Lactoferrin augments BCG vaccine efficacy to generate T helper response and subsequent protection against challenge with virulent Mycobacterium tuberculosis

The ability to control intracellular Mycobacterium tuberculosis (MTB) infection relies on cellular immunity and generation of a strong T-cell helper 1 (TH1) response. Lactoferrin, an iron-binding protein with immune regulatory functions, was investigated as an adjuvant to boost Mycobacterium bovis Bacillus Calmette-Guerin (BCG) efficacy. Lactoferrin was initially shown to augment IL-12(p40) production from macrophages stimulated with LPS. A single immunization of mice with Lactoferrin as an adjunct adjuvant resulted in amplified splenocyte proliferative response to heat-killed BCG, and elevated IL-12(p40) production with increased relative ratios of IL-12/IL-10. Furthermore, splenocyte recall response to HK-BCG was augmented for proinflammatory mediators, TNF-α, IL-1β, and IL-6, approaching responses generated to complete Freund's adjuvant (CFA) immunized controls. Specific responses were identified, with significant elevation of IFN-γ generated during antigenic recall. Subsequent aerosol challenge of Lactoferrin adjuvant immunized mice with virulent M. tuberculosis revealed decreased mycobacterial loads in the lung, and limitation of organism dissemination to a peripheral organ (spleen). These studies indicate that Lactoferrin can act as an adjunct adjuvant to augment cellular immunity and boost BCG efficacy for protection against subsequent challenge with virulent MTB.