Summary Τhe clinical significance of de novo post‐transplant anti‐HLA donor‐specific antibodies (DSA) was evaluated using 4241 serum samples collected between 2000 and 2007 from 597 renal transplant recipients. Patients transplanted before December 1996 (n = 77) were included in the historic group and those transplanted thereafter (n = 520) were included in the study group. All recipients were negative for DSA before transplantation (Tx). Post‐Tx, de novo DSA were detected in 92/597 (15.4%) patients, while 196 had third party anti‐HLA antibodies (DSA‐negative). DSA were more frequent in the historic group (33.8%) compared with the study group (12.7%) (P < 0.001). Anti‐HLA class‐II DSA predominated in both groups (84.6% vs. 69.7%). Recipients of HLA class II‐incompatible grafts developed DSA more frequently than those receiving HLA class II‐compatible grafts (17.9% vs.7.9%, P = 0.003), directed mainly against HLA‐DQ graft molecules (64/446, 14.4%). DSA production was not different between presensitized and nonsensitized patients (P = 0.842). Graft survival was higher in patients without antibodies compared with DSA‐positive (log‐rank test, P = 0.002) and DSA‐negative patients (log‐rank test, P = 0.002). Univariate and multivariate analysis showed independent association for DSA class I (HR = 31.78), DSA class II (HR = 20.92) and non‐DSA (HR = 5.94) and graft failure. We conclude that HLA class II incompatible graft transplantations need careful monitoring and should be avoided in high immunological risk cases.

We analyzed the antibody responses of 564 hospital workers in Athens, Greece, after vaccination with two doses of the BNT162b2 (Comirnaty®; BioNTech and Pfizer) mRNA COVID-19 vaccine. A greater antibody increase was observed in women, younger age groups, previously infected individuals and personnel working in COVID-19 clinics. Notably, individuals with a prior COVID-19 infection mounted a significantly higher antibody titer following the first dose than the rest of the population; the same was true for those working in COVID-19 clinics, even without history of previous infection.

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