CD8+ lymphocytes contribute to immunologic bottlenecks in Mycobacterium tuberculosis infection

Abstract

Abstract Significance: Meta-analysis of human data suggests that M. tuberculosis (Mtb) infection confers protection against subsequent exposure. Our lab demonstrated this in a controlled experimental system using non-human primates. As the best model for natural immunity against TB, it is crucial to explore the mechanisms behind concomitant immunity. We hypothesized that CD8+ T cells would play a key role in preventing disease following secondary challenge. Methods: Chinese cynomolgus macaques were challenged intrabronchially with a genetically barcoded library (LibP) of Mtb, allowing an adaptive response to develop. After clearing the primary infection with anti-TB drugs, CD8+ cells were depleted in half of the cohort. This was followed by a secondary Mtb challenge with a unique barcoded library (LibS). PET-CT scans enabled tracking of lesions that developed after secondary exposure. All granulomas and lymph nodes were isolated at necropsy and sequenced to determine the bacterial source (LibP vs. LibS). Spectral flow cytometry was used to analyze lymphocytes in individual tissues isolated at necropsy, examining the cytokines and other effector molecules produced by that may drive protection in the presence and absence of CD8+ cells. Results: Our data support that CD8 depleted animals lose the ability to contain Mtb after reinfection. CD8+ cells do not appear to prevent establishment of infection independently. However, the bottleneck restricting dissemination, especially to lymph nodes, is loosened in the absence of this population. Thus, CD8+ lymphocytes are critical to immunological protection against Mtb and should be considered as a key component for vaccine and host directed therapy development. Supported by NIH IMPAc-TB (HI-IMPACT) and T32 (5T32AI089443-13)