Infection of HLA-DR1 Transgenic Mice with a Human Isolate of Influenza A Virus (H1N1) Primes a Diverse CD4 T-Cell Repertoire That Includes CD4 T Cells with Heterosubtypic Cross-Reactivity to Avian (H5N1) Influenza Virus

Abstract

The specificity of the CD4 T-cell immune response to influenza virus is influenced by the genetic complexity of the virus and periodic encounters with variant subtypes and strains. In order to understand what controls CD4 T-cell reactivity to influenza virus proteins and how the influenza virus-specific memory compartment is shaped over time, it is first necessary to understand the diversity of the primary CD4 T-cell response. In the study reported here, we have used an unbiased approach to evaluate the peptide specificity of CD4 T cells elicited after live influenza virus infection. We have focused on four viral proteins that have distinct intracellular distributions in infected cells, hemagglutinin (HA), neuraminidase (NA), nucleoprotein, and the NS1 protein, which is expressed in infected cells but excluded from virion particles. Our studies revealed an extensive diversity of influenza virus-specific CD4 T cells that includes T cells for each viral protein and for the unexpected immunogenicity of the NS1 protein. Due to the recent concern about pandemic avian influenza virus and because CD4 T cells specific for HA and NA may be particularly useful for promoting the production of neutralizing antibody to influenza virus, we have also evaluated the ability of HA-and NA-specific CD4 T cells elicited by a circulating H1N1 strain to cross-react with related sequences found in an avian H5N1 virus and find substantial cross-reactivity, suggesting that seasonal vaccines may help promote protection against avian influenza virus.In recent decades, investigators studying both murine and human T-cell responses to influenza virus have succeeded in identifying peptide epitopes from immunized or vaccinated individuals that are the targets of CD4 T cells. These studies suggest a considerable diversity in CD4 responses. Epitopes derived from hemagglutinin (HA), neuraminidase (NA), nuclear protein (NP), polymerase (PB1 and PB2), matrix (M1), and nonstructural protein (NS1) have all been identified (9, 19, 25-28, 32, 61, 64, 85, 86). Our own laboratory previously analyzed the peptide specificity of CD4 T cells in the primary response of HLA-DR1 transgenic mice toward a human isolate of influenza virus and found that the CD4 T-cell repertoire specific for HA alone was diverse and encompassed at least 30 different peptide epitopes (63). In general, studies with humans have been much less systematic than those with the mouse because of the difficulty in obtaining lymphocyte samples from recently infected individuals and because of the complexity of major histocompatibility complex (MHC) molecules expressed in humans. However, recent studies with MHC class II tetramer reagents (19,61,64,72,86) have permitted the visualization of CD4 T cells specific for influenza virus directly ex vivo or after a brief (10-to 14-day) in vitro expansion. Those studies have led to the conclusion that the repertoire of CD4 T cells is more diverse than that of CD8 T cells and that CD4 T cells that are specific for most influenza virus proteins can be ...

Cross-protective TH1 immunity against Aspergillus fumigatus and Candida albicans

“…Interestingly, cross-reactivity is observed in spite of a nonanchor residue substitution. 40 This phenomenon was universally observed in different T-cell clones derived from various donors. In contrast, the p41 epitopes of other Aspergillus species differing in 3 to 7 aa from the A fumigatus sequence are no longer cross-reactive, with the exception of A flavus that shows very weak cross-reactivity in some of the Crf1/p41-specific T-cell clones, which is possibly explained by its higher homology to the A fumigatus sequence than that of the other Aspergillus species.…”

“…The discovery of a defined peptide epitope activating T H 1 cells with cross-reactivity to the 2 most important fungal pathogens in humans is to our knowledge a novel finding and only little is known in mouse models. 37 The concept of heterologous immunity to different pathogens mediated by cross-reactive T cells has until now only been described in detail for viral infections, 38 for example, for influenza virus 39,40 and flavivirus. 41,42 The discovery of this mechanism has initiated the development of new vaccines that will target conserved protein domains of different flaviviral strains for induction of cross-protection.…”

Cutting Edge: CD4 T Cells Generated from Encounter with Seasonal Influenza Viruses and Vaccines Have Broad Protein Specificity and Can Directly Recognize Naturally Generated Epitopes Derived from the Live Pandemic H1N1 Virus

“…The 17-mer peptides overlapping by 11 aa encompassing the entire sequences of HA, neuraminidase (NA), NP, M1, NS1, and PB1 were obtained from the National Institutes of Health Biodefense and Emerging Infections Research Resources Repository, National Institute of Allergy and Infectious Diseases, National Institutes of Health (Bethesda, MD) as previously described (9,10) and reconstituted in PBS, with or without added DMSO, to increase solubility of hydrophobic peptides, and 1 mM DTT, for peptides that contained cysteine. Peptides were pooled and used at 2 mM (final concentration) for each peptide.…”

“…As a source of APCs, PBMCs from the same donor were T depleted using CD4 and CD8 microbeads (Miltenyi Biotec). ELISPOT assays were performed as described (8,9), with some modifications for human samples. Briefly, 96-well filter plates (Millipore, Billerica, MA) were coated with 15 mg/ml purified anti-human IFN-g (clone 1-D1K, MabTech, Cincinnati, OH), washed, and incubated with RPMI 1640 containing 10% FCS to block nonspecific binding.…”

Randomized, double-blind, multi-center, phase III clinical trial to evaluate the immunogenicity and safety of MG1109 (egg-based pre-pandemic influenza A/H5N1 vaccine) in healthy adults

“…In a mouse model, influenza A/H1N1 virus infection induced hetero-subtypic cross-reactivity to the avian influenza A/H5N1 virus. 8 In subjects with detectable pre-vaccination HI titers ( 1:10), the results from the HI and MN assays were not well correlated, indicating non-specific cross-reactive immune responses. Primed subjects were expected to produce higher antibody levels after the first vaccination, but booster effects were not remarkable in subjects with detectable baseline HI titers compared with those with undetectable HI titers.…”