The impact of COVID‐19 vaccination on the alloimmunity of transplant candidates is unknown. We report a case of positive B cell flow cytometry crossmatch in a patient waiting for second kidney transplantation, 37 days after receiving the COVID‐19 vaccine. The preliminary crossmatch, using sample collected before COVID‐19 vaccination, was negative. The antibodies to mismatched donor HLA‐DR7 were detected only with multi‐antigen beads but not with single‐antigen beads, excluding possible prozone effects in solid‐phase antibody assays. The crossmatches were positive with HLA‐DR7–positive surrogates (
n
= 2) while negative with HLA‐DR7–negative surrogates (
n
= 3), which confirms the HLA‐DR7 alloreactivity. The antigen configurations on B lymphocytes are similar to that on the multi‐antigen beads while distinct from the single‐antigen beads. HLA‐DR7 was the repeating mismatched antigen with the failing first kidney allograft. The newly emerged antibody to HLA‐DR7 probably is the consequence of bystander activation of memory response by the COVID‐19 vaccination. This case highlights the importance of verifying allo‐sensitization history and utilizing multiple assays, including cell‐based crossmatch and solid‐phase assays with multi‐antigens. COVID‐19 immunization may deserve special attention when assessing the immunological risk before and after organ transplantation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.