Analysis of the immune response to Hantaan virus nucleocapsid protein C-terminal-specific CD8(+) T cells in patients with hemorrhagic fever with renal syndrome

The Role of Nucleoprotein in Immunity to Human Negative-Stranded RNA Viruses—Not Just Another Brick in the Viral Nucleocapsid

Negative-stranded RNA viruses (NSVs) are important human pathogens, including emerging and reemerging viruses that cause respiratory, hemorrhagic and other severe illnesses. Vaccine design traditionally relies on the viral surface glycoproteins. However, surface glycoproteins rarely elicit effective long-term immunity due to high variability. Therefore, an alternative approach is to include conserved structural proteins such as nucleoprotein (NP). NP is engaged in myriad processes in the viral life cycle: coating and protection of viral RNA, regulation of transcription/replication processes and induction of immunosuppression of the host. A broad heterosubtypic T-cellular protection was ascribed very early to this protein. In contrast, the understanding of the humoral immunity to NP is very limited in spite of the high titer of non-neutralizing NP-specific antibodies raised upon natural infection or immunization. In this review, the data with important implications for the understanding of the role of NP in the immune response to human NSVs are revisited. Major implications of the elicited T-cell immune responses to NP are evaluated, and the possible multiple mechanisms of the neglected humoral response to NP are discussed. The intention of this review is to remind that NP is a very promising target for the development of future vaccines.

Delayed viral clearance despite high number of activated T cells during the acute phase in Argentinean patients with hantavirus pulmonary syndrome

Background

The hallmarks of HPS are increase of vascular permeability and endothelial dysfunction. Although an exacerbated immune response is thought to be implicated in pathogenesis, clear evidence is still elusive. As orthohantaviruses are not cytopathic CD8⁺ T cells are believed to be the central players involved in pathogenesis.

Methods

Serum and blood samples from Argentinean HPS patients were collected from 2014 to 2019. Routine white blood cell analyses, quantification and characterization of T-cell phenotypic profile, viral load, neutralizing antibody response and quantification of inflammatory mediators were performed.

Findings

High numbers of activated CD4⁺ and CD8⁺ T cells were found in all HPS cases independently of disease severity. We found increased levels of some proinflammatory mediators during the acute phase of illness. Nonetheless, viral RNA remained high, showing a delay in clearance from blood up to late convalescence, when titers of neutralizing antibodies reached a high level.

Interpretation

The high activated phenotypic profile of T cells seems to be unable to resolve infection during the acute and early convalescent phases, and it was not associated with the severity of the disease. Thus, at least part of the activated T cells could be induced by the dysregulated inflammatory response in an unspecific manner. Viral clearance seems to have been more related to high titers of neutralizing antibodies than to the T-cell response.

Funding

This work was supported mainly by the Administración Nacional de Laboratorios e Institutos de Salud (ANLIS) “Dr. Carlos Malbrán”. Further details of fundings sources is included in the appendix.

Hemorrhagic Fever with Renal Syndrome: Pathogenesis and Clinical Picture

Hantaan virus (HTNV) causes hemorrhagic fever with renal syndrome (HFRS), which is a zoonosis endemic in eastern Asia, especially in China. The reservoir host of HTNV is field mouse (Apodemus agraricus). The main manifestation of HFRS, including acute kidney injury, increases vascular permeability, and coagulation abnormalities. In this paper, we review the current knowledge of the pathogenesis of HFRS including virus factor, immunity factor and host genetic factors. Furthermore, the treatment and prevention will be discussed.

Hantaan virus infection induces both Th1 and ThGranzyme B+ cell immune responses that associated with viral control and clinical outcome in humans

Hantaviruses infection causing severe emerging diseases with high mortality rates in humans has become public health concern globally. The potential roles of CD4(+)T cells in viral control have been extensively studied. However, the contribution of CD4(+)T cells to the host response against Hantaan virus (HTNV) infection remains unclear. Here, based on the T-cell epitopes mapped on HTNV glycoprotein, we studied the effects and characteristics of CD4(+)T-cell responses in determining the outcome of hemorrhagic fever with renal syndrome. A total of 79 novel 15-mer T-cell epitopes on the HTNV glycoprotein were identified, among which 20 peptides were dominant target epitopes. Importantly, we showed the presence of both effective Th1 responses with polyfunctional cytokine secretion and ThGranzyme B(+) cell responses with cytotoxic mediators production against HTNV infection. The HTNV glycoprotein-specific CD4(+)T-cell responses inversely correlated with the plasma HTNV RNA load in patients. Individuals with milder disease outcomes showed broader epitopes targeted and stronger CD4(+)T-cell responses against HTNV glycoproteins compared with more severe patients. The CD4(+)T cells characterized by broader antigenic repertoire, stronger polyfunctional responses, better expansion capacity and highly differentiated effector memory phenotype(CD27-CD28-CCR7-CD45RA-CD127(hi)) would elicit greater defense against HTNV infection and lead to much milder outcome of the disease. The host defense mediated by CD4(+)T cells may through the inducing antiviral condition of the host cells and cytotoxic effect of ThGranzyme B+ cells. Thus, these findings highlight the efforts of CD4(+)T-cell immunity to HTNV control and provide crucial information to better understand the immune defense against HTNV infection.

Upregulation of IFN-γ and IL-12 is associated with a milder form of hantavirus hemorrhagic fever with renal syndrome

Hantavirus hemorrhagic fever with renal syndrome (HFRS) is a zoonotic disease characterized by acute onset, fever, malaise, and back pain. As the disease progresses, hemorrhagic disturbances and kidney dysfunctions predominate. The examination of tissue collected postmortem supports the premise that virus replication is not responsible for this pathology; therefore, it is widely believed that virus-induced immune responses lead to the clinical manifestations associated with HFRS. The overproduction of inflammatory cytokines is commonly reported in subjects with HFRS and has given rise to the hypothesis that a so-called "cytokine storm" may play a pivotal role in the pathogenesis of this disease. Currently, supportive care remains the only effective treatment for HFRS. Our data show that serum levels of interferon (IFN)-γ, interleukin (IL)-10, CCL2, and IL-12 are upregulated in HFRS cases when compared to healthy controls and the level of upregulation is dependent on the phase and severity of the disease. Furthermore, we observed an association between the mild form of the disease and elevated serum levels of IFN-γ and IL-12. Collectively, these observations suggest that the administration of exogenous IFN-γ and IL-12 may provide antiviral benefits for the treatment of HFRS and, thus, warrants further investigations.

A recombinant pseudotyped lentivirus expressing the envelope glycoprotein of hantaan virus induced protective immunity in mice

Background

Hantaviruses cause acute hemorrhagic fever with renal syndrome (HFRS). Currently, several types of inactivated HFRS vaccines are widely used, however the limited ability of these immunogen to elicit neutralizing antibodies restricts vaccine efficacy. Development of an effective vaccine to overcome this weakness is must.

Methods

In the present study, a recombinant pseudotyped lentivirus bearing the hantaan virus (HTNV) envelope glycoproteins (GP), rLV-M, was constructed. C57BL/6 mice were immunized with the rLV-M and a series of immunological assays were conducted to determine the immunogenicity of the recombinant pseudotyped lentivirus. The humoral and cell-mediated immune responses induced by rLV-M were compared with those of the inactivated HFRS vaccine.

Results

Indirect immunofluorescence assay (IFA) showed the rLV-M expressed target proteins in HEK-293cells. In mice, the rLV-M efficiently induced GP-specific humoral responses and protection against HTNV infection. Furthermore, the rLV-M induced higher neutralizing antibody titers than the inactivated HFRS vaccine control.

Conclusions

The results indicated the potential of using a pseudotyped lentivirus as a delivery vector for a hantavirus vaccine immunogen.

HLA-A2 and B35 restricted hantaan virus nucleoprotein CD8+ T-cell epitope-specific immune response correlates with milder disease in hemorrhagic fever with renal syndrome

BACKGROUND

Hantaan virus (HTNV) infection in humans is a serious public health concern in Asia. A potent T cell activation peptide vaccine from HTNV structure protein represents a promising immunotherapy for disease control. However, the T cell epitopes of the HTNV restricted by the HLA alleles and the role of epitope-specific T cell response after HTNV infection remain largely unexplored.

METHODOLOGY/PRINCIPAL FINDINGS

Five well-conserved novel CD8(+) T-cell epitopes of the HTNV nucleoprotein restricted by the most popular HLA alleles in Chinese Han population were defined with interferon-γ enzyme-linked immunospot assay in 37 patients infected with HTNV during hospitalization. Two epitopes aa129-aa137 and aa131-aa139 restricted by HLA-A2 and B35, respectively, were selected to evaluate the epitope-specific CD8(+) T-cell response. HLA-peptide pentamer complex staining showed that the frequency of single epitope-specific CD8(+) T cell could be detected in patients (95% confidence interval for aa129-aa137: 0.080%-0.208%; for aa131-aa139: 0.030%-0.094%). The frequency of epitope-specific pentamer(+) CD8(+) T-cell response was much higher in mild/moderate patients than in severe/critical ones at the acute stage of the disease. Moreover, the frequency of epitope-specific CD8(+) T cells at acute stage was inversely associated with the peak level of serum creatinine and was positively associated with the nadir platelet counts during the hospitalization. The intracellular cytokine staining and the proliferation assay showed that the effective epitope-specific CD8(+) T cells were characterized with the production of interferon-γ, expression of CD69 and the strong capacity of proliferation.

CONCLUSION/SIGNIFICANCE

The novel HLA class I restricted HTNV nucleoprotein epitopes-specific CD8(+) T-cell responses would be closely related with the progression and the severity of the disease, which could provide the first step toward effective peptide vaccine development against HTNV infection in humans.

Elevated serum concentrations of inflammatory cytokines and chemokines in patients with haemorrhagic fever with renal syndrome

OBJECTIVE

Prospective case-control study, undertaken to investigate serum cytokine and chemokine concentrations during all clinical phases and in different clinical types of haemorrhagic fever with renal syndrome (HFRS).

METHODS

Serum was collected at various disease phases from patients with HFRS (n = 35) and healthy control subjects (n = 10). Tumour necrosis factor (TNF)-α, interleukin (IL)-6, IL-4, interferon (IFN)-γ, IL-8, interferon inducible protein-10 (IP-10) and chemokine (C-C motif) ligand 5 (also known as 'regulated upon activation, normal T-cell expressed and secreted' [RANTES]) were quantified using commercial enzyme-linked immunosorbent assay kits.

RESULTS

Serum concentrations of TNF-α, IL-6, IFN-γ, IL-8, IP-10 and RANTES (but not IL-4) were significantly higher in patients compared with controls. Highest concentrations were generally found during the febrile, hypotensive and oliguric disease phases, as well as in clinically severe and critical cases.

CONCLUSION

Serum concentrations of proinflammatory cytokines and chemokines increased in line with disease severity in HFRS patients.

Pathogenesis of the hantavirus pulmonary syndrome

Hantavirus pulmonary syndrome caused by hantaviruses in the Americas presents as a broad clinical spectrum ranging from brief febrile prodrome with only thrombocytopenia to rapidly progressive fulminant pulmonary edema and shock. This vascular leak syndrome confined almost exclusively to the lung is initiated by the noncytolytic infection of capillary endothelial cells. A number of pathogenic mechanisms have been proposed, including immune cell-mediated injury, cytokine-mediated injury and enhanced VEGF responses from intercellular junctions resulting from highly specific virus–integrin interactions. This review examines evidence for each of these potential mechanisms, with relevant references to its sister syndrome, hemorrhagic fever with renal syndrome, in Eurasia. Any mechanism or combination of mechanisms must be able to explain the massive pulmonary capillary leak at the severe extreme of the spectrum, a disease manifestation without parallel in clinical medicine.

Identification of three novel CTL epitopes within nucleocapsid protein of Hantaan virus

Hantaan virus (HTNV) is a member of the Hantavirus genus that causes human hemorrhagic fever with renal syndrome (HFRS) in humans. The CTL response seems to play a key role in control of viral infection, but only a few HTNV epitopes recognized by the CTLs have been reported. Herein, we screened a panel of overlapping peptides covering the HTNV nucleocapsid protein by ELISPOT assays for those that can elicit IFN-γ production in vitro. Three novel CD8(+) CTL epitopes, N197-205 (RYRTAVCGL), N245-253 (KLLPDTAAV), and N258-266 (GPATNRDYL), were defined on the nucleocapsid protein and were found to be restricted by various HLA alleles including A11, A24, and B7. The epitopes were highly conserved among the reported HTNV strains and other hantanviruses, including Dobrava-Belgrade virus and Seoul virus, supporting their potential use in vaccine designs.

T cells and pathogenesis of hantavirus cardiopulmonary syndrome and hemorrhagic fever with renal syndrome

We previously hypothesized that increased capillary permeability observed in both hantavirus cardiopulmonary syndrome (HCPS) and hemorrhagic fever with renal syndrome (HFRS) may be caused by hantavirus-specific cytotoxic T cells attacking endothelial cells presenting viral antigens on their surface based on clinical observations and in vitro experiments. In HCPS, hantavirus-specific T cell responses positively correlated with disease severity. In HFRS, in one report, contrary to HCPS, T cell responses negatively correlated with disease severity, but in another report the number of regulatory T cells, which are thought to suppress T cell responses, negatively correlated with disease severity. In rat experiments, in which hantavirus causes persistent infection, depletion of regulatory T cells helped infected rats clear virus without inducing immunopathology. These seemingly contradictory findings may suggest delicate balance in T cell responses between protection and immunopathogenesis. Both too strong and too weak T cell responses may lead to severe disease. It is important to clarify the role of T cells in these diseases for better treatment (whether to suppress T cell functions) and protection (vaccine design) which may need to take into account viral factors and the influence of HLA on T cell responses.

Human pathogenic hantaviruses and prevention of infection

Hantaviruses are emerging viruses which are hosted by small mammals. When transmitted to humans, they can cause two clinical syndromes, hemorrhagic fever with renal syndrome or hantavirus cardiopulmonary syndrome. The review compiles the current list of hantaviruses which are thought to be pathogenic in humans on the basis of molecular or at least serological evidence. Whereas induction of a neutralizing humoral immune response is considered to be protective against infection, the dual role of cellular immunity (protection versus immunopathogenicity) is discussed. For active immunisation, inactivated virus vaccines are licensed in certain Asian countries. Moreover, several classical and molecular vaccine approaches are in pre-clinical stages of development. The development of hantavirus vaccines is hampered by the lack of adequate animal models of hantavirus-associated disease. In addition to active immunization strategies, the review summarizes other ways of infection prevention, as passive immunization, chemoprophylaxis, and exposition prophylaxis.