BCG Vaccination Induces Robust CD4⁺ T Cell Responses to Mycobacterium tuberculosis Complex–Specific Lipopeptides in Guinea Pigs

A new class of highly antigenic, MHC-II–restricted mycobacterial lipopeptides that are recognized by CD4-positive T lymphocytes of Mycobacterium tuberculosis–infected humans has recently been described. To investigate the relevance of this novel class of mycobacterial Ags in the context of experimental bacille Calmette-Guérin (BCG) vaccination, Ag-specific T cell responses to mycobacterial lipid and lipopeptide-enriched Ag preparations were analyzed in immunized guinea pigs. Lipid and lipopeptide preparations as well as complex Ag mixtures, such as tuberculin, mycobacterial lysates, and culture supernatants, all induced a similar level of T cell proliferation. The hypothesis that lipopeptide-specific T cells dominate the early BCG-induced T cell response was corroborated in restimulation assays by the observation that Ag-expanded T cells specifically responded to the lipopeptide preparation. A comparative analysis of the responses to Ag preparations from different mycobacterial species revealed that the antigenic lipopeptides are specific for strains of the M. tuberculosis complex. Their intriguing conservation in pathogenic tuberculous bacteria and the fact that these highly immunogenic Ags seem to be actively released during in vitro culture and intracellular infection prompt the urgent question about their role in the fine-tuned interplay between the pathogen and its mammalian host, in particular with regard to BCG vaccination strategies.