Magenta Therapeutics Research Articles

Safety and Cost Effectiveness of Chimeric Antigen Receptor T Cell Therapy in the Outpatient Setting

IntroductionSince the commercial approval of chimeric antigen receptor T cell (CAR-T) therapies, administration and toxicity monitoring have largely been in an inpatient setting due to the risk of significant toxicities such as cytokine release syndrome (CRS) and neurotoxicity in the first 30 days. Administration in the outpatient setting can be safe and cost-effective. Here we report the cost savings and adverse events of CAR-T in an outpatient setting as compared to the inpatient setting.MethodsCost differences of the commercial CD19 CAR-T axicabtagene ciloleucel (axi-cel) and tisangenlecleucel (tisa-cel) among inpatient and outpatient settings in 2020 were investigated using the Vizient Database®. Cost analysis for both settings was done for the initial 30 days post-CAR-T infusion. There were no billing codes for CRS and neurotoxicity till 2021. Clinical surrogates such as fever, hypotension, hypoxia, sepsis were used for CRS while febrile convulsion not otherwise specified (NOS), febrile seizure NOS, altered mental status, somnolence, stupor, and coma were used for neurotoxicity. ICD 10 codes for adverse effects were also used.ResultsIn 2017-2020, there were 81 organizations in the database that performed CAR-T procedures. In 2020, there were 1369 inpatient and 71 outpatient encounters, which were analyzed for cost and adverse events. (Table 1) The incidence of CRS was 43.2% (n=592) and 40.8% (n=29) in inpatient and outpatient groups, while that of neurotoxicity was 37.3% (n=511) and 29.6% (n=21) respectively. For cost analysis, we included the 16 centers (22% of all centers) that offered both inpatient and outpatient administration in 2020. Median inpatient cost was $397,610 ($346,550-$650,749) and median outpatient group cost was $243,050 ($204,344-$408,467). An analysis of variance (ANOVA) was run between inpatient and outpatient cases was found to be significant (P<0.0001). (Table 2) (Figure 1) (Figure 2)ConclusionAs the field of CAR-T therapy continues to grow, outpatient programs are likely to increase. Incidence of adverse effects was lower in the outpatient group, likely patient selection effect. This data suggests that outpatient CAR-T therapy is feasible cost-effective and has the potential to grow and improve value. While it appears to be an attractive option, there is a need for more studies on patient selection and creating a robust outpatient infrastructure is needed. [Display omitted] DisclosuresMahmoudjafari: Incyte: Membership on an entity's Board of Directors or advisory committees; Omeros: Membership on an entity's Board of Directors or advisory committees; GSK: Membership on an entity's Board of Directors or advisory committees. McGuirk: EcoR1 Capital: Consultancy; Novartis: Research Funding; Fresenius Biotech: Research Funding; Novartis: Research Funding; Astelllas Pharma: Research Funding; Bellicum Pharmaceuticals: Research Funding; Kite/ Gilead: Consultancy, Honoraria, Other: travel accommodations, expense, Kite a Gilead company, Research Funding, Speakers Bureau; Gamida Cell: Research Funding; Magenta Therapeutics: Consultancy, Honoraria, Research Funding; Juno Therapeutics: Consultancy, Honoraria, Research Funding; Allovir: Consultancy, Honoraria, Research Funding; Pluristem Therapeutics: Research Funding.

Phase I Dose-Escalation Study of Venetoclax Plus BEAM Followed By Autologous Stem Cell Transplant (ASCT) for Chemoresistant or High-Risk Relapsed/Refractory Non-Hodgkin Lymphoma (NHL)

Phase I Dose-Escalation Study of Venetoclax Plus BEAM Followed By Autologous Stem Cell Transplant (ASCT) for Chemoresistant or High-Risk Relapsed/Refractory Non-Hodgkin Lymphoma (NHL)

Distress, Health-Related Quality of Life (HQOL) and Confidence in Survivorship Information (CSI) in Older (≥60 Years) Hematopoietic Cell Transplant (HCT) Patients

Background: The use of HCT to treat older (≥60 years) patients with hematological malignancies has markedly increased in recent years, however, the long-term effects of HCT on distress, psychosocial functioning, and HQOL in older HCT survivors is largely unknown. Though older HCT survivors have a higher risk of disease recurrence, they may have less access to resources and subsequently experience more pronounced late effects of disease and treatment. Confidence in Survivorship Information (CSI) in this specific age group has not been reported.Methods: We conducted a secondary analysis on a subgroup of patients enrolled in INSPIRE (NCT01602211) and PCORI-SCP (NCT02200133) clinical trials. Eligibility criteria for inclusion include HCT patients who were ≥ 60 years at time of transplant performed in 2003-2014, survived ≥ 1 year post-transplant with no evidence of disease relapse or secondary cancers. Patients were eligible for inclusion irrespective of transplant type (autologous or allogeneic), diagnosis, donor source or conditioning regimen. Primary endpoint was distress level in older HCT survivors; secondary endpoints included CSI and HQOL outcomes. We collected baseline distress level as measured by Cancer and Treatment Distress (CTXD) score, HQOL (measured by SF-12 Mental and Physical Component Summaries (PCS/MCS) and CSI (measured by a 15-item CSI questionnaire). Sociodemographic, disease and transplant factors were extracted from medical databases. Nonparametric (Wilcoxon rank sum/Kruskal-Wallis) test was conducted for comparing 2 or 3 groups. Spearman correlation and univariate linear regression model were used to evaluate associations between CTXD/CSI and PCS/MCS. Bonferroni correlation was used to adjust for multiple pairwise comparisons within age group.Results: A total of 567 patients satisfied the eligibility criteria and were included in this analysis. Median age at time of HCT was 69 years with 57% male; two-thirds were autologous HCT recipients. Table 1 details patient characteristics. The median CTXD score for older HCT survivors was 0.7 (range 0-2.7, SD 0.6) indicating low/insignificant level of distress post-HCT. 20-30% of HCT survivors reported moderate distress when asked about concerns regarding relapse risk, loss of energy and functional decline. Type of transplant (auto vs allo), age group (<65 years, 65-70 years, ≥70 years), and time from HCT (≤2 years vs > 2 years) showed no apparent effect on reported distress level. CSI median score was 1.4 (range 0-2) which remains consistent with the score reported previously by the original trial including all age groups, indicating that older HCT survivors may have similar level of confidence in their survivorship information as their younger counterparts. Of note, close to 20% of the older HCT survivors reported poor CSI when asked about strategies for prevention and treatment of long-term effects of HCT and when asked about their confidence in availability of community resources to deal with long-term HCT complications. No statistically significant correlation was identified between CSI in older survivors and transplant type, time from HCT, or age group. HQOL outcomes indicated a median PCS of 48.2 (range 21.1 - 62.9) and a median MCS of 54.7 (range of 14.9 - 67.2). Interestingly, even though not reflected on the overall median CTXD and CSI scores for this cohort, a significant individual association between CTXD/CSI and PCS/MCS measures of HQOL was found (Figure 1). A subgroup analysis conducted on older alloHCT recipients confirmed the same findings of clinically insignificant distress level (mean CTXD ≤1.1) while having a similar level of CSI when compared to all age groups. Interestingly, time from HCT (≤2 years vs > 2 years) showed no significant effect on distress level reported by older alloHCT survivors, and cGVHD status did not correlate with CTXD or CSI scores nor with PCS/MCS in older alloHCT survivors.Conclusion: This is the largest study to date to investigate patient-reported distress, CSI and HQOL in older HCT survivors. Our data indicate that older HCT survivors have low levels of stress after HCT and had confidence in survivorship information in most aspects of their care. However, targeted interventions should focus on improving strategies for prevention, treatment and availability of community resources to deal with late effects of HCT; aspects reported as points of low CSI by older HCT survivors. [Display omitted] DisclosuresFarhadfar: Incyte: Consultancy. Shaw: Orca bio: Consultancy; mallinkrodt: Other: payments. Devine: Be the Match: Current Employment; Orca Bio: Consultancy, Research Funding; Johnsonand Johnson: Consultancy, Research Funding; Sanofi: Consultancy, Research Funding; Magenta Therapeutics: Current Employment, Research Funding; Tmunity: Current Employment, Research Funding; Vor Bio: Research Funding; Kiadis: Consultancy, Research Funding. Majhail: Anthem, Inc: Consultancy; Incyte Corporation: Consultancy. Wingard: Merck: Consultancy; AlloVir: Consultancy; Celgene: Consultancy; Shire: Consultancy; Janssen: Consultancy; Cidara Therapeutics: Consultancy.

Use of Endpoints in Phase III Randomized Controlled Trials for Acute Myeloid Leukemia over the Last 15 Years: A Systematic Review

Background:The use of objective endpoints is critical for the generalization and clinical implications of a study. Overall survival (OS) has traditionally been used as the gold standard for demonstrating the true clinical benefit of therapy or intervention. We systematically evaluated the proportion of different primary and secondary endpoints used in phase III randomized controlled trials (RCTs) for acute myeloid leukemia (AML), and their trends over time.Methods:Following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines, a comprehensive literature search was conducted on three databases (PubMed, Cochrane, and Clinical trials.gov) using MeSH terms and keywords for “Leukemia, Myeloid, Acute” AND “Randomized Controlled Trials as Topic” from January 2006 to March 2021. We screened 3290 articles. After excluding duplicates, reviews, and irrelevant articles, 241 articles reporting only phase III RCTs with primary and secondary endpoints on AML or its subtypes were included for our systematic review. Primary and secondary endpoints data were extracted from the included studies, and the frequency of various endpoints as well as their yearly frequencies were calculated. Disease-free survival (DFS) was used to represent similar outcomes including event-free survival (EFS), progression-free survival (PFS), leukemia-free survival (LFS), and relapse-free survival (RFS).Results:Our study included 241 phase III RCTs on AML. OS was the primary endpoint in 114 (47%) studies, while DFS and complete remission (CR) were reported as primary endpoints in 67 (28%) and 41 (17%) studies, respectively. Safety/adverse events, relapse rate (RR), graft versus host disease (GvHD) free survival, hematological improvement (HI), minimal residual disease (MRD), and non-relapse mortality (NRM) were used as primary endpoints in 10 (4%), 8 (3%), 5 (2%), 4 (2%), 3 (1%), and 2 (1%) studies respectively. Incidence of hospitalization, fungal disease, lung infiltrates, chronic GvHD, and allogeneic stem cell transplant each were used as primary endpoints in 1 (0.4%) study. (Table 1) Secondary endpoints followed a similar pattern as detailed in Table 2. OS (n=74, 31%), DFS (n=77, 32%) and CR (n=73, 30%) were commonly reported secondary endpoints. Safety/adverse effects, RR, mortality, quality of life (QoL), HI, MRD, incidence/length of hospitalization, and acute/chronic GvHD were used as secondary endpoints in 35 (14.5%), 15 (6%), 13 (5%), 9 (4%), 9 (4%), 7 (3%), 7 (3%), 5 (2%), and 4 (2%) studies, respectively. After 2013, increase in the use of OS (31% to 52%) and CR (15% to 17%) as a primary endpoint was noted, while the use of DFS as a primary endpoint decreased from 52% to 21%. (Table 1) For secondary endpoints, a higher trend in the use of DFS (19% to 35%) and OS (31% to 45%) and a lower trend in the use of CR (35% to 29%) was observed after 2013. (Table 2)Conclusion:Overall survival and disease-free survival were the most used primary and secondary endpoints in phase III randomized controlled trials for AML. There has been an increase in the use of clinically meaningful and objective endpoint of OS over the past 15 years in AML phase III RCTs. [Display omitted] DisclosuresYacoub: Cara: Current equity holder in publicly-traded company; Dynavex: Current equity holder in publicly-traded company; Agios: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; ACCELERON PHARMA: Membership on an entity's Board of Directors or advisory committees; CTI Biopharma: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Incyte: Consultancy, Honoraria, Speakers Bureau; Ardelyx: Current equity holder in publicly-traded company; Seattle Genetics: Honoraria, Speakers Bureau; Hylapharm: Current equity holder in publicly-traded company. Lin: AbbVie, Aptevo Therapeutics, Astellas Pharma, Bio-Path Holdings, Celgene, Celyad, Genentech-Roche, Gilead Sciences, Incyte, Jazz Pharmaceuticals, Novartis, Ono Pharmaceutical, Pfizer, Prescient Therapeutics, Seattle Genetics, Tolero, Trovagene: Research Funding. McGuirk: Pluristem Therapeutics: Research Funding; Novartis: Research Funding; Allovir: Consultancy, Honoraria, Research Funding; Novartis: Research Funding; Gamida Cell: Research Funding; EcoR1 Capital: Consultancy; Juno Therapeutics: Consultancy, Honoraria, Research Funding; Kite/ Gilead: Consultancy, Honoraria, Other: travel accommodations, expense, Kite a Gilead company, Research Funding, Speakers Bureau; Fresenius Biotech: Research Funding; Magenta Therapeutics: Consultancy, Honoraria, Research Funding; Bellicum Pharmaceuticals: Research Funding; Astelllas Pharma: Research Funding.

Intensification of Chemotherapy Using a Modified BFM Backbone for Children, Adolescents and Young Adults with T-Cell Acute Lymphoblastic Leukemia (T-ALL) and T-Cell Lymphoblastic Lymphoma (T-LL) Identifies Highly Chemorefractory Patients Who Benefit from Allogeneic Hematopoietic Stem Cell Transplantation

Background: The prognosis for patients (pts) with relapsed T-ALL and T-LL is dismal. The primary goal of T-ALL/T-LL treatment is to prevent relapse. In the phase 3 Children's Oncology Group (COG) clinical trial AALL1231 (NCT02112916), children, adolescents and young adults (age 1-30 years) with T-ALL and T-LL were treated with a modified augmented BFM (aBFM) backbone that used dexamethasone as the only corticosteroid and included two (rather than one) doses of pegaspargase during induction and delayed intensification. Pts were stratified as standard (SR), intermediate (IR), or very high risk (VHR), primarily based on disease response: morphology, minimal residual disease (MRD) performed by multiparameter flow cytometry at a central reference laboratory) at end of induction and consolidation (T-ALL), and radiographic response for T-LL. Pts were randomized 1:1 to receive/not receive bortezomib during induction and delayed intensification (1.3mg/m 2 x 4 doses per block).VHR T-ALL pts were defined as having day 29 M3 marrow (>25% blasts) or end of consolidation (EOC) MRD >0.1%. 10-15% of T-ALL pts were predicted to be VHR based on COG AALL0434. Pts with induction failure (M3 marrow by morphology) or EOC MRD >0.1% were expected to have 4-yr event-free survival (EFS) of ~66+/-16%. Following consolidation, VHR pts received 3 BFM-based intensification blocks in lieu of interim maintenance (IM). Detectable MRD following the intensification blocks was considered an event and these pts were removed from protocol therapy. VHR ALL pts who had undetectable MRD continued protocol therapy, received delayed intensification, an IM phase with Capizzi escalating methotrexate plus pegaspargase, and maintenance. A secondary aim of AALL1231 was to compare survival in VHR T-ALL pts with EOC MRD ≥ 0.1% but undetectable MRD after intensification of chemotherapy with those who continued to have detectable MRD and were eligible for other treatment strategies, including hematopoietic stem cell transplant (HSCT). This study also analyzed outcomes for pts with M3 marrow at the end of induction.Results: AALL1231 accrued 847 pts (824 eligible and evaluable) of 1400 anticipated from 2014 until early closure. The 3-year EFS for the bortezomib randomization for the SR and IR groups has been reported previously (Teachey, et. al ASH 2020). Because only 2 of 209 T-LL pts were VHR; this report focuses on the outcomes of the 5.2% (32/615) of T-ALL pts who were VHR. In total, 25 VHR T-ALL pts were EOC MRD >0.1%, and 18 of these had MRD sent at the end of HR intensification. Of the 8 pts who became MRD undetectable and continued protocol therapy, only 2 survived (3-year overall survival [OS] 25+15.3%). In contrast, 10 pts who had detectable MRD were taken off protocol and underwent HSCT. Of these 10, only one relapsed (3-year OS 90+12.7%). The 3-year OS for the 10 pts who were M3 at Day 29 was 60.0±17.0%. As there were not enough pts to assess the impact of EOC MRD on pts who were M3 at Day 29, we assessed the impact of EOC MRD on outcomes in M2 (5-25% blasts at Day 29; n = 24) and M3 pts, which defines induction failure in other cooperative groups. M2+M3 T-ALL who were EOC MRD <0.1% (n = 15) had 3-year OS of 86.7±10.0% vs 45.5±15.0% for those with EOC MRD >0.1% (n = 12) pts.Conclusions: T-ALL pts treated on AALL1231 who are EOC MRD ≥0.1% with undetectable MRD after 3 BFM-based intensification blocks had a very poor outcome when treated with standard cytotoxic chemotherapy. In contrast, while patient numbers are small, those pts that remained MRD-positive after 3 intensification blocks and underwent HSCT had an excellent outcome. These data not only impact the recommended treatment for T-ALL pts who are induction and consolidation failures, but also support the importance of the graft-versus-leukemia (GVL) effect in refractory T-ALL. DisclosuresHayashi: Magenta Therapeutics: Consultancy. August: Jazz: Membership on an entity's Board of Directors or advisory committees. Hermiston: Sobi: Consultancy; Novartis: Consultancy. Bollard: Cabeletta Bio: Membership on an entity's Board of Directors or advisory committees; Catamaran Bio and Mana Therapeutics: Other: member and cofounder; SOBI: Other: DSMB. Loh: MediSix therapeutics: Membership on an entity's Board of Directors or advisory committees. Raetz: Pfizer: Research Funding; Celgene: Other: DSMB member. Teachey: BEAM Therapeutics: Consultancy, Research Funding; NeoImmune Tech: Research Funding; Sobi: Consultancy; Janssen: Consultancy.

Outcomes with “Off the Shelf” Allogeneic CD19 Chimeric Antigen Receptor T Cell Therapy for Hematological Malignancies: A Systematic Review and Meta-Analysis

Background:Chimeric antigen receptor T cell (CAR-T) therapy is an adoptive T cell immunotherapy that employs the genetically modified T cell to attack the cancer cell. It is widely studied across various hematological and solid organ malignancies. Several autologous CD19 CAR-T cell therapy constructs are now approved for various B cell lymphomas, including aggressive B cell lymphomas, indolent follicular lymphoma and mantle cell lymphoma, and acute lymphoblastic leukemia (ALL). Autologous CD19 CAR-T cell therapy has unprecedented success in relapsed and refractory disease. Long time to manufacture (2-5 weeks) and manufacture failure are challenges associated with risk of interim death and deterioration of CAR-T candidates with rapidly progressive disease. T cell fitness of the autologous product in heavily pretreated patients is also potentially compromised. To overcome these shortcomings, universal “off the shelf” allogeneic CAR-T cell therapy constructs are being developed and studied. Donor sources include healthy donors and cord or induced pluripotent stem cells (iPSCs). These CAR-T constructs have additional gene modifications to mitigate the risk of rejection and graft versus host disease (GVHD). We performed a systematic review and meta-analysis to assess the safety and efficacy of allogeneic CD19 CAR-T cell therapy.Methods:Four databases (Web of Science/MEDLINE/PubMed, Embase, and Cochrane Registry of Controlled Trials) were searched for this systematic review and meta-analysis following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines using MeSH terms and keywords for “Receptors, Chimeric antigen” OR “Artificial-T-cell receptor” OR “immunotherapy, adoptive” OR “CD-19”. Our search produced 3506 articles and after removing duplicates, 2243 records were screened. After excluding reviews and irrelevant articles, we included 8 prospective trials of allogeneic CD-19 CAR-T cell therapy enrolling two or more than two patients from Jan 2013 to Nov 2020. We also searched ASH 2020 abstracts to include any additional trials. The methodological quality of the included studies was evaluated using NIH quality assessment tool. Inter-study variance was calculated using the Der Simonian-Laird Estimator. Proportions along with 95% confidence Interval (CI) were extracted to compute pooled analysis using the ‘meta’ package by Schwarzer et al. in the R programming language (version 4.16-2).Results:A total of 68 patients from 8 studies were evaluated. Median age was 22.5 (4.8-64) years. (Table 1) The median follow-up time was 10 (2-18) months with median number of prior therapies of 3.2 (2-11) as reported by 5 studies. Underlying diagnosis was acute lymphocytic lymphoma (n=49, 72%), chronic lymphocytic leukemia (n=6, 9%), and non-Hodgkin lymphoma (n=13, 19%). The pooled overall response rate (ORR) was 77% (95% CI 0.63-0.89, I 2 =22%, n=68) with a complete response (CR) of 75% (95% CI 0.57-0.90, I 2 =48%, n=65). The pooled incidence of cytokine release syndrome grade I/II and grade III/IV was 53% (95% CI 0.16-0.89, I 2 =89%, n=65) and 10% (95% CI 0.01-0.25, I 2 =50%, n=65) respectively. Neurotoxicity grade I/II was 12% (95%CI 0.01-0.30, I 2 =47%, p=0.09, n=47) and GVHD grade I/II was 8% (95%CI 0.01-0.19, I 2 =0%, p=0.57 n=53). None of the clinical trials reported the duration of response.Conclusion:“Off the shelf” universal CAR-T therapy is early in development. Our available data suggest that allogeneic CD19 CAR-T constructs offer high ORR and CR rates with acceptable safety profiles. GVHD was mainly low grade (grade I-II). Given these findings, allogeneic CAR-T cell therapy is an attractive option to improve timely access compared to available autologous therapy. Extensive preclinical research to develop novel constructs and several phase I/II clinical trials are ongoing to shape the future of “off the shelf” CAR-T cell therapy. [Display omitted] DisclosuresHoffmann: Pharmcyclics: Consultancy, Honoraria; TG Therapeutics: Consultancy, Honoraria; Novartis: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; celgene: Consultancy, Honoraria. Abhyankar: Incyte/Therakos: Consultancy, Research Funding, Speakers Bureau. McGuirk: Fresenius Biotech: Research Funding; Gamida Cell: Research Funding; Pluristem Therapeutics: Research Funding; EcoR1 Capital: Consultancy; Novartis: Research Funding; Astelllas Pharma: Research Funding; Kite/ Gilead: Consultancy, Honoraria, Other: travel accommodations, expense, Kite a Gilead company, Research Funding, Speakers Bureau; Juno Therapeutics: Consultancy, Honoraria, Research Funding; Magenta Therapeutics: Consultancy, Honoraria, Research Funding; Novartis: Research Funding; Bellicum Pharmaceuticals: Research Funding; Allovir: Consultancy, Honoraria, Research Funding.

Brexucabtagene Autoleucel for Relapsed/Refractory Mantle Cell Lymphoma: Real World Experience from the US Lymphoma CAR T Consortium

Brexucabtagene Autoleucel for Relapsed/Refractory Mantle Cell Lymphoma: Real World Experience from the US Lymphoma CAR T Consortium

Selinexor-Based Regimens in Patients with Multiple Myeloma after Prior Anti-B-Cell Maturation Antigen Treatment

Selinexor-Based Regimens in Patients with Multiple Myeloma after Prior Anti-B-Cell Maturation Antigen Treatment

Outcomes of Aggressive B Cell Lymphoma Patients with No Evidence of Measurable Disease at the Time of CD19 Chimeric Antigen Receptor T Cell Therapy: The Experience from the CAR T Cell Consortium

Outcomes of Aggressive B Cell Lymphoma Patients with No Evidence of Measurable Disease at the Time of CD19 Chimeric Antigen Receptor T Cell Therapy: The Experience from the CAR T Cell Consortium

Major ABO Incompatibility Significantly Influences the Survival and Outcomes after Allogeneic Hematopoietic Cell Transplantation in Leukemia - CIBMTR Analysis

Background: Allogeneic hematopoietic cell transplantation (allo-HCT) is a potentially curative treatment for acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL). While many factors influence the outcomes of allo-HCT in these leukemias, the independent impact of ABO mismatching between the patient and donor remains unclear.Methods: Using the CIBMTR database, we identified adults aged ≥18 years with AML or ALL who underwent allo-HCT from HLA-matched sibling donor (MSD) or 8/8 matched unrelated donor (MUD) between 2008-2018. We excluded patients who underwent transplant from a mismatched donor source or who received an ex-vivo T-cell depleted graft. Patients were stratified into cohorts based on ABO status (match, minor mismatch, major mismatch, bidirectional mismatch). Outcomes such as overall survival (OS), disease free survival (DFS), non-relapse mortality (NRM), relapse, incidence of acute graft versus host disease (GVHD), chronic GVHD, neutrophil engraftment, platelet engraftment and graft failure were evaluated. Survival analysis was done using Kaplan-Meier method and significant predictors were evaluated using Cox-proportional hazard regression method. Multivariate regression model included main effect (ABO status) and covariates (patient age, gender match, disease type, disease status, HCT-CI, Karnofsky performance status, donor type, conditioning intensity/use of TBI, stem cell source, GVHD prophylaxis, ATG/alemtuzumab use, transplant year).Results: Of 4946 patients who met the study criteria, 2741 patients (55.4%) were ABO matched, 1030 patients (20.8%) had minor ABO mismatch, 899 patients (18.1%) had major ABO mismatch and 276 patients (5.6%) had bidirectional ABO mismatch. Graft manipulation for ABO incompatibility was performed in 900 patients (minor ABO mismatch=532; major ABO mismatch=226; bidirectional mismatch=142), however, the information on individual graft manipulation techniques was limited. In multivariable analysis (table 1), major ABO mismatch significantly affected the OS, platelet engraftment and primary graft failure. Compared to ABO matched allo-HCT, major ABO mismatched allo-HCT was associated with worse OS (major mismatch - HR 1.16, 95% CI 1.05-1.29; p=0.005), inferior platelet engraftment (HR 0.83, 95% CI 0.77-0.90; p=<0.001), and higher risk of primary graft failure [4.5% (major mismatch) vs. 3.2% (ABO matched) - HR 1.60, 95% CI 1.12-2.30, p=0.01]. There was a significant interaction between the ABO status and graft type (peripheral blood vs. bone marrow) for the acute GVHD grades 2-4 model, and they are presented separately (table 1). Bidirectional ABO mismatch also significantly impacted the outcomes such as acute GVHD grades 2-4 (in bone marrow stem cell subgroup, HR 0.50, 95%CI 0.27-0.93, p=0.02) in addition to a trend towards inferior survival and NRM (p-value not significant). Other outcomes such as relapse (p=0.41), acute GVHD grades 3-4 (p=0.13), and chronic GVHD (p=0.30) were not significantly influenced by the ABO status.Conclusions: Our study demonstrates that pre-transplant ABO status is an independent predictor of survival and other post-transplant outcomes in a large cohort of patients with AML and ALL undergoing allo-HCT in the recent era. This demonstrates the importance of considering ABO status in the donor selection algorithms and potential strategies to mitigate its adverse impact. Due to the limited information available on graft manipulation strategies, the impact of graft manipulation techniques on the outcomes could not be evaluated and needs to be investigated in future studies. [Display omitted] DisclosuresGuru Murthy: Techspert: Consultancy; Guidepoint: Consultancy; Cancerexpertnow: Honoraria; Qessential: Consultancy; TG therapeutics: Other: Advisory board; Cardinal Health Inc.: Honoraria. Devine: Magenta Therapeutics: Current Employment, Research Funding; Tmunity: Current Employment, Research Funding; Sanofi: Consultancy, Research Funding; Johnsonand Johnson: Consultancy, Research Funding; Orca Bio: Consultancy, Research Funding; Be the Match: Current Employment; Vor Bio: Research Funding; Kiadis: Consultancy, Research Funding. Farhadfar: Incyte: Consultancy. Sharma: Vertex Pharmaceuticals/CRISPR Therapeutics: Other: Salary support paid to institution; Novartis: Other: Salary support paid to institution; Spotlight Therapeutics: Consultancy; Medexus Inc: Consultancy; CRISPR Therapeutics: Other, Research Funding; Vindico Medical Education: Honoraria. Stefanski: Novartis: Honoraria. Pulsipher: Equillium: Membership on an entity's Board of Directors or advisory committees; Adaptive: Research Funding; Jasper Therapeutics: Honoraria. Shaw: mallinkrodt: Other: payments; Orca bio: Consultancy.

Outcomes with Natural Killer Cells Infusion after Allogeneic Hematopoietic Stem Cell Transplantation: A Systematic Review and Meta-Analysis

Background:Natural killer cells (NK) are known to be the first cells that recover after allogeneic hematopoietic stem cell transplant (HCT). NK cells have anti-leukemic and anti-viral properties and are also implicated in the graft versus leukemia (GVL) effect without causing graft versus host disease (GVHD). There is emerging evidence supporting the use of NK cells post-transplant as adoptive immunotherapy to prevent or treat the relapse of hematologic malignancies. Here, we present a systematic review and meta-analysis aimed to investigate the outcomes with NK cells infusion after HCT.Methods:A detailed literature search was conducted for the systematic review and meta-analysis according to the guidelines mentioned in the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA). Population, intervention, comparison, and outcome (PICO) table was developed and three electronic databases (PubMed, Cochrane Library, and ClinicalTrials.gov) were searched through January 2021 using MeSH terms and keywords for “hematologic malignancy and natural killer cells” and “hematopoietic stem cell transplantation and natural killer cells”. No filters or publication time limits were applied for the search. A total of 988 records were identified through database searching. After excluding duplicates, review, and non-relevant articles, we selected 9 studies that reported outcomes with NK cells infusion after HCT. Quality evaluation was done using the NIH quality assessment tool and Inter-study variance was calculated using the Der Simonian-Laird Estimator. Pooled analysis was done using the ‘meta’ package (Schwarzer et al, R programming language) and proportions with 95% confidence intervals (CI) were computed.Results:We identified 9 studies with a total of 149 participants. Out of these, 53 patients were from 4 studies using NK cells for the treatment of relapsed disease after HCT (therapeutic studies) and 96 patients were from 5 studies using NK cells to prevent relapse after HCT (pre-emptive studies).Therapeutic use of NK cells for relapsed disease after HCT: A total of 53 patients from 4 studies were evaluated. The median age of patients was 44.5 (1.9-69) years, and 40% patients were male. The median follow-up was 20 (1-69) months. Overall survival (OS) was reported by two studies at 2 years and was 36.3% and 55%. The pooled complete response (CR) was 18% (95% CI 0.06-0.33, I 2 =0%, n=37) and overall response rate (ORR) was 45% (95% CI 0.20-0.71, I 2 =71%, n=53). The pooled relapse rate was 65% (95% CI 0.32-0.92, I 2 =75%, n=42). The pooled incidence of acute GVHD and chronic GVHD was 15% (95% CI 0.03-0.31, I 2 =41%, n=53) and 8% (95% CI 0.01-0.18, I 2 =0%, n=53) respectively.Pre-emptive use of NK cells to prevent relapse after HCT: A total of 96 patients from 5 studies were evaluated. The median age of patients was 33.5 (2-75) years, and 48% patients were males. The median follow-up was 23.1 (8-81.6) months. The median OS was 1 (0.63-5) years. The pooled CR was 45% (95% CI 0.21-0.70, I 2 =76%, n=83) and ORR was 89% (95% CI 0.57-1.00, I 2 =77%, n=42). The pooled relapse rate was 35% (95% CI 0.20-0.52, I 2 =55%, n=96). The pooled incidence of acute GVHD and chronic GVHD was 30% (95%CI 0.14-0.48, I 2 =61%, n=96) and 8% (95%CI 0.00-0.24, I 2 =73%, n=96) respectively.Conclusion:Infusion of NK cells after HCT to prevent relapsed disease results in favorable outcomes with an acceptable toxicity profile. Optimal use of NK cells infusions after HCT is in a pre-emptive fashion to prevent relapsed disease and the efficacy of NK cells infusions after HCT in the setting of overt hematologic relapse is modest. Our findings suggest the need for large prospective clinical trials to establish the potential benefit of NK cells infusion after HCT to prevent relapse of hematologic malignancies without increased non-relapse mortality. [Display omitted] DisclosuresAbhyankar: Incyte/Therakos: Consultancy, Research Funding, Speakers Bureau. McGuirk: Bellicum Pharmaceuticals: Research Funding; Gamida Cell: Research Funding; Novartis: Research Funding; Novartis: Research Funding; EcoR1 Capital: Consultancy; Fresenius Biotech: Research Funding; Astelllas Pharma: Research Funding; Magenta Therapeutics: Consultancy, Honoraria, Research Funding; Juno Therapeutics: Consultancy, Honoraria, Research Funding; Allovir: Consultancy, Honoraria, Research Funding; Pluristem Therapeutics: Research Funding; Kite/ Gilead: Consultancy, Honoraria, Other: travel accommodations, expense, Kite a Gilead company, Research Funding, Speakers Bureau.

A Phase II Randomized, Double-Blind, Placebo-Controlled, Multicenter Trial to Evaluate the Efficacy of Cmvpepvax for Preventing CMV Reactivation/Disease after Matched Related/Unrelated Donor Hematopoietic Cell Transplant

A Phase II Randomized, Double-Blind, Placebo-Controlled, Multicenter Trial to Evaluate the Efficacy of Cmvpepvax for Preventing CMV Reactivation/Disease after Matched Related/Unrelated Donor Hematopoietic Cell Transplant

Corticosteroid Treatment Impairs Epithelial Regeneration, Limiting Intestinal Recovery in Experimental Graft Vs Host Disease

Corticosteroids (CS) represent first-line treatment for gastrointestinal graft vs host disease (GI GVHD), and CS failure is associated with severe morbidity and mortality. While the immune system is the intended target of CS treatment, the glucocorticoid receptor (GR) is widely expressed, and there is limited understanding of the direct effects of CS on intestinal epithelium following immune-mediated damage.We thus investigated how CS treatment could impact intestinal homeostasis and regeneration following experimental bone marrow transplantation (BMT). In healthy C57BL/6 (B6) mice, in vivo administration of clinically relevant CS doses reduced Ki67 + epithelial proliferation in the ileum (p<0.001; Fig. 1A) without inducing crypt loss or overt pathology. Given the numerous potential effects of systemic administration, we next utilized ex vivo small intestine (SI) organoid cultures to explore direct effects of CS on murine and human epithelium. Assessing a variety of clinically relevant CS agents, we found that methylprednisolone (MP), dexamethasone, and budesonide all decreased murine organoid size without affecting organoid number (p<0.05; only MP shown; Fig. 1B). We also identified that GR-deficient (Nr3c1 -/-) organoids were significantly resistant to growth inhibition by MP (p<0.05), indicating a direct GR-mediated effect of CS on intestinal epithelium leading to reduced growth. Furthermore, MP treatment significantly decreased the size of human organoids generated from primary duodenal tissue without affecting organoid numbers (p<0.001). Organoid culture models were thus highly consistent with the findings from in vivo CS treatment.We next investigated CS effects on epithelial cells during immune-mediated damage. Pre-treatment of mice with 2 mg/kg MP x 7 days in vivo prior to crypt harvest and organoid culture increased organoid sensitivity to T-cell-mediating killing ex vivo (p<0.05). Additionally, modeling steroid-refractory disease, GR-deficient (Nr3c1 -/-) T cells mediated greater killing of SI organoids if co-cultures were performed in the presence of MP (p<0.01). We next investigated CS-mediated effects on epithelial damage in vivo, treating with MP x 7 days starting on day 7 after MHC-mismatched BMT, once GVHD had already been established. Vehicle-treated mice demonstrated GVHD-associated T cell activation, lymphocytic tissue infiltration, and ileal crypt loss compared to BM only controls, as well as increased height and Ki67 + cell frequency in residual crypts reflecting damage-induced regeneration (p<0.001, Fig. 2A-C). Modeling steroid-refractory disease, systemic CS treatment failed to reduce T cell activation or lymphocytic infiltration. However, MP treatment appeared to attenuate regeneration and worsen intestinal pathology, as evidenced by exacerbated crypt loss in association with reduced crypt height and Ki67 + cell frequency (p<0.01; Fig. 2A-C).Despite potential harmful side effects, CS are frequently necessary for treatment of clinical GVHD. We hypothesized that CS-mediated epithelial suppression could be mitigated by concurrent administration of agents capable of inducing tissue regeneration. Interleukin-(IL)-22 has been shown to promote epithelial proliferation and recovery following GI damage. We thus investigated whether IL-22 treatment could counterbalance CS-induced impairment of epithelial recovery in GVHD. Indeed, addition of IL-22 to MP-treated organoids promoted organoid growth without inducing toxicity/organoid loss in both murine and human SI organoid cultures (p<0.001; Fig. 3A and B). Moreover, IL-22 administration in vivo with F-652, a clinical grade recombinant human IL-22 dimer, reversed MP-mediated crypt loss and reduction of crypt height and Ki67 + cell frequency in mice with GVHD (p<0.001; Fig. 3C).In summary, these findings indicate that CS treatment can suppress epithelial proliferation in the intestines and exacerbate GI damage if it fails to control the pathologic immune response. However, deleterious CS side effects can be counterbalanced by promotion of epithelial regeneration, providing rationale for combining immunosuppression with tissue-supporting therapeutics such as IL-22 to optimize intestinal recovery in GVHD. [Display omitted] DisclosuresBlazar: Magenta Therapeutics: Membership on an entity's Board of Directors or advisory committees; BlueRock Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Rheos Medicines: Research Funding; Equilibre Pharmaceuticals Corp: Research Funding; Carisma Therapeutics, Inc: Research Funding; Tmunity Therapeutics: Other: Co-founder. Hanash: Evive Biotech: Ended employment in the past 24 months.

Non-Genotoxic Conditioning for Hematopoietic Stem Cell Transplant Using a Human Antibody Drug Conjugate Targeting C-KIT

For patients undergoing hematopoietic stem cell transplantation (HSCT), conditioning remains a primary source of transplant related morbidity and mortality and limits the broader application of this life-saving therapy. Current conditioning regimens, including total body irradiation and high dose chemotherapy, cause acute toxicity, cytokine storm, increased graft-versus-host disease, and organ damage. In addition, these regimens are also associated with the development of secondary malignancies, autoimmunity, and infertility.To address this significant unmet medical need, we have developed a conditioning regimen using an antibody drug conjugate (ADC) targeting C-KIT (CD117) to specifically deplete host hematopoietic stem cells. CD117 is highly expressed on hematopoietic stem and progenitor cells (HSPCs) and binding to its ligand, stem cell factor, promotes hematopoiesis, self-renewal, and rapid internalization of the receptor. The rapid internalization and selective expression of CD117 on HSPCs make it an ideal target for an ADC-based approach to depleting HSPCs, while limiting systemic toxicity. In addition, CD117 is frequently overexpressed on malignant cells in patients with acute myelogenous leukemia. Thus, an ADC targeting CD117 may provide an opportunity for disease control prior to or concomitant with an HSCT. Previous studies have demonstrated that an antagonistic antibody against CD117 lead to high levels of HSPC depletion and donor engraftment in immunocompromised mice, but failed to facilitate this effect in immunocompetent hosts. To overcome the engraftment barrier, additional studies were conducted with an anti-CD117 antibody conjugated to the ribosome inactivating toxin, saporin, which allowed for robust HSPC depletion and high levels of congenic donor chimerism in immunocompetent mice (Czechowicz et.al., Blood 2016, 128:493).To advance this technology toward the clinic, we have developed a fully human anti-CD117 antibody conjugated to a small molecule toxin capable of depleting proliferating and quiescent cells (CD117-ADC), that demonstrated greater than 90% killing of the leukemia cell line Kasumi-1, and was equally effective at killing primary human CD34+ bone marrow cells during in vitro culture. Humanized NSG mice treated with CD117-ADC had greater than 90% depletion of human HSPCs in the bone marrow, 21 days following a single administration of the ADC. The specificity of CD117-ADC for HSPCs was confirmed by the presence of stable peripheral human lymphocyte populations, and absence of human myeloid cells; indicating a lack of stem and progenitor cells capable of replenishing these short-lived cells. In addition to the ability of CD117-ADC to deplete HSPCs in humanized mice, preliminary data suggests that CD117-ADC is also effective at reducing tumor burden in mice challenged with CD117 expressing tumor cells.Eliminating HSPCs from the stem cell niche with a targeted ADC has the promise to enable the engraftment of donor HSCs, while preventing the systemic toxicity associated with irradiation and chemotherapy. We have demonstrated that an ADC targeting CD117 is capable of depleting human HSPCs in vitro and in vivo and has the potential to reduce tumor burden in mice. Ultimately, this novel approach for safer conditioning prior to HSCT could greatly increase the number of patients eligible for transplant and significantly reduce the damaging side effects associated with current protocols and may provide effective non-genotoxic conditioning for all patients suffering from malignant or non-malignant diseases who require a HSCT. [Display omitted] DisclosuresHartigan:Magenta Therapeutics: Employment, Equity Ownership, Patents & Royalties. Pearse:Magenta Therapeutics: Employment, Equity Ownership. McDonough:Magenta Therapeutics: Employment, Equity Ownership. Proctor:Magenta Therapeutics: Employment, Equity Ownership. Adams:Magenta Therapeutics: Employment, Equity Ownership. McShea:Magenta Therapeutics: Employment, Equity Ownership. Hoban:Magenta Therapeutics: Employment, Equity Ownership. Panwar:Magenta Therapeutics: Employment, Equity Ownership. Hyzy:Magenta Therapeutics: Employment, Equity Ownership. Goncalves:Magenta Therapeutics: Employment, Equity Ownership. Palchaudhuri:Magenta Therapeutics: Employment, Equity Ownership. Boitano:Magenta Therapeutics: Employment, Equity Ownership, Patents & Royalties; Magenta Therapeutics: Employment, Equity Ownership, Patents & Royalties. Cooke:Magenta Therapeutics: Employment, Equity Ownership, Patents & Royalties.

Aryl Hydrocarbon Receptor Antagonists Expand Adult Hematopoietic Stem Cells from Mobilized Peripheral Blood and Bone Marrow and Increase the Dose of CRISPR/Cas9 Gene-Edited NSG-Repopulating Cells

Background. Gene modified hematopoietic stem cell (HSC) transplant is emerging as a promising approach to treat a variety of inherited genetic diseases, but has been hampered by the inability to generate a sufficient dose of gene modified HSCs and the requirement for toxic myeloablative conditioning protocols to achieve engraftment. Ex vivo expansion of gene-modified HSCs is a promising approach to circumvent these challenges as high doses of gene modified cells have the potential to achieve robust engraftment and reduce the requirement for myeloablative conditioning. Several small molecule approaches (SR1, UM171, and HDAC inhibitors) have been reported to expand cord blood (CB) derived HSCs ex vivo but the ability of these agents to expand gene modified adult HSCs is not known. Experiments comparing these approaches for CB expansion has been reported (see Goncalves et al “Phenotype Does Not Always Equal Function: HDAC inhibitors and UM171, but not SR1, Lead to Rapid Upregulation of CD90 on Non-Engrafting CD34+CD90-negative Human Cells”) and found that aryl hydrocarbon receptor (AHR) antagonism is the most effective at expanding NSG-engrafting cells. In a clinical trial of patients receiving MGTA-456, an AHR antagonist-expanded CB CD34+ cell product, engraftment occurred at a median of 14.5 days (r 7-23), which was significantly better than identically-treated historical controls (n=151, p<0.01) (Wagner et al, Cell Stem Cell, 2016). Because of the encouraging clinical results in CB, we identified novel AHR antagonists and evaluated the ability of SR1 and the proprietary AHR antagonists to increase the number of gene modified NSG engrafting cells manufactured from mobilized peripheral blood (mPB) and bone marrow (BM) CD34+ cells.Methods. Novel, small molecules, SR1, HDAC inhibitors, and UM171 were evaluated in the presence of cytokines to expand primary human CD34+ cells ex vivo . Cell number and immunophenotype were assessed by flow cytometry, and HSC function was evaluated by cell and molecular assays in vitro . The expanded cells were transplanted into sub-lethally irradiated NSG mice to evaluate engraftment potential in vivo . For editing studies, mPB and BM CD34+ cells were electroporated with CRISPR/Cas9 RNPs targeting the beta-2 microglobulin (B2M) cell surface protein. Editing rates were evaluated by flow cytometry based on loss of protein expression and TIDE analysis. Edited cells were expanded in the presence of AHR antagonist or vehicle and transplanted into NSG mice. Engraftment and editing rates were evaluated by flow cytometry of the peripheral blood and bone marrow.Results. Based on our results, cultures expanded with an AHR antagonist showed the largest improvement in NSG engraftment levels compared to unmanipulated cells. Culture of CD34+ cells with SR1 or a novel AHR antagonist led to a 6-fold increase in CD34+ number and a significant increase in engraftment in NSG mice relative to vehicle-cultured CB derived CD34+ cells. Our proprietary compound displayed complete AHR antagonism in the dioxin response element luciferase reporter assay and was a more potent antagonist compared to SR1 (a 12-fold increase in potency). To evaluate the ability of the AHR antagonist compound to effectively expand gene edited cells, mPB and BM derived CD34+ cells were treated with either vehicle or AHR antagonist and the following day edited with CRISPR/Cas9 RNPs targeting B2M. Following 7 days of expansion, the vehicle or AHR antagonist-treated cells showed 87% and 84% loss of the target protein, respectively. The expanded culture contained 3.4-fold more CD34+CD90+ cells than the vehicle-treated cells. Upon transplant, mice receiving the expanded cells showed greater than 2-fold increase in engraftment compared to those receiving vehicle-treated cells. Importantly, the editing rates of the expanded cells are maintained in vivo with an average of >75% of the human cells in the periphery of the mice showing loss of target protein.Conclusions. We have demonstrated that AHR antagonism is an effective strategy to expand functional HSCs and that novel small molecules inhibiting AHR can expand gene modified HSCs from mPB and BM. Studies are ongoing to confirm expansion with our proprietary compound of HSCs transduced with lentiviral vectors also leads to improved engraftment. This approach is a promising strategy to improve autologous gene therapy and gene editing via ex vivo HSC expansion. DisclosuresHoban:Magenta Therapeutics: Employment, Equity Ownership. Goncalves:Magenta Therapeutics: Employment, Equity Ownership. Proctor:Magenta Therapeutics: Employment, Equity Ownership. Adams:Magenta Therapeutics: Employment, Equity Ownership. Hyzy:Magenta Therapeutics: Employment, Equity Ownership. George:Magenta Therapeutics: Employment. Boitano:Magenta Therapeutics: Employment, Equity Ownership, Patents & Royalties. Cooke:Magenta Therapeutics: Employment, Equity Ownership, Patents & Royalties.

The Combination of GROβ and AMD3100 Leads to Rapid and Robust Mobilization of Hematopoietic Stem Cells in Nonhuman Primates

▪Introduction: Mobilized peripheral blood grafts are currently the predominant source of hematopoietic stem and progenitor cells (HSPC) for both autologous and allogeneic transplantation. The most common clinical hematopoietic stem cell mobilization protocol is five days of Filgrastim (G-CSF). This regimen requires daily injections, has been associated with bone pain and often results in unpredictably low yields. A rapid mobilization method that ideally only required a single treatment and had robust and predictable kinetics would be a significant improvement over the current standard of care. In mice, a unique CXCR2 agonist, GROβ, induces rapid mobilization of stem and progenitor cells 15 minutes after a single injection. When co-administered with plerixafor (AMD3100), an inhibitor of CXCR4, a synergistic increase in mobilization results, with a graft enriched in highly engraftable hematopoietic stem cells (Hoggatt et al., Blood 2016 128:368). Here, we present data demonstrating that combination treatment with GROβ and AMD3100 synergistically mobilizes CD34+ cells and colony forming units (CFU) in nonhuman primates (NHP).Methods: Cynomolgus macaques were injected with G-CSF (10 µg/kg/day, s.c. for four days), AMD3100 (1 mg/kg, s.c. once) or GROβ (various doses and routes) alone and in combination with AMD3100. Blood was collected at various times post treatment and analyzed by multicolor flow cytometry to quantitate HSPC numbers. Additional aliquots of mobilized blood were plated in methylcellulose and CFU were enumerated seven days later.Results: We tested the effect of GROβ alone or in combination with AMD3100 in Cynomolgus monkeys. As published previously, administration of G-CSF, AMD3100 or G-CSF+AMD3100 induced significant mobilization of hematopoietic stem and progenitor cells. In comparison, a single injection each of GROβ+AMD3100 yielded 4-fold more CD34+ cells compared to four days of G-CSF (p < 0.01). While the combination of G-CSF+AMD3100 mobilized significantly more CD34+ cells compared to GROβ+AMD3100 (p < 0.0001), the numbers of CD34+ CD90+ CD45RA- cells, representing the most primitive of hematopoietic stem and progenitor cells, were equivalent between treatment groups. Similarly, GROβ+AMD3100 treatment elicited 7-fold more CFU compared to animals treated with G-CSF (p < 0.01), 3.5-fold more CFU compared to AMD3100 (p < 0.01) and equivalent CFU compared to G-CSF+AMD3100. Importantly, the frequency of CFU among the CD34+ cells was significantly greater with GROβ+AMD3100 (1 in 4) compared to G-CSF (1 in 10) or G-CSF+AMD3100 (1 in 25). In contrast to the increased CD34+ numbers and CFU, white blood cell (WBC) and neutrophil counts were significantly lower with GROβ+AMD3100 compared to AMD3100 alone or G-CSF+AMD3100.Conclusions: We describe a rapid mobilization method that within four hours of a single treatment results in robust hematopoietic mobilization in nonhuman primates. The GROβ+AMD3100 regimen enriches for primitive CD34+ CD90+ CD45RA- stem and progenitor cells with increased colony forming capacity compared to CD34+ cells mobilized with G-CSF+AMD3100, suggesting a significant graft quality difference with the new regimen. The ability to rapidly mobilize primitive HSC with increased CFU frequency may allow effective single day mobilization of HPSCs for patients requiring a HSCT and be especially useful for HSC based gene therapy and gene editing protocols where HSPC grafts enriched for primitive HSC may reduce manufacturing costs and ensure durability of the gene modified HSC. The ability to achieve increased HSPC numbers without dramatically increasing WBC and neutrophils may be especially advantageous in patient populations where G-CSF mobilization is not well tolerated such as Sickle Cell Disease, or where G-CSF leads to increased disease activity such as in autologous transplant for Multiple Sclerosis. A single treatment that results in robust mobilization that is equivalent to G-CSF may allow for a one-day collection method of donor stem cells, and these findings in nonhuman primates support clinical exploration. DisclosuresFalahee:Magenta Therapeutics: Employment, Equity Ownership. Goncalves:Magenta Therapeutics: Employment, Equity Ownership. Hyzy:Magenta Therapeutics: Employment, Equity Ownership. Proctor:Magenta Therapeutics: Employment, Equity Ownership. Hoggatt:Magenta Therapeutics: Consultancy, Equity Ownership, Patents & Royalties. Morrow:Magenta Therapeutics: Employment, Equity Ownership. Cooke:Magenta Therapeutics: Employment, Equity Ownership, Patents & Royalties.

Reduced Intensity Conditioning for Allogeneic Transplantation: Modified Fludarabine Dose Plus Cyclophosphamide/Total Body Irradiation Yields Promising Outcomes

Reduced intensity conditioning (RIC) extends the curative potential of allogeneic hematopoietic cell transplantation (HCT) to patients with hematologic malignancies unsuitable for myeloablative conditioning. We prospectively studied a RIC HCT approach for patients with hematologic malignancies and sibling or unrelated donors (URD) from 2001-2016. Patients received cyclophosphamide (Cy) 50mg/kg/day IV day -6, fludarabine (Flu) 40mg/m2/d IV days -6 to -2 and TBI 200cGy on day -1 +/- anti-thymocyte globulin (ATG) on days -6 to -4 for those without prior autografting or recent multidrug chemotherapy. After identifying potential increased non-relapse mortality from excess fludarabine metabolite (F-ara-A) exposure we reduced the fludarabine dosing to 30 mg/m2/d IV days -6 to -2 in late 2009.The 292 patients (median age 58: range 19-75); median follow-up 8 years (IQR range 4-12) included 127 with acute myelogenous leukemia (AML) or myelodysplastic syndrome (MDS), 40 aggressive non-Hodgkin lymphoma (NHL), 11 indolent NHL, 21 Hodgkin Lymphoma (HL), 26 multiple myeloma, 14 chronic myeloid leukemia (CML), 23 chronic lymphocytic leukemia (CLL), 17 acute lymphocytic leukemia (ALL), 13 myeloproliferative neoplasms (MPN). Five year overall survival (OS) was 73% (95% CL, 37-90%) for patients with indolent NHL, 53% (95% CL, 36-67%) for aggressive NHL, 55% (95% CL, 31-74%) for HL, 39% (95% CL, 30-48%) for AML/MDS, 32% (95% CL, 15-50%) for myeloma, 50% (95% CL, 23-72%) for CML, 45% (95% CL, 24-46%) for CLL, 15% (95% CL, 2-39%) for MPN and 34% (95% CL, 12-59%) for those with ALL. By donor source, 5 year OS was 46% (95% CL, 40-53%), 25% (95% CL, 6-50%), 38% (95% CL, 22-54%), and 11% (95% CL, 1-35%) using matched sibling donors (n=225), mismatched (MM) sibling PBSC (n=12), matched marrow unrelated donor (URD) (n=37), and matched peripheral blood URD (n=18) (p<0.01) (Figure 1). Fludarabine dosing (30 vs. 40 mg/m2/day x 5) had no significant influence on OS (45 vs. 40%, p=0.42) or 2 year NRM (25% vs. 26%, p=0.86). NRM (overall 26%; 95% CI 21-31%) was significantly worse with MM sibling or URD (either BM or PBSC) compared to matched sibling BM/PBSC. Relapse at 5 years was significantly worse in patients with myeloma (76%) and Hodgkins (53%), intermediate in AML/MDS (37%), but lowest in aggressive (25%) and particularly indolent NHL (0%).These results suggest that: 1) this Cy/Flu/TBI RIC conditioning was well tolerated by an older population; 2) indolent and aggressive NHLs responded best to RIC conditioning highlighting the importance of the graft versus lymphoma (GVL) effect; and 3) reduction in fludarabine dosing did not compromise disease control or survival but did not appear to diminish NRM. Diagnosis, donor source, and HCT-CI remain the dominant factors influencing outcomes. Targeted disease treatments or maintenance therapy to limit relapse might be the best approach to improve overall survival. [Display omitted] DisclosuresBrunstein:Novartis: Research Funding; Magenta Therapeutics: Research Funding. MacMillan:Magenta Therapeutics: Research Funding.

Cellular Stressors Contribute to the Expansion of Multiple Hematopoietic Clones of Varying Leukemic Potential

Hematopoietic stem cells (HSCs) are genetically heterogeneous with each HSC possessing its own unique mutations. Some mutations confer a fitness advantage, allowing the HSCs harboring them to clonally expand. The role of different cellular stressors on this expansion remains unknown, as does the nature of the expanding hematopoietic populations.To address these issues, we designed an error-corrected sequencing assay able to detect somatic variants in 46 genes associated with clonal hematopoiesis or AML/MDS at a variant allele frequency (VAF) of 0.1%. We then characterized clonal hematopoiesis after two distinct types of stress: cytotoxic therapy and hematopoietic transplantation.We first assessed mobilized pheresis samples from three groups: lymphoma or myeloma patients exposed to cytotoxic therapy (n=81), myeloma patients with no such exposure (n=38), and normal donors (n=19). Prior cytotoxic therapy was associated with a significantly increased incidence of clonal hematopoiesis, which was observed in 66/81 (81.5%) of these patients. In fact, most patients with clonal hematopoiesis after cytotoxic therapy had two or more variants detected (median: 3; range: 1-11), suggesting an expansion of multiple clones. Of the 46 genes assessed, we identified six commonly associated with DNA damage response (TP53, PPM1D, ATM, BRCC3, SRCAP, and RAD21) . Variants in these genes were seen in 36/81 (44%) of patients following cytotoxic therapy compared to only 9/57 (16%; P<0.001) of individuals lacking such exposure. In contrast, variants in the other 40 genes were not significantly increased after cytotoxic therapy. These data suggest that cytotoxic therapy provides a fitness advantage to HSCs harboring mutations in certain genes involved in the DNA damage response.To investigate the nature of expanded mutant clones, we sorted pheresis samples with DNMT3A (n=2), TP53 (n=3), or PPM1D (n=3) variants into myeloid and lymphoid populations. In general, variants were detected in both myeloid and lymphoid lineages, suggesting that they arose in HSCs. However, in most cases with TP53 or PPM1D mutant clones, the percentage of cells with the identified variant was higher in myeloid versus T cells (median: 14.2-fold; range: 2.3 to 88.3-fold). This may reflect the quicker turnover of myeloid compared to lymphoid populations and short time period (< 1 year in most cases) between cytotoxic therapy initiation and pheresis collection.We next asked how transplantation influences HSC expansion. We sequenced peripheral blood leukocytes collected 6-12 months after transplantation from 40 of our lymphoma patients (with 104 detected pheresis variants). The VAFs of most of these variants did not change significantly with transplant while variants not initially identified in the pheresis samples often became detectable post-transplant. Several trends were observed. Of 46 DNMT3A variants detected before or after transplant, 15 (32.6%) significantly increased ≥ 2-fold in VAF after transplantation, while 2 (4.3%) decreased. Interestingly, all three clones with R882 codon variants expanded. In contrast, of 21 PPM1D variants, only 2 (9.5%) significantly increased in VAF with transplantation, while 7 (33.3%) decreased (P=0.002). These data suggest that clones expanding after cytotoxic therapy are often long-lived and persist after transplant. As with cytotoxic therapy, the behavior of hematopoietic clones following transplant depends, in part, on what mutations they harbor; however, transplantation-induced selection pressure doesn't necessarily favor the same clones as cytotoxic therapy.Finally, to assess the leukemic potential of expanded clones following cytotoxic therapy, we sequenced bone marrow samples from 134 t-AML/t-MDS patients. They were enriched in TP53 mutations with 34.3% carrying a mutation in this gene. In contrast, variants in other interrogated DNA damage response genes were infrequent in t-AML/t-MDS despite being common after cytotoxic therapy. For example, although variants in PPM1D were detected in a similar percentage of patients following cytotoxic therapy as those in TP53 (17.3% vs. 21.0%), they were only present in 3.0% of t-AML/t-MDS cases (P = 0.008). In total, our data suggests a model in which distinct clones carrying specific mutations expand in response to different cellular stressors. Each clone differs in its leukemic potential due, in part, to the mutations it harbors. DisclosuresVij:Takeda, Onyx: Research Funding; Celgene, Onyx, Takeda, Novartis, BMS, Sanofi, Janssen, Merck: Consultancy. DiPersio:Magenta Therapeutics: Equity Ownership; Celgene, Bioline, Vasculox, Cellworks, Rivervest: Consultancy; Hemedicus, DAVA Oncology: Speakers Bureau; BMS, Asterias, Amphivena, Bluebird: Other: Travel, Accomodations, Expenses.

HHV-6 Prophylaxis with Foscanet Improves Hematopoietic Engraftment after Umbilical Cord Blood Transplantation

Delayed hematopoietic recovery is a major obstacle for successful use of umbilical cord blood (UCB) transplantation. In our recent report of patients receiving non-myeloablative (NMA) UCB transplantation with sirolimus/MMF as GVHD prophylaxis, we observed an association between early post-transplant HHV6 viral reactivation and delayed hematopoietic recovery. Therefore, in order to improve hematopoietic recovery, we added foscarnet (45 mg/kg twice daily) as antiviral prophylaxis for at least 10 days starting at day +7 until neutrophil engraftment. Here we report results in 19 consecutive patients treated with foscarnet and compared results in those treated with acyclovir (n=60, historical control) after NMA UCB transplant with sirolimus/MMF GVHD prophylaxis. The median age for the entire cohort was 63 years (range, 16-73 years). Acute leukemia was the principal indication for transplantation (45%). At the time of transplantation, 25% of the patients had many comorbidities (HCT-CI≥3), 21% had Karnofsky performance status (KPS) ≤80% and nearly 60% were CMV seropositive with 7 patients (9%) having had a prior allogeneic transplant (alloHCT). All patients received the same NMA conditioning regimen consisting of fludarabine (150 mg/m2), cytoxan (50mg/kg) and TBI (200 cGy) with 46% also receiving ATG if there was no recent chemotherapy. Median infused total nucleated cell dose for the entire cohort was 4.1 x107/kg (range, 2.7-9.6 x107/kg). Groups were similar except for prior alloHCT (21% vs. 5%, p=0.03) and lower KPS ≤80% (58% vs. 10%, p <0.01) in recipients of foscarnet as compared to the acyclovir cohort. Cumulative incidence of neutrophil engraftment by day 42 was 100% in the foscarnet group vs. 75% (64-85%) in those treated with acyclovir (p= 0.08). Cumulative incidence of platelet engraftment by 6 months was 95% (69-100%) for foscarnet group vs. 75% (60-90%) for acyclovir group (p=0.02). In multiple regression analysis (Table), after adjusting for CMV serostatus, neutrophil engraftment was 2-fold increased in recipients of prophylactic foscarnet as compared to acyclovir (HR=2.0, CI 95% 1.1-3.6; p= 0.02). Similarly, after adjusting for age and CMV serostatus platelet engraftment was 2.4-fold increased in recipients of foscarnet as compared to acyclovir (HR=2.4, 95% CI 1.3-4.0; p <0.01). In addition, positive recipient CMV serostatus was associated with poor hematopoietic engraftment. These data support the use of prophylactic foscarnet for prevention of HHV-6 reactivation which may delay or prevent successful engraftment after NMA UCB transplantation with sirolimus/MMF as GVHD prophylaxis. [Display omitted] DisclosuresBrunstein:Magenta Therapeutics: Research Funding; Novartis: Research Funding.

HLA-Haploidentical Stem Cell Transplant with Pre-Transplant Immunosuppression for Patients with Sickle Cell Disease

Allogeneic stem cell transplantation (HCT) is curative in patients with severe sickle cell disease (SCD) but a significant number of patients lack a HLA-identical sibling or matched unrelated donor. Mismatched related (haploidentical) HCT with post-transplant cyclophosphamide(PTCY) allows expansion of the donor pool but is complicated by high rates of graft failure. In this report, we describe a favorable haploidentical HCT approach in a limited cohort of sickle cell patients with significant co-morbidities. To reduce the risk of graft failure we administered the conditioning regimen of rabbit anti-thymocyte globulin, busulfan (BU) and fludarabine (FLU) preceded with two courses of pre-transplant immunosuppressive therapy (PTIS) with FLU and dexamethasone (DEX). Graft-versus-host disease (GVHD) prophylaxis consisted of PTCY on days +3 and +4 followed by tacrolimus and mycophenolate mofetil (MMF) starting on day +5. Four patients (ages 13, 19, 19 and 23 years) received T-cell replete haploidentical stem cell infusion. All patients engrafted with 99.9-100% donor chimerism and all patients continue with stable engraftment at the last follow up (5 - 11 months post-transplant). Time to neutrophil engraftment was 14-26 days. Two patients had high levels of donor specific anti-HLA antibodies (DSA), which required the implementation of an antibody management protocol. This facilitated neutrophil engraftment on day +16 and day +26 respectively. One patient developed grade 1 acute GVHD which resolved. 3 patients developed mild, limited skin GVHD which responded to conventional immunosuppressive therapy. Human herpes virus 6 (HHV6) viremia was detected in three patients but resolved without treatment. One patient developed asymptomatic Cytomegalovirus (CMV) viremia which responded appropriately to standard therapy with ganciclovir. The prompt, stable engraftment and low toxicity in the post-transplant period makes PTIS with haploidentical transplant a promising option for the patients with SCD. DisclosuresSun:Baxalta: Consultancy. Wang:Magenta Therapeutics: Consultancy.