HTLV-1 has been linked to a chronic, slowly progressive neurologic condition termed HTLV-1 associated spastic paraparesis or tropical spastic paraparesis (HAM/TSP) which affects about 1% of the infected individuals. The disease is thought to be due to a T cell viral induced immunopathological process. A high frequency of HTLV-1 specific CD8 T cells are found in patients with HAM/TSP. The immune system of patients infected with HTLV-1 appears to be dysregulated, and increased spontaneous T cell proliferation can be demonstrated in vitro. This is in part due to continuous antigenic stimulation and due to transactivation by the HTLV-1 encoded Tax protein of host immunomodulatory genes such as CD80, CD86, IL-2 and its receptor. In addition, an increased viral load has been demonstrated in symptomatic individuals compared to asymptomatic HTLV-1 carriers. It is thought that the local immune response to the virus within the central nervous system plays a role in the pathogenesis of progressive spastic encephalomyeloneuropathy of HAM/TSP. Therefore, reduction of spontaneous T cell proliferation and viral replication, as well as decrease of the compromise of the blood brain barrier may ameliorate the immune-mediated component of the process which leads to inflammatory destruction of nervous tissue in HAM/TSP.

Currently there is no clearly defined, effective treatment of patients with HAM/TSP. Corticosteroids are the mainstay of therapy but provide mostly only transient symptomatic relief. Treatment with human interferon has been shown to improve acute and chronic hepatitis through its anti-viral and cytostatic effects. Further, patients with relapsing-remitting multiple sclerosis, a disease thought to be at least in part a T cell mediated, immunopathological process, exhibit a marked reduction of the frequency of new lesion formation while on this medication. This latter effect may in part be explained by an anti-inflammatory effect of interferon which allows repair of the blood brain barrier. To evaluate possible role interferon beta in the treatment of HAM/TSP, we studied its effect on induction on regulatory factors and spontaneous in vitro proliferation of peripheral blood lymphocytes (PBLs) from HTLV-I infected individuals. Recombinant interferon beta-1b inhibited spontaneous proliferation of PBLs from asymptomatic HTLV-1 carriers and patients with HAM/TSP in a dose dependent manner and induced expression of interferon regulatory factor-2 which is associated with down regulation of proinflammatory cytokines such as interferon gamma. These preliminary results indicate that treatment with interferon-b may ameliorate the immune dysregulation induced by HTLV-1 and may have therapeutic effect in the treatment of HAM/TSP.

Twelve patients will be treated with administration of recombinant human interferon-beta1a. Assessment of efficacy will be based on reduction of spontaneous proliferation and proviral load. As a secondary measure the clinical response of patients will be evaluated. The study will entail an 8-week pretreatment period, a 28-week treatment phase with escalation of the interferon-beta1a dose, and a 12-week post-treatment phase. In cases where dose escalation leads to intolerable side-effects, patients will be continued at the highest tolerated dose of medication. Spontaneous proliferation, viral load, and clinical parameters will be determined monthly.