Genetic absence of PD-1 promotes accumulation of terminally differentiated exhausted CD8+ T cells.
Bottom Line: Increased proliferation between days 8 and 14 postinfection is associated with subsequent decreased CD8(+) T cell survival and disruption of a critical proliferative hierarchy necessary to maintain exhausted populations long term.Ultimately, the absence of PD-1 leads to the accumulation of more cytotoxic, but terminally differentiated, CD8(+) TEX cells.They also highlight a novel role for PD-1 in preserving TEX cell populations from overstimulation, excessive proliferation, and terminal differentiation.
Affiliation: Department of Microbiology and Penn Institute for Immunology, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104 Department of Microbiology and Penn Institute for Immunology, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104.Show MeSH
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Mentions: Previous studies demonstrating potent inhibition of CD8+ T cells by the PD-1 pathway suggest that PD-1 may be essential for the development of T cell exhaustion (Barber et al., 2006; Keir et al., 2008; Wherry, 2011; Frebel et al., 2012). Thus, we tested the hypothesis that PD-1 KO P14 cells would not become exhausted during chronic LCMV infection. First, we examined the ability of WT versus PD-1 KO P14 cells to produce cytokines at day 42 p.i. after ex vivo peptide restimulation. At this time point, WT P14 cells displayed characteristic features of exhaustion. Compared with control memory P14 cells generated after acute LCMV infection, exhausted WT P14 cells less efficiently produced IFNγ (mean of 86% vs. 51%) or coproduced IFNγ and TNF (mean of 76% vs. 8%; Fig. 2 A). Surprisingly, production of IFNγ was even more severely reduced in the PD-1 KO P14 population, with a mean of only 39% of cells producing IFNγ (Fig. 2, A and B). PD-1 KO P14 cells also developed a significant reduction in IFNγ production per cell, as indicated by lower mean fluorescence intensity (MFI) of IFNγ expression compared with WT P14 cells in the same mice (Fig. 2 A and not depicted). In addition, PD-1 KO P14 cells exhibited reduced poly-functionality compared with WT P14 cells, with minimal coproduction of IFNγ and TNF (Fig. 2, A and C). There was a similar trend toward decreased total numbers of PD-1 KO IFNγ+TNF+ cells compared with WT in the spleen (Fig. 2 C). In contrast, the ability to degranulate, as measured by LAMP-1/CD107a staining, was retained (not depicted). Reduced cytokine production in the absence of PD-1 also corresponded with higher expression of multiple other inhibitory receptors, a second key feature of exhaustion. PD-1 KO P14 cells expressed higher Lag-3, 2B4/CD244, CD160, and Tigit than WT P14 cells at day 42 p.i. (Fig. 2 D). A higher frequency of PD-1 KO P14 cells also simultaneously coexpressed Lag-3, 2B4, Tim-3, and CD160 compared with WT cells (Fig. 2 E). Analysis of WT and PD-1 KO P14 cells in separate mice resulted in similar findings, confirming the CD8+ T cell–intrinsic nature of this effect (Fig. 2 F and not depicted). These findings indicate that CD8+ T cell exhaustion can develop in the absence of PD-1. In fact, two defining features of CD8+ TEX cells, loss of cytokine poly-functionality, and elevated inhibitory receptor coexpression, were more severe when CD8+ T cell–intrinsic PD-1 signals were absent.
Affiliation: Department of Microbiology and Penn Institute for Immunology, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104 Department of Microbiology and Penn Institute for Immunology, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104.