Figure 1. Testing for gene expression in humanized mice. Human CD34+ hematopoietic stem cells (HSCs) can be seen expressing a luciferase gene in the bone marrow and spleen of a humanized mouse. The luciferase gene was introduced by injecting an HIV-derived vector into the bone marrow of the mouse, providing proof of concept that this simplified approach can work. The vector has proteins on its surface that enable it to target CD34+ HSCs and therefore a bone marrow transplant is not required to introduce modified HSCs. The mice are generated by injecting human cord blood CD34+ HSCs. After 60 days they are injected with the vector and then two weeks later, Luciferase expression can be seen in the bone marrow and the spleen (shown at day 14). Red areas show the highest level of Luciferase expression and blue shows the lowest level. Image provided by Pin Wang, University of Southern California.