Early Immune Correlates for Asthma See article p. 1995

Toward a Universal Influenza Vaccine See article p. 2057

A Peek into HPV Persistence See article p. 2076

p53 to the Rescue in Emergency Granulopoiesis See article p. 2129

High-risk (hr) human papillomaviruses (HPV) that infect human keratinocytes (KCs) can evade the innate immune response and persist in the host but the precise mechanisms regulating evasion remain uncharacterized. To determine whether hrHPVs can evade innate immune responses by interfering with pattern recognition receptor (PRR) signaling, Albertini et al. (p. 2076) assessed innate immune responses in monolayer and organotypic raft cultures of human KC cells (NIKS cells) stably harboring a high viral load of HPV18 episomal genomes (NIKSmcHPV18), which fully recapitulated the persistent state of infection. NIKSmcHPV18 cells demonstrated a significant reduction of type I and type II IFN mRNA when compared with NIKS cells. Transfection of NIKSmcHPV18 cells with DNA (as a potent inducer of PRR signaling) demonstrated reduced induction of all IFNs at both the gene and protein level but demonstrated increased protein and mRNA expression of IL-6, a downstream target of NF-кB. These data suggest that, whereas HPV18 suppresses induction of both type I and type II IFN production, the inhibitor of HPV18 does not alter NF-кB activation. Interestingly, the adaptor molecule stimulator of IFN genes (STING) and the PRRs cyclic GMP-AMP synthase (cGAS), retinoic acid–inducible gene I (RIG-I), and IFN-γ–inducible protein 16 were poorly expressed or almost undetectable in NIKSmcHPV18 cells stimulated with DNA ligands when compared with stimulated NIKS cells. This suppression occurred primarily at the mRNA, rather than the protein level, suggesting that HPV may transcriptionally repress innate antiviral immune responses during persistent HPV infections. In support of these observations, the authors observed an increase in the repressive heterochromatin marker dimethylation of histone H3 lysine 9 (H3K9me2) at the promoter regions of STING, cGAS, and RIG-I. Altogether, these data support a model in which hrHPV may reduce expression of multiple PRRs and the adaptor molecule STING via transcriptional silencing, facilitating an environment that favors viral persistence. Overall, these findings provide novel insights into HPV18 immune escape mechanisms in human KCs and may facilitate treatment or prevention of HPV18-induced cervical carcinogenesis.

Invariant NKT (iNKT) cells and mucosal associated invariant T (MAIT) cells are innate-like T lymphocytes that use an invariant TCR α-chain to recognize nonpeptide Ags, including lipids. Whereas iNKT cells have been implicated in several mouse models of asthma, the role of MAIT cells in asthma is largely unknown. In this issue, Chandra et al. (p. 1995) examined the role of iNKT and MAIT cells in development of asthma in children with a family history of asthma by determining whether the frequency of these cells in the blood at 1 y of age correlated with development of asthma by age 7 y or with Th2 skewing (enhanced IL-4 compared with IFN-γ production) by in vitro activated CD4+ T lymphocytes from these individuals. These analyses reveal a correlation between higher frequency of MAIT cells at 1 y and a decreased risk of asthma at 7 y of age. iNKT cell population frequency distributions were not related to future asthma development. Although there was no relationship between iNKT cell frequency and house dust extract antigenic activity, increased iNKT cell antigenic activity was associated with decreased probability of developing asthma. Thus, iNKT antigenic activity could serve as a potential marker for increased microbial exposure and subsequent asthma protection. Overall, higher MAIT cell frequency in the blood of 1-y-old children from asthma-prone households correlated with increased IFN-γ–producing CD4+ T cells and protection from asthma development at age 7, suggesting that skewing toward Th1 responses might have a protective function. These results support the notion that increased microbial exposure during the first year of life protects against subsequent development of asthma.

Fanconi anemia (FA) results from mutations in any gene in the Fanconi DNA-repair pathway and is characterized by bone marrow failure (BMF) and clonal progression to acute myeloid leukemia in some patients surviving BMF. Recent studies have demonstrated a critical role for Fanconi C, a component of the DNA-repair pathway, in infection-triggered production of granulocytes, an episodic process called emergency granulopoiesis. Fanconi C–deficient (FANCC−/−) mice are unable to mount an emergency granulopoiesis response and instead develop BMF associated with extensive apoptosis of hematopoietic stem and progenitor cells via a mechanism that remains poorly defined. In this issue, Hu et al. (p. 2129) hypothesized that accumulation of unrepaired DNA replication forks during episodes of emergency granulopoiesis results in activation of p53 to induce apoptosis of cells with DNA damage as a means to protect the bone marrow from genotoxic stress. Compared with wild-type (WT) and p53 haploinsufficient (TP53+/−) mice, in which repeated administration of OVA/aluminum mixture (Alum) to induce multiple emergency granulopoiesis episodes significantly increased circulating granulocytes, treated FANCC−/− mice developed granulocytopenia and BMF. In contrast, compared with FANCC−/− mice, TP53 haploinsufficiency in FANCC−/− mice restored circulating granulocytes and prevented apoptosis of bone marrow progenitors and BMF following induction of emergency granulopoiesis. In FANCC−/− mice, BMF during repeated episodes of emergency granulopoiesis was associated with increasing phosphorylation of both p53 and ataxia telangiectasia and Rad3-related protein (Atr), which facilitates Fanconi pathway activation. In contrast, expression and activation of Atr and p53 were progressively attenuated in FANCC−/−TP53+/− mice following repeated administration of Alum, and this correlated with a decrease in apoptotic cells in the bone marrow. Interestingly, the mortality rate for FANCC−/−TP53+/− mice was significantly greater than for WT or TP53+/− mice and FANCC−/−TP53+/− mice demonstrated significant accumulation of myeloid blasts in the blood and in the bone marrow. Further investigation into mechanisms facilitating simultaneous protection from BMF and acceleration of leukemia during multiple episodes of emergency granulopoiesis in FANCC−/−TP53+/− mice revealed an increase in the number of cells with DNA damage persisting in the bone marrow. Together, these data demonstrate that activation of Atr–with consequential Fanconi C–mediated DNA repair or p53-dependent apoptosis–is an essential component of emergency granulopoiesis. These findings have translational implications for the treatment of Fanconi anemia; whereas p53 inhibitors may improve the innate immune response, they may also have the unintended consequences of accelerating clonal progression and facilitating the development of myeloid leukemias.

Deoxyribonucleic acid vaccines targeting influenza hemagglutinin (HA) protein Ags to MHC class II molecules have been shown to induce Ab-mediated protection against influenza. The use of vaccines containing a mixture of DNA constructs enables targeting of multiple HAs and induction of immunity against several influenza strains. Thus, Anderson et al. (p. 2057) examined the ability of a DNA vaccine containing HA genes for six group 1 influenza viruses to induce strain-specific and cross-reactive anti-HA Abs. The genes were inserted into plasmids encoding a targeting unit that directs the vaccine toward MHC class II molecules. The mixture of MHCII-targeted HAs from six different group 1 A strains (anti–MHCII-MIX) was compared with nontargeted control vaccines in which the targeting unit was replaced with an scFv specific for the synthetic hapten 4-hydroxy-3-iodo-5-nitrophenylacetic acid (anti–NIP-MIX). Immunization of BALB/c mice with anti–MHCII-MIX induced detectable Abs against HAs included in the vaccine mix. Although H1 was not included in the vaccine mixture, the mice were challenged with two H1 influenza subtypes (Cal07 and PR8) to determine whether anti–MHCII-MIX can induce cross-reactive Abs. Mice receiving anti–MHCII-MIX were protected against both weight loss and death after challenge with either Cal07 or PR8. Sera from vaccinated mice were transferred into naive mice, which were subsequently challenged with PR8. Mice receiving anti–MHCII-MIX–vaccinated mouse sera had reduced weight loss and death rates compared with mice vaccinated with anti–NIP-MIX, demonstrating that anti–MHCII-MIX vaccination induced Abs against a subgroup not included in the vaccine mixture. These studies demonstrate that anti–MHCII-MIX induces Ab responses against the six individual HAs included in the vaccine as well as cross-reactive Abs against a subtype not included in the vaccine mixture. Thus, MHCII-targeted DNA vaccines enable induction of broad protection against rapidly evolving viruses.