Because HTLV-1 infection promotes T-cell activation and proliferation [69] and proviral load levels are associated with CD4+ T-cell clonal expansion [70], we wished to assess if there is an association between proviral load and the CD39 expressing CD4+ T-cell subsets in 24 HTLV-1 asymptomatic carriers and 13 HAM/TSP patients. Here, CD4 is linked to tropical spastic paraparesis.