Effect of SARS-CoV-2 mRNA vaccine booster in serologically negative patients with thymic epithelial tumors.

Abstract

e20651 Background: Thymic epithelial tumors (TETs) are rare malignancies associated with humoral and cell-mediated immunity dysregulations. Anti-syndrome coronavirus type 2 (SARS-CoV-2) vaccine is effective at preventing COVID-19 morbidity and mortality. We have previously shown an impaired seroconversion after 1st and 2nd anti-SARS-CoV-2 vaccine doses in TETs patients. The aim of this study was to evaluate the seroconversion rate after the third vaccine dose (booster) in TET patients who remained serologically negative after full vaccination. Methods: Starting from November 2021 to March 2022, consecutive TET patients found to be serologically negative after two SARS-Cov-2 mRNA vaccine (BNT162b2 by Pfizer-BioNTech) doses were enrolled. SARS-CoV-2 spike-binding IgG antibody serological levels were centrally analyzed by chemiluminescent immunoassay (CLIA) at two different time-points: T0 and T1 (before and one month after booster, respectively). Cut-off for Ab titers positivity was > 25 AU/mL. Results: Among the 23 enrolled patients, 10 (43.5%) were female and 13 (56.5%) males; 6 (26%) pts had thymic carcinoma and 17 (74%) had thymoma. Autoimmune disorders were detected in 20 patients (86.9%), of whom 3 (15%) suffered from Myasthenia Gravis, 8 (40%) from Good’s Syndrome, 7 (35%) from both diseases, and 2 (10%) from other autoimmune disorders. By the time of booster administration 2 pts were lost to follow up, 2 pts died, 5 pts suffered from SARS-CoV-2 infection and seroconverted. Of the remaining 14 pts, only 7 (50%) achieved seroconversion. Among these patients, 2 had active cancer disease, whereas the remaining were disease-free. On the other hand, among the 7 patients who did not achieve seroconversion after booster, 6 had active cancer disease. Moreover, 6 of these patients suffered from Good’s Syndrome. Conclusions: Our results suggest that the anti-SARS-CoV-2 third dose could contribute to improved seroconversion of TET patients who did respond to the first two doses. It remains to be investigated why half of the patients are still not achieving seroconversion after the booster and whether this is determined by the presence of active disease or by alterations in humoral and/or cell-mediated immune response. These data may have important clinical implications because they could help to better identify fragile patients who could benefit from improved vaccine protocols or from alternative prophylaxis strategies, such as the use of monoclonal antibodies.