The role of complement-fixing donor-specific antibodies identified by a C1q assay after heart transplantation

Background: The development of donor-specific antibodies (DSA) to human leukocyte antigens (HLA) has been associated with acute rejection and allograft failure after heart transplantation. Not all DSA, however, can fix complement. Methods: To determine the association between complement-fixing DSA and heart transplant outcomes, we retrospectively analyzed results obtained using the C1q solid-phase assay that specifically detects complement-fixing DSA in parallel with the standard IgG assay in 121 adult heart transplant recipients. Results: The 52 recipients who developed post-transplant DSA had a higher incidence of acute cellular rejection (58% vs 19%, P <.001) and antibody-mediated rejection (29% vs 7%, P <.001) than the 69 recipients without DSA. The 24 recipients with C1q+ DSA had more antibody-mediated rejection than the 28 recipients with C1q− DSA (46% vs 14%, P =.012), but there was no difference in the incidence of acute cellular rejection between these two groups. Patients with post-transplant DSA had higher mortality than patients with no DSA (29% vs 13%, P =.031), mainly due to increased incidence of acute rejection. No differences in survival were found between recipients with C1q+ DSA and C1q− DSA. Conclusions: Routine monitoring of DSA post-transplant, and their characterization using the C1q assay, may provide prognostic information for acute rejection after heart transplantation.