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.
Center of Human Virology and Department of Medicine, Thomas Jefferson University, Philadelphia, PA 19107, USA. PHYLLIS.FLOMENBERG@MAIL.TJU.EDU
Melanie
M
Olive
Laurence
L
Eisenlohr
Neal
N
Flomenberg
Susan
S
Hsu
Phyllis
P
Flomenberg
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