Studies of Blood Cell Formation 
David A. Williams, M.D. — Assistant Investigator 
Dr. Williams is also Assistant Professor of Pediatrics at Harvard Medical School. He received his under- 
graduate degree in biology from Indiana State University and his medical degree from Indiana University 
School of Medicine. His postdoctoral training includes a pediatric residency at Children's Hospital Medical 
Center, Cincinnati; research fellowships with Richard Mulligan at the Massachusetts Institute of Technol- 
ogy Center for Cancer Research and the Whitehead Institute for Biomedical Research; and clinical fellow- 
ships in pediatric hematology /oncology at Harvard Medical School, the Children's Hospital, and Dana- 
Farber Cancer Institute. 
THE general goal of our research is to gain a 
better understanding of blood cell formation 
and of how to apply the knowledge to the treat- 
ment of relevant diseases. The work in progress is 
roughly divided into research on the role of the 
bone marrow environment in maintaining blood- 
forming cells in a normal way, on the effect of 
directing the expression of growth-regulating 
genes in specific blood cells in murine models, 
and on the development of gene transfer as a po- 
tential method of correcting human diseases in 
which blood cells are affected. 
Investigating the Bone Marrow 
Environment 
Blood cells are produced and delivered to the 
circulation by precursor, or stem, cells in the 
bone marrow. Balance is carefully maintained be- 
tween production and utilization. Although ad- 
vances have recently been made in explaining the 
control of production of daughter cells, the pro- 
duction of the stem cells is still little understood. 
Bone marrow stem cells reside in a complex 
environment comprising many specialized cells, 
called stromal cells. This microenvironment can 
be recapitulated in vitro. However, investigation 
of stem cell interactions with the microenviron- 
ment has been hampered in the past by the com- 
plex nature of the stromal components. Using mo- 
lecular methods, our laboratory, in collaboration 
with Vikrum Patel at Northwestern University, 
has generated permanent cell lines derived from 
this stromal milieu, and some of these lines have 
been shown to maintain blood formation. More- 
over, they have led to the identification of impor- 
tant proteins of the bone marrow that help to an- 
chor primitive blood-forming cells in the 
appropriate locations. Interaction of blood-form- 
ing cells with such proteins may be important in a 
variety of normal and abnormal functions, in- 
cluding control of blood formation, regeneration 
of stem cells after marrow transplantation, and 
movement of leukemia cells out of the bone 
marrow cavity. 
In another project, cell lines generated from 
mice exhibiting a severe genetic abnormality in 
the bone marrow microenvironment have helped 
to identify the causative molecular lesion as well 
as the normal protein that this defective gene 
should produce. Work done in collaboration 
with Kris Zsebo at Amgen has shown that the pro- 
tein is an important growth factor for very primi- 
tive blood-forming cells. It may prove to be a 
valuable therapeutic tool for bone marrow 
diseases. 
In addition, Steven Paul of our laboratory, in 
collaboration with Yu Chung Yang (currently at 
Indiana University) and Genetics Institute, has 
utilized a stromal cell line generated from pri- 
mate bone marrow to identify and clone another 
new growth factor affecting blood-forming cells 
and lymphocytes. This factor, called interleukin- 
1 1 (IL-1 1), appears to stimulate the growth of B 
lymphocytes and the bone marrow cells that give 
rise to blood platelets. Further characterization 
of the effects of this growth factor in mice is 
under way. 
Regulated Expression of Growth-regulating 
Genes in Hematopoietic Cells 
In order to study the effects of certain growth- 
regulating genes on the behavior of hematopoi- 
etic stem cells, the laboratory is utilizing embry- 
onic stem (ES) cells to generate transgenic mice 
containing foreign genes. Such genes are easily 
introduced into cultured cells. Upon transfer of 
the manipulated cells into embryos, ES cells con- 
tribute to all the tissues of the resulting animals. 
This new and powerful technology allows the ex- 
pression of new genes in specific hematopoietic 
cells (such as red or white blood cells) in adult 
mice. 
Deniz Toksoz of our laboratory is investigating 
the effects of expression of specific growth factor 
genes on the development of blood-forming cells 
in the early mouse embryo. The earliest stage of 
blood formation occurs in the fetal yolk sac. 
Growth-regulating genes, such as macrophage or 
granulocyte colony-stimulating factors, have 
well-defined pharmacologic activities on hemato- 
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