Parallel evolution in the V3 region of HIV type 1 after infection of hemophiliacs from a homogeneous source.

To determine the genetic diversification in the highly functional V3 loop, we followed up five hemophiliacs who were infected by a homogeneous HIV-1 population from a contaminated clotting factor lot. Initially, all patients displayed identical DNA sequences in this part of the proviral env gene. Therefore, this unique outbreak allows us to investigate the biological and genetic development of a common ancestor virus in different patients. A high degree of homology is maintained in the predominant sequences from 5 until 35 months after seroconversion. Only one patient showed a remarkable diversification 3 years postinfection. However, these genetic changes in the V3 region were not associated with disease progression. Discontinuous sequence changes were observed mainly in a region downstream of the V3 loop. Two positions in particular are involved in a sequence evolution within the V3 loop leading to the same amino acids in different patients. These directed changes occurred at sites that are reported to be critical for the specificity of antibodies (position 308) and viral cytopathicity (position 324). However, the parallel evolution was associated neither with differentiation of the viral phenotype nor with progression of the disease.