Zidovudine resensitization and dual HIV-1 resistance to zidovudine and lamivudine in the Delta lamivudine roll-over study

Objective: To study zidovudine resensitization and dual resistance to zidov udine/lamivudine in HIV-1 isolates from nucleoside reverse transcriptase (R T) inhibitor-experienced patients during selective pressure exerted by zido vudine/lamivudine combination therapy. Design and methods: HIV-1 isolates from 29 patients receiving zidovudine/la mivudine combination therapy in the Delta roll-over study were analysed at entry and during a 1 year follow-up period for phenotypic susceptibility to zidovudine and lamivudine in the ANRS PBMC assay. The RT gene from codon 2 0 to 230 and at codon 333 was analysed by nucleotide sequencing of the corr esponding isolates. Results: HIV-1 isolates from 23 of the 29 patients were phenotypically resi stant to zidovudine at baseline; 61% of these patients showed significant z idovudine resensitization during follow-up. The zidovudine IC,, value corre lated positively with log,, plasma HIV-1 RNA (P = 0.02) and negatively with the CD4 cell count (P = 0.004). Zidovudine resensitization (related to acq uisition of the M184V mutation) was transient, with evolution towards dual resistance to zidovudine and lamivudine in 20 of the 29 patients. The pheno type of certain dually resistant isolates coincided with the emergence of m ultiple mutations in the 5' part of the RT gene. Conclusions: M184V-mediated zidovudine resensitization of HIV-1 is transien t in most patients who are given zidovudine/lamivudine combination therapy when zidovudine resistance has already emerged. The subsequent evolution to wards dual phenotypic resistance to zidovudine/lamivudine corresponds to co mplex genotypic profiles.