Increased Expression of Multiple Co-Inhibitory Molecules on Malaria-Induced CD8+ T Cells Are Associated With Increased Function Instead of Exhaustion

Abstract

Activated cytotoxic CD8+ T cells can selectively kill target cells in an antigen-specific manner. However, their prolonged activation often has detrimental effects on tissue homeostasis and function. Indeed, overwhelming cytotoxic activity of CD8+ T cells can drive immunopathology, and therefore, the extent and duration of CD8+ T cell effector function needs to be tightly regulated. One way to regulate CD8+ T cell function is their suppression through engagement of co-inhibitory molecules to their cognate ligands (e.g., LAG-3, PD-1, TIM-3, TIGIT and CTLA-4). During chronic antigen exposure, the expression of co-inhibitory molecules is associated with a loss of T cell function, termed T cell exhaustion and blockade of co-inhibitory pathways often restores T cell function. We addressed the effect of co-inhibitory molecule expression on CD8+ T cell function during acute antigen exposure using experimental malaria. To this end, we infected OT-I mice with a transgenic P. berghei ANKA strain that expresses ovalbumin (PbTG), which enables the characterization of antigen-specific CD8+ T cell responses. We then compared antigen-specific CD8+ T cell populations expressing different levels of the co-inhibitory molecules. High expression of LAG-3 correlated with high expression of PD-1, TIGIT, TIM-3 and CTLA-4. Contrary to what has been described during chronic antigen exposure, antigen-specific CD8+ T cells with the highest expression of LAG-3 appeared to be fully functional during acute malaria. We evaluated this by measuring IFN-γ, Granzyme B and Perforin production and confirmed the results by employing a newly developed T cell cytotoxicity assay. We found that LAG-3high CD8+ T cells are more cytotoxic than LAG-3low or activated but LAG-3neg CD8+ T cells. In conclusion, our data imply that expression of co-inhibitory molecules in acute malaria is not necessarily associated with functional exhaustion but may be associated with an overwhelming T cell activation. Taken together, our findings shed new light on the induction of co-inhibitory molecules during acute T cell activation with ramifications for immunomodulatory therapies targeting these molecules in acute infectious diseases.

Type 1 regulatory T cell-mediated tolerance in health and disease

“…The murine LAG-3 + cells were suppressive irrespective of CD49b expression, and the frequency of LAG-3 + cells in various tissues dwindled to levels seen in naïve mice within days of anti-malarial administration, suggesting these were not long-lived memory cells. Unexpectedly, the co-inhibitory receptor-rich CD8 + T cells had enhanced antigen-specific cytotoxic function ( 143 , 144 ). Based on the presently available evidence, it can be concluded that Tr1-like cells prevent symptomatic malaria infection by protecting against immune-mediated pathology, as demonstrated in mice and humans ( 134 – 136 , 141 ).…”

OMIP‐93: A 41‐color high parameter panel to characterize various co‐inhibitory molecules and their ligands in the lymphoid and myeloid compartment in mice

“…In light of recent advances in antibody-mediated blockade of these pathways [3,4], characterizing immune cells that participate in activating or inhibitory interactions may be of crucial importance to identify opportune targets and develop novel treatments. We and others discovered the expression of multiple co-inhibitory molecules on T cells in the mouse model of cerebral malaria by infecting C57BL/6 mice with Plasmodium berghei ANKA [5][6][7][8], making it an ideal model to establish a panel addressing these challenges. Here, we describe a novel panel and gating strategy to investigate expression of multiple co-inhibitory molecules and their respective ligands on T cells, B cells, NK cells, macrophages/ monocytes, neutrophils, and dendritic cells (DC) in mice.…”