A Recombinant Human Monoclonal Antibody to Human Metapneumovirus Fusion Protein That Neutralizes Virus In Vitro and Is Effective Therapeutically In Vivo

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Human metapneumovirus (HMPV) is a major cause of respiratory disease in infants, the elderly, and immunocompromised individuals worldwide. There is currently no licensed HMPV vaccine. Virus-like particles (VLPs) are an attractive vaccine candidate because they are noninfectious and elicit a neutralizing antibody response. However, studies show that serum neutralizing antibodies are insufficient for complete protection against reinfection and that adaptive T cell immunity is important for viral clearance. HMPV and other respiratory viruses induce lung CD8 ؉ T cell (T CD8 ) impairment, mediated by programmed death 1 (PD-1). In this study, we generated HMPV VLPs by expressing the fusion and matrix proteins in mammalian cells and tested whether VLP immunization induces functional HMPV-specific T CD8 responses in mice. C57BL/6 mice vaccinated twice with VLPs and subsequently challenged with HMPV were protected from lung viral replication for at least 20 weeks postimmunization. A single VLP dose elicited F-and M-specific lung T CD8 s with higher function and lower expression of PD-1 and other inhibitory receptors than T CD8 s from HMPV-infected mice. However, after HMPV challenge, lung T CD8 s from VLP-vaccinated mice exhibited inhibitory receptor expression and functional impairment similar to those of mice experiencing secondary infection. HMPV challenge of VLP-immunized MT mice also elicited a large percentage of impaired lung T CD8 s, similar to mice experiencing secondary infection. Together, these results indicate that VLPs are a promising vaccine candidate but do not prevent lung T CD8 impairment upon HMPV challenge. IMPORTANCEHuman metapneumovirus (HMPV) is a leading cause of acute respiratory disease for which there is no licensed vaccine. Viruslike particles (VLPs) are an attractive vaccine candidate and induce antibodies, but T cell responses are less defined. Moreover, HMPV and other respiratory viruses induce lung CD8 ؉ T cell (T CD8 ) impairment mediated by programmed death 1 (PD-1). In this study, HMPV VLPs containing viral fusion and matrix proteins elicited epitope-specific T CD8 s that were functional with low PD-1 expression. Two VLP doses conferred sterilizing immunity in C57BL/6 mice and facilitated HMPV clearance in antibodydeficient MT mice without enhancing lung pathology. However, regardless of whether responding lung T CD8 s had previously encountered HMPV antigens in the context of VLPs or virus, similar proportions were impaired and expressed comparable levels of PD-1 upon viral challenge. These results suggest that VLPs are a promising vaccine candidate but do not prevent lung T CD8 impairment upon HMPV challenge. in 2001 (1, 2). The virus is a major cause of acute respiratory morbidity and mortality in infants, older adults, and immunocompromised individuals, although serological studies indicate that almost all humans have been infected by 5 years of age (2, 3). There are four subtypes of HMPV classified by genotype: A1, A2, B1, and B2 (4). The fusion (F) protein, which mediates ...

Section: Discussionsupporting

confidence: 83%

Lung CD8⁺T Cell Impairment Occurs during Human Metapneumovirus Infection despite Virus-Like Particle Induction of Functional CD8⁺T Cells

Wen

Schuster

Gilchuk

et al. 2015

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“…Our data suggest that the hMPV-specific antibody response may contribute to protection against or reduction of the severity of the illness. This hypothesis is in accordance with the results from Alvarez and Tripp (2), who showed that the passive transfer of hMPV-immune serum protected naïve BALB/c mice to a certain degree from challenge, and with the results from Williams et al (57), who reported that a neutralizing monoclonal antibody to the F protein conferred protection against challenge (2, 57). Whole-body plethysmography has been used to assess whether acute hMPV infection results in increased AO.…”

Section: Discussionsupporting

confidence: 81%

Age-Associated Aggravation of Clinical Disease after Primary Metapneumovirus Infection of BALB/c Mice

Darniot¹,

Pitoiset²,

Petrella³

et al. 2009

Human metapneumovirus (hMPV) is associated with respiratory tract infections among children and adults. Because hMPV induces significant morbidity and mortality in the elderly, a model of hMPV infection in aged BALB/c mice was established. Young (8 weeks old) and aged (18 months old) mice were intranasally inoculated with hMPV. The infected mice showed respiratory dysfunction, as measured by plethysmography, a marked loss in weight (up to 24%), and severe histopathological abnormalities including bronchiolitis obliterans organizing pneumonia. However, clinical severity was far higher in the aged mice, and none of the young infected mice died. Although virus replication in the lung was greater in the older mice, clearance of virus was not delayed compared to young mice. Production of virus-specific antibody as well as neutralizing antibody was lower. Gamma interferon and monocyte chemotactic protein-1 levels in bronchoalveolar lavage fluid were significantly lower in older mice, whereas interleukin-6 and interleukin-4 levels were significantly higher. We observed by flow cytometry a significant increase in the CD4 ؉ T lymphocytes (P < 0.05) of the aged mice and no difference in CD8 ؉ T-cell recruitment to the respiratory tract between the two groups. The present study investigated the effects of aging on the immunopathogenesis of hMPV infection and suggests that CD4 ؉ T lymphocytes, the cytokine response, or a defect in humoral response may be associated with the increased disease severity observed in the aged mice.

“…This may occur because of limited cross-protective immunity between different strains of HMPV or may indicate that antibody-mediated protection is not sufficient to prevent HMPV infection. However, studies with animal models indicate that passive transfer of anti-HMPV neutralizing antibodies can protect against HMPV replication and disease (45,46,63). Furthermore, in otherwise healthy adults, HMPV infection is typically limited to the upper respiratory tract, suggesting that neutralizing antibodies can ameliorate HMPV disease pathogenesis.…”

Section: Discussionmentioning

confidence: 99%

“…Only the F protein is required for virus assembly, fusion, and entry (13,44). Furthermore, the HMPV F protein is the primary target of neutralizing antibodies (13,23,(45)(46)(47)(48). In contrast, while HMPV G is immunogenic in rodents, G-specific antibodies do not neutralize HMPV and G vaccines provide no protection in animals (47)(48)(49).…”

mentioning

confidence: 99%

Human Metapneumovirus Virus-Like Particles Induce Protective B and T Cell Responses in a Mouse Model

Cox

Erickson

Hastings

et al. 2014

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Human metapneumovirus (HMPV) is a leading cause of respiratory disease in infants, children, and the elderly worldwide, yet no licensed vaccines exist. Live-attenuated vaccines present safety challenges, and protein subunit vaccines induce primarily antibody responses. Virus-like particles (VLPs) are an attractive alternative vaccine approach because of reduced safety concerns compared with live vaccines. We generated HMPV VLPs by expressing viral proteins in suspension-adapted human embryonic kidney epithelial (293-F) cells and found that the viral matrix (M) and fusion (F) proteins were sufficient to form VLPs. We previously reported that the VLPs resemble virus morphology and incorporate fusion-competent F protein (R. H uman metapneumovirus (HMPV) is a leading cause of acute lower respiratory tract infection worldwide, with high prevalence in pediatric, elderly, and immunocompromised patients (1-12). There are no licensed vaccines against HMPV. Several strategies to develop live-attenuated HMPV vaccines have been explored, including cold passage, gene deletion, and chimeric viruses (13-17). While live-virus vaccines elicit humoral and cellular responses, they also pose safety risks. Attenuated virus strains have the potential to revert to a wild-type phenotype and cause disease or be transmitted to nonimmune individuals. For these reasons, live attenuated vaccines are often contraindicated for immunocompromised patients, individuals who are at risk for severe HMPV infections. Moreover, it is often difficult to find the correct balance between attenuation and immunogenicity. Many years of research on respiratory syncytial virus (RSV) live attenuated vaccines attest to the challenges (18)(19)(20)(21)(22).GSubunit protein vaccines against HMPV targeting mainly the fusion (F) protein have been effective in rodent models by inducing B cell responses only (23,24). Experience with formalin-inactivated (FI) RSV and HMPV vaccines in humans and animals further raises concern about imbalanced immunity (25)(26)(27)(28)(29)(30). Studies demonstrate that the generation of antibodies to a denatured F protein or low-affinity nonneutralizing antibodies is associated with enhanced respiratory disease (31-36). Thus, a safe and effective vaccine should induce both potent neutralizing antibodies and cytotoxic T cell responses.A vaccination strategy combining elements of both live virus and subunit vaccines is virus-like particles (VLPs). VLPs are formed by the self-assembly of viral structural proteins but lack