M72 Fusion Proteins in Nanocapsules Enhance BCG Efficacy Against Bovine Tuberculosis in a Mouse Model

Abstract

Mycobacterium bovis is the causative pathogen of bovine tuberculosis (bTB), adisease that affects cattle and other mammals, including humans. Currently, there is noefficient vaccine against bTB, underscoring the need for novel immunization strategies.The M72 fusion protein, composed of three polypeptides derived from Mycobacteriumtuberculosis and M. bovis, has demonstrated protective efficacy against M. tuberculosis inclinical trials when combined with the AS01E adjuvant. Given the established efficacyof nanocapsule formulations as vaccine delivery systems, this study evaluated a novelimmunization strategy combining BCG with either full-length M72 or a truncated M72fused to a streptococcal albumin-binding domain (ABDsM72). Both antigens were encapsulatedin chitosan/alginate nanocapsules and assessed in a murine M. bovis challengemodel. Priming with BCG followed by an M72 boost significantly improved splenic protectioncompared to BCG alone, but it did not enhance pulmonary protection. Notably,boosting with ABDsM72 further increased the proportion of CD4+KLRG1-CXCR3+ T cellsin the lungs of M. bovis-challenged mice, a key correlate of protective immunity. Thesefindings demonstrate that chitosan/alginate-encapsulated antigens enhance BCG-inducedimmunity, supporting their potential as next-generation vaccine candidates for bTB control.