742 Epithelial Cells in Human and Murine Blood and Bone Marrow

Cytokeratin positive cells are frequently found in the blood (BL) and bone marrow (BM) of patients with epithelial cancers and are attributed to metastasis. We document here the reproducible presence of epithelial cells (ECs) in normal human and murine BL and BM. We used four different methods: immunofluorescence microscopy (IF), Krt1-14;mTmG transgenic mice, rtPCR, and flow cytometry. To this end, we have made several novel and interesting findings. First, we discovered rare but reproducible pan-cytokeratin+ cells the size of small lymphocytes in smears and cytospins of untreated human and murine BL and BM. Second, we found that Epithelial Cell Adhesion Molecule positive (EpCAM+) cells in human BL constituted 0.18% ± 0.0004 (SEM; n=7 biological replicates, 4 experimental replicates), and for BM, 3.53%±0.006 (SEM; n=3 b.r., 4 e.r.) of mononuclear cells. In mice, blood EpCAM+ cells constitute 0.45% ± 0.0006 (SEM; n=2 b.r., 4 e.r.) and in BM, 5.17%± 0.001 (SEM; n=3 b.r., 4 e.r.). In mice, virtually all the EpCAM+ cells were immunoreactive to pan-cytokeratin as determined by IF microscopy. Third, using Krt1-14;mTmG transgenic mice, we found low (8.6 native GFP+ cells per 106 cells analyzed (0.085% of viable cells), but significant numbers (p<0.0005) of GFP+ cells in normal murine BM that were not the result of randomness. Fourth, rtPCR detected traces of cytokeratins 14 and 15 in mouse BL and BM. Further, flow cytometric analyses disclosed heterogeneity within the EpCAM+ population of mouse cells when compared with CD45 (0.58% in BM; 0.13% in BL) and CD44 (0.13%) lineage markers. We conclude from these observations that cells expressing cytokeratin proteins and mRNAs are reproducibly detectable among mononuclear cells from human and murine BL and BM. These observations set the stage for determining the functions of these most curious and novel epithelial cells.