Mechanisms of resistance to bispecific antibodies in multiple myeloma. Immunosuppressive tumor microenvironment, reduced T cell fitness, and tumor-intrinsic mechanisms can contribute to multiple myeloma resistance to BsAb. BMPC, bone marrow plasma cells; CTLA-4, cytotoxic T-lymphocyte associated protein 4; LAG-3, lymphocyte activation gene-3; MHC, major histocompatibility complex; PD-1, programmed cell death protein 1; TCR, T cell receptor; TIGIT, T cell immunoreceptor with Ig and ITIM domains; TIM-3, T cell immunoglobulin domain and mucin domain-3; Treg, regulatory T cells.