Dr. Orlic works in the Genetics and Molecular Biology Branch. The research of the Hematopoiesis Section of the Laboratory of Gene Transfer is focused on the pluripotent hematopoietic stem cell (PHSC). This cell type is the progenitor of all cells in the peripheral blood, from erythrocytes to T Iymphocytes.

The section has two research objectives. The first is to use retrovirus-mediated gene transfer to introduce new genetic material into PHSCs either as a model for human gene therapy or to study the effects of disregulated expression of individual genes on the differentiation of hematopoietic cells. The second is to purify PHSCs so their biological properties can be studied. We are particularly interested in determining which signals initiate PHSC differentiation and which signals are responsible for self renewal of these cells.

To test new gene therapy protocols using human PHSCs, we developed a transgenic immunodeficient mouse model to study human hematopoiesis. Immunodeficient transgenic mice were created expressing the human interleukin-3 (IL-3), granulocyte-macrophage colony stimulating factor (GM-CSF), and stem cell factor (SCF) genes. When human bone marrow cells are injected into transgenic SCIDS mice, human cells are detected in the blood for 20-24 weeks. We will use our immunodeficient mouse model to evaluate gene transfer efficiency into primitive human hematopoietic cells.

We have developed strategies to enrich mouse PHSC over 1000 fold, and we are initiating studies on primate and human PHSC. We have identified a subset of cytokine receptor mRNAs expressed in PHSCs, including high levels of the mRNA for the c-kit receptor and moderate levels of mFNA for the IL-3 receptor subunits. We will continue to screen this RNA population for the presence of mFNAs for additional cytokine receptors and other genes expressed uniquely in PHSCs. Since retroviral integration depends on division of the normally quiescent PHSC, we are particularly interested in identifying novel genes that regulate PHSC self renewal.