Functional impairment of "helpless" CD8 + memory T cells is transient and driven by prolonged but finite cognate antigen presentation

Generation of functional CD8 + T cell memory typically requires engagement of CD4 + T cells. However, in certain scenarios, such as acutely-resolving viral infections, effector (T E ) and subsequent memory (T M ) CD8 + T cell formation appear impervious to a lack of CD4 + T cell help during priming. Nonetheless, such "helpless" CD8 + T M respond poorly to pathogen rechallenge. At present, the origin and long-term evolution of helpless CD8 + T cell memory remain incompletely understood. Here, we demonstrate that helpless CD8 + T E differentiation is largely normal but a multiplicity of helpless CD8 T M defects, consistent with impaired memory maturation, emerge as a consequence of prolonged yet finite exposure to cognate antigen. Importantly, these defects resolve over time leading to full restoration of CD8 + T M potential and recall capacity. Our findings provide a unified explanation for helpless CD8 + T cell memory and emphasize an unexpected CD8 + T M plasticity with implications for vaccination strategies and beyond.

Sustained CD28 costimulation is required for self-renewal and differentiation of TCF-1+ PD-1+ CD8 T cells

During persistent antigen stimulation, such as in chronic infections and cancer, CD8 T cells differentiate into a hypofunctional programmed death protein 1-positive (PD-1+) exhausted state. Exhausted CD8 T cell responses are maintained by precursors (Tpex) that express the transcription factor T cell factor 1 (TCF-1) and high levels of the costimulatory molecule CD28. Here, we demonstrate that sustained CD28 costimulation is required for maintenance of antiviral T cells during chronic infection. Low-level CD28 engagement preserved mitochondrial fitness and self-renewal of Tpex, whereas stronger CD28 signaling enhanced glycolysis and promoted Tpex differentiation into TCF-1neg exhausted CD8 T cells (Tex). Furthermore, enhanced differentiation by CD28 engagement did not reduce the Tpex pool. Together, these findings demonstrate that continuous CD28 engagement is needed to sustain PD-1+ CD8 T cells and suggest that increasing CD28 signaling promotes Tpex differentiation into more functional effector-like Tex, possibly without compromising long-term responses.

Intratumoral dendritic cell-CD4+ T helper cell niches enable CD8+ T cell differentiation following PD-1 blockade in hepatocellular carcinoma

Despite no apparent defects in T cell priming and recruitment to tumors, a large subset of T cell rich tumors fail to respond to immune checkpoint blockade (ICB). We leveraged a neoadjuvant anti-PD-1 trial in patients with hepatocellular carcinoma (HCC), as well as additional samples collected from patients treated off-label, to explore correlates of response to ICB within T cell-rich tumors. We show that ICB response correlated with the clonal expansion of intratumoral CXCL13+CH25H+IL-21+PD-1+CD4+ T helper cells ("CXCL13+ TH") and Granzyme K+ PD-1+ effector-like CD8+ T cells, whereas terminally exhausted CD39hiTOXhiPD-1hiCD8+ T cells dominated in nonresponders. CD4+ and CD8+ T cell clones that expanded post-treatment were found in pretreatment biopsies. Notably, PD-1+TCF-1+ (Progenitor-exhausted) CD8+ T cells shared clones mainly with effector-like cells in responders or terminally exhausted cells in nonresponders, suggesting that local CD8+ T cell differentiation occurs upon ICB. We found that these Progenitor CD8+ T cells interact with CXCL13+ TH within cellular triads around dendritic cells enriched in maturation and regulatory molecules, or "mregDC". These results suggest that discrete intratumoral niches that include mregDC and CXCL13+ TH control the differentiation of tumor-specific Progenitor exhasuted CD8+ T cells following ICB.

TREM2 macrophages drive NK cell paucity and dysfunction in lung cancer

Natural killer (NK) cells are commonly reduced in human tumors, enabling many to evade surveillance. Here, we sought to identify cues that alter NK cell activity in tumors. We found that, in human lung cancer, the presence of NK cells inversely correlated with that of monocyte-derived macrophages (mo-macs). In a murine model of lung adenocarcinoma, we show that engulfment of tumor debris by mo-macs triggers a pro-tumorigenic program governed by triggering receptor expressed on myeloid cells 2 (TREM2). Genetic deletion of Trem2 rescued NK cell accumulation and enabled an NK cell-mediated regression of lung tumors. TREM2+ mo-macs reduced NK cell activity by modulating interleukin (IL)-18/IL-18BP decoy interactions and IL-15 production. Notably, TREM2 blockade synergized with an NK cell-activating agent to further inhibit tumor growth. Altogether, our findings identify a new axis, in which TREM2+ mo-macs suppress NK cell accumulation and cytolytic activity. Dual targeting of macrophages and NK cells represents a new strategy to boost antitumor immunity.

Advancing beyond the twists and turns of T cell exhaustion in cancer

Chronic antigen stimulation leads to T cell exhaustion. Nutrient restrictions and other suppressive factors in the tumor microenvironment further exacerbate T cell dysfunction. Better understanding of heterogeneity and dynamics of exhausted CD8 T cells will guide novel therapies that modulate T cell differentiation to achieve more effective antitumor responses.

Hematopoietic Prostaglandin D2 Synthase Controls Tfh/Th2 Communication and Limits Tfh Antitumor Effects

T follicular helper (Tfh) cells are a subset of CD4+ T cells essential in immunity and have a role in helping B cells produce antibodies against pathogens. However, their role during cancer progression remains unknown. The mechanism of action of Tfh cells remains elusive because contradictory data have been reported on their protumor or antitumor responses in human and murine tumors. Like Tfh cells, Th2 cells are also involved in humoral immunity and are regularly associated with tumor progression and poor prognosis, mainly through their secretion of IL4. Here, we showed that Tfh cells expressed hematopoietic prostaglandin D2 (PGD2) synthase in a pSTAT1/pSTAT3-dependent manner. Tfh cells produced PGD2, which led to recruitment of Th2 cells via the PGD2 receptor chemoattractant receptor homologous molecule expressed on Th type 2 cells (CRTH2) and increased their effector functions. This cross-talk between Tfh and Th2 cells promoted IL4-dependent tumor growth. Correlation between Th2 cells, Tfh cells, and hematopoietic PGD2 synthase was observed in different human cancers and associated with outcome. This study provides evidence that Tfh/Th2 cross-talk through PGD2 limits the antitumor effects of Tfh cells and, therefore, could serve as a therapeutic target.

CD28 signaling strength regulates the cell fate of TCF-1+ PD-1+ CD8 T cells

During chronic infections and cancer, CD8 T cells that recognize pathogens/tumors can persist in a dysfunctional state characterized by high expression of the inhibitory receptor Programmed Cell Death (PD)-1. T cell factor (TCF)-1+PD-1+ progenitor exhausted cells (Tpex) maintain the antigen-specific T cell pool by self-renewal and differentiation into effector-like TCF-1negPD-1+CD8 T cells. Previous studies described that among PD-1+ CD8 T cells, only Tpex respond to PD-1 blockade therapy. However, the molecular mechanisms that support Tpex self-renewal or differentiation are not understood. Tpex have high CD28 expression and we demonstrated that CD28 costimulation is required for response to PD-1 targeted therapy. To better understand the role of CD28 on Tpex, we evaluated how reduction or abrogation of CD28 signaling impacted virus-specific CD8 T cells in mice infected with lymphocytic choriomeningitis virus (LCMV). During established chronic infection, deletion of both Cd28 alleles resulted in reduction of Tpex and TCF-1neg subsets. In contrast, when CD28 signaling was reduced (deletion of one allele), TCF-1negPD-1+ CD8 T cells decreased, but the number of Tpex was not affected. RNA sequencing and metabolic assays revealed that sustained CD28 signaling during persistent antigen stimulation is required to maintain mitochondrial fitness of Tpex. Our work supports the novel hypothesis that CD28 signaling strength modulates Tpex fate decision through metabolic regulation. Our data also suggest continuous CD28 signaling is required for long-term maintenance of antigen-specific PD-1+ CD8 T cells. These findings have important implications for checkpoint therapy in cancer.

Abstract 515: Heterogeneity of PD-1hi CD8 T cells associates with response to PD-1 blockade in hepatocellular carcinoma

Blockade of the PD-1 pathway is a therapeutic strategy to reinvigorate T cell responses against tumors, and when combined with other biologic therapies in the first line setting this achieves significant clinical response in about 25% of hepatocellular carcinoma (HCC) patients. We hypothesize that phenotypic diversity of tumor infiltrating T cells can explain, at least partially, the disparate clinical responses to immunotherapy. Here, we analyze the molecular diversity of T cells in tumor, adjacent tissue and tumor-draining lymph node (dLN) by single-cell RNA sequencing of tissue from 23 patients with early stage HCC treated by neoadjuvant PD-1 blockade (NCT03916627; final data to be submitted to AACR 2021 as late breaking abstract). We identify distinct subsets of PD-1hi CD8 T cells with varying degrees of exhaustion and effector gene programs. Compared to parallel analysis of untreated HCC tumors, we observed that PD-1 blockade resulted in expansion of PD-1hi CD8 T cells in the tumor, regardless of clinical response. PD-1hi CD8 T cell subsets were highly clonal and enriched in the tumor compared to adjacent tissue, suggesting specificity to tumor antigens. Remarkably, we find an association between a specific transcriptomic phenotype within PD-1hi CD8 T cells and response to PD-1 blockade. Using T cell receptor (TCR) sequencing to study the differentiation patterns between T cell states, we found that expanded clonotypes present among PD-1hi CD8 T cells were also found in CD8 effector cells; these data identify characteristic clonally related T cell populations that are enriched in clinical responders. Furthermore, we find the dLNs harbor clonotypes of PD-1hi CD8 T cells expanded in the tumor. These clonally expanded CD8 T cells in dLN display features of activation and exhaustion, suggesting a continuous role of dLN in anti-tumor responses. These results will be corroborated with 8 additional patient samples in which we will further analyze the molecular characteristics of tumor-specific CD8 T cells in the TME and dLN. Furthermore, our ongoing sequencing of pre- and post-treatment lesions will enable measurement of CD8 T cell clonal expansion and molecular programs during response or resistance to PD-1 blockade. These results should help unravel the contribution of dLN T cells to response to immunotherapy as well as identify T cell molecular programs at baseline that correlate with response.

Citation Format: Assaf Magen, Pauline Hamon, Etienne Humblin, Alessandra Schanoski, Joel Kim, Jessica Le Berichel, Ephraim Kenigsberg, Myron Schwartz, Thomas Marron, Alice Kamphorst, Miriam Merad. Heterogeneity of PD-1hi CD8 T cells associates with response to PD-1 blockade in hepatocellular carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 515.

The Tumor Microenvironment Impairs Th1 IFNγ Secretion through Alternative Splicing Modifications of Irf1 Pre-mRNA

It is clearly established that the immune system can affect cancer response to therapy. However, the influence of the tumor microenvironment (TME) on immune cells is not completely understood. In this respect, alternative splicing is increasingly described to affect the immune system. Here, we showed that the TME, via a TGFβ-dependent mechanism, increased alternative splicing events and induced the expression of an alternative isoform of the IRF1 transcription factor (IRF1Δ7) in Th1 cells. We found that the SFPQ splicing factor (splicing factor, proline- and glutamine-rich) was responsible for the IRF1Δ7 production. We also showed, in both mice and humans, that the IRF1 alternative isoform altered the full-length IRF1 transcriptional activity on the Il12rb1 promoter, resulting in decreased IFNγ secretion in Th1 cells. Thus, the IRF1Δ7 isoform was increased in the TME, and inhibiting IRF1Δ7 expression could potentiate Th1 antitumor responses.

PARP inhibitor resistance and TP53 mutations in patients treated with olaparib for BRCA-mutated cancer: Four case reports

Loss‑of‑function BRCA mutations are frequent in high‑grade serous ovarian carcinoma. BRCA1 and ‑2 mutations lead to homologous recombination (HR) deficiency. Poly(ADP‑ribose) polymerases (PARP) are enzymes involved in DNA repair. PARP inhibitors (PARPi) lead to DNA damage accumulation in cells deficient in HR. Olaparib (a PARPi) is currently used for the treatment of high‑grade serous ovarian carcinoma with germline or somatic BRCA mutations; however, numerous patients do not respond or eventually develop resistance to these agents. The TP53 gene encodes the p53 protein, which is often referred to as the 'guardian of the genome'. TP53 mutations at diagnosis are known to promote resistance to chemotherapy. In the present study, four cases of patients with BRCA‑mutated cancer treated with olaparib, who progressed following the PARPi treatment, are reported. Exome analyses were performed on a primary tumor biopsy at diagnosis, then on a progressing metastasis following olaparib treatment. Exome analyses following olaparib treatment identified de novo TP53 mutations, as well as increased frequencies of pre‑existing TP53 mutations compared with the primary tumor. In HCT116 TP53^‑/‑ cells carrying BRCA2 pathogenic mutations, TP53 inactivating mutations were associated with lower sensitivity to olaparib in vitro. Thus, inactivating TP53 mutations may be associated to olaparib resistance in the presence of BRCA mutations. In conclusion, the present findings demonstrated resistance to PARPi with de novo TP53 mutations that may be clinically relevant. As TP53 mutations are easily detectable with targeted next‑generation sequencing panels, these may serve as surrogate markers for the onset of PARPi resistance in the context of routine patient management strategies.

CXCR3-CXCL9: It's All in the Tumor

In this issue of Immunity, Chow et al. (2019) show that the CXCR3-CXCL9 axis is required for reinvigoration of intratumoral CD8⁺ T cell responses in response to PD-1 blockade and demonstrate that local guidance to dendritic cells, rather than recruitment of T cells into the tumor, underlies the importance of this chemokine axis.

Transcriptional Programs Underlying Cd4 T Cell Differentiation and Functions

Understanding the basis of cellular differentiation is a fundamental issue in developmental biology but also for the comprehension of pathological processes. In fact, the palette of developmental decisions for naive CD4 T cells is a critical aspect of the development of appropriate immune responses which could control infectious processes or cancer growth. However, the current accumulation of data on CD4 T cells biology reveals a complex world with different helper populations. Naive CD4 T cells can differentiate into different subtypes in response to cytokine stimulation. This stimulation involves a complex transcriptional network implicating the activation of Signal Transducer and Activator of Transcription but also master regulator transcription factors allowing the functions of each helper T lymphocyte subtype. In this review, we will present an overview of the transcriptional regulation which controls process of helper T cells differentiation. We will focus on the role of initiator transcriptional factors and on master regulators but also on other nonspecific transcriptional factors which refine the T helper polarization to stabilize or modulate the differentiation program.

TRAIL receptor gene editing unveils TRAIL-R1 as a master player of apoptosis induced by TRAIL and ER stress

TRAIL induces selective tumor cell death through TRAIL-R1 and TRAIL-R2. Despite the fact that these receptors share high structural homologies, induction of apoptosis upon ER stress, cell autonomous motility and invasion have solely been described to occur through TRAIL-R2. Using the TALEN gene-editing approach, we show that TRAIL-R1 can also induce apoptosis during unresolved unfolded protein response (UPR). Likewise, TRAIL-R1 was found to co-immunoprecipitate with FADD and caspase-8 during ER stress. Its deficiency conferred resistance to apoptosis induced by thaspigargin, tunicamycin or brefeldin A. Our data also demonstrate that tumor cell motility and invasion-induced by TRAIL-R2 is not cell autonomous but induced in a TRAIL-dependant manner. TRAIL-R1, on the other hand, is unable to trigger cell migration owing to its inability to induce an increase in calcium flux. Importantly, all the isogenic cell lines generated in this study revealed that apoptosis induced TRAIL is preferentially induced by TRAIL-R1. Taken together, our results provide novel insights into the physiological functions of TRAIL-R1 and TRAIL-R2 and suggest that targeting TRAIL-R1 for anticancer therapy is likely to be more appropriate owing to its lack of pro-motile signaling capability.

TH9 cells in anti-tumor immunity

IL-9 was initially identified as a T cell growth factor with a potential oncogenic activity. Accordingly, IL-9 drives tumor growth in most hematological cancers. However, the links between IL-9 and cancer progression have been recently revisited following the discovery of T_H9 cells. T_H9 cells, which have been characterized in 2008 as a proinflammatory CD4 T cell subset that promotes protection against parasites and drives tissue inflammation in colitis, actually harbor potent IL-9-dependent anti-cancer properties in solid tumors and especially melanoma. While the molecular mechanisms underlying these observations are still being investigated, T_H9 cells were demonstrated to activate both innate and adaptive immune responses, thereby favoring anti-cancer immunity and tumor elimination. Human T_H9 cells have also been identified in cancer tissues, but their functions remain elusive. The present review aims to discuss the anti-cancer potential of T_H9 cells and their possible clinical relevance for cancer immunotherapy.