OAB-021: BCMA-specific ADC MEDI2228 and Daratumumab induce synergistic myeloma cytotoxicity via enhanced IFN-driven innate immune responses and expression of CD38 and NKG2D ligands

Background Efforts are required to improve potency and durability of CD38- and BCMA-based immunotherapies in human multiple myeloma (MM). Methods We here delineated the molecular and cellular mechanisms underlying novel immunomodulatory effects triggered by BCMA pyrrolobenzodiazepine (PBD) antibody drug conjugate MEDI2228 which may augment efficacy of these immunotherapies. RNA sequencing followed by gene set enrichment analysis showed that MEDI2228 significantly enriched IFN I-signaling and induced type I interferon (IFN I)-stimulated genes (ISGs) in MM cell lines. The most MEDI2228-enhanced IFN-driven genes include chemokines/cytokines and receptors (i.e., CXCL9/10, CCL4L1/2, CCL22, CCL1/3/4/5, CCL3L1/3, TNFSF9/10, CSF2 (GM-CSF), CCR7), RSAD2, CASP1, ISGs (i.e., XAF1, TRIMs, IFITs, ISG15, GBP2/3, OAS1/2/L, RNASEL, MX1/2, FAS), RUNX3, GZMB, IKBKE, IRF1/6/7/9, STAT1/2/4/6, MB21D1(CGAS), TMEM173 (STING), IFIT1/2/3/5, and SOCS1/2/3. Results Regardless of genetic heterogeneity and resistance to current anti-MM therapies, MEDI2228 induced dose- and time-dependent DNA damage-ATM/ATR-CHK1/2 pathways, activation of cGAS-STING-TBK1-IRF3 and STAT1-IRF1-signaling cascades, as well as increased CD38 expression. It overcame CD38 downregulation triggered by IL6 and bone marrow stromal cell culture supernatant (BMSC-sup), via activation of STAT1-IRF1 without phosphorylation of STAT3 in immunomodulatory drugs (IMiDs)- and bortezomib-resistant MM cell lines. In contrast, MEDI2228 did not change CD38 expression and survival in BCMA-negative NK effector cells. Significantly, MEDI2228 with anti-CD38 monoclonal antibody Daratumumab (Dara) synergistically induced NK-mediated lysis of MM cell lines and autologous resistant patient MM cells, even in the presence of BMSC-sup and BMSCs. In parallel, MEDI2228 increased membrane expression of NKG2D ligands (NKG2DLs), i.e., MICA/B and ULBPs, in all MM cells tested, including Dara-resistant patient cells, correlating with enhanced MM cell susceptibility to NK cell killing. Since MEDI2228, but not its MMAF-ADC homolog M3 even used at >1-log higher concentrations enhanced surface expression of CD38 and NKG2DLs on MM cells, the potent DDR-mediated immunomodulation triggered by MEDI2228 vs M3 is critical in rendering MM cells more susceptible to Dara-induced NK cell killing. Importantly, M2 still activated STAT1/IRF1 signaling to induce CD38 and MICA/B expression in MM tumors grown in mice. All MM1S tumor-bearing NSG mice reconsituted with human NK cells became tumor-free following a single low dose M2 with Dara treatment, with 100% host survival. Conclusions Taken together, our data showed that MEDI2228 restored MM sensitivity to CD38 targeting by Dara without depleting NK cells and potentiated immunogenic cell death of MM cells. These results therefore provide the mechanistic rationale for clinical evaluation of combination CD38- and BCMA-directed immunotherapies to further improve patient outcome in MM.