Gene therapy is a potential treatment for
hemophilia, wherein cells transduced with a normal
factor IX gene could provide a continuous in vivo source of circulating
factor IX. In this study, we examined the potential use of hematopoietic cells as a target for
factor IX gene therapy. Human
myeloid leukemia cells (HL-60) were transduced by retroviral vectors carrying a normal human
factor IX cDNA under control of either the Moloney murine leukemia virus long terminal repeat (MoMuLV LTR) (LIXSN), the SV40 promoter (LNSVIX), or a cytomegalovirus (CMV) promoter (LNCIX).
Factor IX production was measured in the transduced cells both in the uninduced state and after induction of granulocytic differentiation [with
dimethylsulfoxide (
DMSO)] or monocytoid differentiation [with
phorbol myristic
acetate (PMA)]. Transcription of
factor IX from the MoMuLV LTR was seen in all cells, with a two-fold increase upon differentiation. Induction with PMA led to an 8- to 15-fold increase in
factor IX transcripts from an internal CMV promoter. No
factor IX transcripts from the internal SV40 promoter were detected. Immunoreactive
factor IX protein was identified by Western blot from induced HL-60 cells transduced by either LIXSN or LNCIX.
Factor IX production by HL-60 cells transduced by LNCIX ranged from 38-93 ng/10(6) cells/24 hr following induction of monocytic differentiation. The
factor IX antigen titer was directly related to
factor IX coagulant titer (r = 0.98; p < 0.001). These data indicate that human myelomonocytic cells are capable of performing the necessary post-translational modifications to produce functional
factor IX.(ABSTRACT TRUNCATED AT 250 WORDS)