Summary
To study and evaluate the potential of the haematopoietic system as a target for gene
therapy in haemophilia A, we have infected murine bone-marrow cells with a recombinant
retrovirus encoding blood-coagulation factor VIII and the bacterial enzyme neomycin-phosphotransferase.
After transplantation of the infected bone marrow into lethally irradiated mice, the
presence of intact vector could be demonstrated in DNA isolated from individual haematopoietic
progenitor-cell-derived spleen colonies. About 8% of the spleen colonies were shown
to contain the intact vector. Selection for resistance to the neomycin analogue G418
prior to transplantation specifically killed the uninfected bone-marrow cells and,
as a result, over 90% of the spleen colonies contained the factor VIII vector. However,
expression of factor VIII in vivo, either at the RNA or at the protein level could
not be demonstrated. From these data we conclude that: 1) retroviral vectors can be
used to transfer factor-VIII cDNA into haematopoietic progenitor cells; 2) the vector
sequences are expressed immediately after integration; and 3) transcription of the
vector is repressed in the progenitor-cell-derived cells.