Role of Multidrug Resistance Proteins in Nonresponders to Immunomodulatory Therapy for Noninfectious Uveitis

Purpose Nearly a third to half of patients with noninfectious uveitis (NIU) fail to achieve control with immunomodulatory therapy (IMT). Multidrug resistance (MDR) proteins are transmembrane proteins that allow efflux of intracellular drugs, leading to drug resistance. The aim of our study was to compare MDR protein function in blood CD4+ cells between responders and nonresponders to IMT. Methods We included NIU patients on IMT for ≥6 months and corticosteroid dose ≤10 mg/d. Nonresponders to treatment were those with worsening (two or more steps) of inflammation in the past 3 months on full-dose immunosuppressive therapy. MDR function was assessed by Rhodamine-123 dye retention in blood CD4+ cells. Three nonresponders were treated with adjunctive oral cyclosporine A (CSA, MDR inhibitor) therapy for 2 months and reevaluated. Results Fourteen NIU patients were recruited. Most (n = 8) had Vogt-Koyanagi-Harada disease. These included nine nonresponders and five responders to IMT. Nonresponders produced significantly higher MDR function and proinflammatory cytokines (interferon γ, tumor necrosis factor α, interleukin 17, and Granulocyte Macrophage Colony Stimulating Factor (GM-CSF)) than responders. In vitro CSA treatment of CD4+ cells inhibited MDR expression and proinflammatory cytokine production while increasing Foxp3. Finally, adjunctive oral CSA therapy led to improvement in clinical inflammatory scores with a concurrent decrease in MDR function and proinflammatory cytokine secretion. Conclusions MDR function is significantly higher in CD4+ T cells of nonresponders to IMT. Adjunctive CSA therapy may decrease MDR function and allow improvement in treatment response to IMT. Translational Relevance Our study highlights the need for MDR inhibition strategies in NIU patients not responding to IMT for improving the efficacy of anti-inflammatory therapy.