Harnessing the Full Potential of Regulatory T Cells by mRNA-induced Antigen Specificity

Abstract

Abstract Regulatory T cells (Tregs) are crucial in inducing and maintaining tolerance, and already have shown clinical potential. In this study, we describe an efficient non-viral engineering method by TCR-encoding mRNA electroporation, while also exploring the potential of further promoting on-target effects by disrupting the endogenous TCR using a fully RNA-based CRISPR/Cas9 technology. Endogenous TCR disruption prior to TCR-transfection resulted in more than 90% blockade of the endogenous TCR expression and a similar high (>85%) but more homogenous expression of the transgenic TCR. Importantly, following antigen-specific TCR-induced stimulation, both engineered Tregs significantly increased the expression of multiple activation and suppression markers. Moreover, the engineered Tregs outcompeted polyclonal Tregs in suppressing antigen-specific effector T cell proliferation and performed better in blocking moDC maturation, even in the presence of antigen-activated effector T cells. Secretome screening revealed a distinct anti-inflammatory profile for TCR-Tregs. On the other hand, TCR-engineered KO Tregs co-expressed anti-inflammatory cytokines together with some pro-inflammatory cytokines, but qualitatively different from their effector Th counterparts. Hence, an anti-inflammatory profile with Th cell features is seen with TCR-engineered KO Tregs. In conclusion, we show that this versatile approach can be used to induce the functional expression of a transgenic TCR, but also for CRISPR/Cas9-mediated disruption of endogenous TCRs with high efficiency using an RNA-based platform. Comparison between polyclonal Tregs and TCR engineered Tregs in EAE using an HLA-transgenic mouse model is now being investigated. National Multiple Sclerosis Society (RG-1612-26484)