Plasma HIV-1 copy number and in vitro infectivity of plasma prior to and during combination antiretroviral treatment

Some studies on untreated patients have shown a general correlation between plasma HIV copy number and plasma infectivity in in vitro models. Recent o bservations also indicate that HIV-RNA level is an important predictor of p erinatal transmission and may also have a role in heterosexual transmission . To further analyse the correlation between HIV viral load and plasma infe ctivity, we studied the relationship between HIV-1 plasma copy number and p lasma infectivity prior to and during treatment with antiretroviral combina tion regimens in HIV-1 infected adults. Plasma infectivity was assessed in vitro by coculture of plasma from HIV-positive patients with PHA-stimulated fresh PBMC from uninfected donors. A positive plasma isolation, in almost all cases (43/45) and irrespective of treatment status, was associated with an HIV viral load higher than 100 000 copies per mi, with higher plasma HI V-I RNA values in isolation-positive samples compared with isolation-negati ve samples (median values, 710 000 vs. 37 500 copies per mi, respectively). SI and NSI strains had similarly high viral load values (470 000 vs. 790 0 00 copies per mi), but CD4 counts were lower in the SI phenotype group. Our data indicate that low levels of viral load are only exceptionally associa ted with isolation from plasma in the in vitro model we used. This observat ion confirms indirectly the presence of an association between viral load a nd infectivity. The requisite of a high plasma viral load in order to obtai n infectivity (i.e. positivity of HIV isolation from plasma) also seems mai ntained under antiretroviral treatment, adding confidence in the conclusion that reductions in viral load translate into reduction of plasma infectivi ty. Due to the extreme complexity of factors determining transmission, a ve ry prudent interpretation of the results is essential when information from experimental studies has to be transferred to clinical situations requirin g assessment of risks or clinical decisions. (C) 2000 Elsevier Science B.V. All rights reserved.