A temperature-responsive PLA-based nanosponge as a novel nanoadjuvant and efficient delivery carrier of Ag85B for effective vaccine against Mycobacterium tuberculosis.

Background: Tuberculosis (TB) is a contagious disease and the second leading cause of death worldwide. The Bacille Calmette-Guérin (BCG) vaccine, the only licensed TB vaccine, has insufficient protective efficacy in adults, necessitating the development of new TB vaccines. Ag85B, a protein-subunit TB vaccine, is a promising candidate due to its high immunogenicity. However, its hydrophobicity presents challenges in manufacturing, expression, and purification, and Ag85B alone does not elicit sufficient immune stimulation. To overcome these limitations, this study aimed to design a temperature-responsive amine-terminated polylactic acid (PLA)-based nanosponge (aPNS) as both a nanoadjuvant and an efficient delivery carrier for Ag85B.

Methods: Ag85B was produced using an EZtag fusion tag vector, achieving high product yield and purity. It was then loaded into aPNS, a nanoparticle system with a PLA core and Pluronic shell, through a temperature-responsive process at 4 °C that preserved protein bioactivity. The stability and sustained-release profile of Ag85B@aPNS were evaluated. In vitro cytotoxicity and cellular uptake studies were conducted using macrophages. Protective efficacy and immunogenicity were assessed in M. tuberculosis-challenged mice and BCG-primed mice.

Results: The Ag85B protein was successfully produced and loaded into aPNS, which exhibited good colloidal stability and a sustained-release profile. Neither the synthesized Ag85B nor the aPNS showed significant cytotoxicity. aPNS enhanced the cellular uptake of antigens by macrophages. Compared to BCG, Ag85B@aPNS demonstrated superior protective efficacy against M. tuberculosis in mice and improved immunogenicity in BCG-primed mice.

Conclusion: Ag85B@aPNS is a viable candidate for TB vaccination, showing potential as both a standalone vaccine and a BCG-booster. Its ability to enhance immunogenicity and provide protection highlights its promise in addressing the limitations of current TB vaccines.