Why antibody isotype matters for immunotherapy.

Monoclonal antibodies (mAbs), engineered to recognize disease-associated antigens, are central to cancer immunotherapy due to their ability to block or eliminate malignant cells by engaging immune effector mechanisms. Yet many tumors evade or suppress these responses, limiting durable clinical benefit and highlighting the need to optimize antibody-based strategies. A critical determinant of mAb activity is antibody isotype, which governs interactions with Fc receptors, complement pathways, and immune effector cells. While most approved therapeutics employ immunoglobulin G1 (IgG1) for its robust immune-stimulating capacity, evidence suggests that context-dependent isotype selection could improve efficacy. Here, we review the structural and functional properties of human IgG and IgA subclasses, with a focus on anti-CD20 rituximab in two- and three-dimensional models of human B-cell lymphoma. We further discuss how antigen density, tumor architecture, and host variables influence antibody-mediated effector functions. Together, these considerations highlight opportunities to refine antibody isotype selection for more individualized cancer immunotherapy.