Systemic and mucosal immunity induced by BCG vector expressing outer-surface protein A of Borrelia burgdorferi

THE bacillus Calmette–Guerin (BCG) is a live attenuated strain of Mycobacterium bovis which offers potential advantages as a vector for mucosal delivery of antigens 1–3 . Recombinant BCG elicits protective humoral immune responses to a variety of antigens 4 . Furthermore, BCG binds specifically to microfold cells 5 present in the epithelium overlying lymphoid follicles throughout the mucosal immune system 6–8 . Here we show that a single intra-nasal vaccination with recombinant BCG expressing the outer-surface protein A antigen from B. burgdorferi 9 results in a prolonged (more than one year) protective systemic IgG response and a highly sustained secretory IgA response which is disseminated throughout the mucosal immune system. Furthermore, intranasal immunization induces marked, organized lymphocyte accumulation in the proximal nasopharyngeal lymphoid tissue as well as at distal mucosal sites; the appearance and persistence of lymphoid aggregates correlates with the secretory immune responses. Thus intranasal immunization with recombinant BCG is a powerful method for inducing long-lasting secretory and systemic immune responses.