Monoclonal Antibodies Targeting Bacillus Calmette–Guérin (BCG) Outer Membrane Proteins Confer Protection Against Tuberculosis

Abstract

Tuberculosis (TB), caused by the Mycobacterium tuberculosis complex (MTBC), is a persistent global health crisis, remaining the world’s leading infectious killer. There were abundant outer membrane proteins (OMPs) distributed in the bacterial cell wall, while fewer proteins were identified and characterized as antigens that could induce protective antibodies against TB. The OMPs of BCG were extracted with the detergent N-octyl-β-D-glucopyranoside, and the extracted proteins were used to immunize mice to generate an antibody library. Subsequently, the library underwent HAT/HT screening, and five specific monoclonal antibodies (mAbs) targeting OMPs with higher titers named 9C5, 14E9, 9F6, 7B10, and 6F4 were obtained. Among the five mAbs, 9C5, 14E9, and 9F6 could increase macrophage phagocytosis, inhibit the mycobacteria growth in peripheral blood mononuclear cells (PBMCs), and enhance the fusion of phagosomes and lysosomes in macrophages. Mice were immunized with the three antibodies before being challenged with M. bovis, among which two antibodies, 14E9 and 9C5, exhibited a preventive effect against TB infection. Furthermore, antibody 9C5 also showed a therapeutic effect, characterized by significant decreases in lung burden and ameliorated lung lesions. The antigens targeted by the two antibodies 9C5 and 14E9 were identified by coimmunoprecipitation (co-IP) combined with mass spectrometry (MS), and the results demonstrated that antibodies 9C5 and 14E9 recognize BCG_2760c and MPB83, respectively. This research promotes a better understanding of host protective humoral immunity by BCG vaccination and the roles of antibodies in TB vaccine design and development.