Isolation and characterization of HTLV-I from symptomatic family members with tropical spastic paraparesis (HTLV-I encephalomyeloneuropathy).

Human T lymphotropic virus type I (HTLV-I) was isolated from peripheral blood- and cerebrospinal fluid-derived mononuclear cells of a 13-y-old boy and from the peripheral blood lymphocytes of both his parents. All three had IgG antibodies to HTLV-I and varying degrees of the clinical features of tropical spastic paraparesis (TSP). The son also had IgM antibodies specific for HTLV-I in his serum. Isolations were successfully made from peripheral blood lymphocytes and cerebrospinal fluid lymphocytes stimulated with interleukin-2 or cocultivated with umbilical cord blood mononuclear cells. Established cell lines contained HTLV-I antigen by immunfluorescence and cell-associated virus by electron microscopy; cells became transformed in vitro as determined by their continuous growth in the absence of exogenous interleukin-2. This boy is the youngest TSP patient known to be reported, and the isolation of HTLV-I from all three family members suggests the causative role of this virus in TSP.