NASHVILLE--An experimental high-speed clinical cell selection
device has been shown to be capable of isolating a pure population
of hematopoietic stem cells (HSCs), essentially free from cancer
cells, and the machine's developer (SyStemix, Inc., Palo Alto,
Calif) has received FDA allowance for an active IND (investigational
new drug) for clinical testing of HSCs purified by cell selection
in cancer patients who are undergoing transplantation.
Speaking at a scientific session of the American Society of Hematology
(ASH) meeting, Chris Reading, PhD, said that the high-speed fluorescence-activated
cell sorting (HS-FACS) process can isolate HSCs at speeds of 15,000
to 30,000 cells per second, five to 10 times faster than conventional
sorters. The isolated HSCs retain the ability to self-renew and
propagate, he noted.
The sorter can select HSCs, and thus deplete tumor cells simultaneously,
and can process stem cells in large enough numbers to be of therapeutic
value, Dr. Reading said. Although the mobilization of stem cells
into the peripheral blood varies widely among patients, SyStemix
expects to be able to sort the required number of cells for
transplantation in a few hours.
Dr. Reading, director of cell procesing at Systemix, reported
that in mobilized peripheral blood samples from multiple myeloma
patients,processing with the high-speed sorter created a 90% pure
population of HSCs.
In five such samples,flow cytometric analysis showed a tumor burden
in the starting material of 100,000,000,000 cells (range,100,000,000
to 4,000,000,000). In ten such samples, after high speed cell
sorting , myeloma cells were reduced to below the level of quantitation
(1 in 1,000,000 or 0.001%).
The isolated HSCs are defined by the presence of cell-surface
markers CD34 and Thy-1 (which are lost as a cell develops into
a mature blood cell) and the absence of other surface markers
found on lineage-committed or mature cells (lineage negative or
In contrast to CD34+Thy+Lin- populations isolated in the SyStemix
process, CD34+ populations, targeted in other cell selection devices,
can be described as mixed populations that contain progenitor
cells, a varying number of stem cells, and possibly cancer cells.
It is the CD34+Thy+Lin- cell that is the self-renewing and pluripotent
stem cell, he said.