Characterization of a Subtype D Human Immunodeficiency Virus Type 1 Isolate That Was Obtained from an Untreated Individual and That Is Highly Resistant to Nonnucleoside Reverse Transcriptase Inhibitors

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Abstract
Human immunodeficiency virus type 1 (HIV-1) isolates derived from HIV-infected, treatment-naive Ugandan infants were propagated and tested for sensitivity to antiretroviral (ARV) drugs. Although most subtype A and D isolates displayed inhibition profiles similar to those of subtype B strains, a subtype D isolate identified as D14-UG displayed high-level resistance to nevirapine in peripheral blood mononuclear cell cultures (>2,000-fold) and in MT4 cell cultures (∼800-fold) but weaker resistance to delavirdine (∼13-fold) and efavirenz (∼8-fold) in MT4 cell cultures. To investigate the possible mechanism for this resistance to nonnucleoside reverse transcriptase (RT) inhibitors (NNRTIs), the RT coding region in pol was sequenced and compared to the consensus RT sequence of NNRTI-resistant and NNRTI-sensitive subtype A, B, and D HIV-1 isolates. D14-UG did not contain the classic amino acid substitutions conferring NNRTI resistance (e.g., Y181C, K103N, and G190A) but did have some putative sites associated with drug resistance, I135L, T139V, and V245T. Wild-type and mutated protease-RT genes from D14-UG and an NNRTI-sensitive subtype D isolate from Uganda (D13-UG) were cloned into pNL4-3 to produce recombinant viruses and to determine the effects of the mutations on susceptibility to ARV drugs, specifically, NNRTIs. The results showed that I135L and/or V245T mutations can confer high-level resistance to nevirapine and delavirdine as well as low level cross-resistance to efavirenz. Finally, ex vivo fitness analyses suggested that NNRTI-resistant sites 135L and 245T in wild-type isolate D14-UG may reduce RT fitness but do not have an impact on the fitness of the primary HIV-1 isolate.

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