*Purpose: African American renal transplant recipients (RTR) exhibit more immunoreactivity to allografts which may contribute to chronic rejection. This study investigated race-sex influences on ex vivo immunoreactivity and the quantitative (cells/µl) and qualitative (HLADR expression) relationship to peripheral T regulatory cells(Tregs) and drug exposure in stable Caucasian and African American RTR receiving mycophenolic acid and tacrolimus minimization.

*Methods: Thirty-eight stable RTR greater than 1 yr post-transplant completed a 12-hour study with serial collections at trough, 4, 8 and 12 hours. The immune response potential was evaluated by interleukin-2 (IL-2) and Interferon gamma (IFN-Ɣ) production by CD3+CD4+ T cells after ex-vivo treatment with PMA/Ionomycin with Brefeldin-A. Peripheral Tregs: CD3+CD4+CD25+CD127- and the immunosuppressive potential (HLADR expression) were determined by flow cytometric immunophenotyping. Tacrolimus and mycophenolic acid area under the curve 0-12 hours(AUC0-12) were determined. Data was represented as AUC0-12 of Cell Sub-populations and drug exposure [Mean(SE)] and analyzed by univariate ANOVA.

*Results: Table 1 summarizes major findings. Tacrolimus and mycophenolic acid troughs were within the therapeutic range with no group differences. Tacrolimus AUC0-12 was higher in African Americans(P=0.025) with no group differences in mycophenolic acid AUC0-12. No correlations of ex vivo immunoreactivity with Tregs or immunosuppressive drug exposure were found.

*Conclusions: Increased IFN-Ɣ and L-2 from CD3+CD4+ T cells quantitated greater ex vivo immunoreactivity in African American male RTR with no relationship to Tregs or immunosuppressive drug exposure. These findings warrent additional investigation into disparity in race-sex immunoreactivity during tacrolimus minimization post-renal transplant.

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