SARS-CoV-2 vaccine response in CAR T-cell therapy recipients: A systematic review and preliminary observations

Evolving data suggest that SARS-CoV-2 vaccine responses are blunted in allogeneic hematopoeitic cell transplant (HCT) recipients. Responses to the vaccine in chimeric antigen receptor T-cell (CAR-T) therapy are unknown and are likely to be even more diminished. We manually searched vital databases and identified 5 studies that have so far reported COVID-19 vaccine response in a total of 70 CAR-T recipients. The cumulative humoral response rate across all 5 studies was 31%. However, the results are not generalizable due to non-standardized units of humoral response measurement and a lack of external validation. Heterogeneity existed in studies regarding the timing of vaccination post-CAR-T, intervals between the vaccine doses, platforms of response assessment, vaccine platforms, and pre-vaccine immune status. CAR-T-related factors that independently impact vaccine response to prevent COVID-19 have further been reviewed. We conclude that the results must be interpreted with caution given the limitations of small sample sizes, differences in immunoassays, lack of standard definitions and clinical correlates of SARS-CoV-2 immune response, and lack of cellular responses. Until large-scale, homogenous prospective data become available, these preliminary observations will help transplant and infectious disease clinicians with their decision-making while providing care to this profoundly immunosuppressed cohort of patients.