Liver-Resident Memory CD8 + T Cells Form a Front-Line Defense against Malaria Liver-Stage Infection

The tissue-resident regulatory T cell pool is shaped by transient multi-tissue migration and a conserved residency program

The tissues are the site of many important immunological reactions, yet how the immune system is controlled at these sites remains opaque. Recent studies have identified Foxp3+ regulatory T (Treg) cells in non-lymphoid tissues with unique characteristics compared with lymphoid Treg cells. However, tissue Treg cells have not been considered holistically across tissues. Here, we performed a systematic analysis of the Treg cell population residing in non-lymphoid organs throughout the body, revealing shared phenotypes, transient residency, and common molecular dependencies. Tissue Treg cells from different non-lymphoid organs shared T cell receptor (TCR) sequences, with functional capacity to drive multi-tissue Treg cell entry and were tissue-agnostic on tissue homing. Together, these results demonstrate that the tissue-resident Treg cell pool in most non-lymphoid organs, other than the gut, is largely constituted by broadly self-reactive Treg cells, characterized by transient multi-tissue migration. This work suggests common regulatory mechanisms may allow pan-tissue Treg cells to safeguard homeostasis across the body.

A liver immune rheostat regulates CD8 T cell immunity in chronic HBV infection

Chronic hepatitis B virus (HBV) infection affects 300 million patients worldwide1,2, in whom virus-specific CD8 T cells by still ill-defined mechanisms lose their function and cannot eliminate HBV-infected hepatocytes3-7. Here we demonstrate that a liver immune rheostat renders virus-specific CD8 T cells refractory to activation and leads to their loss of effector functions. In preclinical models of persistent infection with hepatotropic viruses such as HBV, dysfunctional virus-specific CXCR6+ CD8 T cells accumulated in the liver and, as a characteristic hallmark, showed enhanced transcriptional activity of cAMP-responsive element modulator (CREM) distinct from T cell exhaustion. In patients with chronic hepatitis B, circulating and intrahepatic HBV-specific CXCR6+ CD8 T cells with enhanced CREM expression and transcriptional activity were detected at a frequency of 12-22% of HBV-specific CD8 T cells. Knocking out the inhibitory CREM/ICER isoform in T cells, however, failed to rescue T cell immunity. This indicates that CREM activity was a consequence, rather than the cause, of loss in T cell function, further supported by the observation of enhanced phosphorylation of protein kinase A (PKA) which is upstream of CREM. Indeed, we found that enhanced cAMP-PKA-signalling from increased T cell adenylyl cyclase activity augmented CREM activity and curbed T cell activation and effector function in persistent hepatic infection. Mechanistically, CD8 T cells recognizing their antigen on hepatocytes established close and extensive contact with liver sinusoidal endothelial cells, thereby enhancing adenylyl cyclase-cAMP-PKA signalling in T cells. In these hepatic CD8 T cells, which recognize their antigen on hepatocytes, phosphorylation of key signalling kinases of the T cell receptor signalling pathway was impaired, which rendered them refractory to activation. Thus, close contact with liver sinusoidal endothelial cells curbs the activation and effector function of HBV-specific CD8 T cells that target hepatocytes expressing viral antigens by means of the adenylyl cyclase-cAMP-PKA axis in an immune rheostat-like fashion.

Repeat controlled human Plasmodium falciparum infections delay bloodstream patency and reduce symptoms

Resistance to clinical malaria takes years to develop even in hyperendemic regions and sterilizing immunity has rarely been observed. To evaluate the maturation of the host response against controlled repeat exposures to P. falciparum (Pf) NF54 strain-infected mosquitoes, we systematically monitored malaria-naïve participants through an initial exposure to uninfected mosquitoes and 4 subsequent homologous exposures to Pf-infected mosquitoes over 21 months (n = 8 males) (ClinicalTrials.gov# NCT03014258). The primary outcome was to determine whether protective immunity against parasite infection develops following repeat CHMI and the secondary outcomes were to track the clinical signs and symptoms of malaria and anti-Pf antibody development following repeat CHMI. After two exposures, time to blood stage patency increases significantly and the number of reported symptoms decreases indicating the development of clinical tolerance. The time to patency correlates positively with both anti-Pf circumsporozoite protein (CSP) IgG and CD8 + CD69+ effector memory T cell levels consistent with partial pre-erythrocytic immunity. IFNγ levels decrease significantly during the participants' second exposure to high blood stage parasitemia and could contribute to the decrease in symptoms. In contrast, CD4-CD8 + T cells expressing CXCR5 and the inhibitory receptor, PD-1, increase significantly after subsequent Pf exposures, possibly dampening the memory response and interfering with the generation of robust sterilizing immunity.

Comprehensive study of the interplay between immunological and metabolic factors in hepatic steatosis

The pathophysiology of hepatic steatosis is thoroughly reviewed in this comprehensive report, with particular attention to the complex interactions between inflammatory pathways, insulin resistance, lipid metabolism, metabolic dysregulation, and immunological responses in the liver including non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatohepatitis (NASH), and hepatocellular carcinoma (HCC). The study highlights the role of immune cell regulation in disease progression and explores the potential of immune cell-specific treatments for treating hepatic disorders. The development of liver disorders is significantly influenced by immune cells, including dendritic cells, T cells, and natural killer cells. Clinical investigations show that immune cell-specific treatments can effectively reduce liver fibrosis and inflammation. Future research should focus on finding new immunological targets for therapeutic interventions, as well as addressing the management challenges associated with NAFLD/NASH. Hepatic immune microorganisms also impact liver homeostasis and disorders. Improvements in immune cell regulation and liver transplantation methods give patients hope for better prognoses. Important phases include optimizing the selection of donors for malignancy of the liver, using machine perfusion for organ preservation, and fine-tuning immunosuppressive strategies. For focused treatments in hepatic steatosis, it is imperative to understand the intricate interactions between immune and metabolic variables. Understanding the liver's heterogeneous immune profile, encompassing a range of immune cell subpopulations, is crucial for formulating focused therapeutic interventions. To improve patient care and outcomes in hepatic illnesses, there is an urgent need for further research and innovation. Therefore, to effectively treat hepatic steatosis, it is important to enhance therapeutic techniques and maximize liver transplantation strategies.

Intestinal tissue-resident memory T cells maintain distinct identity from circulating memory T cells after in vitro restimulation

Resident memory T (TRM) cells have been recently established as an important subset of memory T cells that provide early and essential protection against reinfection in the absence of circulating memory T cells. Recent findings showing that TRM expand in vivo after repeated antigenic stimulation indicate that these memory T cells are not terminally differentiated. This suggests an opportunity for in vitro TRM expansion to apply in an immunotherapy setting. However, it has also been shown that TRM may not maintain their identity and form circulating memory T cells after in vivo restimulation. Therefore, we set out to determine how TRM respond to antigenic activation in culture. Using Listeria monocytogenes and LCMV infection models, we found that TRM from the intraepithelial compartment of the small intestine expand in vitro after antigenic stimulation and subsequent resting in homeostatic cytokines. A large fraction of the expanded TRM retained their phenotype, including the expression of key TRM markers CD69 and CD103 (ITGAE). The optimal culture of TRM required low O2 pressure to maintain the expression of these and other TRM-associated molecules. Expanded TRM retained their effector capacity to produce cytokines after restimulation, but did not acquire a highly glycolytic profile indicative of effector T cells. The proteomic analysis confirmed TRM profile retention, including expression of TRM-related transcription factors, tissue retention factors, adhesion molecules, and enzymes involved in fatty acid metabolism. Collectively, our data indicate that limiting oxygen conditions supports in vitro expansion of TRM cells that maintain their TRM phenotype, at least in part, suggesting an opportunity for therapeutic strategies that require in vitro expansion of TRM.

Preclinical evaluation of therapeutic vaccines for chronic hepatitis B that stimulate antiviral activities of T cells and NKT cells

Background & Aims

Liver diseases resulting from chronic HBV infection are a significant cause of morbidity and mortality. Vaccines that elicit T-cell responses capable of controlling the virus represent a treatment strategy with potential for long-term effects. Here, we evaluated vaccines that induce the activity of type I natural killer T (NKT) cells to limit viral replication and license stimulation of conventional antiviral T-cells.

Methods

Vaccines were prepared by conjugating peptide epitopes to an NKT-cell agonist to promote co-delivery to antigen-presenting cells, encouraging NKT-cell licensing and stimulation of T cells. Activity of the conjugate vaccines was assessed in transgenic mice expressing the complete HBV genome, administered intravenously to maximise access to NKT cell-rich tissues.

Results

The vaccines induced only limited antiviral activity in unmanipulated transgenic hosts, likely attributable to NKT-cell activation as T-cell tolerance to viral antigens is strong. However, in a model of chronic hepatitis B involving transfer of naive HBcAg-specific CD8+ T cells into the transgenic mice, which typically results in specific T-cell dysfunction without virus control, vaccines containing the targeted HBcAg epitope induced prolonged antiviral activity because of qualitatively improved T-cell stimulation. In a step towards a clinical product, vaccines were prepared using synthetic long peptides covering clusters of known HLA-binding epitopes and shown to be immunogenic in HLA transgenic mice. Predictions based on HLA distribution suggest a product containing three selected SLP-based vaccines could give >90 % worldwide coverage, with an average of 3.38 epitopes targeted per individual.

Conclusions

The novel vaccines described show promise for further clinical development as a treatment for chronic hepatitis B.

Impact and Implications

Although there are effective prophylactic vaccines for HBV infection, it is estimated that 350-400 million people worldwide have chronic hepatitis B, putting these individuals at significant risk of life-threatening liver diseases. Therapeutic vaccination aimed at activating or boosting HBV-specific T-cell responses holds potential as a strategy for treating chronic infection, but has so far met with limited success. Here, we show that a glycolipid-peptide conjugate vaccine designed to coordinate activity of type I NKT cells alongside conventional antiviral T cells has antiviral activity in a mouse model of chronic infection. It is anticipated that a product based on a combination of three such conjugates, each prepared using long peptides covering clusters of known HLA-binding epitopes, could be developed further as a treatment for chronic hepatitis B with broad global HLA coverage.

Tissue-resident memory T cells: decoding intra-organ diversity with a gut perspective

Tissue-resident memory T cells (TRM) serve as the frontline of host defense, playing a critical role in protection against invading pathogens. This emphasizes their role in providing rapid on-site immune responses across various organs. The physiological significance of TRM is not just confined to infection control; accumulating evidence has revealed that TRM also determine the pathology of diseases such as autoimmune disorders, inflammatory bowel disease, and cancer. Intensive studies on the origin, mechanisms of formation and maintenance, and physiological significance of TRM have elucidated the transcriptional and functional diversity of these cells, which are often affected by local cues associated with their presence. These were further confirmed by the recent remarkable advancements of next-generation sequencing and single-cell technologies, which allow the transcriptional and phenotypic characterization of each TRM subset induced in different microenvironments. This review first overviews the current knowledge of the cell fate, molecular features, transcriptional and metabolic regulation, and biological importance of TRM in health and disease. Finally, this article presents a variety of recent studies on disease-associated TRM, particularly focusing and elaborating on the TRM in the gut, which constitute the largest and most intricate immune network in the body, and their pathological relevance to gut inflammation in humans.

Superior protection in a relapsing Plasmodium cynomolgi rhesus macaque model by a chemoprophylaxis with sporozoite immunization regimen with atovaquone-proguanil followed by primaquine

BACKGROUND

To gain a deeper understanding of protective immunity against relapsing malaria, this study examined sporozoite-specific T cell responses induced by a chemoprophylaxis with sporozoite (CPS) immunization in a relapsing Plasmodium cynomolgi rhesus macaque model.

METHODS

The animals received three CPS immunizations with P. cynomolgi sporozoites, administered by mosquito bite, while under two anti-malarial drug regimens. Group 1 (n = 6) received artesunate/chloroquine (AS/CQ) followed by a radical cure with CQ plus primaquine (PQ). Group 2 (n = 6) received atovaquone-proguanil (AP) followed by PQ. After the final immunization, the animals were challenged with intravenous injection of 104 P. cynomolgi sporozoites, the dose that induced reliable infection and relapse rate. These animals, along with control animals (n = 6), were monitored for primary infection and subsequent relapses. Immunogenicity blood draws were done after each of the three CPS session, before and after the challenge, with liver, spleen and bone marrow sampling and analysis done after the challenge.

RESULTS

Group 2 animals demonstrated superior protection, with two achieving protection and two experiencing partial protection, while only one animal in group 1 had partial protection. These animals displayed high sporozoite-specific IFN-γ T cell responses in the liver, spleen, and bone marrow after the challenge with one protected animal having the highest frequency of IFN-γ+ CD8+, IFN-γ+ CD4+, and IFN-γ+ γδ T cells in the liver. Partially protected animals also demonstrated a relatively high frequency of IFN-γ+ CD8+, IFN-γ+ CD4+, and IFN-γ+ γδ T cells in the liver. It is important to highlight that the second animal in group 2, which experienced protection, exhibited deficient sporozoite-specific T cell responses in the liver while displaying average to high T cell responses in the spleen and bone marrow.

CONCLUSIONS

This research supports the notion that local liver T cell immunity plays a crucial role in defending against liver-stage infection. Nevertheless, there is an instance where protection occurs independently of T cell responses in the liver, suggesting the involvement of the liver's innate immunity. The relapsing P. cynomolgi rhesus macaque model holds promise for informing the development of vaccines against relapsing P. vivax.

A replication competent Plasmodium falciparum parasite completely attenuated by dual gene deletion

Vaccination with infectious Plasmodium falciparum (Pf) sporozoites (SPZ) administered with antimalarial drugs (PfSPZ-CVac), confers superior sterilizing protection against infection when compared to vaccination with replication-deficient, radiation-attenuated PfSPZ. However, the requirement for drug administration constitutes a major limitation for PfSPZ-CVac. To obviate this limitation, we generated late liver stage-arresting replication competent (LARC) parasites by deletion of the Mei2 and LINUP genes (mei2-/linup- or LARC2). We show that Plasmodium yoelii (Py) LARC2 sporozoites did not cause breakthrough blood stage infections and engendered durable sterilizing immunity against various infectious sporozoite challenges in diverse strains of mice. We next genetically engineered a PfLARC2 parasite strain that was devoid of extraneous DNA and produced cryopreserved PfSPZ-LARC2. PfSPZ-LARC2 liver stages replicated robustly in liver-humanized mice but displayed severe defects in late liver stage differentiation and did not form liver stage merozoites. This resulted in complete abrogation of parasite transition to viable blood stage infection. Therefore, PfSPZ-LARC2 is the next-generation vaccine strain expected to unite the safety profile of radiation-attenuated PfSPZ with the superior protective efficacy of PfSPZ-CVac.

Regenerating murine CD8+ lung tissue resident memory T cells after targeted radiation exposure

Radiation exposure occurs during medical procedures, nuclear accidents, or spaceflight, making effective medical countermeasures a public health priority. Naïve T cells are highly sensitive to radiation-induced depletion, although their numbers recover with time. Circulating memory CD8+ T cells are also depleted by radiation; however, their numbers do not recover. Critically, the impact of radiation exposure on tissue-resident memory T cells (TRM) remains unknown. Here, we found that sublethal thorax-targeted radiation resulted in the rapid and prolonged numerical decline of influenza A virus (IAV)-specific lung TRM in mice, but no decline in antigen-matched circulating memory T cells. Prolonged loss of lung TRM was associated with decreased heterosubtypic immunity. Importantly, boosting with IAV-epitope expressing pathogens that replicate in the lungs or peripheral tissues or with a peripherally administered mRNA vaccine regenerated lung TRM that was derived largely from circulating memory CD8+ T cells. Designing effective vaccination strategies to regenerate TRM will be important in combating the immunological effects of radiation exposure.

Memory T cells: promising biomarkers for evaluating protection and vaccine efficacy against leishmaniasis

Understanding the immune response to Leishmania infection and identifying biomarkers that correlate with protection are crucial for developing effective vaccines. One intriguing aspect of Leishmania infection is the persistence of parasites, even after apparent lesion healing. Various host cells, including dendritic cells, fibroblasts, and Langerhans cells, may serve as safe sites for latent infection. Memory T cells, especially tissue-resident memory T cells (TRM), play a crucial role in concomitant immunity against cutaneous Leishmania infections. These TRM cells are long-lasting and can protect against reinfection in the absence of persistent parasites. CD4+ TRM cells, in particular, have been implicated in protection against Leishmania infections. These cells are characterized by their ability to reside in the skin and rapidly respond to secondary infections by producing cytokines such as IFN-γ, which activates macrophages to kill parasites. The induction of CD4+ TRM cells has shown promise in experimental immunization, leading to protection against Leishmania challenge infections. Identifying biomarkers of protection is a critical step in vaccine development and CD4+ TRM cells hold potential as biomarkers, as their presence and functions may correlate with protection. While recent studies have shown that Leishmania-specific memory CD4+ T-cell subsets are present in individuals with a history of cutaneous leishmaniasis, further studies are needed to characterize CD4+ TRM cell populations. Overall, this review highlights the importance of memory T cells, particularly skin-resident CD4+ TRM cells, as promising targets for developing effective vaccines against leishmaniasis and as biomarkers of immune protection to assess the efficacy of candidate vaccines against human leishmaniasis.

Regulatory T cells in inflamed liver are dysfunctional in murine primary biliary cholangitis

Primary biliary cholangitis (PBC) is a chronic autoimmune disease characterized by immune-mediated destruction of intrahepatic small bile ducts. CD8 T cells play a critical role in biliary destruction. However, regulatory T cells (Tregs) have also been identified in the portal tracts of PBC patients. This study tested the hypothesis that hepatic Tregs in PBC were dysfunctional in suppressing immune responses in disease by using our human PBC-like autoimmune cholangitis (AIC) mouse model induced by 2-octynoic acid-conjugated ovalbumin (2-OA-OVA). Our results showed that female and male mice immunized with 2-OA-OVA developed AIC; however, female AIC mice had more severe liver inflammation and fibrosis than male AIC mice. Levels of functional effector CD8 T cells and their chemoattractants, CXCL9 and CXCL10, in the liver were markedly elevated in female AIC mice than in male AIC mice. These results reinforce that CD8 T cells are the primary effector cells in PBC. The number of hepatic Tregs in AIC mice was also higher than in saline-treated mice, but there was no difference between male and female AIC mice. The suppressive function of AIC Tregs was evident despite a discrepancy in the changes in their co-inhibitory receptors and inhibitory cytokines. However, the expansion of hepatic Tregs by low-dose IL-2 treatment did not reduce immune responses to AIC, which may be due to the dysfunction of Tregs in inhibiting T cells. In conclusion, the function of Tregs in the inflamed liver of PBC was insufficient, and low-dose IL-2 treatment could not restore their function to suppress pathological immune responses. Transferring normal Tregs or directly targeting effector CD8 T cells may be beneficial for treating PBC.

A hepatic network of dendritic cells mediates CD4 T cell help outside lymphoid organs

While CD4+ T cells are a prerequisite for CD8+ T cell-mediated protection against intracellular hepatotropic pathogens, the mechanisms facilitating the transfer of CD4-help to intrahepatic CD8+ T cells are unknown. Here, we developed an experimental system to investigate cognate CD4+ and CD8+ T cell responses to a model-antigen expressed de novo in hepatocytes and reveal that after initial priming, effector CD4+ and CD8+ T cells migrate into portal tracts and peri-central vein regions of the liver where they cluster with type-1 conventional dendritic cells. These dendritic cells are locally licensed by CD4+ T cells and expand the number of CD8+ T cells in situ, resulting in larger effector and memory CD8+ T cell pools. These findings reveal that CD4+ T cells promote intrahepatic immunity by amplifying the CD8+ T cell response via peripheral licensing of hepatic type-1 conventional dendritic cells and identify intrahepatic perivascular compartments specialized in facilitating effector T cell-dendritic cell interactions.

IL-21, not IL-17A, exacerbates murine primary biliary cholangitis

Primary biliary cholangitis (PBC) is a chronic autoimmune liver disease caused by intrahepatic bile duct injuries, resulting in fibrosis, cirrhosis, and eventually liver failure. T helper (Th) 17 cells are proposed to involve in the pathogenesis of PBC. However, how and which Th17 cell-derived cytokines affect PBC remains unclear. In this study, we investigated the effects of Th17 effector cytokines, including interleukin (IL)-17A, IL-17F, and IL-21 in PBC using a xenobiotic-induced mouse model of autoimmune cholangitis (inducible chemical xenobiotic models of PBC) treated with cytokine-expressing adeno-associated virus. Our results showed that administration of IL-17A, the well-known main cytokine produced by Th17 cells, did not augment liver inflammation or fibrosis. In contrast, we noted IL-17A-treated mice had lower hepatic Th1 cell numbers and higher hepatic CD11b+Ly6G+ polymorphonuclear myeloid-derived suppressor cell numbers. IL-17F did not alter liver inflammation or fibrosis. However, the administration of IL-21 exacerbated liver inflammatory responses and portal cell infiltration. IL-21 markedly increased the numbers of activated CD8+ T cells and liver tissue-resident memory CD8+ T cells. Moreover, IL-21 aggravates liver fibrosis in mice with autoimmune cholangitis. These results emphasized that not IL-17A but IL-21 in Th17 cell-derived cytokines affected the pathogenesis of PBC. IL-21 enhanced liver inflammation and progression to fibrosis by enhancing the numbers and effector activities of CD8+ T cells. Delineation of the effects of different Th17 effector cytokines in PBC offers clues for developing new therapeutic approaches.

Ultra-low volume intradermal administration of radiation-attenuated sporozoites with the glycolipid adjuvant 7DW8-5 completely protects mice against malaria

Radiation-attenuated sporozoite (RAS) vaccines can completely prevent blood stage Plasmodium infection by inducing liver-resident memory CD8+ T cells to target parasites in the liver. Such T cells can be induced by 'Prime-and-trap' vaccination, which here combines DNA priming against the P. yoelii circumsporozoite protein (CSP) with a subsequent intravenous (IV) dose of liver-homing RAS to "trap" the activated and expanding T cells in the liver. Prime-and-trap confers durable protection in mice, and efforts are underway to translate this vaccine strategy to the clinic. However, it is unclear whether the RAS trapping dose must be strictly administered by the IV route. Here we show that intradermal (ID) RAS administration can be as effective as IV administration if RAS are co-administrated with the glycolipid adjuvant 7DW8-5 in an ultra-low inoculation volume. In mice, the co-administration of RAS and 7DW8-5 in ultra-low ID volumes (2.5 µL) was completely protective and dose sparing compared to standard volumes (10-50 µL) and induced protective levels of CSP-specific CD8+ T cells in the liver. Our finding that adjuvants and ultra-low volumes are required for ID RAS efficacy may explain why prior reports about higher volumes of unadjuvanted ID RAS proved less effective than IV RAS. The ID route may offer significant translational advantages over the IV route and could improve sporozoite vaccine development.

CD8+ Tissue-Resident Memory T Cells: Versatile Guardians of the Tissue

Tissue-resident memory T (Trm) cells are a subset of T cells maintained throughout life within nonlymphoid tissues without significant contribution from circulating memory T cells. CD8+ Trm cells contribute to both tissue surveillance and direct elimination of pathogens through a variety of mechanisms. Reactivation of these Trm cells during infection drives systematic changes within the tissue, including altering the state of the epithelium, activating local immune cells, and contributing to the permissiveness of the tissue for circulating immune cell entry. Trm cells can be further classified by their functional outputs, which can be either subset- or tissue-specific, and include proliferation, tissue egress, and modulation of tissue physiology. These functional outputs of Trm cells are linked to the heterogeneity and plasticity of this population, and uncovering the unique responses of different Trm cell subsets and their role in immunity will allow us to modulate Trm cell responses for optimal control of disease.

CD8+ Trms against malaria liver-stage: prospects and challenges

Attenuated sporozoites provide a valuable model for exploring protective immunity against the malarial liver stage, guiding the design of highly efficient vaccines to prevent malaria infection. Liver tissue-resident CD8+ T cells (CD8+ Trm cells) are considered the host front-line defense against malaria and are crucial to developing prime-trap/target strategies for pre-erythrocytic stage vaccine immunization. However, the spatiotemporal regulatory mechanism of the generation of liver CD8+ Trm cells and their responses to sporozoite challenge, as well as the protective antigens they recognize remain largely unknown. Here, we discuss the knowledge gap regarding liver CD8+ Trm cell formation and the potential strategies to identify predominant protective antigens expressed in the exoerythrocytic stage, which is essential for high-efficacy malaria subunit pre-erythrocytic vaccine designation.

Adenoviruses vectored hepatitis C virus vaccine cocktails induce broadly specific immune responses against multi-genotypic HCV in mice

BACKGROUND

Hepatitis C virus (HCV) vaccines are an urgent need to prevent hepatitis C and its further progression of hepatocellular carcinoma. Since the promising T cell based chimpanzee adenovirus and modified vaccinia virus Ankara vectorial HCV vaccines were failed in clinical phase II trial, the vaccine designs to improve protection efficacy in combination of cellular and humoral immunity have been hypothesized against multi-genotypic HCV.

METHODS

Eight HCV vaccine strains were constructed with two novel adenovirus vectors (Sad23L and Ad49L) encoding E1E2 or NS3-5B proteins of HCV genotype (Gt) 1b and 6a isolates, covering 80 % HCV strains prevalent in south China and south-east Asia. Eight HCV vaccine strains were grouped into Sad23L-based vaccine cocktail-1 and Ad49L-based vaccine cocktail-2 for vaccinating mice, respectively.

RESULTS

The immunogenicity of a single dose of 107-1010 PFU HCV individual vaccines was evaluated in mice, showing weak specific antibody to E1 and E2 protein but a dose-dependent T cell response to E1E2/NS3-5B peptides, which could be significantly enhanced by boosting with an alternative vector vaccine carrying homologous antigen. Prime-boost vaccinations with vaccine cocktail-1 and cocktail-2 induced significantly higher cross-reactive antibody and stronger T cell responses to HCV Gt-1b/6a. The high frequency of intrasplenic and intrahepatic NS31629-1637 CD8+ T cell responses were identified, in which the high proportion of TRM and TEM cells might play an important role against HCV infection in liver.

CONCLUSIONS

Prime-boost regimens with HCV vaccine cocktails elicited the broad cross-reactive antibody and robust T cell responses against multi-genotypic HCV in mice.

Recruiting Natural Killer T Cells to Improve Vaccination: Lessons from Preclinical and Clinical Studies

The capacity of type I natural killer T (NKT) cells to provide stimulatory signals to antigen-presenting cells has prompted preclinical research into the use of agonists as immune adjuvants, with much of this work focussed on stimulating T cell responses to cancer. In attempting to evaluate this approach in the clinic, our recent dendritic-cell based study failed to show an advantage to adding an agonist to the vaccine. Here we present potential limitations of the study, and suggest why other simpler strategies may be more effective. These include strategies to target antigen-presenting cells in the host, either through promoting efficient transfer from injected cell lines, facilitating uptake of antigen and agonist as injected conjugates, or encapsulating the components into injected nanovectors. While the vaccine landscape has changed with the rapid uptake of mRNA vaccines, we suggest that there is still a role for recruiting NKT cells in altering T cell differentiation programmes, notably the induction of resident memory T cells.

More time to kill: A longer liver stage increases T cell-mediated protection against pre-erythrocytic malaria

Liver stage (LS) Plasmodia mature in 2-2.5 days in rodents compared to 5-6 days in humans. Plasmodium-specific CD8+ T cell expansion differs across these varied timespans. To mimic the kinetics of CD8+ T cells of human Plasmodium infection, a two-dose challenge mouse model that achieved 4-5 days of LS antigen exposure was developed. In this model, mice were inoculated with a non-protective, low dose of late-arresting, genetically attenuated sporozoites to initiate T cell activation and then re-inoculated 2-3 days later with wild-type sporozoites. Vaccines that partially protected against traditional challenge completely protected against two-dose challenge. During the challenge period, CD8+ T cell frequencies increased in the livers of two-dose challenged mice but not in traditionally challenged mice, further suggesting that this model better recapitulates kinetics of CD8+ T cell expansion in humans during the P. falciparum LS. Vaccine development and antigen discovery efforts may be aided by using the two-dose challenge strategy.

Variable long-term protection by radiation-, chemo-, and genetically-attenuated Plasmodium berghei sporozoite vaccines

Long-term protection against malaria remains one of the greatest challenges of vaccination against this deadly parasitic disease. Whole-sporozoite (WSp) malaria vaccine formulations, which target the Plasmodium parasite's pre-erythrocytic stages, include radiation-attenuated sporozoites (RAS), early- and late-arresting genetically-attenuated parasites (EA-GAP and LA-GAP, respectively), and chemoprophylaxis with sporozoites (CPS). Although all these four vaccine formulations induce protective immune responses in the clinic, data on the longevity of the antimalarial protection they afford remain scarce. We employed a mouse model of malaria to assess protection conferred by immunization with P. berghei (Pb)-based surrogates of these four WSp formulations over a 36-week period. We show that EA-GAP WSp provide the lowest overall protection against an infectious Pb challenge, and that while immunization with RAS and LA-GAP WSp elicits the most durable protection, the protective efficacy of CPS WSp wanes rapidly over the 36-week period, most notably at higher immunization dosages. Analyses of liver immune cells show that CD44hi CD8+ T cells in CPS WSp-immunized mice express increased levels of the co-inhibitory PD-1 and LAG-3 markers compared to mice immunized with the other WSp formulations. This indicates that memory CD8+ T cells elicited by CPS WSp immunization display a more exhausted phenotype, which may explain the rapid waning of protection conferred by the former. These results emphasize the need for a detailed comparison of the duration of protection of different WSp formulations in humans and suggest a more beneficial effect of RAS and LA-GAP WSp compared to EA-GAP or CSP WSp.

Heterogeneity in killing efficacy of individual effector CD8+ T cells against Plasmodium liver stages

Vaccination strategies in mice inducing high numbers of memory CD8+ T cells specific to a single epitope are able to provide sterilizing protection against infection with Plasmodium sporozoites. We have recently found that Plasmodium-specific CD8+ T cells cluster around sporozoite-infected hepatocytes but whether such clusters are important in elimination of the parasite remains incompletely understood. Here, we used our previously generated data in which we employed intravital microscopy to longitudinally image 32 green fluorescent protein (GFP)-expressing Plasmodium yoelii parasites in livers of mice that had received activated Plasmodium-specific CD8+ T cells after sporozoite infection. We found significant heterogeneity in the dynamics of the normalized GFP signal from the parasites (termed 'vitality index' or VI) that was weakly correlated with the number of T cells near the parasite. We also found that a simple model assuming mass-action, additive killing by T cells well describes the VI dynamics for most parasites and predicts a highly variable killing efficacy by individual T cells. Given our estimated median per capita kill rate of k = 0.031/h we predict that a single T cell is typically incapable of killing a parasite within the 48 h lifespan of the liver stage in mice. Stochastic simulations of T cell clustering and killing of the liver stage also suggested that: (i) three or more T cells per infected hepatocyte are required to ensure sterilizing protection; (ii) both variability in killing efficacy of individual T cells and resistance to killing by individual parasites may contribute to the observed variability in VI decline, and (iii) the stable VI of some clustered parasites cannot be explained by measurement noise. Taken together, our analysis for the first time provides estimates of efficiency at which individual CD8+ T cells eliminate intracellular parasitic infection in vivo.

Cytolytic circumsporozoite-specific memory CD4+ T cell clones are expanded during Plasmodium falciparum infection

Clinical immunity against Plasmodium falciparum infection develops in residents of malaria endemic regions, manifesting in reduced clinical symptoms during infection and in protection against severe disease but the mechanisms are not fully understood. Here, we compare the cellular and humoral immune response of clinically immune (0-1 episode over 18 months) and susceptible (at least 3 episodes) during a mild episode of Pf malaria infection in a malaria endemic region of Malawi, by analysing peripheral blood samples using high dimensional mass cytometry (CyTOF), spectral flow cytometry and single-cell transcriptomic analyses. In the clinically immune, we find increased proportions of circulating follicular helper T cells and classical monocytes, while the humoral immune response shows characteristic age-related differences in the protected. Presence of memory CD4+ T cell clones with a strong cytolytic ZEB2+ T helper 1 effector signature, sharing identical T cell receptor clonotypes and recognizing the Pf-derived circumsporozoite protein (CSP) antigen are found in the blood of the Pf-infected participants gaining protection. Moreover, in clinically protected participants, ZEB2+ memory CD4+ T cells express lower level of inhibitory and chemotactic receptors. We thus propose that clonally expanded ZEB2+ CSP-specific cytolytic memory CD4+ Th1 cells may contribute to clinical immunity against the sporozoite and liver-stage Pf malaria.

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.

Immunological characteristics of CD103+CD8+ Tc cells in the liver of C57BL/6 mouse infected with plasmodium NSM

CD103 is an important marker of tissue-resident memory T cells (TRM) which play important roles in fighting against infection. However, the immunological characteristics of CD103+ T cells are not thoroughly elucidated in the liver of mouse infected with Plasmodium. Six- to eight-week-old C57BL/6 mice were infected with Plasmodium yoelii nigeriensis NSM. Mice were sacrificed on 12-16 days after infection and the livers were picked out. Sections of the livers were stained, and serum aspartate aminotransferase (AST) and alanine transaminase (ALT) levels were measured. Moreover, lymphocytes in the liver were isolated, and the expression of CD103 was determined by using qPCR. The percentage of CD103 on different immune cell populations was dynamically observed by using flow cytometry (FCM). In addition, the phenotype and cytokine production characteristics of CD103+CD8+ Tc cell were analyzed by using flow cytometry, respectively. Erythrocyte stage plasmodium infection could result in severe hepatic damage, a widespread inflammatory response and the decrease of CD103 expression on hepatic immune cells. Only CD8+ Tc and γδT cells expressed higher levels of CD103 in the uninfected state.CD103 expression in CD8+ Tc cells significantly decreased after infection. Compared to that of CD103- CD8+ Tc cells, CD103+ CD8+ Tc cells from the infected mice expressed lower level of CD69, higher level of CD62L, and secreted more IL-4, IL-10, IL-17, and secreted less IFN-γ. CD103+CD8+ Tc cells might mediate the hepatic immune response by secreting IL-4, IL-10, and IL-17 except IFN-γ in the mice infected with the erythrocytic phase plasmodium, which could be involved in the pathogenesis of severe liver damage resulted from the erythrocytic phase plasmodium yoelii nigeriensis NSM infection.

T cell control of SARS-CoV-2: When, which, and where?

Efficient immune protection against viruses such as SARS-CoV-2 requires the coordinated activity of innate immunity, B and T cells. Accumulating data point to a critical role for T cells not only in the clearance of established infection, but also for aborting viral replication independently of humoral immunity. Here we review the evidence supporting the contribution of antiviral T cells and consider which of their qualitative features favour efficient control of infection. We highlight how studies of SARS-CoV-2 and other coronaviridae in animals and humans have provided important lessons on the optimal timing (When), functionality and specificity (Which), and location (Where) of antiviral T cells. We discuss the clinical implications, particularly for the development of next-generation vaccines, and emphasise areas requiring further study.

The role of tissue resident memory CD4 T cells in Salmonella infection: Implications for future vaccines

Salmonella infections cause a wide range of intestinal and systemic disease that affects global human health. While some vaccines are available, they do not mitigate the impact of Salmonella on endemic areas. Research using Salmonella mouse models has revealed the important role of CD4 T cells and antibody in the development of protective immunity against Salmonella infection. Recent work points to a critical role for hepatic tissue-resident memory lymphocytes in naturally acquired immunity to systemic infection. Thus, understanding the genesis and function of this Salmonella-specific population is an important objective and is the primary focus of this review. Greater understanding of how these memory lymphocytes contribute to bacterial elimination could suggest new approaches to vaccination against an important human pathogen.

Tissue-resident and innate-like T cells in patients with advanced chronic liver disease

Chronic liver disease results from the orchestrated interplay of components of innate and adaptive immunity in response to liver tissue damage. Recruitment, positioning, and activation of immune cells can contribute to hepatic cell death, inflammation, and fibrogenesis. With disease progression and increasing portal pressure, repeated translocation of bacterial components from the intestinal lumen through the epithelial and vascular barriers leads to persistent mucosal, hepatic, and systemic inflammation which contributes to tissue damage, immune dysfunction, and microbial infection. It is increasingly recognised that innate-like and adaptive T-cell subsets located in the liver, mucosal surfaces, and body cavities play a critical role in the progression of advanced liver disease and inflammatory complications of cirrhosis. Mucosal-associated invariant T cells, natural killer T cells, γδ T cells, and tissue-resident memory T cells in the gut, liver, and ascitic fluid share certain characteristic features, which include that they recognise microbial products, tissue alarmins, cytokines, and stress ligands in tissues, and perform effector functions in chronic liver disease. This review highlights recent advances in the comprehension of human tissue-resident and unconventional T-cell populations and discusses the mechanisms by which they contribute to inflammation, fibrosis, immunosuppression, and antimicrobial surveillance in patients with cirrhosis. Understanding the complex interactions of immune cells in different compartments and their contribution to disease progression will provide further insights for effective diagnostic interventions and novel immunomodulatory strategies in patients with advanced chronic liver disease.

Phenotype and fate of liver-resident CD8 T cells during acute and chronic hepacivirus infection

Immune correlates of hepatitis C virus (HCV) clearance and control remain poorly defined due to the lack of an informative animal model. We recently described acute and chronic rodent HCV-like virus (RHV) infections in lab mice. Here, we developed MHC class I and class II tetramers to characterize the serial changes in RHV-specific CD8 and CD4 T cells during acute and chronic infection in C57BL/6J mice. RHV infection induced rapid expansion of T cells targeting viral structural and nonstructural proteins. After virus clearance, the virus-specific T cells transitioned from effectors to long-lived liver-resident memory T cells (TRM). The effector and memory CD8 and CD4 T cells primarily produced Th1 cytokines, IFN-γ, TNF-α, and IL-2, upon ex vivo antigen stimulation, and their phenotype and transcriptome differed significantly between the liver and spleen. Rapid clearance of RHV reinfection coincided with the proliferation of virus-specific CD8 TRM cells in the liver. Chronic RHV infection was associated with the exhaustion of CD8 T cells (Tex) and the development of severe liver diseases. Interestingly, the virus-specific CD8 Tex cells continued proliferation in the liver despite the persistent high-titer viremia and retained partial antiviral functions, as evident from their ability to degranulate and produce IFN-γ upon ex vivo antigen stimulation. Thus, RHV infection in mice provides a unique model to study the function and fate of liver-resident T cells during acute and chronic hepatotropic infection.

CXCR3 Provides a Competitive Advantage for Retention of Mycobacterium tuberculosis-Specific Tissue-Resident Memory T Cells Following a Mucosal Tuberculosis Vaccine

Mycobacterium tuberculosis is a major human pathogen, and new vaccines are needed to prevent transmission. Mucosal vaccination may confer protection against M. tuberculosis by stimulating tissue-resident memory (TRM) CD4+ T cells in the lungs. The chemokine receptor CXCR3 promotes lung recruitment of T cells, but its role in TRM development is unknown. This study demonstrates the recombinant influenza A virus vaccine PR8.p25, expressing the immunodominant M. tuberculosis T cell epitope p25, induces CXCR3 expression on p25-specific CD4+ T cells in the lungs so that the majority of vaccine-induced CD4+ TRM expresses CXCR3 at 6 weeks. However, CXCR3-/- mice developed equivalent antigen-specific CD4+ T cell responses to wild-type (WT) mice following PR8.p25, and surprisingly retained more p25-specific CD4+ TRM in the lungs than WT mice at 6 weeks. The adoptive transfer of CXCR3-/- and WT P25 T cells into WT mice revealed that the initial recruitment of vaccine-induced CD4+ T cells into the lungs was independent of CXCR3, but by 6 weeks, CXCR3-deficient P25 T cells, and especially CXCR3-/- TRM, were significantly reduced compared to CXCR3-sufficient P25 T cells. Therefore, although CXCR3 was not essential for CD4+ TRM recruitment or retention, it provided a competitive advantage for the induction of M. tuberculosis-specific CD4+ TRM in the lungs following pulmonary immunization.

Memory T Cells in the Immunoprevention of Cancer: A Switch from Therapeutic to Prophylactic Approaches

Cancer immunoprevention, the engagement of the immune system to prevent cancer, is largely overshadowed by therapeutic approaches to treating cancer after detection. Vaccines or, alternatively, the utilization of genetically engineered memory T cells could be methods of engaging and creating cancer-specific T cells with superb memory, lenient activation requirements, potent antitumor cytotoxicity, tumor surveillance, and resilience against immunosuppressive factors in the tumor microenvironment. In this review we analyze memory T cell subtypes based on their potential utility in cancer immunoprevention with regard to longevity, localization, activation requirements, and efficacy in fighting cancers. A particular focus is on how both tissue-resident memory T cells and stem memory T cells could be promising subtypes for engaging in immunoprevention.

mRNA vaccine against malaria tailored for liver-resident memory T cells

Malaria is caused by Plasmodium species transmitted by Anopheles mosquitoes. Following a mosquito bite, Plasmodium sporozoites migrate from skin to liver, where extensive replication occurs, emerging later as merozoites that can infect red blood cells and cause symptoms of disease. As liver tissue-resident memory T cells (Trm cells) have recently been shown to control liver-stage infections, we embarked on a messenger RNA (mRNA)-based vaccine strategy to induce liver Trm cells to prevent malaria. Although a standard mRNA vaccine was unable to generate liver Trm or protect against challenge with Plasmodium berghei sporozoites in mice, addition of an agonist that recruits T cell help from type I natural killer T cells under mRNA-vaccination conditions resulted in significant generation of liver Trm cells and effective protection. Moreover, whereas previous exposure of mice to blood-stage infection impaired traditional vaccines based on attenuated sporozoites, mRNA vaccination was unaffected, underlining the potential for such a rational mRNA-based strategy in malaria-endemic regions.

Metabolic programs of T cell tissue residency empower tumour immunity

Tissue resident memory CD8+ T (TRM) cells offer rapid and long-term protection at sites of reinfection1. Tumour-infiltrating lymphocytes with characteristics of TRM cells maintain enhanced effector functions, predict responses to immunotherapy and accompany better prognoses2,3. Thus, an improved understanding of the metabolic strategies that enable tissue residency by T cells could inform new approaches to empower immune responses in tissues and solid tumours. Here, to systematically define the basis for the metabolic reprogramming supporting TRM cell differentiation, survival and function, we leveraged in vivo functional genomics, untargeted metabolomics and transcriptomics of virus-specific memory CD8+ T cell populations. We found that memory CD8+ T cells deployed a range of adaptations to tissue residency, including reliance on non-steroidal products of the mevalonate-cholesterol pathway, such as coenzyme Q, driven by increased activity of the transcription factor SREBP2. This metabolic adaptation was most pronounced in the small intestine, where TRM cells interface with dietary cholesterol and maintain a heightened state of activation4, and was shared by functional tumour-infiltrating lymphocytes in diverse tumour types in mice and humans. Enforcing synthesis of coenzyme Q through deletion of Fdft1 or overexpression of PDSS2 promoted mitochondrial respiration, memory T cell formation following viral infection and enhanced antitumour immunity. In sum, through a systematic exploration of TRM cell metabolism, we reveal how these programs can be leveraged to fuel memory CD8+ T cell formation in the context of acute infections and enhance antitumour immunity.

Homeostatic PD-1 signaling restrains EOMES-dependent oligoclonal expansion of liver-resident CD8 T cells

The co-inhibitory programmed death (PD)-1 signaling pathway plays a major role in the context of tumor-specific T cell responses. Conversely, it also contributes to the maintenance of peripheral tolerance, as patients receiving anti-PD-1 treatment are prone to developing immune-related adverse events. Yet, the physiological role of the PD-1/PDL-1 axis in T cell homeostasis is still poorly understood. Herein, we show that under steady-state conditions, the absence of PD-1 signaling led to a preferential expansion of CD8+ T cells in the liver. These cells exhibit an oligoclonal T cell receptor (TCR) repertoire and a terminally differentiated exhaustion profile. The transcription factor EOMES is required for the clonal expansion and acquisition of this differentiation program. Finally, single-cell transcriptomics coupled with TCR repertoire analysis support the notion that these cells arise locally from liver-resident memory CD8+ T cells. Overall, we show a role for PD-1 signaling in liver memory T cell homeostasis.

Induction of liver-resident memory T cells and protection at liver-stage malaria by mRNA-containing lipid nanoparticles

Recent studies have suggested that CD8+ liver-resident memory T (TRM) cells are crucial in the protection against liver-stage malaria. We used liver-directed mRNA-containing lipid nanoparticles (mRNA-LNPs) to induce liver TRM cells in a murine model. Single-dose intravenous injections of ovalbumin mRNA-LNPs effectively induced antigen-specific cytotoxic T lymphocytes in a dose-dependent manner in the liver on day 7. TRM cells (CD8+ CD44hi CD62Llo CD69+ KLRG1-) were induced 5 weeks after immunization. To examine the protective efficacy, mice were intramuscularly immunized with two doses of circumsporozoite protein mRNA-LNPs at 3-week intervals and challenged with sporozoites of Plasmodium berghei ANKA. Sterile immunity was observed in some of the mice, and the other mice showed a delay in blood-stage development when compared with the control mice. mRNA-LNPs therefore induce memory CD8+ T cells that can protect against sporozoites during liver-stage malaria and may provide a basis for vaccines against the disease.

Liver-resident CD44hiCD27- γδT Cells Help to Protect Against Listeria monocytogenes Infection

BACKGROUND & AIMS

Gamma delta (γδ) T cells are heterogeneous and functionally committed to producing interferon (IFN)-γ and interleukin (IL)-17. γδT cells are defined as tissue-resident lymphocytes in barrier tissues. Among them, IL-17-producing γδT cells are relatively abundant in the liver. However, a systematic and comprehensive understanding of the residency characteristics and function of hepatic IL-17A+ γδT cells is lacking.

METHODS

We undertook a single-cell analysis of γδT17 cells derived from murine livers. A parabiosis model was used to assess tissue residency. Fluorescence-activated cell sorting and adoptive transfer experiments were used to investigate the response and protective role of liver-resident CD44hiCD27- γδT cells in Listeria monocytogenes infection. Transwell assay was used to assess the role of macrophages in the chemotaxis of liver-resident CD44hiCD27- γδT cells.

RESULTS

We identified hepatic IL-17A-producing γδT cells as CD44hiCD27- γδT cells. They had tissue-resident characteristics and resided principally within the liver. Vγ6+ T cells also exhibited liver-resident features. Liver-resident CD44hiCD27- γδT cells had significantly increased proliferation capacity, and their proportion rapidly increased after infection. Some CD44hiCD27- γδT cells could produce IL-17A and IFN-γ simultaneously in response to Lm infection. Adoptive transfer of hepatic CD44hiCD27- γδT cells into Lm-infected TCRδ-/- mice led to markedly lower bacterial numbers in the liver. Hepatic macrophages promoted the migration and accumulation of liver-resident CD44hiCD27- γδT cells into infection sites.

CONCLUSIONS

Liver-resident CD44hiCD27- γδT cells protect against Lm infection. Hepatic macrophages coordinate with liver-resident CD44hiCD27- γδT cells and contribute to the clearance of Lm at the early stage of infection corporately.

Ultra-low volume intradermal administration of radiation-attenuated sporozoites with the glycolipid adjuvant 7DW8-5 completely protects mice against malaria

Malaria is caused by Plasmodium parasites and was responsible for over 247 million infections and 619,000 deaths in 2021. Radiation-attenuated sporozoite (RAS) vaccines can completely prevent blood stage infection by inducing protective liver-resident memory CD8+ T cells. Such T cells can be induced by 'prime-and-trap' vaccination, which here combines DNA priming against the P. yoelii circumsporozoite protein (CSP) with a subsequent intravenous (IV) dose of liver-homing RAS to "trap" the activated and expanding T cells in the liver. Prime-and-trap confers durable protection in mice, and efforts are underway to translate this vaccine strategy to the clinic. However, it is unclear whether the RAS trapping dose must be strictly administered by the IV route. Here we show that intradermal (ID) RAS administration can be as effective as IV administration if RAS are co-administrated with the glycolipid adjuvant 7DW8-5 in an ultra-low inoculation volume. In mice, the co-administration of RAS and 7DW8-5 in ultra-low ID volumes (2.5 μL) was completely protective and dose sparing compared to standard volumes (10-50 μL) and induced protective levels of CSP-specific CD8+ T cells in the liver. Our finding that adjuvants and ultra-low volumes are required for ID RAS efficacy may explain why prior reports about higher volumes of unadjuvanted ID RAS proved less effective. The ID route may offer significant translational advantages over the IV route and could improve sporozoite vaccine development.

Targeting dendritic cells to advance cross-presentation and vaccination outcomes

Dendritic cells (DCs) are a complex network of specialised antigen-presenting cells that are critical initiators of adaptive immunity. Targeting antigen directly to DCs in situ is a vaccination strategy that selectively delivers antigen to receptors expressed by DC subtypes. This approach exploits specific DC subset functions of antigen uptake and presentation. Here, we review DC-targeted vaccination strategies that are designed to elicit effective cross-presentation for CD8+ T cell immunity. In particular, we focus on approaches that exploit receptors highly expressed by mouse and human cDCs equipped with superior cross-presentation capacity. These receptors include DEC205, Clec9A and XCR1. Targeting DC receptors Clec12A, Clec4A4 and mannose receptor is also reviewed. Outcomes of DC-targeted vaccination in mouse models through to human clinical trials is discussed. This is a promising new vaccination approach capable of directly targeting the cross-presentation pathway for prevention and treatment of tumours and infectious diseases.

Memory CD8+ T cell-mediated protection against liver-stage malaria

Nearly half of the world's population is at risk of malaria, a disease caused by the protozoan parasite Plasmodium, which is estimated to cause more than 240,000,000 infections and kill more than 600,000 people annually. The emergence of Plasmodia resistant to chemoprophylactic treatment highlights the urgency to develop more effective vaccines. In this regard, whole sporozoite vaccination approaches in murine models and human challenge studies have provided substantial insight into the immune correlates of protection from malaria. From these studies, CD8+ T cells have come to the forefront, being identified as critical for vaccine-mediated liver-stage immunity that can prevent the establishment of the symptomatic blood stages and subsequent transmission of infection. However, the unique biological characteristics required for CD8+ T cell protection from liver-stage malaria dictate that more work must be done to design effective vaccines. In this review, we will highlight a subset of studies that reveal basic aspects of memory CD8+ T cell-mediated protection from liver-stage malaria infection.

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.

Regulation of systemic metabolism by tissue-resident immune cell circuits

Recent studies have demonstrated that tissue homeostasis and metabolic function are dependent on distinct tissue-resident immune cells that form functional cell circuits with structural cells. Within these cell circuits, immune cells integrate cues from dietary contents and commensal microbes in addition to endocrine and neuronal signals present in the tissue microenvironment to regulate structural cell metabolism. These tissue-resident immune circuits can become dysregulated during inflammation and dietary overnutrition, contributing to metabolic diseases. Here, we review the evidence describing key cellular networks within and between the liver, gastrointestinal tract, and adipose tissue that control systemic metabolism and how these cell circuits become dysregulated during certain metabolic diseases. We also identify open questions in the field that have the potential to enhance our understanding of metabolic health and disease.

STAT4 increases the phenotypic and functional heterogeneity of intestinal tissue-resident memory T cells

Tissue-resident memory T cells (Trms) are an important subset of lymphocytes that are lodged within non-lymphoid tissues and carry out diverse functions to control local pathogen replication. CD103 has been used to broadly define subsets of Trms within the intestine, with CD103+ and CD103- subsets having unique transcriptional profiles and effector functions. Here we identify signal transducer and activator of transcription 4 (STAT4) as an important regulator of CD103- Trm differentiation. STAT4-deficient cells trafficked to the intestine and localized to areas of infection but displayed impaired Trm differentiation with fewer CD103- Trms. Single-cell RNA-sequencing demonstrated that STAT4-deficiency led to a reduction in CD103- Trm subsets and expansion of a single population of CD103+ cells. Alterations in Trm populations were due, in part, to STAT4-mediated inhibition of transforming growth factor (TGF)-β-driven expression of Trm signature genes. STAT4-dependent Trm populations expressed genes associated with cytokine production and cell migration, and STAT4-deficient Trm cells had altered localization within the tissue and reduced effector function after reactivation in vivo. Overall, our data indicate that STAT4 leads to increased differentiation of CD103- Trms, in part by modulating the expression of TGF-β-regulated genes, and results in increased Trm heterogeneity and function within the intestinal tissue.

Distinct immune responses associated with vaccination status and protection outcomes after malaria challenge

Understanding immune mechanisms that mediate malaria protection is critical for improving vaccine development. Vaccination with radiation-attenuated Plasmodium falciparum sporozoites (PfRAS) induces high level of sterilizing immunity against malaria and serves as a valuable tool for the study of protective mechanisms. To identify vaccine-induced and protection-associated responses during malarial infection, we performed transcriptome profiling of whole blood and in-depth cellular profiling of PBMCs from volunteers who received either PfRAS or noninfectious mosquito bites, followed by controlled human malaria infection (CHMI) challenge. In-depth single-cell profiling of cell subsets that respond to CHMI in mock-vaccinated individuals showed a predominantly inflammatory transcriptome response. Whole blood transcriptome analysis revealed that gene sets associated with type I and II interferon and NK cell responses were increased in prior to CHMI while T and B cell signatures were decreased as early as one day following CHMI in protected vaccinees. In contrast, non-protected vaccinees and mock-vaccinated individuals exhibited shared transcriptome changes after CHMI characterized by decreased innate cell signatures and inflammatory responses. Additionally, immunophenotyping data showed different induction profiles of vδ2+ γδ T cells, CD56+ CD8+ T effector memory (Tem) cells, and non-classical monocytes between protected vaccinees and individuals developing blood-stage parasitemia, following treatment and resolution of infection. Our data provide key insights in understanding immune mechanistic pathways of PfRAS-induced protection and infective CHMI. We demonstrate that vaccine-induced immune response is heterogenous between protected and non-protected vaccinees and that inducted-malaria protection by PfRAS is associated with early and rapid changes in interferon, NK cell and adaptive immune responses. Trial Registration: ClinicalTrials.gov NCT01994525.

Optimal generation of hepatic tissue-resident memory CD4 T cells requires IL-1 and IL-2

Hepatic CD4 tissue-resident memory T cells (TRM) are required for robust protection against Salmonella infection; however, the generation of this T cell population is poorly understood. To interrogate the contribution of inflammation, we developed a simple Salmonella-specific T cell transfer system that allowed direct visualization of hepatic TRM formation. Salmonella-specific (SM1) T cell receptor (TCR) transgenic CD4 T cells were activated in vitro and adoptively transferred into C57BL/6 mice while hepatic inflammation was induced by acetaminophen overdose or L. monocytogenes infection. In both model systems, hepatic CD4 TRM formation was accentuated by local tissue responses. Liver inflammation also enhanced the suboptimal protection provided by a subunit Salmonella vaccine which typically induces circulating memory CD4 T cells. To further elucidate the mechanism of CD4 TRM formation in response to liver inflammation, various cytokines were examined by RNAseq, bone marrow chimeras, and in vivo neutralization. Surprisingly, IL-2 and IL-1 were found to enhance CD4 TRM formation. Thus, local inflammatory mediators enhance CD4 TRM populations and can boost the protective immunity provided by a suboptimal vaccine. This knowledge will be foundational for the development of a more effective vaccine against invasive nontyphoidal salmonellosis (iNTS).

Induction of antigen specific intrahepatic CD8+ T cell responses by a secreted heat shock protein based gp96-Ig-PfCA malaria vaccine

Introduction

A highly efficacious and durable vaccine against malaria is an essential tool for global malaria eradication. One of the promising strategies to develop such a vaccine is to induce robust CD8+ T cell mediated immunity against malaria liver-stage parasites.

Methods

Here we describe a novel malaria vaccine platform based on a secreted form of the heat shock protein, gp96-immunoglobulin, (gp96-Ig) to induce malaria antigen specific, memory CD8+ T cells. Gp96-Ig acts as an adjuvant to activate antigen presenting cells (APCs) and chaperone peptides/antigens to APCs for cross presentation to CD8+ T cells.

Results

Our study shows that vaccination of mice and rhesus monkeys with HEK-293 cells transfected with gp96-Ig and two well-known Plasmodium falciparum CSP and AMA1 (PfCA) vaccine candidate antigens, induces liver-infiltrating, antigen specific, memory CD8+ T cell responses. The majority of the intrahepatic CSP and AMA1 specific CD8+ T cells expressed CD69 and CXCR3, the hallmark of tissue resident memory T cells (Trm). Also, we found intrahepatic, antigen-specific memory CD8+ T cells secreting IL-2, which is relevant for maintenance of effective memory responses in the liver.

Discussion

Our novel gp96-Ig malaria vaccine strategy represents a unique approach to induce liver-homing, antigen-specific CD8+ T cells critical for Plasmodium liver-stage protection.

Role of immune responses for development of NAFLD-associated liver cancer and prospects for therapeutic modulation

The liver is the central metabolic organ of the body regulating energy and lipid metabolism and at the same time has potent immunological functions. Overwhelming the metabolic capacity of the liver by obesity and sedentary lifestyle leads to hepatic lipid accumulation, chronic necro-inflammation, enhanced mitochondrial/ER-stress and development of non-alcoholic fatty liver disease (NAFLD), with its pathologic form nonalcoholic steatohepatitis (NASH). Based on knowledge on pathophysiological mechanisms, specifically targeting metabolic diseases to prevent or slow down progression of NAFLD to liver cancer will become possible. Genetic/environmental factors contribute to development of NASH and liver cancer progression. The complex pathophysiology of NAFLD-NASH is reflected by environmental factors, particularly the gut microbiome and its metabolic products. NAFLD-associated HCC occurs in most of the cases in the context of a chronically inflamed liver and cirrhosis. Recognition of environmental alarmins or metabolites derived from the gut microbiota and the metabolically injured liver create a strong inflammatory milieu supported by innate and adaptive immunity. Several recent studies indicate that the chronic hepatic microenvironment of steatosis induces auto-aggressive CD8+CXCR6+PD1+ T cells secreting TNF and upregulating FasL to eliminate parenchymal and non-parenchymal cells in an antigen independent manner. This promotes chronic liver damage and a pro-tumorigenic environment. CD8+CXCR6+PD1+ T cells possess an exhausted, hyperactivated, resident phenotype and trigger NASH to HCC transition, and might be responsible for a less efficient treatment response to immune-check-point inhibitors - in particular atezolizumab/bevacizumab. Here, we provide an overview of NASH-related inflammation/pathogenesis focusing on new discoveries on the role of T cells in NASH-immunopathology and therapy response. This review discusses preventive measures to halt disease progression to liver cancer and therapeutic strategies to manage NASH-HCC patients.

Tissue-resident immune cells in the pathogenesis of multiple sclerosis

BACKGROUND

Multiple sclerosis (MS) is a chronic inflammatory autoimmune disease of the central nervous system (CNS) in which genetic and environmental factors contribute to disease progression. Both innate and adaptive immune cells, including T cells, B cells, activated macrophages and microglia, have been identified to be involved in the pathogenesis of MS, leading to the CNS inflammation, neurodegeneration and demyelination. In recent years, there has been considerable progress in understanding the contribution of tissue-resident immune cells in the pathogenesis of MS.

METHODS

We performed a keyword-based search in PubMed database. We combined "multiple sclerosis" with keywords, such as tissue-resident memory T cells, microglia to search for relevant literatures in PubMed.

RESULTS AND CONCLUSION

In this review, we comprehensively describe the characteristics of tissue-resident memory T cells and microglia, summarize their role in the pathogenesis of MS, and discuss their interaction with other immune cells in the CNS.

Tissue CD14+CD8+ T cells reprogrammed by myeloid cells and modulated by LPS

The liver is bathed in bacterial products, including lipopolysaccharide transported from the intestinal portal vasculature, but maintains a state of tolerance that is exploited by persistent pathogens and tumours1-4. The cellular basis mediating this tolerance, yet allowing a switch to immunity or immunopathology, needs to be better understood for successful immunotherapy of liver diseases. Here we show that a variable proportion of CD8+ T cells compartmentalized in the human liver co-stain for CD14 and other prototypic myeloid membrane proteins and are enriched in close proximity to CD14high myeloid cells in hepatic zone 2. CD14+CD8+ T cells preferentially accumulate within the donor pool in liver allografts, among hepatic virus-specific and tumour-infiltrating responses, and in cirrhotic ascites. CD14+CD8+ T cells exhibit increased turnover, activation and constitutive immunomodulatory features with high homeostatic IL-10 and IL-2 production ex vivo, and enhanced antiviral/anti-tumour effector function after TCR engagement. This CD14+CD8+ T cell profile can be recapitulated by the acquisition of membrane proteins-including the lipopolysaccharide receptor complex-from mononuclear phagocytes, resulting in augmented tumour killing by TCR-redirected T cells in vitro. CD14+CD8+ T cells express integrins and chemokine receptors that favour interactions with the local stroma, which can promote their induction through CXCL12. Lipopolysaccharide can also increase the frequency of CD14+CD8+ T cells in vitro and in vivo, and skew their function towards the production of chemotactic and regenerative cytokines. Thus, bacterial products in the gut-liver axis and tissue stromal factors can tune liver immunity by driving myeloid instruction of CD8+ T cells with immunomodulatory ability.