*Purpose: An anti-malarial agent, Chloroquine (CQ), has been widely used for the treatment of rheumatoid arthritis and lupus. Although the precise mechanisms of CQ are not well understood, CQ may reduce peptide-MHCII protein cellular expression. One result of this downregulation is the modulation of effector CD4+ T cell response. Because this mechanism differs from other anti-rejection drugs, CQ could be well suited to supplement current immunosuppressive regimens. However, there is very little insight into the effect of CQ directly inhibiting T cell proliferation. In this study, we used human in vitro assays to assess the ability of CQ to directly inhibit T cell proliferation.

*Methods: Blood was collected in acid citrate dextrose and peripheral blood mononuclear cells (PBMCs) were isolated by ficoll-hypaque gradient centrifugation. PBMCs were labeled with a cell trace dye and stimulated with CD3/28 dynabeads (non-specific activator of T cells). Medium control well was untreated PBMCs. PBMCs were treated with increasing concentrations CQ at 1, 3, 10, or 30 μM. After 5-7 days in culture, PBMCs were stained with 7-Amino-Actinomycin D (7-AAD), CD3-AmCyan, CD4-phycoerythrin, and CD8- allophycocyanin and analyzed on a BD fluorescence-activated cell sorting Canto II.

*Results: Figure 1: Inhibition of CD4+ & CD8+ T Cells with increasing concentration of CQ. Errors bars indicate standard error of the measurement

*Conclusions: These preliminary results demonstrate CQ inhibiting T cell proliferation in a dose-dependent manner. The frequency of T cell proliferation is still high at a concentration of 3uM suggesting the drug is not inhibiting T cell proliferation directly. The decrease in T cell proliferation at higher concentrations appears to be associated with toxicity of the drug as indicated by the increased frequency of dead cells (7-AAD⁺). Current investigation is directed towards determining CQ’s impact on MHC expression using human in vitro assays and monitoring transplant patients currently on CQ.

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