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The lymphocytes in peripheral blood and cerebrospinal fluid of patients with chronic progressive multiple sclerosis (MS) were characterized with monoclonal antibodies to surface antigens of T cells, helper/inducer T cells and suppressor/cytotoxic T cells. The influence of cyclophosphamide treatment on these immune parameters was investigated. Compared to healthy persons, the mononuclear cell fraction of the peripheral blood of patients with chronic progressive MS consisted of normal %s of T cells and helper/inducer T cells, but decreased %s of suppressor/cytotoxic T lymphocytes. Intensive as well as chronic treatment of MS patients with cyclophosphamide resulted in a decline in the %s of T cells and helper/inducer T cells, whereas the %s of suppressor/cytotoxic T cells returned to normal. In cerebrospinal fluid, cyclophosphamide also induced a relative decrease in the % of helper/inducer T cells and an increase in the % of suppressor/cytotoxic T cells compared to untreated MS patients. Intensive as well as chronic therapy with cyclophosphamide both led to a significant decrease in the absolute number of T cells and T cell subsets in the blood of the patients.

Moderate doses of cyclophosphamide can cause effects on lymphocytes that may last for some time after discontinuation of the treatment. Since cyclophosphamide is also often used at high doses, we studied the short- and long-term effects of such a high dose (8 grams in 20 days) in 50 patients with chronic progressive multiple sclerosis with the use of monoclonal antibodies. The treatment caused a depletion of lymphocytes, especially CD4+ cells resulting in a significant decrease of the CD4/CD8 ratio. These changes can still be found up to 13.5 years after treatment. Although there was some recovery in the first few years after treatment this was only partial. Therefore, some of the effects of high dose cyclophosphamide on cellular immunity may be permanent. These changes should be taken into account when studying immune parameters or considering new treatments in these patients.