P-067: High dimensional CyTOF analysis of the immune system of multiple myeloma patients with different responses to lenalidomide maintenance

Background In this phase 2 study patients received 3 cycles of RVD (lenalidomide, bortezomib and dexamethasone) followed by autologous stem cell transplantation (ASCT) and lenalidomide maintenance. We evaluated the bone marrow (BM) immune profile with CyTOF (cytometry by time-of-flight) at treatment start and during lenalidomide maintenance focusing on two different response groups: good and poor responders at pre- and post-treatment phases. Our hypothesis was that there could be distinct differences in immune cell profiles between these groups, especially in T and NK cell subsets and exhausted T-cells. Methods Twenty-six patients were included in this study, 18 from this trial. BM samples were collected from all 18 patients at diagnosis, from 11 the 1st sample when achieved good response during maintenance after a median of 21 (6-46) months and the 2nd sample if good response was maintained after a median of 56 (45-67) months and from 5 patients at relapse after a median of 6 (2-23) months. Patients in good response cohort (n=11) had progression-free survival (PFS) > 5 years. For comparison we included 4 BM samples, taken at good response after ASCT from MM patients not exposed to lenalidomide and 4 BM samples collected from age-matched, healthy donors. Results With a median follow-up of 81 (13-97) months the median PFS was not reached in the good response cohort and was less than 18 months in the poor response cohort. CyTOF analysis revealed distinct good (GR) and poor responder’s (PR) immune signatures at baseline level. GR, baseline group has shifted phenotype of T cells toward the CD8 T cells, expressing markers, attributed to the cytotoxicity (CD45RA, CD57), as well as having slightly higher abundance of CD8 TE and lower abundance of CD8 naive T cells. Total T cell amounts were significantly higher in good responders. Increased expression of CD56, CD57, and CD16 were also seen on NK cells in good responders at the baseline, indicating both maturation and cytotoxic potential of NKs. In contrast, a significant decrease of CD56 and CD16 expression suggesting reduced cytotoxic potential and increase of CD57 were seen on NKs in poor responders, baseline indicating senescence status a phenotype associated with exhaustion. Treatment stimulates the expression of cytotoxic/effector-like phenotype on T cells which is confirmed by the significantly increased amounts of CD4 and CD8 effector memory cells, with the respective decrease of naive cells. Conclusions Patients responded to the treatment, have higher effector/cytotoxic cells, expressing higher levels of CD57 and/or CD45RA for T cells, and CD57, CD16, and CD56 for NK cells. Additionally, those patients have less degree of tumor burden as well as decreased expression of chemokine receptors (CCR7, CCR6, CXCR4, CXCR3, and CXCR5). Good responders showed the increase in effector memory CD4 and CD8 subsets of T cells abundance, indicating even the higher cytotoxic effect of immune system.