Yassine, Farah

AbstractThe challenge of disease relapsed/refractory (R/R) remains a therapeutic hurdle in chimeric antigen receptor (CAR) T‐cell therapy, especially for hematological diseases, with chronic lymphocytic leukemia (CLL) being particularly resistant to CD19 CAR T cells. Currently, there is no approved CAR T‐cell therapy for CLL patients. In this study, we aimed to address this unmet medical need by choosing the B‐cell activating factor receptor (BAFF‐R) as a promising target for CAR design against CLL. BAFF‐R is essential for B‐cell survival and is consistently expressed on CLL tumors. Our research discovered that BAFF‐R CAR T‐cell therapy exerted the cytotoxic effects on both CLL cell lines and primary B cells derived from CLL patients. In addition, the CAR T cells exhibited cytotoxicity against CD19‐knockout CLL cells that are resistant to CD19 CAR T therapy. Furthermore, we were able to generate BAFF‐R CAR T cells from small blood samples collected from CLL patients and then demonstrated the cytotoxic effects of these patient‐derived CAR T cells against autologous tumor cells. Given these promising results, BAFF‐R CAR T‐cell therapy has the potential to meet the long‐standing need for an effective treatment on CLL patients.

Abstract B-cell chronic lymphocytic leukemia (B-CLL) is the most common leukemia in adults with CD19-targeting CAR T-cell therapy showing an excellent initial curative response. However, 10-20% of patients who receive anti-C19 CAR T-cell treatment experience relapse due to CD19 antigen loss. B-cell activating factor receptor (BAFF-R) that is expressed on the surface of normal and neoplastic B cells mediates the survival of mature peripheral B cells along with the B-cell receptor. Since B-CLL is characterized by apoptotic disruption and subsequent accumulation of mature B cells, BAFF-R is a logical, novel target for CAR T-cell therapy directed against B-CLL, especially if CD19 antigen loss occurs. In this study, we first manufactured BAFF-R CAR T-cells by infecting healthy donor Tnaïve/memory (Tn/mem) cells with BAFF-R CAR lentivirus before evaluating the antitumor activity of BAFF-R CAR T-cells on wild type MEC-1 (a B-CLL cell line), modified MEC-1, and primary cell lines. Antigen-specific cytotoxicity and activation of the BAFF-R CAR T-cells or control CD19 CAR T-cells were determined upon incubation with B-CLL cell lines and patient-derived primary B-CLL by measuring degranulation and IFN-γ release, respectively. BAFF-R CAR T-cells demonstrated substantial cytotoxicity against MEC-1, CD19-deficient MEC-1, and primary B-CLL cell lines; CD19 CAR T-cells showed no effect on CD19-deficient MEC-1 cells but did show effects with primary B-CLL and MEC-1 cells. Similarly, the release of IFN-γ was greater when BAFF-R CAR T-cells were co-cultured with CD19-deficient MEC-1 or primary B-CLL compared to CD19 CAR T-cells co-cultured with CD19-deficient MEC-1. In summary, BAFF-R CAR T-cells exert significant antitumor properties not only on patient-derived primary B-CLL cells but also on a CD19-deficient B-CLL cell line. We, therefore, assert BAFF-R-targeting CAR T-cells to be a novel therapeutic avenue for patients newly diagnosed with B-CLL and patients experiencing relapsed B-CLL after anti-CD19 therapy. Citation Format: Yan Luo, Kaihin Lui, Tommy T. To, Andrew liu, Farah Yassine, Mohamed A. Kharfan Dabaja, Martha E. Gadd, Hong Qin. Antitumor activity of BAFF-R targeting CAR T-cells on chronic lymphocytic leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2855.

e19049 Background: Prognosis of COVID-19 is poor in the setting of immunosuppression. Casirivimab/imdevimab (REGEN-COV), bamlanivimab, and sotrovimab are investigational monoclonal antibodies (MoAbs) authorized for treatment of mild/moderate COVID-19 for patients (pts) 12 years or older and who are at high-risk for progression to severe COVID-19. These neutralizing antibodies, against SARS-CoV-2 spike proteins, have been shown to decrease risk of progression to severe disease. Recipients of allogeneic stem cell transplants (allo-SCT) or chimeric antigen T cell therapy (CAR T cell) represent a high risk population. However, treatment outcomes with these MoAbs in these pts are not well described. Methods: This retrospective study included 33 consecutive adult pts who developed mild/moderate COVID-19 and received anti-spike SARS-CoV-2 MoAbs between December 2020 and November 2021. Allo-SCT (N=27) or CAR T cell (N=6) recipients were included, and outcomes were analyzed separately. Pts received REGEN-COV (N=19), bamlanivimab (N=11), or sotrovimab (N=1), missing (N=2). Results: In the allo-SCT cohort (N=27), median age at time of COVID-19 was 55 (23-76) years. Median time from allo-SCT to COVID-19 was 31 (22-64) months. Two pts received CAR T-cell therapy prior to allo-SCT. Diagnoses included leukemia or myeloid diseases (82%), lymphoma (11%), or myeloma (7%). Transplant characteristics are summarized (Table). Thirteen pts were vaccinated against SARS-CoV-2 prior to breakthrough COVID-19. Events considered included hospitalization due to COVID-19, disease progression, or death from any cause. The 6-month event-free and overall survivals were 81% and 91%, respectively. In the CAR T cell recipients cohort (N=6), 4 pts received axicabtagene ciloleucel for diffuse large B-cell or follicular lymphoma and 2 received brexucabtagene autoleucel for mantle cell lymphoma. The median follow-up was 8 (1-11) months. Two pts received autologous SCT prior to COVID-19. Median time from CAR T cell therapy to COVID-19 was 10 (3-24) months. Three pts were vaccinated prior to COVID-19. Only 1 pt was hospitalized due to severe COVID-19 requiring mechanical ventilation leading to death. Conclusions: These results show a potential benefit of MoAbs in high-risk pts, namely allo-SCT or CAR T cell recipients. Future studies should evaluate the role of prophylactic use MoAbs in these populations. A comparative analysis with a matched control cohort (who did not receive MoAbs) will be provided at the meeting. [Table: see text]

Abstract Background: AHCT is a standard of care treatment for eligible patients (pts) with MM. Most consensus guidelines recommend that at the time of first AHCT, enough APBHC should be collected to perform two AHCT. However, recent studies have shown that with each decade after 1990, the use of cryopreserved APBHC for a salvage AHCT has declined and is now in the range of 4.6-15% in the decade between 2010-2018. The collection and storage of APBHC for two AHCT incurs additional costs and a prior single center cost analysis revealed that having had collected for just one AHCT in a cohort of 726 MM pts would have saved 3.8 million USD between 1993 and 2011. 1 Most centers that perform AHCT for MM pts continue to collect and store PBAHC for 2 AHCT. Herein we evaluate utilization trends and costs associated with cryopreserved APBHC in patients with MM. Methods: We retrospectively evaluated the clinicopathologic data from 440 patients with MM who underwent APBHC mobilization and collection at Mayo Clinic Florida between 2010 and 2019. The number of apheresis/collection sessions and APBHC product collection yields were determined for patients who were mobilized by any method. We estimated the costs involved in PBSC collection (apheresis) and cryopreservation storage based on our institution-specific charges as of May 2021. The cost of 1 session of APBHC collection/apheresis was $4,680 and the cost of 1 year of APBHC cryopreservation was $4,790 per patient. Statistical analysis was performed using JMP Pro 15 (SAS). Chi-square and Fischer exact tests were used to carry out univariate analysis for categorical variables and Wilcoxon rank sum/Kruskal Wallis for continuous variables. Results: Patient demographics are shown in Table 1. 440 pts underwent at least one collection session and 347 underwent at least 1 AHCT. The median number of mobilization sessions was 1 (95% CI 1.0-1.03), the median number of collection/apheresis sessions was 2.0 (95% CI 2.39-2.59), 84.3% (n=371) required ≥1 collection session. The median number of CD34 stem cells collected was 7.6 x10 6 (95% CI 7.76-8.19 x10 6), and the median number of infused CD34 cells was 4 x10 6(95% CI 4.13-4.37x10 6). The median cost of total collection sessions (defined as # of apheresis/collection sessions x $4,680) was $9,360 per pt (95% CI $11,181-$12,100). The median cost of cryopreservation (defined as # of years of storage x $4,790) was $19,160 per pt (95% CI $9,682-$22,252). The median number of years of storage was 4 (95% CI 4.11-4.65). 77(17.5%) pts have had APBHC in storage for <2 years, 218 (49.5%) have had APBHC in storage for 2-5 years, and 145 (33%) had have APBHC in storage for >5 years. The median time from MM diagnosis to AHCT was 9.0 months (range 13.8-18.5). 82% of patients collected enough APBHC (≥6x10 6, at least 3x10 6 per AHCT)for 2 AHCT. 8% of patients had all APBHC infused during their first AHCT, 83.5% had half of their APBHC infused during their first AHCT, and 8.1% had a different amount of APBHC infused during their first AHCT thus 91.6% of patients who collected APBHC had cells in storage. The median OS for the entire cohort after AHCT was 94.7 months (95% CI 88.6-100). Out of 347 patients who had stem cells in cryopreservation, 5 (1.4%) underwent a salvage AHCT and 3 (0.9%) underwent a tandem AHCT. 61% percent of patients had ≥1 excess collection sessions for APBHC that ultimately went unused. The median cost of excess collection sessions was $4,680 per pt (range, $4,680-$32,760) and the median total cost for excess collection sessions plus costs for storage was $23,840 per pt (range, $4,680-$85,450). The sum of costs of excess collection sessions was $2,077,920 and the sum of costs of cryopreservation was $5,812,665. Conclusion: The results of this single center analysis show that only 1.4% of patients underwent a salvage AHCT between 2010 and 2019 while 91.6% had APBHC left in storage which confirms the increase in storage of cryopreserved APBHC and declining trend in the use of stored APBHC for salvage AHCT in pts with MM. This is likely due to the advent of next generation novel therapies such as monoclonal antibodies, proteasome inhibitors and immunomodulatory agents. Excess collections, and cryopreservation of unused APBHC incur a cost of nearly $8 million. Institutional policies regarding universal APBHC collection and long-term storage should be reevaluated. 1Phipps C, et al. Bone Marrow Transplantation 2015:50;663-667. Figure 1 Figure 1. Disclosures Murthy: CRISPR Therapeutics: Research Funding. Ailawadhi: Sanofi: Consultancy; Medimmune: Research Funding; Genentech: Consultancy; Ascentage: Research Funding; Pharmacyclics: Consultancy, Research Funding; Xencor: Research Funding; Janssen: Consultancy, Research Funding; Amgen: Consultancy, Research Funding; AbbVie: Consultancy; Beigene: Consultancy; GSK: Consultancy, Research Funding; BMS: Consultancy, Research Funding; Takeda: Consultancy; Cellectar: Research Funding; Karyopharm: Consultancy.