HLA, Vpu and ADCC correlates of a unique Chinese HIV-1 Positive village cohort

The recent relative success of the Thai Vaccine trial and failure of the STEP trial have prompted renewed calls for a ‘back to basics’ approach. This premise dictates a greater and clearer understanding of the various immune parameters at play in HIV infection. The overall aim of this project was to look at different immune parameters at play in our unique Chinese SM HIV-1 cohort, which has an unusually high proportion of slow progressors. The unique dynamics of the SM cohort make it ideal for studying immune parameters.
As the HLA Class I region has been shown to have the strongest genetic association with durable control of HIV, we set out to investigate the HLA correlates for our unique SM cohort. We recruited a neighbouring Han village cohort for comparisons, and employed stringent statistical tests for our analysis. Our analysis revealed that there was no enrichment of any specific HLA alleles in the SM cohort. This may be due to the limited study size, or that the protective effect has waned over time.
Next we were interested in the immune pressure exerted on Vpu protein, which has been shown recently to be critical in HIV release from the cell, and not many studies have focused on Vpu. We did not find any statistically significant associations in our analysis of HIV-HLA associated polymorphisms in Vpu, and our screening ELISPOTS using overlapping peptides did not reveal any T-cell responses to the protein. However, our analysis for NK-mediated pressure, identified a single amino acid position in the Vpu sequence which was significantly associated with the presence of a specific KIR gene (p = 0.0047): In amino acid position 14 of Vpu, HIV-1 sequences (59%) derived from KIR2DS1+ individuals encoded for a valine (V) whereas the consensus amino acid alanine (A) at this position is found in the vast majority (76%) of KIR2DS1- individuals. This is extremely interesting as Vpu position 14 has been shown to be critical for interaction with the host restriction factor, tetherin.
We next explored further the role of NK cells in relation to antibody-dependent cell-mediated cytotoxicity (ADCC), and antibody-dependent cell-mediated virus inhibition (ADCVI). Using an adapted ADCC-ICS assay, we found ADCC responses to Env in 37% of the SM cohort, with five subjects also having responses to Vpu peptides. We devised an Enzyme-linked Immunosorbent Assay (ELISA) which allowed us to map the Vpu ADCC epitopes in the SM cohort. We also wanted to know whether the Env/Vpu ADCC responders also displayed ADCVI activity. We optimised the ADCVI assay in our lab using HIV NL4-3 as our infecting strain of virus. All 5 Env/Vpu responders had very similar inhibition of virus – nearing 95 %, in the ADCVI assay. We followed up on these 5 Env/Vpu ADCVI responders and tried to get more plasma – unfortunately we were only able to get plasma from one subject – SM 017 as the rest could not be traced. This patient – SM 017 2011- demonstrated the prozone effect, and we hypothesise that the ADCC antibody titres have increased in SM 017 over the years, to augment the ADCC response in vivo.
In conclusion, in this study, we analyse host genetic, virological, and immunologic factors to enrich our understanding of HIV/AIDS parameters in a unique Chinese slow progressors cohort. We build up on the HLA database for slow progressors, and demonstrate a KIR association with Vpu amino acid position 14, something which has not been reported before. We demonstrate ADCC responses in the SM cohort, and also optimised an ELISA-based assay to reduce amount of plasma used for the ADCC-ICS assay. We plan now to isolate the antibodies from a unique patient, and possibly, identify the first Vpu ADCC antibody.

Advisor: Rowland-Jones, S
Dong, T
McMichael, A