Hepatitis C virus (HCV) seroconversion among HCV-uninfected transplant recipients from HCV-infected (NAT+/Antibody+) or HCV-exposed (NAT-/Antibody+) donors has been reported. However, the origin of anti-HCV antibody and the implications of seroconversion remain unknown. We longitudinally tested plasma from HCV-uninfected kidney (n = 31) or heart transplant recipients (n = 9) of an HCV NAT+ organ for anti-HCV antibody (both IgG and IgM isotypes). Almost half of all participants had detectable anti-HCV antibody at any point during follow-up. The majority of antibody-positive individuals became positive within 1-3 days of transplantation, and 6 recipients had detectable antibody on the first day posttransplant. Notably, all anti-HCV antibody was IgG, even in samples collected posttransplant day 1. Late seroconversion was uncommon (approximate to 20%-25% of antibody+ recipients). Early antibody persisted over 30 days in kidney recipients, whereas early antibody dropped below detection in 50% of heart recipients within 2 weeks after transplant. Anti-HCV antibody is common in HCV-uninfected recipients of an HCV NAT+ organ. The IgG isotype of this antibody and the kinetics of its appearance and durability suggest that anti-HCV antibody is donor derived and is likely produced by a cellular source. Our data suggest that transfer of donor humoral immunity to a recipient may be much more common than previously appreciated
