Avirulent ME49Δgra5Protecting Hosts AgainstToxoplasma gondiiInfection and Breast Tumors

AbstractToxoplasma gondiiis the causative agent of toxoplasmosis, a zoonotic disease that poses a threat to human health and a considerable loss to livestock farming. At present, clinical therapeutic drugs mainly targetT. gondiitachyzoites and fail to eradicate bradyzoites. Developing a safe and effective vaccine against toxoplasmosis is urgent and important.T. gondiipossesses dense granule organelles that secrete immunogenic dense granule proteins (GRAs). GRA5 localizes to the parasitophorous vacuole membrane (PVM) in the tachyzoite stage and to the cyst wall in the bradyzoite stage. Here we report thatgra5knockoutT. gondiistrain is avirulent and fails to form cysts, but stimulates sero-conversion in mice. We next investigated the protective efficacy of ME49Δgra5vaccination againstT. gondiiinfection. All the immunized mice survived the challenge infection with either wild-type RH, ME49, VEG tachyzoites or ME49 cysts. Remarkably, ME49Δgra5tachyzoites inoculationin situattenuated the growth of murine breast tumor (4T1) in mice and prevented 4T1’s lung metastasis. ME49Δgra5inoculation might upregulate the levels of Th1 cytokines and tumor-infiltrating T cells in tumor microenvironment (TME) and trigger anti-tumor responses by increasing the number of NK, B, T cells, macrophages, and dendritic cells (DCs) in spleen. Collectively, the results support the potential of ME49Δgra5as attenuated live vaccine againstT. gondiiinfection and breast cancer.Author summaryThe zoonotic toxoplasmosis poses a great disease burden to humans and big loss to livestock farming. At present, clinical therapeutic drugs mainly targetT. gondiitachyzoites but have no effect on bradyzoites. A safe and effective vaccine against toxoplasmosis is urgent and important. Dense granule proteins (GRAs) are a group of immunoactive proteins secreted byT. gondiidense granule organelles. GRA5 is located on the parasitophorous vacuole membrane (PVM) at the tachyzoite stage and on the cyst wall at the bradyzoite stage. We discovered that thegra5knockoutT. gondiistrain became avirulent and failed to form cysts in mice. ME49Δgra5immunized mice survived the challenge infection of wild-type RH, ME49, and VEG tachyzoites, and ME49 cysts. Meanwhile, ME49Δgra5tachyzoites inoculationin situremarkably attenuated the growth of murine breast tumor (4T1) in mice including the injected and distant tumors, as well as prevented 4T1’s lung metastasis. This results support the potential of ME49Δgra5as attenuated live vaccine againstT. gondiiinfection and breast cancer.