Impact of Previous Allogeneic Hematopoietic Stem Cell Transplantation on Chimeric Antigen Receptor (CAR) T Cell Treatment for Relapsed/Refractory Multiple Myeloma.

BACKGROUND: Anti-BCMA-directed chimeric antigen receptor (CAR) T cells are effective treatment for patients with refractory/relapsed multiple myeloma (RRMM). However, little is known about the impact of previous allogeneic hematopoietic stem cell transplantation (allo-HSCT) on lymphocyte collection for production of CAR T cells and subsequent treatment with CAR T cells. PATIENTS AND METHODS: We performed a retrospective analysis of cellular composition of lymphocyte collections, CAR T cell expansion and treatment outcomes of RRMM patients undergoing therapy with idecabtagene vicleucel (ide-cel) with and without history of allo-HSCT. 27 patients (11/27 female) with median age 63 (range 39-75) years were analyzed. Five patients (19%) had the history of allo-HSCT median of 5.5 years before ide-cel. RESULTS: Prior to apheresis, the white blood cell, absolute lymphocyte counts, CD3+ cells and monocytes did not differ in patients with and without prior allo-HSCT. We also noticed no differences in the collected CD3+ yields or cellular compositions of lymphocyte collections. One year after ide-cel infusion, the progression-free survival and overall survival of patients with and without previous allo-HSCT did not differ with 60% and 45% respectively (P = .58) and 66.7% and 74% respectively (P = .84). The highest expansion of CAR T was detected between day 7 after infusion and showed no difference regarding previous allo-HSCT (P = .71). No graft-versus-host disease during the follow-up was detected. CONCLUSION: Our data confirm that the treatment with ide-cel is feasible for patients with prior allo-HSCT. Furthermore, allo-HSCT did not influence cellular composition of lymphocyte collections, clinical outcome or in vivo expansion of ide-cel.

The natural human IgM antibody PAT-SM6 induces apoptosis in primary human multiple myeloma cells by targeting heat shock protein GRP78.

In contrast to other haematological malignancies, targeted immunotherapy has not entered standard treatment regimens for de novo or relapsed multiple myeloma (MM) yet. While a number of IgG-formatted monoclonal antibodies are currently being evaluated in clinical trials in MM, our study aimed to investigate whether the fully human IgM monoclonal antibody PAT-SM6 that targets a tumour-specific variant of the heat shock protein GRP78 might be an attractive candidate for future immunotherapeutic approaches. We here show that GRP78 is stably and consistently expressed on the surface on tumour cells from patients with de novo, but also relapsed MM and that binding of PAT-SM6 to MM cells can specifically exert cytotoxic effects on malignant plasma cells, whereas non-malignant cells are not targeted. We demonstrate that the induction of apoptosis and, to a lesser extent, complement dependent cytotoxicity is the main mode of action of PAT-SM6, whereas antibody dependent cellular cytotoxicity does not appear to contribute to the cytotoxic properties of this antibody. Given the favourable safety profile of PAT-SM6 in monkeys, but also in a recent phase I trial in patients with malignant melanoma, our results form the basis for a planned phase I study in patients with relapsed MM.