Induction of neutralizing antibodies against HTLV-I envelope proteins after combined genetic and protein immunizations in mice.

Direct DNA inoculation can induce both protective humoral and cellular responses against several viruses. The HTLV-I envelope glycoproteins are the major antigens recognized by sera of HTLV-I infected patients that generate neutralizing immune responses in vitro and in vivo. We compared immune responses elicited after a single inoculation of two plasmids encoding the complete HTLV-I envelope proteins followed or not by gp62 Baculovirus recombinant protein boosts in BALB/c mice. First, we observe that the coexpression of env and rex genes is not sufficient to raise a detectable specific humoral response after a single DNA inoculation. Protein boosts generated a high antibody response in mice primed with DNA expressing HTLV-I envelope proteins as compared to naive and negative control vector primed groups. This humoral response presented high neutralizing antibody titers. These results suggest that a single inoculation of DNA expressing HTLV-I env gene can stimulate memory B-cell clones that are able to respond effectively to subsequent encounters with HTLV-I envelope proteins and a specific cellular T helper cell response in mice.

Characterization of new syncytium-inhibiting monoclonal antibodies implicates lipid rafts in human T-cell leukemia virus type 1 syncytium formation.

We have previously shown that erythroleukemia cells (K562) transfected with vascular adhesion molecule 1 (VCAM-1) are susceptible to human T-cell leukemia virus type 1 (HTLV-1)-induced syncytium formation. Since expression of VCAM-1 alone is not sufficient to render cells susceptible to HTLV-1 fusion, K562 cells appear to express a second molecule critical for HTLV-induced syncytium formation. By immunizing mice with K562 cells, we have isolated four monoclonal antibodies (MAbs), K5.M1, K5.M2, K5.M3, and K5.M4, that inhibit HTLV-induced syncytium formation between infected MT2 cells and susceptible K562/VCAM1 cells. These MAbs recognize distinct proteins on the surface of cells as determined by cell phenotyping, immunoprecipitation, and Western blot analysis. Since three of the proteins recognized by the MAbs appear to be GPI linked, we isolated lipid rafts and determined by immunoblot analysis that all four MAbs recognize proteins that sort entirely or in large part to lipid rafts. Dispersion of lipid rafts on the cells by cholesterol depletion with beta-cyclodextrin resulted in inhibition of syncytium formation, and this effect was not seen when the beta-cyclodextrin was preloaded with cholesterol before treating the cells. The results of these studies suggest that lipid rafts may play an important role in HTLV-1 syncytium formation.

Comparison of anthelmintic effects of two doses of ivermectin on intestinal strongyloidiasis in patients negative or positive for anti-HTLV-1 antibody.

Coinfection with HTLV-1 (T lymphotropic virus type I) has been observed in approximately 38% of cases of Strongyloides stercoralis infection in Japan. In the present study, we investigated whether the dose of ivermectin corresponding to approximately twice the conventional therapeutic dose could improve the anthelmintic rate without adverse effects in patients with intestinal strongyloidiasis, particularly in those positive for anti-HTLV-1 antibody. A single dose of 6 mg ivermectin (mean, 110 microg/kg) was administered and the same single dose was repeated 2 weeks later in 312 patients with intestinal strongyloidiasis during the period from 1990 to 1999. The long-term anthelmintic rate during the period of 12 months from 4 months after treatment was 77% (117/152) in all patients, and 92.7% (89/96) and 50% (28/56) in those negative and positive for anti-HTLV-1 antibody, respectively. Between 2000 and 2003, ivermectin was administered at 200 microg/kg in 97 patients, and repeated 2 weeks later. The long-term anthelmintic rate was 96.8% (60/62) in all patients, and 100% (42/42) and 90% (18/20) in those negative and positive for anti-HTLV-1 antibody, respectively. These results showed that the long-term anthelmintic rates in all patients in the 200 microg/kg dose group, and especially in those positive for anti-HTLV-1 antibody, were significantly higher than the respective rates of the 110 microg/kg dose group. Based on these results and the observed safety of the double dose of ivermectin, the recommended dose of ivermectin for treatment of intestinal strongyloidiasis should be 200 microg/kg in patients positive for anti-HTLV-1 antibody.