Divergent molecular networks program functionally distinct CD8+ skin-resident memory T cells

Skin-resident CD8+ T cells include distinct interferon-γ-producing [tissue-resident memory T type 1 (TRM1)] and interleukin-17 (IL-17)-producing (TRM17) subsets that differentially contribute to immune responses. However, whether these populations use common mechanisms to establish tissue residence is unknown. In this work, we show that TRM1 and TRM17 cells navigate divergent trajectories to acquire tissue residency in the skin. TRM1 cells depend on a T-bet-Hobit-IL-15 axis, whereas TRM17 cells develop independently of these factors. Instead, c-Maf commands a tissue-resident program in TRM17 cells parallel to that induced by Hobit in TRM1 cells, with an ICOS-c-Maf-IL-7 axis pivotal to TRM17 cell commitment. Accordingly, by targeting this pathway, skin TRM17 cells can be ablated without compromising their TRM1 counterparts. Thus, skin-resident T cells rely on distinct molecular circuitries, which can be exploited to strategically modulate local immunity.

Tissue-resident memory T (TRM ) cells: Front-line workers of the immune system

Tissue-resident memory T (TRM ) cells play a vital role in local immune protection against infection and cancer. The location of TRM cells within peripheral tissues at sites of pathogen invasion allows for the rapid detection and elimination of microbes, making their generation an attractive goal for the development of next-generation vaccines. Here, we discuss differential requirements for CD8+ TRM cell development across tissues with implications for establishing local prophylactic immunity, emphasizing the role of tissue-derived factors, local antigen, and adjuvants on TRM cell generation in the context of vaccination.

Stem-like exhausted and memory CD8+ T cells in cancer

T cells can acquire a broad spectrum of differentiation states following activation. At the extreme ends of this continuum are short-lived cells equipped with effector machinery and more quiescent, long-lived cells with heightened proliferative potential and stem cell-like developmental plasticity. The latter encompass stem-like exhausted T cells and memory T cells, both of which have recently emerged as key determinants of cancer immunity and response to immunotherapy. Here, we discuss key similarities and differences in the regulation and function of stem-like exhausted CD8+ T cells and memory CD8+ T cells, and consider their context-specific contributions to protective immunity in diverse outcomes of cancer, including tumour escape, long-term control and eradication. Finally, we emphasize how recent advances in the understanding of the molecular regulation of stem-like exhausted T cells and memory T cells are being explored for clinical benefit in cancer immunotherapies such as checkpoint inhibition, adoptive cell therapy and vaccination.

Serotonin reduction in post-acute sequelae of viral infection

Post-acute sequelae of COVID-19 (PASC, "Long COVID") pose a significant global health challenge. The pathophysiology is unknown, and no effective treatments have been found to date. Several hypotheses have been formulated to explain the etiology of PASC, including viral persistence, chronic inflammation, hypercoagulability, and autonomic dysfunction. Here, we propose a mechanism that links all four hypotheses in a single pathway and provides actionable insights for therapeutic interventions. We find that PASC are associated with serotonin reduction. Viral infection and type I interferon-driven inflammation reduce serotonin through three mechanisms: diminished intestinal absorption of the serotonin precursor tryptophan; platelet hyperactivation and thrombocytopenia, which impacts serotonin storage; and enhanced MAO-mediated serotonin turnover. Peripheral serotonin reduction, in turn, impedes the activity of the vagus nerve and thereby impairs hippocampal responses and memory. These findings provide a possible explanation for neurocognitive symptoms associated with viral persistence in Long COVID, which may extend to other post-viral syndromes.

Single-cell protein expression profiling resolves circulating and resident memory T cell diversity across tissues and infection contexts

Memory CD8⁺ T cells can be broadly divided into circulating (T_CIRCM) and tissue-resident memory T (T_RM) populations. Despite well-defined migratory and transcriptional differences, the phenotypic and functional delineation of T_CIRCM and T_RM cells, particularly across tissues, remains elusive. Here, we utilized an antibody screening platform and machine learning prediction pipeline (InfinityFlow) to profile >200 proteins in T_CIRCM and T_RM cells in solid organs and barrier locations. High-dimensional analyses revealed unappreciated heterogeneity within T_CIRCM and T_RM cell lineages across nine different organs after either local or systemic murine infection models. Additionally, we demonstrated the relative effectiveness of strategies allowing for the selective ablation of T_CIRCM or T_RM populations across organs and identified CD55, KLRG1, CXCR6, and CD38 as stable markers for characterizing memory T cell function during inflammation. Together, these data and analytical framework provide an in-depth resource for memory T cell classification in both steady-state and inflammatory conditions.

The SWI/SNF chromatin remodeling complexes BAF and PBAF differentially regulate epigenetic transitions in exhausted CD8+ T cells

CD8⁺ T cell exhaustion (Tex) limits disease control during chronic viral infections and cancer. Here, we investigated the epigenetic factors mediating major chromatin-remodeling events in Tex-cell development. A protein-domain-focused in vivo CRISPR screen identified distinct functions for two versions of the SWI/SNF chromatin-remodeling complex in Tex-cell differentiation. Depletion of the canonical SWI/SNF form, BAF, impaired initial CD8⁺ T cell responses in acute and chronic infection. In contrast, disruption of PBAF enhanced Tex-cell proliferation and survival. Mechanistically, PBAF regulated the epigenetic and transcriptional transition from TCF-1⁺ progenitor Tex cells to more differentiated TCF-1^- Tex subsets. Whereas PBAF acted to preserve Tex progenitor biology, BAF was required to generate effector-like Tex cells, suggesting that the balance of these factors coordinates Tex-cell subset differentiation. Targeting PBAF improved tumor control both alone and in combination with anti-PD-L1 immunotherapy. Thus, PBAF may present a therapeutic target in cancer immunotherapy.

Runx3 drives a CD8+ T cell tissue residency program that is absent in CD4+ T cells

Tissue-resident memory T cells (TRM cells) provide rapid and superior control of localized infections. While the transcription factor Runx3 is a critical regulator of CD8+ T cell tissue residency, its expression is repressed in CD4+ T cells. Here, we show that, as a direct consequence of this Runx3-deficiency, CD4+ TRM cells lacked the transforming growth factor (TGF)-β-responsive transcriptional network that underpins the tissue residency of epithelial CD8+ TRM cells. While CD4+ TRM cell formation required Runx1, this, along with the modest expression of Runx3 in CD4+ TRM cells, was insufficient to engage the TGF-β-driven residency program. Ectopic expression of Runx3 in CD4+ T cells incited this TGF-β-transcriptional network to promote prolonged survival, decreased tissue egress, a microanatomical redistribution towards epithelial layers and enhanced effector functionality. Thus, our results reveal distinct programming of tissue residency in CD8+ and CD4+ TRM cell subsets that is attributable to divergent Runx3 activity.

ICOS-play: dressing T cells for residency

Efficient generation of tissue-resident memory T (T_RM) cells is essential for long-lived immune protection in barrier tissues. Peng et al. now show that the costimulatory molecule ICOS enhances CD8⁺ T_RM cell lodgment by promoting early tissue retention.

Sphingosine 1-phosphate receptor 5 (S1PR5) regulates the peripheral retention of tissue-resident lymphocytes

Tissue-resident memory T (TRM) cells provide long-lasting immune protection. One of the key events controlling TRM cell development is the local retention of TRM cell precursors coupled to downregulation of molecules necessary for tissue exit. Sphingosine-1-phosphate receptor 5 (S1PR5) is a migratory receptor with an uncharted function in T cells. Here, we show that S1PR5 plays a critical role in T cell infiltration and emigration from peripheral organs, as well as being specifically downregulated in TRM cells. Consequentially, TRM cell development was selectively impaired upon ectopic expression of S1pr5, whereas loss of S1pr5 enhanced skin TRM cell formation by promoting peripheral T cell sequestration. Importantly, we found that T-bet and ZEB2 were required for S1pr5 induction and that local TGF-β signaling was necessary to promote coordinated Tbx21, Zeb2, and S1pr5 downregulation. Moreover, S1PR5-mediated control of tissue residency was conserved across innate and adaptive immune compartments. Together, these results identify the T-bet-ZEB2-S1PR5 axis as a previously unappreciated mechanism modulating the generation of tissue-resident lymphocytes.

Decoding Tissue-Residency: Programming and Potential of Frontline Memory T Cells

Memory T-cell responses are partitioned between the blood, secondary lymphoid organs, and nonlymphoid tissues. Tissue-resident memory T (Trm) cells are a population of immune cells that remain permanently in tissues without recirculating in blood. These nonrecirculating cells serve as a principal node in the anamnestic response to invading pathogens and developing malignancies. Here, we contemplate how T-cell tissue residency is defined and shapes protective immunity in the steady state and in the context of disease. We review the properties and heterogeneity of Trm cells, highlight the critical roles these cells play in maintaining tissue homeostasis and eliciting immune pathology, and explore how they might be exploited to treat disease.

Ptpn2 and KLRG1 regulate the generation and function of tissue-resident memory CD8+ T cells in skin

Tissue-resident memory T cells (T_RM cells) are key elements of tissue immunity. Here, we investigated the role of the regulator of T cell receptor and cytokine signaling, Ptpn2, in the formation and function of T_RM cells in skin. Ptpn2-deficient CD8⁺ T cells displayed a marked defect in generating CD69⁺ CD103⁺ T_RM cells in response to herpes simplex virus type 1 (HSV-1) skin infection. This was accompanied by a reduction in the proportion of KLRG1⁻ memory precursor cells and a transcriptional bias toward terminal differentiation. Of note, forced expression of KLRG1 was sufficient to impede T_RM cell formation. Normalizing memory precursor frequencies by transferring equal numbers of KLRG1⁻ cells restored T_RM generation, demonstrating that Ptpn2 impacted skin seeding with precursors rather than downstream T_RM cell differentiation. Importantly, Ptpn2-deficient T_RM cells augmented skin autoimmunity but also afforded superior protection from HSV-1 infection. Our results emphasize that KLRG1 repression is required for optimal T_RM cell formation in skin and reveal an important role of Ptpn2 in regulating T_RM cell functionality.

Systemic Inflammation Suppresses Lymphoid Tissue Remodeling and B Cell Immunity during Concomitant Local Infection

Concurrent infection with multiple pathogens occurs frequently in individuals and can result in exacerbated infections and altered immunity. However, the impact of such coinfections on immune responses remains poorly understood. Here, we reveal that systemic infection results in an inflammation-induced suppression of local immunity. During localized infection or vaccination in barrier tissues including the skin or respiratory tract, concurrent systemic infection induces a type I interferon-dependent lymphopenia that impairs lymphocyte recruitment to the draining lymph node (dLN) and induces sequestration of lymphocytes in non-draining LN. This contributes to suppressed fibroblastic reticular cell and endothelial cell expansion and dLN remodeling and impairs induction of B cell responses and antibody production. Our data suggest that contemporaneous systemic inflammation constrains the induction of regional immunity.

Organ-specific isoform selection of fatty acid binding proteins in tissue-resident lymphocytes

Tissue-resident memory T (TRM) cells exist throughout the body where they are poised to mediate local immune responses. Although studies have defined a common mechanism of residency independent of location, there is likely to be a level of specialization that adapts TRM cells to their given tissue of lodgment. It has been shown that TRM cells in the skin rely on the uptake of exogenous fatty acids for their survival and upregulate fatty acid binding proteins (FABP) 4 and FABP 5 as part of their transcriptional program. However, FABPs exist as a larger family of isoforms with different members selected in a tissue-specific fashion that is optimized for local fatty acid availability. Here we show that although TRM cells in a range of tissue widely express FABPs, they are not restricted to FABP 4 and 5. Instead, TRM cells show varying patterns of isoform usage that are determined by tissue-derived factors. These patterns are malleable since TRM cells relocated to different organs modify their FABP expression in line with their new location. As a consequence, these results argue for tissue-specific overlays to the TRM cell residency program, including FABP expression that is tailored to the particular tissue of TRM cell lodgment.

PTPN2 phosphatase deletion in T cells promotes anti-tumour immunity and CAR T-cell efficacy in solid tumours

Although adoptive T-cell therapy has shown remarkable clinical efficacy in haematological malignancies, its success in combating solid tumours has been limited. Here, we report that PTPN2 deletion in T cells enhances cancer immunosurveillance and the efficacy of adoptively transferred tumour-specific T cells. T-cell-specific PTPN2 deficiency prevented tumours forming in aged mice heterozygous for the tumour suppressor p53. Adoptive transfer of PTPN2-deficient CD8⁺ T cells markedly repressed tumour formation in mice bearing mammary tumours. Moreover, PTPN2 deletion in T cells expressing a chimeric antigen receptor (CAR) specific for the oncoprotein HER-2 increased the activation of the Src family kinase LCK and cytokine-induced STAT-5 signalling, thereby enhancing both CAR T-cell activation and homing to CXCL9/10-expressing tumours to eradicate HER-2⁺ mammary tumours in vivo. Our findings define PTPN2 as a target for bolstering T-cell-mediated anti-tumour immunity and CAR T-cell therapy against solid tumours.

Tissue-Resident Memory T Cells in Cancer Immunosurveillance

Following their activation and expansion in response to foreign threats, many T cells are retained in peripheral tissues without recirculating in the blood. These tissue-resident CD8⁺ memory T (T_RM) cells patrol barrier surfaces and nonlymphoid organs, where their critical role in protecting against viral and bacterial infections is well established. Recent evidence suggests that T_RM cells also play a vital part in preventing the development and spread of solid tumors. Here, we discuss the emerging role of T_RM cells in anticancer immunity. We highlight defining features of tumor-localizing T_RM cells, examine the mechanisms through which they have recently been shown to suppress cancer growth, and explore their potential as future targets of cancer immunotherapy.

TCF-1 limits the formation of Tc17 cells via repression of the MAF-RORγt axis

Mielke et al. show that TCF-1 limits IL-17–producing CD8⁺ T (Tc17) cell development from double-positive thymocytes through the sequential suppression of MAF and RORγt, while cementing conventional CD8⁺ T cell fate.

Interleukin (IL)-17–producing CD8⁺ T (Tc17) cells have emerged as key players in host-microbiota interactions, infection, and cancer. The factors that drive their development, in contrast to interferon (IFN)-γ–producing effector CD8⁺ T cells, are not clear. Here we demonstrate that the transcription factor TCF-1 (Tcf7) regulates CD8⁺ T cell fate decisions in double-positive (DP) thymocytes through the sequential suppression of MAF and RORγt, in parallel with TCF-1–driven modulation of chromatin state. Ablation of TCF-1 resulted in enhanced Tc17 cell development and exposed a gene set signature to drive tissue repair and lipid metabolism, which was distinct from other CD8⁺ T cell subsets. IL-17–producing CD8⁺ T cells isolated from healthy humans were also distinct from CD8⁺IL-17⁻ T cells and enriched in pathways driven by MAF and RORγt. Overall, our study reveals how TCF-1 exerts central control of T cell differentiation in the thymus by normally repressing Tc17 differentiation and promoting an effector fate outcome.

Tissue-resident memory T cells mediate melanoma surveillance and are targets of immunotherapy

Non-recirculating tissue-resident memory T (TRM) cells reside permanently in epithelial tissues where they are known to protect against infection. TRM cells have now been identified in various human cancers where they correlate with improved patient outcomes, but the mechanisms through which they may mediate protective tumour immunity remain unclear. Using a novel mouse model of transplantable cutaneous melanoma, we show that tumour-specific TRM cells form spontaneously in the epithelial tumour microenvironment where they protect against cancer development independently of circulating memory T cells. A proportion of epicutaneously inoculated mice remained free of macroscopic tumours long after inoculation, and intravital imaging revealed that these mice harboured dormant melanoma cells in their skin that were dynamically surveyed by tumour-specific TRM cells. Depletion of TRM cells from these mice triggered melanoma escape, indicating that TRM cells suppress tumour progression by promoting cancer-immune equilibrium. Further, we found that pre-activated T cells transferred to tumour-bearing mice in a model of adoptive cell therapy gave rise to TRM cells that inhibited the growth of established melanoma. These tumour-specific TRM cells retained their capacity to execute effector functions and protect against tumour growth despite expression of various inhibitory molecules typically associated with T cell dysfunction. Combined, our findings reveal TRM cells to be durable mediators of anti-tumour immunity and suggest that targeting TRM cell responses could serve as a novel immunotherapeutic strategy to drive elimination of solid tumours.

Tissue-resident memory T cells orchestrate tumour-immune equilibrium

The immune system can prevent tumour development by engaging in a process termed cancer immunosurveillance, during which immune cells such as T cells restrict tumour growth either by completely eradicating cancer cells in a process of 'elimination' or by suppressing cancer cell outgrowth by establishing a state of tumour-immune 'equilibrium'. Most cancers develop within epithelial layers of tissues but circulating T cells are largely excluded from these epithelial tissue compartments in the absence of infection or overt inflammation. In contrast, CD8⁺ tissue-resident memory T (T_RM) cells reside permanently within epithelial layers of peripheral tissues without recirculating in blood. Accumulating evidence suggests that T_RM cells are found in diverse human solid cancers where they correlate with improved prognosis and can protect against tumour challenge in mice. However, the mechanisms through which these cells mediate cancer protection are poorly understood. In our recent study (Park SL et al, Nature 565(7739), 2019) we developed a melanoma model that allowed us to identify a critical role for T_RM cells in the establishment and maintenance of tumour-immune equilibrium in skin. Our findings provide insight into the immune cell populations important for maintaining long-term tumour dormancy in peripheral tissues and imply that targeting T_RM cells may serve as a novel cancer treatment strategy.

Tissue-resident memory CD8+ T cells promote melanoma-immune equilibrium in skin

The immune system can suppress tumour development both by eliminating malignant cells and by preventing the outgrowth and spread of cancer cells that resist eradication¹. Clinical and experimental data suggest that the latter mode of control-termed cancer-immune equilibrium¹-can be maintained for prolonged periods of time, possibly up to several decades^2-4. Although cancers most frequently originate in epithelial layers, the nature and spatiotemporal dynamics of immune responses that maintain cancer-immune equilibrium in these tissue compartments remain unclear. Here, using a mouse model of transplantable cutaneous melanoma⁵, we show that tissue-resident memory CD8⁺ T cells (T_RM cells) promote a durable melanoma-immune equilibrium that is confined to the epidermal layer of the skin. A proportion of mice (~40%) transplanted with melanoma cells remained free of macroscopic skin lesions long after epicutaneous inoculation, and generation of tumour-specific epidermal CD69⁺ CD103⁺ T_RM cells correlated with this spontaneous disease control. By contrast, mice deficient in T_RM formation were more susceptible to tumour development. Despite being tumour^-free at the macroscopic level, mice frequently harboured melanoma cells in the epidermal layer of the skin long after inoculation, and intravital imaging revealed that these cells were dynamically surveyed by T_RM cells. Consistent with their role in melanoma surveillance, tumour-specific T_RM cells that were generated before melanoma inoculation conferred profound protection from tumour development independently of recirculating T cells. Finally, depletion of T_RM cells triggered tumour outgrowth in a proportion (~20%) of mice with occult melanomas, demonstrating that T_RM cells can actively suppress cancer progression. Our results show that T_RM cells have a fundamental role in the surveillance of subclinical melanomas in the skin by maintaining cancer-immune equilibrium. As such, they provide strong impetus for exploring these cells as targets of future anticancer immunotherapies.

Distinct recirculation potential of CD69+CD103- and CD103+ thymic memory CD8+ T cells

Tissue-resident memory T (T_RM) cells occupy peripheral and lymphoid tissues where they confer protection against local infection. While epithelial CD8⁺ T_RM cells coexpress CD69 and CD103, CD103^- memory cells have been described in various organs and are often presumed non-recirculating based on their expression of CD69. We found that both CD69⁺CD103⁺ and CD69⁺CD103^- memory cells populated the thymus upon transfer of CD8⁺ effector T cells into uninfected recipients. Transcriptionally and phenotypically, CD103⁺ thymic cells resembled non-lymphoid T_RM cells, whereas CD69⁺CD103^- cells displayed a profile that was more closely related to recirculating cells. Although CD69 was required for optimal CD103⁺ T_RM formation, its expression alone did not identify permanently resident cells, as CD69⁺CD103^- cells disappeared from the thymus following antibody-mediated depletion of recirculating cells. Our findings highlight a distinct migration potential of phenotypically divergent thymic CD8⁺ memory T cells and emphasise the inadequacy of CD69 as a marker of tissue residency.

Effect of DA-9701, a novel prokinetic agent, on stress-induced delayed gastric emptying and hormonal changes in rats

BACKGROUND

DA-9701 is a novel prokinetic agent formulated with Pharbitis Semen and Corydalis Tuber. This study aimed to evaluate the effect of DA-9701 on stress-induced delay in gastric emptying and changes in plasma adrenocorticotropic hormone and ghrelin levels in rats.

METHODS

Changes in gastric emptying in response to different durations of stress were evaluated. Gastric emptying was compared between the following groups: (i) nonstressed vehicle- or DA-9701-treated group, (ii) nonstressed vehicle- or mosapride-treated group, (iii) 2-h stressed vehicle- or DA-9701-treated group, and (iv) 2-h stressed vehicle- or mosapride-treated group. Water immersion restraint stress was used as the stressor. DA-9701 or mosapride at 3 mg kg(-1) was administered to the rats after subjecting them to 2-h stress, and then gastric emptying was measured using the phenol red method.

KEY RESULTS

Gastric emptying was significantly delayed in the 2-h stressed group compared with the nonstressed group. Mosapride administration resulted in significant recovery from the stress-induced delay in gastric emptying. Gastric emptying in the rats that underwent 2-h stress followed by DA-9701 administration was not significantly different from that in the nonstressed group. The plasma adrenocorticotropic hormone and active ghrelin levels in the 2-h stressed group were significantly higher than those in the nonstressed group. These increases were significantly inhibited by DA-9701.

CONCLUSIONS & INFERENCES

The administration of DA-9701 improved delayed gastric emptying and inhibited the hormonal changes induced by stress, suggesting that DA-9701 can be used as a gastroprokinetic agent for the treatment of delayed gastric emptying, particularly that associated with stress.

Bowenoid epidermotropic metastatic squamous cell carcinoma

Epidermotropic metastatic squamous cell carcinoma produced full-thickness cellular atypia of bowenoid carcinoma in situ or vulvar intraepithelial neoplasia, grade 3 (VIN 3), in a 73-year-old woman who had past history of uterine cervical carcinoma. The presence of intravascular tumor cell nests and areas showing smooth continuity of the malignant squamous cell nodules with the adjoining benign epidermis supported the possibility of the epidermotropic metastasis. To our knowledge, metastatic epidermotropic squamous carcinoma clinicopathologically simulating primary Bowen's disease has not been reported.

Purification and properties of Lactobacillus plantarum inducible malic enzyme

Inducible malic enzyme (l-malate:NAD oxidoreductase [decarboxylating], EC 1.1.1.39) was isolated from Lactobacillus plantarum and purified about 100-fold with 27% yield of the original activity. Kinetic studies with the purified malic enzyme yielded the following results: pH optimum, 7.6 to 8.0; K(m) for l-malate, 0.38 mM; K(m) for NAD, 0.072 mM; and K(m) for MnCl(2), 0.048 mM. It was shown that this enzyme was inhibited by high concentrations of substrate and nicotinamide adenine dinucleotide (NAD), indicating it may be regulated by substrate or NAD. Molecular weight of 130,000 +/- 10,000 was determined by Sephadex gel filtration and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The isoelectric point, determined by isoelectrofocusing, was 4.3 at 7 C. Isoelectrofocusing also resolved three active peaks which focused at pH 4.19, 4.31, and 4.40.