Concomitant Mycobacterium tuberculosis infection promotes lung tumor growth through enhancing Treg development

Lung cancer is the most common malignancy in humans. An increased population of CD4(+)Foxp3(+) regulatory T cells (Tregs) in the tumor-associated microenvironment plays an important role in cancer immune evasion. The exact role and the involved mechanisms of concomitant H37Rv infection in non-small cell lung cancer (NSCLC) development are still not clear. Here, we showed that H37Rv infection promoted NSCLC cell growth with a higher percentage of Tregs found in draining lymph nodes. We also determined in vitro that H37Rv infection induced macrophage maturation and PD-L1 expression, which promoted Treg proportion, with enhanced proliferation suppression function. Mechanism analysis revealed that AKT-mTORC1 signal was important for PD-L1 expression induced by H37Rv infection. Suppressing of AKT-mTORC1 signal by rapamycin or raptor deficiency showed decreased PD-L1 levels which further reduced Treg proportion in a co-culture system. Finally, tumor-bearing mice injected with H37Rv plus rapamycin enhance the immune response of lung cancer compared with injected with H37Rv alone. This study demonstrated that concomitant H37Rv infection promote NSCLC tumor immune eacape through enhancing Treg proportion.