Induction of the Full-Length FoxP3 Splice Variant during ex vivo Transformation of Human CD4+ T Lymphocytes into Regulatory T Cells

Abstract

Regulatory T cells (Tregs) control immune responses to autoantigens and play a key role in suppressing autoimmune reactions during the development of autoimmune diseases. One of the approaches to personalized regenerative therapy for autoimmune diseases is enhancing the proliferative and suppressive activities of Tregs ex vivo. The transcription factor Forkhead box protein P3 (FoxP3) is a key regulator of the proliferative and suppressive activities of Tregs. FoxP3 pre-mRNA undergoes alternative splicing, and the full-length splice variant stimulates Treg proliferation and suppressive activity. In this study, we used cells obtained from three healthy donors and three patients with multiple sclerosis to compared the levels of FoxP3 splice variants in Tregs during their ex vivo expansion (expanded Tregs, eTregs) and Tregs generated by transformation of CD4⁺ T cells (transformed Tregs, tTregs). The full-length FoxP3 splice variant predominated in tTregs during the transformation process, which was accompanied by the increased proliferative and suppressive activities of these cells. In contrast, ex vivo expansion of eTregs did not alter the proportions of FoxP3 splice variants; these cells proliferated less actively and exhibited lower suppressive activity than tTregs. Our findings demonstrate that transformation of CD4⁺ T cells into Tregs is accompanied by an increase in the proportion of the full-length FoxP3 splice variant. Therefore, transformation may represent a more effective strategy than expansion of mature Tregs for generation of highly proliferative and suppressive cells in regenerative medicine.