Immunological properties of mononuclear cells from blood stem cell harvests following mobilization with erythropoietin + G-CSF in cancer patients

Biology and clinical effects of natural killer cells in allogeneic transplantation

PURPOSE OF REVIEW

Following allogeneic hematopoietic cell transplantation, donor-derived natural killer (NK) cells target recipient hematopoietic cells, resulting in an antileukemia effect and a lower incidence of graft rejection. NK cells do not mediate and may diminish graft versus host disease. Here we review the determinants of NK cell alloreactivity and their implications for adoptive NK cell therapy.

RECENT FINDINGS

NK cell alloreactivity has been defined by the absence of recipient MHC class I ligands for donor inhibitory killer immunoglobulin-like receptor (KIR) receptors, as predicted by a number of algorithms. Recently, the role of activating NK receptors and their cognate ligands has received more attention. The beneficial clinical effect of NK-cell alloreactivity has not been uniformly demonstrated, likely reflecting differences in conditioning regimens, graft components and posttransplant immune suppression. Investigations of NK cell phenotype and function after transplantation have helped demonstrate which NK cell subsets mediate the graft versus leukemia effect. These advances have proceeded in parallel with increasing facility in GMP-grade bulk purification and administration of NK cell preparations.

SUMMARY

NK cells are a heterogeneous population of lymphocytes with diverse patterns of target-cell recognition and effector function. Further clinical and functional correlations will help maximize their potential for clinical benefit.

Hematopoietic Progenitor Cell Mobilization by Granulocyte Colony-Stimulating Factor and Erythropoietin in the Absence of Matrix Metalloproteinase-9

The use of mobilized hematopoietic progenitor cells (HPC) has largely replaced the use of bone marrow HPC for autologous and allogeneic transplantation; however, the mechanisms of HPC mobilization remain unclear. A better understanding of these mechanisms, may allow the development of improved (potentially more rapid and/or higher yield) HPC mobilization strategies, especially for patients who mobilize poorly using current mobilization protocols. Clinically, granulocyte colony-stimulating factor (G-CSF) is widely used to induce HPC mobilization, and evidence suggests that metalloproteinase enzymes released by activated granulocytes play an important role in the G-CSF-induced HPC mobilization. These enzymes may act to disrupt putative cell-cell and/or cell-extracellular matrix interactions within the hematopoietic microenvironment thereby releasing HPC into the blood. Matrix metalloproteinase-9 (MMP-9) appears to be important for G-CSF-induced mobilization. Using an MMP-9 knock-out (KO) mouse model, we investigated the role of MMP-9 in G-CSF and erythropoietin (EPO)-based HPC mobilization at clinically relevant cytokine doses. There were few hematologic or hematopoietic differences between the wild-type and MMP-9KO mice during steady-state hematopoiesis. When treated subcutaneously with EPO (500 U/kg per day) and G-CSF (15 microg/kg per day) for 5 days and assayed on day 6, similarly increased extramedullary hematopoiesis and numbers of HPC in the spleen and blood were observed for both the wild-type and MMP-9KO mice. These data demonstrate that MMP-9 is not required for EPO + G-CSF mobilization and that alternative mobilization mechanisms must be active at clinically relevant cytokine concentrations.

Monocyte-mediated T-cell suppression and augmented monocyte tryptophan catabolism after human hematopoietic stem-cell transplantation

T-cell dysfunction after human hematopoietic stem-cell transplantation (HSCT) is generally attributed to intrinsic T-cell defects. Here we show that the characteristic impaired proliferative responses to polyclonal stimulation of post-HSCT peripheral blood mononuclear cells (PB-MCs) were markedly (4-fold) improved by T-cell enrichment. Conversely, addback of post-HSCT monocytes to these enriched T cells dampened their proliferative responses, suggesting that post-HSCT monocytes effectively mediate T-cell suppression. As a mechanism possibly contributing to monocyte-mediated T-cell suppression, we investigated monocyte tryptophan catabolism by indoleamine 2,3-dioxygenase into kynurenine, which has been implicated in regulating T-cell responses. Compared with controls, all post-HSCT monocyte-containing cell cultures (total PBMCs, monocytes, and monocyte/T-cell cocultures), but not monocyte-depleted populations, secreted elevated amounts of kynurenine. Blockade of tryptophan catabolism improved the proliferative responses. The slightly increased kynurenine release and substantial release of neopterin by unstimulated post-HSCT monocytes suggests that they were in a state of continuous activation. Superimposed on this state, stimulation of these cells caused a striking, additional increase (10-fold) in kynurenine release, and they triggered marked apoptosis of autologous post-HSCT T cells. We conclude that the amplified kynurenine release by post-HSCT monocytes, particularly induced upon stimulation, may underlie their suppressor activity, which in turn may contribute to the depressed T-cell immune responses after HSCT.

Clinical applications of granulocyte colony-stimulating factor: an update and summary

The discovery of granulocyte colony-stimulating factor (G-CSF) and its potential to regulate neutrophil production and function in the inflammatory process has opened an exciting new era for the supportive care of patients with hematological and malignant diseases. Extensive experience has been gained worldwide with G-CSF therapy, and G-CSF is widely employed clinically, primarily because the safety profile appears to be fairly innocuous. A broad consensus has emerged regarding the clinical utility of G-CSF in neutropenic conditions due to chemotherapy. Furthermore, much interest has focused on the use of G-CSF to mobilize CD34+ hematopoietic stem cells from the marrow to the peripheral blood for use in hematopoietic transplantation. The promising results with G-CSF have promoted further studies, e.g., in immunocompetent patients or in granulocyte transfusion therapy. Here, we review the potential clinical role of G-CSF and describe its future perspectives.

Immunologic profiles of effector cells and peripheral blood stem cells mobilized with different hematopoietic growth factors

BACKGROUND

Peripheral blood stem cells (PBSC) have become the preferred source of stem cells for autologous transplantation because of the technical advantage and the shorter time to engraftment. Mobilization of CD34(+) cells into the peripheral blood can be achieved by the administration of G-CSF or GM-CSF, or both, alone or in combination with chemotherapy. G-CSF and GM-CSF differ somewhat in the number and composition of CD34(+) cells and effector cells mobilized to the peripheral blood. However, the molecular mechanism underlying the release and engraftment of CD34(+) cells is poorly understood.

PURPOSE

The purpose of this review is to give a recent update on the type and immunological properties of effector cells and CD34(+) cells mobilized by the different growth factors with emphasis on A) mobilization of T cells, natural killer cells, and dendritic cells; B) coexpression of adhesion molecules such as VLA-4 and L-selectin in mobilized PBSC collection, and C) coexpression of CXCR4-the receptor for the stromal-derived differentiation factor 1-with latest information shedding light on the molecular mechanism underlying the release and subsequent engraftment of CD34(+) cells.

CONCLUSIONS

A) The reported suppression of T cell and NK cell functions in PBSC apheresis collections in patients primed with G-CSF or GM-CSF is controversial and may merely reflect low effector cell activity before mobilization. B) A decrease in the expression of adhesion molecules such as VLA-4 and L-selectin is a necessary requirement for the release of CD34(+) cells to the peripheral blood. C) A decrease in the expression of CXCR4 is a necessary requirement for the release of CD34(+) cells to the peripheral blood and correlates with mobilization success.

Mobilization of dendritic cells and NK cells in non-Hodgkin's lymphoma patients mobilized with different growth factors

Conflicting results have been reported regarding the effect of various growth factors on the mobilization of natural killer (NK) cells and dendritic cells in patients undergoing stem cell mobilization for autotransplantation. We compared the extent of mobilization of NK cells and dendritic cells in non-Hodgkin's (NHL) patients undergoing mobilization with granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage (GM)-CSF, or GM-CSF followed by G-CSF. Overall, 35 patients were studied. NK cells and dendritic were quantitated by flow cytometry. NK cells were defined as the sum of CD56(+) cells and CD56/CD16(+) cells. Dendritic cells were defined as the sum of CD80(+) and CD80(+)/CD14(+) cells. NK activity was determined by by microcytotoxicity assay. NK activity correlated well with the total amount of CD56(+) cells mobilized to the peripheral blood. Patients in the three arms of the study mobilized similar amounts of NK cells and NK activity, and patients who lacked NK activity in the peripheral blood, before mobilization, lacked NK activity in their apheresis collections. In contrast to NK cell mobilization, mobilization of dendritic cells/kg was three- to five-fold higher in patients mobilized with GM-CSF-containing regimens compared to patients mobilized with G-CSF alone. We conclude that GM-CSF-containing mobilization regimens are superior for dendritic cell mobilization but similar in the mobilization of NK cells. Therefore, we recommend using GM-CSF-containing regimens for patients undergoing ex vivo or in vivo manipulation of dendritic cells.

Blood stem cell transplantation: factors influencing cellular immunological reconstitution

Recovery of immune function following stem cell transplantation is necessary for a good outcome. Immune recovery is facilitated by transplanting higher numbers of cells than neutrophil or platelet reconstitution requires. Estimates from studies in the allogeneic setting suggest the minimum stem cell dose to achieve optimal lymphocyte recovery is about 10(7) CD34+ cells/kg. Increasing the number of autologous stem cells infused potentially increases the risk of reinfusing tumor cells. Transplanted mature immune cells apparently have very limited early contribution to cellular immune recovery. Mobilizing cytokines permit collection of greater numbers of stem cells, but they also can polarize T cells with potentially significant consequences, for example, granulocyte colony-stimulating factor (G-CSF) decreases the antitumor cytotoxic effector functions of cells. Although this could be a disadvantage in the autologous setting, it might decrease graft versus host disease in the allogeneic setting. Thus, identification of cytokines, which alone or in combination provide the most potent mobilizing effect to permit the collection of the highest number of stem cells without inadvertent detrimental polarization of the responses of immune cells, and employment of cytokines posttransplantation, which direct differentiation of the stem cells along the most desirable pathways, for example, to generate antitumor immune responses, might improve immunological outcome. A future emphasis should be to better define the cytokines and target cell populations that provide optimal immune reconstitution rather than focusing solely on rapid hematological recovery. More complete immunological reconstitution in a greater proportion of patients should be accompanied by improvements in outcomes of blood stem cell transplantation.