Immune Profiling of Relapsed or Refractory Multiple Myeloma Patients Treated with Pomalidomide and Low-Dose Dexamethasone in Combination with Daratumumab

Background: Multiple myeloma clinical trial CC-4047-MM-014 (NCT01946477) is a Phase II study designed to test the safety and efficacy of pomalidomide and low-dose dexamethasone alone (arm A) or in combination with daratumumab, an anti-CD38 antibody, (arm B) subjects with relapsed or refractory multiple myeloma who have received a first or second line treatment of lenalidomide-based therapy. Immunomodulatory agents (IMiD® compounds) continue to be the backbone of multiple myeloma therapy especially when combined with monoclonal antibodies, more specifically pomalidomide had been shown previously to enhance T cell- and NK cell-mediated immunity. We sought to characterize on-treatment pharmacodynamic changes of immune biomarkers associated with POM + LoDEX + DARA administration (arm B) using multicolor flow cytometry panels designed to characterize T-cell subsets and CD38+ expressing cells.

IMiD agents are the backbone of combination regimens in the treatment of patients with newly diagnosed or relapsed and/or refractory multiple myeloma. The anti-myeloma properties of these agents derive from a dual mechanism of pro-apoptotic effects on tumor cells as well as enhanced immune stimulation. An understanding of how IMiD agents interact with new monoclonal antibodies to modify patient immune profiles offers key insights into the role of such in innate and adaptive immunity in determining patient outcomes.

Methods and Results: Peripheral blood samples were collected at screening, Cycle1 Days 1, 8, and 15, and Cycle 2 Days 1 and 15 to monitor pharmacodynamic changes in populations of T cells, NK cells, monocytes and MDSCs by flow cytometry. From 112 patients enrolled in Arm B, 98 patients had baseline and post-treatment specimens available for these analyses. As expected, combination treatment with POM + LoDEX + DARA led to decreased peripheral counts of CD56⁺CD16⁺ NK cells as well as CD4⁺CD38⁺ and CD8⁺CD38⁺ T cell subpopulations. Decreased counts were also noted in CD3^-CD19⁺ B cells. In contrast, total counts of CD14⁺ monocytes and CD3⁺CD4⁺ or CD3⁺CD8⁺ T cells were stably maintained and pronounced increases were observed in proliferating CD4⁺Ki-67⁺ and CD8⁺Ki-67⁺ T cells. Further, when examined as a percent of total counts, increases were observed in CD14⁺ monocytes, CD3⁺CD4⁺ and CD3⁺CD8⁺ T-cells, with decreases in CD3^-CD19⁺ B-cells and CD3^-CD56⁺CD16⁺ NK cells. Correlation of these pharmacodynamic changes with clinical outcomes will be presented. In addition, baseline immune profiling of specific cell population subsets and associations with best overall response and progression-free survival is currently being analyzed.

Conclusions: The triplet regimen POM + LoDEX + DARA has shown notable clinical activity with deep and durable responses in relapsed multiple myeloma patients progressed and are or refractory to lenalidomide. Immune characterization here is consistent with a model for clinical activity in which the loss of CD56⁺CD16⁺ NK cells along with a concomitant immune suppression by loss of CD38⁺CD4⁺ and CD38⁺CD8⁺ T- cells is offset by an increase in proliferating cytotoxic CD4⁺Ki-67⁺ and CD8⁺Ki-67⁺ T-cell populations. Our results demonstrate that patients treated with the POM + LoDEX + DARA combination do not demonstrate impairment in the innate and adaptive immune compartments and, in contrast, show significant proliferative activity in the subsets of CD4, CD8 and NK cells following treatment. Pomalidomide had been shown previously to enhance T cell- and NK cell-mediated immunity; these data are consistent with a mechanism of action in which pomalidomide administration facilitates the ability to overcome immunosuppressive effects of Dara and LoDex. Potential associations of immune biomarkers with patient outcomes is ongoing and will be updated.