Title: Defining Immune Cell Profiles and their Role in Predicting Therapeutic Response in Multiple Myeloma
Description: Multiple myeloma (MM) is a plasma cell malignancy that presents with bone marrow plasmacytosis, monoclonal paraproteinemia, and associated end organ damage, including anemia, renal dysfunction and bone disease, amongst others (23, 38, 39). The growth and survival of myeloma cells is driven by inherent genomic perturbations as well as influence of the bone marrow microenvironment (17). Numerous constituents of the bone marrow (BM) microenvironment, including immune cells, are affected both directly and indirectly by MM cells, leading to immune cell dysfunction. The most prominent immune deficiency lies in the humoral immune response, which manifests as low uninvolved immunoglobulin (UIg) levels in serum.^

We hypothesize that observed low UIg levels and immune dysfunction are due to alterations in the developmental stages of the B cell-compartment in MM bone marrow and associated T and B cell subset alterations; and that B and T cell subset analysis can aid in understanding the immune abnormalities in MM. To address this hypothesis, we utilized multicolor flow cytometry to study the B cell compartment in BM samples from normal donor, smoldering, newly-diagnosed and relapsed MM patients, and to discern immune cell-subsets we utilized the PBMCs collected from newly-diagnosed MM patients enrolled in the DFCI-IFM 10-106 study (2). Patients in this study received state-of-the-art combination therapy with lenalidomide (immunomodulatory agent), bortezomib (proteasome inhibitor) and dexamethasone (steroid) (RVD).^

We planned to assess how B cell subsets and imbalances in the T cell-compartment contribute to the framework of the disease, and to distinguish immune parameters that can be useful to predict outcome following RVD treatment. Our analysis of BM samples showed that pro-B cells with renewal capacity were lower in the BM of smoldering myeloma (SMM) (12 ±3.1; p<0.05), relapsed/refractory myeloma (RRMM) (3.1±1.6; p<0.05) and MM (19.2±4.9) compared to normal BM samples (NBM) (25.1±3) suggesting that aberrations in B cell development may contribute to suppressed UIg in MM. Next, we evaluated PBMCs from patients enrolled on the 10-106 study and achieved complete remission (CR) (N=13) with those not achieving CR (N=18) following therapy. We observed significant differences in patients achieving CR versus those not achieving CR in B2 cells (63.6±4.6l vs. 42.1±3.9, respectively; p<0.05), CD3 cells (61±2.7 vs. 38.9±5.7, respectively; p<0.05); CD4 cells (63.4±3.7 vs.^

37.1±5.5, respectively; p<0.05); Th2 cells (73±6.1 vs. 47.7±5.9, respectively; p<0.05), and PD-1 expressing CD8 T cells (63.2±8 vs. 39.5±6.1, respectively; p<0.05) and decrease in Th1 cells (23.3±5.6 vs. 46.3±5.4, respectively). These differences were also observed when absolute numbers of each cell type were computed. Our preliminary results suggest the potential of these markers measured at diagnosis to predict CR in MM patients following RVD treatment. This data warrants a larger study in this patient population, to decipher how B cell function is affected in MM, and what subsequent effects occur on cell-mediated immunity controlled by T helper cells.