CD40LG and infection: To assess the capacity of de novo recruitment of naive T cells (excluding cross-reactive clones targeting the S-II part) we compared S-I-specific CD40L+4-1BB+ CD4+ T cells of donors undergoing heterologous AZ-BNT-BNT with homologous BNT-BNT-BNT vaccination and additionally to natural infection after BNT-BNT vaccination (BNT-BNT-INF) by droplet scRNA-seq three months post last antigen encounter.