Abstract
Recipients after hematopoietic stem cell transplantation (HSCT) or chimeric antigen receptor T-cell (CAR-T) therapy are at increased risk for unfavorable outcomes after SARS-CoV-2 infection. The efficacy of COVID-19 vaccines remains undetermined in this vulnerable population, we therefore conducted a pooled analysis to evaluate the immune response after vaccination. A total of 46 studies were finally included, comprising 4757 HSCT and 174 CAR-T recipients. Our results indicated that HSCT and CAR-T recipients had an attenuated immune response to SARS-CoV-2 vaccination compared with healthy individuals, while time interval between transplant and vaccination, immunosuppressive therapy (IST) and lymphocyte counts at vaccination significantly affected the humoral response in HSCT recipients. In addition, seroconversion was significantly higher in patients with BCMA-based CAR-T than those with CD19-based CAR-T. Thus, an adapted vaccination strategy for HSCT and CAR-T recipients may be required, and further research on the effect of a booster dose of COVID-19 vaccine and the role of cellular response after vaccination is warranted.