The Respiratory Environment Diverts the Development of Antiviral Memory CD8 T Cells

Characterization of the Anti-Viral and Vaccine-Specific CD8+ T Cell Composition upon Treatment with the Cancer Vaccine VSV-GP

Numerous factors influence the magnitude and effector phenotype of vaccine-induced CD8+ T cells, thereby potentially impacting treatment efficacy. Here, we investigate the effect of vaccination dose, route of immunization, presence of a target antigen-expressing tumor, and heterologous prime-boost with peptide vaccine partner following vaccination with antigen-armed VSV-GP. Our results indicate that a higher vaccine dose increases antigen-specific CD8+ T cell proportions while altering the phenotype. The intravenous route induces the highest proportion of antigen-specific CD8+ T cells together with the lowest anti-viral response followed by the intraperitoneal, intramuscular, and subcutaneous routes. Moreover, the presence of a B16-OVA tumor serves as pre-prime, thereby increasing OVA-specific CD8+ T cells upon vaccination and thus altering the ratio of anti-tumor versus anti-viral CD8+ T cells. Interestingly, tumor-specific CD8+ T cells exhibit a different phenotype compared to bystander anti-viral CD8+ T cells. Finally, the heterologous combination of peptide and viral vaccine elicits the highest proportion of antigen-specific CD8+ T cells in the tumor and tumor-draining lymph nodes. In summary, we provide a basic immune characterization of various factors that affect anti-viral and vaccine target-specific CD8+ T cell proportions and phenotypes, thereby enhancing our vaccinology knowledge for future vaccine regimen designs.

Dendritic cells: the yin and yang in disease progression

Dendritic cells (DCs) are antigen presenting cells that link innate and adaptive immunity. DCs have been historically considered as the most effective and potent cell population to capture, process and present antigens to activate naïve T cells and originate favorable immune responses in many diseases, such as cancer. However, in the last decades, it has been observed that DCs not only promote beneficial responses, but also drive the initiation and progression of some pathologies, including inflammatory bowel disease (IBD). In line with those notions, different therapeutic approaches have been tested to enhance or impair the concentration and role of the different DC subsets. The blockade of inhibitory pathways to promote DCs or DC-based vaccines have been successfully assessed in cancer, whereas the targeting of DCs to inhibit their functionality has proved to be favorable in IBD. In this review, we (a) described the general role of DCs, (b) explained the DC subsets and their role in immunogenicity, (c) analyzed the role of DCs in cancer and therapeutic approaches to promote immunogenic DCs and (d) analyzed the role of DCs in IBD and therapeutic approaches to reduced DC-induced inflammation. Therefore, we aimed to highlight the "yin-yang" role of DCs to improve the understand of this type of cells in disease progression.

Antigen non-specific CD8+ T cells accelerate cognitive decline in aged mice following respiratory coronavirus infection

Primarily a respiratory infection, numerous patients infected with SARS-CoV-2 present with neurologic symptoms, some continuing long after viral clearance as a persistent symptomatic phase termed "long COVID". Advanced age increases the risk of severe disease, as well as incidence of long COVID. We hypothesized that perturbations in the aged immune response predispose elderly individuals to severe coronavirus infection and post-infectious sequelae. Using a murine model of respiratory coronavirus, mouse hepatitis virus strain A59 (MHV-A59), we found that aging increased clinical illness and lethality to MHV infection, with aged animals harboring increased virus in the brain during acute infection. This was coupled with an unexpected increase in activated CD8+ T cells within the brains of aged animals but reduced antigen specificity of those CD8+ T cells. Aged animals demonstrated spatial learning impairment following MHV infection, which correlated with increased neuronal cell death and reduced neuronal regeneration in aged hippocampus. Using primary cell culture, we demonstrated that activated CD8+ T cells induce neuronal death, independent of antigen-specificity. Specifically, higher levels of CD8+ T cell-derived IFN-γ correlated with neuronal death. These results support the evidence that CD8+ T cells in the brain directly contribute to cognitive dysfunction following coronavirus infection in aged individuals.

Exposure to the Gram-Negative Bacteria Pseudomonas aeruginosa Influences the Lung Dendritic Cell Population Signature by Interfering With CD103 Expression

Lung dendritic cells (DCs) are divided into two major populations, which include CD103⁺XCR1⁺ cDC1s and CD11b⁺Sirpα⁺ cDC2s. The maintenance of their relative proportions is dynamic and lung inflammation, such as caused by exposure to lipopolysaccharide (LPS), a component of the outer membrane of Gram-negative bacteria, can have a significant impact on the local cDC signature. Alterations in the lung cDC signature could modify the capacity of the immune system to respond to various pathogens. We consequently aimed to assess the impact of the Gram-negative bacteria Pseudomonas aeruginosa on lung cDC1 and cDC2 populations, and to identify the mechanisms leading to alterations in cDC populations. We observed that exposure to P. aeruginosa decreased the proportions of CD103⁺XCR1⁺ cDC1s, while increasing that of CD11b⁺ DCs. We identified two potential mechanisms involved in this modulation of lung cDC populations. First, we observed an increase in bone marrow pre-DC IRF4 expression suggesting a higher propensity of pre-DCs to differentiate towards the cDC2 lineage. This observation was combined with a reduced capacity of lung XCR1⁺ DC1s to express CD103. In vitro, we demonstrated that GM-CSF-induced CD103 expression on cDCs depends on GM-CSF receptor internalization and RUNX1 activity. Furthermore, we observed that cDCs stimulation with LPS or P. aeruginosa reduced the proportions of intracellular GM-CSF receptor and decreased RUNX1 mRNA expression. Altogether, these results suggest that alterations in GM-CSF receptor intracellular localization and RUNX1 signaling could be involved in the reduced CD103 expression on cDC1 in response to P. aeruginosa. To verify whether the capacity of cDCs to express CD103 following P. aeruginosa exposure impacts the immune response, WT and Cd103^-/- mice were exposed to P. aeruginosa. Lack of CD103 expression led to an increase in the number of neutrophils in the airways, suggesting that lack of CD103 expression on cDC1s could favor the innate immune response to this bacterium.

Enhanced generation of influenza-specific tissue resident memory CD8 T cells in NK-depleted mice

Natural Killer (NK) cells are among the first effectors to directly contact influenza and influenza-infected cells and their activation affects not only their intrinsic functions, but also subsequent CD8+ T cell responses. We utilized a NK cell depletion model to interrogate the contribution of NK cells to the development of anti-influenza CD8+ T cell memory. NK cell ablation increased the number of influenza-specific memory CD8+ T cells in the respiratory tract and lung-draining lymph node. Interestingly, animals depleted of NK cells during primary influenza infection were protected as well as their NK-intact counterparts despite significantly fewer reactivated CD8+ T cells infiltrating the respiratory tract after lethal, heterosubtypic challenge. Instead, protection in NK-deficient animals seems to be conferred by rapid reactivation of an enlarged pool of lung tissue-resident (TRM) memory cells within two days post challenge. Further interrogation of how NK cell ablation enhances respiratory TRM indicated that TRM development is independent of global and NK cell derived IFN-γ. These data suggest that reduction in NK cell activation after vaccination with live, non-lethal influenza virus increases compartmentalized, broadly protective memory CD8+ T cell generation and decreases the risk of CD8+ T cell-mediated pathology following subsequent influenza infections.

IRF4-dependent dendritic cells regulate CD8+ T-cell differentiation and memory responses in influenza infection

Acute respiratory disease caused by influenza viruses is imperfectly mitigated by annual vaccination to select strains. Development of vaccines that elicit lung-resident memory CD8⁺ T cells (T_RM) would offer more universal protection to seasonal and emerging pandemic viruses. Understanding how lung-resident dendritic cells (DCs) regulate T_RM differentiation would be an important step in this process. Here, we used CD11c-cre-Irf4^f/f (KO) mice, which lack lung-resident IRF4-dependent CD11b⁺CD24^hi DCs and show IRF4 deficiency in other lung cDC subsets, to determine if IRF4-expressing DCs regulate CD8⁺ memory precursor cells and T_RM during influenza A virus (IAV) infection. KO mice showed defective CD8⁺ T-cell memory, stemming from a deficit of T regulatory cells and memory precursor cells with decreased Foxo1 expression. Transfer of wild-type CD11b⁺CD24^hi DCs into KO mice restored CD8⁺ memory precursor cell numbers to wild-type levels. KO mice recovered from a primary infection harbored reduced numbers of CD8⁺ T_RM and showed deficient expansion of IFNγ⁺CD8⁺ T cells and increased lung pathology upon challenge with heterosubtypic IAV. Thus, vaccination strategies that harness the function of IRF4-dependent DCs could promote the differentiation of CD8⁺ T_RM during IAV infection.