OAB-054: Single-cell RNA-sequencing identifies immune biomarkers of response to immunotherapy in patients with high-risk Smoldering Myeloma

Background Patients with Smoldering Multiple Myeloma (SMM) are typically observed until progression, but early treatment of high-risk patients may improve outcomes. Clinical and genomic biomarkers can be used to identify SMM patients at high risk of progression, however parallel profiling of the tumor immune microenvironment (TIME) may further improve prediction models. Methods Here, we performed single-cell RNA-sequencing on CD138- immune cells from 40 samples of 14 patients enrolled in a Phase II trial of Elotuzumab, Lenalidomide, and Dexamethasone, in patients with high-risk SMM (E-PRISM) to develop biomarkers for optimal patient selection and monitoring of response to treatment. Specifically, we profiled 33 bone marrow (BM) samples collected at baseline (n=11), cycle 9, Day 1 (C9D1, n=13) and EOT (n=9), and 7 peripheral blood mononuclear cell (PBMC) samples collected at baseline (n=4) and C9D1 (n=3). Results We found that higher abundance of mature B-cells, Th17 cells and GZMK+ T and NK cells and lower abundance of hematopoietic progenitor cells and plasmacytoid dendritic cells are associated with significantly longer progression-free survival (PFS) in SMM patients under treatment. This signal can be summarized by how normal-like the patients’ immune composition is at baseline, whereby patients whose immune composition is normal-like have significantly shorter PFS (p=0.031). This model suggests that at least some of the compositional changes observed in disease reflect the immune system’s capacity to react successfully to the immune challenge posed by the tumor, which we termed immune reactivity. Baseline immune reactivity may help to identify patients who will benefit the most from early treatment. Furthermore, we found that the expansion of tissue-resident NK cells and exhausted GZMK+ CD8+ T-cells at C9D1 of treatment is associated with significantly shorter PFS (p=0.039), suggesting that these immune biomarkers may help to monitor response to immunotherapy. Lastly, we found that patients would be classified the same way in terms of our immune biomarkers, had we assayed their peripheral blood instead of their bone marrow, suggesting that minimally invasive immune profiling for prognostication and monitoring may be feasible. Conclusion We used single-cell RNA-sequencing to profile the immune microenvironment of patients with high-risk SMM in a Phase II trial of Elotuzumab, Lenalidomide and Dexamethasone and developed immune biomarkers of response to treatment. Our study may usher in a next generation of clinical assays that assess both tumor biology and immune state, as well as common clinical biomarkers, in the marrow or blood, to accurately predict who may benefit from early treatment, monitor response and improve patient outcomes.