Different outcome in the first two patients with an HIV-1 multinucleoside drug-resistant T69SSS insertion in Spain

A novel multidrug-resistance mechanism has been described in human immunodeficiency virus type 1 (HIV-1), which involves the insertion of 6 bp between codons 69 and 70 in the reverse transcriptase (RT) gene. Herein, we report the first two patients in Spain carrying viral populations with the 69-SS insert coupled to the T69S mutation. Both patients were selected because of the lack of signal at positions 69/70 in the LiPA RT test despite being reactive to the remaining probes on the LiPA strip. The presence of the T69SSS complex was confirmed by sequence analysis. A common feature for both subjects was their past history with zidovudine monotherapy and zidovudine plus either didanosine or zalcitabine later on in the presence of persistent virus replication. Remarkably, the introduction of triple therapy in patient 1 soon after the emergence of the insert-containing viral strain produced its total displacement, which correlated with a sustained suppression in viral load.