The adenovirus capsid protein hexon contains a highly conserved human CD4+ T-cell epitope.
The immunogenicity of adenovirus vectors remains a major obstacle to their safe and efficacious use for gene therapy. In order to identify T-cell epitopes directly from adenoviruses, four viral protein sequences were screened for the well-characterized 9-mer HLA-A2 binding motif. Peripheral blood mononuclear cells (PBMC) from healthy adults were tested for responses to 17 selected viral peptides using a short-term interferon-gamma ELISPOT assay. Memory T-cell responses were identified to a single peptide derived from the major capsid protein hexon in 5 of 6 HLA-A2-positive donors. Unexpectedly, responses to this hexon peptide were also detected in 4 of 6 HLA-A2-negative donors, and responder cells were identified as CD4(+) T cells by immunomagnetic depletion experiments. A longer 15-mer peptide, H910-924, was identified as the optimal CD4(+) T-cell epitope. This hexon epitope induces strong proliferative T-cell responses that can be blocked by a monoclonal antibody against HLA-DR, and molecular HLA typing of donors suggests that the peptide response is restricted by multiple HLA-DR alleles. Additionally, quantitative analysis of responses to H910-924 and whole adenovirus reveals that the frequency of circulating CD4(+) T cells specific for this single hexon epitope (mean = 61 per 10(6) PBMC) represents up to one third of the total adenovirus-specific T-cell response. Finally, comparison of hexon sequences from over 20 different human adenovirus serotypes indicates that H910-924 is highly conserved. In most individuals, therefore, T-cell responses to this hexon epitope will be induced by all adenovirus vectors, including "gutted" vectors packaged with capsid proteins and vectors based on different serotypes.
Olive
Melanie
M
Center of Human Virology and Department of Medicine, Thomas Jefferson University, Philadelphia, PA 19107, USA. PHYLLIS.FLOMENBERG@MAIL.TJU.EDU
Eisenlohr
Laurence
L
Flomenberg
Neal
N
Hsu
Susan
S
Flomenberg
Phyllis
P
D000256:Adenoviridae / Q000235:genetics / Q000276:immunology*; D000293:Adolescent; D000328:Adult; D000368:Aged; D000595:Amino Acid Sequence; D000956:Antigens, Viral / Q000276:immunology; D015704:CD4 Antigens / Q000276:immunology*; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D036022:Capsid Proteins / Q000235:genetics / Q000276:immunology*; D002460:Cell Line; D017124:Conserved Sequence; D003602:Cytotoxicity, Immunologic; D018984:Epitopes, T-Lymphocyte; D015789:HLA-A2 Antigen / Q000276:immunology; D006684:HLA-DR Antigens / Q000276:immunology; D006801:Humans; D007371:Interferon-gamma / Q000378:metabolism; D008875:Middle Aged; D008969:Molecular Sequence Data
D000956:Antigens, Viral; D015704:CD4 Antigens; D036022:Capsid Proteins; D018984:Epitopes, T-Lymphocyte; D015789:HLA-A2 Antigen; D006684:HLA-DR Antigens; C018315:hexon capsid protein, Adenovirus; D007371:Interferon-gamma