Basic Science Programme / Phenotype and HIV Disease Progression Study Project

Lead Research Organisation: MRC/UVRI Uganda Research Unit on AIDS


There are different subtypes of HIV infection which differ genetically. The main subtypes circulating in Uganda are subtypes A and D and recombinants of these. The different genetic subtypes each come in two different versions (phenotypes) with regards to their functionality. Whilst the genetic structure of the phenotypes of the same virus is identical, phenotypes differ e.g. with regards to the type of receptors they make use of in order to connect and infect a target cell. For this process, HIV needs to interact with several different receptor and co-receptor molecules which are located on the surface of the target cell. In order to infect CD4 cells, HIV requires either to use a co-receptor named CCR5 or a co-receptor named CXCR4. Virus using the former is called R5 virus, and that using the latter is called X4 virus. X4 virus is associated with faster disease progression than R5 virus and generally occurs later in the cause of HIV infection. |It would be of interest to better understand what influences the switch of HIV from phenotype R5 to X4. Understanding the biological mechanisms behind this switch may e.g. allow the development of therapeutic interventions that could slow disease progression. Our research aims to identify the factors that are associated with this switch or may even have a causal function. Lastly we are trying to determine whether the dynamics of events around the switch from R5 to X4 virus infection differs between different genotypes of HIV.

Technical Summary

As HIV disease progresses at individual level, a switch occurs from co-receptor CCR5 to CXCR4 tropic viruses. It is not well understood why this happens and why this switch seems to occur earlier in individuals infected with HIV subtype D than A. We investigate whether this switch is likely due to the expression of these co-receptors on CD4 cells or blood cytokine levels.||Methods: We attempt to determine whether the abundance of HIV coreceptors, quantified by either the percent of total CD4+ T-cells expressing CCR5 or CXCR4, or the density of these coreceptors on these cells, change during the course of HIV infection. Whole blood samples from patients enrolled in clinical studies of HIV infection are investigated. On group of individuals have a CD4 count of less than 200 cells/5l and another a CD4 count of more than 500 cells/5l. Specimens were eligible only from individuals who had not yet started antiretroviral therapy and had no current opportunistic infections. For each sample 100?l aliquots of fresh, whole blood is stained with CD3-FITC, CD4-PerCP-Cy5.5, and either CCR5-PE, CXCR4-PE or their respective isotype controls to determine the percent of CD4+ cells expressing CCR5 or CXCR4. Each sample is being gated on the CD3+ population. The average size of the CD4+ T-cells is recorded allowing us to calculate the density of CCR5 and CXCR4 on CD4+ T-cells using the mean fluorescent intensity (MFI). A human Th1 and Th2 cytokine CBA kit is used to measure plasma cytokine levels.
Description HIV phenotype studies 
Organisation Imperial College London
Country United Kingdom 
Sector Academic/University 
PI Contribution Our staff went to train at St Mary's Hospital, Imperial College in Prof Weber's laboratory to learn phenotyping of viruses.
Collaborator Contribution Training of staff and contribution to publication
Impact This resulted in training of our staff in phenotyping of viruses Publications Pub No 17310935
Description Tat antigen characterization 
Organisation National Center for Scientific Research (Centre National de la Recherche Scientifique CNRS)
Department Evolution Education Research
Country France 
Sector Public 
PI Contribution We provided specimens processed and conducted some of the laboratory tests
Collaborator Contribution Provision of tat proteins and other reagents and training
Impact Tat proteins from different subtypes and with different phenotypic characteristics were provided. This work led to further understanding of the role of tat proteins in disease progression
Description Policy makers 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Primary Audience Policymakers/politicians
Results and Impact Presentation of research findings to policy makers

There was interest in the possible importance of HIV subtypes in the current HIV epidemic
Year(s) Of Engagement Activity 2006