Role of non-HLA antigens in cardiac transplant rejection

Although immunosuppressive drugs improve short term survival, rejection incidence and long term survival remain largely unchanged in heart transplant patients. While Human Leukocyte Antigen (HLA) is a common initiator of graft-specific immune responses, non-HLA antibody mediated rejection (AMR) also commonly occurs. Furthermore, non-HLA antibodies have been implicated in cell mediated rejection and cardiac allograft vasculopathy. Therefore, there is a need to identify the role of non-HLA antigens in heart transplant rejection. Serum from heart transplant patients lacking donor specific anti-HLA antibodies was collected longitudinally; pre-transplantation, acute rejection, and post-rejection for patients with AMR and matched controls. Serum IgG was used to form anti-human heart affinity columns and antigenic proteins from donor heart extracts captured. Antigens were eluted from the columns and subjected to LC-MS/MS. Longitudinal graft-specific changes in immune response were calculated. Response toward non-HLA antigens increased longitudinally, with 41 high prevalence antigens found in ≥50% of the cohort. Co-culturing cardiomyocyte and endothelial cells with patient IgG indicated cell function changes correlated with specific antigens (e.g., Prohibitin). Immunofluorescence staining of patient biopsies revealed that longitudinal increase in antigen expression correlated with non-HLA antibody response. The non-HLA antigens identified in this study elicit acute and chronic graft-specific adaptive immune responses in heart transplant recipients. Antibodies against these non-HLA antigens induced cellular dysfunction by changing expression of their target protein in the donor heart.