Identification and frequency of circulating CD4 + T lymphocytes specific to Benzylpenicillin in healthy donors

Background Drug hypersensitivity is known to rely on a drug-specific T-cell response. Amplitude of antigen-specific T-cell response is partly controlled by the size of the antigen-specific naive CD4+ T-cell repertoire, but estimate of this repertoire has never been investigated for allergenic drugs. The purpose of this study was to evaluate the frequency of benzylpenicillin-specific CD4+ T lymphocytes in healthy donors. Methods Co-cultures were established with CD4+ T lymphocytes from healthy donors and mature autologous dendritic cells loaded with benzylpenicillin coupled to human serum albumin. CD4+ T lymphocytes were stimulated once a week for 4 weeks with benzylpenicillin coupled to human serum albumin. The CD4+ T-cell response was measured using an interferon-γ ELISPOT assay. Frequency of benzylpenicillin-specific naive CD4+ T lymphocytes was then calculated using the Poisson distribution law. Results Results showed the presence of benzylpenicillin-specific CD4+ T lymphocytes in 9 of 10 tested healthy donors irrespective of their HLA typing, with a mean frequency of 0.29 cells per million of CD4+ T cells. Experiments performed on naive (CD45RA+) and on memory (CD45RO+) CD4+ T lymphocytes showed that these benzylpenicillin-specific CD4+ T lymphocytes belonged to the naive T-cell subpopulation. Conclusion This study showed for the first time the existence of naive CD4+ T lymphocytes specific to benzylpenicillin in healthy donors.