The reason why bone marrow cells home into the bone after intravenous administration is because a continuous production of Stromal Derived Factor-1 (SDF-1) by the bone marrow stromal compartments. The gradient of SDF-1 is also retains the early CD34+ bone marrow hematopoietic stem cells in the bone marrow.
The current patent covers compositions of matter that inhibit the interaction between SDF-1 and its receptor (CXCR-4). By inhibiting this interaction the bone marrow cells leave the stroma and enter systemic circulation. The same approach is used to induce mobilization of bone marrow hematopoietic stem cells by the administration of antibodies to VCAM.
Why it is important to induce entry of hematopoietic stem cells into the systemic compartment is so that they may be collected for stem cell transplants, or alternatively in order to allow a higher number of stem cells to go to the area of injured tissue.