In PI-naïve patients in our study, the insertions persisted for long periods in the absence of PI pressure. In one patient, the insertion persisted for more than 4 years,

with the virus diplaying a dramatic decrease in replicative capacity. Our results are in accordance with those of previous studies reporting that the presence of insertions decreased enzyme activity [8]. Conversely, Kim et al. used recombinant virus and reported an advantage in cell culture of virus with the insertion in the absence of PIs compared with virus without the insertion [7]. Regarding in-patients whose insert-mutated protease find more was selected under PI drug pressure, this occurred in a context of a multiresistant protease and following a long period of viral replication under Bortezomib molecular weight PIs. As described by Paolucci et al., the impact of the insertion on viral replication is difficult to predict,

depending on the nature of the inserted amino acids and the pattern of drug-resistance-associated mutations [11]. For example, a differential impact on the replication rate was found between a G and a TN insertion at codon 35, the former resulting in an enhancement and the latter in an inhibition of virus replication [11]. In our study, we did not find similar results as the E35ET and E35EG insertions displayed by virus from two PI-naïve patients resulted in the same dramatic decrease in replicative capacity, with no substantial impact on PI resistance level. In our study, one of the PI-naïve patients was successfully treated with lopinavir monotherapy, arguing for a retained susceptibility

to PI for this insert-containing virus. The absence of a decrease in viral susceptibility was confirmed by Kim et al., who found no significant change in the IC50 of IDV, SQV and NFV in the presence of an insertion; and by Paolucci et al., who used recombinant virus from patient-derived HIV sequences [7,11]. Conversely, Kozisek et al., who analysed mutated recombinant protease variants from two patients with or without insertions at positions 33 and 35, found an increased resistance to PIs [10]. Overall, protease insertions are not only observed in PI-treated patients but also in PI-naïve Janus kinase (JAK) patients. In PI-naïve patients, protease insertion virus can persist for a long time, exhibiting a decreased viral replicative capacity with no impact on resistance level. In PI-experienced patients, protease insertion virus may be selected in the context of other PI-resistance mutations after a long period of exposure to PIs with no specific impact on resistance level or replicative capacity. In addition, as in our study all PI-naïve patients who harboured virus with a protease insertion were infected with a non-B subtype, further studies on larger series of patients are needed to determine whether HIV subtype has an impact on the prevalence of protease insertions.