In a review article Miller [1] reported on the state of the art of human gene therapy as it was summarized in a meeting at the end of December 1991. The human trials in which human genes were successfully transferred in vitro to mark cells of patients and for gene therapy of genetic disorders. The approved gene therapy trials are based on the use of: (a) retroviral vectors and (b) liposomes which contain plasmid DNA that have been found useful in gene transfer into human cells under culture conditions in vitro for administration to the donor of the cell by injection. One of the aims of human gene therapy is to advance anticancer treatment protocols by using human genes whose products have been shown to have suppressive effects on tumor progression. Another aim is to introduce an active human gene which is missing in patients with single gene mutations (e.g., low-density lipoprotein receptor gene transfer to hepatocytes from lowdensity lipoprotein receptor deficient patients; adenosine desaminase gene transfer to lymphocytes from adenosine desaminase deficient patients [ 1 ]).
The crucial elements in gene therapy are the gene delivery vectors. The approved gene transfer trials in human cells utilize retroviral vectors from which all the viral genes are removed or altered and replication of viral