Toxoplasma gondii and a Cancer Biology Dichotomy: A Systematic Review of Experimental Studies of Its Antitumor and Pro-Tumor Effects

Toxoplasma gondii (T. gondii) is an intracellular parasite known to modulate host immunity and cellular signaling, raising interest in its potential influence on cancer biology. A systematic review was conducted to evaluate experimental evidence on the antitumor or pro-tumor effects of T. gondii infection and parasite-derived antigens and to categorize the underlying mechanisms. PubMed was searched through 9 September 2024, and 54 eligible experimental studies were included (41 in vivo, 10 in vitro, and three combined). Forty-six studies reported antitumor effects, two pro-tumor effects, one stage-dependent divergent effects (acute infection/antitumor vs. chronic infection/pro-tumor), and five highlighted T. gondii-associated cancer-pertinent signaling pathways. Antitumor effects were observed following acute infection and exposure to parasite antigens, certain recombinant proteins, and exosomal microRNA miR-155-5p. Dominant mechanistic categories included activation of innate and adaptive immunity and reversal of tumor microenvironment immunosuppression (notably Th1-driven IL-12/IFN-γ responses, antitumor M1 macrophage polarization), induction of apoptosis, anti-angiogenesis, molecular mimicry and modulation of cancer-pertinent pathways. Conversely, pro-tumor effects were seen with chronic infection and exposure to ROP18 effector protein and miR-21. Future translational research should focus on rigorous evaluation of the safety and efficacy of attenuated non-replicating T. gondii strains and/or select recombinant antigens for potential cancer T. gondii-based immunotherapy.