Regulatory T cells are critical for maintaining immune tolerance. Recent studies have confirmed their therapeutic suppressive potential to modulate immune responses in organ transplant and autoimmune diseases. However, the unknown and nonspecific antigen recognition of polyclonal Tregs has impaired their therapeutic potency in initial clinical findings. To address this limitation, antigen specificity can be conferred to Tregs by engineering the expression of transgenic T-cell receptor (TCR) or chimeric antigen receptor (CAR). In contrast to TCR Tregs, CAR Tregs are major histocompatibility complex (MHC) independent and less dependent on interleukin-2 (IL-2). Furthermore, CAR Tregs maintain Treg phenotype and function, home to the target tissue and show enhanced suppressive efficacy compared to polyclonal Tregs. Additional development of engineered CAR Tregs is needed to increase Tregs’ suppressive function and stability, prevent CAR Treg exhaustion, and assess their safety profile. Further understanding of Tregs therapeutic potential will be necessary before moving to broader clinical applications. Here, we summarize recent studies utilizing CAR Tregs in modulating immune responses in autoimmune diseases, transplantation, and gene therapy and future clinical applications.

Immune responses to adeno-associated virus (AAV) capsids limit the therapeutic potential of AAV gene therapy. Herein, we model clinical immune responses by generating AAV capsid-specific chimeric antigen receptor (AAV-CAR) T cells. We then modulate immune responses to AAV capsid with AAV-CAR regulatory T cells (Tregs). AAV-CAR Tregs in vitro display phenotypical Treg surface marker expression, and functional suppression of effector T cell proliferation and cytotoxicity. In mouse models, AAV-CAR Tregs mediated continued transgene expression from an immunogenic capsid, despite antibody responses, produced immunosuppressive cytokines, and decreased tissue inflammation. AAV-CAR Tregs are also able to bystander suppress immune responses to immunogenic transgenes similarly mediating continued transgene expression, producing immunosuppressive cytokines, and reducing tissue infiltration. Taken together, AAV-CAR T cells and AAV-CAR Tregs are directed and powerful immunosuppressive tools to model and modulate immune responses to AAV capsids and transgenes in the local environment.

Adeno-associated virus (AAV)-mediated gene therapies have provided promising treatments for numerous neurological disorders. Redosing of AAV to the central nervous system (CNS) is an attractive research area due to both the somewhat immunologically privileged status of the CNS as well as the possibility of reduced glial transgene expression over time following a single injection. Continued study of the immune responses to both intraparenchymal and intra-CSF delivery of AAV mediated gene therapies, as well as the continued study of immunosuppressive regimens, could allow for eventual redosing in patients.

Cutaneous gene therapy has the potential to treat a wide range of skin disorders, but effective delivery remains limited by the skin's barrier properties and immune surveillance. Here, we identify AAVrh32.33 as a potent vector for targeting dermal stromal compartments. Following systemic administration in mice, AAVrh32.33 mediated robust and durable transgene expression, with preferential targeting of dermal fibroblasts and hair follicle bulge cells. Expression peaked at one month and persisted for up to two years, highlighting its suitability for chronic conditions. To reduce immunogenicity, a dominant CD8⁺ T cell epitope was disrupted, generating the IDPΔ variant. This modification attenuated peptide-specific T cell responses while preserving stromal transduction. In human skin explants, IDPΔ achieved high levels of gene expression, primarily in dermal fibroblasts and precursors, confirming translational relevance. Finally, vectors encoding CCL17, CCL20, and CCL22 demonstrated localized targeted therapeutic gene delivery in both healthy and inflamed skin, underscoring the feasibility of using this platform to reshape local immune responses. Together, these findings establish AAVrh32.33 and IDPΔ as promising platforms for durable cutaneous gene therapy, with direct applications in diseases such as vitiligo where long-term modulation of the dermal microenvironment is essential.