The human T lymphotropic virus type I (HTLV-I) is the etiologic agent of a chronic progressive myelopathy known as HTLV-I associated myelopathy/tropical spastic paraparesis (HAM/TSP), a disease clinically similar to the chronic progressive form of multiple sclerosis (MS). An understanding of the pathogenesis of a neurologic disease with a known viral etiology (HTLV-I and HAM/TSP) will aid in defining similar mechanisms of pathogenesis in MS, a disease of unknown etiology in which viruses have been suspected to play a role. Additionally, other viruses have also been associated with MS and particular attention has recently focused on the human herpesvirus type 6 (HHV-6). Investigative research on HHV-6 and MS have led to the study of other disorders that may also be associated with this virus including epilepsy, neurological complications following allogeneic bone marrow transplant, and encephalitis. Areas of research addressing these neurovirological and neuroimmunological issues consist of: I) The host immune response to viruses from patients with HAM/TSP and MS with particular focus on cytotoxic virus-specific CD8+ and CD4+ CD25+ T regulatory cells; II) The role of HHV-6 in the pathogenesis of MS and other chronic neurological disorders of the central nervous system; III) The translation of an understanding of these basic virological and immunological mechanisms associated with viruses associated with neurologic disease to immunotherapeutic strategies for the treatment of these disorders. The major findings of these studies have been: 1) Increased HTLV-I specific CD8+ cells have been shown to be elevated in the peripheral blood and CSF of HAM/TSP patients and directly proportional to the amount of HTLV-I proviral DNA and RNA. These antigen-specific T cells are considered to be immunopathogenic and may be directly involved in virus-host interactions in the CNS. Direct observations of these antigen-specific CD8+ T cells in spinal cord sections of HAM/TSP have been demonstrated and support a role for these cells in the pathogenesis of this disorder. 2) Recently, dysregulation of the newly described cytokine, interleukin-15 (IL-15), has been implicated in the pathogenesis of a number of immune mediated diseases including HAM/TSP. Collaborative research by the Viral Immunology Section, NINDS and the Metabolism Branch, NCI suggests that up-regulation of IL-15 may sustain the persistent expansion of virus-specific CD8+ T cells in HAM/TSP. A phase I clinical trial for the treatment of HAM/TSP has been FDA approved that blocks the action of IL-15 using a novel humanized monoclonal antibody, Hu MiK-beta-1. We will assess the effects of intravenously administered Hu-MiK-beta-1 on the cellular immune response in patients with HAM/TSP, with particular focus on virus-specific memory CD8+ T cells. Secondary outcomes to be measured will be clinical responses, including toxicity, and the effect on CD4+CD25+ T regulatory cells. As IL-15 over expression has been demonstrated in patients in a wide variety of autoimmune disorders including, rheumatoid arthritis, inflammatory bowel disease, multiple sclerosis and psoriasis, the successful application of Hu MiK-beta-1 in HAM/TSP has significant and broad therapeutic implications. 3) An understanding of how HTLV-I infects cells is an important area of investigation that may also lead to therapeutic strategies to intervene in HTLV-I associated disease. Recently, the glucose transporter type 1 (GLUT1) was reported to be the main binding receptor for HTLV-I. However, we have demonstrated that while overexpression of GLUT1 increased cell-cell transmission of HTLV-1, it did not increase either the binding of soluble HTLV-1 surface glycoproteins or the entry of HTLV-1 virions. Rather, we provide evidence that the majority of binding to the involved interactions with heparin surface proteoglycans (HSPG). These results indicate that both GLUT1 and HSPGs play an important role in HTLV infection. 4) CD4+CD25+ regulatory T cells are important in the maintenance of immunological self-tolerance and in the prevention of autoimmune diseases. We have demonstrated that in HTLV-I infected CD4+CD25+ T cells of patients with HAM/TSP the expression of the forkhead transcription factor Foxp3, a specific marker of regulatory T cells, was lower than that of healthy individuals. We have shown reduced protein expression of Fox-P3 positive T regulatory cells in patients with HAM/TSP. We also have demonstrated that HTLV-I tax had a direct inhibitory effect for the Foxp3 expression and inhibited the regulatory function of these cells. We have defined a number of transcriptional mechanisms that control human FoxP3 that are directly related control by HTLV-I tax. These results suggest that direct human retroviral infection of CD4+CD25+ T cells may be associated with the pathogenesis of HTLV-I associated neurologic disease through the dysregulation of CD4+CD25+ regulatory T cells. 5) An understanding of the role of regulatory T cells in HAM/TSP had led to the analysis of this T cell subset in patients with MS. Using assays and approaches developed in the HTLV-I - HAM/TSP system, we cannot demonstrate an alteration in the T regulatory cells (either in number or in function) in the peripheral blood of MS patients compared to healthy controls. However, in a clinical trial with humanized anti-IL2 receptor (daclizumab) in MS, we have observed a significant reduction in this important regulatory population in all patients treated. In addition, a surprising number of daclizumab-treated MS patients have manifested skins lesions and attempts are currently underway to determine if this clinical observation is related to the disregulation of T regulatory cells. 6) Using a proteomic approach to generate disease specific protein profiles (Surface Enhanced Laser Desorption Ionization Time-Of-Flight Mass Spectroscopy (SELDI)) we have defined phenotypic ?signatures? within HTLV-1-infected sera that can discriminate HTLV-I infected patients with neurologic disease from patients with HTLV-I associated malignancies. These protein ?fingerprint? changes can be used for diagnostics, prognostics and early detection of disease. We have extended this work from HAM/TSP to MS and have begun an extensive proteomic profile analysis of sera from patients with multiple sclerosis and controls including healthy individuals and patients with other inflammatory and neurologic disease. Discrete protein profiles have been obtained that distinguish these groups. Bioinformatical and proteomic analytical approaches are being used to determine if signatures can be defined that discriminate severity and type of disease. 7) We continue to extend our work on the detection of HHV-6 from brain resections of patients with mesial temporal lobe epilepsy and patients with neurologic complications following allogeneic bone marrow transplants. Our observations that HHV-6 variant B can be demonstrated in epilepsy CNS tissue continue to be supported with larger number of samples. We have isolated this virus from explanted primary astrocyte cell cultures and have shown a dysregulation of glutamate uptake in HHV-6 infected astrocyte cell lines. As there are a number of antiviral HHV-6 compounds currently available we have shown that these drugs have different sensitivities in HHV-6 infected glial cells compared to virus-infected lymphocytes. These data suggest that different treatment strategies should be considered when trying to clear this virus from the periphery or the CNS.
Showing the most recent 10 out of 66 publications
