Gene transfer into experimental brain tumors mediated by adenovirus, herpes simplex virus, and retrovirus vectors

Three vectors derived from retrovirus, herpes simplex virus type 1 (HSV), and adenovirus were compared in cultured rat 9L gliosarcoma cells for gene transfer efficiency and in a 9L rat brain tumor model for histologic pattern and distribution of foreign gene delivery, as well as for associated tumor necrosis and inflammation. At a multiplicity of infection of 1, in vitro transfer of a foreign gene (lacZ from Escherichia coli) into cells was more efficient with either the replication-defective retrovirus vector or the replication-conditional thymidine kinase (TK)-deficient HSV vector than with the replication-defective adenovirus vector. In vivo, stereotactic injections of each vector into rat brain tumors revealed three main histopathologic findings: (i) retrovirus and HSV vector-mediated gene transfer was relatively selective for cells within the tumor, whereas adenovirus vector-mediated gene transfer occurred into several types of endogenous neural cells, as well as into cells within the tumor; (ii) gene transfer to multiple infiltrating tumor deposits without apparent gene transfer to intervening normal brain tissue occurred uniquely in one animal inoculated with the HSV vector, and (iii) extensive necrosis and selective inflammation in the tumor were evident with the HSV vector, whereas there was minimal evidence of tumor necrosis and inflammation with either the retrovirus or adenovirus vectors.