Clinical Relevance of Donor-Specific IgM Antibodies in HLA Incompatible Renal Transplantation: A Retrospective Single-Center Study.

Immunoglobulin G (IgG) antibodies against donor human leukocyte antigens (HLA) are monitored in the pre-and post-transplant period due to their established role in predicting rejection and renal allograft survival. However, the role of immunoglobulin M (IgM) anti-HLA donor-specific antibodies (DSA) is not fully understood, especially in highly-sensitized patients undergoing direct transplantation. We designed this study to determine whether IgM DSA predicts rejection episodes and/or graft failure. Samples from 92 patients who had undergone HLA-antibody incompatible transplants were tested at 5 time points: days -8 (pre-plasmapheresis), 0, 7, 14, and 30 using Luminex microbead assay with ethylenediaminetetraacetic acid containing wash buffer (LABScreen®, One Lambda, Canoga Park, CA). IgM was defined positive if the mean fluorescence values were greater than 2000. Presence of pre- and post-transplant IgM was correlated with early antibody mediated rejection episodes (within 30 days post-transplantation) and graft failure. Statistical analyses were performed using SPSS IBM software. Graft survival estimates were death-censored. The presence of pre-transplant IgM DSA did not predict rejection (p=0.83) or graft failure (p=0.424). The post-transplant IgM DSA levels peaked at day 14 (similar to IgG DSA levels). Presence of IgM DSA post-transplant (de novo and resynthesis) was not associated with rejection (p=0.83). However, post-transplant IgM was associated with graft failure (p=0.037). This study shows additional testing of post-transplant IgM DSA over and above IgG is important as post-transplant IgM DSA is associated with graft failure.