In vivo engineering of mobilized stem cell grafts with the immunomodulatory drug FTY720 for allogeneic transplantation.

The immunological attributes of stem cell grafts play an important role in the outcome of allogeneic stem cell transplants. Currently, ex vivo manipulation techniques such as bulk T-cell depletion or positive selection of CD34(+) cells are utilized to improve the immunological attributes of grafts and minimize the potential for graft-versus-host disease (GvHD). Here, we demonstrate a novel graft engineering technique, which utilizes the immunomodulatory drug FTY720 for in vivo depletion of naïve T (TN ) cells from donor G-CSF-mobilized grafts without ex vivo manipulation. We show that treatment of donor mice with FTY720 during mobilization depletes grafts of TN cells and prevents lethal GvHD following transplantation in a major mismatch setting. Importantly, both stem cells and NK cells are retained in the FTY720-treated grafts. FTY720 treatment does not negatively affect the engraftment potential of stem cells as demonstrated in our congenic transplants or the functionality of NK cells. In addition, potentially useful memory T cells may be retained in the graft. These findings suggest that FTY720 may be used to optimize the immunological attributes of G-CSF-mobilized grafts by removing potentially deleterious TN cells which can contribute to GvHD, and by retaining useful cells which can promote immunity in the recipient.

Sphingosine-1-phosphate facilitates trafficking of hematopoietic stem cells and their mobilization by CXCR4 antagonists in mice.

CXCL12 and VCAM1 retain hematopoietic stem cells (HSCs) in the BM, but the factors mediating HSC egress from the BM to the blood are not known. The sphingosine-1-phosphate receptor 1 (S1P(1)) is expressed on HSCs, and S1P facilitates the egress of committed hematopoietic progenitors from the BM into the blood. In the present study, we show that both the S1P gradient between the BM and the blood and the expression of S1P(1) are essential for optimal HSC mobilization by CXCR4 antagonists, including AMD3100, and for the trafficking of HSCs during steady-state hematopoiesis. We also demonstrate that the S1P(1) agonist SEW2871 increases AMD3100-induced HSC and progenitor cell mobilization. These results suggest that the combination of a CXCR4 antagonist and a S1P(1) agonist may prove to be sufficient for mobilizing HSCs in normal donors for transplantation purposes, potentially providing a single mobilization procedure and eliminating the need to expose normal donors to G-CSF with its associated side effects.

Vedolizumab Efficacy Is Associated With Decreased Intracolonic Dendritic Cells, Not Memory T Cells.

BACKGROUND: Vedolizumab, an antibody blocking integrin α4ß7, is a safe and effective therapy for Crohn's disease and ulcerative colitis. Blocking α4ß7 from binding its cognate addressin MAdCAM-1 on intestinal blood vessel endothelial cells prevents T cells from migrating to the gut mucosa in animal models. However, data supporting this mechanism of action in humans is limited. METHODS: We conducted a cross-sectional case-control study to evaluate the effect of vedolizumab on intestinal immune cell populations while avoiding the confounding effect of resolving inflammation on the cellularity of the colonic mucosa in treatment-responsive patients. Colon biopsies from 65 case subjects receiving vedolizumab were matched with biopsies from 65 control individuals, similar in disease type, medications, anatomic location, and inflammation. Biopsies were analyzed by flow cytometry and full messenger RNA transcriptome sequencing of sorted T cells. RESULTS: No difference was seen between vedolizumab recipients and control individuals in the quantity of any antigen-experienced T lymphocyte subset or in the quality of the transcriptome in any experienced T cell subset. Fewer naïve colonic B and T cells were seen in vedolizumab recipients than control individuals, regardless of response. However, the most striking finding was a marked reduction in CD1c+ (BDCA1+) dendritic cells exclusively in vedolizumab-responsive patients. In blood, these dendritic cells ubiquitously express high levels of α4ß7, which is rapidly downregulated upon vedolizumab exposure. CONCLUSIONS: The clinical effects of vedolizumab reveal integrin α4ß7-dependent dendritic cell migration to the intestinal mucosa to be central to inflammatory bowel disease pathogenesis.

Vedolizumab had no effect on the number or gene expression of memory T lymphocytes in the colons of recipients relative to control individuals. However, the colons of vedolizumab-responsive patients had distinctly fewer dendritic cells, which in blood express the most integrin α4ß7.

CXCR4 mediates the homing of B cell progenitor acute lymphoblastic leukaemia cells to the bone marrow via activation of p38MAPK.

The mechanisms regulating the migration of leukaemic cells between the blood and bone marrow compartments remain obscure, but are of fundamental importance for the dissemination of the disease. This study investigated the in vivo homing of human B cell progenitor acute lymphoblastic leukaemia (ALL) cells to the femoral bone marrow of non-obese diabetic severe combined immunodeficient (NOD/SCID) mice. It was demonstrated that patient ALL cells use the chemokine axis, chemokine (CXC motif) receptor 4 (CXCR4)/ chemokine (CXC motif) ligand 12 (CXCL12), to home to the femoral marrow. CXCL12-mediated signalling through p38 mitogen-activated protein kinase (MAPK) was required for optimal homing. In contrast, the homing of normal peripheral blood CD34(+) cells and the cytokine-dependent CD34(+) cell line Mo7e was independent of p38MAPK, consistent with the dependence of these cells, as well as normal CD34(+) CD19(+) B cell progenitors, on PI-3K/AKT signalling. Altogether, our data provide clarification of the direct role of CXCL12 in the bone marrow homing of ALL cells and demonstrate unique signalling molecule usage that may have therapeutic implications for this disease.

Plerixafor (AMD3100) induces prolonged mobilization of acute lymphoblastic leukemia cells and increases the proportion of cycling cells in the blood in mice.

The CXCR4 antagonist Plerixafor (AMD3100) induces the rapid mobilization of hematopoietic stem and progenitor cells into the blood in mice and humans. AMD3100 similarly induces the mobilization of human acute lymphoblastic leukemia (ALL) cells into the blood in mice. In this study, the temporal response of pre-B ALL cells to AMD3100 was compared with that of normal hematopoietic progenitor cells (HPC) using an NOD/SCID xenograft model of ALL and BALB/c mice, respectively. ALL cells remained in the circulation up to 6 hours after AMD3100 administration, by which time normal HPCs were no longer detectable. AMD3100 also increased the proportion of actively cycling ALL cells in the peripheral blood. Together, these data suggest that ALL cells are more sensitive to the effects of bone marrow disruption than normal progenitors. Using the NOD/SCID xenograft model, we demonstrated that AMD3100 increased the efficacy of the cell cycle specific drug vincristine, resulting in reduced disease levels in the blood and spleens of animals over 3 weeks and extended the survival of NOD/SCID mice with ALL. These data demonstrate that mobilizing agents can increase the therapeutic effect of cell cycle dependent chemotherapeutic agents.