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Background CD4 T-cell production of IFNɣ is essential to prevent dissemination of pulmonary Mtb, though is less effective at controlling infection within the lung. Because T cells are most effective in the context of direct interactions with Mtb-infected cells, we sought to determine the location of CD4 T-cell antigen sensing and IFNɣ production within granulomas. Methods We used a murine ultra-low-dose aerosol infection, developed by our lab, where most mice are infected by a single bacillus, resulting in a solitary granuloma that is more similar to human granulomas. We examined the lungs of wild-type mice 35 days later for patterns of T-cell activation with quantitative confocal imaging. This analysis was next performed following adoptive co-transfer of Th1 polarized Mtb-specific cells and control cells of irrelevant specificity (OVA). To determine the effect of TGFβ on IFNɣ production, we examined mice that lack the TGFβR on T cells (TGFβR.KO). Finally, we examined whether this effect was Th1 cell-intrinsic with an adoptive transfer of Th1-polarized Mtb-specific cells with (Tg.WT) and without (Tg.KO) the TGFβR. Results Despite many CD4 T cells localizing to the granuloma and undergoing T-cell receptor (TCR) activation (pS6), IFNɣ production was not significantly increased in the granuloma compared with a distal lung site (Figure 1). This pattern of localization and activation was found to be similar in the Mtb-specific (but not control) Th1 cells (Figure 2). In contrast, CD4 T cells from TGFβR.KO mice produced more IFNɣ within the granuloma (Figure 3). Lastly, Tg.KO cells transferred into wild-type mice produced increased IFNɣ compared with Tg.WT, mirroring the findings in TGFβR.KO mice (Figure 4). Conclusion CD4 T cell production of IFNɣ is decreased within the granuloma, where it can be most effective, despite evidence of ongoing TCR stimulation in Mtb-specific cells. We have shown that by alleviating the effects of TGFβ signaling, even terminally-differentiated Mtb-specific Th1 cells can produce more IFNɣ within the granuloma. While this modest increase suggests that there are additional mechanisms at play which warrant further exploration, these findings have the potential to guide immunotherapeutic development, especially given that TGFβ inhibitors are already in phase III clinical trials for other purposes. Disclosures All Authors: No reported Disclosures.

1885. T-helper 1 (Th1) Production of Interferon Gamma (IFNγ) Is Directly Inhibited by TGFβ Within Pulmonary Mycobacterium tuberculous (Mtb) Granulomas