John Oxford

Preexisting influenza-specific CD4 + T cells correlate with disease protection against influenza challenge in humans

Protective immunity against influenza virus infection is mediated by neutralizing antibodies, but the precise role of T cells in human influenza immunity is uncertain. We conducted influenza infection studies in healthy volunteers with no detectable antibodies to the challenge viruses H3N2 or H1N1. We mapped T cell responses to influenza before and during infection. We found a large increase in influenza-specific T cell responses by day 7, when virus was completely cleared from nasal samples and serum antibodies were still undetectable. Preexisting CD4+, but not CD8+, T cells responding to influenza internal proteins were associated with lower virus shedding and less severe illness. These CD4+ cells also responded to pandemic H1N1 (A/CA/07/2009) peptides and showed evidence of cytotoxic activity. These cells are an important statistical correlate of homotypic and heterotypic response and may limit severity of influenza infection by new strains in the absence of specific antibody responses. Our results provide information that may aid the design of future vaccines against emerging influenza strains.

Viral Load Drives Disease in Humans Experimentally Infected with Respiratory Syncytial Virus

RATIONALE Respiratory syncytial virus (RSV) is the leading cause of childhood lower respiratory infection, yet viable therapies are lacking. Two major challenges have stalled antiviral development: ethical difficulties in performing pediatric proof-of-concept studies and the prevailing concept that the disease is immune-mediated rather than being driven by viral load. OBJECTIVES The development of a human experimental wild-type RSV infection model to address these challenges. METHODS Healthy volunteers (n = 35), in five cohorts, received increasing quantities (3.0-5.4 log plaque-forming units/person) of wild-type RSV-A intranasally. MEASUREMENTS AND MAIN RESULTS Overall, 77% of volunteers consistently shed virus. Infection rate, viral loads, disease severity, and safety were similar between cohorts and were unrelated to quantity of RSV received. Symptoms began near the time of initial viral detection, peaked in severity near when viral load peaked, and subsided as viral loads (measured by real-time polymerase chain reaction) slowly declined. Viral loads correlated significantly with intranasal proinflammatory cytokine concentrations (IL-6 and IL-8). Increased viral load correlated consistently with increases in multiple different disease measurements (symptoms, physical examination, and amount of nasal mucus). CONCLUSIONS Viral load appears to drive disease manifestations in humans with RSV infection. The observed parallel viral and disease kinetics support a potential clinical benefit of RSV antivirals. This reproducible model facilitates the development of future RSV therapeutics.

Preliminary Assessment of the Efficacy of a T-Cell–Based Influenza Vaccine, MVA-NP+M1, in Humans

A single vaccination with MVA-NP+M1 boosts T-cell responses to conserved influenza antigens in humans. Protection against influenza disease and virus shedding was demonstrated in an influenza virus challenge study.

1918 influenza pandemic caused by highly conserved viruses with two receptor-binding variants.

The “Spanish influenza pandemic swept the globe in the autumn and winter of 1918–19, and resulted in the deaths of approximately 40 million people. Clinically, epidemiologically, and pathologically, the disease was remarkably uniform, which suggests that similar viruses were causing disease around the world. To assess the homogeneity of the 1918 pandemic influenza virus, partial hemagglutinin gene sequences have been determined for five cases, including two newly identified samples from London, United Kingdom. The strains show 98.9% to 99.8% nucleotide sequence identity. One of the few differences between the strains maps to the receptor-binding site of hemagglutinin, suggesting that two receptor-binding configurations were co-circulating during the pandemic. The results suggest that in the early stages of an influenza A pandemic, mutations that occur during replication do not become fixed so that a uniform “consensus” strain circulates for some time.

Animal models in influenza vaccine testing

The threat of a pandemic outbreak of influenza A H5N1 and H2N2 has brought attention to the development of new vaccines. Regulatory authorities require companies to provide data proving the effectiveness of vaccines, which cannot, however, be based on real efficacy data in humans. A weight-of-evidence approach may be used, based on evidence of protection in an appropriate animal model and the satisfaction of the surrogate end points in the clinical situation. In this review, we will discuss various animal species that can be infected with influenza. The main animals used for testing vaccines destined for human use are laboratory mice and ferrets and, to a lesser extent, macaques. We will focus particularly on these species.

A plant-produced influenza subunit vaccine protects ferrets against virus challenge

Background  Influenza A viruses are of major concern for public health, causing worldwide epidemics associated with high morbidity and mortality. Vaccines are critical for protection against influenza, but given the recent emergence of new strains with pandemic potential, and some limitations of the current production systems, there is a need for new approaches for vaccine development.

Associations between Human Leukocyte Antigens and Nonresponsiveness to Influenza Vaccine

Influenza remains a major cause of morbidity and mortality, particularly in at-risk groups where vaccination reduces complications of infection but is not universally protective. In order to determine whether human leukocyte antigen (HLA) class II polymorphisms modulate anti-influenza antibody responses to vaccination, a cohort of HLA-typed at-risk donors was investigated. The subjects were recruited from a single urban family practice. Hemagglutination-inhibition (HAI) titers were measured immediately before and 28 days after subunit vaccination. Nonresponsiveness was defined as failure to mount an HAI response to any component of the trivalent influenza vaccine. When the nonresponders and responders with HLA class II were compared, the nonresponder group had more HLA-DRB1*07-positive donors (13/32 vs. 6/41 responders; P=.016, Fishers exact test) and fewer HLA-DQB1*0603-9/14-positive donors (2/32 vs. 14/41 responders; P=.0045). Thus, polymorphisms in HLA class II molecules appear to modulate antibody responses to influenza vaccination.

World War I may have allowed the emergence of “Spanish” influenza

The 1918 influenza pandemic caused 40 million deaths, and so dwarfed in mortality and morbidity the preceding pandemic of 1889 and the 1957 and 1968 pandemics. In retrospect, much can be learnt about the source, the possible subterranean spread of virus, and the genetic basis of virulence. The World Health Organization has urged every nation to prepare a pandemic plan for the first global outbreak of the 21st century. We present an appraisal of epidemiological and mortality evidence of early outbreaks of respiratory disease in France and the UK in the years 1915 to 1917. Certain of these earlier focal outbreaks--called epidemic bronchitis rather than influenza--occurred during the winter months when influenza was known to be in circulation, and presented with a particular heliotrope cyanosis that was so prominent in the clinical diagnosis in the world pandemic outbreak of 1918-1919 (the Great Pandemic). The outbreaks in army camps at Etaples in France and Aldershot in the UK in 1916-1917 caused very high mortality in 25-35 year olds. Increased deaths from bronchopneumonia and influenza were also recorded in England. We deduce that early focal outbreaks of influenza-like disease occurred in Europe and on the balance of probability the Great Pandemic was not initiated in Spain in 1918 but in another European country in the winter of 1916 or 1917. We suggest that the pandemic had its origins on the Western Front, and that World War I was a contributor.

Preclinical Evaluation of a Replication-Deficient Intranasal ΔNS1 H5N1 Influenza Vaccine

Background We developed a novel intranasal influenza vaccine approach that is based on the construction of replication-deficient vaccine viruses that lack the entire NS1 gene (ΔNS1 virus). We previously showed that these viruses undergo abortive replication in the respiratory tract of animals. The local release of type I interferons and other cytokines and chemokines in the upper respiratory tract may have a “self-adjuvant effect”, in turn increasing vaccine immunogenicity. As a result, ΔNS1 viruses elicit strong B- and T- cell mediated immune responses. Methodology/Principal Findings We applied this technology to the development of a pandemic H5N1 vaccine candidate. The vaccine virus was constructed by reverse genetics in Vero cells, as a 5∶3 reassortant, encoding four proteins HA, NA, M1, and M2 of the A/Vietnam/1203/04 virus while the remaining genes were derived from IVR-116. The HA cleavage site was modified in a trypsin dependent manner, serving as the second attenuation factor in addition to the deleted NS1 gene. The vaccine candidate was able to grow in the Vero cells that were cultivated in a serum free medium to titers exceeding 8 log10 TCID50/ml. The vaccine virus was replication deficient in interferon competent cells and did not lead to viral shedding in the vaccinated animals. The studies performed in three animal models confirmed the safety and immunogenicity of the vaccine. Intranasal immunization protected ferrets and mice from being infected with influenza H5 viruses of different clades. In a primate model (Macaca mulatta), one dose of vaccine delivered intranasally was sufficient for the induction of antibodies against homologous A/Vietnam/1203/04 and heterologous A/Indonesia/5/05 H5N1 strains. Conclusion/Significance Our findings show that intranasal immunization with the replication deficient H5N1 ΔNS1 vaccine candidate is sufficient to induce a protective immune response against H5N1 viruses. This approach might be attractive as an alternative to conventional influenza vaccines. Clinical evaluation of ΔNS1 pandemic and seasonal influenza vaccine candidates are currently in progress.

Potential role of human challenge studies for investigation of influenza transmission

The importance of different routes of influenza transmission (including the role of bioaerosols) and the ability of masks and hand hygiene to prevent transmission remain poorly understood. Interest in transmission of influenza has grown as the effectiveness of prevention measures implemented during the 2009 H1N1 pandemic are questioned and as plans to better prepare for the next pandemic are debated. Recent studies of naturally infected patients have encountered difficulties and have fallen short of providing definitive answers. Human challenge studies with influenza virus date back to the 1918 pandemic. In more recent decades they have been undertaken to investigate the efficacy of antiviral agents and vaccines. Could experimental challenge studies, in which volunteers are deliberately infected with influenza virus, provide an alternative approach to the study of transmission? Here, we review the latest intervention studies and discuss the potential of challenge studies to address the remaining gaps in our knowledge.