T-independent response mediated by oncolytic tanapoxvirus recombinants expressing interleukin-2 and monocyte chemoattractant protein-1 suppresses human triple negative breast tumors.

Human triple negative breast cancer (TNBC) is an aggressive disease, associated with a high rate of recurrence and metastasis. Current therapeutics for TNBC are limited, highly toxic and show inconsistent efficacy due to a high degree of intra-tumoral and inter-tumoral heterogeneity. Oncolytic viruses (OVs) are an emerging treatment option for cancers. Several OVs are currently under investigation in preclinical and clinical settings. Here, we examine the oncolytic potential of two tanapoxvirus (TPV) recombinants expressing mouse monocyte chemoattractant protein (mMCP)-1 [also known as mCCL2] and mouse interleukin (mIL)-2, in human TNBC, in vitro and in vivo. Both wild-type (wt) TPV and TPV recombinants demonstrated efficient replicability in human TNBC cells and killed cancer cell efficiently in a dose-dependent manner in vitro. TPV/∆66R/mCCL2 and TPV/∆66R/mIL-2 expressing mCCL2 and mIL-2, respectively, suppressed the growth of MDA-MB-231 tumor xenografts in nude mice significantly, as compared to the mock-injected tumors. Histological analysis of tumors showed areas of viable tumor cells, necrotic foci and immune cell accumulation in virus-treated tumors. Moreover, TPV/∆66R/mIL-2-treated tumors showed a deep infiltration of mononuclear immune cells into the tumor capsule and focal cell death in tumors. In conclusion, TPV recombinants expressing mCCL2 and mIL-2 showed a significant therapeutic effect in MDA-MB-231 tumor xenografts, in nude mice through induction of potent antitumor immune responses. Considering the oncolytic potency of armed oncolytic TPV recombinants expressing mCCL2 and mIL-2 in an experimental nude mouse model, these viruses merit further investigation as alternative treatment options for human breast cancer.

A unique bivalent binding and inhibition mechanism by the yatapoxvirus interleukin 18 binding protein.

Interleukin 18 (IL18) is a cytokine that plays an important role in inflammation as well as host defense against microbes. Mammals encode a soluble inhibitor of IL18 termed IL18 binding protein (IL18BP) that modulates IL18 activity through a negative feedback mechanism. Many poxviruses encode homologous IL18BPs, which contribute to virulence. Previous structural and functional studies on IL18 and IL18BPs revealed an essential binding hot spot involving a lysine on IL18 and two aromatic residues on IL18BPs. The aromatic residues are conserved among the very diverse mammalian and poxviruses IL18BPs with the notable exception of yatapoxvirus IL18BPs, which lack a critical phenylalanine residue. To understand the mechanism by which yatapoxvirus IL18BPs neutralize IL18, we solved the crystal structure of the Yaba-Like Disease Virus (YLDV) IL18BP and IL18 complex at 1.75 Šresolution. YLDV-IL18BP forms a disulfide bonded homo-dimer engaging IL18 in a 2∶2 stoichiometry, in contrast to the 1∶1 complex of ectromelia virus (ECTV) IL18BP and IL18. Disruption of the dimer interface resulted in a functional monomer, however with a 3-fold decrease in binding affinity. The overall architecture of the YLDV-IL18BP:IL18 complex is similar to that observed in the ECTV-IL18BP:IL18 complex, despite lacking the critical lysine-phenylalanine interaction. Through structural and mutagenesis studies, contact residues that are unique to the YLDV-IL18BP:IL18 binding interface were identified, including Q67, P116 of YLDV-IL18BP and Y1, S105 and D110 of IL18. Overall, our studies show that YLDV-IL18BP is unique among the diverse family of mammalian and poxvirus IL-18BPs in that it uses a bivalent binding mode and a unique set of interacting residues for binding IL18. However, despite this extensive divergence, YLDV-IL18BP binds to the same surface of IL18 used by other IL18BPs, suggesting that all IL18BPs use a conserved inhibitory mechanism by blocking a putative receptor-binding site on IL18.

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.

Yaba-like disease virus chemokine receptor 7L, a CCR8 orthologue.

Yaba-like disease virus (YLDV) gene 7L encodes a seven-transmembrane G protein-coupled receptor with 53 % amino acid identity to human CC chemokine receptor 8 (CCR8). Initial characterization of 7L showed that this 56 kDa cell-surface glycoprotein binds human CCL1 with high affinity (Kd=0.6 nM) and induces signal transduction by activation of heterotrimeric G proteins and downstream protein kinases. Further characterization of YLDV 7L is presented here and shows that murine CC chemokines can induce G-protein activation via the 7L receptor, despite having a low binding affinity for this receptor. In addition, when expressed by recombinant vaccinia virus (VACV), YLDV 7L was found on the outer envelope of VACV extracellular enveloped virus. The contribution of 7L to poxvirus pathogenesis was investigated by infection of mice with a recombinant VACV expressing 7L (vDeltaB8R-7L) and was compared with the outcome of infection by parental and revertant control viruses. In both intranasal and intradermal models, expression of 7L caused attenuation of VACV. The role of this protein in viral virulence is discussed.

Yaba-like disease virus protein 7L is a cell-surface receptor for chemokine CCL1.

Yaba-like disease virus (YLDV) genes 7L and 145R are located on opposite ends of the genome and are predicted to encode 7-transmembrane proteins (7-TM) that share 53 and 44 % amino acid identity, respectively, to human CC chemokine receptor 8 (hCCR8). In this report, we demonstrate that early after infection with YLDV, cells acquire the ability to bind human CCL1. By expression of genes 7L and 145R in vaccinia virus, we demonstrated that each protein is glycosylated and is exposed on the cell surface with the N terminus outside the cell. Protein 7L, but not 145R, is able to bind hCCL1 (K(d)=0.6+/-0.13 nM) and couple to heterotrimeric G-proteins and to activate the extracellular signal-regulated kinases (ERK1/2). 7L binds several chemokines including the viral chemokines vMIPI and vMIPII and hCCL7/MCP3. This binding seems species-specific as 7L does not bind the murine orthologues of CCL1 and CCL7 in the assays used. This represents the first example of a poxviral 7-TM chemokine receptor that has functional interactions with a human chemokine.

Multiple anti-cytokine activities secreted from tanapox virus-infected cells.

Tanapox virus (TPV) produces a mild disease in humans characterized by transient fever, one or more nodular skin lesions and regional lymphadenopathy. We demonstrate that TPV-infected cells, but not mock-infected cells, secrete an early 38 kDa glycopeptide that, unlike any other known protein, binds to human (h) interferon-gamma, hIL-2 and hIL-5. In concomitant experiments this polypeptide failed to bind to hIL-1 alpha, hIL-3, hIL-4, hIL-6, hIL-7, hIL-8 or hIL-10. Inhibition of hIL-2 and hIL-5 biological activities were demonstrated using a hIL-2-dependent mouse T cell line (HT-2) and a hIL-5-dependent erythroleukemia cell line (TF-1), respectively. The 38 kDa polypeptide also inhibited the bioactivity of interferon-gamma. Taken together, our results suggest that TPV has evolved multiple pathways to disarm both TH1 cell-mediated (IL-2 and interferon-gamma) and TH2-associated (IL-5) immune responses for its infectivity with remarkable genetic economy.