PF578 THE BONE MARROW MICROENVIRONMENT OF MULTIPLE MYELOMA PROMOTES MYELOMA RELATED ANEMIA BY SUPPRESSING THE DIFFERENTIATION OF HEMATOPOIETIC STEM CELLS

Abstract

Background:Multiple myeloma (MM) is a hematopoietic malignancy characterized by monoclonal plasma cells infiltrating the bone marrow thereby leading to anemia and lytic bone lesions. MM patients always manifest severe anemia, which may significantly contribute to the increase of patient mortality.Aims:The mechanisms underlying myeloma related anemia have not been fully elucidated. Research in the last decade has shown that hematopoietic stem/progenitor cells (HSPCs) differentiation are modulated by a complex multicellular microenvironment in the bone marrow. We tend to verify that the MM microenvironment play a pivotal role in their hematopoietic differentiation.Methods:We evaluated 776 patients with newly diagnosed MM (NDMM) in our hospital. Bone marrow samples from 50 patients with NDMM and 10 bone marrow controls from healthy donors were analyzed by flow cytometry and were assessed by CFC assays.Results:The clinical analysis showed that there were 80% (620/776) MM patients with anemia at diagnosed and more than 60% patients had moderate or severe anemia. These data also indicate that anemia is correlated with bone lesions in the MM patients. The flow cytometry was utilized to detect the CD138+ cells and CD34+ HSPCs in the same patient. We found that the degree of anemia was positively correlated with their number of CD138+ cells. The number of CD34+ HSPCs in the bone marrow was negatively correlated with the number of CD138+ cells (r = −0.526, P = 0.0082). The data indicated that the percentage of HSPCs in NDMM patients was significantly lower than that of normal controls (P < 0.001). We did not find the variation of HSC (Lin‐CD34+CD38‐) number in MM microenvironment. However, the ratio of HPC (Lin‐CD34+CD38+) significantly decreased (P < 0.001). And the proportion of downstream megakaryocyte‐erythrocyte progenitors (MEP) of the HSPCs was decreased significantly (P < 0.0001) in MM patients. The proportion of granulocyte‐macrophage progenitors (GMP) was increased in MM patients compared to healthy donors (P < 0.01). The ability of colony forming of CD34+ cells from MM patients was significantly suppressed than that of normal controls, especially in the forming of BFU‐E (P < 0.01).To explore the extrinsic reasons for the suppression of erythropoiesis differentiation, we performed a CFC assay by co‐culture CD34+ cells from healthy donors with BM plasma of MM patients. It is as expected that the patient's bone marrow plasma severely inhibited the formation of BFU‐Es. The further detect with ELISA showed that the expression ofTGFβ, IL‐1β, CCL3 in bone marrow plasma of MM patients was increased (P < 0.01). Our RNA‐seq data indicated that the expression of transcription factors, GATA1 and KLF1 was significantly decreased in MM CD34+ cells.Summary/Conclusion:Bone marrow microenvironment of multiple myeloma suppresses hematopoietic stem cells differentiation and promotes the myeloma associated anemia. High level of tumor burden is positively correlated with the degree of hemoglobin reduction. The bone marrow microenvironment with high level of TGFβ, IL‐1β and CCL3 might be the important reasons for anemia in MM patients. The transcription factors mediated in the erythropoiesis were down regulated by MM microenvironment.