Immune Profiling of Relapsed/Refractory Multiple Myeloma Patients Treated with Venetoclax in Combination with Dexamethasone (VenDex), Daratumumab and Dexamethasone (VenDd), and Daratumumab, Bortezomib and Dexamethasone (VenDVd)

▪ Background: The BCL-2 family of anti-apoptotic proteins (e.g., BCL-2, BCL-XL, MCL-1) are important regulators of lymphocyte development and are therapeutic targets for hematologic malignancies, including multiple myeloma (MM). Venetoclax (Ven) is a highly selective, potent, oral BCL-2 inhibitor that induces apoptosis in MM cells and has shown synergistic activity with bortezomib (Velcade; V) and dexamethasone (Dex or d). Combination of the CD38 monoclonal antibody (mAb) daratumumab (D) with Ven is hypothesized to further increase anti-myeloma activity based upon dual mechanisms of pro-apoptotic effects on tumor cells as well as enhanced immune stimulation. Pre-clinically and in healthy human subjects, Ven treatment leads to enrichment of CD8+ T effector memory cells, while resulting in loss of CD4+ and CD8+ naïve T-cells, however the potential immunomodulatory effect of Ven in MM is unknown. Results presented herein describe the pharmacodynamic changes observed in immune cell subsets in relapsed/refractory (R/R) MM patients (pts) treated with VenDex, VenDd, and VenDVd. Methods: Peripheral blood samples were collected at day 1 of cycles 1-5 to characterize pharmacodynamic changes in B- and T-cell sub-populations by multicolor flow cytometry in Ven MM clinical trials M13-367 (NCT01794520) and M15-654 (NCT03314181). M13-367 is a phase 1/2 study of VenDex in t(11;14) R/R MM, and M15-654 is a phase 1/2 study of VenDd in t(11;14) R/R MM (Part 1) and VenDVd in R/R MM (Part 2). As of 12 June 2019, 15 out of 31 pts treated with VenDex in phase 2 of M13-367, 19 out of 24 pts treated in Part 1 (VenDd), and 19 out of 24 pts treated in Part 2 (VenDVd) of M15-654 had baseline and post-treatment specimens available for analysis. Results: Consistent with previous findings that B-cells are highly dependent upon BCL-2 for cell survival, each Ven-containing regimen (VenDex, VenDd, and VenDVd) resulted in rapid and sustained reduction (~90% decrease from baseline by end of cycle 1) in peripheral B-cell (CD19+/CD5-) counts (Figure). In subgroup analyses, naïve B-cells (CD27-/IgM+) were significantly reduced in pts treated with each regimen, however regulatory B-cells (CD27+/CD24+) remained largely unaffected. In addition, a decrease in plasmablasts (CD27+CD38+CD20-) were only observed in pts treated with D-containing regimens (VenDd and VenDVd), which is consistent with expression of CD38 in this subgroup. In contrast to B-cells, CD3+ T-cells were minimally reduced (~20-30%