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

Abstract

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 ...

Aberrant T cell immunity triggered by human Respiratory Syncytial Virus and human Metapneumovirus infection

“…149 Supporting this notion, hMPV-specific effector CD8 C T cells, in BALB/c mice that lack protective anti-hMPV antibodies and in the absence of CD4 C T cells, no detection of virus load and reduction of lung disease were found upon hMPV infection, suggesting that the cytotoxic activity of CD8 C T cells alone can confer protection against hMPV 140 and highlighting the importance of CD8 C T cells in controlling hMPV infection. Moreover, when specific hMPV M2 CTLs were transferred into RAG-1¡/¡ mice, these lymphocytes protected the host of hMPV challenge.…”

“…153 In other studies, immunization of mMT mice with virus-like particles encoding the hMPV F and M proteins, generates hMPV F-specific and M-specific CD8 C T cells in lungs, but their function is impaired, as inhibitory receptors are upregulated on these cells, similar to what is seen in WT C57BL/6 mice under a second hMPV infection. 149 On the other hand, the depletion of CD8 C T cells in hMPV-infected BALB/c mice resulted in a lower lung pathological score, although to a lesser degree than depletion of only CD4 C T cells. 140 By other part, mice that was depleted of neutrophils showed a significant reduction of TNF-a and IL-13 secreted by CD8 C T cells suggesting that neutrophils modulate the production of these cytokines by CD8 C T cells, 141 In this manner, CD8 C T cells that infiltrate in the airways and secrete TNF-a and IL13 contribute to the lung pathology triggered by hMPV infection in mice.…”

Multiple Inhibitory Pathways Contribute to Lung CD8+ T Cell Impairment and Protect against Immunopathology during Acute Viral Respiratory Infection

“…Ten days post-infection, the left lung lobes were inflated with 10% formalin and fixed for 24 hours, embedded in paraffin, sectioned at 5-µm, and stained with hematoxylin and eosin. Slides were evaluated by an experienced veterinary pathologist (KLB) blinded to the groups and scored using an established method (1-rare perivascular cuffs of lymphocytes and plasma cells 2–5 cells thick; 2-lymphoplasmacytic perivascular and peribronchiolar cuffing; 3-perivascular and peribronchiolar cuffing and focal neutrophilic infiltration and necrosis in the alveoli and bronchiole-alveolar junction; and 4-marked perivascular cuffing with interstitial inflammation and widespread necrosis) (41). …”

Human metapneumovirus in the preterm neonate: current perspectives

“…Animal studies show that these subgroups are not fully antigenically distinct and that there is cross-protective immunity. 7,14–16 Therefore, similar to RSV, a single-antigen vaccine or prophylactic antibody would suffice.…”

“…114 These particles are effective at inducing B- and T-cell responses in animal models and confer protection against viruses of both subgroups. 16,115 …”