One of the major challenges facing cell
biology is to recreate human tissues in vitro for reimplantation.
Tissue cultures depend on a special category of cells: stem cells
capable of multiplying - for self-renewal of the stock - and of
differentiation to turn into specialised cells.
Research scientists and doctors are showing particular interest
in blood stem cells or hematopoietic stem cells (HSC), found
in the red bone marrow. These form every type of blood cell (red
corpuscles, immune cells or platelets). In vitro cultivation
of HSC could therefore provide a means to produce immune cells for
patients with a bone marrow deficiency or red corpuscles to treat
anaemia - or even to create a complete blood substitute for transfusions.
Multiplying without differentiation
All transplants require a sufficient supply of blood stem cells
to reimplant and, above all, regenerate the tissue. However, as
with all organs and blood, there are not enough donors. In the specific
case of HSC, produced by the red marrow in the long bones - such
as the femur or sternum - major surgery is needed to obtain the
sample and this, in turn, has deterred many a compatible donor.
What is needed, therefore, is to amplify the rare supply
of HSC available. There are two difficulties: stem cells are resting
cells, which means they do not divide spontaneously and when they
start proliferation and differentiation, they rapidly die. For this
reason, the objective of the European Hematopoietic Bioreactor
project was to amplify the HSC in vitro and achieve self-renewal,
without differentiation or ageing. Eight research teams worked on
this project for four years under the EU's Biotech 2 programme.
Umbilical cord blood
The first thing which the partners in this project did was to choose
a source of hematopoietic stem cells which solves the donor problem:
blood from the umbilical cord which is generally destroyed after
birth. HSC from the umbilical cord are of higher quality, less prone
to infection and, above all, less likely to be rejected by the recipient
than bone marrow cells. 'We realised that the blood from a single
cord, that is between 80 and 120 ml, contained as many blood stem
cells as a normal sample of between 800 and 1200 ml from a donor,'
explained project coordinator Dr Jacques Hatzfeld. 'Even these few
drops of blood from a single cord can be amplified in vitro
to produce enough stem cells for a graft on an adult.'
These precious cells are therefore recovered and cultured in bioreactors-
a medium kept under constant control. Normally, however, cell division
inhibitors keep the blood stem cells resting. The research teams
countered this with molecules capable of blocking the inhibitors,
thus clearing the way for the cells to enter the division phase.
Next, they succeeded in slowing down the irreversible differentiation
process. In this way, the HSC culture self-renews for over 100 days.
Now the scientists are looking for ways of speeding up this self-renewal.
Placenta blood banks
Throughout Europe, particularly in Germany, France, Italy and Spain,
umbilical cord and placenta blood banks are gradually being built
up in the form of frozen samples, which, when the time comes, can
then be amplified using the technique developed in this project.
Before each sample is taken, the mother's blood is tested, to make
sure that it is free of infections, and HLA-typed (1).
The advantage of these HSC banks is that they considerably shorten
the wait for a transplant. Once a compatible cell sample is found,
it is available for the recipient immediately, compared with a wait
of several weeks for a bone marrow transplant. In the longer term,
doctors hope to build up a stock of compatible blood stem cells
for each patient, from which they would produce the type of cell
needed by the patient (lymphocytes, red corpuscles, etc.), depending
on the case. It is already possible to control the results of HSC
culture differentiation, by adding appropriate nutrients and growth
Towards other tissue cultures
Another branch of this project is developing culture media containing
no animal protein to reduce the risk of transmission of pathogens
such as prions or viruses to humans. 'We have developed a medium
containing no serumalbumin or transferin from cattle or human beings
to carry the fatty acids and iron indispensable for any cell culture.
We have replaced them by uncontaminated synthetic molecules performing
the same function,' stated Dr Hatzfeld.
The blood stem cells used by these European researchers are, therefore,
in a way a model which can be used in the future for other tissues
in which industrial partners are already showing interest, such
as liver, pancreas, bone or muscle. The way is therefore open to
culturing stem cells for human tissues in Europe.
(1) HLA molecules: the
'identity card' carried by cells and deciding compatibility between
donor and recipient.
Hematopoietic Bioreactor: a model for human somatic stem cell
Docteur Jacques Hatzfeld,
Laboratoire de Biologie des cellules souches somatiques humaines
- Unité Propre de Recherche 1983 CNRS, 94 800 Villejuif.
Fax: +33-1- 49 58 33 15
E-mail : firstname.lastname@example.org
- Laboratoire Génétique Moléculaire et
Intégration des Fonctions Cellulaires, Centre National
de la Recherche Scientifique, Villejuif, France (coordinator)
- Institute of Molecular Medicine, John Radcliffe Hospital,
Oxford, United Kingdom
- Laboratorio di Biologia Cellulare, Istituto Superiore della
Sanità, Rome, Italy
- Rhône Poulenc Rorer R&D, Vitry-sur-Seine, France
- Helmut Hund GmbH, Wetzlar-Nauborn, Germany
- Integra Biosciences GmbH, Fernwald, Germany
- Novo-Nordisk A/S, Bagsvaerd, Denmark
- Instituut Hematologie, Erasmus Universiteit, Rotterdam,
Umbilical cord and placenta blood banks in
the form of frozen, amplifiable samples, could considerably shorten
the wait for a transplant.