Simian Varicella Virus Infection, Latency, and Reactivation
The Varicella-zoster virus (VZV) causes clinically mild chickenpox in children and then becomes latent in ganglionic neurons. However, in older or immunocompromised individuals showing increasing loss of T-cell-mediated immunity with age results in virus reactivation, manifesting as zoster or shingles, primarily in the elderly. Zoster is a huge health issue, affecting approximately one million Americans each year. Neurological complications of zoster include postherpetic neuralgia, myelitis, meningoencephalitis, retinitis, vasculopathy and multiple ocular disorders. Zostavax immunization is highly successful, reducing zoster by 51% and neurological complication by 66%. Yet even if every person >60 yr old were vaccinated, there will still be at least 500,000 zoster patients, nearly half of whom will experience neurological complication. VZV only causes disease in humans and testing is limited by overall inability to obtain tissues.
Our laboratory has shown the nonhuman primate counterpart virus, simian varicella virus (SVV) infects monkeys, shows clinical, virological and pathological features of acute disease, latency and reactivation that parallel VZV infection in humans, thus providing an exceptional model to study the molecular pathogenesis of varicella infection. In the past five years, we showed that SVV becomes latent in ganglionic neurons and can be experimentally reactivated by immunosuppression. Yet how SVV spreads during primary infection and reactivation is unknown. Our work has shown that after primary exposure, virus infects alveolar macrophages and/or dendritic cells in lungs and memory T cells in blood. Later SVV-infected T cells were found in ganglia, lymph nodes and in skin lesions close to blood vessels. Early after zoster, we also found that ganglia contained few SVV antigen-positive neurons, and CD8 T-cell infiltration correlated with CXCL10 transcript levels but not with SVV antigen expression, whereas lymph nodes contained SVV DNA and abundant viral antigen. Because lung, lymph node and ganglia are infected before skin rash appears, and because the most pronounced histopathological changes have been found in lungs and lymph nodes, our current studies are focusing on the delineation of virus trafficking of the virus through these organs and the cells, molecular signals, and routes, whether hematogenous or trans-axonal, involved in virus dissemination. We are also testing immunomodulatory therapeutics for controls of infection are also underway. In additional collaborations, chimeric varicella viruses are being tested to delineate genes responsible for varicella latency, and ultimately, control of reactivation.
Preclinical Vaccine Efficacy Trials for Simian Varicella-SIV Vaccine
A safe and effective vaccine is needed to control the worldwide AIDS epidemic caused by the human immunodeficiency virus (HIV). The Varicella-zoster virus (VZV) causes clinically mild chickenpox in children and then becomes latent in ganglionic neurons. In 1995, the live attenuated VZVOka vaccine, VARIVAX®, was FDA approved and licensed for routine childhood vaccination, in infants as early as 12months of age. VARIVAX® was shown to be highly immunogenic, very successful, with an efficacy rate of 90-95%, and extremely safe, even in some immunosuppressed patients, including HIV infected children with depressed CD4+ T cells. As such, this chickenpox virus is an attractive vaccine vector to express foreign antigens of other pathogens.
The simian varicella virus (SVV), closely related to VZV, causes a natural, varicella-like disease in nonhuman primates. We have developed a unique recombinant, experimental live-attenuated rSVV-SIV vaccine based on the SVV vector by inserting expressing SIV genes into the vector. Rhesus macaques immunized with this recombinant rSVV-SIV vaccine induced immune responses to SIV and reduced plasma SIV loads by as much as 100-fold following challenge with SIV by intravenous inoculation. The vaccine was shown to increase CD4+ proliferation, and SIV-specific polyfunctional CD4 and CD8 responses that were significantly associated with viral load reduction. Effector memory cells were suggested to be involved, similar to findings with another herpesvirus, CMV vector vaccine. These findings are significant as other studies have shown that similar reductions in SIV or HIV blood load may result in reduced disease transmission and progression.
Further studies are underway in my laboratory to ultimately establish a pediatric, live, attenuated recombinant varicella-AIDS vaccine protocol to vaccinate and produce virus specific immunity in infants and young children, at a time when their immune systems are extremely active and well before sexual maturity to protect them against mucosal HIV infection. We are currently conducting additional preclinical trials to further test the ability of this unique rSVV-SIV vaccine to be boosted with either SIV DNA or SIV protein and if, with extended rest prior to SIV challenge will 1) be safe, 2) promote maximum virus specific immune responses 3) provide protection against mucosal SIV challenge without increasing SIV susceptibility and 4) preexisting SVV immunity will not diminish the vaccine induced immune responses. We are currently testing how these Boost immunization strategies and mucosal SIV challenge in SVV naïve and SVV seropositive infant rhesus are affected by immunization route, virus specific immune responses, targeted epitopes, effects of preexisting SVV immunity, and protection against an SIV mucosal challenge. Such outcomes would hasten development of a counterpart rVZV-HIV vaccine, streamlined approvals and subsequent clinical human trials. A safe and effective pediatric rVZV-HIV vaccine would be a monumental AIDS prevention strategy, especially for children in areas of the world with endemic HIV infection.
Papillomavirus Infection and Progression to Cervical Cancer
Human papillomavirus (HPV) is one of the most common sexually transmitted infections and a significant cause of cervical, anal, and other cancers worldwide. Human immunodeficiency virus (HIV) positive men and women have a higher prevalence of HPV infections and HPV-associated disease and cancers than HIV negative individuals. Rhesus papillomavirus virus type 1 (RhPV-1), isolated from a metastatic rhesus penile cancer shares many genetic and phenotypic similarities to the highly carcinogenic human isolate HPV type 16.
Our laboratory conducted an infection study to characterize inoculum dose response with inoculation of Rhesus macaques each with increasing doses of RhPV1 as well as a control group inoculated with non-replicating RhPV1. Monthly evaluations were performed. After ten months, all 12 animals were intravenously inoculated with SIVmac239 and monitored clinically for an additional three months and RhPV1 and SIV viral loads were monitored for effects of SIV co-infection on pathology. Cervical infection of female rhesus macaques with RhPV1 resulted in 100% infection in all dose groups confirming the susceptibility of the rhesus macaque and utility of RhPV1 and RhPV1-SIV rhesus models for pathogenesis studies. Clinical evidence of RhPV1 virus-specific progressive cellular changes were observed for 33% of the high-dose RhPV1 inoculated animals. Animals receiving the mid and low dose RhPV1 inoculum were neither consistently infected nor showed progression to disease. Following SIV inoculation, viral loads and kinetics of co-infection were similar in all RhPV1 dose groups and showed losses of CD4 cells and critical immune functions by SIV infection. Progression of cervical cytological changes in the high-dose RhPV1 infected animals following SIV co-infection suggests that SIV immunodeficiency may contribute to RhPV1 progressive disease.
Respiratory Syncytial Virus Infection and Pathogenesis
Respiratory Syncytial virus (RSV) is a major cause of serious lower respiratory tract disease in infants and young children accounting for over 120,000 hospitalizations annually in the U.S. alone. No effective vaccine is available, and the current antiviral drug available has limited use. Severe disease, characterized by bronchiolitis or pneumonia, may be life-threatening, especially in infants between 6 weeks and 6 months of age. Hospitalized children with underlying heart and lung conditions are at the most risk for severe complications. Virtually all children are exposed to RSV by age 2. Immunity to RSV is not long-lasting and symptomatic re-infection is common at all ages. RSV is also a major cause of severe respiratory disease in older adults with over 78% of all RSV related deaths occurring in persons age 65 or older. Annually in the U.S., RSV is responsible for an estimated 180,000 hospitalizations and 11,000 – 17,000 deaths of older adults. Individuals in nursing homes, those with underlying respiratory and cardiopulmonary disease, cancer patients, and immunocompromised patients are at greatest risk for severe, even fatal, RSV infection. Even otherwise healthy elderly individuals are susceptible to debilitating RSV respiratory disease.
An effective RSV vaccine is currently unavailable, but is urgently needed since there is no effective antiviral agent against RSV. A formalin inactivated RSV vaccine given to children in the 1960's failed to induce protective immunity and actually led to an enhanced severe disease following natural exposure to RSV. The enhanced disease was associated with cell-mediated pulmonary inflammation and eosinophilia. Live, attenuated RSV vaccines have had limited success in human clinical trials and are hampered by safety concerns. Subunit vaccines, including those composed of purified RSV F and/or G, do not stimulate long-lasting immunity and may induce enhanced pulmonary disease after RSV challenge. A nonhuman primate model of RSV infection and disease has been developed in my laboratory and is being utilized to test various RSV vaccine candidates and therapeutics.
