Ashokkumar Manickam [1,2], Luke Elizabeth Hanna*, Ujjwal Neogi*
Affiliates:  National Institute for Research in Tuberculosis (ICMR), Chennai, India  Karolinska Institute, Stockholm, Sweden
The genetic diversity of HIV-1 is a major challenge for HIV vaccine design. Among the repertoire of transmitted viral variants, the virus isolate(s) that establishes successful infection has not yet been well characterized. An insight into the salient features of the transmitted/founder (TF) virus would go a long way in the design of an effective vaccine against HIV. The major goal of the present study is to characterize the fitness, infectivity and properties of viral variants that establish infection in a group of HIV-1 infected infants within two months of the infection.
Blood samples were collected from infants between 15 days and 2 months after dilevery, whose mothers were HIV-1 positive at the time of pregnancy. One sample from a chronically infected adult was included as control. Viral RNA was extracted from the plasma, followed by cDNA synthesis, amplification of HIV-1 envelope gp120 and cloning in pMNgp120 plasmid. Multiple clones were selected and tested for infectivity. The infectious molecular clones were tested for co-receptor tropism with GHOST cell line expressing either CCR5, CXCR4 or CXCR6, maraviroc (MVC) drug sensitivity assay (DSA) and per-particle infectivity estimation in TZM-bl cell with luciferase reporter gene assay.
All study subjects were infected with HIV-1CIN viruses. Totally, 60 infectious clones were identified out of 145 clones screened from 8 patients’ samples. All of the recombinant viruses were identified as R5-tropic except one clonal virus as dual (R5/X4) tropic. Interestingly 11 viruses from five infants also used CXCR6 as the co-receptor for viral entry. Relatively higher EC50 values for MVC-sensitivity were observed in most of the clonal virus derived from infants than the viral isolates derived from adult sample indicating a reduced susceptibility against MVC. Interestingly, the infectious potential of the single viral particle from the TF virus of the infants was found to be higher than the virus from the adult.
For very first time, CXCR6-co-receptor usage in TF virus from recently diagnosed infants was identified in addition to reported R5 co-receptor usage. This indicates that co-receptor usage during the early establish differs in tropism. Also the sensitivity for MVC appears to be significantly lower for TF HIV-1C viruses than recombinant viruses’ derived chronically infected adult patient. Enhanced infectivity of a single TF viral particle at a single round infection could be an important characteristic of the unique quasispecies that are responsible for the spread of HIV.