Leukocyte dynamics in health and disease: in vivo labelling of dividing leukocytes using deuterated water

Large controversies exist as to how long immune cells live, how fast they are
produced, and how fast they die in a healthy individual. Lack of insight in a
healthy situation hampers research focused on how leukocyte dynamics are
changed when the immune system is disturbed, as is the case in HIV-1 infection
or hematopoietic stem cell transplantation. A recently developed technique
named stable isotope labelling has made it possible to study cell dynamics in
vivo, under physiological circumstances. In this study we intend to give the
label "deuterium" to individuals as heavy water, to determine the turnover
parameters of diverse leukocyte populations in health (young adults, healthy
seniors of 60 years and older, healthy individuals that had their thymus
removed at young age), and compare these to situations that disturb the immune
system (HIV-1 infection, hematopoietic stem cell transplantation (HSCT)). A
better insight in these basic parameters is essential if we want to answer more
concrete questions, like whether in HIV-infection chronic immune activation or
a homeostatic response to CD4 T cell depletion is responsible for the increased
CD4 T cell turnover, and whether in lymphopenic HSCT-patients an active
homeostatic response is triggered or not. Eventually, a better understanding of
the dynamic basis of such disturbances will help in the development or
improvement of therapeutic interventions.

Objective of this study is to determine the turnover of leukocyte populations
in health (young, old) and how this compares to situations in which the immune
system is disturbed ((HIV-1 infection, HSCT, thymectomy).

The study entails an open observational study, consisting of temporary
consumption of stable-isotope-labelled (deuterated, or heavy) water (2H2O), and
prospective blood and urine sampling for laboratory tests. Blood withdrawals
are done maximally 7 times during the period that heavy water is taken
(uplabelling phase), and maximally 7 or 8 times in the period thereafter
(delabelling phase). From the blood samples several cell populations will be
sorted, after which the deuterium enrichment in DNA isolated from these
populations can be determined by a combination of gas chromatography and mass
spectometry (GC-MS). Frequent sampling of urine permits the correction of label
intake by an individual at a given time point.

The burden for participants of this study is minimal. Intake of small amounts
of 2H2O as described in this study is not harmful and the daily intake during
the uplabelling phase can take place at home. Only the initial bolus of 2H2O
of 10 ml per kg of body weight, which is given in little doses at the day care,
can possibly cause some dizziness or nausea. Blood withdrawals take place
maximally 7 times in the period during which 2H2O is taken (uplabelling phase)
and 7 times in the period after stopping 2H2O intake (delabelling phase). If
necessary and possible, an 15th blood withdrawal will be done at least a year
after stopping 2H2O intake. Hence, participants will visit the UMC Utrecht 14
to 15 times. Where feasible, these visits will coincide with regular control
visits (HSCT patients, HIV-patients). Blood withdrawals can on rare occasions
lead to subcutaneous hematomas. An exception to the UMC visits are the healthy
individuals of 60 years and older: all blood withdrawals except the first one
will be carried out at the old people's home instead of the UMC Utrecht.