SURVIVAL AND DIFFERENTIATION OF RAT AND HUMAN EPIDERMAL GROWTH FACTOR-RESPONSIVE PRECURSOR CELLS FOLLOWING GRAFTING INTO THE LESIONED ADULTCENTRAL-NERVOUS-SYSTEM

Epidermal Growth Factor (EGF)-responsive stem cells isolated from the developing central nervous system (CNS) can be expanded exponentially in culture while retaining the ability to differentiate into neurons a nd glia. As such, they represent a possible source of tissue for neura l transplantation, providing they can survive and mature following gra fting into the adult brain. In this study we have shown that purified rat stem cells generated from either the embryonic mesencephalon or th e striatum can survive grafting into the striatum of rats with either ibotenic acid or nigrostriatal dopamine lesions. However, transplanted stem cells do not survive as a large mass typical of primary embryoni c CNS tissue grafts, but in contrast form thin grafts containing only a small number of surviving cells. There was no extensive migration of transplanted stem cells labeled with either the lac-z gene or bromode oxyuridine into the host region surrounding the graft, although a smal l number of labeled cells were seen in the ventral striatum some dista nce from the site of implantation. Some of these appeared to different iate into dopamine neurons, particularly when the developing mesenceph alon was used as the starting material for generating the stem cells. EGF-responsive stem cells could also be isolated from the mesencephalo n of developing human embryos and expanded in culture, but only grew i n large numbers when the gestational age of the embryo was greater tha n 11 weeks. Purified human CNS stem cells were also transplanted into immunosuppressed rats with nigrostriatal lesions and formed thin graft s similar to those seen when using rat stem cells. However, when prima ry cultures of human mesencephalon were grown with EGF for only 10 day s and this mixture of stem cells and primary neural tissue was transpl anted into the dopamine-depleted striatum, large well-formed grafts de veloped. These contained mostly small undifferentiated cells intermixe d with a number of well-differentiated TH-positive neurons. These resu lts show that purified populations of rat or human EGF-responsive CNS stem cells do not form large graft masses or migrate extensively into the surrounding host tissues when transplanted into the adult striatum . However, modifications of the growth conditions in vitro may lead to an improvement of their survival in vivo. (C) 1996 Academic Press, In c.