Conventional type I dendritic cells maintain a reservoir of proliferative tumor-antigen specific TCF-1+ CD8+ T cells in tumor-draining lymph nodes

In tumors, a subset of CD8+ T cells expressing the transcription factor TCF-1 drives the response to immune checkpoint blockade. We examined the mechanisms that maintain these cells in an autochthonous model of lung adenocarcinoma. Longitudinal sampling and single-cell sequencing of tumor-antigen specific TCF-1+ CD8+ T cells revealed that while intratumoral TCF-1+ CD8+ T cells acquired dysfunctional features and decreased in number as tumors progressed, TCF-1+ CD8+ T cell frequency in the tumor draining LN (dLN) remained stable. Two discrete intratumoral TCF-1+ CD8+ T cell subsets developed over time-a proliferative SlamF6+ subset and a non-cycling SlamF6- subset. Blocking dLN egress decreased the frequency of intratumoral SlamF6+ TCF-1+ CD8+ T cells. Conventional type I dendritic cell (cDC1) in dLN decreased in number with tumor progression, and Flt3L+anti-CD40 treatment recovered SlamF6+ T cell frequencies and decreased tumor burden. Thus, cDC1s in tumor dLN maintain a reservoir of TCF-1+ CD8+ T cells and their decrease contributes to failed anti-tumor immunity.

PD-1+ Tcf1+ CD8+ T cells from established chronic infection can form memory while retaining a stableimprint of persistent antigen exposure

Virus-specific PD1+ Tcf1+ memory-like CD8+ T cells (TMLs) maintain the CD8+ T cell response during chronic viral infection. However, the fate of these cells following cessation of persistent antigen exposure has been unclear. Here, we find that TMLs persist upon transfer into antigen-free hosts and form memory following recall stimulation. Phenotypic, functional, and transcriptome analyses show that TML-derived memory cells resemble those arising in response to acute, resolved infection, but they retain features of chronically stimulated cells, including elevated PD-1 and Tox and reduced cytokine expression. This chronic infection imprint is largely accounted for by constitutive Tox expression. Virus-specific Tcf1+ CD8+ T cells that persist after clearance of systemic infection also display a chronic infection imprint. Notwithstanding, renewed virus exposure induces a recall response, which controls virus infection in part. Thus, cessation of chronic antigen exposure yields a memory CD8+ T cell compartment that reflects prior stimulation.

TCF-1 regulates HIV-specific CD8+ T cell expansion capacity

Although many HIV cure strategies seek to expand HIV-specific CD8+ T cells to control the virus, all are likely to fail if cellular exhaustion is not prevented. A loss in stem-like memory properties (i.e., the ability to proliferate and generate secondary effector cells) is a key feature of exhaustion; little is known, however, about how these properties are regulated in human virus-specific CD8+ T cells. We found that virus-specific CD8+ T cells from humans and nonhuman primates naturally controlling HIV/SIV infection express more of the transcription factor TCF-1 than noncontrollers. HIV-specific CD8+ T cell TCF-1 expression correlated with memory marker expression and expansion capacity and declined with antigenic stimulation. CRISPR-Cas9 editing of TCF-1 in human primary T cells demonstrated a direct role in regulating expansion capacity. Collectively, these data suggest that TCF-1 contributes to the regulation of the stem-like memory property of secondary expansion capacity of HIV-specific CD8+ T cells, and they provide a rationale for exploring the enhancement of this pathway in T cell-based therapeutic strategies for HIV.

In Situ Maturation and Tissue Adaptation of Type 2 Innate Lymphoid Cell Progenitors

Innate lymphoid cells (ILCs) are generated early during ontogeny and persist predominantly as tissue-resident cells. Here, we examined how ILCs are maintained and renewed within tissues. We generated a single cell atlas of lung ILC2s and found that Il18r1+ ILCs comprise circulating and tissue-resident ILC progenitors (ILCP) and effector-cells with heterogeneous expression of the transcription factors Tcf7 and Zbtb16, and CD103. Our analyses revealed a continuous differentiation trajectory from Il18r1+ ST2- ILCPs to Il18r- ST2+ ILC2s, which was experimentally validated. Upon helminth infection, recruited and BM-derived cells generated the entire spectrum of ILC2s in parabiotic and shield chimeric mice, consistent with their potential role in the renewal of tissue ILC2s. Our findings identify local ILCPs and reveal ILCP in situ differentiation and tissue adaptation as a mechanism of ILC maintenance and phenotypic diversification. Local niches, rather than progenitor origin, or the developmental window during ontogeny, may dominantly imprint ILC phenotypes in adult tissues.

IL-17A-producing T cells exacerbate fine particulate matter-induced lung inflammation and fibrosis by inhibiting PI3K/Akt/mTOR-mediated autophagy

Fine particulate matter (PM2.5) is the primary air pollutant that is able to induce airway injury. Compelling evidence has shown the involvement of IL-17A in lung injury, while its contribution to PM2.5-induced lung injury remains largely unknown. Here, we probed into the possible role of IL-17A in mouse models of PM2.5-induced lung injury. Mice were instilled with PM2.5 to construct a lung injury model. Flow cytometry was carried out to isolate γδT and Th17 cells. ELISA was adopted to detect the expression of inflammatory factors in the supernatant of lavage fluid. Primary bronchial epithelial cells (mBECs) were extracted, and the expression of TGF signalling pathway-, autophagy- and PI3K/Akt/mTOR signalling pathway-related proteins in mBECs was detected by immunofluorescence assay and Western blot analysis. The mitochondrial function was also evaluated. PM2.5 aggravated the inflammatory response through enhancing the secretion of IL-17A by γδT/Th17 cells. Meanwhile, PM2.5 activated the TGF signalling pathway and induced EMT progression in bronchial epithelial cells, thereby contributing to pulmonary fibrosis. Besides, PM2.5 suppressed autophagy of bronchial epithelial cells by up-regulating IL-17A, which in turn activated the PI3K/Akt/mTOR signalling pathway. Furthermore, IL-17A impaired the energy metabolism of airway epithelial cells in the PM2.5-induced models. This study suggested that PM2.5 could inhibit autophagy of bronchial epithelial cells and promote pulmonary inflammation and fibrosis by inducing the secretion of IL-17A in γδT and Th17 cells and regulating the PI3K/Akt/mTOR signalling pathway.

HIV-1-induced cytokines deplete homeostatic innate lymphoid cells and expand TCF7-dependent memory NK cells

Human immunodeficiency virus 1 (HIV-1) infection is associated with heightened inflammation and excess risk of cardiovascular disease, cancer and other complications. These pathologies persist despite antiretroviral therapy. In two independent cohorts, we found that innate lymphoid cells (ILCs) were depleted in the blood and gut of people with HIV-1, even with effective antiretroviral therapy. ILC depletion was associated with neutrophil infiltration of the gut lamina propria, type 1 interferon activation, increased microbial translocation and natural killer (NK) cell skewing towards an inflammatory state, with chromatin structure and phenotype typical of WNT transcription factor TCF7-dependent memory T cells. Cytokines that are elevated during acute HIV-1 infection reproduced the ILC and NK cell abnormalities ex vivo. These results show that inflammatory cytokines associated with HIV-1 infection irreversibly disrupt ILCs. This results in loss of gut epithelial integrity, microbial translocation and memory NK cells with heightened inflammatory potential, and explains the chronic inflammation in people with HIV-1.

The transcription factor c-Myb regulates CD8+ T cell stemness and antitumor immunity

Stem cells are maintained by transcriptional programs that promote self-renewal and repress differentiation. Here, we found that the transcription factor c-Myb was essential for generating and maintaining stem cells in the CD8+ T cell memory compartment. Following viral infection, CD8+ T cells lacking Myb underwent terminal differentiation and generated fewer stem cell-like central memory cells than did Myb-sufficient T cells. c-Myb acted both as a transcriptional activator of Tcf7 (which encodes the transcription factor Tcf1) to enhance memory development and as a repressor of Zeb2 (which encodes the transcription factor Zeb2) to hinder effector differentiation. Domain-mutagenesis experiments revealed that the transactivation domain of c-Myb was necessary for restraining differentiation, whereas its negative regulatory domain was critical for cell survival. Myb overexpression enhanced CD8+ T cell memory formation, polyfunctionality and recall responses that promoted curative antitumor immunity after adoptive transfer. These findings identify c-Myb as a pivotal regulator of CD8+ T cell stemness and highlight its therapeutic potential.

T cell factor-1 controls the lifetime of CD4+ CD8+ thymocytes in vivo and distal T cell receptor α-chain rearrangement required for NKT cell development

Natural killer T (NKT) cells are a component of innate and adaptive immune systems implicated in immune, autoimmune responses and in the control of obesity and cancer. NKT cells develop from common CD4+ CD8+ double positive (DP) thymocyte precursors after the rearrangement and expression of T cell receptor (TCR) Vα14-Jα18 gene. Temporal regulation and late appearance of Vα14-Jα18 rearrangement in immature DP thymocytes has been demonstrated. However, the precise control of lifetime of DP thymocytes in vivo that enables distal rearrangements remains incompletely defined. Here we demonstrate that T cell factor (TCF)-1, encoded by the Tcf7 gene, is critical for the extended lifetime of DP thymocytes. TCF-1-deficient DP thymocytes fail to undergo TCR Vα14-Jα18 rearrangement and produce significantly fewer NKT cells. Ectopic expression of Bcl-x_L permits Vα14-Jα18 rearrangement and rescues NKT cell development. We report that TCF-1 regulates expression of RORγt, which regulates DP thymocyte survival by controlling expression of Bcl-x_L. We posit that TCF-1 along with its cofactors controls the lifetime of DP thymocytes in vivo.

Regulation of thymocyte survival by transcriptional coactivators

A majority of the developing T cells are eliminated by apoptosis because they do not meet the positive and negative selection criteria. Developing T cells are thus susceptible to apoptotic signals. On the other hand, there are mechanisms to prevent developing T cells from premature apoptosis. Maintenance of a fine balance between life and death is thus critical for successful completion of T-cell development. Our recent studies demonstrated an essential role of transcriptional coactivators in maintaining such a balance for developing T cells. Transcriptional coactivators are recruited by transcriptional factors to quantitatively regulate gene expression via modifying chromatin structure. Two transcriptional factors, TCF-1 and ROR gamma t, are required to upregulate the levels of Bcl-xL, a critical survival factor for CD4+CD8+ double-positive thymocytes. However, TCF-1 and ROR gamma t by themselves are not sufficient to stimulate Bcl-xL expression. Transcriptional coactivator beta-catenin recruited by TCF-1, and steroid receptor coactivators (SRCs) recruited by ROR gamma t, are also required for optimal stimulation of Bcl-xL expression. Thus, transcriptional coactivators are a substantial component of the transcriptional machinery to regulate thymocye survival, ensuring the completion of T-cell development.