Persistent infection with herpes simplex virus type 1 in an Ia antigen-positive murine macrophage cell line

Bioluminescent imaging reveals divergent viral pathogenesis in two strains of Stat1-deficient mice, and in αßγ interferon receptor-deficient mice

Pivotal components of the IFN response to virus infection include the IFN receptors (IFNR), and the downstream factor signal transducer and activator of transcription 1 (Stat1). Mice deficient for Stat1 and IFNR (Stat1(-/-) and IFNαßγR(-/-) mice) lack responsiveness to IFN and exhibit high sensitivity to various pathogens. Here we examined herpes simplex virus type 1 (HSV-1) pathogenesis in Stat1(-/-) mice and in IFNαßγR(-/-) mice following corneal infection and bioluminescent imaging. Two divergent and paradoxical patterns of infection were observed. Mice with an N-terminal deletion in Stat1 (129Stat1(-/-) (N-term)) had transient infection of the liver and spleen, but succumbed to encephalitis by day 10 post-infection. In stark contrast, infection of IFNαßγR(-/-) mice was rapidly fatal, with associated viremia and fulminant infection of the liver and spleen, with infected infiltrating cells being primarily of the monocyte/macrophage lineage. To resolve the surprising difference between Stat1(-/-) and IFNαßγR(-/-) mice, we infected an additional Stat1(-/-) strain deleted in the DNA-binding domain (129Stat1(-/-) (DBD)). These 129Stat1(-/-) (DBD) mice recapitulated the lethal pattern of liver and spleen infection seen following infection of IFNαßγR(-/-) mice. This lethal pattern was also observed when 129Stat1(-/-) (N-term) mice were infected and treated with a Type I IFN-blocking antibody, and immune cells derived from 129Stat1(-/-) (N-term) mice were shown to be responsive to Type I IFN. These data therefore show significant differences in viral pathogenesis between two commonly-used Stat1(-/-) mouse strains. The data are consistent with the hypothesis that Stat1(-/-) (N-term) mice have residual Type I IFN receptor-dependent IFN responses. Complete loss of IFN signaling pathways allows viremia and rapid viral spread with a fatal infection of the liver. This study underscores the importance of careful comparisons between knockout mouse strains in viral pathogenesis, and may also be relevant to the causation of HSV hepatitis in humans, a rare but frequently fatal infection.

Preclinical safety testing of DISC-hGMCSF to support phase I clinical trials in cancer patients

BACKGROUND

DISC-hGMCSF is a gH-deleted HSV-2 based vector expressing human GM-CSF that is being developed for cancer immunotherapy. To support first clinical use, a range of preclinical safety studies were performed using DISC-hGMCSF in addition to DISC-murine-GMCSF and the backbone vector, TA-HSV.

METHODS

The toxicity of the DISC vectors was assessed by repeated dose, neurovirulence and neuroinvasiveness studies in mice, and by safety studies in rabbits, guinea pigs and athymic nude mice. Studies were also conducted to determine whether the vector could establish latency in local ganglia in mice following intradermal injection, and whether it could reactivate from the latent state. The vector biodistribution following intravenous administration was also investigated in mice, using PCR to detect vector DNA.

RESULTS

The DISC vectors were essentially non-toxic in all the systems studied. No adverse reactions were seen in mice receiving four intravenous doses of DISC-mGMCSF and the results from studies of neurovirulence, neuroinvasiveness, local tolerance in rabbit, general safety in mice and guinea pigs and safety in athymic nude mice were consistent with DISC being unable to replicate and cause disease. The vector could establish latency in local ganglia in mice, but at low efficiency, and could not reactivate infectious virions. Following intravenous administration, vector DNA was widely distributed up to Day 28, but by Day 56 had disappeared from gonads and brain and was only found in blood and liver.

CONCLUSION

The panel of safety studies provided evidence that DISC-hGMCSF will be unable to replicate and cause disease, and has low toxicity in man. These data were presented to the Medicines Control Agency and the Gene Therapy Advisory Committee as part of the regulatory submissions for a clinical trial in melanoma patients. These submissions have been approved, and DISC-hGMCSF has now entered a phase I clinical trial in the UK by direct intratumoural injection.

Spontaneous shift of an HSV type 1 productive, persistently infected macrophage-like culture to a non-productive culture

A herpes simplex virus type 1 (HSV1) productive, persistently infected murine macrophage-like culture was obtained by infection at low multiplicity (0.001). Persistent cultures were characterized by spontaneously ceasing to produce infectious viruses after initial HSV1 production. A similar pattern of virus production was observed in cultures obtained by reinfection of the persistent macrophages with the original virus. Nonetheless, in persistent and reinfected cultures (17/18) which did not produce infectious viruses, viral proteins were detected by immunoblot, although their molecular weight, number and pattern differed among the cultures.

Latent infection of SCID mice with herpes simplex virus 1 and lethal cutaneous lesions in pregnancy

Some SCID mice survived primary infection with herpes simplex virus 1 without the development of peripheral lesions but established coculture-positive ganglionic latency when a low dose of a wild-type strain was inoculated intracutaneously. The latency was also evidenced by the development of the fatal zosteriform skin lesions and the isolation of the virus during pregnancy. We consider that the viral entry into neurons without successive replication, rather than the arrest of the lytic infection within the cells, is an important mechanism in the establishment of latency.

Stimulation of lymphokines in Jurkat cells persistently infected with vaccinia virus

The response of the human CD4+ T-cell line Jurkat to infection with vaccinia virus was investigated. Virus titers peaked approximately 3 to 4 days after infection, while cell growth paralleled that of uninfected cells, indicating that growth rates were not appreciably affected by viral infection. Results from plaque assays and fluorescence-activated cell sorter (FACS) analyses of virus antigens demonstrated that a persistent infection in which the percentage of infected cells and the virus titers fluctuated from passage to passage was established. Further characterization of the persistent infection revealed that the virus influences cellular functions. Induction of interleukin-2 (IL-2) and IL-2 receptor alpha (IL-2R alpha) in Jvac cells was shown by enzyme-linked immunosorbent assay and FACS analysis, respectively. Hybridization of cellular RNA with cloned probes confirmed the increased IL-2 expression and demonstrated that Jvac cells also expressed more IL-6 but not gamma interferon (IFN-gamma) or IL-1 beta. Dual-antibody staining and FACS analysis for vaccinia virus antigens and IL-2R alpha indicated that IL-2R alpha expression was restricted to the infected cells. Jvac cells were also resistant to superinfection, an additional proof that persistent infection elicited phenotypic changes in the cell population.

Characterization of glycoprotein C-negative mutants of herpes simplex virus type 1 isolated from a patient with keratitis

Recently three strains of herpes simplex virus type 1 (HSV-1), which did not react with Micro Trak Herpes (Syva Co.), were isolated by us from a patient with recurrent herpetic keratitis. In this study we characterized these strains of HSV-1 and found them to be HSV-1 gC- mutants which are very rare isolates from humans. The properties of the HSV-1 strains regarding plaque morphology on Vero cells and chick embryo fibroblasts and viral DNA analysis were the same as those of the usual HSV-1 strains. An immunofluorescence study using anti-gC-1 monoclonal antibody and SDS-PAGE analysis of radiolabeled viral glycoproteins showed that these strains are deficient in gC-1. They were virulent for mice and sensitive to acyclovir and bromovinyldeoxyuridine. Furthermore the infectivity of the strains was inactivated by complement though the phenomenon was not observed in the usual HSV-1 strains. This finding suggests that protection from damages by complement is an important function of gC. In keratitis the effects of complement are thought to be minimal because of the scanty blood supply and this may be the reason why these strains were isolated from the cornea.