Phage display peptide libraries have enabled the discovery of peptides that selectively target specific organs. Selection of organ‐specific peptides is mediated through binding of peptides displayed on phage coat protein to adhesion molecules expressed within targeted organs. Hematopoietic stem cells selectively home to bone marrow, and certain adhesion receptors critical to this function have been demonstrated. Using a phage display library, we identified a specific peptide that trafficked to murine bone marrow in vivo. We independently isolated exactly the same heptapeptide from the entire library by in vitro biopanning on primitive lineage‐depleted, Hoechst 33342dull/rhodamine 123dull murine bone marrow stem cells and confirmed peptide binding to these cells by immunofluorescence studies. We demonstrated bone marrow–specific homing of the peptide by an in vivo assay in which the animals were injected with the phage displaying peptide sequence, and immunofluorescence analysis of multiple organs was performed. We also showed that the peptide significantly decreased the homing of stem cells to the bone marrow but not to the spleen 3 hours after transplantation using fluorescently labeled Lin−Sca+ hematopoietic cells in an in vivo homing assay. The peptide sequence has a partial (5/7) amino acid sequence homology with a region of CD84. This discovery represents the first application of the phage display methodology to the bone marrow and stem cells and led to the identification of a specific heptapeptide that homes to bone marrow, binds to primitive stem cells, and plays a role in stem cell homing.

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Summary. Umbilical cord blood is an alternative stem cell source for patients without matched family donors. In this study, we examined several parameters that have not been studied in detail ± radiation dose, cell dose, age of mice, and maternal and neonatal characteristics of the cord blood donor ± that affect engraftment of cord blood in non-obese diabetic±severe combined immunodeficient (NOD±scid) mice. Engraftment, measured using flow cytometry analyses of human CD45 1 cells, was highest in 400 cGy-treated mice. Successful engraftment was demonstrated up to 6 months, with a mean engraftment of 31% (range 0± 67%) of human cells in recipient bone marrow. Engraftment was skewed to B lymphocytes. The radiation dose of 350 cGy resulted in superior survival of the murine recipients compared with 400 cGy (P 0.03). The sex of the NOD±scid recipients had a significant effect on survival (female superior to male, P 0´01), but not on engraftment. There were high levels of variability among different cord units and among animals injected with the same cord unit. This variability may limit the clinical usefulness of the NOD±scid mice as hosts for the quantification of human stem cells.