Bispecific antibodies in solid tumors: An Italian Association of Medical Oncology (AIOM) multidisciplinary perspective on immunology and vaccination.

The clinical use of bispecific antibodies (BsAbs) in solid tumors is rapidly expanding, yet evidence-based guidance on infection prevention and vaccination in this setting remains limited. We performed a critical narrative review integrating immunological mechanisms, available clinical data, and multidisciplinary expert opinion to inform vaccination strategies for patients with solid tumours treated with BsAbs. BsAbs can induce transient or sustained immune perturbations, including T-cell hyperactivation, lymphocyte redistribution, functional exhaustion, cytokine-mediated immune dysregulation, and, in selected contexts, B-cell impairment. These effects may reduce vaccine-induced humoral and cellular responses and increase vulnerability to infectious complications. Optimization of vaccination status before BsAb initiation is therefore advisable, as pre-treatment immunisation is more likely to achieve effective immune priming. Inactivated vaccines, including influenza, pneumococcal, SARS-CoV-2, hepatitis B (HBV), and recombinant herpes zoster vaccines, can be administered before or, when necessary, during therapy, whereas live attenuated vaccines should be avoided during active treatment. Vaccination timing during BsAb therapy should be individualised, taking into account the treatment schedule and immune recovery. Current recommendations rely largely on indirect evidence from haematological malignancies and other T-cell redirecting therapies. These considerations are essential to support treatment continuity, reduce preventable morbidity, and guide future prospective studies in patients with solid tumors treated with BsAbs.