Utility of Quantum Dots for Labeling and Tracking Leukemic Cell Lines, Human Bone Marrow and CD 34+ Umbilical Cord Blood.

Quantum dots (QDs) are nanometer scale fluorescent semiconductors that have recently garnered much interest as agents for imaging. QDs have several advantages over conventional fluorescent imaging probes, including high quantum yield, broad absorption spectra and minimal photobleaching. QDs have been used little in hematology.

We studied hematologic cells to determine whether they could be labeled with QDs, whether QDs could be seen after multiple cell divisions, whether QDs remained visible as cells differentiate and whether QDs could target specific antigens on the surface of cells. Using QDs attached to an endocytosed protein, we could intracellularly label all hematologic cells tested, including multiple leukemic cell lines (HL-60 and KG-1), normal human and murine bone marrow, leukemic human bone marrow (AML and CML) and normal human CD34+ cells. The QDs are easily detected by FACS and microscopy.

By counting cell divisions using the cell membrane dye PKH26, we show that QDs can be seen in leukemic cell lines and primary cells through more than four cell divisions. Some cells from leukemic cell lines retain QDs for up to two weeks. We are also able to see QDs in cells through differentiation. We labeled HL-60 cells and cultured them with either 1,25 dihydroxy vitamin D or DMSO. QDs were seen in monocytic-like and neutrophil-like progeny of the labeled HL-60 cells. After labeling CD34+ cells and culturing them in appropriate cytokines, QDs were observed in the resultant monocytes.

We were also able to target QDs specifically to cells expressing certain cell surface antigens. QDs complexed to streptavidin and a biotinylated anti-CD33 antibody homed to myelogenous leukemic cell lines but not lymphomatous cell lines. In summary, we show for the first time that QDs effectively label and track hematolgic cells, adding a new option when addressing cell fate questions in hematology.