UCSF

Lung transplant immunosuppression regimens generally include the calcineurin inhibitor tacrolimus. We hypothesized that mean residual expression (MRE) of calcineurin-dependent genes assesses rejection and infection risk better than does tacrolimus trough. We prospectively followed 44 lung allograft recipients at 2 to 18 months posttransplant and measured changes in whole blood interleukin-2, interferon-γ, and granulocyte-macrophage colony-stimulating factor gene expression following a tacrolimus dose. Posttransplant duration, immunosuppressive medication levels, and bronchoscopic rejection and infection assessments were compared with MRE by using generalized-estimating equation-adjusted models. Prednisolone effect on MRE was assessed ex vivo in blood samples from nontransplanted controls. Tacrolimus concentration inhibiting 50% of cytokine production (IC₅₀ ) was measured in a pretransplant subset. Results showed that MRE did not change with diagnosis of rejection but that airway infection was associated with a 20% absolute decrease (95% confidence interval 11%-29%). MRE increased with time after transplant but was not associated with tacrolimus trough. Interestingly, MRE correlated inversely with corticosteroid dose in the study cohort and ex vivo. Pretransplant tacrolimus IC₅₀ depended on the cytokine measured and varied between individuals, suggesting a range in baseline responses to tacrolimus. We conclude that MRE identifies infection risk in lung allograft recipients, potentially integrating calcineurin inhibitor and steroid effects on lymphocyte effector function.