In the last 15 years, close to 40% of combat injuries sustained by Service members involved severe extremity and craniofacial trauma. Despite the best reconstructive efforts using native tissue, these injuries frequently result in need of amputations. Eighty percent of amputees are then permanently retired while experiencing amputation-related disabilities that include poor professional and social interactions. Vascularized composite allotransplantation (VCA; the transplant of limbs or facial components) has become a viable approach for functional restoration and enables patients to return to a higher quality of life than that afforded by any currently available prosthesis. However, the toxic and debilitating side effects (e.g., infections, nephrotoxicity, cardiovascular disease, diabetes, and cancer) of immunosuppressive drug therapy, needed to prevent transplant rejection by the patient immune system, counterbalances the benefits of VCA and prevents its widespread use. Minimizing immunosuppression, or even altering the recipient’s immune system to tolerate the transplant, will impact the lives of countless Service members by pushing the benefit/risk ratio toward making VCA safer and more broadly applicable.

In the research arena, a major focus is on exploiting the natural mechanisms of regulation embedded in the immune system to curb the anti-graft destructive activities responsible for rejection. There is great optimism in the concept of promoting so-called regulatory T cells, fundamental controllers of the destructive arm of the immune system (T and B lymphocytes). Regulatory T cells are powerful cells, but they are not particularly abundant. The experimental strategies currently explored rely on increasing their number via either: (1) extraction and expansion outside the body for re-infusion or (2) administration of drugs that stimulate regulatory T cell proliferation in the body. Although ongoing trials are showing promising results, these approaches still present significant drawbacks. In the case of expanding extracted regulatory T cells, manufacturing issues, along with concerns about the safety and stability of the massively expanded cells, limit the clinical applicability of this approach. In the case of drug-mediated approach to expand regulatory T cells directly in the patient, there is currently a concern that transplant-destructive lymphocytes could also be amplified or, conversely, that a general expansion of regulatory T cells could impair the immune responses to life-threatening insults. Identifying a simple intervention that would promote the expansion of a selected group of regulatory T cells with protective activity toward the transplant, while leaving the rest unaltered, would have tremendous therapeutic potential.

To tackle this problem, we will merge improved knowledge of the immune system with cutting-edge advances in biomaterial design and protein bioengineering. Our innovative idea is to create a new biomaterial class of nanoparticles that can interact specifically with regulatory T cells and promote the selective expansion of graft protective ones. Because they mimic naturally occurring cells of the immune system, we call our product Tolerogenic artificial Antigen Presenting Cells (TolAPC). These particles will be designed from materials that are generally regarded as safe and that degrade in water, precluding any risk to the patient. The goal of this proposal is to identify the optimal composition of TolAPC and to demonstrate their capacity to selectively interact with regulatory T cells. Performing studies both in vitro and in mouse models, we will delineate the proper composition of TolAPC that can mitigate the rejection response to a transplant.

The design we have envisioned for TolAPC is modular, allowing to target any desired population of regulatory T cells protecting specific body tissues by simply swapping proteins loaded on the particle surface. Additionally, TolAPC design maximizes the half-life of a drug that promotes regulatory T cell expansion, while restricting its effect to the desired sub-population, which will minimize side effects caused by systemic exposure. Moreover, TolAPC can be administered via different routes to target different areas of the body and tailor their effects. Finally, the formulation of TolAPC is amenable to additional modifications, including the encapsulation of drugs (e.g., immunosuppressive drugs) to maximize their therapeutic activity, as well as surface functionalization to increase retention in specific tissues. Thus, TolAPCs represent a scalable transformative platform technology with a simple design that is amenable to the creation of powerful immune-modulatory strategies, making our proposal responsive to two Focus Areas: immunomodulation approaches and mechanisms, optimizing immunosuppressive drug regimens. As an acellular therapy, TolAPC can be easily and inexpensively scaled up for manufacture, distribution, storage, and use facilitating translation in ways that are not possible with cellular therapies.