Subtype C HIV-1 is currently responsible for the majority of new infections in the
world, particularly in parts of Africa where the adult prevalence rate is as high as
15%. In the absence of a viable vaccine in the near future, the study of new
neutralising antibodies that can inhibit virus entry is urgently needed. To understand
the subtype C HIV-1 envelopes, the env gene was cloned directly from 15 patient
plasma samples obtained from a few countries in Africa and in the UK, and 18
replication-competent chimeric viruses were created. These envelopes were then
characterised and compared with other envelopes in standard reference panels. We
then exploited the unique properties of llama heavy-chain antibodies to create
antibody fragments (VHH) that can recognise HIV-1 envelopes and prevent
infection. Four VHH that recognise a conformation dependent epitope on gp41 were
isolated from a llama that was immunised with recombinant gp140 derived from a
subtype B’/C isolate after panning of the phage libraries on recombinant gp41. These
VHH were more potent in neutralising subtype C isolates than subtype B isolates.
Based on the success of an earlier study on VHH that recognise an epitope
overlapping the CD4 binding site on gp120, a novel strategy was used to isolate
variants of the VHH to create a family-specific VHH library. Thirty-one new VHH
were characterised and grouped according to their neutralisation breadth against 3
subtype C viruses. The neutralisation breadth of the VHH correlated with its
dissociation rate with gp120, and was found to be dependent on 3 amino acid
residues in the third complementarity determining region of the VHH. These VHH
may have further use in applications such as HIV-1 microbicides development and
immunogen design through reverse immunology