Favorable Progression-Free Survival Associated with Immune Bio-Markers Modulated By Pomalidomide in Relapsed/Refractory Multiple Myeloma: An Analysis of Phase III Study

We have previously shown that immune cells, including regulatory T cells, Th17 cells, myeloid-derived suppressor cells and NK cells are abnormal in multiple myeloma (MM). It is well demonstrated that immune-modulatory drugs like pomalidomide (POM) have shown impact on various immune sub-populations in pre-clinical studies. Relapsed/refractory (RR) MM (N=540) patients were randomized to be bortezomib and dexamethasone (Vd) with or without pomalidomide POM (Vd) in a large Phase III CC4047-MM007 (OPTIMISMM, NCT01734928) study, allowing for critical investigation into the impact of POM on immune cell-subset. We have analyzed 197 RRMM patients utilizing 366 peripheral blood samples collected at screening, day 8 of cycle 1 and day 8 of cycle 3 using 98 immune biomarker-panel with multi-color flow to identify changes with POM exposure in various sub-populations of B, T, & NK cells. The primary objective was to investigate association of PFS with the modulation of predictive and prognostic immune bio-markers by POM. The analyzed patient-treatment cohorts had identical characteristics as the total patient population and was balanced for the 2-treatment arms, overall patient characteristics and response.

Among B-Cell-subpopulations, we observed significant up-regulation of B1b cells (CD19+CD43+) and down-regulation of regulatory B cells (Bregs, CD19+CD5+CD43-) by the PVd arm as compared with the Vd arm. A significant increase in MZB cells were observed in both arms. Patients with a higher proportion of either CD19+ B cells or Bregs at screening showed significantly favorable PFS (logrank p value < 0.05) in the PVd arm as compared with the VD arm, which indicates that these markers are predictive of PFS for PVd treatment. Moreover, patients with a higher proportion of either [naïve B cells (CD19+CD27-IgD+)] or [CD95+ B cells that display germinal center differentiation features (CD19+ CD185+) at cycle 1 day 8] showed significantly favorable PFS in PVd arm (logrank p value < 0.05); however, they were not prognostic with the Vd arm alone. This indicates that the early impact of Pom on these cell types may provide a prognostic bio-marker outcome following PVd therapy in B cell-compartment at cycle 1.

Among T-Cell subpopulations, we observed that patients with higher proportion of CD4+ T cells at screening showed significantly favorable PFS in PVd arm, indicating a predictive marker. We observed significantly favorable PFS in PVd arm in both patients with a higher number of CD8 T cells expressing OX-40 at cycle 3 day 8 and patients with lower number of CD4 T cells or Tfh cells (CD4+CD185+) expressing PD-1 or regulatory T cells expressing (low CD127+ and high CD25+) HLA-DR at cycle 3 day 8, indicating prognostic markers. The studied markers were neither predictive nor prognostic for the Vd arm alone.

The total proportion of NK cells were significantly elevated following the Pom-containing regimen as early as day 8 of cycle 1 and persisted at cycle 3 as compared to the Vd arm. Among NK cell-subpopulations, we observed that the patients with either a higher proportion of NK cells without expressing KIR molecules or a lower proportion of NKT cells expressing CD158b KIR molecule at screening had significantly superior PFS with in the PVd, which indicates that each is a predictive marker. Finally, we showed that patients with either a higher proportion of NK cells expressing activation marker NKG2D, or a lower number of CD158b expressing NK cells at cycle 3 had significantly improved PFS with the PVd arm but not with the Vd arm, which indicates the prognostic nature of these markers.

In summary, this large randomized study identified specific immunophenotypes at screening and after exposure to pomalidomide combinations, allowing for the identification of predictive and prognostic markers for favorable PFS, respectively.