From Molecular Biology to Therapy of Human Disease 
Studies in mice and rats confirm previous re- 
ports that the efficiency of engraftment is rela- 
tively poor (less than 1 percent) . We have stud- 
ied autologous hepatocellular transplantation in 
baboons as a model for human anatomy and surgi- 
cal methods. Transplantation resulted in consti- 
tution of approximately 5 percent of the host 
liver from the hepatocellular graft without 
, complications. 
We have explored the possibility of hepatocel- 
lular transplantation and gene therapy in utero. 
Heterologous hepatocellular transplantation was 
performed in fetal lambs at 80-85 percent gesta- 
tion by infusion of cells into the umbilical vein. 
Flow cytometry of hepatocytes recovered from 
transplanted animals demonstrated that 1.5-4.5 
percent of hepatocytes originated from the graft. 
Transient Gene Therapy by in Vivo 
Gene Delivery 
Other laboratories have reported that DNA 
coupled to asialoglycoproteins can be targeted to 
the liver in vivo, but that expression of these 
genes is transient (days) . We are interested in the 
possibility that transient expression might be the 
most efficacious approach to treating MCM defi- 
ciency, which is characterized by periods of rela- 
tive stability punctuated by life-threatening epi- 
sodes of acidosis. We have demonstrated in vivo 
delivery of MCM to the livers of experimental 
mice using asialoorosomucoid-polylysine-DNA 
conjugates and are currently studying the conse- 
quences of this gene delivery. In particular, we 
are concerned with demonstrating that DNA is 
completely eliminated after the period of tran- 
sient expression, since damage to chromoso- 
mal DNA from inadvertent integrations is one 
of the major potential risks. Vectors will be con- 
structed with suicide sequences to eliminate in- 
tegrated DNA. 
Future Directions 
Successful gene therapy requires attention not 
only to methods for gene delivery and gene ex- 
pression, but consideration of the metabolic, cel- 
lular, clinical, and social consequences of ge- 
netic manipulation. We are attempting to 
establish a broad base of expertise and experi- 
ence, using MCM deficiency as a model. This 
should enable rational development of clinical 
trials involving somatic gene therapy in the 
future. 
250 
