV(+) and HC immunomes. At 1 year, both HIV(+) transplant recipient cohorts had higher absolute numbers of activated T cells, effector T cells and CD8+ T cells than HCs (Wilcoxon rank-sum test, p<0.0031). HIV(+) autologous and allogeneic HSCT recipients also had lower numbers of CD4+ T cells, naïve T cells and activated NK cells compared to HCs (p<0.0031). FIS also identified 20 immune cell subsets that defined the difference between HIV(+) autologous and allogeneic HSCT recipients immunomes at 1 year, with CD8+/CD27- effector T cell subset exerting the highest impact on the difference. Preliminary functional mass cytometry analysis of 2 HIV(+) allo-HSCT recipients and 2 HCs showed that: 1) IFNʏ production by CD8+ T cells was increased above that of HCs at all time points. 2) Expanded populations of CD4+/T-bet+ cytotoxic cells expressing granzyme B and perforin, and CD8+ cytotoxic T cells expressing granzyme B and perforin, persisted in HIV(+) allo-HSCT recipients at all time points, but not in HCs. 3) NK cells retained an ability to produce IFNʏ in response to stimulation with IL-12 and IL-18 in HIV(+) allo-SCT recipients. 4) Monocytes showed an enhanced production of TNFα in response to stimulation with LPS in HIV(+) allo-HSCT recipients compared to HCs at 1 year post-HSCT. Conclusion. Chronic HIV infection confers the pro-inflammatory immune features on the phenotypic and functional profiling of the T lymphocyte immunome of stem cell transplant recipients, irrespective of allogeneic or autologous stem cell donor source. Disclosures Devine: Bristol Myers: Other: Grant for monitoring support & travel support; Kiadis Pharma: Other: Protocol development (via institution); Magenta Therapeutics: Other: Travel support for advisory board; My employer (National Marrow Donor Program) has equity interest in Magenta. Noy:Janssen: Consultancy; Medscape: Honoraria; Prime Oncology: Honoraria; NIH: Research Funding; Pharamcyclics: Research Funding; Raphael Pharma: Research Funding. Popat:Bayer: Research Funding; Incyte: Research Funding; Jazz: Consultancy. Hofmeister:Celgene: Honoraria; Janssen: Membership on an entity's Board of Directors or advisory committees; Nektar: Honoraria, Membership on an entity's Board of Directors or advisory committees; Karyopharm: Membership on an entity's Board of Directors or advisory committees; Imbrium: Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Membership on an entity's Board of Directors or advisory committees. Navarro:Atara Biotherapeutics: Employment, Equity Ownership. Behbehani:Fluidigm corporation: Other: Travel funding. Lozanski:Boehringer Ingelheim: Research Funding; Beckman Coulter: Research Funding; Stemline Therapeutics Inc.: Research Funding; Genentec: Research Funding. Baiocchi:Prelude: Consultancy.

Key Points MRD response has value as a prognostic factor for blinatumomab treatment in R/R B-cell precursor ALL. MRD response was associated with better outcomes in terms of OS and RFS in blinatumomab-treated R/R ALL.

Abstract Studying gene expression and clinical outcome data from 136 clinical trials for patients with cancer (~21,000 patients with 26 cancer types), we found CD25 as one of the strongest predictors of poor clinical outcome in patients with B-cell malignancies, but not in other cancer types. This was unexpected because CD25 is known as one of three chains of the IL2 receptor on T-cells and NK-cells. Interleukin-2 (IL2) functions as essential T-cell growth factor. IL2 signals through β- and γ-, but not α-chains (CD25) of its heterotrimeric receptor. CD25-deficiency causes lymphoproliferation and autoimmunity, however, its mechanistic role is unclear. Our experiments based on genetic mouse models and engineered patient-derived B-cell leukemia and lymphoma xenografts revealed that CD25 expressed on B-cells is not an IL2 receptor chain, but in fact binds the B-cell receptor (BCR) to regulate its activity. Suggesting IL2-independent functions, defects in CD25-/-B-cells were not replicated in IL2-deficient mice. CD25 bound the BCR but not IL2Rβ- and IL2Rγ-chains. IL2Rβ- and IL2Rγ-chains can pair with other chains to form receptors for different cytokine-ligands. However, CD25 represents the first example of a cytokine receptor chain that binds to the BCR for negative feedback regulation. Likewise, in T-cells, CD25 had a bifunctional role and either functioned as IL2 receptor chain or as negative feedback regulator of T-cell receptor signaling. CD25-function was regulated by cell-membrane translocation, which required phosphorylation of its cytoplasmic tail at S268 (see schematic, left). In a family with monogenic autoimmunity, a mutation immediately preceding S268 compromised CD25-surface translocation, which was restored by homology-directed repair of the S268 motif. CD25-interactome analyses identified PKCd as critical effector molecule downstream of CD25 to mediate B-cell selection during normal B-cell development and calibrate oncogenic BCR signaling in B-cell tumors. In B-cell malignancies, BCR-dependent survival and proliferation signals are often substituted by oncogenic BCR-mimics (e.g. BCR-ABL1, JAK2, BRAFV600E, LMP2A, CD79B mutations; see schematic, right). Accordingly, we identified CD25 surface-expression as biomarker of oncogenic BCR-signaling and predictor of poor clinical outcomes. CD25-/-B-cell leukemia failed to initiate fatal disease in transplant recipients. Owing to imbalances of oncogenic BCR-signaling and p53-checkpoint activation, CD25-/- B-cell leukemia failed to initiate fatal disease in transplant recipients. In patient-derived xenograft models of drug-resistant B-cell malignancies, treatment with a CD25-specific antibody drug-conjugate (ADCT-301) extended survival of transplant recipients or eradicated disease. These findings identified CD25 as previously unrecognized feedback regulator of oncogenic BCR-signaling and provide a rationale for therapeutic targeting of CD25 in refractory B-cell malignancies. Figure. Figure. Disclosures Forman: Mustang Therapeutics: Other: Licensing Agreement, Patents & Royalties, Research Funding. Weinstock:Genentech/Roche, Monsanto: Consultancy; Novartis: Consultancy, Research Funding; Novartis, Astra Zeneca, Abbvie, Aileron, Surface Oncology, Daiichi Sankyo: Research Funding; Novartis, Dragonfly, Travera, DxTerity, Travera: Consultancy; Travera: Equity Ownership; Astra Zeneca, JAX, Samumed, Regeneron, Sun Pharma, Prescient: Patents & Royalties. Uzel:Novartis: Research Funding.