Raw starch microparticles as BCG adjuvant: Their efficacy depends on the virulence of the infection strains.

The persistence of tuberculosis (TB) as one of the top 10 causes of death worldwide, the growing incidence of multidrug-resistant tuberculosis and the controversial efficacy of the Bacille Calmette-Guérin (BCG) vaccine drives the development of new generation multistage vaccines against this disease that can boost BCG-primed immunity. The use of polymeric microparticles for this purpose increases due to their advantages, especially their good safety levels and intrinsic immunostimulant properties. We recently explored and demonstrated the reinforcing and adjuvant potential of starch microparticles (SMPs) that administered intranasally to BCG-primed BALB/c mice, alone or in combination with a recombinant antigen, increased survival rates and induced a reduction of bacterial load in the lungs of mice infected with tuberculosis. Here, we tested the effect of SMPs added to the BCG vaccine as adjuvant to the whole-cell vaccine and investigated their contribution to the improvement of the protective efficacy of subcutaneous vaccination in mice challenged with virulent strains of Mycobacterium tuberculosis. As expected, our results were dependent on the infection strains, showing that virulence is a crucial factor that affects the adjuvant activity of SMPs. Our results also confirm the adjuvant activity of this carbohydrate and its usefulness in diverse vaccination strategies not only for mucosal but also for parenteral administration.