Neospora caninum: a new class of biopharmaceuticals in the therapeutic arsenal against cancer

Abstract

BackgroundMicroorganisms that can be used for their lytic activity against tumor cells as well as inducing or reactivating antitumor immune responses are a relevant part of the available immunotherapy strategies. Viruses, bacteria and even protozoa have been largely explored with success as effective human antitumor agents. To date, only one oncolytic virus—T-VEC—has been approved by the US Food and Drug Administration for use in biological cancer therapy in clinical trials. The goal of our study is to evaluate the potential of a livestock pathogen, the protozoan Neospora caninum, non-pathogenic in humans, as an effective and safe antitumorous agent.Methods/ResultsWe demonstrated that the treatment of murine thymoma EG7 by subcutaneous injection of N. caninum tachyzoites either in or remotely from the tumor strongly inhibits tumor development, and often causes their complete eradication. Analysis of immune responses showed that N. caninum had the ability to 1) lyze infected cancer cells, 2) reactivate the immunosuppressed immune cells and 3) activate the systemic immune system by generating a protective antitumor response dependent on natural killer cells, CD8-T cells and associated with a strong interferon (IFN)-γ secretion in the tumor microenvironment. Most importantly, we observed a total clearance of the injected agent in the treated animals: N. caninum exhibited strong anticancer effects without persisting in the organism of treated mice. We also established in vitro and an in vivo non-obese diabetic/severe combined immunodeficiency mouse model that N. caninum infected and induced a strong regression of human Merkel cell carcinoma. Finally, we engineered a N. caninum strain to secrete human interleukin (IL)-15, associated with the alpha-subunit of the IL-15 receptor thus strengthening the immuno-stimulatory properties of N. caninum. Indeed, this NC1-IL15hRec strain induced both proliferation of and IFN-γ secretion by human peripheral blood mononuclear cells, as well as improved efficacy in vivo in the EG7 tumor model.ConclusionThese results highlight N. caninum as a potential, extremely effective and non-toxic anticancer agent, capable of being engineered to either express at its surface or to secrete biodrugs. Our work has identified the broad clinical possibilities of using N. caninum as an oncolytic protozoan in human medicine.

Trypanosoma cruzi-Derived Molecules Induce Anti-Tumour Protection by Favouring Both Innate and Adaptive Immune Responses

“…In this context, the function of IFN-γ in inducing an increase in CD69 expression in NK cells was essential [ 27 ]. In addition, the infection with N. caninum [ 28 ], Leishmania amazonensis [ 29 ], and T. gondii [ 16 ] increased the levels of NK cells mainly through an IFN-γ-dependent pathway. Other works also describe the anti-tumour immunity induced by Toxoplasma gondii injection in melanoma preclinical models [ 16 , 17 ].…”

Anti-Tumor Effect of Parasitic Protozoans

“…However, the work was hampered by controversial results and the complicated international political situation, and so the molecular basis of this phenomenon has remained elusive [ 5 ]. Moreover, several live-attenuated protozoan parasites including Leishmania infantum and L. tropica [ 6 ], Neospora caninum [ 7 ], and Toxoplasma gondii [ 8 ] have all lately been employed as antitumor biological agents via intratumoral injection, all of which decreased tumor development and local inflammation ( Figure 1 ). The injection of live N. caninum tachyzoites either in or remotely from the tumor, successfully treated murine thymoma EG7 by strongly activating the natural killer cell- (NK cell-) and CD8-T cell-dependent protective antitumor response associated with interferon (IFN)-γ secretion in the tumor microenvironment, resulting in the lysis of the cancer cell [ 7 ].…”

“…Moreover, several live-attenuated protozoan parasites including Leishmania infantum and L. tropica [ 6 ], Neospora caninum [ 7 ], and Toxoplasma gondii [ 8 ] have all lately been employed as antitumor biological agents via intratumoral injection, all of which decreased tumor development and local inflammation ( Figure 1 ). The injection of live N. caninum tachyzoites either in or remotely from the tumor, successfully treated murine thymoma EG7 by strongly activating the natural killer cell- (NK cell-) and CD8-T cell-dependent protective antitumor response associated with interferon (IFN)-γ secretion in the tumor microenvironment, resulting in the lysis of the cancer cell [ 7 ]. Researchers from Ege University Medical School first reported that intratumoral administration of attenuated Leishmania strains in 4T1 breast cancer-bearing mice promoted M1 dominant activation of macrophages in spleen and tumor tissues with induction of proinflammatory cytokines that helps the generation of protective Th1 responses [ 6 , 9 ].…”

“…As reported by Chen, et al [ 41 ], three clinical trials based on Plasmodium immunotherapy against advanced cancers have been approved and are underway with clinical safety guaranteed. In addition, the infection of N. caninum [ 7 ], Leishmania amazonensis [ 42 ], and T. gondii [ 43 ] increased the levels of NK cells mainly through an IFN-γ-dependent pathway. Moreover, toxoplasma infection can induce the conversion of NK cells into ILC1-like cells which are Eomes-dependent and the changes appear permanent [ 44 ], which may help defend against tumors.…”

“…In mice implanted with murine Lewis lung cancer (LLC) cells, malaria parasite infection promotes the maturation of DCs through up-regulating the expression of CD80 and CD86 resulting in the activation of T cells [ 39 ]. Recently, Lantier, et al [ 7 ] found that unlike dead parasites or soluble tachyzoites antigens, live N. caninum tachyzoites are able to activate murine or human DCs to secret proinflammatory cytokines, which convincingly suggests that the use of live tachyzoites is a necessary condition for immunotherapeutic treatment. In fact, four days after the injection of live tachyzoites, they observed recruitment of DCs, along with a high increase of IFN-γ and IL-12, indicating a measurable and systemic immune response against EG7 thymoma in mice.…”