Hematopoietic stem cell homing and engraftment require several adhesion interactions, which are not fully understood. Engraftment of nonobese/severe combined immunodeficiency (NOD/SCID) mice by human stem cells is dependent on the major integrins very late activation antigen–4 (VLA-4); VLA-5; and to a lesser degree, lymphocyte function associated antigen–1 (LFA-1). Treatment of human CD34+cells with antibodies to either VLA-4 or VLA-5 prevented engraftment, and treatment with anti–LFA-1 antibodies significantly reduced the levels of engraftment. Activation of CD34+ cells, which bear the chemokine receptor CXCR4, with stromal derived factor 1 (SDF-1) led to firm adhesion and transendothelial migration, which was dependent on LFA-1/ICAM-1 (intracellular adhesion molecule–1) and VLA-4/VCAM-1 (vascular adhesion molecule–1). Furthermore, SDF-1–induced polarization and extravasation of CD34+/CXCR4+ cells through the extracellular matrix underlining the endothelium was dependent on both VLA-4 and VLA-5. Our results demonstrate that repopulating human stem cells functionally express LFA-1, VLA-4, and VLA-5. Furthermore, this study implies a novel approach to further advance clinical transplantation.

Chronic hepatitis C virus (HCV) and hepatitis B virus (HBV) infection is accompanied by inflammation and fibrosis eventually leading to cirrhosis. The chemokine CXCL12 is involved in chronic inflammatory conditions. The role of the CXCL12/CXCR4 pathway in HCV-and HBV-associated liver inflammation and fibrosis was therefore studied. The levels and tissue localization of CXCL12 in liver and plasma of HCV and HBV patients were tested using immunohistochemistry and ELISA. The expression and function of CXCR4 on liver-infiltrating lymphocytes (LIL) were tested by FACS and transwell migration assays. We found that CXCL12 is expressed by bile duct epithelial cells in normal liver tissue. Bile duct proliferation and liver fibrosis in chronic HCV and HBV infection result in the anatomical re-distribution of CXCL12 in the liver. Moreover, CXCL12 is up-regulated in the endothelium of neo-bloodvessels formed in active inflammatory foci and is significantly elevated, compared with controls, in the plasma of patients with advanced liver fibrosis. Complementing these observations were others indicating that over 50% of LIL express CXCR4 and, in response to CXCL12, migrated and adhered to fibronectin. These observations suggest an important role for the CXCL12/CXCR4 pathway in recruitment and retention of immune cells in the liver during chronic HCV and HBV infection.

IntroductionHuman natural killer (NK) cells are predominantly large granular lymphocytes (LGLs), the majority of which express CD16 and CD56 cell-surface antigens. A small subset of NK cells lacks CD16 and expresses high levels of CD56 and CD94. Another major CD56 ϩ population is composed of T cells that express the CD3 antigen. The human peripheral blood lymphocyte (PBL) NK T-cell population is enriched with CD8 ϩ T cells of effector phenotypes. NK and NK T cells can mediate cytolysis of tumor cells and virus-infected cells. 1,2 To improve responses against metastatic tumors, a variety of adoptive cellular strategies have been tested. Among the techniques most studied and developed is the use of lymphokine-activated killer (LAK) cells. LAK cells express surface markers characteristic of NK cells, including CD56 and CD16, and rarely express the common T-cell marker CD3. 3,4 The LAK activity is induced from a population of resting lymphoid cells by in vitro exposure of these cells to a supraphysiologic concentration of IL-2 (500-1000 IU/mL). 3,4 NK and NK T cells are also key effector cells mediating the graft-versus-leukemia (GVL) effect, which is used to control minimal residual disease (MRD) and for the reinduction of remission in chronic myelogenous leukemia patients who relapse after allogeneic stem cell transplantation. 1,[5][6][7][8] These cells are also important for low-intensity conditions and nonmyeloablative allogeneic stem cell transplantation, which are currently being performed not only in hematologic malignancies, but also in solid tumors such as renal cell carcinoma. 9 In hematogenic metastasis, such as that of prostate cancer, breast cancer, and neuroblastoma, the malignant cells home, arrest, and develop in the BM. 10,11 In order to extract their function, NK and NK T cells must reach the BM. However, the mechanism that regulates the trafficking of these cells to the BM is unknown.Chemokines and their receptors have an essential role in the recruitment and tissue localization of cells from the immune system. 12 NK cells have mainly been reported to express chemokine receptors from the CXC family, such as CXCR1-4 and CXC3R1. In contrast, CD56 ϩ , CD16 Ϫ , CD3 ϩ NK T cells have been shown to express the chemokine receptors CCR1, CCR2, CCR5, and CCR6 from the CC family and the chemokine receptors CXCR 3, CXCR4, and CXCR6 from the CXC family. 13,14 The chemokine receptor CXCR4 and its ligand, CXCL12, have been shown to play a crucial role in the trafficking and tissue localization of human hematopoietic stem cells and breast tumor cells to hematopoietic organs. 15,16 This makes the chemokine-receptor pair CXCL12/CXCR4 of particular interest in investigating their own role in the homing of NK and NK T cells to the BM microenvironment. Here we show that the homing of NK and NK T cells to the BM was dependent upon G protein signaling and CXCR4 and was inhibited by IL-2 treatment. Upon activation of these cells with IL-2, CXCR4 expression was reduced, whereas the expression of CXCR3 on the cell surface...

Hematopoietic stem cell homing and engraftment require several adhesion interactions, which are not fully understood. Engraftment of nonobese/severe combined immunodeficiency (NOD/SCID) mice by human stem cells is dependent on the major integrins very late activation antigen–4 (VLA-4); VLA-5; and to a lesser degree, lymphocyte function associated antigen–1 (LFA-1). Treatment of human CD34+cells with antibodies to either VLA-4 or VLA-5 prevented engraftment, and treatment with anti–LFA-1 antibodies significantly reduced the levels of engraftment. Activation of CD34+ cells, which bear the chemokine receptor CXCR4, with stromal derived factor 1 (SDF-1) led to firm adhesion and transendothelial migration, which was dependent on LFA-1/ICAM-1 (intracellular adhesion molecule–1) and VLA-4/VCAM-1 (vascular adhesion molecule–1). Furthermore, SDF-1–induced polarization and extravasation of CD34+/CXCR4+ cells through the extracellular matrix underlining the endothelium was dependent on both VLA-4 and VLA-5. Our results demonstrate that repopulating human stem cells functionally express LFA-1, VLA-4, and VLA-5. Furthermore, this study implies a novel approach to further advance clinical transplantation.