Intact HLA Not β2m-free Heavy Chain-Specific HLA Class I Antibodies Are Predictive of Graft Failure

Background. We investigated the effects of intact and beta 2m-free heavy chain (HC)-specific human leukocyte antigen (HLA) class I antibodies on long-term graft survival. Methods. HLA class I mixed antigen beads were used to detect intact and beta 2m-free HC-specific antibodies, whereas elution buffer-treated beads were used to detect antibodies against beta 2m-free HC. Donor-specific antibodies (DSAs) were identified using single-antigen beads. Complement-dependent cytotoxicity assays were performed to determine the cytotoxicity of DSA. Results. Three hundred seventy-nine of 994 of patients (38%) had antibodies against intact HLA and beta 2m-free HC. There was no survival rate difference between antibody-positive and -negative groups. When the 379 an tibody-positive patients were further tested with beta 2m-free HC-coated beads, 179 of them with antibodies only against intact form of antigens had a 4-year graft survival rate of 76%, which is significantly lower than that of 200 patients with antibodies against beta 2m-free HC of HLA antigens (88%, P=0.0056). Patients with intact antigen specific DSAs had a significantly lower graft survival rate as compared with those with no DSAs (70% vs. 89%, P=0.0073). More patients with strong donor-specific cytotoxic antibodies lost allografts than those with weak-cytotoxic or noncytotoxic antibodies. However, cytotoxic activity of DSA was not correlated to antibody level. Conclusions. We concluded that intact antigen-specific antibodies, especially DSAs, are predictive of graft failure. DSAs were not always cytotoxic. Strong cytotoxic activity of DSA was associated with a higher rate of graft loss but not correlated to the antibody level. Antibodies against beta 2m-free HC negatively interfere with the predictive value of intact antigen-specific antibodies.