BACKGROUND: Human Leukocyte Antigen (HLA) class-II genes, particularly HLA-DR2 and HLA-DR3, and the gut microbiota are intricately linked to the pathobiology of multiple sclerosis (MS) through their ability to regulate host immunity, a critical factor in disease pathogenesis. An imbalance between anti-inflammatory CD4+ Tregs and pro-inflammatory IL-17A-secreting CD4+ Th17 cells is thought to drive disease. However, a key unresolved question is whether HLA-class II-restricted CD4+IL-17A cells can influence Treg populations and the extent to which gut microbiota regulate this IL-17A-Treg axis. Therefore, we utilized humanized transgenic mice expressing the HLA class-II gene and deficient in mouse class-II molecules, where all CD4+ T cells are selected on the human HLA class-II molecule, closely mimicking human immune responses. RESULTS: Utilizing IL-17A-deficient (DR3.IL-17A-/-) mice expressing HLA-DR3 (HLA-DRβ1*0301), we show that IL-17A deficiency enriches beneficial gut bacteria, including Prevotella species, enhances peroxisome proliferator-activated receptor (PPAR) signaling, and increases FoxP3+ regulatory T (Treg) cells and IL-10 production. The importance of gut microbiota in promoting Tregs and anti-inflammatory responses was confirmed by administering Prevotella copri, a common commensal in human gut, which mirrored the effects observed in IL-17A-deficient mice by inducing PPAR signaling and Treg population. Moreover, DR3.IL-17A-/- mice exhibited a marked reduction in EAE severity compared to IL-17A-sufficient (DR3) mice, underscoring the enhanced functional capacity of the Treg population in mitigating disease progression. Cohousing experiments validated the role of gut microbiota in immune regulation including Treg induction, as demonstrated by the transfer of Prevotella species from IL-17A-deficient mice to IL-17A-sufficient mice, increased Treg populations and attenuated EAE severity in recipient DR3 mice. CONCLUSIONS: This study redefines IL-17A's role in immune regulation, emphasizing its ability to directly influence gut microbiota composition and the abundance of Treg-promoting bacteria. Thus, gut microbiota-targeted therapies, particularly those promoting Treg-inducing bacteria like Prevotella species, hold promise for treating autoimmune diseases by modulating host immune responses. Video Abstract.

Lung cancer is the leading cause of cancer-related deaths worldwide and, despite advances in treatment, immune suppression remains an obstacle to effective therapy. Effector CD4+ T cells (CD4+ Teffs) are critical for antitumor immunity, but their function is often inhibited by regulatory T cells (Tregs), which accumulate in lung tumors and mediate suppressive functions through multiple mechanisms. This suppression leads to tumor progression and poor patient outcomes. However, the mechanisms underlying Treg-mediated suppression are not fully understood. Herein, we identify the extracellular ATP receptor P2RX7 as a key regulator of Treg function in lung tumors. In a murine lung cancer model induced by Lewis lung carcinoma cells, we found that P2RX7 enhanced the suppressive capacity of tumor-infiltrating Tregs, promoting tumor growth. In T cell–specific P2RX7-KO mice, reduced Treg infiltration was accompanied by increased CD4+ Teff accumulation and improved tumor control. Treg-specific P2RX7-KO mice exhibited reduced tumor growth, confirming a Treg-intrinsic role of P2RX7. Suppression assays revealed that tumor-infiltrating wild-type Tregs had greater suppressive activity compared to P2RX7-KO Tregs, which failed to inhibit type 1 and Tfh-like responses. This was associated with increased tumor-specific IgG production by lung B cells in P2RX7-KO mice. We also observed that wild-type Tregs expressed higher levels of the immunosuppressive molecule CTLA-4 when compared to P2RX7-KO Tregs. Thus, we conclude that P2RX7 expression on Tregs is essential for their suppressive function in lung cancer and targeting of P2RX7 may constitute a strategy to improve lung cancer treatment by alleviating Treg-mediated immune suppression.

Multiple sclerosis (MS) is an autoimmune disease affecting the central nervous system (CNS) with the immune system attacking myelin sheaths leading to neuronal death. While several disease-modifying therapies are available to treat MS, these therapies are not universally effective and do not stop disease progression. More personalized long-term treatment options that target specific aspects of the disease, such as reducing relapse frequency, delaying disability accumulation, and addressing symptoms that impact daily functioning, as well as therapies that can promote neuroprotection and repair are needed. Chimeric Antigen Receptor (CAR) Tcell therapies have revolutionized cancer treatment by intravenously (IV) administering a defined dose of T cells with high specificity provided by the CAR. An autologous CAR T cell therapy using suppressive regulatory T cells (Tregs) inducing long-lasting tolerance would be the ideal treatment for patients. Hence, we expanded the application of CAR-T cells by introducing a CAR into Tregs to treat MS patients. We developed a myelin oligodendrocyte glycoprotein (MOG)-specific CAR Treg cell therapy for patients with MS. MOG is expressed on the outer membrane of the myelin sheath, the insulating layer the forms around nerves, making it an ideal target for CAR Treg therapy. Our lead candidate is a 2nd generation CAR, composed of an anti-MOG scFv screened from a large human library. In vitro, we demonstrated CAR-dependent functionality and showed efficacy in vivo using a passive EAE mouse model. Additionally, the MOG-CAR Tregs have very low tonic signaling with a desirable signal-to-noise ratio resulting in a highly potent CAR. In summary our data suggest that MOG-CAR Tregs are a promising MS treatment option with the potential to induce long-lasting tolerance in patients.