Exosomes are an effective vaccine against congenital toxoplasmosis in mice.

Toxoplasmosis is a serious disease in humans and may cause abortion or congenital infection if a woman is exposed to the disease for the first time during pregnancy. Infection before pregnancy normally results in immunity protecting the foetus, suggesting that it may be possible to block vertical transmission of the parasite by appropriate vaccination before pregnancy. We found that the vaccination of CBA/J mice, before pregnancy, with exosomes secreted by SRDCs pulsed in vitro with Toxoplasma gondii-derived antigens (TAg) induced a protective response in the pups. Indeed, vaccination resulted in the presence of significantly fewer cysts in pup brains. This protection was associated with strong humoral responses in the serum in vivo. We also observed cellular responses in vivo, with cell proliferation associated with the production of cytokines by the splenocytes. Thus, exosomes are nucleic acid-free vesicles able to induce immune responses correlated with protection against T. gondii infection in a congenital model. They are therefore a potentially useful tool for vaccination against infectious disease.