Rodent malaria: BCG-induced protection and immunosuppression

Area of Science:

• Immunology
• Parasitology
• Vaccinology

Background:

• Investigating the efficacy of Mycobacterium bovis, bacille Calmette-Guérin (BCG) and irradiated sporozoites as malaria vaccines.
• Assessing the protective immune responses against Plasmodium berghei sporozoite challenge in murine models.

Purpose of the Study:

• To evaluate the protective effects of BCG and irradiated sporozoites, individually and in combination, against Plasmodium berghei infection.
• To determine the impact of BCG on pre-existing immunity induced by irradiated sporozoites.

Main Methods:

• Swiss mice were immunized with a single dose of Mycobacterium bovis, strain BCG, or irradiated Plasmodium berghei sporozoites.
• Combined immunization strategies and sequential administration were tested.
• Mice were challenged with Plasmodium berghei sporozoites, and protection was assessed, including rechallenge experiments.

Main Results:

• BCG vaccination provided significant but incomplete protection against primary sporozoite challenge.
• Immunization with irradiated sporozoites induced greater protection and solid immunity upon rechallenge compared to BCG.
• Simultaneous BCG and irradiated sporozoite immunization showed synergistic protection only under specific timing conditions; BCG suppressed existing irradiated sporozoite-induced immunity.

Conclusions:

• Irradiated sporozoites are a more effective immunogen for inducing robust and lasting protection against Plasmodium berghei than BCG alone.
• The timing of administration is critical for any synergistic effect between BCG and irradiated sporozoites.
• BCG can interfere with and suppress immunity generated by irradiated sporozoite vaccination.