(PA-204) Daratumumab-based Quadruplet Therapy in Functional High-risk RRMM (fRRMM) Patients Promotes CD8 T Cell Activation and Expansion in the Immune Microenvironment

The Multiple Myeloma Research Foundation (MMRF) and its partners launched the MyDRUG platform clinical trial (NCT03732703) to evaluate the safety and efficacy of genomically-guided treatments for functional relapsed/refractory myeloma patients (fRRMM). fHRMM patients with no discernible activating mutations and who had received 1-3 prior therapies (exposed to at least one proteasome inhibitor and an IMiD) were given a combination of daratumumab (D), ixazomib (I), pomalidomide (P) and dexamethasone (d) (D-IPd) quadruplet therapy. The goal of this study is to evaluate the immunomodulatory effects of daratumumab-(anti-CD38)-based therapy on fHRMM patients enrolled in the MMRF-sponsored MyDRUG umbrella clinical trial over the duration of therapy and to correlate immune changes with patient response immediately following the first two cycles of therapy.

Methods:

Bone marrow (BM) aspirates were then collected from patients prior to therapy (BL), after 2 cycles (EOC2), after 4 cycles (EOC4) of the quadruplet therapy and at the end of treatment or disease progression (EOT). Immune and tumor fractions were enriched by CD138 selection. Here, CD138- bone marrow mononuclear cells were isolated and transcriptionally profiled by scRNAseq and scTCRseq.

Results: Single-cell RNA and TCR profiles were generated from ~90,000 cells across 41 samples from 16 subjects. scRNAseq identified CD3+ T cells, NK cells, classical and non-classical monocytes and B cells. CD8+ T cells were further resolved into their subsets including precursor (T_PEX) and terminally exhausted T cells (T_EX) within the bone marrow microenvironment. Within the CD8+ T cell compartment, an expansion of the effector memory (T_EM) cell population was observed following 2-cycles of therapy (EOC2). However, this T_EM expansion was not sustained at timepoint EOC4.  Towards the end of therapy, enrichment of precursors to exhausted and terminal dysfunctional effector memory cells (T_EMRA) was observed. Subjects with partial (PR), very good partial (VGPR) and complete (CR) best overall responses showed an initial increase in T_EM cells followed by a slow expansion of T_EX and T_EMRA cells over time. Longitudinal tracking of T cell clonality showed preferential progressive expansion of T_EMRA cells after the therapy. We mapped hyperexpanded (more than 16 copies) clonotypes, presumed to be tumor-reactive, to various CD8+ T cell subsets. These hyperexpanded clonotypes mapped to the T_EMRA, T_EX and T_EM CD8+ T cells. Analysis of TCR repertoires clonality and diversity also demonstrated a reduced richness and increased clonality of CD8+ TCRs in responders.

Conclusions: These data indicate that p</span>aired single cell RNA and TCR sequencing of BM T cells from RRMM patients receiving D-IPd quadruplet therapy revealed a selective expansion of clonotypic CD8+ T cells. These results support further explorations of rational combinations of targeted and immune therapies for greater efficacy in this disease.