Tanapoxvirus lacking a neuregulin-like gene regresses human melanoma tumors in nude mice.

Neuregulin (NRG), an epidermal growth factor is known to promote the growth of various cell types, including human melanoma cells through ErbB family of tyrosine kinases receptors. Tanapoxvirus (TPV)-encoded protein TPV-15L, a functional mimic of NRG, also acts through ErbB receptors. Here, we show that the TPV-15L protein promotes melanoma proliferation. TPV recombinant generated by deleting the 15L gene (TPVΔ15L) showed replication ability similar to that of wild-type TPV (wtTPV) in owl monkey kidney cells, human lung fibroblast (WI-38) cells, and human melanoma (SK-MEL-3) cells. However, a TPV recombinant with both 15L and the thymidine kinase (TK) gene 66R ablated (TPVΔ15LΔ66R) replicated less efficiently compared to TPVΔ15L and the parental virus. TPVΔ15L exhibited more robust tumor regression in the melanoma-bearing nude mice compared to other TPV recombinants. Our results indicate that deletion of TPV-15L gene product which facilitates the growth of human melanoma cells can be an effective strategy to enhance the oncolytic potential of TPV for the treatment of melanoma.

Oncolytic tanapoxvirus expressing FliC causes regression of human colorectal cancer xenografts in nude mice.

Colorectal cancers are significant causes of morbidity and mortality and existing therapies often perform poorly for individuals afflicted with advanced disease. Oncolytic virotherapy is an emerging therapeutic modality with great promise for addressing this medical need. Herein we describe the in vivo testing of recombinant variants of the tanapoxvirus (TPV). Recombinant viruses were made ablated for either the 66R gene (encoding a thymidine kinase), the 2L gene (encoding a TNF-binding protein), or both. Some of the recombinants were armed to express mouse chemotactic protein 1 (mCCL2/mMCP-1), mouse granulocyte-monocyte colony stimulating factor (mGM-CSF), or bacterial flagellin (FliC). Tumors were induced in athymic nude mice by implantation of HCT 116 cells and subsequently treated by a single intratumoral injection of one of the recombinant TPVs. Histological examination showed a common neoplastic cell type and a range of immune cell infiltration, necrosis, and tumor cell organization. Significant regression was seen in tumors treated with virus TPV/Δ2L/Δ66R/fliC, and to a lesser extent the recombinants TPV/Δ2L and TPV/Δ66R. Our results suggest that oncolytic recombinants of the TPV armed with activators of the innate immune response may be effective virotherapeutic agents for colorectal cancers in humans and should be explored further to fully realize their potential.

The tanapoxvirus 15L protein is a virus-encoded neuregulin that promotes viral replication in human endothelial cells.

Studies on large double-stranded DNA (dsDNA) viruses such as poxviruses have been helpful in identifying a number of viral and cellular growth factors that contribute to our broad understanding of virus-host interaction. Orthopoxviruses and leporipoxviruses are among the most studied viruses in this aspect. However, tanapoxvirus (TPV), a member of the genus Yatapoxvirus, still remains largely unexplored, as the only known hosts for this virus are humans and monkeys. Here, we describe the initial characterization of an epidermal growth factor (EGF)-like growth factor mimicking human neuregulin from TPV, expressed by the TPV-15L gene. Assays using a baculovirus-expressed and tagged TPV-15L protein demonstrated the ability to phosphorylate neuregulin receptors. Neuregulins represent a large family of EGF-like growth factors that play important roles in embryonic endocardium development, Schwann and oligodendrocyte survival and differentiation, localized acetylcholine receptor expression at the neuromuscular junction, and epithelial morphogenesis. Interestingly, certain neuregulin molecules are able to target specific tissues through interactions with heparin sulfate proteoglycans via an immunoglobulin (Ig)-like domain. Analyses of TPV-15L revealed no Ig-like domain, but it retains the ability to bind heparin and phosphorylate neuregulin receptors, providing compelling evidence that TPV-15L is a functional mimetic of neuregulin. TPV-15L knockout virus experiments demonstrate that the virus replicates in human umbilical vein endothelial cells less efficiently than wild-type TPV-Kenya, indicating that this is a nonessential protein for virus viability but can serve a stimulatory role for replication in some cultured cells. However, the precise role of this protein in host-virus interaction still remains to be deduced.

Suppression of neointimal hyperplasia following angioplasty-induced vascular injury in pigs infected with swinepox virus.

Many patients suffering from angina pectoris are treated with percutaneous coronary intervention (PCI) and quickly develop angiographic renarrowing, or restenosis, at the site of PCI treatment. Restenosis is thought to arise from the combinatorial activation of thrombotic and inflammatory responses. The inflammatory response responsible for restenosis is also thought to involve the activation of a cascade of serine proteases and its subsequent regulation. Poxviruses are known to possess a variety of immunomodulatory strategies, some of which target serine proteases, cytokines, and chemokines. To this end we evaluated whether systemic species-specific swinepox virus (SPV) infection could induce sufficient host-immune modulation to promote an anti-inflammatory and anti-proliferative effect, thereby preventing restenosis. Two groups of domestic feeder pigs were used - the first group was experimentally infected with SPV (n= 11) and the second group served as an uninfected control (n= 5). A week after infection, the pigs were anesthetized and percutaneous transluminal coronary angioplasty (PTCA) was performed in the left anterior descending coronary artery using X-ray fluoroscopy to visualize the balloon and record angiograms. Three weeks post infection, the pigs were euthanized and balloon angioplasty injured arteries were harvested and examined. We observed a statistically significant reduction of restenosis in SPV-infected pigs (p = 0.05) compared to control pigs and conclude that systemic swinepox virus infection causes sufficient host immune suppression to significantly reduce restenosis in pigs after balloon angioplasty injury.

Tumor necrosis factor inhibitors from poxviruses with an emphasis on tanapoxvirus-2L protein.

Viruses have evolved strategies to counteract host defenses. Some tactics employ viral proteins to neutralize host immune effector proteins such as cytokines, chemokines and their receptors, which help coordinate the host responses against the virus. Tumor necrosis factor (TNF) is one of the crucial pro-inflammatory/anti-viral cytokines involved in inflammatory and autoimmune diseases. Poxvirus anti-immune proteins represent some of the most complex and efficient mechanisms of regulating TNF and its pathological effects. These proteins have considerable potential for treating TNF-related diseases. Here we discuss two major classes of poxvirus-TNF inhibitors focusing on the tanapoxvirus (TPV)-2L protein, previously called TPV-gp38. TPV-2L has been shown to interact and biologically neutralize human (h)TNF, and has been indirectly associated with the inhibition of other cytokines (hIFN-γ, hIL-2 and hIL-5). The TPV-2L protein alone has been expressed, purified and shown to bind with high affinity to hTNF, but lacked binding to the other cytokines. Further studies identified sequential binding of hß2-microglobulin and hα2-macroglobulin to TPV-2L. The ability of a single viral protein to form multi-protein complexes suggests that TPV might also possess other novel strategies of evading the immune system. Reviewed here are patented poxvirus TNF-binding proteins and their genes to evaluate their potential therapeutic value.

Interaction of human TNF and beta2-microglobulin with Tanapox virus-encoded TNF inhibitor, TPV-2L.

Tanapox virus (TPV) encodes and expresses a secreted TNF-binding protein, TPV-2L or gp38, that displays inhibitory properties against TNF from diverse mammalian species, including human, monkey, canine and rabbit. TPV-2L also has sequence similarity with the MHC-class I heavy chain and interacts differently with human TNF as compared to the known cellular TNF receptors or any of the known virus-encoded TNF receptor homologs derived from many poxviruses. In order to determine the TNF binding region in TPV-2L, various TPV-2L C-terminal truncations and internal deletions were created and the muteins were expressed using recombinant baculovirus vectors. C-terminal deletions from TPV-2L resulted in reduced binding affinity for human TNF and specific mutants of TNF that discriminate between TNF-R1 and TNF-R2. However, deletion of C-terminal 42 amino acid residues totally abolished the binding of human TNF and its mutants. Removal of any of the predicted internal domains resulted in a mutant TPV-2L protein incapable of binding to human TNF. Deletion of C-terminal residues also affected the ability of TPV-2L to block TNF-induced cellular cytotoxicity. In addition to TNF, TPV-2L can also form complexes with human beta2-microglobulin to form a novel macromolecular complex. In summary, the TPV-2L protein is a bona fide MHC-1 heavy chain family member that binds and inhibits human TNF in a fashion very distinct from other known poxvirus-encoded TNF inhibitors, and also can form a novel complex with the human MHC-1 light chain, beta2-microglobulin.

TGF-beta signaling in dendritic cells is a prerequisite for the control of autoimmune encephalomyelitis.

One unresolved issue in immune tolerance is what prevents self-reactive T cells from activation. In this study, we used a transgenic mouse model of targeted functional inactivation of TGF-betaR signaling in CD11c(+) cells (CD11c(dnR) mice) and showed a direct impact on the development of experimental autoimmune encephalomyelitis (EAE). We found that MOG(35-55) immunization of CD11c(dnR) mice results in strong inflammation of CNS, high frequency of T cells in CNS, increased levels of T helper 1 (T(H)1) and T(H)17 cytokines in the periphery, and lack of remission from EAE. Once crossed with mice prone to autoimmunity, double-transgenic CD11c(dnR)Mog(TCR) mice revealed a spontaneous EAE-like disease characterized by early infiltration of activated myelin-specific T cells into CNS, activation of microglial cells, inflammation of CNS, dysfunction of locomotion, and premature death. We constructed chimeric mice and demonstrated that inactivation of TGF-betaR signaling in dendritic cells (DCs) results in augmented EAE-associated T cell responses. Our data provide direct evidence that TGF-beta can control autoimmunity via actions on DCs.

Microglia recognize double-stranded RNA via TLR3.

Microglia are CNS resident innate immune cells of myeloid origin that become activated and produce innate proinflammatory molecules upon encountering bacteria or viruses. TLRs are a phylogenetically conserved diverse family of sensors for pathogen-associated molecular patterns that drive innate immune responses. We have recently shown that mice deficient in TLR3 (TLR3(-/-) mice) are resistant to lethal encephalitis and have reduced microglial activation after infection with West Nile virus, a retrovirus that produces dsRNA. We wished to determine whether microglia recognize dsRNA through the TLR3 pathway. In vitro, murine wild-type primary cultured microglia responded to synthetic dsRNA polyinosinic-polycytidylic acid (poly(I:C)) by increasing TLR3 and IFN-beta mRNA and by morphologic activation. Furthermore, wild-type microglia dose dependently secreted TNF-alpha and IL-6 after poly(I:C) challenge, whereas TLR3(-/-) microglia produced diminished cytokines. Activation of MAPK occurred in a time-dependent fashion following poly(I:C) treatment of wild-type microglia, but happened with delayed kinetics in TLR3(-/-) microglia. As an in vivo model of encephalitis, wild-type or TLR3(-/-) mice were injected intracerebroventricularly with poly(I:C) or LPS, and microglial activation was assessed by cell surface marker or phospho-MAPK immunofluorescence. After intracerebroventricular injection of poly(I:C), microgliosis was clearly evident in wild-type mice but was nearly absent in TLR3(-/-) animals. When taken together, our results demonstrate that microglia recognize dsRNA through TLR3 and associated signaling molecules and suggest that these cells are key sensors of dsRNA-producing viruses that may invade the CNS.