Application of CAR-Treg Technology to Regulate VCA Rejection

Rationale: Vascularized composite allotransplantation (VCA), including face, limb, and penile transplantation, is now a viable therapy to restore the appearance and function of patients with severe tissue loss. Thanks to the development of a unique relationship between plastic surgery and transplantation, VCA is being performed in more and more centers throughout the United States and the world. A limitation of current VCA approaches is that powerful immunosuppressive drugs are used to stop the patient's immune system from rejecting the graft. These drugs have many side effects, such as increasing the risk of cardiovascular and kidney disease, and because they globally suppress the immune system, they put patients at high risk of infection and cancer. Moreover, in the long term, conventional immunosuppression often fails to prevent rejection, with more than half of patients experiencing transient or permanent graft rejection. There is an urgent need to develop new treatments that are more effective and less toxic to control the immune response to VCA.

Our team is focused on harnessing one of the natural ways that the immune system uses to regulate itself. Specifically, a special type of white blood cell known as T regulatory cells (or Tregs) has a unique ability to prevent inappropriate immune responses. We know from past research that this function of Tregs can be applied in transplantation and, at least in animal models, can promote long-term graft acceptance in the absence of long-term immunosuppressive therapy. We recently made a significant improvement in how Tregs can be used therapeutically in transplantation by applying a cell engineering strategy that has led to a revolution in cancer immunotherapy. This strategy involves the creation of a custom-designed protein called a chimeric antigen receptor (CAR) which, when expressed on Tregs, makes them much more potent and specific. We have already extensively tested CAR-expressing Tregs in models of bone marrow and solid organ transplantation, and now we are working with a biotech company (TxCell/Sangamo) to develop a first-in-human clinical trial of CAR-Treg therapy in kidney transplantation. Our combined expertise in Treg biology, VCA immunotherapy, and CAR-Tregs positions us to make rapid progress in this highly innovative, yet clinically feasible, approach.

Objectives: The hypothesis behind this proposal is that CAR-Treg therapy should be an effective way to minimize VCA rejection. Our objectives are to use mouse models of VCA to test whether CAR-Treg therapy can prevent VCA rejection and to further optimize the custom-designed CAR so that it is maximally effective.

Focus Area: Develop novel approaches for immune tolerance and reduce the toxicity of standard immunosuppression.

Patient Impact: This work will help make VCA accessible to patients who would benefit from a transplant of tissues such as a face, arm, leg, and/or penis. In the past 15 years, ~40% of combat injuries sustained by Service members involved severe extremity and craniofacial trauma. There are also many civilians who have accidents causing similar injuries. Many of these patients would benefit from VCA.

Clinical Applications, Benefits, and Risks: CAR-Treg therapy (with or without a novel immunosuppressive protocol) would be applicable in any patient undergoing VCA. The most likely first application would be in upper extremity (e.g., hand) transplantation, since this is the most commonly performed form of this procedure and, hence, the largest patient population. The benefit would be the opportunity to reduce conventional immunosuppressive therapy and thus reduce its associated side effects, as well as the overall risk of rejection. The main risk of CAR-Treg therapy is that it may not work as expected and lead to unwanted episodes of rejection. If this were to happen, then conventional immunosuppression could be quickly restored and, if deemed necessary, CAR-Tregs could be eliminated by use of T cell depleting drugs.

Time to Patient-Related Outcome: First-in-human trials of our A2-CAR Treg therapy are planned in living donor kidney transplantation in 2019. Therefore, by the end of this project (2022), we will be able to draw from the safety data emerging from this study and move to a VCA application. In partnership with Sangamo (see Intellectual Property Attachment), we anticipate there will be an opportunity to leverage an existing drug (i.e., CAR-Treg) manufacturing protocol, which includes our proprietary A2-CAR sequence, and the method to generate human CAR-Tregs for clinical use.

Benefit to Patients/Families with Traumatic Injury: Improving the outcomes of VCA will change its benefit/risk ratio and make it a safer and more broadly applicable therapy. This would mean more people (military and general public) could benefit from this therapy, resulting in a significant improvement in quality of life for both the affected individuals and their families. Knowledge accrued in this project will also be transferable to other diseases that affect Service members where similar methods to control immunity could be applied (i.e., end-stage organ failure and autoimmunity).

Benefit to Reconstructive Transplant Research: We believe our work will establish a framework for the continuous optimization of CAR-Treg therapeutic use (by the scientific community). Moreover, our studies will identify whether unique interactions between VCA and Tregs need to be accounted for.