Additional mutations detected in sequential HIV-1 isolates from ZDV-treated patients.

Sequential isolates from four patients under zidovudine (ZDV) therapy were obtained using PBMC coculture in the absence or in the presence of 0.25 microM ZDV. PBMC-based HIV susceptibility assay demonstrated the emergence of ZDV-resistance in the sequential isolates from the four patients. Except in one case, the isolates obtained in the presence of ZDV did not exhibit a greater resistance pattern than their counterparts obtained in the absence of the drug. In parallel, partial reverse transcriptase gene sequence was determined directly on amplified products from proviral DNA. In addition to the mutations previously described at the critical codons 41, 67, 70, 215, and 219, numerous additional mutations were found in either ZDV-sensitive or ZDV-resistant isolates. The mutation Thr215Tyr was not observed in a case of highly resistant virus (ZDV IC50 > 6.25 microM), while the mutation Lys70Arg was found in either resistant or sensitive ones. The analysis of additional mutations did not reveal any clear pattern for ZDV resistance but pointed out the existence of highly variable regions neighbouring the five critical codons. Neither nucleotide sequence nor PBMC-based susceptibility assay provided unambiguous data about pretherapy isolates or early on-therapy isolates which could predict the emergence of ZDV resistance in further samples.