Chimeric antigen receptor-modified T (CAR-T) cell therapies are gaining wider use in relapsed and refractory malignancies. However, data on vaccination in this population is lacking. We evaluated T cell responses in an established cohort of CAR-T recipients and healthy controls before and after 2019 to 2020 influenza vaccination. Peripheral blood mononuclear cells were isolated from healthy controls and patients who received the 2019 to 2020 influenza vaccine pre- or post-CD19, CD20, or B cell maturation antigen CAR-T. T cells were expanded in vitro for 10 days with peptide libraries for hemagglutinin (HA) and nucleoprotein from the 2019 to 2020 vaccine influenza A strains and analyzed by flow cytometry following interferon-γ/tumor necrosis factor-α (IFNγ/TNFα) intracellular staining. Antibody response was evaluated by a hemagglutination inhibition assay. Twenty-nine participants, including eight immunocompetent adults, seven pre-CAR-T, and 14 post-CAR-T patients, were evaluated. IFNγ