The role of flow cytometry-detected IgG and IgM anti-donor antibodies in cardiac allograft recipients

Background. At our transplant center, cardiac allograft recipients undergo transplantation following a negative IgG anti-human globulin (AHG) crossmatch (XM). Flow cytometry crossmatching (FCXM) is a more sensitive XM procedure than the AHG XM procedure, yet there is limited information regarding the clinical relevance of FCXM to cardiac allograft outcome. Methods. FCXM was performed retrospectively using the pretransplant sera from 140 recipients of primary cardiac allografts who underwent transplantation after AHG-IgG-NEG XM. The FCXM results were correlated to posttransplant rejection and patient survival. Results. All of the patients were auto-XM-NEG, Twenty-two of 140 patients (16%) displayed IgG(+) FCXM and had a significantly poorer 1-year survival rate than did 57 of the FCXM-NEG recipients (68% vs. 86%, P<0.02). Moreover, 50% of the IgG(+) FCXM recipients experienced early rejections (less than or equal to 14 days postoperatively) compared with only 16% for the FCXM-NEG recipients (P<0.01). The survival rate of 92% for IgM(+) FCXM recipients (n=37) was significantly improved compared with the 86% survival rate for FCXM-NEG control recipients (P<0.05), suggesting a protective role for IgM. Consistent with this interpretation is that the 1-year survival rate of 79% for the IgG, IgM FCXM(+) recipients (n=24) was significantly better than the 68% survival rate for the IgG(+) FCXM recipients (P<0.02). Conclusions. These data suggest that IgG(+) FCXM identifies a subset of AHG-IgG-NEG XM cardiac allograft recipients who are at risk for early rejections and poor survival. In contrast, the presence of IgM may be beneficial to survival.