LAUSR

Solid organ transplant recipients are at high risk for the development of severe forms of COVID-19. However, the role of immunosuppression in the morbidity and mortality of the immune phenotype during COVID-19 in transplant recipients remains unknown. In this retrospective study, we compared peripheral blood T and B cell functional and surface markers, as well as serum antibody development during 29 cases of mild (World Health Organization 9-point Ordinal Scale (WOS) of 3-4) and 22 cases of severe COVID-19 (WOS 5-8) in solid organ transplant (72% kidney transplant) recipients hospitalized in our center. Patients who developed severe forms of COVID-19 presented significantly lower CD3+ (median 344/mm3 (inter quartile range 197; 564) vs. 643/mm3 (397; 1251), and CD8+ T cell counts (124/mm3 (76; 229) vs. 240/mm3 (119; 435). However, activated CD4+ T cells were significantly more frequent in severe forms (2.9% (1.37; 5.72) vs. 1.4% (0.68; 2.35), counterbalanced by a significantly higher proportion of Tregs (3.9% (2.35; 5.87) vs 2.7% (1.9; 3.45)). A marked decrease in the proportion of NK cells was noted only in severe forms. In the B cell compartment, transitional B cells were significantly lower in severe forms (1.2% (0.7; 4.2) vs. 3.6% (2.1; 6.2). Nonetheless, a majority of transplant recipients developed antibodies against SARS-CoV-2 (77% and 83% in mild and severe forms respectively). Thus, our data revealed immunological differences between mild and severe forms of COVID 19 in solid organ transplant recipients, similar to previous reports in the immunocompetent population.