Frape-1 and Frape-3: Two different recombinant retroviruses encoding the same human marker gene

A major goal in retroviral-based gene therapy is to establish methods that allow for the selection and tracking of transduced cell populations. Ex viv o gene marking of normal and malignant hemopoietic cells allows the cells t o be followed subsequently in vivo. For in vivo applications, a neutral mar ker gene that is nonimmunogenic is desirable. To track two distinctively tr eated cell populations in a single individual, we designed and constructed two retroviral vectors; both of these vectors encode a truncated form of th e human low-affinity nerve growth factor receptor, a neutral gene that does not transduce signals and is expected to be nonimmunogenic in humans. The two vectors, named Frape-1 and Frape-3, are identical at the protein level but differ at the DNA level, containing restriction sites that allow easy d etection by polymerase chain reaction analysis. We show that cell lines and primary CD34(+) cells can be readily transduced with these vectors and tha t transduced cells can be distinguished by polymerase chain reaction- and v ector-specific restriction sites. These vectors will be useful for toxicity studies on in vivo gene therapy and for determining the source of relapse in hematological malignancies.