Abstract Text: Regulatory T cells (Tregs), a CD4+ T cell subpopulation critical to immune homeostasis, play a role in self-tolerance, allograft tolerance and prevention of fetal rejection during pregnancy. Interleukin 2 (IL-2) is a pleiotropic cytokine which drives proliferation of both Tregs and conventional T cells via the heterotrimeric IL-2 receptor (IL-2R, CD25/CD122/CD132). Enhancing IL-2 selectivity to maximize Treg activity while minimizing other effects is of therapeutic interest. MK-6194, an IL-2 Fc fusion mutein, has enhanced binding to the high-affinity IL-2R and reduced CD122/CD132 dependency, favoring Treg expansion. As previously described, Tregs from humanized MK-6194-treated mice have demonstrated FOXP3 and CD25 expression, characteristic of enhanced function and stability. To further characterize the behavior of a selective IL-2 mutein, we tested the effects of an MK-6194 surrogate molecule in an established model of alloantigen-specific Treg expansion in which ex vivo mixed lymphocyte reactions (MLRs) using HLA-mismatched PBMCs from healthy donors are performed in the presence of co-stimulatory blockade. MK-6194 mutein-supplemented MLRs showed greater Treg expansion. These Tregs had demethylated Foxp3 epigenetic signatures characteristic of functionally suppressive cells. Flow cytometric assessment of Treg markers including Foxp3, Helios and CD161 suggested these were functional and stable Tregs. Further, MK-6194 surrogate-expanded Tregs efficiently suppressed autologous CD8+ T cell proliferation, activation (HLA-DR+/CD25+) and cytotoxicity (Granzyme B+/Perforin+). Together these results indicate that the MK-6194 family of IL-2 muteins can expand functional, stable and immunosuppressive Tregs. These data support further evaluation of a role for MK-6194 in achieving transplant tolerance and in treatment of autoimmune and inflammatory diseases.
