Acute viral infections typically generate functional effector CD8+ T cells (TCD8) that aid in pathogen clearance. However, during acute viral lower respiratory infection (LRI), lung TCD8 are functionally impaired and do not optimally control viral replication. T cells also become unresponsive to antigen during chronic infections and cancer via signaling by inhibitory receptors like programmed cell death-1 (PD-1). PD-1 also contributes to TCD8 impairment during viral LRI, but how it regulates TCD8 impairment and the connection between this state and T cell exhaustion during chronic infections is unknown. Here we show that PD-1 operates in a cell-intrinsic manner to impair lung TCD8. In light of this, we compared global gene expression profiles of impaired epitope-specific lung TCD8 to functional spleen TCD8 in the same human metapneumovirus (HMPV)-infected mice. These two populations differentially regulate hundreds of genes, including the upregulation of numerous inhibitory receptors by lung TCD8. We then compared the gene expression of TCD8 during HMPV infection to those in acute or chronic LCMV infection. We find that the immunophenotype of lung TCD8 more closely resembles T cell exhaustion late into chronic infection than functional effector T cells arising early in acute infection. Finally, we demonstrate that trafficking to the infected lung alone is insufficient for TCD8 impairment or inhibitory receptor upregulation, but that viral antigen-induced TCR signaling is also required. Our results indicate that viral antigen in infected lungs rapidly induces an exhaustion-like state in lung TCD8, characterized by progressive functional impairment and upregulation of numerous inhibitory receptors.

Type I interferon (IFN) is a key mediator of antiviral immunity. Human metapneumovirus (HMPV) inhibits IFN signaling, but does not encode homologues of known IFN antagonists. We tested the hypothesis that a specific viral protein prevents type I IFN signaling by targeting signal transducer and activator of transcription-1 (STAT1). We found that human airway epithelial cells (capable of expressing IFNs) became impaired for STAT1 phosphorylation even without direct infection due to intrinsic negative feedback. HMPV-infected Vero cells (incapable of expressing IFN) displayed lower STAT1 expression and impaired STAT1 phosphorylation in response to type I IFN treatment compared to mock-infected cells. Transient overexpression of HMPV small hydrophobic (SH) protein significantly inhibited STAT1 phosphorylation and signaling, and recombinant virus lacking SH protein was unable to inhibit STAT1 phosphorylation. Our results indicate a role for the SH protein of HMPV in the downregulation of type I IFN signaling through the targeting of STAT1.

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 ...

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Expression of coregulated imprinted genes, H19 and Igf2, is monoallelic and parent-of-origin-dependent. Like most imprinted genes, H19 and Igf2 are regulated by a differentially methylated imprinting control region (ICR). CTCF binding sites and DNA methylation at the ICR have previously been identified as key cis-acting elements required for proper H19/Igf2 imprinting. Here, we use mouse models to elucidate further the mechanism of ICR-mediated gene regulation. We specifically address the question of whether sequences outside of CTCF sites at the ICR are required for paternal H19 repression. To this end, we generated two types of mutant ICRs in the mouse: (i) deletion of intervening sequence between CTCF sites (H19ICRΔIVS), which changes size and CpG content at the ICR; and (ii) CpG depletion outside of CTCF sites (H19ICR-8nrCG), which only changes CpG content at the ICR. Individually, both mutant alleles (H19ICRΔIVS and H19ICR-8nrCG) show loss of imprinted repression of paternal H19. Interestingly, this loss of repression does not coincide with a detectable change in methylation at the H19 ICR or promoter. Thus, neither intact CTCF sites nor hypermethylation at the ICR is sufficient for maintaining the fully repressed state of the paternal H19 allele. Our findings demonstrate, for the first time in vivo, that sequence outside of CTCF sites at the ICR is required in cis for ICR-mediated imprinted repression at the H19/Igf2 locus. In addition, these results strongly implicate a novel role of ICR size and CpG density in paternal H19 repression.