Contribution of the Tumor Microenvironment to Metabolic Changes Triggering Resistance of Multiple Myeloma to Proteasome Inhibitors

Virtually all patients with multiple myeloma become unresponsive to treatment with proteasome inhibitors over time. Relapsed/refractory multiple myeloma is accompanied by the clonal evolution of myeloma cells with heterogeneous genomic aberrations, diverse proteomic and metabolic alterations, and profound changes of the bone marrow microenvironment. However, the molecular mechanisms that drive resistance to proteasome inhibitors within the context of the bone marrow microenvironment remain elusive. In this review article, we summarize the latest knowledge about the complex interaction of malignant plasma cells with its surrounding microenvironment. We discuss the pivotal role of metabolic reprograming of malignant plasma cells within the tumor microenvironment with a subsequent focus on metabolic rewiring in plasma cells upon treatment with proteasome inhibitors, driving multiple ways of adaptation to the treatment. At the same time, mutual interaction of plasma cells with the surrounding tumor microenvironment drives multiple metabolic alterations in the bone marrow. This provides a tumor-promoting environment, but at the same time may offer novel therapeutic options for the treatment of relapsed/refractory myeloma patients.

Deciphering mechanisms of immune escape to inform immunotherapeutic strategies in multiple myeloma

Multiple myeloma is an incurable cancer characterized by the uncontrolled growth of malignant plasma cells nurtured within a permissive bone marrow microenvironment. While patients mount numerous adaptive immune responses directed against their disease, emerging data demonstrate that tumor intrinsic and extrinsic mechanisms allow myeloma cells to subvert host immunosurveillance and resist current therapeutic strategies. Myeloma downregulates antigens recognized by cellular immunity and modulates the bone marrow microenvironment to promote uncontrolled tumor proliferation, apoptotic resistance, and further hamper anti-tumor immunity. Additional resistance often develops after an initial clinical response to small molecules, immune-targeting antibodies, immune checkpoint blockade or cellular immunotherapy. Profound quantitative and qualitative dysfunction of numerous immune effector cell types that confer anti-myeloma immunity further supports myelomagenesis, disease progression and the emergence of drug resistance. Identification of tumor intrinsic and extrinsic resistance mechanisms may direct the design of rationally-designed drug combinations that prevent or overcome drug resistance to improve patient survival. Here, we summarize various mechanisms of immune escape as a means to inform novel strategies that may restore and improve host anti-myeloma immunity.

Actors on the Scene: Immune Cells in the Myeloma Niche

Two mechanisms are involved in the immune escape of cancer cells: the immunoediting of tumor cells and the suppression of the immune system. Both processes have been revealed in multiple myeloma (MM). Complex interactions between tumor plasma cells and the bone marrow (BM) microenvironment contribute to generate an immunosuppressive milieu characterized by high concentration of immunosuppressive factors, loss of effective antigen presentation, effector cell dysfunction, and expansion of immunosuppressive cell populations, such as myeloid-derived suppressor cells, regulatory T cells and T cells expressing checkpoint molecules such as programmed cell death 1. Considering the great immunosuppressive impact of BM myeloma microenvironment, many strategies to overcome it and restore myeloma immunosurveillance have been elaborated. The most successful ones are combined approaches such as checkpoint inhibitors in combination with immunomodulatory drugs, anti-monoclonal antibodies, and proteasome inhibitors as well as chimeric antigen receptor (CAR) T cell therapy. How best to combine anti-MM therapies and what is the optimal timing to treat the patient are important questions to be addressed in future trials. Moreover, intratumor MM heterogeneity suggests the crucial importance of tailored therapies to identify patients who might benefit the most from immunotherapy, reaching deeper and more durable responses.

High-density neutrophils in MGUS and multiple myeloma are dysfunctional and immune-suppressive due to increased STAT3 downstream signaling

To understand neutrophil impairment in the progression from MGUS through active MM, we investigated the function of mature, high-density neutrophils (HDNs), isolated from peripheral blood. In 7 MM, 3 MGUS and 3 healthy subjects by gene expression profile, we identified a total of 551 upregulated and 343 downregulated genes in MM-HDN, involved in chemokine signaling pathway and FC-gamma receptor mediated phagocytosis conveying in the activation of STAT proteins. In a series of 60 newly diagnosed MM and 30 MGUS patients, by flow-cytometry we found that HDN from MM, and to a lesser extend MGUS, had an up-regulation of the inducible FcγRI (also known as CD64) and a down-regulation of the constitutive FcγRIIIa (also known as CD16) together with a reduced phagocytic activity and oxidative burst, associated to increased immune-suppression that could be reverted by arginase inhibitors in co-culture with lymphocytes. In 43 consecutive newly-diagnosed MM patients, who received first-line treatment based on bortezomib, thalidomide and dexamethasone, high CD64 could identify at diagnosis patients with inferior median overall survival (39.5 versus 86.7 months, p = 0.04). Thus, HDNs are significantly different among healthy, MGUS and MM subjects. In both MGUS and MM neutrophils may play a role in supporting both the increased susceptibility to infection and the immunological dysfunction that leads to tumor progression.

Intracytoplasmic Lysozyme in Malignant Hematologic Disorders: An Immunoperoxidase Study

Intracytoplasmic lysozynie was studied by the peroxidase antiperoxidase (PAP) and protein A-peroxidase methods in 130 cases of various myeloproliferative and lymphoproliferative disorders and 21 lymph nodes and bone marrow metastases from solid primary tumors. This marker, which can be identified in formalin or Zenker-fixed tissues, as well as in peripheral blood and bone marrow smears, proved useful to distinguish malignant myeloid and histiocytic tumors from malignant lymphoid and undifferentiated epithelial metastases. The diagnostic application of these findings are discussed.

Role of Immunotherapy in Targeting the Bone Marrow Microenvironment in Multiple Myeloma: An Evolving Therapeutic Strategy

Multiple myeloma (referred to henceforth as myeloma) is a B-cell malignancy characterized by unregulated growth of plasma cells in the bone marrow. The treatment paradigm for myeloma underwent significant evolution in the last decade, with an improved understanding of the pathogenesis of the disease as well as the development of therapeutic agents that target not only the tumor cells but also their microenvironment. Despite these therapeutic advances, the prognosis of patients with relapsed or refractory myeloma remains poor. Accordingly, a need exists for new therapeutic avenues that can overcome resistance to current therapies and improve survival outcomes. In addition, myeloma is associated with progressive immune dysregulation, with defects in T-cell immunity, natural killer cell function, and the antigen-presenting capacity of dendritic cells, resulting in a tumor microenvironment that promotes disease tolerance and progression. Together, the immunosuppressive microenvironment and oncogenic mutations activate signaling networks that promote myeloma cell survival. Immunotherapy incorporates novel treatment options (e.g., monoclonal antibodies, antibody-drug conjugates, chimeric antigen receptor T-cell therapy, immune checkpoint inhibitors, bispecific antibodies, and tumor vaccines) either alone or in combination with existing lines of therapies (e.g., immunomodulatory agents, proteasome inhibitors, and histone deacetylase inhibitors) to enhance the host anti myeloma immunity within the bone marrow microenvironment and improve clinical response. Following the U.S. Food and Drug Administration approval of daratumumab and elotuzumab in 2015, more immunotherapeutic agents are expected to be become available as valuable treatment options in the near future. This review provides a basic understanding of the role of immunotherapy in modulating the bone marrow tumor microenvironment and its role in the treatment of myeloma. Clinical efficacy and safety of recently approved therapeutic monoclonal antibodies (daratumumab, elotuzumab) are discussed, along with the therapeutic potential of emerging immunotherapies (antibody-drug conjugates, chimeric antigen receptor T-cell therapy, tumor vaccines, and immune checkpoint inhibitors).

Immune responses in multiple myeloma: role of the natural immune surveillance and potential of immunotherapies

Multiple myeloma (MM) is a tumor of terminally differentiated B cells that arises in the bone marrow. Immune interactions appear as key determinants of MM progression. While myeloid cells foster myeloma-promoting inflammation, Natural Killer cells and T lymphocytes mediate protective anti-myeloma responses. The profound immune deregulation occurring in MM patients may be involved in the transition from a premalignant to a malignant stage of the disease. In the last decades, the advent of stem cell transplantation and new therapeutic agents including proteasome inhibitors and immunoregulatory drugs has dramatically improved patient outcomes, suggesting potentially key roles for innate and adaptive immunity in disease control. Nevertheless, MM remains largely incurable for the vast majority of patients. A better understanding of the complex interplay between myeloma cells and their immune environment should pave the way for designing better immunotherapies with the potential of very long term disease control. Here, we review the immunological microenvironment in myeloma. We discuss the role of naturally arising anti-myeloma immune responses and their potential corruption in MM patients. Finally, we detail the numerous promising immune-targeting strategies approved or in clinical trials for the treatment of MM.

Neutrophil and lymphocyte function in patients with diabetes mellitus

Neutrophil granulocyte chemotaxis and intraneutrophilic and plasma levels of lysozyme as well as the number of T and B lymphocytes and lymphocyte transformation in vitro on stimulation with mitogens and microbial antigens were studied in four groups of patients with diabetes mellitus (DM). Twelve patients with insulin-dependent diabetes mellitus (IDDM) and ketoacidosis and 4 patients with non-insulin-dependent diabetes mellitus were studied at the time of diagnosis and before and after start of treatment. Ten patients with IDDM of less than 10 years' duration which had been difficult to regulate well and 10 patients with IDDM well regulated for more than 20 years were studied at their regular outpatient visits. Apart from a slight increase in plasma lysozyme in group 1 from the first to the second examination, we found no differences between diabetics and healthy control persons. It is concluded that if patients with DM are more susceptible to infections, it is probably caused by elements of neutrophil or lymphocyte function not examined in this study or by factors unrelated to immunity.

Invasive aspergillosis as an opportunistic infection in nonallografted patients with multiple myeloma: a European Organization for Research and Treatment of Cancer/ Invasive Fungal Infections Cooperative Group and the Intergroupe Français du Myélome

We report the occurrence of invasive aspergillosis (IA) in nonallografted patients with multiple myeloma (MM) who were treated at hematology or oncology centers in Europe during 1984-1996. Thirty-one cases met the criteria for definitive (21 [68%]) or probable (10 [32%]) IA. Of these cases, 23 (74%) were reported during 1992-1996. Twenty-nine cases (94%) occurred in patients with Durie-Salmon stage 3 MM, and 2 (6%) occurred in patients with Durie-Salmon stage 2 MM. The median time between MM and IA diagnoses was 8 months (range, 1-75 months). Sixteen patients (51%) had a neutrophil count </=500/mm3 for a median duration of 19 days (range, 10-37 days). Fourteen patients (45%) had recently received corticosteroid therapy, and 11 (36%), high doses of melphalan. Twenty-eight patients had primary pulmonary IA, and 3 had primary sinus IA. Forty-five percent of patients were considered to have died of IA. IA occurs as a potentially lethal opportunistic infection in intensively treated nonallografted patients with myeloma.

Elevated plasma lysozyme in Hodgkin's disease. An indicator of increased macrophage activity?

Plasma lysozyme levels were studied in 42 patients with Hodgkin's disease and were found significantly increased. Plasma lysozyme varied with the stage of the disease and with symptoms, but did not correlate with the histological subtype or with blood neutrophil and monocyte counts. Serial measurements in four patients on MOPP treatment showed a rapid decrease following treatment. The increased plasma lysozyme in Hodgkin's disease stems most likely from the macrophage system, either because the macrophages are hyperactive and/or because the malignant cell in Hodgkin's disease is of macrophage origin.