OA – 56: Single cell analyses of bone marrow immune microenvironment in RRMM subjects treated with MEK1/2 inhibitors reveal IRF1-mediated IFN/PDL1 signaling axes
Senior Scientist Multiple Myeloma Research Foundation Durham, North Carolina, United States
Introduction: 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 high-risk relapsed/refractory myeloma subjects (RRMM). Myeloma subjects with activating mutations in NRAS, KRAS or BRAF ("MAPK Pathway") were treated with cobimetinib, a MEK1/2 inhibitor approved for the treatment of melanoma. The goal of our study is to evaluate the effects of cobimetinib on the immune repertoire and cell-cell dynamics of myeloma subjects over the treatment course at single-cell resolution.
Methods: Targeted sequencing of BM samples from subjects enrolled in MyDRUG trial was used to identify those with RAS or BRAF mutations. These subjects were treated with cobimetinib and dexamethasone (cobi-dex) for two 28-day cycles, then in combination with an ixazomib, pomalidomide and dexamethasone (IPd) backbone therapy until disease progression. BM samples were collected from subjects prior to therapy (baseline/BL), after 2 cycles of cobi-dex therapy (EOC2), after 2 cycles of cobi-dex + IPd (EOC4), and at the end of treatment or at disease progression (EOT). BM samples were processed into CD138+ myeloma cell and CD138- "immune cell” fractions and the CD138- immune cell fraction profiled by single-cell RNA-sequencing (3’-scRNAseq) at up to four time points. Additionally, the residual plasma cells in these CD138- immune cell fractions were also profiled.
Results: Transcriptome profiles were generated from 50,121 cells across 22 samples from 9 subjects with tumor MAPK Pathway mutations at entry: BRAF (p.K483Q, p.V600E, n=2); KRAS (p.Q61H, p.G12V, p.G12R, n=3); NRAS (p.Q61H, p.Q61R, p.Q61K, n=4). Immune cell types identified include NK and T cells, CD14+, CD16+, CD14+CD16+ Monocytes, Granulocyte Monocyte Progenitors (GMP), B-cells, Plasma and Dendritic cells. Notably, in the monocyte/macrophage compartment, IRF1 is upregulated after cobi-dex treatment (EOC2) relative to baseline samples. IRF1 is a transcription factor involved in upregulating genes involved in the interferon response. Ingenuity pathway analysis suggests IFNg pathway activation in monocytes driven by STAT1 and IRF1 signaling after cobi-dex treatment. Furthermore, CD8 T cells post MEK1/2 inhibition exhibit increased expression of CD274 (PD-L1), CD69 and interferon response signaling genes (IFIT2, IFIT3, OASL, IFIT1), revealing cell-cell mediated interactions in the tumor microenvironment that are being modulated by MEK inhibition.
Conclusions: These data indicate that targeted kinase inhibition with cobi-dex activates IRF1-mediated IRF1/IFNg and PD-L1 signaling axes in the tumor microenvironment of RRMM subjects. These results support further explorations of rational combinations of targeted and immune therapies for greater efficacy in this disease.