Explore the vast range of titles available.

Delineation of the steps that lead to immune-related adverse effects indicates that checkpoint-mediated suppression of autoreactive T cells occurs within peripheral target tissues rather than at the point of lymph node activation.

Barrier tissues such as the skin contain various populations of immune cells that contribute to protection from infections. These include recently identified tissue-resident memory T cells (T RM). In the skin, these memory CD8 ⁺ T cells reside in the epidermis after being recruited to this site by infection or inflammation. In this study, we demonstrate prolonged persistence of epidermal T RM preferentially at the site of prior infection despite sustained migration. Computational simulation of T RM migration within the skin over long periods revealed that the slow rate of random migration effectively constrains these memory cells within the region of skin in which they form. Notably, formation of T RM involved a concomitant local reduction in dendritic epidermal γδ T-cell numbers in the epidermis, indicating that these populations persist in mutual exclusion and may compete for local survival signals. Accordingly, we show that expression of the aryl hydrocarbon receptor, a transcription factor important for dendritic epidermal γδ T-cell maintenance in skin, also contributes to the persistence of skin T RM. Together, these data suggest that skin tissue-resident memory T cells persist within a tightly regulated epidermal T-cell niche.

Tissue-resident memory T (Trm) cells permanently localize to portals of pathogen entry, where they provide immediate protection against reinfection. To enforce tissue retention, Trm cells up-regulate CD69 and down-regulate molecules associated with tissue egress; however, a Trm-specific transcriptional regulator has not been identified. Here, we show that the transcription factor Hobit is specifically up-regulated in Trm cells and, together with related Blimp1, mediates the development of Trm cells in skin, gut, liver, and kidney in mice. The Hobit-Blimp1 transcriptional module is also required for other populations of tissue-resident lymphocytes, including natural killer T (NKT) cells and liver-resident NK cells, all of which share a common transcriptional program. Our results identify Hobit and Blimp1 as central regulators of this universal program that instructs tissue retention in diverse tissue-resident lymphocyte populations.

Although circulating memory T cells provide enhanced protection against pathogen challenge, they often fail to do so if infection is localized to peripheral or extralymphoid compartments. In those cases, it is T cells already resident at the site of virus challenge that offer superior immune protection. These tissue-resident memory T (TRM) cells are identified by their expression of the α-chain from the integrin αE(CD103)β7, and can exist in disequilibrium with the blood, remaining in the local environment long after peripheral infections subside. In this study, we demonstrate that long-lived intraepithelial CD103+CD8+ TRM cells can be generated in the absence of in situ antigen recognition. Local inflammation in skin and mucosa alone resulted in enhanced recruitment of effector populations and their conversion to the TRM phenotype. The CD8+ TRM cells lodged in these barrier tissues provided long-lived protection against local challenge with herpes simplex virus in skin and vagina challenge models, and were clearly superior to the circulating memory T-cell cohort. The results demonstrate that peripheral TRM cells can be generated and survive in the absence of local antigen presentation and provide a powerful means of achieving immune protection against peripheral infection.

Although memory T cells within barrier tissues can persist as permanent residents, at least some exchange with blood. The extent to which this occurs is unclear. Here we show that memory CD4 + T cells in mouse skin are in equilibrium with the circulation at steady state. These cells are dispersed throughout the inter-follicular regions of the dermis and form clusters with antigen presenting cells around hair follicles. After infection or administration of a contact sensitizing agent, there is a sustained increase in skin CD4 + T-cell content, which is confined to the clusters, with a concomitant CCL5-dependent increase in CD4 + T-cell recruitment. Skin CCL5 is derived from CD11b + cells and CD8 + T cells, with the elimination of the latter decreasing CD4 + T-cell numbers. These results reveal a complex pattern of tissue-retention and equilibration for CD4 + memory T cells in skin, which is altered by infection and inflammation history. Memory T cells are vital responders to skin inflammation, but cell localization and dynamics of exchange with the bloodstream are not clear. Here the authors use parabiosis and intravital microscopy to show that CD4 + memory T cells equilibrate with the circulation and cluster around hair follicles in response to CCL5-dependent responses to viral infection or contact sensitization.

Tissue-resident CD8+ memory T (TRM) cells are immune cells that permanently reside at tissue sites where they play an important role in providing rapid protection against reinfection. They are not only phenotypically and functionally distinct from their circulating memory counterparts, but also exhibit a unique transcriptional profile. To date, the local tissue signals required for their development and long-term residency are not well understood. So far, the best-characterised tissue-derived signal is transforming growth factor-β (TGF-β), which has been shown to promote the development of these cells within tissues. In this study, we aimed to determine to what extent the transcriptional signatures of TRM cells from multiple tissues reflects TGF-β imprinting. We activated murine CD8+ T cells, stimulated them in vitro by TGF-β, and profiled their transcriptomes using RNA-seq. Upon comparison, we identified a TGF-β-induced signature of differentially expressed genes between TGF-β-stimulated and -unstimulated cells. Next, we linked this in vitro TGF-β-induced signature to a previously identified in vivo TRM-specific gene set and found considerable (>50%) overlap between the two gene sets, thus showing that a substantial part of the TRM signature can be attributed to TGF-β signalling. Finally, gene set enrichment analysis further revealed that the altered gene signature following TGF-β exposure reflected transcriptional signatures found in TRM cells from both epithelial and non-epithelial tissues. In summary, these findings show that TGF-β has a broad footprint in establishing the residency-specific transcriptional profile of TRM cells, which is detectable in TRM cells from diverse tissues. They further suggest that constitutive TGF-β signaling might be involved for their long-term persistence at tissue sites.

Tissue-resident memory T (TRM) cells were originally identified as a tissue-sequestered population of memory T cells that show lifelong persistence in non-lymphoid organs. That definition has slowly evolved with the documentation of TRM cells having variable terms of tissue residency combined with a capacity to return to the wider circulation. Nonetheless, reductionist experiments have identified an archetypical population of TRM cells showing intrinsic permanent residency in a wide range of non-lymphoid organs, with one notable exception: the lungs. Despite the fact that memory T cells generated during a respiratory infection are maintained in the circulation, local TRM cell numbers in the lung decline concomitantly with a decay in T cell-mediated protection. This Perspective describes the mechanisms that underpin long-term T cell lodgement in non-lymphoid tissues and explains why residency is transient for select TRM cell subsets. In doing so, it highlights the unusual nature of memory T cell egress from the lungs and speculates on the broader disease implications of this process, especially during infection with SARS-CoV-2.In this Perspective, Francis Carbone considers the unique characteristics of the tissue-resident memory T (TRM) cell populations that develop in the lungs. He discusses how the different properties of lung TRM cells may affect immunity to lung infections, including SARS-CoV-2.

Host protection against cutaneous herpes simplex virus 1 (HSV-1) infection relies on the induction of a robust adaptive immune response. Here, we show that Nav 1.8 + sensory neurons, which are involved in pain perception, control the magnitude of CD8 T cell priming and expansion in HSV-1-infected mice. The ablation of Nav 1.8 -expressing sensory neurons is associated with extensive skin lesions characterized by enhanced inflammatory cytokine and chemokine production. Mechanistically, Nav 1.8 + sensory neurons are required for the downregulation of neutrophil infiltration in the skin after viral clearance to limit the severity of tissue damage and restore skin homeostasis, as well as for eliciting robust CD8 T cell priming in skin-draining lymph nodes by controlling dendritic cell responses. Collectively, our data reveal an important role for the sensory nervous system in regulating both innate and adaptive immune responses to viral infection, thereby opening up possibilities for new therapeutic strategies. Herpes simplex virus 1 (HSV-1) is a neurotropic virus that often cause pain via the induction of ulcer or blisters. Here the authors show, in mouse models of HSV-1 infection, that the pain-perceiving nociceptor Nav 1.8 + neurons contribute to regulating both innate and adaptive immune responses against HSV-1, thereby offering a potential target for therapy.

The functions of individual dendritic cell subsets in the skin are unclear. Heath and colleagues now show that langerin-positive CD103 + dermal dendritic cells are the main migratory subtype able to cross-present antigen. Skin-derived dendritic cells (DCs) include Langerhans cells, classical dermal DCs and a langerin-positive CD103 + dermal subset. We examined their involvement in the presentation of skin-associated viral and self antigens. Only the CD103 + subset efficiently presented antigens of herpes simplex virus type 1 to naive CD8 + T cells, although all subsets presented these antigens to CD4 + T cells. This showed that CD103 + DCs were the migratory subset most efficient at processing viral antigens into the major histocompatibility complex class I pathway, potentially through cross-presentation. This was supported by data showing only CD103 + DCs efficiently cross-presented skin-derived self antigens. This indicates CD103 + DCs are the main migratory subtype able to cross-present viral and self antigens, which identifies another level of specialization for skin DCs.

Herpes simplex viruses (HSV) are significant human pathogens that provide one of the best-described examples of viral latency and reactivation. HSV latency occurs in sensory neurons, being characterized by the absence of virus replication and only fragmentary evidence of protein production. In mouse models, HSV latency is especially stable but the detection of some lytic gene transcription and the ongoing presence of activated immune cells in latent ganglia have been used to suggest that this state is not entirely quiescent. Alternatively, these findings can be interpreted as signs of a low, but constant level of abortive reactivation punctuating otherwise silent latency. Using single cell analysis of transcription in mouse dorsal root ganglia, we reveal that HSV-1 latency is highly dynamic in the majority of neurons. Specifically, transcription from areas of the HSV genome associated with at least one viral lytic gene occurs in nearly two thirds of latently-infected neurons and more than half of these have RNA from more than one lytic gene locus. Further, bioinformatics analyses of host transcription showed that progressive appearance of these lytic transcripts correlated with alterations in expression of cellular genes. These data show for the first time that transcription consistent with lytic gene expression is a frequent event, taking place in the majority of HSV latently-infected neurons. Furthermore, this transcription is of biological significance in that it influences host gene expression. We suggest that the maintenance of HSV latency involves an active host response to frequent viral activity.