Organ transplantation remains the definitive treatment option for patients with end-stage organ failure. Maintenance of functional allografts requires organ recipients to stay on immune- suppressive drugs. However, most allografts have a limited lifespan because of the chronic rejection initiated by the host alloimmune responses. The majority of immunosuppressive treatments are targeted to the effector immune cells, such as T cells, leaving the root of alloimmune responses—alloantigen presentation—untouched and leading to an immune equilibrium which eventually is shifted toward graft rejection. Regulatory T cells (Tregs) with user- defined specificity could be harnessed to induce immune suppression at desired tissues. They also preserve the ability to tolerize antigen-presenting cells (APCs) through contact-dependent cellular crosstalk. Our vision is to develop a robust allospecific immune regulatory strategy that restricts alloimmune T cell responses at both the effector site (allograft) and the alloantigen presentation site(graft draining lymphoid tissue) to shift the immune equilibrium to long-term suppression in the allograft while keeping the remainder of the host immune system fully operational. By leveraging the ability of chimeric antigen receptor (CAR) to recognize any desired target and a lymph node targeting molecular vaccine to specifically deliver the target to lymph node APCs, we will engineer an orthogonal synthetic vaccine to bridge crosstalk between CAR Tregs and APCs via the CAR-directed interaction with its cognate bio-inert ligand synthetically displayed on APCs. This synthetic vaccine-mediated crosstalk will have two outcomes: 1) APC- to-CAR Treg signaling promotes CAR Treg expansion and migration to the allograft for targeted suppression with enhanced regulatory functions. 2) CAR Treg-to-APC signaling tolerizes APC to restrict alloreactive T cell priming and to promote the generation of induced regulatory T cells (iTregs), which enforces a self-sustaining immunosuppression cycle via “infectious tolerance”. We will evaluate the synthetic crosstalk in murine allotransplantation models. If successful, this platform technology could be implemented across a broad landscape for precision control of pathological conditions, including autoimmune diseases, graft-versus-host disease, and transplant rejection.