Polycytotoxic T lymphocytes in human tuberculosis

Tuberculosis (TB) remains a major global health challenge, with millions of new infections and deaths annually. This thesis highlights the roles of innate and adaptive immune responses in TB, focusing on how different immune cells contribute to controlling the infection. The primary aim was to understand how polycytotoxic T lymphocytes (P-CTL) contribute to the restriction of Mycobacterium tuberculosis (Mtb) growth in primary human macrophages. P-CTL are defined by their simultaneous expression of granzyme B, perforin, and granulysin. All three effector molecules act together to mediate antimicrobial activity. Here, we describe the identification, purification, and functional characterization of P-CTL and their interaction with Mtb-infected macrophages. P-CTL circulate in the peripheral blood of healthy donors with a low and variable frequency (1 % - 5 %). To characterize their immune functions, we purified two subsets of unconventional T cells with an enhanced frequency of P-CTL based on the expression of prototypical NK cell receptors NKG2A and NKG2C. We found that both receptors are sufficiently enrich for P-CTL (up to 50 %). NKG2C+ T cells featured a greater cytotoxicity and constitutive degranulation, while NKG2A+ T cells released higher levels of IFN-γ and IL-10. Strikingly, both subsets significantly inhibit the growth of intracellular Mtb, which correlated with the frequency of P-CTL. Initial encounter (24 hrs.) with an oxygen-restricted environment did not significantly affect the frequency of P-CTL. Moreover, we found that P-CTL are induced by stimulation with soluble mycobacterial antigens, further substantiating their preventive role in the control of infectious diseases. Still, it is necessary to enhance the frequency of P-CTL to harness them for therapeutic immune interventions. We utilized the well-known cytokine IL-2, but co-stimulation could not significantly increase the frequency of P-CTL in Mtb-specific T cells. This thesis discusses the potential role of NKG2A and NKG2C T cells in early TB infection and suggests that targeting these receptors could be a novel strategy for TB immunotherapy. Due to their prominent antimicrobial activity, targeting P-CTL should be considered for novel vaccination strategies to combat severe infectious diseases.