CCR5 and CXCR4 tropism and CD4 kinetics in HIV-1 infection

Lead Research Organisation: St George's University of London
Department Name: Department of Cellular and Molecular Sci

Abstract

HIV infection causes disease by progressively depleting the number of a particular type of immune cells, ?CD4 cells?. We do not fully understand how infection results in loss of CD4 cells over time. Although HIV infects and destroys CD4 cells directly, the body normally just makes more cells to replace the lost ones.

We believe that what determines how HIV affects the body?s CD4 cells is the exact type of cell it infects. There are several sub-types of CD4 cells. Different strains of virus prefer to infect different sub-types of CD4 cell according to the receptors (like locking devices) on the cell surface. Two receptors, ?CCR5? and ?CXCR4?, appear particularly important. We hypothesise that the interaction between the viral CCR5/CXCR4 preference (?tropism?), the type of cell infected and the speed at which those cells are dividing determines the long-term effect of HIV on CD4 cell numbers.

To investigate this concept, we will measure how fast different sub-types of CD4 cells are dividing and disappearing within the body. Although much has been learnt from investigating cells and viruses in test tubes, answering such questions about CD4 loss can only be done by studying virus and CD4 cells within the body of people infected with HIV. We have recently developed a way of doing this using glucose containing an excess of deuterium. Deuterium is a naturally-occurring non-radioactive form (or isotope) of hydrogen which behaves exactly like hydrogen but can be measured using a mass spectrometer. We will give deuterium-labelled glucose (which is harmless) as a drink (half-hourly for 10 hours) to people with HIV infection, then take blood samples over the following 3 weeks. The glucose is used by dividing, but not non-dividing, cells to make new DNA. By separating the cells into their subtypes and measuring the deuterium in their DNA using a mass spectrometer, we can measure how fast CD4 subtypes divide and how long they survive in the body. We will also test the virus in the bloodstream for its CCR5/CXCR4 tropism. We will compare the results to those from a group of people without HIV infection.

We will use these measurements to create a mathematical picture or ?model? of how HIV interacts with different immune cells to explain why CD4 cells are destroyed slowly over time and why changes in viral tropism trigger accelerated loss of CD4 cells.

Technical Summary

Progressive loss of CD4+ T cells is the cardinal feature of HIV infection. However, the pivotal mechanisms which drive CD4 cell loss remain poorly understood. Although immune activation and accelerated CD4 cell turnover are thought to be important contributors to such loss, the chemokine tropism of the dominant viral strain appears to be critical. HIV-1 entry into CD4+ T cells depends on interaction between envelope, CD4 and a co-receptor, CCR5 or CXCR4 for R5 and X4 viruses respectively. R5 viruses dominate early in disease but a switch to X4 triggers more rapid CD4 decline. We hypothesise that the dominant viral tropism and the rate of CD4 decline is determined by the kinetics of the T cell subpopulations for which the virus is tropic.

We propose to measure in vivo lymphocyte proliferation and death rates using deuterium-labelled glucose as a tracer for cell division in human volunteers. Specifically we aim to investigate: (1)The relative turnover rates of CCR5 and CXCR4 na?ve and memory lymphocytes in HIV-uninfected individuals, and (2) The effects of X4 and R5 viral strains on the turnover rates of CCR5 and CXCR4 na?ve and memory T cells in HIV-infected individuals before and after antiretroviral therapy.
From the above we propose to define a quantitative kinetic model to explain why the switch from R5 to X4 tropic viruses is associated with accelerated CD4 T cell decline.

Subjects will receive 6,6-D2-glucose as an oral solution half-hourly for 10 hours, a methodology we have previously validated. Cells will be sorted according to expression of CD4, CD45, CCR5 and CXCR4 by flow cytometry, DNA will be extracted and analysed by gas chromatography mass spectrometry for deuterium content. Data will be modelled to yield proliferation and disappearance rates of individual cell populations. Data will be related to the dominant viral tropism.

We believe that the findings will have important implications for understanding the pathophysiology of HIV infection and explaining how CD4 depletion occurs. Such data would form the basis for developing novel immunological strategies for HIV infection and understanding the potential cellular impact of novel agents currently being developed to interfere with virus-chemokine interactions.

Publications

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Asquith B (2009) Lymphocyte kinetics in health and disease. in Trends in immunology

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Macallan D (2013) Immune responses to HIV and vaccination in Medicine

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Macallan Derek (2009) CD4+ T cell turnover is related to chemokine-receptor expression and HIV viral co-receptor tropism (Abstract) in Proceedings of the 17th Conference on Retroviruses and Opportunistic Infections (CROI 2010)

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Pawelec G (2010) Immunosenescence and Cytomegalovirus: where do we stand after a decade? in Immunity & ageing : I & A

 
Description LLR Project Grant
Amount £50,180 (GBP)
Funding ID 12064 
Organisation Leukaemia and Lymphoma Research 
Sector Charity/Non Profit
Country United Kingdom
Start 12/2012 
End 12/2015
 
Description LLR project grant
Amount £66,918 (GBP)
Funding ID 12024 
Organisation Leukaemia and Lymphoma Research 
Sector Charity/Non Profit
Country United Kingdom
Start 04/2012 
End 04/2015
 
Title Analysis of LC kinetics by chemokine analysis 
Description As a result of this research we have developed new approaches to analysis of lymphocyte kinetics according to chemokine receptor expression. New cell sorting protocls were developed and new approaches to modelling of quantitative data were employed. 
Type Of Material Model of mechanisms or symptoms - human 
Year Produced 2013 
Provided To Others? Yes  
Impact Still to be published and disseminated 
 
Title Model of LC kinetics in HIV 
Description As a result of this research we have developed novel models for understanding how CD4+ T cells interact with HIV to cause CD4 cell depletion. 
Type Of Material Model of mechanisms or symptoms - human 
Provided To Others? Yes  
Impact To be published and disseminated 
 
Title Models of Lymphocyte kinetics 
Description With Dr Becca Asquith at Imperial College, we have developed approaches to analysis of lymphocyte labelling kinetics. A publication manuscript has been submitted and is under review. 
Type Of Material Data analysis technique 
Year Produced 2014 
Provided To Others? Yes  
Impact Better understanding of labelling kinetics 
 
Description Collaboration on Lymphocyte kinetics in HIV 
Organisation Royal Free Hospital
Country United Kingdom 
Sector Hospitals 
PI Contribution Clinical studies of turnover of CD4 T cells in HIV
Collaborator Contribution Collaboration in data analysis and interpretationCollaboration in data analysis, interpretation and presentationcollaboration on analysis of HIV viral tropismsCollaboration on mathematical modelling of lymphocyte kinetics
Impact Abstract presentation at CROI 2011
Start Year 2006
 
Description Collaboration on Lymphocyte kinetics in HIV 
Organisation St Mary's Hospital, London
Country United Kingdom 
Sector Hospitals 
PI Contribution Clinical studies of turnover of CD4 T cells in HIV
Collaborator Contribution Collaboration in data analysis and interpretationCollaboration in data analysis, interpretation and presentationcollaboration on analysis of HIV viral tropismsCollaboration on mathematical modelling of lymphocyte kinetics
Impact Abstract presentation at CROI 2011
Start Year 2006
 
Description Collaboration on Lymphocyte kinetics in HIV 
Organisation University of Oxford
Department Jenner Institute
Country United Kingdom 
Sector Academic/University 
PI Contribution Clinical studies of turnover of CD4 T cells in HIV
Collaborator Contribution Collaboration in data analysis and interpretationCollaboration in data analysis, interpretation and presentationcollaboration on analysis of HIV viral tropismsCollaboration on mathematical modelling of lymphocyte kinetics
Impact Abstract presentation at CROI 2011
Start Year 2006
 
Description Collaboration on Lymphocyte kinetics in HIV 
Organisation University of Oxford
Department Jenner Institute
Country United Kingdom 
Sector Academic/University 
PI Contribution Clinical studies of turnover of CD4 T cells in HIV
Collaborator Contribution Collaboration in data analysis and interpretationCollaboration in data analysis, interpretation and presentationcollaboration on analysis of HIV viral tropismsCollaboration on mathematical modelling of lymphocyte kinetics
Impact Abstract presentation at CROI 2011
Start Year 2006
 
Description Collaboration with KCH London on CLL 
Organisation King's College London
Department Research Section of Molecular Haematology
Country United Kingdom 
Sector Academic/University 
PI Contribution Development of a new project to evaluate the effect of T cell inhibition on in vivo CLL Leukaemic cell turnover
Collaborator Contribution Development of a new project to evaluate the effect of T cell inhibition on in vivo CLL Leukaemic cell turnover
Impact Award of two grants from Leukaemia Lymphoma Research
Start Year 2010
 
Description NIH 
Organisation National Institutes of Health (NIH)
Department Vaccine Research Center (VRC)
Country United States 
Sector Public 
PI Contribution New collaboration with Dr R Koup's group at the Vaccine Research Center, at NIH Bethesda was developed in 2009. this builds on work dones as part of this MRC project.
Collaborator Contribution Development of new concepts and new projects. Learning new techniques and skills.
Impact New proposal currently being drafted
Start Year 2009
 
Description Lunch Club talk for elderly 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Type Of Presentation Keynote/Invited Speaker
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact about 50 mostly elderly people attended a talk on ageing and the immune system
"Lunch Plus" hosted by New Malden Baptist church, Surrey - 21/5/2012

Approached by several elderly people willing to participate in research
Year(s) Of Engagement Activity 2012