Reciprocal activation of human T-lymphotropic viruses in HTLV-I-transformed cells superinfected with HIV-1.

The finding of dual HTLV-I and HIV-1 infection in populations at risk for AIDS raises the possibility that interaction between the two viruses might have clinical significance. It was shown that HTLV-I enhances HIV-1 expression, but whether HIV-1 activates HTLV-I remains to be demonstrated. To study HTLV-I behaviour following HIV-1 infection, we superinfected cells from two HTLV-I transformed cell lines with HIV-1 (strain IIIB). Viral RNA analysis indicated that HTLV-I expression in the doubly infected cells was moderately enhanced. Moreover, CAT assays in HTLV-I transformed cells transiently transfected with HTLV-I LTR-CAT disclosed higher activity in the HIV-1 superinfected cultures. This enhancement was observed only after infection with active HIV-1 virus, but not following exposure to inactivated viral particles or transfection with HIV-1 tat gene.