T-cell turnover during HIV infection; production and life span of T-cells in HIV infected
individuals during cART

It seems that depletion of naive T-cells during chronic HIV infection is caused
by persistent activation of the immune system. This activation makes naive and
memory T-cells differentiate continuously, thereby slowly exhausting the
peripheral CD4 T-cell reservoir.
When HIV infected individuals have less than 200 CD4 T-cells per microliter
blood or have an AIDS-indicator disease they are classified as having *acquired
Immunodeficiency Syndrome * (AIDS). At this stage patients are more
susceptible for other infections, due to a malfunctioning immune system.
In order not to reach this stage of the disease, HIV infected individuals start
antiretroviral therapy (cART) when they have less than 350 CD4 T-cells per
microliter blood. The goal of this therapy is to increase in CD4 T-cell numbers
due to repression of the virus. Some patients respond very well to this
therapy, whereas others hardly show an increase in CD4 T-cell numbers in spite
of viral repression.
The generally accepted explanation is that this is due to different T-cell
production rates in these individuals. In this study we would like to
investigate whether death of newly produced CD4 T-cells also contributes to
this process and hence to the difference between individuals.
We would like to measure the production and death (turnover) of CD4 T-cells in
HIV infected individuals that reconstitute their CD4 T-cell number well during
HAART and in individuals that do not. We would do this by labeling newly
produced cells with deuterium, using deuterated water. By measuring different
T-cell populations (recent thymic emigrants, naive- en memory T-cells), this
technique allows us to follow the fate of newly produced naive T-cells. We are
going to compare deuterated water labeling of HIV-1 infected individuals that
reconstitute well with that of HIV-1 infected individuald that do not, together
with Ki67 and CD31 staining and TREC analysis.
This way we measure the production rate of new T-cells in HIV infected
individuals on cART as well as the rate at which these cells disappear again.
With this information, we can determine whether the production rate or the
lifespan (or both) of newly produced cells is reponsible for the degree of
reconstitution.
Differences in the extent of T-cell production and/or death between the primary
study group (immunological responders) and the control group (immunological
non-responders) will tell us why there is a difference in reconstitution: in
the immunological non-responders fewer cells are being produced or the cells
are shorter lived. It has been assumed that there are two processes influencing
the degree of reconstitution:
1) A homeostatic response to low cell numbers in the depleted pool, i.e., a
lymphopenia-induced proliferation.
2) Immune activation, both directly, by the virus, through activation of
Toll-like receptors on dendritic cells, and indirectly, resulting from
increased permeability of the gut, through which bacterial translocation occurs
and immunogenic products end up in the circulation.
The deepening research question can be formulated as: What are the relative
contributions of (lymphopenia-induced) homeostasis and immune activation to the
production and death rates of T cells? Answering this question is highly
relevant, because insights in the relative contributions of homeostasis and
immune activation during disease and recovery provide leads for the improvement
of treatment for HIV infection.

With this research we aim at gaining more insight into the reason for the fact
that some individuals reconstitute well during cART whereas other do not. Also,
we would like to investigate what mechanism is responsible for reconstituting
the CD4 T-cell compartment.

Twenty five individuals will participate in this study. These are 15 HIV-1
infected individuals who reconstitute well during cART (= increase in CD4
T-cells to > 350/ul blood and an undetectable viral load) and 10 HIV infected
individuals who are treated with cART and have undetectable viral load, but
who's CD4 T-cell numbers are still below 350/ul blood. Theere are 5 HIV-1
infected individuals that do not reconstitute well during cART, who are
participants in the deuterated water part of the MIRS study. They are also used
as controls. The total duration of participation in this study is 24 weeks. The
planning within these 24 weeks is as follows;

-Week 1-6:
Intake of deuterated water: On the first day of the study an amount of water
has to be drunk that is equal to 10ml per kg bodywater (=60% of body weight)
. This will be 350-550 ml for most individuals. Next, participants will be
asked to drink 1/8 of this amount once daily from day 2 until day 42.
Blood and urine donation: During the first 6 weeks of the study, participants
will donate 50ml blood and urine 4 times.
Questionnaire: At each study visit, the participants will fill in a
questionnaire in order to check whether they have had conditions that might
influence T-cell turnover, since the last visit. For instance, influenza.
-Week 7-24:
Intake of deuterated water: Participants do not have to take deuterated water
anymore in this phase of the study.
Blood and urine donation: From week 7 until week 24, again participants will
donate 50ml blood and urine 5 times.
Questionnaire: Again, at each visit a questionnaire will be filled in.

The start date of the study will be aimed June 1st 2010 and the end date will
then be December 1st 2020.

The burden on the participants consists of a single intake of 10 ml deuterated
water per kg bodywater. Thereafter 1,25 ml per kg body water will be taken once
daily, for a duration of 42 days. The first intake of deuterated water will be
a burden for the patient, because temporary dizziness and/or nausea can occur.
Participants therefore have to be monitored for the first few hours after
initial intake. We estimate the burden of the rest of the daily intakes, that
take place at home, to be minimal. The amount of fluid are very small and also,
there is no chance of dizziness and/or nausea.
Furthermore, during the period of heavy water intake, 50 ml of blood will be
drawn and urine will be donated 4 times and in the 18 weeks after cessation of
heavy water intake again 5 times. This will take place in the UMC Utrecht and
we will try to plan these visits together with standard visits as much as
possible, thereby minimizing the burden on the participant. The total volume of
blood that is drawn (450 ml in 6 months) can be missed by adults, also HIV
infected individuals.

The intake of above mentioned amounts of heavy water does not damage the health
of participants. Therefore, to our knowledge, the risk of participation in this
study is negligible.