Pathogenesis of HTLV-I-associated inflammation: Exploration through therapeutic intervention

HAM/TSP is a chronic disease of the spinal cord, caused by a virus called HTLV-I. Worldwide approximately 20 million persons are infected, many in member states of the Commonwealth. Infection with HTLV-I is lifelong, and about 3% will develop this chronic debilitating disease, of which half will become wheelchair dependent. We, and others, have shown a strong and persistent immune response to HTLV-I in carriers and patients with HAM/TSP, but this fails to clear the virus. However, carriers with a low burden of virus in the blood have a low risk of developing disease. The immune response in these carriers seems better able to kill infected cells. A less efficient response is associated with a higher viral burden that drives the immune response with a resultant release of chemicals by the immune cells that inadvertently cause harm, most especially to cells in the spinal cord. Our understanding of HAM/TSP suggests that targeting the immune response should improve the health of our patients especially if the disease is diagnosed early. To identify the best type of treatment we are planning three studies of drugs that target the immune response in different ways. Each has been used in other inflammatory conditions but never before studied in HAM/TSP. We aim to study the extent and duration of the clinical response and to associatedthis with the different effects that the therapies have on the immune response and on the number of HTLV-I infected cells in the blood. This in turn will improve our knowledge and understanding of the disease and should lead to better therapy. Our results will be shared with our patients through a newsletter and made available on the clinic website.

Human T-Lymphotropic Virus Type I (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP)is a chronic, disabling, frequently painful condition for which no effective treatment has been found. As well as hosting HTLV-I infection, T-lymphocytes are implicated in the pathogenesis of HAM, having been demonstrated in circulating blood, cerebrospinal fluid and the spinal cord of patients, with the secretion of neurotoxic cytokines damaging by-stander cells the favoured hypothesis. Previous studies have investigated, amongst others, corticosteroids, vitamin C, interferons, heparin and nucleoside analogues without clear demonstration of more than transient improvement.
Successful therapy or prevention of HAM/TSP might be achieved by:
? Inhibiting T-cell activation (i.e. suppressing HTLV-I transcription, reducing HTLV-I replication and suppressing T-cell responsiveness to antigen)
? Targeting key mediators of HTLV-I-associated inflammation (i.e. inhibiting neurotoxic cytokines)
? Reducing the number of T-cells (i.e. depleting the substrate for infection as well as depleting the cells implicated in HTLV-I-associated inflammation)
We therefore propose to investigate three novel therapies for HAM.
First, ciclosporin A, to down regulate the immune response to HTLV-I both centrally and peripherally. Second, an anti-tumour necrosis factor antibody (Infliximab) to target a key neurotoxic cytokine. Third, the use of a humanised anti-CD52 monoclonal antibody (Campath-1H) to deplete T-lymphocytes and thereby reduce both the viral burden and the inflammatory response.
We will use these clinical studies to dissect the pathogenesis of HAM in vivo.
Each therapy will be administered in an open-label study of 6 - 10 patients for 12 months with a further 6 months follow-up. The outcome measures will be clinical, virological and immunological. Thus in addition to routine safety biochemisty and haematology, we will measure disability and markers of inflammation. We will explore viral burden, by quantify HTLV-I load in peripheral blood and CSF lymphocytes using real-time PCR, viral activity, by detection of HTLV Tax expression ex vivo, and viral replication, by detection of HTLV 2 LTR DNA circles in peripheral blood lymphocytes. We will access the effect of therapy on the cellular immune response using a lytic efficiency assay to determine HTLV-I specific cytotoxic T-lymphocyte function and ELISAs and ELIspots to quantify the cytokine response.
Results will be presented at international and national conferences and published in peer-reviewed journals. The results will be presented in suitable terminology for patients with HAM/TSP through a clinic website. We anticipate that the results will inform the design of a multicentre, randomised controlled trial of therapy for HAM/TSP.