(756) Immunogenicity of COVID-19 Vaccination in Cardiac Transplant Recipients: 5 Months Follow-Up after the 3rd Dose

PURPOSE: Vaccination against COVID 19 has been shown to improve outcomes after transplant. There are prior reports of vaccines leading to sensitization in transplant recipients, however, little is known about the development of de novo (dn) anti-HLA antibodies (abs) after COVID-19 vaccination (COVAX). The purpose of this study was to prospectively survey immunological markers in heart transplant recipients after receiving their 3rd dose of COVAX. METHODS: Thirty-one subjects (mean 30 months post-transplant) were evaluated 1, 3and 5 months after COVAX. Single antigen bead assay for anti-HLA abs (thresholdMFI >1000), COVID-19 spike abs (threshold ≥250 U/mL) and donor/recipientcell free DNA testing (threshold ratio >.12) were performed. RESULTS: (Table 1, Fig 1): Over 5 months, 32% of subjects developed dn anti-HLA abs and 19%developed dn donor specific abs (DSA). Antibodies developed by 1 month with titers decreasing by 5 months. All sensitized subjects developed Class II antibodies, with 60% having concomitant Class I. One of four subjects with pre COVAX DSAs had a significant rise after COVAX. No significant cellular or antibody mediated rejection was seen during follow up, but 32% of subjects demonstrated a new rise in cell free DNA. We did not see a temporal relationship between intercurrent COVID infection and dn DSA during study follow up. CONCLUSION: After the 3(rd) COVAX dose, one third of subjects developed dn anti-HLA abs and one fifth dn DSAs. These preliminary findings warrant further study, especially as additional boosters are recommended.