Friday, May 9, 2025
5/9/2025
Th9 cells and protective TB immunity - -γ-producing Th1 cells have been extensively studied for development of novel vaccines and therapeutics against Mycobacterium tuberculosis (Mtb) infection. However, recent studies demonstrate that Mtb-specific Th1 cells alone do not predict protection against tuberculosis (TB). Therefore, although Th1 cells are required for controlling Mtb replication, other types of immune cells may be needed to prevent infection and eradicate the bacteria. We recently found that a subset of IL-9-producing CD4+ T cells (Th9) can mediate protective immunity against Mtb infection. Th9 cells can be differentiated from naïve CD4+ T cells with TGF-β and IL-4, and play important roles in antitumor immunity and immunity related to allergic reactions. The role of Th9 cells in Mtb infection, however, remain largely unknown. We discovered a role for Th9 cells in TB immunity when we analyzed the transcriptomes in CD4+ T cells from healthy volunteers vaccinated with BCG and from people with latent TB infection (LTBI). IL-9 mRNA in CD4+ T cells topped the list of genes increased after BCG vaccination and LTBI. A significant increase in IL-9 production by bronchoalveolar lavage (BAL) cells after stimulation with infectious Mtb was observed only in LTBI patients and people vaccinated with oral (PO) BCG, indicating induction of Mtb-specific Th9 memory responses. To test whether Th9 cells mediate intracellular Mtb killing, we differentiated Mtb-specific Th9 cells from ESAT6-TCR transgenic mice and co-cultured these Th9 cells with Mtb-infected murine macrophages. Intracellular mycobacterial growth was significantly reduced in macrophages after interacting with Th9 cells. Moreover, neutralizing IL-9 abolished the inhibitory effects of Th9 cells, while addition of recombinant IL-9 alone inhibited intracellular bacterial growth. Furthermore, adoptive transfer of Mtb-specific Th9 cells into syngeneic RAG1/2-/- mice suppresses Mtb growth in vivo. In addition, we found that IL-9 was increased and Mtb growth decreased in mice deficient in MCPIP1, a new RNA-binding protein affecting T cell activation. Deletion of MCPIP1 in Th9 cells resulted in a significantly enhanced IL-9 production upon restimulation. Based on our preliminary findings, we hypothesize that Mtb-specific Th9 cells represent a distinct subset of CD4+ T cells important for protective TB immunity. Strategies inducing Mtb- specific Th9 cells could be used to develop more effective TB vaccines and/or immunotherapies. We propose three aims to test this novel hypothesis: Aim 1 to determine the effects of Mtb-specific Th9 cells on protective TB immunity; Aim 2 to define the roles of IL-9 in vaccine-induced protection against Mtb infection using genetically engineered mice, and Aim 3 to identify the source for IL-9 in PBMC and BAL cells from BCG vaccinated individuals, and the mechanisms of Mtb-specific Th9 cell-mediated bacterial killing in human macrophages. These studies will have a significant impact on improving our understanding of host protective immune mechanisms against Mtb infection, and provide the rationale for targeting Mtb-specific Th9 cells as a new strategy for more effective TB vaccines and/or immunotherapies against Mtb infection.
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