VACCINATION WITH PLASMID DNA ENCODING MYCOBACTERIAL ANTIGEN 85A STIMULATES A CD4(-CELL EPITOPIC REPERTOIRE BROADER THAN THAT STIMULATED BY MYCOBACTERIUM-TUBERCULOSIS H37RV INFECTION() AND CD8(+) T)

Vaccination of mice with plasmid DNA carrying the gene far the major s ecreted mycobacterial antigen 85A (Ag85A) from Mycobacterium tuberculo sis is a powerful technique for generating robust specific Th1 helper T-cell responses, CD8(+)-mediated cytotoxicity, and protection against M. tuberculosis challenge (K. Huygen et al., Nat. Med. 2:893-898, 199 6). We have now analyzed in more detail the antigen-specific immune CD 4(+)- and CD8(+)-T-cell responses induced in BALB/c mice vaccinated wi th Ag85A DNA and have compared these responses to those generated by i ntravenous infection with M. tuberculosis. T-cell-epitope mapping, as measured by interleukin-2 and gamma interferon secretion from splenic T cells restimulated in vitro with synthetic 20-mer peptides spanning the complete mature sequence of Ag85A, demonstrated that DNA vaccinati on stimulated a stronger and broader T-cell response than did M. tuber culosis infection. Moreover, elevated cytotoxic T lymphocyte (CTL) act ivity against Ag85A-transfected and peptide-pulsed P815 target cells c ould be generated exclusively by vaccination with plasmid DNA, not fol lowing M. tuberculosis infection. By using DNA vaccination, three Ag85 A CTL epitopes with predicted major histocompatibility complex class I binding moths were defined. One of them was previously reported as a dominant, promiscuously recognized T-cell epitope in healthy humans wi th primary infections. These data strengthen the potential of DNA vacc ination with respect to inducing antituberculous immunity in humans.