Quantitation of human immunodeficiency virus type 1 group O load in plasma by measuring reverse transcriptase activity

Abstract

We have evaluated the use of an ultrasensitive reverse transcriptase (RT) activity assay to monitor plasma viremia in two human immunodeficiency virus type 1 (HIV-1) group O-infected patients treated with stavudine, lamivudine, and indinavir. After a initial decline in RT levels observed at 4 weeks of therapy, RT-based plasma viremia returned to baseline values at 28 or 44 weeks of treatment. The rebound in levels of RT activity was associated with the detection of phenotypic resistance to lamivudine and with the Met184Val mutation. Analysis of RT activity in plasma provides a sequence-independent means of monitoring virus loads in HIV-1 group O-infected patients.

FIG. 1

Histories of antiretroviral therapy, RT-based plasma viral loads, and CD4⁺ lymphocyte counts for two HIV-1 group O-infected patients (ESP2 and ESP3). AZT, zidovudine; ddI, didanosine; d4T, stavudine; 3TC, lamivudine; IDV, indinavir; RTV, ritonavir; SQV, saquinavir.

FIG. 2

Determination of phenotypic resistance to 3TC of HIV-1 from plasma of two HIV-1 group O-infected patients (ESP2 and ESP3) by measuring levels of RT inhibition by 5 μM 3TC-TP (5). Results of duplicate tests of plasma samples obtained before (Pre) and during treatment with lamivudine, stavudine, and indinavir (week 28 [28w] in patient ESP2 and weeks 16 [16w] and 44 [44w] in patient ESP3) are shown. Samples were adjusted to similar levels of RT activity before testing. Signal from Amp-RT reactions containing 50 μM nevirapine (NVP) are also shown. S, lamivudine-sensitive HIV-1 reference virus (xxBRU_pitt); R, lamivudine-resistant HIV-1 reference virus (M184V_pitt); Neg, uninfected control supernatant.