Protective role of follicular CXCR5+CD8+ T cells against dengue virus 2 infection

An angel or a devil? Current view on the role of CD8+ T cells in the pathogenesis of myasthenia gravis

BACKGROUND

Myasthenia gravis (MG) and the experimental autoimmune MG (EAMG) animal model are characterized by T-cell-induced and B-cell-dominated autoimmune diseases that affect the neuromuscular junction. Several subtypes of CD4+ T cells, including T helper (Th) 17 cells, follicular Th cells, and regulatory T cells (Tregs), contribute to the pathogenesis of MG. However, increasing evidence suggests that CD8+ T cells also play a critical role in the pathogenesis and treatment of MG.

MAIN BODY

Herein, we review the literature on CD8+ T cells in MG, focusing on their potential effector and regulatory roles, as well as on relevant evidence (peripheral, in situ, cerebrospinal fluid, and under different treatments), T-cell receptor usage, cytokine and chemokine expression, cell marker expression, and Treg, Tc17, CD3+CD8+CD20+ T, and CXCR5+ CD8+ T cells.

CONCLUSIONS

Further studies on CD8+ T cells in MG are necessary to determine, among others, the real pattern of the Vβ gene usage of autoantigen-specific CD8+ cells in patients with MG, real images of the physiology and function of autoantigen-specific CD8+ cells from MG/EAMG, and the subset of autoantigen-specific CD8+ cells (Tc1, Tc17, and IL-17+IFN-γ+CD8+ T cells). There are many reports of CD20-expressing T (or CD20 + T) and CXCR5+ CD8 T cells on autoimmune diseases, especially on multiple sclerosis and rheumatoid arthritis. Unfortunately, up to now, there has been no report on these T cells on MG, which might be a good direction for future studies.

Role of CXCR5+ CD8+ T cells in human hepatitis B virus infection

The replication of HBV in hepatocytes can be effectively inhibited by lifelong antiviral therapy. Because of the long-term presence of HBV reservoirs, the virus rebound frequently occurs once the treatment is stopped, which poses a considerable obstacle to the complete removal of the virus. In terms of gene composition, regulation of B cell action and function, CXCR5+ CD8+ T cells are similar to CXCR5+ CD4+ T follicular helper cells, while these cells are characterized by elevated programmed cell death 1 and cytotoxic-related proteins. CXCR5+ CD8+ T cells are strongly associated with progression in inflammatory and autoimmune diseases. In addition, CXCR5 expression on the surface of CD8+ T cells is mostly an indicator of memory stem cell-like failure in progenitor cells in cancer that are more responsive to immune checkpoint blocking therapy. Furthermore, the phenomena have also been demonstrated in some viral infections, highlighting the duality of the cellular immune response of CXCR5+ CD8+ T cells. This mini-review will focus on the function of CXCR5+ CD8+ T cells in HBV infection and discuss the function of these CD8+ T cells and the potential of associated co-stimulators or cytokines in HBV therapeutic strategies.

Dissecting the Protective Effect of CD8+ T Cells in Response to SARS-CoV-2 mRNA Vaccination and the Potential Link with Lymph Node CD8+ T Cells

SARS-CoV-2 vaccines have played a crucial role in effectively reducing COVID-19 disease severity, with a new generation of vaccines that use messenger RNA (mRNA) technology being administered globally. Neutralizing antibodies have featured as the heroes of vaccine-induced immunity. However, vaccine-elicited CD8⁺ T cells may have a significant impact on the early protective effects of the mRNA vaccine, which are evident 12 days after initial vaccination. Vaccine-induced CD8⁺ T cells have been shown to respond to multiple epitopes of SARS-CoV-2 and exhibit polyfunctionality in the periphery at the early stage, even when neutralizing antibodies are scarce. Furthermore, SARS-CoV-2 mRNA vaccines induce diverse subsets of memory CD8⁺ T cells that persist for more than six months following vaccination. However, the protective role of CD8⁺ T cells in response to the SARS-CoV-2 mRNA vaccines remains a topic of debate. In addition, our understanding of CD8⁺ T cells in response to vaccination in the lymph nodes, where they first encounter antigen, is still limited. This review delves into the current knowledge regarding the protective role of polyfunctional CD8⁺ T cells in controlling the virus, the response to SARS-CoV-2 mRNA vaccines, and the contribution to supporting B cell activity and promoting immune protection in the lymph nodes.

Current Understanding of the Role of T Cells in Chikungunya, Dengue and Zika Infections

Arboviral infections such as Chikungunya (CHIKV), Dengue (DENV) and Zika (ZIKV) are a major disease burden in tropical and sub-tropical countries, and there are no effective vaccinations or therapeutic drugs available at this time. Understanding the role of the T cell response is very important when designing effective vaccines. Currently, comprehensive identification of T cell epitopes during a DENV infection shows that CD8 and CD4 T cells and their specific phenotypes play protective and pathogenic roles. The protective role of CD8 T cells in DENV is carried out through the killing of infected cells and the production of proinflammatory cytokines, as CD4 T cells enhance B cell and CD8 T cell activities. A limited number of studies attempted to identify the involvement of T cells in CHIKV and ZIKV infection. The identification of human immunodominant ZIKV viral epitopes responsive to specific T cells is scarce, and none have been identified for CHIKV. In CHIKV infection, CD8 T cells are activated during the acute phase in the lymph nodes/blood, and CD4 T cells are activated during the chronic phase in the joints/muscles. Studies on the role of T cells in ZIKV-neuropathogenesis are limited and need to be explored. Many studies have shown the modulating actions of T cells due to cross-reactivity between DENV-ZIKV co-infections and have repeated heterologous/homologous DENV infection, which is an important factor to consider when developing an effective vaccine.

CXCR5+CD8+ T cells: A Review of their Antibody Regulatory Functions and Clinical Correlations

CD8⁺ T cells have conventionally been studied in relationship to pathogen or tumor clearance. Recent reports have identified novel functions of CXCR5⁺CD8⁺ T cells that can home to lymphoid follicles, a key site of antibody production. In this review we provide an in-depth analysis of conflicting reports regarding the impact of CXCR5⁺CD8⁺ T cells on antibody production and examine the data supporting a role for antibody-enhancement (B cell "helper") and antibody-downregulation (antibody-suppressor) by CXCR5⁺CD8⁺ T cell subsets. CXCR5⁺CD8⁺ T cell molecular phenotypes are associated with CD8-mediated effector functions including distinct subsets that regulate antibody responses. Co-inhibitory molecule PD-1, among others, distinguish CXCR5⁺CD8⁺ T cell subsets. We also provide the first in-depth review of human CXCR5⁺CD8⁺ T cells in the context of clinical outcomes and discuss the potential utility of monitoring the quantity of peripheral blood or tissue infiltrating CXCR5⁺CD8⁺ T cells as a prognostic tool in multiple disease states.

COVID-19 severity associates with pulmonary redistribution of CD1c+ DCs and inflammatory transitional and nonclassical monocytes

SARS-CoV-2 is responsible for the development of coronavirus disease 2019 (COVID-19) in infected individuals, who can either exhibit mild symptoms or progress toward a life-threatening acute respiratory distress syndrome (ARDS). Exacerbated inflammation and dysregulated immune responses involving T and myeloid cells occur in COVID-19 patients with severe clinical progression. However, the differential contribution of specific subsets of dendritic cells and monocytes to ARDS is still poorly understood. In addition, the role of CD8+ T cells present in the lung of COVID-19 patients and relevant for viral control has not been characterized. Here, we have studied the frequencies and activation profiles of dendritic cells and monocytes present in the blood and lung of COVID-19 patients with different clinical severity in comparison with healthy individuals. Furthermore, these subpopulations and their association with antiviral effector CD8+ T cell subsets were also characterized in lung infiltrates from critical COVID-19 patients. Our results indicate that inflammatory transitional and nonclassical monocytes and CD1c+ conventional dendritic cells preferentially migrate from blood to lungs in patients with severe COVID-19. Thus, this study increases the knowledge of specific myeloid subsets involved in the pathogenesis of COVID-19 disease and could be useful for the design of therapeutic strategies for fighting SARS-CoV-2 infection.

The elusive identity of CXCR5+ CD8 T cells in viral infection and autoimmunity: Cytotoxic, regulatory, or helper cells?

Our knowledge on the development and functions of CXCR5⁺ CD8 T cells is rudimentary when confronted to other extensively studied CD8 T cell subsets. A decade ago, it became apparent that CD8 T cells possess two additional and rather unexpected functional properties other than cytotoxicity, one involving what is known as B cell helper activity and the other involving suppression of self-reactive responses generally known as T cell regulation. Although these adaptive responses are well-known functions of CD4 T cells, they remain poorly understood in CD8 T cells. Thus far, three subsets of CXCR5⁺ CD8 T cells have been identified. The first subset of CXCR5⁺ CD8 T cells is present in chronic viral infections and is referred to as progenitors of exhausted T cells showing heightened proliferative and cytotoxic properties as compared to CXCR5^- CD8 T cells. The second subset of CXCR5⁺ CD8 T cells functions as regulatory T cells that inhibit CD4 T follicular helper (Tfh) humoral responses and the development of autoantibodies. The third subset of CXCR5⁺ CD8 T cells was identified in mice with mutations in immunoregulatory genes (i.e. FOXP3 and IL-2-deficient mice) and involves CD8 T cells with Tfh-like properties that promote humoral autoimmunity through interaction with B cells. This review summarizes the phenotype, function, and differentiation of CXCR5⁺ CD8 T cells.