Belantamab Mafodotin Triggers Immune Invigoration in Multiple Myeloma Via Inflammatory and Immunogenic Cell Death [scRNA-seq]

Belantamab mafodotin, an antibody-drug conjugate targeting B-cell maturation antigen, has demonstrated significant clinical efficacy in combination therapies for relapsed or refractory multiple myeloma. Belantamab mafodotin exerts therapeutic effects through the cytotoxic action of its payload, monomethyl auristatin F, along with its ability to mediate antibody-induced cell death. Significant long-term clinical responses were previously observed in monotherapy treatment – even in patients undergoing dose holds – suggesting involvement of the adaptive immune system. Here, we show that belantamab mafodotin induces markers of immunogenic and inflammatory cell death in vitro and ex vivo. Belantamab mafodotin monotherapy treatment results in an acute inflammatory response that is detectable in patient serum within 24 hours, with increases in granzyme B, CXCL9, CCL3, and CCL4 linked to response depth. High expression of receptors LRP1 and TLR2 that mediate immunogenic cell death on patients’ monocytoid (monocyte/macrophage) cells suggests an important function of the monocytoid lineage to mediate the observed inflammation and immunogenic cell death cascades. Inflammation is followed by remodeling of the innate and adaptive immune system, with a reduction in immune inhibitory signaling alongside the emergence of a CD4 granzyme B-expressing cell population in patients who are in remission vs those that relapse. The ability of belantamab mafodotin to promote adaptive immune responses in addition to its cytotoxic activity may help explain the durable responses observed in treated patients with relapsed/refractory multiple myeloma, despite dose and schedule modifications. Viably frozen bone marrow mononuclear cells, taken from patients treated with belantamab mafodotin, were defrosted and underwent long read single cell RNA sequencing via a 10X encapsulation protocol and cDNA library amplification, followed by conversion to an ONT long read library that was then sequenced on a Promethion flow cell. Additionally, freshly isolated bone marrow mononuclear cells from non-malignant control patients underwent the same sequencing approach.