CD8 TRM Cells Research Articles

Evolutionary diversity of CXCL16-CXCR6: Convergent substitutions and recurrent gene loss in sauropsids.

The CXCL16-CXCR6 axis is crucial for regulating the persistence of CD8 tissue-resident memory T cells (TRM). CXCR6 deficiency lowers TRM cell numbers in the lungs and depletes ILC3s in the lamina propria, impairing mucosal defence. This axis is linked to diseases like HIV/SIV, cancer, and COVID-19. Together, these highlight that the CXCL16-CXCR6 axis is pivotal in host immunity. Previous studies of the CXCL16-CXCR6 axis found genetic variation among species but were limited to primates and rodents. To understand the evolution and diversity of CXCL16-CXCR6 across vertebrates, we compared approximately 400 1-to-1 CXCR6 orthologs spanning diverse vertebrates. The unique DRF motif of CXCR6 facilitates leukocyte adhesion by interacting with cell surface-expressed CXCL16 and plays a key role in G-protein selectivity during receptor signalling; however, our findings show that this motif is not universal. The DRF motif is restricted to mammals, turtles, and frogs, while the DRY motif, typical in other CKRs, is found in snakes and lizards. Most birds exhibit the DRL motif. These substitutions at the DRF motif affect the receptor-Gi/o protein interaction. We establish recurrent CXCR6 gene loss in 10 out of 36 bird orders, including Galliformes and Passeriformes, Crocodilia, and Elapidae, attributed to segmental deletions and/or frame-disrupting changes. Notably, single-cell RNA sequencing of the lung shows a drop in TRM cells in species with CXCR6 loss, suggesting a possible link. The concurrent loss of ITGAE, CXCL16, and CXCR6 in chickens may have altered CD8 TRM cell abundance, with implications for immunity against viral diseases and vaccines inducing CD8 TRM cells.

Tissue-resident memory T cells: Harnessing their properties against infection for cancer treatment.

We have rapidly gained insights into the presence and function of T lymphocytes in non-lymphoid tissues, the tissue-resident memory T (TRM) cells. The central pillar of adaptive immunity has been expanded from classic central memory T cells giving rise to progeny upon reinfection and effector memory cells circulating through the blood and patrolling the tissues to include TRM cells that reside and migrate inside solid organs and tissues. Their development and maintenance have been studied in detail, providing exciting clues on how their unique properties used to fight infections may benefit therapies against solid tumors. We provide an overview of CD8 TRM cells and the properties that make them of interest for vaccination and cancer therapies.

Transient Therapeutic Inhibition of Multiple Costimulatory Molecules Modulates Persistence of Lung Tissue-resident Memory T cells

Abstract Costimulatory molecules, crucial for priming of T cells, development of T cell memory, and establishment of inflammatory diseases, have an unknown role in prolonged survival of Tissue-resident memory T (Trm) cells and the maintenance of relapsing inflammation. Single-cell RNA-seq data from asthmatic lungs revealed high expression of OX40, CD30L, and ICOS on CD4 T cells, aligning with transcriptomic analysis of allergen-reactive mouse CD4 Trm cells in a relapsing asthma model. Accordingly, the transient blockade of ICOSL alone or CD30L and OX40L together during tertiary allergen inhalation effectively reduced the expansion of CD44hiCD62LloCD4+ lung Trm by 40-50%, further reducing to 80-90% when concurrently targeting all three molecules and corresponding to dramatically decreased lung inflammation. Administering FTY720 with the blocking antibodies highlighted costimulatory molecules govern reactivation of both lung Trm and circulatory memory T cells that contribute to the maintenance of Trm pool. Costimulation blockade limited Trm proliferation and their continued responsiveness upon future allergen insults, explaining improved lung function. Dual blockade of ICOSL with OX40L, or ICOSL with CD30L, reproduced the effects of blocking all molecules together in limiting persistence of high numbers of functional Trm, suggesting that targeting ICOS signaling along with CD30 or OX40 signaling holds promise as a clinical treatment for various immune-mediated inflammatory diseases

IL-17 and IFN-γ-producing Respiratory Tissue-Resident Memory CD4 T Cells Persist for Decades in Adults Immunized as Children With Whole-Cell Pertussis Vaccines.

The objective was to determine if antigen-specific tissue-resident memory T (TRM) cells persist in respiratory tissues of adults immunized as children with whole-cell pertussis (wP) or acellular pertussis (aP) vaccines. Mononuclear cells from tonsil or nasal tissue cells were cultured with Bordetella pertussis antigens and TRM cells quantified by flow cytometry. Adults immunized with wP vaccines as children had significantly more interleukin 17A (IL-17A) and interferon-γ (IFN-γ)-producing TRM cells that respond to B. pertussis antigens in respiratory tissues when compared with aP-primed donors. Our findings demonstrate that wP vaccines induce CD4 TRM cells that can persist in respiratory tissues for decades.

Virus-specific TRM cells of both donor and recipient origin reside in human kidney transplants.

Tissue-resident lymphocytes (TRLs) are critical for local protection against viral pathogens in peripheral tissue. However, it is unclear if TRLs perform a similar role in transplanted organs under chronic immunosuppressed conditions. The present study aimed to characterize the TRL compartment in human kidney transplant nephrectomies and examine its potential role in antiviral immunity. The TRL compartment of kidney transplants contained diverse innate(-like) and adaptive TRL populations expressing the canonical residency markers CD69, CD103, and CD49a. Chimerism of donor and recipient cells was present in 43% of kidney transplants and occurred in all TRL subpopulations. Paired single-cell transcriptome and T-cell receptor (TCR) sequencing showed that donor and recipient tissue-resident memory T (TRM) cells exhibit striking similarities in their transcriptomic profiles and share numerous TCR clonotypes predicted to target viral pathogens. Virus dextramer staining further confirmed that CD8 TRM cells of both donor and recipient origin cexpress TCRs with specificities against common viruses, including CMV, EBV, BK polyomavirus, and influenza A. Overall, the study results demonstrate that a diverse population of TRLs resides in kidney transplants and offer compelling evidence that TRM cells of both donor and recipient origin reside within this TRL population and may contribute to local protection against viral pathogens.

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.

Abstract 3464: Dynamics of resident memory (Trm) cell responses between skin and draining lymph nodes during primary and recall responses to melanoma

Abstract Tissue resident memory (TRM) cells reside durably in tissues where they serve as a vital component of protective anti-tumor immunity. In mice, TRM cells are defined by their expression of tissue retention markers such as CD69 and CD103, and lack of egress markers such as CD62L, CCR7 and S1PR1. We previously showed that depletion of regulatory T cells induces the generation of protective CD8 Trm cells in skin and draining LNs of B16 melanoma tumor-excised mice. While tumor specific Trm cells were shown to stably reside in tissues at steady state, little is known about their migration between tissue compartments and circulation during primary and recall responses to melanoma. Using gp100-specific transgenic pmel CD8 T cells expressing a Kaede-GFP photoconvertible marker, we investigated the trafficking patterns of tumor Ag specific CD8+ T-cells that were labeled in situ by exposure to UV light in the skin. During primary tumor growth, we observed pronounced movement of antigen-experienced pmel cells through skin to tumor-draining LNs. This trafficking behavior could be inhibited by treatment with FTY720, indicating its S1PR-dependence. Such movement was no longer evident at memory timepoints. However, re-challenge with B16 cells in the dermis induced rapid pmel T cell egress to both LNs and circulation. Recallenge-mediated Trm cell skin egress was confirmed using anti-Thy1.1 monoclonal antibody to deplete circulating and lymphoid memory, while preserving skin TRM. Here we found that skin TRM proliferate and transiently increase expression of Tbet, but go on to generate a durable secondary Trm response in lymph nodes. These data highlight T cell movement between tissues during Trm programming and recall responses to cancer, and shed light on a potential mechanism for the generation TRM populations in tumor-draining lymph nodes. Moreover, our results highlight the potential for retrograde movement of Trm responses from peripheral tissue reservoirs to participate more broadly in systemic anti-tumor immunity. Citation Format: Cameron Messier, Nikhil Khatwani, Aaron Hawkes, Yuyang (Poppy) Huang, Mary Jo Turk. Dynamics of resident memory (Trm) cell responses between skin and draining lymph nodes during primary and recall responses to melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3464.

Bystander activation of tissue-resident memory CD4 T cells: Getting by with a little help from unfamiliar T-cell friends.

Reexposure to a pathogen triggers the activation of memory T cells that have already encountered a similar microbe. These long-lived CD4 T cells either circulate through the blood and tissues or reside within organs and are referred to as tissue-resident T cells (CD4 TRM ). In the current issue of the European Journal of Immunology [Eur. J. Immunol. 2023. 53: 2250247] issue, Curham etal. found that tissue-resident memory CD4 T cells in the lung and nasal tissues can respond to noncognate immune challenges. CD4 TRM cells, which were formed in response to Bordetella pertussis, proliferated and produced IL-17A in response to a secondary challenge with heat-killed Klebsiella pneumonia or lipopolysaccharide (LPS). This bystander response depends on the presence of dendritic cells that provide inflammatory cytokines. Furthermore, post K. pneumonia, intranasal immunization with whole cell pertussis vaccine reduced bacterial burden in the nasal tissue in a CD4 T-cell-dependent manner. The study indicates that the noncognate activation of TRM may serve as an innate-like immune response that rapidly develops before establishing a new pathogen-specific adaptive immune response.

Bystander activation of Bordetella pertussis-induced nasal tissue-resident memory CD4 T cells confers heterologous immunity to Klebsiella pneumoniae.

Tissue-resident memory CD4 T (TRM ) cells induced by infection with Bordetella pertussis persist in respiratory tissues and confer long-term protective immunity against reinfection. However, it is not clear how they are maintained in respiratory tissues. Here, we demonstrate that B. pertussis-specific CD4 TRM cells produce IL-17A in response to in vitro stimulation with LPS or heat-killed Klebsiella pneumoniae (HKKP) in the presence of dendritic cells. Furthermore, IL-17A-secreting CD4 TRM cells expand in the lung and nasal tissue of B. pertussis convalescent mice following in vivo administration of LPS or HKKP. Bystander activation of CD4 TRM cells was suppressed by anti-IL-12p40 but not by anti-MHCII antibodies. Furthermore, purified respiratory tissue-resident, but not circulating, CD4 T cells from convalescent mice produced IL-17A following direct stimulation with IL-23 and IL-1β or IL-18. Intranasal immunization of mice with a whole-cell pertussis vaccine induced respiratory CD4 TRM cells that were reactivated following stimulation with K. pneumoniae. Furthermore, the nasal pertussis vaccine conferred protective immunity against B. pertussis but also attenuated infection with K. pneumoniae. Our findings demonstrate that CD4 TRM cells induced by respiratory infection or vaccination can undergo bystander activation and confer heterologous immunity to an unrelated respiratory pathogen.

CD8 tissue-resident memory T cells bridge the gap between humoral and cell-mediated immunity

Tissue-resident memory T (TRM) cells exert antiviral effects in situ using a variety of cell-intrinsic mechanisms. In this issue of Mucosal Immunology, Rosato and colleagues demonstrate that mucosal CD8 TRM cells can also facilitate the extravasation of antibodies with neutralizing capacities by modulating transcytotic receptors and vascular permeability, thus revealing a new mechanism by which TRM cells modulate humoral responses and protect the host from incoming pathogens.

A single-cell analysis framework allows for characterization of CSF leukocytes and their tissue of origin in multiple sclerosis.

Peripheral central nervous system (CNS)-infiltrating lymphocytes are a hallmark of relapsing-remitting multiple sclerosis. Tissue-resident memory T cells (TRM) not only populate the healthy CNS parenchyma but also are suspected to contribute to multiple sclerosis pathology. Because cerebrospinal fluid (CSF), unlike CNS parenchyma, is accessible for diagnostics, we evaluated whether human CSF, apart from infiltrating cells, also contains TRM cells and CNS-resident myeloid cells draining from the parenchyma or border tissues. Using deep generative models, we integrated 41 CSF and 14 CNS parenchyma single-cell RNA sequencing (scRNAseq) samples from eight independent studies, encompassing 120,629 cells. By comparing CSF immune cells collected during multiple sclerosis relapse with cells collected during therapeutic very late antigen-4 blockade, we could identify immune subsets with tissue provenance across multiple lineages, including CNS border-associated macrophages, CD8 and CD4 TRM cells, and tissue-resident natural killer cells. All lymphocytic CNS-resident cells shared expression of CXCR6 but showed differential ITGAE expression (encoding CD103). A common signature defined CD4 and CD8 TRM cells by expression of ZFP36L2, DUSP1, and ID2. We further developed a user interface-driven application based on this analysis framework for atlas-level cell identity transfer onto new CSF scRNAseq data. Together, these results define CNS-resident immune cells involved in multiple sclerosis pathology that can be detected and monitored in CSF. Targeting these cell populations might be promising to modulate immunopathology in progressive multiple sclerosis and other neuroinflammatory diseases.

Single-cell RNA transcriptome analysis of CNS immune cells reveals CXCL16/CXCR6 as maintenance factors for tissue-resident T cells that drive synapse elimination

BackgroundEmerging RNA viruses that target the central nervous system (CNS) lead to cognitive sequelae in survivors. Studies in humans and mice infected with West Nile virus (WNV), a re-emerging RNA virus associated with learning and memory deficits, revealed microglial-mediated synapse elimination within the hippocampus. Moreover, CNS-resident memory T (TRM) cells activate microglia, limiting synapse recovery and inducing spatial learning defects in WNV-recovered mice. The signals involved in T cell-microglia interactions are unknown.MethodsHere, we examined immune cells within the murine WNV-recovered forebrain using single-cell RNA sequencing to identify putative ligand-receptor pairs involved in intercellular communication between T cells and microglia. Clustering and differential gene analyses were followed by protein validation and genetic and antibody-based approaches utilizing an established murine model of WNV recovery in which microglia and complement promote ongoing hippocampal synaptic loss.ResultsProfiling of host transcriptome immune cells at 25 days post-infection in mice revealed a shift in forebrain homeostatic microglia to activated subpopulations with transcriptional signatures that have previously been observed in studies of neurodegenerative diseases. Importantly, CXCL16/CXCR6, a chemokine signaling pathway involved in TRM cell biology, was identified as critically regulating CXCR6 expressing CD8+ TRM cell numbers within the WNV-recovered forebrain. We demonstrate that CXCL16 is highly expressed by all myeloid cells, and its unique receptor, CXCR6, is highly expressed on all CD8+ T cells. Using genetic and pharmacological approaches, we demonstrate that CXCL16/CXCR6 not only is required for the maintenance of WNV-specific CD8 TRM cells in the post-infectious CNS, but also contributes to their expression of TRM cell markers. Moreover, CXCR6+CD8+ T cells are required for glial activation and ongoing synapse elimination.ConclusionsWe provide a comprehensive assessment of the role of CXCL16/CXCR6 as an interaction link between microglia and CD8+ T cells that maintains forebrain TRM cells, microglial and astrocyte activation, and ongoing synapse elimination in virally recovered animals. We also show that therapeutic targeting of CXCL16 in mice during recovery may reduce CNS CD8+ TRM cells.

Resident CD8+ T-cells drive dysplastic repair of aged lungs following viral pneumonia

Abstract Global studies have established age as the most critical risk factor in determining morbidity and mortality following respiratory viral infections such as influenza and SARS-CoV2. Previous studies from our group identified non-resolving inflammation in aged lungs post influenza infection, primarily driven by the persistence of tissue resident memory (Trm) CD8 T-cells. We also observed sustained impaired lung function in aged COVID19 convalescents, which negatively correlated with levels of pulmonary CD8 Trm cells. While critical for acute antiviral responses, we have demonstrated that this population is pathologic rather than protective following viral clearance during aging, evidenced by improved outcomes upon its depletion. Upon severe lung damage during viral infection, epithelial progenitor cells characterized by cytokeratin 5 (Krt5) expression are mobilized for repair. However, these cells are known to be incapable of differentiating into functional ATI and ATII cells, instead persisting as dysplastic epithelial scars, a process known to be exacerbated with age. Thus, in addition to mortality during acute infection, aged individuals also experience adverse long-term outcomes due to dysfunctional repair of the lung. We identified that Krt5 cysts typically associate with CD8 Trm cells, suggesting potential immune-epithelial crosstalk. Furthermore, upon depletion of pulmonary CD8 Trm cells, we observed a reduction in Krt5 cysts, increased ATI and ATII levels, and improved lung function. Hence, we hypothesize that the interactions between CD8 Trm cells and Krt5 cysts are responsible for sub-optimal repair and aim to manipulate this crosstalk to promote functional repair of the aged lung following viral pneumonia. Supported by grants from NIH - AI147394, AG047156, and AG069264 and Mayo Clinic CBD Research Fund

Intranasal, not parenteral, vaccination induces the formation of tissue-resident memory CD8 T cells in nasal mucosa that rapidly clear influenza virus infection

Abstract Respiratory tract infections are among the leading causes of death. While current vaccines reduce severe disease, they provide suboptimal mucosal protection (e.g. against influenza virus and SARS-CoV-2). Nasal vaccines offer an advantage by quickly limiting viral shedding, in part by generating tissue-resident memory (Trm) CD8 T cells in the nasal mucosa. But little is known about the molecular requirements for this Trm formation. The common paradigm is that lymphocytes home to tissues after having been imprinted within draining lymph nodes to express a tissue-specific combination of trafficking molecules, and Trm cells form rapidly from this pool. To probe the paradigm of tissue homing to the nasal mucosa, we compared CD8 T cell trafficking following intranasal and intramuscular vaccination. To investigate the trafficking molecules expressed by CD8 T cells and nasal cells we generated a single-cell RNA sequencing profile of the nasal mucosa over the course of an acute influenza infection. We found significantly more CD8 Trm cells in the nasal mucosa following intranasal vaccination that rapidly cleared influenza infection. Notably, CD8 T cells could be “pulled” into the nasal mucosa with an inflammatory stimulus following intramuscular vaccination, suggesting a new strategy for generating nasal CD8 Trm cells. Unlike canonical T cell homing to the gut and skin, nasal CD8 T cell trafficking depended on a4/VCAM1 (not a4b7/MADCAM1 or P and E-Selectin), and CD8 T cells expressed high levels of CXCR3 and CXCR6. This combination of trafficking molecules suggests a distinct multi-step adhesion cascade for CD8 T cell recruitment to the nasal mucosa and provides critical insights to rationally design vaccines for respiratory tract protection. Supported by grants from NIH (R01 AR068383-01, P01 AI 112521) and HMS-AbbVie Alliance

Multiplatform Single-Cell Analysis Identifies Immune Cell Types Enhanced in Pulmonary Fibrosis.

Immune cells have been implicated in idiopathic pulmonary fibrosis (IPF), but the phenotypes and effector mechanisms of these cells remain incompletely characterized. We performed mass cytometry to quantify immune cell subsets in lungs of 12 patients with IPF and 15 organ donors without chronic lung disease and used existing single-cell RNA-sequencing data to investigate transcriptional profiles of immune cells overrepresented in IPF. Among myeloid cells, we found increased numbers of alveolar macrophages (AMØs) and dendritic cells (DCs) in IPF, as well as a subset of monocyte-derived DCs. In contrast, monocyte-like cells and interstitial macrophages were reduced in IPF. Transcriptomic profiling identified an enrichment for IFN-γ response pathways in AMØs and DCs from IPF, as well as antigen processing in DCs and phagocytosis in AMØs. Among T cells, we identified three subsets of memory T cells that were increased in IPF, including CD4+ and CD8+ resident memory T cells (TRM) and CD8+ effector memory cells. The response to the IFN-γ pathway was enriched in CD4 TRM and CD8 TRM cells in IPF, together with T cell activation and immune response-regulating signaling pathways. Increased AMØs, DCs, and memory T cells were present in IPF lungs compared with control subjects. In IPF, these cells possess an activation profile indicating increased IFN-γ signaling and upregulation of adaptive immunity in the lungs. Together, these studies highlight critical features of the immunopathogenesis of IPF.

Limited Predictive or Prognostic Role of Tumor-Infiltrating Tissue-Resident Memory CD8 T Cells in Patients with Hepatocellular Carcinoma Receiving Immunotherapy.

Simple SummaryTotal tumor-infiltrating CD8 T cells inconsistently correlate with the efficacy of immune checkpoint blockade (ICB) in hepatocellular carcinoma. Tumor-infiltrating CD8 tissue-resident memory T cells (TRM) are considered a surrogate of tumor-specific T cells and correlated better with survival in patients with melanoma, non–small-cell lung cancer, head and neck cancer or bladder cancer who received ICB. However, in this study, compared with total tumor-infiltrating CD8 T cells, tumor-infiltrating CD8 TRM cells failed to provide additional advantages in predicting the efficacy of ICB-based immunotherapy in patients with hepatocellular carcinoma.Purpose: Tumor-infiltrating tissue-resident memory CD8 T cells (CD8 TRM; CD103+ CD8+) are considered tumor-specific and may correlate better with the tumor response to immune checkpoint blockade (ICB). This study evaluated the association of tumor-infiltrating CD8 TRM and their subsets with the efficacy of immunotherapy in patients with advanced hepatocellular carcinoma (HCC). Experimental Design: Consecutive HCC patients who received ICB in prospective trials were analyzed. Formalin-fixed paraffin-embedded tumor sections were stained for DAPI, CD8, CD103, CD39, programmed cell death-1 (PD-1), and programmed cell death ligand 1 (PD-L1) using a multiplex immunohistochemical method. The densities of CD8 T cells, CD8 TRM, and CD39+ or PD-L1+ subsets of CD8 TRM were correlated with tumor response and overall survival (OS). Results: A total of 73 patients were identified, and 48 patients with adequate pretreatment tumor specimens and complete follow-up were analyzed. A median of 32.7% (range: 0–92.6%) of tumor-infiltrating CD8 T cells were TRM. In subset analyses, 66.6% ± 34.2%, 69.8% ± 33.4%, and 0% of CD8 TRM cells coexpressed CD39, PD-L1, and PD-1, respectively. The objective response rates for CD8 T cell-high, CD8 TRM-high, CD39+ CD8 TRM-high, and PD-L1+ CD8 TRM-high groups were 41.7%, 37.5%, 37.5%, and 29.2%, respectively. Patients with CD8 T cell-high, but not those with CD8 TRM-high, CD39+ CD8 TRM-high, or PD-L1+ CD8 TRM-high, tumors, had significantly prolonged OS (p = 0.0429). Conclusions: Compared with total tumor-infiltrating CD8 T cells, tumor-infiltrating CD8 TRM or their subsets failed to provide additional advantages in predicting the efficacy of immunotherapy for HCC.

Mesenteric lymph node priming licenses intestinal CD103+ CD8 tissue-resident memory T cell development

Abstract CD8 tissue-resident memory T (TRM) cells provide front-line protective immunity at barrier tissues; however, mechanisms regulating their development are not completely understood. Priming dictates the migration of effector CD8 T cells to the tissue, while factors in the tissue induce in situ TRM cell differentiation. Whether priming also regulates in situ differentiation of CD8 TRM cells has not been addressed. Here, we demonstrate that T cell priming in the mesenteric lymph nodes (MLN) was the principal determinant of CD103+ CD8 TRM cell differentiation in the intestine. In contrast, CD8 T cells primed in the spleen were inefficient at differentiating into intestinal CD103+ TRM cells. Moreover, both CD103− and CD103+ naïve T cells were highly efficient in differentiating into CD103+ TRM cells in the intestine after priming in the MLN, suggesting preconditioning of naïve T cells by TGF-b during homeostasis had little impact on intestinal CD103+ TRM cell differentiation. We further demonstrate that MLN priming initiated CD103+ CD8 TRM cell signature gene expression and licensed rapid CD103+ CD8 TRM precursor cell differentiation in response to factors in the tissue by providing retinoic acid signaling to CD8 T cells. Thus, MLN priming is specialized to license intestinal CD103+ CD8 TRM cell development.

Prime-Trap immunization with protective liver stage antigen, MIF-4G and Kb17 peptide, induces liver CD8 TRM cells and protection against Plasmodium berghei malaria

Abstract Exposure to Plasmodium sporozoites (spz), the causative agent of malaria, induces anti-disease immunity, but fails to protect against repeated Plasmodium infections. In contrast, multiple immunizations with radiation-attenuated Plasmodium spz (RAS) induce sterile lasting protection in humans, non-human primates, and murine models. The mechanisms of protective immunity are multifactorial and CD8 T cells are considered sine qua none of protection. The Plasmodium berghei (Pb) RAS-induced protection in C57Bl/6 mice correlates with a network of liver stage antigens (LS Ags)-activated liver CD8 T cell subsets including resident memory (RM) CD8 TRM cells. A protective Pb LS Ag, termed MIF-4G, induced liver CD8 T cells that recognize H-2Kb-restricted epitope, Kb17. One of the current efforts to improve malaria vaccines focuses on maximizing the induction of liver CD8 TRM cells by Prime-Trap immunization regimen. Here we asked if priming with DNA-MIF-4G followed by trapping with Adenovirus serotype 5 (Ad5) vectored-Kb17 would induce Kb17-specific liver CD8 TRM cells as well as protection against Pb spz challenge. Liver Kb17-specific CD8 TRM cells (CD69+CXCR6+) exceeded the number of these cells in the spleens, 27% vs 2%, respectively. Protection measured by liver parasite burden was CD8 T cell dependent. In contrast, prime:boost immunization with DNA/Ad5 MIF-4G induced only 8% liver CD8 TRM cells, as did control immunization with DNA/Ad5 empty vector. Utilizing LS Ags and the corresponding CD8 T cell-inducing epitopes in Prime-Trap immunization lends itself for further explorations as an ancillary approach to malaria vaccine regimens where liver CD8 TRM may be crucial in preventing virulent blood stages by targeting LS parasites.

TGF-β: Many Paths to CD103+ CD8 T Cell Residency.

CD8 tissue-resident memory T (TRM) cells primarily reside in nonlymphoid tissues without recirculating and provide front-line protective immunity against infections and cancers. CD8 TRM cells can be generally divided into CD69+ CD103− TRM cells (referred to as CD103− TRM cells) and CD69+ CD103+ TRM cells (referred to as CD103+ TRM cells). TGF-β plays a critical role in the development and maintenance of CD103+ CD8 TRM cells. In this review, we summarize the current understanding of tissue-specific activation of TGF-β mediated by integrins and how it contributes to CD103+ CD8 TRM cell development and maintenance. Furthermore, we discuss the underlying mechanisms utilized by TGF-β to regulate the development and maintenance of CD103+ CD8 TRM cells. Overall, this review highlights the importance of TGF-β in regulating this unique subset of memory CD8 T cells that may shed light on improving vaccine design to target this population.

Age-Related Dynamics of Lung-Resident Memory CD8+ T Cells in the Age of COVID-19.

Following respiratory viral infections or local immunizations, lung resident-memory T cells (TRM) of the CD8 lineage provide protection against the same pathogen or related pathogens with cross-reactive T cell epitopes. Yet, it is now clear that, if homeostatic controls are lost following viral pneumonia, CD8 TRM cells can mediate pulmonary pathology. We recently showed that the aging process can result in loss of homeostatic controls on CD8 TRM cells in the respiratory tract. This may be germane to treatment modalities in both influenza and coronavirus disease 2019 (COVID-19) patients, particularly, the portion that present with symptoms linked to long-lasting lung dysfunction. Here, we review the developmental cues and functionalities of CD8 TRM cells in viral pneumonia models with a particular focus on their capacity to mediate heterogeneous responses of immunity and pathology depending on immune status.