Memory Immunity Against COVID-19: A Less Effective Response in Organ Transplant Recipients?

Vaccination against COVID-19 has transformed the fight against the pandemic. However, the immune response to vaccination is not uniform across all individuals. Solid organ transplant recipients are among the high-risk groups for severe COVID-19 due to their weakened immune systems, compromised by immunosuppressive medications required to prevent graft rejection. This study examines the role of SARS-CoV-2-specific memory B cells in post-vaccination immunity, assessing their capacity to induce a protective response in this vulnerable population.

The study analyzed immune responses in 148 organ transplant recipients and 32 immunocompetent individuals who received multiple booster doses. Concurrently, a randomized controlled trial (RCT) was conducted with 25 transplant patients who had not developed neutralizing antibodies (NAb) after three vaccine doses. Two immunosuppressive strategies were compared:

• Standard exposure ;
• Reduced exposure to calcineurin inhibitors.

The primary evaluation criteria were SARS-CoV-2-specific NAb levels and memory B and T cell responses at different times post-vaccination. 

The results of this study indicated that:

• Transplant recipients show a weaker and delayed memory immune response (after the fourth dose) compared to immunocompetent individuals;

• SARS-CoV-2-specific memory B cells are strongly correlated with neutralizing antibody levels;

• SARS-CoV-2-specific memory B cells and IL-2-producing T cells serve as strong predictive markers for seroconversion and protection against severe COVID-19 in transplant recipients;

• Shifting from a standard to a reduced immunosuppressive strategy supports a more robust and faster immune response after the fourth vaccine dose.