Although advances in our understanding of gene abnormalities in diseases involving blood organs and other tissues has been remarkable in recent years, the ability to introduce or manipulate expression of genes in target cells through gene therapy methods has been limited. Although a number of powerful viral vectors have been developed and utilized in both experimental and human systems, a number of issues, particularly safety, have demonstrated the need to develop non-viral based vectors for gene therapy. Recent discoveries have also demonstrated that it is essential to target normal hematopoietic stem cells (HSC), cells which have the potential to both self-renew and to give rise to all cell types in a given tissue, as well as leukemic stem cells (LSC), a subpopulation of cancer cells which confer the self-renewal properties of the malignant leukemic clone. Normal human HSC, and a majority of LSC, express the stem cell antigen CD34, and this proposal will utilize the specificity of this surface marker, as well as a novel murine model in which murine HSC express the human CD34 antigen. Therefore, the long range goals of this project are to develop novel non-viral gene therapy methods targeting normal and leukemic stem cells. In order to accomplish these goals, we propose the following Specific Aims: (1) to test human CD34 antibody mediated siRNA delivery in human CD34 cell lines;(2) to test human CD34 antibody mediated siRNA in murine models in vivo;and (3) to test whether human CD34 antibody mediated silencing of BCR/ABL or SALL4 will inhibit proliferation and leukemia-initiating ability of human primary myeloid LSCs. Accomplishment of these goals will set the stage for clinical trials, as well as lead to development of therapies directed against other oncogenes as well as altering stem cell gene expression.
A major problem in gene therapy is altering gene expression in specific cell types, and a major problem in cancer therapy is targeting the cancer stem cell, the small number of cells in the cancer or leukemia that are responsible for the propagation of the vast bulk of the tumor population. Failure to target these leukemic stem cells is thought to be responsible for treatment failure, especially in diseases like chronic myelogenous leukemia in which effective therapies for the bulk of the leukemic cells is available. The overall goal of this proposal is to develop methods of downregulating cancer inducing genes in a specific way in leukemic stem cells in order to target this cell and prevent the development of resistance.