Normalization of the Immunological Microenvironment and Sustained Minimal Residual Disease Negativity: Do We Need Both for Long-Term Control of Multiple Myeloma?

Over the past two decades, the treatment landscape for multiple myeloma (MM) has progressed significantly, with the introduction of several new drug classes that have greatly improved patient outcomes. At present, it is well known how the bone marrow (BM) microenvironment (ME) exerts an immunosuppressive action leading to an exhaustion of the immune system cells and promoting the proliferation and sustenance of tumor plasma cells. Therefore, having drugs that can reconstitute a healthy BM ME can improve results in MM patients. Recent findings clearly demonstrated that achieving minimal residual disease (MRD) negativity and sustaining MRD negativity over time play a pivotal prognostic role. However, despite the achievement of MRD negativity, patients may still relapse. The understanding of immunologic changes in the BM ME during treatment, complemented by a deeper knowledge of plasma cell genomics and biology, will be critical to develop future therapies to sustain MRD negativity over time and possibly achieve an operational cure. In this review, we focus on the components of the BM ME and their role in MM, on the prognostic significance of MRD negativity and, finally, on the relative contribution of tumor plasma cell biology and BM ME to long-term disease control.