A Uracil Auxotroph Toxoplasma gondii Exerting Immunomodulation to Inhibit Breast Cancer Growth and Metastasis

Abstract Background: Breast cancer is the most common cause of cancer-related death among women, and patients with triple-negative breast cancer (TNBC) have poor prognosis, so it is necessary to develop new effective therapies urgently. Recent studies have demonstrated that uracil auxotroph Toxoplasma gondii vaccine displays antitumor effects. Here, we examined the immunotherapy effects of an attenuated uracil auxotroph strain of T. gondii against 4T1 murine breast cancer.Methods: We constructed a uracil auxotroph strain, the orotidine 5′-monophosphate decarboxylase gene deleted strain of T. gondii (RH-Δompdc) with the CRISPR/Cas9 technology. Its virulence in vitro and in vivo was determined by parasite replication assay, plaque assay, the parasite burden detection in mice peritoneal fluids and the survival analysis of T. gondii infection mice. Its immune modulation ability was evaluated by cytokines detection. Its antitumor effect was evaluated after its in situ inoculation to 4T1 tumors in mouse model, the tumor volume was measured, the 4T1 lung metastasis was detected by H&E and Ki67 antibody staining, and the cytokines levels were measured by ELISA.Results: RH-Δompdc strain could proliferate normally with uracil supplement, however, it was unable to propagate without uracil and in vivo, which implicated that it is avirulent to the hosts. This mutant showed vaccine characteristics that it could induce intense immune responses both in vitro and in vivo by boosting the expression of inflammatory cytokines significantly. RH-Δompdc in situ inoculation to the 4T1 tumors in mice could inhibit the tumor growth, reduce the lung metastasis, promote the survival of the tumor-bearing mice, and also increase the secretion of Th1 cytokines IL-12 and IFN-γ both in serum and in the tumor microenvironment (TME). Conclusion: The uracil auxotroph RH-Δompdc inoculation to the 4T1 tumors stimulated the anti-infection and antitumor immunity in mice, resulted in the inhibition of tumor growth and metastasis, the promotion in survival of the tumor-bearing mice, and the increasing secretion of IL-12 and IFN-γ both in serum and in the TME. Our findings implied that the immunomodulation resulted by RH-Δompdc could be a potential antitumor strategy.