Critical Residues in the CC′ Ridge of the Human Nectin1 Receptor V Domain Enable Herpes Simplex Virus Entry into the Cell and Act Synergistically with the Downstream Region

AbstractThe site on nectin1 receptor required for herpes simplex virus (HSV) entry into the cell was previously mapped to the 64–94 region, encompassing the predicted CC′C" region of the immunoglobulin V domain. Within it lies a minimal HSV entry site (residues 77–94). Here we transferred the 65–76 region (C strand and CC′ loop) and portions, or single amino acids, thereof to nectin2, a homolog nonfunctional for wt HSV-1 entry. Replacement of the seven- or of three-amino-acid-long stretches from nectin1 to nectin2 (amino acids 69–75, 69–71, or 72–75) transferred wt HSV-1 and BHV-1 entry activity and enhanced HSV-2, PrV, and HSV-HSV(U21) entry to levels observed with nectin1. Thus, the CC′ ridge is sufficient to mediate wt HSV entry at a reduced level and responsible for the wide virus range of the receptor. Altogether the HSV entry site appears to be composed of contiguous synergistic regions, 64–76 and 77–94, each independently capable of mediating virus entry at reduced efficiency

The simultaneous insertion of two ligands in gD for the cultivation of oncolytic HSVs in non-cancer cells and the retargeting to cancer receptors

Insertion of a single chain antibody (scFv) to HER2 (human epidermal growth factor receptor 2) in gD, gH, or gB gives rise to herpes simplex viruses (HSVs) specifically retargeted to HER2-positive cancer cells, hence in highly specific non-attenuated oncolytic agents. Clinical grade virus production can not rely on cancer cells. Recently, we developed a double retargeting strategy whereby gH carries the GCN4 peptide for retargeting to the non-cancer producer Vero-GCN4R cell line, and gD carries the scFv to HER2 for cancer retargeting. Here, we engineered double retargeted recombinants, which carry both the GCN4 peptide and the scFv to HER2 in gD. Novel, more advantageous detargeting strategies were devised, so as to optimize the cultivation of the double-retargeted recombinants. Nectin1 detargeting was achieved by deletion of aa 35-39, 214-223, or 219-223, and replacement of the deleted sequences with one of the two ligands. The latter two deletions were not attempted before. All recombinants exhibited the double retargeting to HER2 and to the Vero-GCN4R cells, as well as detargeting from the natural receptors HVEM and nectin1. Of note, some recombinants grew to higher yields than others. The best performing recombinants carried a gD deletion as small as 5 amino acids, and grew to titers similar to those exhibited by the singly retargeted R-LM113, and by the non-retargeted R-LM5. This study shows that double retargeting through insertion of two ligands in gD is feasible and, when combined with appropriate detargeting modifications, can result in recombinants highly effectivein vitroandin vivo.IMPORTANCEThere is increasing interest in oncolytic viruses, following FDA and EMA approval of the oncolytic HSV OncovexGM-CSF, and, mainly, because they greatly boost the immune response to the tumor and can be combined with immunotherapeutic agents, particularly immune checkpoint inhibitors. A strategy to gain high cancer specificity and avoid virus attenuation is to retarget the virus tropism to cancer-specific receptors of choice. However, cultivation of retargeted oncolytics in cells expressing the cancer receptor may not be approvable by regulatory agencies. We devised a strategy for their cultivation in non-cancer cells. Here, we describe a double retargeting strategy, based on the simultaneous insertion of two ligands in gD, one for retargeting to a producer, universal Vero cell derivative, one for retargeting to the HER2 cancer receptor. These insertions were combined with novel, minimally-disadvantageous detargeting modifications. The current and accompanying studies teach how to best achieve the clinical-grade cultivation of retargeted oncolytics

Prominent role of the Ig-like V domain in trans-interactions of nectins. Nectin3 and nectin 4 bind to the predicted C-C'-C"-D beta-strands of the nectin1 V domain.

Nectins form a family of integral molecules that belong to the immunoglobulin superfamily. Their ectodomain is made of three Ig-like domains (V, C, C). This family comprises at least five members, namely nectin1, -2, -3, -4, and poliovirus receptor (PVR), that are involved in different physiological and pathological processes. (i) Nectins are adhesion molecules localized at adherens junctions in epithelial cells. (ii) Some nectins act as poliovirus or alpha-herpesvirus receptors (nectin1). (iii) Nectin1 mutations are involved in orofacial developmental abnormalities in humans. Adhesion properties of nectins are mediated by Ca(2+)-independent homophilic and heterophilic processes through ectodomain trans-interactions. We have described a nectin trans-hetero-interaction network: nectin3 binds to nectin1, nectin2, and PVR; nectin1 also binds to nectin4. In the present study we compared the affinities of the different trans-interactions mediated by nectin1. We found that the K(D) of nectin1/nectin3 and nectin1/nectin4 interactions is 1 and 100 nm, respectively, whereas the K(D) of the nectin1-mediated homophilic interaction is 1 microm. We show that nectin1/nectin3 and nectin1/nectin4 trans-hetero-interactions were mediated through trans V to V domain interactions, whereas C domains contributed to increase the affinity of the interaction. Nectin3 and nectin4 share a common binding region in the nectin1 V domain: (i) nectin3 strongly competed with nectin4 binding, (ii) nectin3 and nectin4 binding to nectin1 was reduced by a number of monoclonal antibodies directed against the nectin1 V domain, and (iii) the glycoprotein D of herpes simplex virus-1 that binds to the V domain of nectin1 reduced nectin3 and nectin4 binding. Finally, using chimeric nectin1/PVR receptors where PVR V domain beta-strands were substituted with the corresponding regions of nectin1, the nectin3 and nectin4 minimal binding region on nectin1 V domain was mapped to the C-C'-C"-D beta-strands

Persistence of Human Herpesvirus 7 in Normal Tissues Detected by Expression of a Structural Antigen

Human herpesvirus 7 (HHV-7) infection in histologically normal human tissues was investigated by immunohistochemical detection of the 85-kDa tegument phosphoprotein (pp85) encoded by the U14 gene. So far, two cell types were recognized as sites of HHV-7 infection in vivo: CD4+ T lymphocytes, believed to be the site of latent infection, and epithelial cells of salivary glands, the site of productive infection and viral shedding. Unexpectedly, cells expressing the HHV-7 structural antigen were detectable in lungs, skin, and mammary glands. Morphologically and phenotypically, they were distinct from lymphocytes. Liver, kidney, and tonsils were positive, although the number of HHV-7-positive cells was low. Large intestine, spleen, and brain were negative. Different from the current notion of the state of HHV-7 in humans, the results show that a variety of tissues harbor cells at a late stage of infection and suggest that HHV-7 causes a persistent rather than a true latent infectio

Efficacy of Systemically Administered Retargeted Oncolytic Herpes Simplex Viruses—Clearance and Biodistribution in Naïve and HSV-Preimmune Mice

We investigated the anticancer efficacy, blood clearance, and tissue biodistribution of systemically administered retargeted oncolytic herpes simplex viruses (ReHVs) in HSV-naive and HSV-preimmunized (HSV-IMM) mice. Efficacy was tested against lung tumors formed upon intravenous administration of cancer cells, a model of metastatic disease, and against subcutaneous distant tumors. In naive mice, HER2- and hPSMA-retargeted viruses, both armed with mIL-12, were highly effective, even when administered to mice with well-developed tumors. Efficacy was higher for combination regimens with immune checkpoint inhibitors. A significant amount of infectious virus persisted in the blood for at least 1 h. Viral genomes, or fragments thereof, persisted in the blood and tissues for days. Remarkably, the only sites of viral replication were the lungs of tumor-positive mice and the subcutaneous tumors. No replication was detected in other tissues, strengthening the evidence of the high cancer specificity of ReHVs, a property that renders ReHVs suitable for systemic administration. In HSV-IMM mice, ReHVs administered at late times failed to exert anticancer efficacy, and the circulating virus was rapidly inactivated. Serum stability and in vivo whole blood stability assays highlighted neutralizing antibodies as the main factor in virus inactivation. Efforts to deplete mice of the neutralizing antibodies are ongoing

The Egress of Herpesviruses from Cells: the Unanswered Questions

The presence of herpes simplex virus (HSV) capsids attached to invaginated cytoplasmic vesicles led Stackpole (15) to propose that capsids undergo envelopment at the inner nuclear membrane, de-envelopment at the outer nuclear membrane, and finally reenvelopment at cytoplasmic membranes. Over the years this model attracted numerous adherents principally on the basis of evidence that the extracellular virions lack proteins present in intracellular virions accumulating in the perinuclear space (11, 14). An alternative hypothesis was recently presented by Wild et al. (17) on the basis of the observation that nuclear pores become grossly enlarged in cells infected with wild-type virus. Two hypotheses have emerged. The first is that HSV virions undergo envelopment at the inner nuclear membrane, de-envelopment at the outer nuclear membrane or extensions thereof, and reenvelopment in cytoplasmic organelles (double envelopment model). The second hypothesis is that virions mature and egress the cell via two pathways. A minority, primarily early in infection, becomes enveloped at the inner nuclear membrane and is transported in vesicles to the extracellular space. The majority enters the cytoplasm late in infection through enlarged nuclear pores and becomes enveloped at cytoplasmic membranes, mainly Golgi and post-Golgi. Challenges to existing theories are the fabric of science, and no other recent controversy has generated as much discussion as the challenge to the double envelopment hypothesis. The letter by Mettenleiter and Minson and the response by Wild (10) sustain the respective models but do not define the problems associated with each model or the data necessary to reaffirm or reject them

A Heptad Repeat in Herpes Simplex Virus 1 gH, Located Downstream of the α-Helix with Attributes of a Fusion Peptide, Is Critical for Virus Entry and Fusion

Entry of herpes simplex virus 1 (HSV-1) into cells occurs by fusion with cell membranes; it requires gD as the receptor binding glycoprotein and the trigger of fusion, and the trio of the conserved glycoproteins gB, gH, and gL to execute fusion. Recently, we reported that the ectodomain of HSV-1 gH carries a hydrophobic α-helix (residues 377 to 397) with attributes of an internal fusion peptide (T. Gianni, P. L. Martelli, R. Casadio, and G. Campadelli-Fiume, J. Virol. 79:2931-2940, 2005). Downstream of this α-helix, a heptad repeat (HR) with a high propensity to form a coiled coil was predicted between residues 443 and 471 and was designated HR-1. The simultaneous substitution of two amino acids in HR-1 (E450G and L453A), predicted to abolish the coiled coil, abolished the ability of gH to complement the infectivity of a gH-null HSV mutant. When coexpressed with gB, gD, and gL, the mutant gH was unable to promote cell-cell fusion. These defects were not attributed to a defect in heterodimer formation with gL, the gH chaperone, or in trafficking to the plasma membrane. A 25-amino-acid synthetic peptide with the sequence of HR-1 (pep-gH(wt25)) inhibited HSV replication if present at the time of virus entry into the cell. A scrambled peptide had no effect. The effect was specific, as pep-gH(wt25) did not reduce HSV-2 and pseudorabies virus infection. The presence of a functional HR in the HSV-1 gH ectodomain strengthens the view that gH has attributes typical of a viral fusion glycoprotein