Cytotoxic T cell immunity in response to chronic infections and tumours is maintained by a specialized population of CD8
T cells that exhibit hallmarks of both exhausted and memory cells and give ...rise to terminally differentiated exhausted effector cells that contribute to viral or tumour control. Importantly, recent work suggests these cells, which we refer to as 'precursor exhausted' T (T
) cells, are responsible for the proliferative burst that generates effector T cells in response to immune checkpoint blockade targeting programmed cell death 1 (PD1), and increased T
cell frequencies have recently been linked to increased patient survival. We believe the recent discovery of T
cells not only represents a paradigm shift in our understanding of the mechanisms that maintain CD8
T cell responses in chronic infections and tumours but also opens up unexpected avenues for the development of new and innovative therapeutic approaches. In this Opinion article, we discuss the differentiation and function of T
cells and suggest that targeting these cells may be key for successful immunotherapy.
Anti-viral immunity continuously declines over time after SARS-CoV-2 infection. Here, we characterize the dynamics of anti-viral immunity during long-term follow-up and after BNT162b2 ...mRNA-vaccination in convalescents after asymptomatic or mild SARS-CoV-2 infection. Virus-specific and virus-neutralizing antibody titers rapidly declined in convalescents over 9 months after infection, whereas virus-specific cytokine-producing polyfunctional T cells persisted, among which IL-2-producing T cells correlated with virus-neutralizing antibody titers. Among convalescents, 5% of individuals failed to mount long-lasting immunity after infection and showed a delayed response to vaccination compared to 1% of naïve vaccinees, but successfully responded to prime/boost vaccination. During the follow-up period, 8% of convalescents showed a selective increase in virus-neutralizing antibody titers without accompanying increased frequencies of circulating SARS-CoV-2-specific T cells. The same convalescents, however, responded to vaccination with simultaneous increase in antibody and T cell immunity revealing the strength of mRNA-vaccination to increase virus-specific immunity in convalescents.
Differentiation and fate of virus-specific CD8
T cells after cessation of chronic antigen stimulation is unclear. Here we show that a TCF1
CD127
PD1
hepatitis C virus (HCV)-specific CD8
T-cell subset ...exists in chronically infected patients with phenotypic features of T-cell exhaustion and memory, both before and after treatment with direct acting antiviral (DAA) agents. This subset is maintained during, and for a long duration after, HCV elimination. After antigen re-challenge the less differentiated TCF1
CD127
PD1
population expands, which is accompanied by emergence of terminally exhausted TCF1-CD127-PD1
HCV-specific CD8
T cells. These results suggest the TCF1
CD127
PD1
HCV-specific CD8
T-cell subset has memory-like characteristics, including antigen-independent survival and recall proliferation. We thus provide evidence for the establishment of memory-like virus-specific CD8
T cells in a clinically relevant setting of chronic viral infection and we uncover their fate after cessation of chronic antigen stimulation, implicating a potential strategy for antiviral immunotherapy.
Cognate antigen signal controls CD8
T cell priming, expansion size and effector versus memory cell fates, but it is not known if and how it modulates the functional features of memory CD8
T cells. ...Here we show that the strength of T cell receptor (TCR) signaling controls the requirement for interleukin-2 (IL-2) signals to form a pool of memory CD8
T cells that competitively re-expand upon secondary antigen encounter. Combining strong TCR and intact IL-2 signaling during priming synergistically induces genome-wide chromatin accessibility in regions targeting a wide breadth of biological processes, consistent with greater T cell functional fitness. Chromatin accessibility in promoters of genes encoding for stem cell, cell cycle and calcium-related proteins correlates with faster intracellular calcium accumulation, initiation of cell cycle and more robust expansion. High-dimensional flow-cytometry analysis of these T cells also highlights higher diversity of T cell subsets and phenotypes with T cells primed with stronger TCR and IL-2 stimulation than those primed with weaker strengths of TCR and/or IL-2 signals. These results formally show that epitope selection in vaccine design impacts memory CD8
T cell epigenetic programming and function.
Antitumor T cell responses involve CD8
T cells with high affinity for mutated self-antigen and low affinity for nonmutated tumor-associated Ag. Because of the highly individual nature of ...nonsynonymous somatic mutations in tumors, however, immunotherapy relies often on an effective engagement of low-affinity T cells. In this study, we studied the role of T cell affinity during peripheral priming with single-peptide vaccines and during the effector phase in the tumor. To that end, we compared the antitumor responses after OVA
(N4) peptide vaccination of CD8
T cells carrying TCRs with high (OT-1) and low (OT-3) avidity for the N4 peptide in B16.N4 tumor-bearing C57BL/6 mice. Additionally, we assessed the response of OT-1 cells to either high-affinity (B16.N4) or low-affinity (B16.T4) Ag-expressing tumors after high-affinity (N4) or low-affinity (T4) peptide vaccination. We noticed that although low-affinity tumor-specific T cells expand less than high-affinity T cells, they express lower levels of inhibitory receptors and produce more cytokines. Interestingly, tumor-infiltrating CD8
T cells show similar in vivo re-expansion capacity to their counterparts in secondary lymphoid organs when transferred to tumor-free hosts, suggesting that T cells in tumors may be rekindled upon relief of tumor immunosuppression. Moreover, our results show that αPD-1 treatment enhances tumor control of high- and low-affinity ligand-expressing tumors, suggesting that combination of high-affinity peripheral priming by altered peptide ligands and checkpoint blockade may enable tumor control upon low-affinity Ag recognition in the tumor.
In chronic infection and cancer, T cells acquire a dysfunctional state characterized by the expression of inhibitory receptors. In vitro studies implicated the phosphatase Shp-2 downstream of these ...receptors, including PD-1. However, whether Shp-2 is responsible in vivo for such dysfunctional responses remains elusive. To address this, we generated T cell-specific Shp-2-deficient mice. These mice did not show differences in controlling chronic viral infections. In this context, Shp-2-deleted CD8+ T lymphocytes expanded moderately better but were less polyfunctional than control cells. Mice with Shp-2-deficient T cells also showed no significant improvement in controlling immunogenic tumors and responded similarly to controls to α-PD-1 treatment. We therefore showed that Shp-2 is dispensable in T cells for globally establishing exhaustion and for PD-1 signaling in vivo. These results reveal the existence of redundant mechanisms downstream of inhibitory receptors and represent the foundation for defining these relevant molecular events.
Display omitted
•Shp-2 modulates selected T cell exhaustion features•Shp-2 is not required for the global dysfunctional state of exhausted T cells•Anticancer α-PD-1 treatment is beneficial in mice with Shp-2-deficient T cells
In vitro data indicate that Shp-2 is engaged by PD-1 and contributes to T cell exhaustion. Rota et al. show that Shp-2-deficient T cells acquire a dysfunctional state when exposed to chronic antigen in vivo and respond to PD-1 blockade, indicating the existence of additional signaling factors.
Single-cell RNA sequencing in principle offers unique opportunities to improve the efficacy of contemporary T-cell based immunotherapy against cancer. The use of high-quality single-cell data will ...aid our incomplete understanding of molecular programs determining the differentiation and functional heterogeneity of cytotoxic T lymphocytes (CTLs), allowing for optimal therapeutic design. So far, a major obstacle to high depth single-cell analysis of CTLs is the minute amount of RNA available, leading to low capturing efficacy. Here, to overcome this, we tailor a droplet-based approach for high-throughput analysis (tDrop-seq) and a plate-based method for high-performance in-depth CTL analysis (tSCRB-seq). The latter gives, on average, a 15-fold higher number of captured transcripts per gene compared to droplet-based technologies. The improved dynamic range of gene detection gives tSCRB-seq an edge in resolution sensitive downstream applications such as graded high confidence gene expression measurements and cluster characterization. We demonstrate the power of tSCRB-seq by revealing the subpopulation-specific expression of co-inhibitory and co-stimulatory receptor targets of key importance for immunotherapy.
Competition for nutrients like glucose can metabolically restrict T cells and contribute to their hyporesponsiveness during cancer. Metabolic adaptation to the surrounding microenvironment is ...therefore key for maintaining appropriate cell function. For instance, cancer cells use acetate as a substrate alternative to glucose to fuel metabolism and growth. Here, we show that acetate rescues effector function in glucose-restricted CD8+ T cells. Mechanistically, acetate promotes histone acetylation and chromatin accessibility and enhances IFN-γ gene transcription and cytokine production in an acetyl-CoA synthetase (ACSS)-dependent manner. Ex vivo acetate treatment increases IFN-γ production by exhausted T cells, whereas reducing ACSS expression in T cells impairs IFN-γ production by tumor-infiltrating lymphocytes and tumor clearance. Thus, hyporesponsive T cells can be epigenetically remodeled and reactivated by acetate, suggesting that pathways regulating the use of substrates alternative to glucose could be therapeutically targeted to promote T cell function during cancer.
Display omitted
•Acetate restores IFN-γ in TILs and T cells under prolonged glucose-restriction•Acetate promotes histone acetylation and chromatin accessibility in T cells•ACSS expression contributes to optimal effector T cell function during cancer
Qiu et al. show that acetate enhances histone acetylation, chromatin accessibility, and effector function in glucose-restricted CD8+ T cells. The authors find that manipulation of acetate-handling pathways influences cytokine production of tumor-infiltrating CD8+ T cells, which could have therapeutic implications for activating CD8+ T cell effector function in the tumor microenvironment.
The pool of beta cell-specific CD8
T cells in type 1 diabetes (T1D) sustains an autoreactive potential despite having access to a constant source of antigen. To investigate the long-lived nature of ...these cells, we established a DNA methylation-based T cell 'multipotency index' and found that beta cell-specific CD8
T cells retained a stem-like epigenetic multipotency score. Single-cell assay for transposase-accessible chromatin using sequencing confirmed the coexistence of naive and effector-associated epigenetic programs in individual beta cell-specific CD8
T cells. Assessment of beta cell-specific CD8
T cell anatomical distribution and the establishment of stem-associated epigenetic programs revealed that self-reactive CD8
T cells isolated from murine lymphoid tissue retained developmentally plastic phenotypic and epigenetic profiles relative to the same cells isolated from the pancreas. Collectively, these data provide new insight into the longevity of beta cell-specific CD8
T cell responses and document the use of this methylation-based multipotency index for investigating human and mouse CD8
T cell differentiation.
PDF
