What does CCR5 virus mean in relation to using maraviroc?
I’ve recently taken a tropism blood test to see if I was suitable to switch to maraviroc.
I understand that I need to have CCR5 co-receptors in my white blood cells for this medication to work successfully.
The results came back today and I have been told that I have a mix of CCR5 and CXCR4 co-receptors, and that I would not be suitable for this medication.
What does this mix of CCR5/CXCR4 mean? Does this indicate that I been infected with 2 different strains of HIV?
Thank-you for your email.
Different HIV drugs work at different stages of the viral life cycle (the way HIV enters and duplicates within cells).
HIV has to enter a CD4 cell to use it to replicate. The process of attaching to the CD4 cell uses two main stages.
Stage one involves the virus attaching to the CD4 receptor on the surface of the CD4 cell. Stage two involves a co-receptor, without which infection cannot occur.
The major coreceptor is called CCR5 (or R5). Maraviroc binds to this receptor, preventing HIV from using it to get into the cell. So maraviroc is also called a CCR5 inhibitor.
Although most HIV uses CCR5 to enter a cell, some virus uses a different receptor called CXCR4. Sometimes these are abbreviated to R5 and X4 viruses. The word tropism is used to describe which corecptor is used by a different virus, ie HIV using R5 is called R5-tropic.
Most people (90% or more) are infected with R5 virus. Over time though, usually over many years, in some people the HIV slowly changes to being able to use both R5 and X4. In advanced HIV some people switch to exclusively using X4.
This is very common. More than half the participants looking to join maraviroc study were not able to use this drug because they had X4 virus. Some were dual or mixed tropic and had both X4 and R5 virus.
In people whose virus attaches to both receptors, a CCR5 inhibitor will not work.
When you have a tropism test it looks at the type of HIV virus in your body. This test is checking to see how HIV works, and which receptor it attaches to. Because your tropism test has showed that your virus can attach to both types of receptor maraviroc would not be effective in treating your infection.
This is more likely to reflect the development of HIV, but it could be that you were reinfected with a different virus. About 10% of new infections in a recent French study were with X4 virus. It’s worth asking your doctor these questions because s/he will have a better undestanding of your case history.
Can I ask why you are thinking about changing treatment?
Further information about maraviroc and CD4 receptors is on our website at the following links:
Technical reviews of studies looking at CCR5 and CXCR4 receptors and HIV: