Critical Aspects of Clinical Trial Design for Novel Cell and Gene Therapies

Table 1

Comparison of tissue/cell sources for cell replacement strategies in PD.

Type of cell	Availability/expandability/proliferation	Capacity to differentiate into DA phenotypes	Tumor formation potential	Ethical concerns	GID	Major advantage
Fetal VM tissue	+/−	+++	−	+	+	Clinical experience
Embryonic stem cells	+++	++	+	++	?	Expandability and differentiation
Neural stem cells	+	+	+/−	+/−	?	Opportunity of autotransplantation
Mesenchymal somatic stem cells	+	+/−	?	−	?	Opportunity of autotransplantation
Reprogrammed somatic cells	++	++	+	+	?	Easily approached autologous source (e.g., fibroblasts retrieved from skin biopsies)

(?): unknown, (−): none, (+/−): poor, (+): some, (++): readily observable, (+++): extensive.