The role of the protease cleavage sites in viral fitness and drug resistance in HIV-1 subtype C.

Abstract

There is an increasing number of patients failing second line highly active antiretroviral therapy

(AZT, DDI and LPV/r) in South Africa, where HIV-1 subtype C predominates. Mutations at gag

cleavage sites (CS) have been found to correlate with resistance mutations in protease (PR).

Therefore, it is important to collect data on subtype C protease and gag sequences from patients

as these mutations may affect the efficacy of protease inhibitor (PI) containing drug regimens.

In this study, 30 subtype-C infected second-line failures were genotyped using the ViroSeqTM

resistance genotyping kit and the gag region from these isolates were then characterised. These

sequences were then compared to 30 HIV-1 subtype C infected first-line failures (PI-naïve) and

subtype B, C and group M naïve sequences that were downloaded from the Los Alamos

Sequence Database. Amino acid diversity at the CS was measured using Mega version 4.0. To

investigate the effect of CS mutations on replication capacity, a mutation was introduced by

site-directed mutagenesis (Stratagene’s QuikChange Site-Directed Mutagenesis kit).

Of the 30 second-line failures that we genotyped, only 16 had resistance mutations in PR and 23

in gag. The most frequent major PI mutations were: I54V/L, M46I, V82A, and I84V and in gag

CS were V390L/I and A431V. Interestingly the A431V mutation significantly correlated with

protease mutations M46I/L, I54V and V82A. The virus carrying the A431V mutation in vitro

was found to have a lower replication capacity compared to the wild type.

These findings emphasize the need for further investigation of gag mutations and their

contribution to the evolution of HIV resistance to PIs.