Evaluation of Multiple Myeloma Minimal Residual Disease by using Next Generation Flow in patients undergoing Daratumumab consolidation therapy

Multiple Myeloma (MM) is a Plasma Cells (PCs) malignancy characterized by the uncontrolled proliferation of pathologic PCs in the Bone Marrow (BM) and, sometimes, extra-medullary sites. Myeloma PCs secrete a monoclonal nonfunctional immunoglobulin (M protein) whose accumulation causes the typical clinical symptoms of the disease, such as hypercalcemia, renal impairment, anemia and bone lesions (i.e., CRAB criteria). In the recent years, the introduction of new drugs has improved Patients Free Survival (PFS) and Overall Survival (OS). For instance, Daratumumab (Dara) is an anti-CD38 monoclonal antibody that, binding to the overexpressed CD38 receptor on PCs, may induce death of myeloma cells via several Fc-dependent mechanisms, including Antibody-Dependent Cell-mediated Cytotoxicity (ADCC), Antibody-Dependent Cellular Phagocytosis (ADCP), and Complement-Dependent Cytotoxicity (CDC), and plays an immunomodulatory effect via withdrawal of the CD38-expressing immune suppressor cells. Dara efficacy has been demonstrated in several studies, in combination with other drugs, as induction therapy or for the treatment of relapsed MM patients. However, in many cases MM patients may still relapse or develop resistance to treatment regimens, leading to the necessity of better and higher-sensitive techniques to monitor Minimal Residual Disease (MRD) and discriminate patients at risk for relapsing. In this context, Next Generation Flow (NGF) is a high-standardized and sensitive technique that, in a rapid and low-cost way, permits to monitor MM MRD and obtain a sensitivity of 10-5, necessary to define MRD negativity. Starting from December 2018, a pilot experimental study has been set up at the Hematology Unit of Policlinico Le Scotte in Siena, with the aim to evaluate Daratumumab efficacy as a consolidation therapy in 50 MM patients in Very Good Partial Response (VGPR). The MRD of the enrolled MM patients was evaluated by NGF at the time of enrollment, and then at 2 months of treatment, and every 6 months up to 2 years. The aims of my research project are: 1) to confirm that NGF is a high specific technique that permits nowadays to discriminate the MRD status of MM patients after an initial induction treatment; 2) to evaluate Daratumumab efficacy as consolidation therapy, in particular, to determine MRD negativity at time 6 months, which represent the first endpoint of the pilot study; 3) to understand Daratumumab role in controlling the disease and prolonging Overall Survival Rate and Progression-Free Survival of MM patients. A total of 47 MM patients in VGPR have been enrolled up until now. Comparing the response of 39/47 (83%) MM patients who reached the first endpoint of 6 months (mos) of Dara treatment, we observed that 12/39 (31%) achieved MRD negativity, of which 8/12 (67%) were “early responders” and could obtain MRD negative status already at 2 months of treatment, while the other 4/12 (33%) achieved MRD negativity just at 6 months. 29/47 (62%), 19/47 (40%) and 13/47 (28%) patients have been evaluated at the subsequent timepoints of 12, 18 and 24 months respectively, with 2/8 (25%) of the “early responders” patients, negative since 2 mos, persisting in MRD negative status. The high heterogeneity of response we observed needs to be correlated first of all to type of treatment received by MM patients before starting Dara, as the study confirms that undergoing at least one Autologous Stem Cell Transplantation (ASCT) can help patients reducing the pathogenicity of MM and achieving a deeper response with respect to patients not receiving an ASCT; cytogenetic risk correlations, instead, need a larger cohort of patients and/or comparison with other treatment regimens. Lastly, by looking at the percentage of clonal PCs vs normal PCs in those patients who maintain a MRD positive status, we observed a decrease of pathologic MM PCs during Dara treatment, and a tendency to “stabilize” with a low percentage at longer timepoints from Dara treatment, as they could be maintained under control and persist into MM patients without causing relapse. These results demonstrate that Daratumumab is effective as consolidation therapy in MM patients in VGPR, as it induces MRD negativity in some patients and could help “checkmate” pathologic plasma cells, that may persist in MRD positive patients but with a very low tumor burden. Flow MRD negativity should be followed in the next years to better clarify which is the percentage of patients who could be cured or long survivors. The persistence of residual monoclonal plasma cells may be also related to other mechanisms, correlated to immunity of myeloma patients or to the microenvironment, who may help keeping in truck the disease, since myeloma pathogenesis is strictly linked to both reduction of immunity and exploitation of BM microenvironment for the growing of tumor cells. Further future investigations may help elucidate mechanisms underlying responses to therapy in myeloma patients, especially those that are treated with monoclonal antibodies, and find a way to ameliorate remission rate and Progression Free Survival.