Kang Tang

In hemorrhagic fever with renal syndrome (HFRS) caused by Hantaan virus (HTNV), virus-specific CD8 ⁺ T cells mediate both viral clearance and immunopathology. Here, we characterized a CD8 ⁺ regulatory T cell (Treg) subset restricted by HLA-E (and its murine ortholog Qa-1) in HFRS patients and in a murine HTNV infection model. CD8 ⁺ Tregs (CD122 ⁺ Eomes ⁺ CD49d ^lo KIR ⁺ ), a subset substantially enriched for HLA-E-restricted T cells, were significantly reduced in peripheral blood of HFRS patients and displayed a terminally differentiated profile with elevated expression of KLRG-1, NKG2A, CTLA-4, and Fas-L, correlating with disease severity. Two HTNV glycoprotein-derived nonapeptides that bound Qa-1 were identified. Following immunization with the identified HTNV peptides and subsequent HTNV challenge, wild-type (WT) mice showed attenuated renal immunopathology, whereas D227K knock-in mice (with disrupted Qa-1-CD8/TCR interaction) showed enhanced viral clearance in the spleen and kidney but exacerbated renal immunopathology. Mechanistically, Qa-1-restricted CD8 ⁺ Tregs from WT mice suppressed effector CD8 ⁺ T cell proliferation in a peptide-specific, CD8/TCR-dependent manner via enhanced TGF-β secretion. Strikingly, D227K mutation dichotomously reshaped Treg phenotype: bulk polyclonal CD8 ⁺ Tregs displayed compensatory upregulation of inhibitory receptors (NKG2A, CTLA-4, PD-1) and TGF-β, whereas epitope-specific CD8 ⁺ Tregs showed impaired antigen-specific suppressive function and attenuated TGF-β production. Collectively, these findings indicate that HLA-E/Qa-1-restricted CD8 ⁺ Tregs can restrain immunopathology during HTNV infection, potentially at the cost of delayed viral elimination. Modulation of this axis may provide insights for therapeutic strategies in HFRS and related viral hemorrhagic fevers.

Hantaan virus (HTNV) is the predominant causative agent of hemorrhagic fever with renal syndrome (HFRS) in China, yet no specific antiviral therapy is currently available. Neutralizing antibodies (NAbs) represent a promising strategy, but most existing anti-HTNV NAbs are heterologous and carry immunogenicity risks. Here, two fully human antibodies from a previously established human anti-HTNV phage display library were generated and characterized. KJJ3, a VL-VL tandem antibody derived from clone 3–12, showed weak binding to inactivated HTNV and minimal neutralizing activity (IC₅₀ = 27.12 μg/mL). However, KJJ4, an engineered IgG4 antibody derived from clone 4–19 and carrying the S108P hinge mutation to prevent Fab-arm exchange, bound inactivated HTNV antigen and recombinant glycoprotein Gn (residues 19–371) in a dose-dependent manner, with only weak binding to Gc. Surface plasmon resonance yielded an association rate constant of 4.70 × 10³ M⁻¹s⁻¹, a dissociation rate constant of 3.06 × 10⁻³ s⁻¹, and an equilibrium dissociation constant of 650 nM for monomeric Gn_19–371. In a Vero E6 focus-reduction microneutralization assay, KJJ4 neutralized HTNV in vitro with an IC₅₀ of 2.879 μg/mL. These data establish KJJ4 as a fully human anti-HTNV antibody with experimentally defined in vitro binding and neutralizing activity, warranting further evaluation in animal models of HTNV infection.

CX3CL1, also named fractalkine or neurotactin, is the only known member of the CX3C chemokine family that can chemoattract several immune cells. CX3CL1 exists in both membrane-anchored and soluble forms, with each mediating distinct biological activities. CX3CL1 signals are transmitted through its unique receptor, CX3CR1, primarily expressed in the microglia of the central nervous system (CNS). In the CNS, CX3CL1 acts as a regulator of microglia activation in response to brain disorders or inflammation. Recently, there has been a growing interest in the role of CX3CL1 in regulating cell adhesion, chemotaxis, and host immune response in viral infection. Here, we provide a comprehensive review of the changes and function of CX3CL1 in various viral infections, such as human immunodeficiency virus (HIV), SARS-CoV-2, influenza virus, and cytomegalovirus (CMV) infection, to highlight the emerging roles of CX3CL1 in viral infection and associated diseases.

CX3CL1, also named fractalkine or neurotactin, the only known member of the CX3C chemokine family that can chemoattract several immune cells. CX3CL1 exists in both membrane-anchored and soluble forms, each mediating distinct biological activities. CX3CL1 signals are transmitted through its unique receptor, CX3CR1, primarily expressed in microglia of central nervous system (CNS). In the CNS, CX3CL1 acts as a regulator of microglia activation in response to brain disorders or inflammation. Recently, there has been a growing interest in the roles of CX3CL1 in regulating cell adhesion, chemotaxis, and host immune response in viral infection. Here, we provide a comprehensive review of the changes and function of CX3CL1 in various viral infections such as human immunodeficiency virus (HIV), SARS-CoV-2, influenza virus and cytomegalovirus (CMV) infection, to highlight the emerging roles of CX3CL1 in viral infection and the associated diseases.

We evaluated cellular immune responses induced by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines in an immunized population based on HLA-E-restricted CD8⁺ T cell epitope identification. HLA-E-restricted SARS-CoV-2 CD8⁺ T cell nonamer peptides were predicted with software. An HLA-E-transfected K562 cell binding assay was used to screen for high-affinity peptides. IFN-γ enzyme-linked immunospot assays were used to identify HLA-E-restricted epitopes. An HLA-E/epitope tetramer was employed to detect the frequencies of epitope-specific CD8⁺ T cells. Four CD8⁺ T cell epitopes on the spike protein of SARS-CoV-2 restricted by both HLA-E*0101 and E*0103 were identified. HLA-E-restricted epitope-specific IFN-γ-secreting CD8⁺ T cell responses could be detected in individuals vaccinated with SARS-CoV-2 vaccines. Importantly, the frequencies of epitope-specific CD8⁺ T cells in Ad5-nCoV vaccinated individuals were higher than in individuals vaccinated with recombinant protein or inactivated vaccines. Moreover, the frequencies of epitope-specific CD8⁺ T cells could be maintained for at least 120 days after only one dose of Ad5-nCoV vaccine, while the frequencies of epitope-specific CD8⁺ T cells decreased in individuals after two doses of Ad5-nCoV vaccine. These findings may contribute to a more comprehensive evaluation of the protective effects of vaccines for SARS-CoV-2; meanwhile, they may provide information to characterize HLA-E-restricted CD8⁺ T cell immunity against SARS-CoV-2 infection.

Hantaan virus (HTNV) infection can cause severe hemorrhagic fever with renal syndrome (HFRS). Inflammatory monocytes (iMOs) are involved in early antiviral responses. Previous studies have found that blood iMOs numbers increase in the acute phase of HFRS. Here, we further identified the phenotypic characteristics of iMOs in HFRS and explored whether phenotypic changes in iMOs were associated with HFRS severity. Blood samples from 85 HFRS patients were used for phenotypic analysis of iMOs by flow cytometry. Plasma HTNV load was determined using RT-PCR. THP-1 cells overexpressing CD226 were used to investigate the effects of CD226 on HLA-DR/DP/DQ and CD80 expression. A mouse model was used to test macrophage phenotype following HTNV infection. The proportion of CD226^- iMOs in the acute phase of HFRS was 66.83 (35.05-81.72) %, which was significantly higher than that in the convalescent phase (5.32 (1.36-13.52) %) and normal controls (7.39 (1.15-18.11) %) (p < 0.0001). In the acute phase, the proportion of CD226^- iMOs increased more in patients with more severe HFRS and correlated positively with HTNV load and negatively with platelet count. Notably, CD226^- iMOs expressed lower levels of HLA-DR/DP/DQ and CD80 than CD226⁺ iMOs, and overexpression CD226 could enhance the expression of HLA-DR/DP/DQ and CD80. In a mouse model, HTNV also induced the expansion of CD226^- macrophages, with decreased expression of I-A/I-E and CD80. CD226^- iMOs increased during HTNV infection and the decrease in CD226 hampered the expression of HLA-DR/DP/DQ and CD80, which may promote the immune escape of HTNV and exacerbate clinical symptoms.

Diabetic cardiomyopathy (DCM) is one of the main complications in type I diabetic patients. Activated macrophage is critical for directing the process of inflammation during the development of DCM. The present study focused on the roles of CD226 on macrophage function during the DCM progression. It has been found that the number of cardiac macrophages in the hearts of streptozocin (STZ)‐induced diabetes mice was significantly increased compared with that in non‐diabetes mice, and the expression level of CD226 on cardiac macrophages in STZ‐induced diabetes mice was higher than that in non‐diabetes mice. CD226 deficiency attenuated the diabetes‐induced cardiac dysfunction and decreased the proportion of CD86 ⁺ F4/80 ⁺ macrophages in the diabetic hearts. Notably, adoptive transfer of Cd226 ^−/− ‐ bone marrow derived macrophages (BMDMs) alleviated diabetes‐induced cardiac dysfunction, which may be due to the attenuated migration capacity of Cd226 ^−/− ‐BMDM under high glucose stimulation. Furthermore, CD226 deficiency decreased the macrophage glycolysis accompanying by the downregulated hexokinase 2 (HK2) and lactate dehydrogenase A (LDH‐A) expression. Taken together, these findings revealed the pathogenic roles of CD226 played in the process of DCM and provided a basis for the treatment of DCM.

Hantaan virus (HTNV) infection causes an epidemic of hemorrhagic fever with renal syndrome (HFRS) mainly in Asia. It is well known that T cells mediated anti-viral immune response. Although previous studies showed that double positive T (DP T) cells, a little portion of T lymphocytes, were involved in adaptive immune response during virus infection, their kinetic changes and roles in HTNV infection have not yet been explored. In this study, we characterized DP T cells from HFRS patients based on flow cytometry data combined with scRNA-seq data. We showed that HTNV infection caused the upregulation of DP T cells in the peripheral blood, which were correlated with disease stage. The scRNA-seq data clustered DP T cells, unraveled their gene expression profile, and estimated the ordering of these cells. The production of granzyme B and CD107a from DP T cells and the abundant TCR distribution indicated the anti-viral property of DP T cells. In conclusion, this study identified, for the first time, an accumulation of DP T cells in the peripheral blood of HFRS patients and suggested these DP T cells belonging to CD8⁺T cells lineage. The DP T cells shared the similar characteristics with cytotoxic T cells (CTL) and exerted an anti-viral role in HFRS.