PROJECT SUMMARY CD4+ T cells are the field generals of the immune system, providing instructions to innate immune cells, B cells, and other T cells to coordinate effective responses against non-self or altered-self antigens. The goal of this exploratory proposal is to advance a new class of soluble T cell engagers, which we have generated through biomimetic engineering, to redirect CD4+ T cell responses for therapeutic purposes. Normally, CD4+ T cell responses emerge from the integration of molecular interactions that occur at the interface between a CD4+ T cell and an antigen presenting cell (APC). These include but are not limited to: signals generated in response to antigenic peptides presented by MHCII molecules (pMHCII) that result from the coordinated actions of the T cell receptor (TCR), three signaling modules (CD3δε, CD3γε, CD3ζζ), and the coreceptor module CD4; interactions between LFA-1 on the T cell and ICAM-1 on the APC that provide adhesion and contribute to signaling; CD28 engagement of CD80 or CD86 on the APC that provides a critical costimulatory signal for IL-2 production and proliferation; and, CTLA-4 engagement of the same costimulatory ligands that serve to limit the magnitude of the response. The work proposed herein will explore the utility of biomimetic stimulators (BMiMS) – soluble reagents that have a novel antigen targeting region on one end and a CD4+ T cell stimulatory region on the other. The idea underlying BMiMS is that they can be used to make a target cell look like an APC and elicit physiological CD4+ T cell responses. In this proposal we will specifically work to: 1) optimize the production of BMiMS; 2) explore their functionality in vitro; and, 3) explore their functionality in vivo. The proposed work will provide us with the preliminary data needed to apply for larger proposals to further test and refine BMiMS function in vivo for use as therapeutic reagents. The long-term goal will be to initiate clinical trials to evaluate the efficacy of BMiMS as therapeutic reagents.