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 used in cancer therapy is limited by their dose-dependent myelosuppression. A way to overcome this problem would be to insert the drug-resistance 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 objective of this study was to determine if we could obtain long-term persistence and expression of proviral CD in hematopoietic cells following transplantation of CD-transduced bone marrow cells in mice. Muring hematopoietic cells were transduced with an MFG retroviral vector containing CD cDNA and transplanted into lethally irradiated mice. The recipient 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 and analyzed for CD proviral DNA by PCR, CD activity by enzyme assay, and drug resistance to Ara-C by clonogenic assay. We detected the presence of the CD proviral DNA in most of the samples examined. Approximately 1 year after transplantation several mice showed increased expression of CD activity in these tissues and some mice displayed signs of Ara-C resistance. These data demonstrate that persistent in vivo expression of proviral CD can be achieved in transduced hematopoietic cells and indicate some potential of this gene for chemoprotection to improve the efficacy of cytosine nucleoside analogues in cancer therapy.