VZV T cell-mediated immunity

Simian varicella virus infection of Chinese rhesus macaques produces ganglionic infection in the absence of rash

Varicella-zoster virus (VZV) causes varicella (chickenpox), becomes latent in ganglia along the entire neuraxis, and may reactivate to cause herpes zoster (shingles). VZV may infect ganglia via retrograde axonal transport from infected skin or through hematogenous spread. Simian varicella virus (SVV) infection of rhesus macaques provides a useful model system to study the pathogenesis of human VZV infection. To dissect the virus and host immune factors during acute SVV infection, we analyzed four SVV-seronegative Chinese rhesus macaques infected intratracheally with cell-associated 5 × 10³ plaque-forming units (pfu) of SVV-expressing green fluorescent protein (n = 2) or 5 × 10⁴ pfu of wild-type SVV (n = 2). All monkeys developed viremia and SVV-specific adaptive B- and T-cell immune responses, but none developed skin rash. At necropsy 21 days postinfection, SVV DNA was found in ganglia along the entire neuraxis and in viscera, and SVV RNA was found in ganglia, but not in viscera. The amount of SVV inoculum was associated with the extent of viremia and the immune response to virus. Our findings demonstrate that acute SVV infection of Chinese rhesus macaques leads to ganglionic infection by the hematogenous route and the induction of a virus-specific adaptive memory response in the absence of skin rash.

Varicella-zoster virus glycoproteins B and E are major targets of CD4+ and CD8+ T cells reconstituting during zoster after allogeneic transplantation

BACKGROUND

After allogeneic hematopoietic stem-cell transplantation patients are at increased risk for herpes zoster as long as varicella-zoster virus specific T-cell reconstitution is impaired. This study aimed to identify immunodominant varicella-zoster virus antigens that drive recovery of virus-specific T cells after transplantation.

DESIGN AND METHODS

Antigens were purified from a varicella-zoster virus infected cell lysate by high-performance liquid chromatography and were identified by quantitative mass spectrometric analysis. To approximate in vivo immunogenicity for memory T cells, antigen preparations were consistently screened with ex vivo PBMC of varicella-zoster virus immune healthy individuals in sensitive interferon-γ ELISpot assays. Candidate virus antigens identified by the approach were genetically expressed in PBMC using electroporation of in vitro transcribed RNA encoding full-length proteins and were then analyzed for recognition by CD4(+) and CD8(+) memory T cells.

RESULTS

Varicella-zoster virus encoded glycoproteins B and E, and immediate early protein 62 were identified in immunoreactive lysate material. Predominant CD4(+) T-cell reactivity to these proteins was observed in healthy virus carriers. Furthermore, longitudinal screening in allogeneic stem-cell transplantation patients showed strong expansions of memory T cells recognizing glycoproteins B and E after onset of herpes zoster, while immediate early protein 62 reactivity remained moderate. Reactivity to viral glycoproteins boosted by acute zoster was mediated by both CD4(+) and CD8(+) T cells.

CONCLUSIONS

Our data demonstrate that glycoproteins B and E are major targets of varicella-zoster virus specific CD4(+) and CD8(+) T-cell reconstitution occurring during herpes zoster after allogeneic stem-cell transplantation. Varicella-zoster virus glycoproteins B and E might form the basis for novel non-hazardous zoster subunit vaccines suitable for immunocompromised transplant patients.

Review: The neurobiology of varicella zoster virus infection

Varicella zoster virus (VZV) is a neurotropic herpesvirus that infects nearly all humans. Primary infection usually causes chickenpox (varicella), after which virus becomes latent in cranial nerve ganglia, dorsal root ganglia and autonomic ganglia along the entire neuraxis. Although VZV cannot be isolated from human ganglia, nucleic acid hybridization and, later, polymerase chain reaction proved that VZV is latent in ganglia. Declining VZV-specific host immunity decades after primary infection allows virus to reactivate spontaneously, resulting in shingles (zoster) characterized by pain and rash restricted to one to three dermatomes. Multiple other serious neurological and ocular disorders also result from VZV reactivation. This review summarizes the current state of knowledge of the clinical and pathological complications of neurological and ocular disease produced by VZV reactivation, molecular aspects of VZV latency, VZV virology and VZV-specific immunity, the role of apoptosis in VZV-induced cell death and the development of an animal model provided by simian varicella virus infection of monkeys.

Aciclovir and varicella-zoster-immunoglobulin in solid-organ transplant recipients

Clear recommendations for the management of acute varicella-zoster virus (VZV) infections for cases of significant exposure and the use of prophylactic drugs after solid-organ transplantation are missing due to the lack of evidence by prospective studies. Heterogeneity in patient groups, patient numbers, age groups, immunosuppressive regimens, timing, and dosage of aciclovir and/or varicella-zoster immunoglobulin (VZIG), pre-transplant vaccination or VZV wild-type infection and inconsistency of data make comparability of different studies impossible. Although the benefit of aciclovir and/or VZIG is uncertain in immunosuppressed children, prospective controlled double-blind studies are not feasible for ethical considerations as fatal cases with disseminating varicella disease are well known in these patient groups despite the use of aciclovir and/or VZIG, whereas severe side-effects of these drugs are rare. However, a reporting bias is likely as mainly severe or fatal cases might have been predominantly published or cases of successfully used aciclovir and/or VZIG in mild cases or in cases of breakthrough infections after vaccination. As neither VZIG prophylaxis nor treatment with intravenous aciclovir offers complete protection against severe VZV infection to immunosuppressed pediatric solid-organ transplant recipients, high priority should be given to vaccination against VZV prior to transplantation, and, most importantly, in their close contact persons. Clinical observations suggest that only assessment of humoral immunity together with cellular immunity may allow predication about protection in exposed patients.

Efficacy of live zoster vaccine in preventing zoster and postherpetic neuralgia

Declining cell-mediated immunity to varicella zoster virus (VZV) in elderly individuals results in virus reactivation manifest by zoster (shingles) and postherpetic neuralgia (PHN). To prevent virus reactivation, a new VZV vaccine (Zostavax; Merck) that boosts cell-mediated immunity to VZV was developed. The 3-year Shingles Prevention Study showed that Zostavax significantly reduced burden of disease because of zoster and PHN. Despite its cost-effectiveness for adults aged 65-75 years, as determined in the United States, Canada and UK, <2% of immunocompetent adults over age 60 years in the United States were immunized in 2007. This was because of a combination of lack of patient awareness of the vaccine, physicians' uncertainty about the duration of protection and different cost-sharing plans for immunization. Nevertheless, zoster vaccine is safe, effective and highly recommended for immunization of immunocompetent individuals over age 60 years with no history of recent zoster.

Prevention strategies for herpes zoster and post-herpetic neuralgia

Impairment of varicella zoster virus (VZV)-specific cell-mediated immunity, including impairment due to immunosenescence, is associated with an increased risk of developing herpes zoster (HZ), whereas levels of anti-VZV antibodies do not correlate with HZ risk. This crucial role of VZV-specific cell-mediated immunity suggests that boosting these responses by vaccination will be an effective strategy for reducing the burden of HZ. Other strategies focus on preventing the major complication of HZ--post-herpetic neuralgia. These strategies include pre-emptive treatment with drugs such as tricyclic antidepressants, anticonvulsants and analgesics.