BACKGROUND: : Little is known on the immune response to SARS-CoV-2 vaccination in recipients of allogeneic hematopoietic stem cell transplantation (Allo-HSCT). However, a few studies have reported that adequate protection could be provided to this population. OBJECTIVE(S): : The purpose of this study was to evaluate which factors can predict the efficacy of SARS-CoV-2 vaccination in these specifically immunosuppressed patients. STUDY DESIGN: : Specific anti Spike (S) antibody responses were assessed in a cohort of 117 Allo-HSCT recipients after two injections of BNT162b2 mRNA SARS-CoV-2 vaccine (V1 and V2). Factors considered liable to influence the antibody response and analyzed in this series were the interval between Allo-HSCT and V1, donor source, recipient and donor age, current immunosuppressive/chemotherapy (I/C) treatment and levels of CD4(+)and CD8(+) T-cells, B-cells and NK-cells at the time of V1. RESULTS: : Overall, the S-antibody response rate, evaluated at a median of 35 days after V2, was 82.9% for the entire cohort, with 71 patients (61%) reaching the highest titre. In univariate analysis, a lower pre-V1 median total lymphocyte count, lower CD4+ T-cell and B-cell counts as well as ongoing I/C treatment and a haploidentical donor were characteristic of non-humoral responders. However, multiparameter analysis showed that B-cell aplasia was the only factor predicting the absence of a specific immune response (Odd Ratio 0.01, 95%CI [0.00 – 0.10], p <10(−3)). Indeed, the rate of humoral response was 9.1% in patients with B-cell aplasia, vs 95.9% in patients with a B-cell count higher than 0 (p<10(−9)). CONCLUSION(S): : These results advocate for the prescription of anti-SARS-CoV-2 vaccination in Allo-HSCT recipients as early as peripheral B-cell levels can be detected, suggesting also a need for a close monitoring of B-cell reconstitution after Allo-HSCT.
B-cell aplasia is the most powerful predictive marker for poor humoral response after BNT162b2 mRNA SARS-CoV-2 vaccines in recipients of allogeneic hematopoietic stem cell transplantation