Myxoma Virus Expressing Human Interleukin-12 Does Not Induce Myxomatosis in European Rabbits

Abstract

Myxoma virus (MV) is a candidate for oncolytic virotherapy due to its ability to selectively infect and kill tumor cells, yet MV is a species-specific pathogen that causes disease only in European rabbits. To assess the ability of MV to deliver cytokines to tumors, we created an MV (vMyxIL-12) that expresses human interleukin-12 (IL-12). vMyxIL-12 replicates similarly to wild-type MV, and virus-infected cells secrete bioactive IL-12. Yet, vMyxIL-12 does not cause myxomatosis, despite expressing the complete repertoire of MV proteins. Thus, vMyxIL-12 exhibits promise as an oncolytic candidate and is safe in all known vertebrate hosts, including lagomorphs.Myxoma virus (MV) is a poxvirus and the prototypic member of the Leporipoxvirus genus. MV is the causative agent of myxomatosis, a lethal and deblilitating disease of European rabbits (Oryctolagus cuniculus), characterized by profound systemic immunosuppression (11,12). MV has been completely sequenced (5), and many virus-encoded immunomodulatory proteins have been identified (2,20,32,41). A significant number of individual MV genes have been genetically removed, and the effect on the ability of the knockout virus to cause mxyomatosis has been evaluated (18,19). Ablation of some viral genes had minor effects on the ability of the virus to cause disease in rabbits, while others were attenuated to the point that the virus no longer causes significant pathology. These studies, combined with concomitant in vitro analysis of the individual viral gene products, have provided many insights into the mechanism by which MV causes disease in rabbits (20,32).Although MV cannot cause disease in any vertebrate species other than lagomorphs, it has been demonstrated that MV can preferentially infect and kill human cancer cells (33). This has led to studies examining MV as a virotherapeutic for human cancer. The ability of MV to infect and clear tumors in vivo has been demonstrated in a model for human glioblastoma, where intratumoral injection of MV effectively "cured" human gliomas in immunocompromised mice (23). The ability of MV to infect human tumor cells has been linked to activity of cellular Akt kinase (36), and drugs that act on this host signaling pathway have been shown to augment MV infection (30).To stimulate an anticancer immune response within a largely nonresponsive tumor microenvironment, cytokine therapy has been employed. Interleukin-12 (IL-12) is produced by antigenpresenting cells (29) and acts as an important mediator of T-cell responses through promoting T type 1 immunity (15).IL-12 exhibits significant antitumor effects in both animal models and human patients, yet the toxicity induced by systemic administration prevented further use clinically (15,22,26,28,34,35,37). Thus, local dosing of IL-12 within tumors has been explored. IL-12 has been delivered to murine (14) and human (4) tumors using IL-12 encapsulated microspheres (14) or irradiated tumor cells transfected with an IL-12 expression plasmid (13). Viral vectors, including herpesvirus (3, 38-40) a...

Advances in Oncolytic Virus Therapy for Glioma

“…Similarly the inclusion of IL-2 has been shown to result in the induction of immunotherapy, and subsequent tumor rejection in other tumor models [98]. Similar results were observed with the inclusion of IL-12 and GM-CSF which were intended to enhance OV therapy by ultimately facilitating an adaptive immune response in tumors [75, 99–102]. Based on these studies several patents have been issued which describe novel OVs encoding for T-cell co-stimulatory factors, pro-inflammatory cytokines, chemokines, and intercellular adhesion molecules designed to increase the autologous antitumor vaccination by OV [76, 95, 103].…”

Oncolytic virotherapy for malignant glioma: translating laboratory insights into clinical practice

“…Anti-tumor immune response can also be enhanced by the use of genetically engineered oncolytic viruses loaded with genes that encode for many cytokines. Researchers have recently shown that mice treated with vector constructs that were able to encode for interleukin-2 (IL-2) (Mizuno et al, 2000), IL-4 (Post et al, 2007), or IL-12 (Stanford et al, 2007) cytokines presented a rapid and sustained tumor regression.…”

Myxoma Virus Expressing Interleukin-15 Fails To Cause Lethal Myxomatosis in European Rabbits

“…Studies of determinants of the MYXV host range outside of rabbit cells have led to investigations into the oncolytic potential of MYXV against human cancer cells (2,10,28,31). Also, genetic manipulation of MYXV continues to produce next-generation recombinant MYXVs with reduced virulence and enhanced oncolytic potential (2,26).…”