RETROVIRAL TRANSFER AND LONG-TERM EXPRESSION OF HUMAN CYTIDINE DEAMINASE CDNA IN HEMATOPOIETIC-CELLS FOLLOWING TRANSPLANTATION IN MICE

The chemotherapeutic effectiveness of cytosine nucleoside analogues us ed in cancer therapy is limited by their dose-dependent myelosuppressi on. A way to overcome this problem would be to insert the drug-resista nce gene cytidine deaminase (CD), into normal hematopoietic cells. CD catalyzes the deamination and pharmacological inactivation of cytosine nucleoside analogues, such as cytosine arabinoside (Ara-C). The objec tive of this study was to determine if we could obtain long-term persi stence and expression of proviral CD in hematopoietic cells following transplantation of CD-transduced bone marrow cells in mice. Muring hem atopoietic cells were transduced with an MFG retroviral vector contain ing CD cDNA and transplanted into lethally irradiated mice. The recipi ent mice were administered three courses of 10-15 h i.v. infusions of Ara-C (75-110 mg/kg). Blood, marrow and spleen samples were obtained a nd analyzed for CD proviral DNA by PCR, CD activity by enzyme assay, a nd drug resistance to Ara-C by clonogenic assay. We detected the prese nce of the CD proviral DNA in most of the samples examined. Approximat ely 1 year after transplantation several mice showed increased express ion of CD activity in these tissues and some mice displayed signs of A ra-C resistance. These data demonstrate that persistent in vivo expres sion of proviral CD can be achieved in transduced hematopoietic cells and indicate some potential of this gene for chemoprotection to improv e the efficacy of cytosine nucleoside analogues in cancer therapy.