The acceptable reactive crossmatch (ARC), post-transplant monitoring, and their impact on kidney transplantation: a single center experience.

Although the adverse allograft outcomes associated with HLA antibodies are well documented, some controversy exists regarding the importance of low-level donor specific anti-HLA antibodies (DSA). To provide further detail on this controversy, we prospectively looked at low-level DSA in negative T- and B-cell flow cytometric crossmatch (FCXM) or acceptable reactive crossmatch (ARC) patients who each underwent protocol based post-transplant antibody monitoring. HLA Class I and II antibody screening and specificity determination was conducted via a solid phase assay (SPA) and FCXM versus donor and autologous T and B cells. Post-transplant patients were immunosuppressed with quadruple maintained immunosuppressive therapy, rabbit anti-thymocyte globulin induction, and HLA antibody monitoring. Out of 31 ARC patients transplanted, 65% had a PRA > 50% and 26% showed increased DSA at 7-14 days post-transplant. Antibody mediated rejection (AMR) was treated with pharmacological and/or plasmapheresis (PP) therapy. DSA were lowered and remained at low-levels (MFI 1000- 3000) or below FCXM cutoffs. None of the 31 patients transplanted developed de-novo antibodies. Two patients lost their allografts, one to polyoma (BK) virus, and one to antibody mediated rejection (AMR). In conclusion, our experience demonstrates that patients deemed higher risk for an immunological event due to low-level DSA should be transplanted with an ARC and followed post-transplant according to an established alloantibody monitoring protocol. With close monitoring, 5-year outcomes can be expected to approach that of low-immunologic risk transplant patients.