Journal of Neuroscience, Vol 14, 7553-7562, Copyright © 1994 by Society for Neuroscience
Long-term delayed vascularization of human neural transplants to the rat brain
C Geny, S Naimi-Sadaoui, R Jeny, AM Belkadi, SL Juliano and M Peschanski
INSERM CJF 91-02, Neuroplasticite et Greffes Intracerebrales, Faculte de Medecine, Creteil, France.
Human neural transplants are being developed to treat Parkinson's disease.
Previous characterization of human transplants focused on neuronal
development, while little is known of the interaction between the
transplant and its environment, among which blood is of prime importance.
We evaluated here the formation of blood vessels in human neural xenografts
placed into the brain of rats immunosuppressed with cyclosporin A. Using
capillary wall markers, we found that human transplants remain virtually
nonvascularized for more than 1 month. Angiogenesis takes place very slowly
and the density of blood vessels is still quite poor after 3 months, the
fine structure of these capillaries, when they form, is apparently normal.
Functional studies indicate that the vascular network formed in the
transplant allows blood circulation and exhibits a working barrier to
macromolecules. Glucose uptake and consumption and cytochrome oxidase
activity are almost undetectable up to 3 months after grafting. These
results demonstrate that vascularization is much delayed in human
xenografts into the rat brain. This delay is likely to be dependent on the
maturation of the transplanted tissue. A dedifferentiation of human
endothelial cells cotransplanted with neural cells occurs since
histochemical and immunocytochemical markers revealing endothelial cells in
the human fetus are not present up to 1 month in the transplant. The origin
of this phenomenon is a matter of speculation. How neural cells survive and
mature in such conditions are issues of prime interest for the future of
human neural grafting.