T cell receptor signaling strength establishes the chemotactic properties of effector CD8+ T cells that control tissue-residency

Immunological Mechanisms and Effects of Bacterial Infections in Acute-on-Chronic Liver Failure

Acute-on-chronic liver failure (ACLF) is a severe clinical syndrome characterized by high morbidity and mortality rates. Bacterial infection is a frequent precipitating factor and complication in ACLF patients, significantly worsening patient outcomes. Elucidating the mechanisms underlying bacterial infections and their impact on ACLF pathophysiology is crucial for developing effective therapies to reduce infection rates and mortality. Current research highlights that immune suppression in ACLF increases susceptibility to bacterial infections, which in turn exacerbate immune dysfunction. However, a comprehensive review summarizing the emerging mechanisms underlying this immunosuppression is currently lacking. This review aims to provide an overview of the latest research, focusing on alterations in the immune responses of innate immune cells-including monocytes, macrophages, and neutrophils-as well as adaptive immune cells such as T and B lymphocytes during the onset and progression of bacterial infections in ACLF. In addition, recent advances in immunomodulatory therapies, including stem cell-based interventions, will also be discussed.

Neoadjuvant anti-4-1BB confers protection against spontaneous metastasis through low-affinity intratumor CD8 + T cells in triple-negative breast cancer

Neoadjuvant immunotherapy seeks to harness the primary tumor as a source of relevant tumor antigens to enhance systemic anti-tumor immunity through improved immunological surveillance. Despite having revolutionized the treatment of patients with high-risk early-stage triple-negative breast cancer (TNBC), a significant portion of patients remain unresponsive and succumb to metastatic recurrence post-treatment. Here, we found that optimally scheduled neoadjuvant administration of anti-4-1BB monotherapy was able to counteract metastases and prolong survival following surgical resection. Phenotypic and transcriptional profiling revealed enhanced 4-1BB expression on tumor-infiltrating intermediate (T int ), relative to progenitor (T prog ) and terminally exhausted (T term ) T cells. Furthermore, T int was enriched in low-affinity T cells. Treatment with anti-4-1BB drove clonal expansion of T int , with reduced expression of tissue-retention marker CD103 in T prog . This was accompanied by increased TCR clonotype sharing between paired tumors and pre-metastatic lungs. Further interrogation of sorted intratumor T cells confirmed enhanced T cell egress into circulation following anti-4-1BB treatment. In addition, gene signature extracted from anti-4-1BB treated T int was consistently associated with improved clinical outcomes in BRCA patients. Combinatorial neoadjuvant anti-4-1BB and ablation of tumor-derived CXCL16 resulted in enhanced therapeutic effect. These findings illustrate the intratumor changes underpinning the efficacy of neoadjuvant anti-4-1BB, highlighting the reciprocity between local tissue-retention and distant immunologic fortification, suggesting treatment can reverse the siphoning of intratumor T cells to primary tumor, enabling redistribution to distant tissues and subsequent protection against metastases.

Regulation of intestinal tissue‑resident memory T cells: a potential target for inflammatory bowel disease

Tissue-resident memory T (TRM) cells are populations which settle down in non-lymphoid tissues instead of returning to secondary lymph organs after the antigen presentation. These cells can provide rapid on-site immune protection as well as long-term tissue damage. It is reported that TRM cells from small intestine and colon exhibited distinctive patterns of cytokine and granzyme expression along with substantial transcriptional and functional heterogeneity. In this review, we focus on the reason why they lodge in intestinal tract, their developmental plasticity of going back to to circulation, as well as their regulators associated with retention, maintenance, exhaustion and metabolism. We also elaborate their role in the inflammatory bowel disease (IBD) and discuss the potential therapeutic strategies targeting TRM cells.

Local antigen encounter promotes generation of tissue-resident memory T cells in the large intestine

Upon infection, CD8+ T cells that have been primed in the draining lymph nodes migrate to the invaded tissue, where they receive cues prompting their differentiation into tissue-resident memory cells (Trm), which display niche-specific transcriptional features. Despite the importance of these cells, our understanding of their molecular landscape and the signals that dictate their development remains limited, particularly in specific anatomical niches such as the large intestine (LI). Here, we report that LI Trm-generated following oral infection exhibits a distinct transcriptional profile compared to Trm in other tissues. Notably, we observe that local cues play a crucial role in the preferential establishment of LI Trm, favoring precursors that migrate to the tissue early during infection. Our investigations identify cognate antigen recognition as a major driver of Trm differentiation at this anatomical site. Local antigen presentation not only promotes the proliferation of effector cells and memory precursors but also facilitates the acquisition of transcriptional features characteristic of gut Trm. Thus, antigen recognition in the LI favors the establishment of Trm by impacting T cell expansion and gene expression.

A mass cytometry method pairing T cell receptor and differentiation state analysis

T cell antigen receptor (TCR) recognition followed by clonal expansion is a fundamental feature of adaptive immune responses. Here, we present a mass cytometric (CyTOF) approach to track T cell responses by combining antibodies for specific TCR Vα and Vβ chains with antibodies against T cell activation and differentiation proteins in mice. This strategy identifies expansions of CD8+ and CD4+ T cells expressing specific Vβ and Vα chains with varying differentiation states in response to Listeria monocytogenes, tumors and respiratory influenza infection. Expanded T cell populations expressing Vβ chains could be directly linked to the recognition of specific antigens from Listeria, tumor cells or influenza. In the setting of influenza infection, we found that common therapeutic approaches of intramuscular vaccination or convalescent serum transfer altered the TCR diversity and differentiation state of responding T cells. Thus, we present a method to monitor broad changes in TCR use paired with T cell phenotyping during adaptive immune responses.

Protective function and differentiation cues of brain-resident CD8+ T cells during surveillance of latent Toxoplasma gondii infection

Chronic Toxoplasma gondii infection induces brain-resident CD8+ T cells (bTr), but the protective functions and differentiation cues of these cells remain undefined. Here, we used a mouse model of latent infection by T. gondii leading to effective CD8+ T cell-mediated parasite control. Thanks to antibody depletion approaches, we found that peripheral circulating CD8+ T cells are dispensable for brain parasite control during chronic stage, indicating that CD8+ bTr are able to prevent brain parasite reactivation. We observed that the retention markers CD69, CD49a, and CD103 are sequentially acquired by brain parasite-specific CD8+ T cells throughout infection and that a majority of CD69/CD49a/CD103 triple-positive (TP) CD8+ T cells also express Hobit, a transcription factor associated with tissue residency. This TP subset develops in a CD4+ T cell-dependent manner and is associated with effective parasite control during chronic stage. Conditional invalidation of Transporter associated with Antigen Processing (TAP)-mediated major histocompatibility complex (MHC) class I presentation showed that presentation of parasite antigens by glutamatergic neurons and microglia regulates the differentiation of CD8+ bTr into TP cells. Single-cell transcriptomic analyses revealed that resistance to encephalitis is associated with the expansion of stem-like subsets of CD8+ bTr. In summary, parasite-specific brain-resident CD8+ T cells are a functionally heterogeneous compartment which autonomously ensure parasite control during T. gondii latent infection and which differentiation is shaped by neuronal and microglial MHC I presentation. A more detailed understanding of local T cell-mediated immune surveillance of this common parasite is needed for harnessing brain-resident CD8+ T cells in order to enhance control of chronic brain infections.

Lymphatic vessel transit seeds cytotoxic resident memory T cells in skin draining lymph nodes

Lymphatic transport shapes the homeostatic immune repertoire of lymph nodes (LNs). LN-resident memory T cells (TRMs) play an important role in site-specific immune memory, yet how LN TRMs form de novo after viral infection remains unclear. Here, we tracked the anatomical distribution of antiviral CD8+ T cells as they seeded skin and LN TRMs using a model of vaccinia virus-induced skin infection. LN TRMs localized to the draining LNs (dLNs) of infected skin, and their formation depended on the lymphatic egress of effector CD8+ T cells from the skin, already poised for residence. Effector CD8+ T cell transit through skin was required to populate LN TRMs in dLNs, a process reinforced by antigen encounter in skin. Furthermore, LN TRMs were protective against viral rechallenge in the absence of circulating memory T cells. These data suggest that a subset of tissue-infiltrating CD8+ T cells egress from tissues during viral clearance and establish a layer of regional protection in the dLN basin.

T Cell Surveillance during Cutaneous Viral Infections

The skin is a complex tissue that provides a strong physical barrier against invading pathogens. Despite this, many viruses can access the skin and successfully replicate in either the epidermal keratinocytes or dermal immune cells. In this review, we provide an overview of the antiviral T cell biology responding to cutaneous viral infections and how these responses differ depending on the cellular targets of infection. Much of our mechanistic understanding of T cell surveillance of cutaneous infection has been gained from murine models of poxvirus and herpesvirus infection. However, we also discuss other viral infections, including flaviviruses and papillomaviruses, in which the cutaneous T cell response has been less extensively studied. In addition to the mechanisms of successful T cell control of cutaneous viral infection, we highlight knowledge gaps and future directions with possible impact on human health.

Persistent B Cell-Derived MHC Class II Signaling Is Required for the Optimal Maintenance of Tissue-Resident Helper T Cells

Emerging studies have identified the critical roles of tissue-resident memory CD8+ T (TRM) and B (BRM) cells in the protection against mucosal viral infections, but the underlying mechanisms regulating robust development of TRM and BRM cells remain incompletely understood. We have recently shown that tissue-resident helper CD4+ T (TRH) cells, developed following influenza virus infection, function to sustain the optimal maintenance of TRM and BRM cells at the mucosal surface. In this study, we have explored the cellular and molecular cues modulating lung TRH persistence after influenza infection in C57BL/6 mice. We found that TRH cells were colocalized in tertiary lymphoid structures (TLSs) with local B cells. Abolishing TLSs or the depletion of B cells impaired lung TRH cell numbers. Of note, we found that persistent TCR signaling is needed for the maintenance of TRH cells after the clearance of infectious influenza virus. Furthermore, selective ablation of B cell-derived MHC class II resulted in partial reduction of lung TRH cell number after influenza infection. Our findings suggest that the interaction between lung-resident TRH cells and B cells, along with persistent Ag stimulation, is required to maintain TRH cells after respiratory viral infection.

CD4 memory has a hierarchical structure created by requirements for infection-derived signals at an effector checkpoint

Our recent studies reveal that the persistence, location, and amount of both antigen and signals that induce pathogen recognition responses determine the number of CD4 memory cells, the subsets that develop, their location, and hence their protective efficacy. Non-replicating vaccines provide antigen that is short-lived and generate low levels of only some memory subsets that are mostly restricted to secondary lymphoid tissue. In contrast, exposure to long-lived replicating viruses and bacteria provides high levels of diverse antigens in sites of infection and induces strong pathogen recognition signals for extended periods of time, resulting in much higher levels of memory cells of diverse subsets in both lymphoid and nonlymphoid sites. These include memory subsets with highly potent functions such as T follicular helpers and cytotoxic CD4 effectors at sites of infection, where they can most effectively combat the pathogen early after re-infection. These effectors also do not develop without antigen and pathogen recognition signals at the effector stage, and both subsets must receive these signals in the tissue sites where they will become resident. We postulate that this leads to a hierarchical structure of memory, with the strongest memory induced only by replicating pathogens. This paradigm suggests a likely roadmap for markedly improving vaccine design.

Polyomavirus Wakes Up and Chooses Neurovirulence

JC polyomavirus (JCPyV) is a human-specific polyomavirus that establishes a silent lifelong infection in multiple peripheral organs, predominantly those of the urinary tract, of immunocompetent individuals. In immunocompromised settings, however, JCPyV can infiltrate the central nervous system (CNS), where it causes several encephalopathies of high morbidity and mortality. JCPyV-induced progressive multifocal leukoencephalopathy (PML), a devastating demyelinating brain disease, was an AIDS-defining illness before antiretroviral therapy that has "reemerged" as a complication of immunomodulating and chemotherapeutic agents. No effective anti-polyomavirus therapeutics are currently available. How depressed immune status sets the stage for JCPyV resurgence in the urinary tract, how the virus evades pre-existing antiviral antibodies to become viremic, and where/how it enters the CNS are incompletely understood. Addressing these questions requires a tractable animal model of JCPyV CNS infection. Although no animal model can replicate all aspects of any human disease, mouse polyomavirus (MuPyV) in mice and JCPyV in humans share key features of peripheral and CNS infection and antiviral immunity. In this review, we discuss the evidence suggesting how JCPyV migrates from the periphery to the CNS, innate and adaptive immune responses to polyomavirus infection, and how the MuPyV-mouse model provides insights into the pathogenesis of JCPyV CNS disease.

Lymphatic vessel transit seeds precursors to cytotoxic resident memory T cells in skin draining lymph nodes

Resident memory T cells (TRM) provide rapid, localized protection in peripheral tissues to pathogens and cancer. While TRM are also found in lymph nodes (LN), how they develop during primary infection and their functional significance remains largely unknown. Here, we track the anatomical distribution of anti-viral CD8+ T cells as they simultaneously seed skin and LN TRM using a model of skin infection with restricted antigen distribution. We find exquisite localization of LN TRM to the draining LN of infected skin. LN TRM formation depends on lymphatic transport and specifically egress of effector CD8+ T cells that appear poised for residence as early as 12 days post infection. Effector CD8+ T cell transit through skin is necessary and sufficient to populate LN TRM in draining LNs, a process reinforced by antigen encounter in skin. Importantly, we demonstrate that LN TRM are sufficient to provide protection against pathogenic rechallenge. These data support a model whereby a subset of tissue infiltrating CD8+ T cells egress during viral clearance, and establish regional protection in the draining lymphatic basin as a mechanism to prevent pathogen spread.