Niels van de Donk, MD, PhD, VU University Medical Center, Amsterdam, Netherlands, discusses mechanisms of resistance to immunotherapy in patients with multiple myeloma. Heterogenous subclones, a polar microenvironment, and stromal cells in the bone marrow can contribute to drug resistance. The heterogeneity of multiple myeloma means every subclone cannot be targeted, and an increase of immunosuppressor cells in a polar microenvironment can impair immunotherapy. Stromal cells in the bone marrow can also protect myeloma cells against antibodies such as daratumumab. More therapy-specific mechanisms of resistance also exist in the context of CD38 antibodies, and B-cell maturation antigen (BCMA)-targeting antibodies. This interview took place during the 7th World Congress on Controversies in Multiple Myeloma (COMy), 2021.