ALBERT

Description: †These authors contributed equally. Introduction Ide-cel, an anti-BCMA CAR T cell therapy, has demonstrated promising efficacy in the phase I CRB-401 trial in relapsed/refractory multiple myeloma (MM) (objective response rate, 85%; median progression-free survival [PFS], 11.8 months [95% CI: 6.2, 17.8]), but a subset of patients failed to respond and the duration of response varied across patients (Raje et al, N Engl J Med. 2019). A systematic examination of patient, product, and post-infusion correlates of overall and long-term response could offer biological insight into heterogeneous efficacy as well as provide biomarkers to guide post-CAR T disease management and future CAR T manufacturing and patient enrollment efforts. Soluble BCMA was of particular interest due to its expression on malignant and healthy plasma cells and its role as a composite measure of disease burden in MM. Methods We performed a retrospective analysis of 33 patients from the phase I CRB-401 study of ide-cel. The concentrations of ten immune-related factors in the blood (GMCSF, IFN-γ, IL-10, IL-1b, IL-2, IL-6, IL-8, MCP-1, TNF-α) and soluble BCMA were measured by ELISA before and after infusion with ide-cel along with 290 ide-cel CAR T-cell drug product attributes measured by flow cytometry and immunoassays. The absolute concentrations and fold-changes from baseline were assessed for correlation with overall and long-term response using univariate and multivariate (random forests) approaches. Results Several CAR T-cell drug product covariates nominally associated with longer PFS included reduced senescence phenotype in CD4 CAR T-cells and increased IL-2 and TNF-α production (P 〈 0.05). Pre-infusion levels of soluble BCMA correlated with serum monoclonal protein (M-protein) levels in 20 of 33 patients for whom M-protein levels were measurable (ρ = .49; P = 0.03) and with concentrations of the involved free light chain (ρ = .59; P = 0.005) in 23 of 33 patients with measurable levels. Our investigation of soluble BCMA levels in patients achieving a partial response (PR) or better confirmed significant decreases in soluble BCMA levels relative to nonresponders (NR) as early as seven days post-infusion (median reduction of 50% for ≥ PR vs. median increase of 27% for NR, P = 0.02). The fold-change in soluble BCMA 1 month after infusion stratified patients who achieved a PR or better from those who did not (P = 0.0001). Notably, patients who maintained a response to ide-cel for ≥ 18 months (M18 R) experienced a greater depth of clearance of soluble BCMA at month 2 (median concentration of 1835 ng/L for M18 R vs. 6299 ng/L for M18 NR, P = 0.002). The induction of IL-6 and TNF-α in blood on days 1-9 post-infusion was also higher in patients with a PR or better in response to ide-cel (e.g. IL-6 median fold change increase at day 2 of 2.9 for ≥ PR vs. 0.7 for NR, P = 0.001), consistent with an active inflammatory response and higher levels of CAR T expansion. Conclusions These data from CRB-401 identify candidate drug product attributes and soluble factors that correlate with response to ide-cel and potentially MM-directed cellular therapies in general. These data suggest that changes in soluble BCMA may be a robust biomarker of both early and durable responses to ide-cel and the depth of clearance of soluble BCMA at 2 months post-infusion may identify patients at risk of progression before standard markers of myeloma progression have emerged. Further molecular characterization of drug product attributes, including CyTOF and RNA sequencing, is ongoing to identify additional biomarkers associated with clinical outcomes following ide-cel treatment. These data will help inform future strategies to improve the efficacy of ide-cel and validation in a larger cohort is ongoing. Disclosures Thompson: Celgene Corporation: Employment, Equity Ownership. Jiang:Juno Therapeutics, a Celgene Company: Employment, Equity Ownership. Campbell:Celgene Corporation: Employment, Equity Ownership. Fuller:Celgene Corporation: Employment, Equity Ownership. Kaiser:Celgene Corporation: Employment. Mashadi-Hossein:Celgene Corporation: Employment, Equity Ownership. Rytlewski:Adaptive Biotechnologies: Equity Ownership; Juno Therapeutics, a Celgene Company: Employment, Equity Ownership. Martin:Celgene Corporation: Employment, Equity Ownership. Finney:bluebird bio Inc.: Employment. Kleinsteuber:bluebird bio Inc.: Employment, Equity Ownership. Alonzo:bluebird bio Inc.: Employment, Equity Ownership. Pandya:bluebird bio Inc.: Employment. Agarwal:Celgene Corporation: Employment, Equity Ownership. Hege:Celgene Corporation: Employment, Equity Ownership, Patents & Royalties; Arcus Biosciences: Membership on an entity's Board of Directors or advisory committees; Society for Immunotherapy of Cancer: Membership on an entity's Board of Directors or advisory committees; Mersana Therapuetics: Membership on an entity's Board of Directors or advisory committees. Raje:Merck: Consultancy; Takeda: Consultancy; Janssen: Consultancy; Celgene Corporation: Consultancy; Amgen Inc.: Consultancy; Bristol-Myers Squibb: Consultancy. Munshi:Celgene: Consultancy; Oncopep: Consultancy; Amgen: Consultancy; Janssen: Consultancy; Takeda: Consultancy; Abbvie: Consultancy; Adaptive: Consultancy. Hause:Juno Therapeutics, a Celgene Company: Employment, Equity Ownership. OffLabel Disclosure: ide-cel /bb2121 is an investigational agent and not yet approved in the US

Description: Background: Patients (pts) with relapsed and refractory multiple myeloma (RRMM) experience unsatisfactory outcomes with established treatment modalities. In the pivotal phase 2 KarMMa study (NCT03361748), idecabtagene vicleucel (ide-cel, bb2121) demonstrated frequent, deep, and durable responses in triple-class exposed pts with RRMM, with an overall response rate (ORR) of 73% and a complete response rate of 33% (Munshi et al. J Clin Oncol. 2020;38[suppl, abstr]:8503). The overall safety profile of ide-cel was also manageable. The median time to onset and duration of cytokine release syndrome (CRS) were 1 d and 5 d, respectively, and the median time to onset and duration of neurotoxicity (NT) were 2 d and 3 d; the frequencies of higher-grade CRS and NT were low. Evaluated here are the T cell phenotypes, soluble factors, and cytokines associated with ide-cel activation, CRS, NT, and tumor responses over time in pts who received ide-cel in the KarMMa study. Methods: After longitudinal sampling of peripheral blood post-ide-cel infusion in the KarMMa study (N=128), plasma was analyzed for levels of proinflammatory cytokines and inflammation-related soluble factors; serum was evaluated for soluble BCMA (sBCMA) as a peripheral surrogate measure of tumor burden, and peripheral blood mononuclear cells were assessed by flow cytometry for memory phenotypes of CAR T cells. Associations between these features over time after ide-cel infusion were evaluated in the context of ORR, ongoing response at 9 mo, and grade ≥2 CRS and NT. Response at 9 mo was selected for analysis because this visit was proximal to the median progression-free survival (PFS) reported in all ide-cel-treated pts in KarMMa. The 9-mo responders were defined as pts with assessments 〉8 mo postinfusion and no progression before 10 mo postinfusion. Results: The levels of both CD4+ and CD8+ populations of CAR T cells increased to a greater degree postinfusion in responders and were skewed towards a higher fraction of CD8+ cells through peak expansion. Cell expansion in responders was characterized by an increased proportion of TEM in CAR T cells (CCR7−/CD45RA−) for both CD4+ and CD8+ subsets. Congruent with dominant TEM expansion, characteristic TEM-associated proinflammatory cytokines, such as IFN-ɣ and IL-6, were consistently upregulated early after infusion. Peak IFN-ɣ and IL-6 levels occurred a median of 4 d postinfusion, and 90% of pts (5th−95th percentile) had IFN-ɣ and IL-6 peaks 21 d and 15 d postinfusion, respectively, which was in line with the observed early onset of CRS and NT. Pharmacodynamic responses, shown by decreases in sBCMA after infusion, also occurred consistently early after infusion, and the sBCMA nadir occurred in 90% of pts 7 d−85 d postinfusion (5th−95th percentile; median, 31 d). Early sBCMA clearance below the limit of detection of the assay was associated with longer responses, and median PFS was significantly longer in pts with undetectable sBCMA vs detectable sBCMA at 2 mo (12.3 mo [95% CI, 11.6−17.7] vs 2.9 mo [95% CI, 1.9−3.1]; P

Description: Introduction: B-cell maturation antigen (BCMA) is primarily expressed by malignant and normal plasma cells, making it an attractive target for the treatment of multiple myeloma (MM). bb21217 is a BCMA-directed chimeric antigen receptor (CAR) T cell therapy that uses the same CAR molecule as idecabtagene vicleucel (ide-cel, bb2121), but adds the PI3K inhibitor bb007 during manufacturing to enrich the drug product (DP) for memory-like T cells, thereby reducing the proportion of highly differentiated or senescent T cells. We conducted correlative analyses to investigate the mechanistic hypothesis that CAR+ T cells with memory like phenotypes may persist and function longer, which may be one determinant of duration of response (DOR). Methods: An ongoing phase I clinical study (CRB-402; NCT03274219) is assessing safety and efficacy of bb21217 in relapsed/refractory MM patients. A total of 44 patients had PBMCs, collected from apheresis, and DP characterized by RNA sequencing (RNAseq) and mass Cytometry (CyTOF). The correlation of T cell phenotype with peak expansion, response and DOR per IMWG Uniform Response Criteria was explored. P-values were determined by Wilcoxon test, Spearman correlation, or Cox PH regression on DOR with categorical marker values (high/low). Results: In this patient population, substantial cross patient heterogeneity in T cell phenotypes was observed both in PBMCs and DP. Late differentiation/senescent markers in PBMCs were negatively correlated with clinical response. In particular, patients whose DP had higher expression of CD57 had lower peak expansion (p

Description: Introduction: Identifying prior therapy exposures that affect the patient or their peripheral blood mononuclear cell (PBMC) material is one strategy to optimize outcomes to CAR T cell therapy. Alkylating agents commonly used in multiple myeloma management, such as cyclophosphamide, have been reported to impair the proliferative capacity of T lymphocytes and to blunt their functional activity (Ercolini et al. J Exp Med. 2005;201:1591; Banissi et al. Cancer Immunol Immunother. 2009;58:1627; Litterman et al. J Immunol. 2013;190:6259). In the pivotal phase 2 KarMMa trial (NCT03361748) investigating the BCMA-directed CAR T cell therapy idecabtagene vicleucel (ide-cel, bb2121) in triple-class exposed patients with RRMM, 80% of patients had a history of prior anticancer treatment with ≥1 alkylating agents. In this retrospective analysis, patient and PBMC characteristics associated with time from last dose of alkylating agent(s) until apheresis of PBMCs for CAR T cell manufacture were identified. Methods: PBMCs isolated from patient apheresis material, which serves as starting material for CAR T cell manufacturing, were immunophenotyped by polychromatic flow cytometry for markers associated with T cell differentiation, memory, senescence, and exhaustion. Data from relevant prespecified clinical and exploratory endpoints were collected, and a novel implementation of left-censored time-to-event analysis (Ware et al. Biometrics. 1976;32:459) was used to identify statistically significant relationships between washout time after prior alkylator exposure (encompassing 14 individual drugs) and patient and PBMC variables. Dose intensity of prior alkylators was not considered due to sparse annotations in the patient histories. Optimal cutpoints were identified for each variable that maximized the proportional hazard of receiving an alkylator between patients above and below the cutpoint, and P values were adjusted for testing multiple cutpoints. Relationships were verified by nonparametric correlation, in which alkylator washout was encoded as 1/log(−washout). Results: More recent exposure to an alkylating agent (after diagnosis but before apheresis) was associated with patients receiving more prior therapies per year to manage their disease (hazard ratio [HR]=2.63, ρ=−0.54, P

Description: BCMA targeting chimeric antigen receptor (CAR) T cell therapy has shown deep and durable responses in multiple myeloma. However, relapse following therapy is frequently observed, and mechanisms of resistance remain ill-defined. Here, we perform single cell genomic characterization of longitudinal samples from a patient who relapsed after initial CAR T cell treatment with lack of response to retreatment. We report selection, following initial CAR T cell infusion, of a clone with biallelic loss of BCMA acquired by deletion of one allele and a mutation that creates an early stop codon on the second allele. This loss leads to lack of CAR T cell proliferation following the second infusion and is reflected by lack of soluble BCMA in patient serum. Our analysis suggests the need for careful detection of BCMA gene alterations in multiple myeloma cells from relapse following CAR T cell therapy.

Description: Chimeric antigen receptor (CAR) T-cell therapy targeting B cell maturation antigen (BCMA) has provided deep (73% - 100%) responses in relapsed/refractory multiple myeloma (MM). However, median PFS has been less than 12 months, and amongst the small number of patients retreated at the time of progression with the same CAR T product, responses have been infrequent. This highlights development of resistance that may preclude effectiveness of the 2ndinfusion, and may also underly relapse following response to the initial CAR-T cell therapy. Here, we have investigated one of the resistance mechanisms using longitudinal single cell transcriptomic and bulk genomic analysis. This patient had relapsed/refractory IgG lambda MM with hypodiploidy and a complex karyotype with t(8;12) (q24;q14), clonal t(11;14) (q13;q32), and clonal deletion 13. Patient received 150x106CAR+ T cells (ide-cel) and achieved partial response, with duration of response of 8 months. The patient was retreated with 450 x106CAR+ T cells at relapse, but with no response. To delineate the resistance mechanism, we evaluated the bone marrow (BM) niche using 37658 cells from eight time points from before 1st CAR T cell infusion to 2 months after 2nd CAR T cell infusion, and identified 13 clusters consisting of hematopoietic cells and MM/plasma cells. Using RT-PCR based detection, we observed engineered CAR T cells only at 2 weeks after first infusion, when maximal CAR T cell expansion was observed. We did not observe infused CAR T cells with single cell RNAseq after 2ndinfusion, but a limited expansion was confirmed using RT-PCR.Re-clustering of the T cell cluster showed an increased proportion of CD4+ helper and T regulatory cells (Treg) 2 weeks after 1st infusion. In contrast, TREG proportion remained constant at the 2nd infusion, suggesting other causes for lack of expansion of CAR-T cells. We also did not identify any significant increase in the proportion of cells expressing immune check point inhibitory markers or in accessory cell types with immune inhibitory function in MM BM. Since we did not delinate a role of the BM milieu mediating suppression of CAR-T cell expansion and function following 2ndinfusion, we next explored tumor intrinsic factors. Soluble BCMA level (produced predominantly by MM cells) was high before the first CAR T cell infusion and dropped significantly to a very low level coinciding with the clinical response; however, it remained low even at the time of relapse with increase burden of MM, indicating a lack of BCMA production by MM cells. We therefore investigated genomic changes in MM cells at the time of relapse. Our single cell analysis of BM samples identified 3 samples (at the time of relapse and post 2ndCAR T cell infusion) with significant numbers of MM cells, evidenced by expression of CD138 and XBP1 (marker of plasma cells), CCND1 (upregulated in this patient with t(11;14)) and lack of RB1 (downregulated in this patient with del13). Imputation of copy number alterations scRNAseq showed that the majority of MM cells had a deletion of 16p, including the BCMA locus located on 16p13.13. We further validated these findings using deep whole exome sequencing (WES) of purified CD138+ cells collected after the second CAR T infusion. Before first CAR T cell infusion, 4% MM cells showed deletion 17p, while after second infusion both WES and scRNAseq prediction showed that del17p and del16p were clonal, and longitudinal scRNAseq analysis indicated that del17p and del16p co-occurred in the same clone. Moreover, WES identified a subclonal nonsense mutation (p.Q38*) in BCMA that creates an early stop codon in the BCMA gene. This biallelic BCMA deletion, acquired with one copy loss and a 2ndloss-of-function mutation, provides the molecular basis for lack of BCMA expression in MM cells at the time of relapse. Our data showed that both TP53 and BCMA had deletion in one allele and mutation in the second allele. These results identify biallelic loss of BCMA locus as a potential resistance mechanism to BCMA targeting therapy. Our results highlight the need to investigate sBCMA as a potential indicator of BCMA loss at relapse, and to carry out detailed transcriptomic or genomic analysis to confirm mutations. Moreover, these data also demonstrate the ability of MM cells to survive without BCMA expression. With the growing number of BCMA targeting therapeutic modalities under development, we would expect to see such occurrences more commonly in the future. Disclosures Fulciniti: NIH: Research Funding. Campbell:BMS: Current Employment, Current equity holder in publicly-traded company. Petrocca:bluebird, bio: Current Employment, Current equity holder in publicly-traded company. Hege:Bristol Myers Squibb: Current Employment, Current equity holder in publicly-traded company, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company), Patents & Royalties: numerous, Research Funding; Celgene (acquired by Bristol Myers Squibb): Ended employment in the past 24 months; Mersana Therapeutics: Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees; Arcus Biosciences (Former Board of Directors): Divested equity in a private or publicly-traded company in the past 24 months. Kaiser:BMS: Current Employment, Current equity holder in publicly-traded company. Anderson:Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Sanofi-Aventis: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Millenium-Takeda: Membership on an entity's Board of Directors or advisory committees; Oncopep and C4 Therapeutics.: Other: Scientific Founder of Oncopep and C4 Therapeutics.. Munshi:C4: Current equity holder in private company; Legend: Consultancy; OncoPep: Consultancy, Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties; BMS: Consultancy; Janssen: Consultancy; Adaptive: Consultancy; Amgen: Consultancy; AbbVie: Consultancy; Karyopharm: Consultancy; Takeda: Consultancy.