P-066: Effect of Daratumumab (DARA), Cyclophosphamide (C), T Halidomide (T) and Dexamethasone (D) combination of Lymphocyte populations of transplant eligible newly diagnosed Multiple Myeloma patients

Background The CTD combination have both an immunomodulatory and immunosuppressive activity on multiple myeloma (MM) patients (pts) treatment. Dara, an antiCD38-antibody, effect on the immune system was already described, but few studies analyzed specifically lymphocytes population. We hypothesized that Dara-CTD combination could impact on lymphocytes subsets during treatment. The primary endpoint was to quantify subpopulations of lymphocytes in TE NDMM pts during Dara-CTD treatment phases. Secondary endpoint was to describe B cells subsets during the same phases. Methods Peripheral blood of 14 pts at four different time points was collected: at diagnose, after four cycles of Dara-CTD, after two consolidation cycles post ASCT and before maintenance therapy. Flow cytometry was used to detect lymphocyte surface molecules including CD3, CD4, CD5, CD8, CD16, CD19, CD20, CD38, CD45 and CD56 in the scatter plot. Results B cells were isolated and subpopulations (naive B cells, non-class switched memory B cells, class switched memory B cells, IgD-CD27- memory B cells and plasmablasts) were detected by CD20, CD24, CD27, CD38, CD45 and IgD. The median of T, B and NK lymphocytes subsets at diagnosis were 1153×103/µL, 205×103/µL and 284×103/µL cells, respectively. After 4 cycles of Dara-CTD the median of T, B and NK cells dropped significantly to 889×103/µL, 12×103/µL and 11×103/µL, respectively (p Conclusions This preliminary data suggest that Dara-CTD induces general lymphopenia on (T, B and NK) populations after induction phase. It was identified that T cells recovery was complete after two consolidations cycles while the recovery of B and NK cells was slowly but continuously.