ABSTRACT
I. INTRODUCTION Since many terms in the field of stem cell biology can be ambiguous, we here define our use of terminology:
Primitiveness: a quality that reflects the position of a stem cell in the developmental hierarchy; a very primitive stem cell is thought to have extensive proliferative capacity which is reflected in the repopulation kinetics; for example, long-term repopulation with late onset characterizes a primitive stem cell. Less primitive stem cells repopulate faster but have less differentiation capacity.
