Memory B cell response to SARS-CoV-2 vaccination in people with heart and lung transplantation: Identification of associated clinical factors.

Solid organ transplant recipients (SOT) have shown impaired immune responses to infection and vaccination. Here, serological data collected in heart and lung transplant recipients after vaccination against SARS-CoV-2 were analyzed using dimensionality reduction, clustering algorithms and statistical methods to define factors associated with immune responsiveness. Transplanted organ type, bivalent Omicron-adapted vaccine administration, and immunosuppressive regimen were associated with distinct serological profiles. These factors were associated with significant differences in the RBD-specific memory B cell (MBC) responses. Indeed, a lower frequency of MBC recognizing both wild-type and Omicron BA.2 RBD was detected in lung versus heart transplant recipients. Administration of the bivalent Omicron-adapted fifth dose was associated with the modulation of RBD-specific MBC phenotypes, and the mycophenolate mofetil (MMF) treatment was associated with significantly lower humoral and MBC responses in heart transplant recipients. This work identifies factors associated with vaccine-induced immune responses in SOT recipients, useful to inform tailored vaccination strategies.