DESCRIPTION: (Applicant's Abstract) The purpose of this application is to develop better vectors and reagents that will improve the genetic therapy of brain tumors. The applicant's overall strategy is novel and circumvents present technological limitations in at least three fundamentally important ways. First, it permits the targeted delivery of specific genes to cancer cells, avoiding for the most part normal tissue. Second, his strategy reduces many important safety concerns associated with present gene therapy approaches. Finally, it improves on the efficiency of gene delivery and the low virus titers available. The applicant's strategy involves the specific delivery of the modified human ecotropic retrovirus receptor (MERR) to targeted cells. During the period in which MERR is expressed on those cells they will become infectable by ecotropic retroviruses carrying a desired therapeutic gene. An important component of his technology is the use of monoclonal antibodies and their antigen binding domains for targeting human tumors. The applicant will use targeting components, such as antibodies in conjunction with a retrovirus receptor to permit infection of non- permissive cells from one species by a virus from another species. For example, he will construct fusion proteins between the targeting component (e.g., VH and VL genes of a monoclonal antibody) and the receptor. This approach greatly enhances safety and provides the only means of targeting for gene therapy available today. The applicant has accumulated substantial preliminary data indicating that the approach will work. This application seeks to complete in vitro studies, move the technology into animal models and eventually to clinical protocols.