B-cell regeneration during therapy has been considered as a strong prognostic factor in multiple myeloma (MM). However, the effects of therapy and hemodilution in bone marrow (BM) B-cell recovery have not been systematically evaluated during follow-up. MM (n = 177) and adult (≥50y) healthy donor (HD; n = 14) BM samples were studied by next-generation flow (NGF) to simultaneously assess measurable residual disease (MRD) and residual normal B-cell populations. BM hemodilution was detected in 41 out of 177 (23%) patient samples, leading to lower total B-cell, B-cell precursor (BCP) and normal plasma cell (nPC) counts. Among MM BM, decreased percentages (vs. HD) of BCP, transitional/naïve B-cell (TBC/NBC) and nPC populations were observed at diagnosis. BM BCP increased after induction therapy, whereas TBC/NBC counts remained abnormally low. At day+100 postautologous stem cell transplantation, a greater increase in BCP with recovered TBC/NBC cell numbers but persistently low memory B-cell and nPC counts were found. At the end of therapy, complete response (CR) BM samples showed higher CD19− nPC counts vs. non-CR specimens. MRD positivity was associated with higher BCP and nPC percentages. Hemodilution showed a negative impact on BM B-cell distribution. Different BM B-cell regeneration profiles are present in MM at diagnosis and after therapy with no significant association with patient outcome.

Despite recent advances in multiple myeloma (MM), the incorporation of novel agents and measurable residual disease (MRD) monitoring in low-income countries remains a challenge. Although lenalidomide maintenance (M-Len) after autologous stem cell transplantation (ASCT) has been associated with improved outcomes and MRD has refined the prognosis of complete response (CR) cases, until now, there have been no data on the benefits of these approaches in Latin America. Here, we evaluate the benefits of M-Len and MRD using next-generation flow cytometry (NGF-MRD) at Day + 100 post-ASCT (n = 53). After ASCT, responses were evaluated based on the International Myeloma Working Group criteria and NGF-MRD. MRD was positive in 60% of patients with a median progression-free survival (PFS) of 31 months vs. not reached (NR) for MRD-negative cases (p = 0.05). The patients who received M-Len continuously had a significantly better PFS and overall survival (OS) than those without M-Len (median PFS: NR vs. 29 months, p = 0.007), with progression in 11% vs. 54% of cases after a median follow-up of 34 months, respectively. In a multivariate analysis, MRD status and M-Len therapy emerged as independent predictors of PFS (median PFS of M-Len/MRD− vs. no M-Len/MRD+ of NR vs. 35 months, respectively; p = 0.01). In summary, M-Len was associated with improved survival outcomes in our real-world MM cohort in Brazil, with MRD emerging as a useful reproducible tool to identify patients at an earlier risk of relapse. The inequity in drug access remains a hurdle in countries with financial constraints, with a negative impact on MM survival.

Introduction: Several studies have shown the role of the immune system in the development of MM, but there is no systematic description of normal B-cell regeneration during treatment points. Recently, EuroFlow consortium has developed NGF panel with high sensitivity to evaluated MRD and potentially, to assess of the normal B-cell compartment of patients with MM. Aims: Here we evaluated the B cell regeneration pattern of bone marrow (BM) from patients with MM by Next Generation Flow (NGF) cytometry at diagnosis and at minimal residual disease (MRD) time points of treatment. Material and Methods: Overall 190 samples of MM patients (45% female and 55% male, median age of 65 years - 37 to 87 years, of which: 16 at diagnosis, 30 post-induction, 76 D+100, 59 maintenance/consolidation and 9 out of treatment, and 8 samples of BM healthy donor - HD (≥ 50 years). At the moment treatment, D+100 were included samples from two research centers: HCS/USAL (n=64) and HUCFF/UFRJ (n=12). Induction regimens were composed of triple protocols (PI + IMIDs + Steroids); followed by high doses of melphalan with ASCT, while patients in maintenance/consolidation followed second line treatment regimens - IP+IMIDs and/or PIs+Steroids and/or monoclonal antibodies or INF or IPs. All samples of BM were subjected to bulk cell lysis with ammonium chloride solution for >107 cell acquisition and labeled with a combination of 10 antibodies - Panel EuroFlow MM MRD.Results: Of the 174 post treatment samples, 36% presented MRD- and 64% MRD+. At diagnosis, patients exhibit a significant reduction of precursors B cells and normal plasma cells (nPC) relative to HD, probably a reflection of the occupation of their binding sites by cPC. At post-induction, there was an increase in precursors B, compared to MM patients at diagnosis, associated with a reduction of mature B-cell (transitional/naïve and memory), regardless of MRD status. Concerning the nPC compartment, a reduction was observed, relative to HD. During treatment, reduction of the tumor burden leaves these sites free for precursors B, which rapidly recover while leads to a drastic decrease in mature B cells and regeneration of the precursors to mature B-cells is slower. On the other hand, in D+100, independent of the MRD status, there was a post treatment medullary recovery, with an increase in B precursors and transitional/naïve B-cells, in contrast, with a reduction of memory B-cells. Out of treatment, we observed a recovery of precursors B, mature B-cells and increase of nPC, but the immune recovery of these nPC is not sufficient to reach the levels of a healthy individual. Conclusion: NGF emerges as an optimal approach for simultaneous assessment of the BM regeneration profile of B-cells and the MRD status. After starting therapy, MM patients re-establish the compartments of B-cell precursors and transitional/naïve B-lymphocytes; however, memory B cells and nPC do not recovery until the end of treatment. This study is a starting point for exploring the importance of the B cells of the medullary microenvironment in the MM. Its potential impact on patient outcome deserving further investigations Disclosures Puig: Takeda: Consultancy, Honoraria; Celgene: Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Research Funding. Mateos:Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; GSK: Consultancy, Membership on an entity's Board of Directors or advisory committees; GSK: Consultancy, Membership on an entity's Board of Directors or advisory committees.