Mechanisms of Resistance to Novel Immunotherapies in B-Cell Lymphomas: Focus on CAR T and Bispecific Antibodies

Treatment paradigms for B-cell lymphomas have evolved significantly in the last decades. Nevertheless, the widespread clinical use of immunotherapy has demonstrated that it invariably leads to the development of resistance. This review outlines the underlying molecular mechanisms of resistance associated with emerging immunotherapeutic strategies, including Chimeric Antigen Receptor (CAR) T cell therapy and bispecific antibodies (BsAbs). In high-grade B-cell lymphomas, nearly 50% of patients progress following CAR T treatment due to host-related factors affecting CAR T cell proliferation and persistence, as well as tumor-intrinsic factors, such as loss of CD19 epitope expression, trogocytosis, and other genomic alterations (e.g., <i>CD19</i> mutations, chromothripsis, APOBEC mutational activity, and deletions of <i>RHOA</i>). Additional genomic and epigenetic events, including mutations, alternative splicing of <i>CD19</i>, and aberrant promoter methylation, further contribute to resistance. BsAbs, representing an off-the-shelf T-cell-redirecting strategy, have recently shown promising single-agent efficacy with a manageable toxicity profile, predominantly characterized by T cell overactivation syndromes. Similarly to CAR T cell therapy, BsAb resistance arises through diverse mechanisms, such as antigen loss, T cell dysfunction (exhaustion and regulatory T cell activation), tumor-intrinsic alterations (e.g., <i>TP53</i> mutations and <i>MYC</i> amplifications), and immunosuppressive influences from the tumor microenvironment. These findings underscore the complexity of immune evasion in B-cell lymphomas and highlight the ongoing need to optimize immunotherapeutic strategies and develop combination approaches to overcome resistance.