Question

Is there a reason why CD4 counts fluctuate? I have been enrolled in a phase III clinical trial for the "quad" for 8 weeks. At the start my viral load was at 4,000+ copies and my CD4 was around 620. Within 2 weeks my viral load was undetectable and my CD4% has gone up from 30% to 37% however my CD4 has dropped to 377. It seems like a big drop to me and the researchers didn't seem concerned unless it drops below 300 - but I would think CD4 counts would go up - not down. So are the factors or reasons why this particular number has dropped or why CD4 counts fluctuate. Thanks.

Answer

Thanks for the question.
CD4 cells are distributed throughout the body...in the blood, lungs, heart, intestines, brain,etc. Infact the vast majority of all CD4 cells are out in the tissues, not floating in the blood. They can find and attack infection best at the source in the tissues of the body. However, we only measure CD4 counts in the liquid part of the blood....so in essence we are looking only at the tip of a very large iceberg. As that iceberg bobs in and out of the water the amount we see goes up and down. That is, as the CD4 cells move in and out of the blood to the tissues the number can fluctuate (even from morning to night). The CD4% can be more stable since the proportion of T cells that are CD4 is consistent between what is in the blood and tissues (just like the content and makeup of the part of the iceberg above and below the water line). Good luck on tyhe QUAD trial you have had a very good initial response.

Joe