Impairment of lymphopoiesis and myelopoiesis in mice reconstituted with bone marrow–hematopoietic progenitor cells expressing SDF-1–intrakine

Homing and Engraftment of Hematopoietic Stem Cells Following Transplantation: A Pre-Clinical Perspective

Hematopoietic stem-cell (HSC) transplantation (HSCT) is used to treat various hematologic disorders. Use of genetically modified mouse models of hematopoietic cell transplantation has been critical in our fundamental understanding of HSC biology and in developing approaches for human patients. Pre-clinical studies in animal models provide insight into the journey of transplanted HSCs from infusion to engraftment in bone-marrow (BM) niches. Various signaling molecules and growth factors secreted by HSCs and the niche microenvironment play critical roles in homing and engraftment of the transplanted cells. The sustained equilibrium of these chemical and biologic factors ensures that engrafted HSCs generate healthy and durable hematopoiesis. Transplanted healthy HSCs compete with residual host cells to repopulate stem-cell niches in the marrow. Stem-cell niches, in particular, can be altered by the effects of previous treatments, aging, and the paracrine effects of leukemic cells, which create inhospitable bone-marrow niches that are unfavorable for healthy hematopoiesis. More work to understand how stem-cell niches can be restored to favor normal hematopoiesis may be key to reducing leukemic relapses following transplant.

Innate immunity orchestrates the mobilization and homing of hematopoietic stem/progenitor cells by engaging purinergic signaling-an update

Bone marrow (BM) as an active hematopoietic organ is highly sensitive to changes in body microenvironments and responds to external physical stimuli from the surrounding environment. In particular, BM tissue responds to several cues related to infections, strenuous exercise, tissue/organ damage, circadian rhythms, and physical challenges such as irradiation. These multiple stimuli affect BM cells to a large degree through a coordinated response of the innate immunity network as an important guardian for maintaining homeostasis of the body. In this review, we will foc++us on the role of purinergic signaling and innate immunity in the trafficking of hematopoietic stem/progenitor cells (HSPCs) during their egression from the BM into peripheral blood (PB), as seen along pharmacological mobilization, and in the process of homing and subsequent engraftment into BM after hematopoietic transplantation. Innate immunity mediates these processes by engaging, in addition to certain peptide-based factors, other important non-peptide mediators, including bioactive phosphosphingolipids and extracellular nucleotides, as the main topic of this review. Elucidation of these mechanisms will allow development of more efficient stem cell mobilization protocols to harvest the required number of HSPCs for transplantation and to accelerate hematopoietic reconstitution in transplanted patients.

Fibrotic liver microenvironment promotes Dll4 and SDF-1-dependent T-cell lineage development

The reconstitution of the T-cell repertoire and quantity is a major challenge in the clinical management of HIV infection/AIDS, cancer, and aging-associated diseases. We previously showed that autologous bone marrow transfusion (BMT) via the hepatic portal vein could effectively restore CD4+ T-cell count in AIDS patients also suffering from decompensated liver cirrhosis. In the current study, we characterized T-cell reconstitution in a mouse model of liver fibrosis induced by CCl4 and found that T-cell reconstitution after BMT via hepatic portal vein was also greatly enhanced. The expression of Dll4 (Delta-like 4), which plays an important role in T-cell progenitor expansion, was elevated in hepatocytes of fibrotic livers when compared to normal livers. This upregulation of Dll4 expression was found to be induced by TNFα in an NFκB-dependent manner. Liver fibroblasts transfected with Dll4 (LF-Dll4) also gained the capacity to promote T-cell lineage development from hematopoietic stem cells (HSCs), resulting in the generation of DN2 (CD4 and CD8 DN 2) and DN3 T-cell progenitors in vitro, which underwent a normal maturation program when adoptively transferred into Rag-2 deficient hosts. We also demonstrated a pivotal role of SDF-1 produced by primary liver fibroblasts (primary LF) in T-lineage differentiation from HSCs. These results suggest that Dll4 and SDF-1 in fibrotic liver microenvironment could promote extrathymic T-cell lineage development. These results expand our knowledge of T-cell development and reconstitution under pathological conditions.

Biased antagonism of CXCR4 avoids antagonist tolerance

Repeated dosing of drugs targeting G protein-coupled receptors can stimulate antagonist tolerance, which reduces their efficacy; thus, strategies to avoid tolerance are needed. The efficacy of AMD3100, a competitive antagonist of the chemokine receptor CXCR4 that mobilizes leukemic blasts from the bone marrow into the blood to sensitize them to chemotherapy, is reduced after prolonged treatment. Tolerance to AMD3100 increases the abundance of CXCR4 on the surface of leukemic blasts, which promotes their rehoming to the bone marrow. AMD3100 inhibits both G protein signaling by CXCR4 and β-arrestin1/2-dependent receptor endocytosis. We demonstrated that biased antagonists of G protein-dependent chemotaxis but not β-arrestin1/2 recruitment and subsequent receptor endocytosis avoided tolerance. The peptide antagonist X4-2-6, which is derived from transmembrane helix 2 and extracellular loop 1 of CXCR4, limited chemotaxis and signaling but did not promote CXCR4 accumulation on the cell surface or cause tolerance. The activity of X4-2-6 was due to its distinct mechanism of inhibition of CXCR4. The peptide formed a ternary complex with the receptor and its ligand, the chemokine CXCL12. Within this complex, X4-2-6 released the portion of CXCL12 critical for receptor-mediated activation of G proteins but enabled the rest of the chemokine to recruit β-arrestins to the receptor. In contrast, AMD3100 displaced all components of the chemokine responsible for CXCR4 activation. We further identified a small molecule with similar biased antagonist properties to those of X4-2-6, which may provide a viable alternative to patients when antagonist tolerance prevents drugs from reaching efficacy.

Sphingosine 1-Phosphate Signaling and Its Pharmacological Modulation in Allogeneic Hematopoietic Stem Cell Transplantation

Allogeneic haemopoietic stem cell transplantation (HSCT) is increasingly used to treat haematological malignant diseases via the graft-versus-leukaemia (GvL) or graft-versus-tumour effects. Although improvements in infectious disease prophylaxis, immunosuppressive treatments, supportive care, and molecular based tissue typing have contributed to enhanced outcomes, acute graft-versus-host disease and other transplant related complications still contribute to high mortality and significantly limit the more widespread use of HSCT. Sphingosine 1-phosphate (S1P) is a zwitterionic lysophospholipid that has been implicated as a crucial signaling regulator in many physiological and pathophysiological processes including multiple cell types such as macrophages, dendritic cells, T cells, T regulatory cells and endothelial cells. Recent data suggested important roles for S1P signaling in engraftment, graft-versus-host disease (GvHD), GvL and other processes that occur during and after HSCT. Based on such data, pharmacological intervention via S1P modulation may have the potential to improve patient outcome by regulating GvHD and enhancing engraftment while permitting effective GvL.

Lymphoid differentiation of hematopoietic stem cells requires efficient Cxcr4 desensitization

The CXCL12/CXCR4 signaling exerts a dominant role in promoting hematopoietic stem and progenitor cell (HSPC) retention and quiescence in bone marrow. Gain-of-function CXCR4 mutations that affect homologous desensitization of the receptor have been reported in the WHIM Syndrome (WS), a rare immunodeficiency characterized by lymphopenia. The mechanisms underpinning this remain obscure. Using a mouse model with a naturally occurring WS-linked gain-of-function Cxcr4 mutation, we explored the possibility that the lymphopenia in WS arises from defects at the HSPC level. We reported that Cxcr4 desensitization is required for quiescence/cycling balance of murine short-term hematopoietic stem cells and their differentiation into multipotent and downstream lymphoid-biased progenitors. Alteration in Cxcr4 desensitization resulted in decrease of circulating HSPCs in five patients with WS. This was also evidenced in WS mice and mirrored by accumulation of HSPCs in the spleen, where we observed enhanced extramedullary hematopoiesis. Therefore, efficient Cxcr4 desensitization is critical for lymphoid differentiation of HSPCs, and its impairment is a key mechanism underpinning the lymphopenia observed in mice and likely in WS patients.

Altered CXCL12 expression reveals a dual role of CXCR4 in osteosarcoma primary tumor growth and metastasis

PURPOSE

Better understanding of the molecular mechanisms of metastasis-the major cause of death in osteosarcoma (OS)-is a key for the development of more effective metastasis-suppressive therapy. Here, we investigated the biological relevance of the CXCL12/CXCR4 axis in OS.

METHODS

We interfered with CXCL12/CXCR4 signaling in CXCR4-expressing human 143-B OS cells through stable expression of CXCL12, of its competitive antagonist P2G, or of CXCL12-KDEL, designed to retain CXCR4 within the cell. Intratibial OS xenograft mouse model metastasizing to the lung was used to assess tumorigenic and metastatic potential of the manipulated cell lines.

RESULTS

Constitutive expression of native CXCL12 promoted lung metastasis without affecting tumor growth. Stable expression of P2G or CXCL12-KDEL significantly accelerated tumor growth but diminished lung metastasis. Tumors grown from P2G- or CXCL12-KDEL-expressing cells contained higher levels of CXCR4-encoding mRNA going along with a higher percentage of CXCR4-expressing tumor cells. Lung metastases of all groups were predominantly enriched with CXCR4-expressing tumor cells.

CONCLUSION

Higher abundance of CXCR4 possibly contributed to increased local retention of tumor cells by bone marrow-derived CXCL12, reflected in the increased primary tumor growth and decreased number of lung metastases in P2G and CXCL12-KDEL groups. Higher percentage of CXCR4-expressing lung metastatic cells compared to the corresponding primary tumors point to important functions of the CXCL12/CXCR4 axis in late steps of metastasis. In conclusion, based on the here reported results, local treatment of lung metastases with novel CXCR4-targeting therapeutics might be considered and favored over anti-CXCR4 systemic therapy.

Evidence for the involvement of sphingosine-1-phosphate in the homing and engraftment of hematopoietic stem cells to bone marrow

The α-chemokine stromal-derived factor 1 (SDF-1), which binds to the CXCR4 receptor, directs migration and homing of CXCR4⁺ hematopoietic stem/progenitor cells (HSPCs) to bone marrow (BM) stem cell niches. Nevertheless, it is also known that CXCR4^−/− fetal liver-derived hematopoietic stem cells engraft into BM and that blockade of CXCR4 by its antagonist AMD3100 does not prevent engraftment of HSPCs. Because of this finding of SDF-1-CXCR4-independent BM homing, the unique role of SDF-1 in HSPC homing has recently been challenged. While SDF-1 is the only chemokine that chemoattracts HSPCs, other chemoattractants for these cells have recently been described, including the bioactive phosphosphingolipid sphingosine-1-phosphate (S1P). To address the potential role of S1P in homing of HSPCs to BM, we performed hematopoietic transplants into mice deficient in BM-expressed sphingosine kinase 1 (Sphk1^−/−) using hematopoietic cells from normal control mice as well as cells from mice in which floxed CXCR4 (CXCR4^fl/fl) was conditionally deleted. We observed the presence of a homing and engraftment defect in HSPCs of Sphk1^−/− mice that was particularly profound after transplantation of CXCR4^−/− BM cells. Thus, our results indicate that BM-microenvironment-expressed S1P plays a role in homing of HSPCs. They also support the concept that, in addition to the SDF-1-CXCR4 axis, other chemotactic axes are also involved in homing and engraftment of HSPCs.

Membrane lipid rafts, master regulators of hematopoietic stem cell retention in bone marrow and their trafficking

Cell outer membranes contain glycosphingolipids and protein receptors, which are integrated into glycoprotein microdomains, known as lipid rafts, which float freely in the membrane bilayer. These structures have an important role in assembling signaling molecules (e.g., Rac-1, RhoH and Lyn) together with surface receptors, such as the CXCR4 receptor for α-chemokine stromal-derived factor-1, the α4β1-integrin receptor (VLA-4) for vascular cell adhesion molecule-1 and the c-kit receptor for stem cell factor, which together regulate several aspects of hematopoietic stem/progenitor cell (HSPC) biology. Here, we discuss the role of lipid raft integrity in the retention and quiescence of normal HSPCs in bone marrow niches as well as in regulating HSPC mobilization and homing. We will also discuss the pathological consequences of the defect in lipid raft integrity seen in paroxysmal nocturnal hemoglobinuria and the emerging evidence for the involvement of lipid rafts in hematological malignancies.

Stromal cell-derived factor-1 G801A polymorphism and the risk factors for cervical cancer

Although certain studies have demonstrated no association between the stromal cell‑derived factor‑1 (SDF1‑3') G801A single nucleotide polymorphism (SNP) and cervical carcinoma, the interactions between the SDF1‑3' G801A SNP and contraceptive use, menopausal status, parity and tobacco smoking remain to be fully elucidated. Using polymerase chain reaction‑restriction fragment length polymorphism, the distribution of SDF1‑3' G801A genotypes in patients with cervical cancer (n=462) against control groups (n=497) was investigated. Logistic regression analysis, adjusting for age, pregnancy, oral contraceptive use, tobacco smoking and menopausal status, did not identify the SDF1‑3' G801A polymorphism as a genetic risk factor for cervical cancer. The adjusted odds ratio (OR) for patients with the A/G, vs. G/G genotype was 1.203, with a 95% confidence interval (CI) of 0.909‑1.591 (P=0.196). The adjusted OR for the A/A, vs. G/G genotype was 1.296 (95% CI=0.930‑1.807; P=0.125) and for the A/A or A/G, vs. G/G genotype was 1.262 (95% CI=0.964‑1.653; P=0.090)]. The P‑value of the χ2 test of the trend observed for the SDF1‑3' G801A polymorphism was at the borderline of being statistically significant (ptrend=0.0484). Stratified analyses between the distribution of the SDF1‑3' G801A genotypes and cervical cancer risks demonstrated that this polymorphism may be a risk factor for patients with a positive history of tobacco smoking (1.778; 95% CI=1.078‑2.934; P=0.0235). These findings suggested that the SDF1‑3' G801A polymorphism may be a genetic risk factor for cervical cancer in patients with a positive history of tobacco smoking.

SDF-1/CXCR4 axis in Tie2-lineage cells including endothelial progenitor cells contributes to bone fracture healing

CXC chemokine receptor 4 (CXCR4) is a specific receptor for stromal-derived-factor 1 (SDF-1). SDF-1/CXCR4 interaction is reported to play an important role in vascular development. On the other hand, the therapeutic potential of endothelial progenitor cells (EPCs) in fracture healing has been demonstrated with mechanistic insight of vasculogenesis/angiogenesis and osteogenesis enhancement at sites of fracture. The purpose of this study was to investigate the influence of the SDF-1/CXCR4 pathway in Tie2-lineage cells (including EPCs) in bone formation. We created CXCR4 gene conditional knockout mice using the Cre/loxP system and set two groups of mice: Tie2-Cre(ER) CXCR4 knockout mice (CXCR4(-/-) ) and wild-type mice (WT). We report here that in vitro, EPCs derived from of CXCR4(-/-) mouse bone marrow demonstrated severe reduction of migration activity and EPC colony-forming activity when compared with those derived from WT mouse bone marrow. In vivo, radiological and morphological examinations showed fracture healing delayed in the CXCR4(-/-) group and the relative callus area at weeks 2 and 3 was significantly smaller in CXCR4(-/-) group mice. Quantitative analysis of capillary density at perifracture sites also showed a significant decrease in the CXCR4(-/-) group. Especially, CXCR4(-/-) group mice demonstrated significant early reduction of blood flow recovery at fracture sites compared with the WT group in laser Doppler perfusion imaging analysis. Real-time RT-PCR analysis showed that the gene expressions of angiogenic markers (CD31, VE-cadherin, vascular endothelial growth factor [VEGF]) and osteogenic markers (osteocalcin, collagen 1A1, bone morphogenetic protein 2 [BMP2]) were lower in the CXCR4(-/-) group. In the gain-of-function study, the fracture in the SDF-1 intraperitoneally injected WT group healed significantly faster with enough callus formation compared with the SDF-1 injected CXCR4(-/-) group. We demonstrated that an EPC SDF-1/CXCR4 axis plays an important role in bone fracture healing using Tie2-Cre(ER) CXCR4 conditional knockout mice.

A novel view of the adult bone marrow stem cell hierarchy and stem cell trafficking

This review presents a novel view and working hypothesis about the hierarchy within the adult bone marrow stem cell compartment and the still-intriguing question of whether adult bone marrow contains primitive stem cells from early embryonic development, such as cells derived from the epiblast, migrating primordial germ cells or yolk sac-derived hemangioblasts. It also presents a novel view of the mechanisms that govern stem cell mobilization and homing, with special emphasis on the role of the complement cascade as a trigger for egress of hematopoietic stem cells from bone marrow into blood as well as the emerging role of novel homing factors and priming mechanisms that support stromal-derived factor 1-mediated homing of hematopoietic stem/progenitor cells after transplantation.

Innate immunity as orchestrator of bone marrow homing for hematopoietic stem/progenitor cells

The first step that precedes hematopoietic transplantation is elimination of pathological hematopoiesis by administration of myeloablative doses of radiochemotherapy. This eliminates hematolymphopoietic cells and at the same time damages hematopoietic microenvironment in bone marrow (BM). The damage of BM tissue leads to activation of complement cascade (CC), and bioactive CC cleavage fragments modulate several steps of BM recovery after transplantation of hematopoietic stem progenitor cells (HSPCs). Accordingly, C3 cleavage fragments (soluble C3a/desArgC3a and solid phase iC3b) and generation of soluble form of C5b-C9 also known as membrane attack complex (MAC) as well as release of antimicrobial cationic peptides from stromal cells (cathelicidin or LL-37 and beta-2 defensin) promote homing of HSPCs. To support this, C3 cleavage fragments and antimicrobial cationic peptides increase homing responsiveness of transplanted HSPCs to stroma-derived factor-1 (SDF-1) gradient. Furthermore, damaged BM cells release several other chemoattractants for HSPCs such as bioactive lipids sphingosine-1-phosphate (S1P) and ceramide-1-phosphate (C1P) and chemotactic purines (ATP and UTP). In this chapter, we will discuss the current view on homing of transplanted HSPCs into BM that in addition to SDF-1 is orchestrated by CC, antimicrobial cationic peptides, and several other prohoming factors. We also propose modulation of CC as a novel strategy to optimize/accelerate homing of HSPCs.

The expanding family of bone marrow homing factors for hematopoietic stem cells: stromal derived factor 1 is not the only player in the game

The α-chemokine stromal derived factor 1 (SDF-1), which binds to the CXCR4 and CXCR7 receptors, directs migration and homing of CXCR4⁺ hematopoietic stem/progenitor cells (HSPCs) to bone marrow (BM) and plays a crucial role in retention of these cells in stem cell niches. However, this unique role of SDF-1 has been recently challenged by several observations supporting SDF-1-CXCR4-independent BM homing. Specifically, it has been demonstrated that HSPCs respond robustly to some bioactive lipids, such as sphingosine-1-phosphate (S1P) and ceramide-1-phosphate (C1P), and migrate in response to gradients of certain extracellular nucleotides, including uridine triphosphate (UTP) and adenosine triphosphate (ATP). Moreover, the responsiveness of HSPCs to an SDF-1 gradient is enhanced by some elements of innate immunity (e.g., C3 complement cascade cleavage fragments and antimicrobial cationic peptides, such as cathelicidin/LL-37 or β2-defensin) as well as prostaglandin E2 (PGE2). Since all these factors are upregulated in BM after myeloblative conditioning for transplantation, a more complex picture of homing emerges that involves several factors supporting, and in some situations even replacing, the SDF-1-CXCR4 axis.

Proper desensitization of CXCR4 is required for lymphocyte development and peripheral compartmentalization in mice

Desensitization controls G protein-dependent signaling of chemokine receptors. We investigate the physiologic implication of this process for CXCR4 in a mouse model harboring a heterozygous mutation of the Cxcr4 gene, which engenders a desensitization-resistant receptor. Such anomaly is linked to the warts, hypogammaglobulinemia, infections, myelokathexis (WHIM) syndrome, a human rare combined immunodeficiency. Cxcr4(+/mutant(1013)) mice display leukocytes with enhanced responses to Cxcl12 and exhibit leukopenia as reported in patients. Treatment with CXCL12/CXCR4 antagonists transiently reverses blood anomalies, further demonstrating the causal role of the mutant receptor in the leukopenia. Strikingly, neutropenia occurs in a context of normal bone marrow architecture and granulocyte lineage maturation, indicating a minor role for Cxcr4-dependent signaling in those processes. In contrast, Cxcr4(+/1013) mice show defective thymopoiesis and B-cell development, accounting for circulating lymphopenia. Concomitantly, mature T and B cells are abnormally compartmentalized in the periphery, with a reduction of primary follicles in the spleen and their absence in lymph nodes mirrored by an unfurling of the T-cell zone. These mice provide a model to decipher the role of CXCR4 desensitization in the homeostasis of B and T cells and to investigate which manifestations of patients with WHIM syndrome may be overcome by dampening the gain of CXCR4 function.

The role of innate immunity in trafficking of hematopoietic stem cells-an emerging link between activation of complement cascade and chemotactic gradients of bioactive sphingolipids

Hematopoietic stem and progenitor cells (HSPCs) circulate under steady-state conditions at detectable levels in peripheral blood (PB). The phenomenon of enforced release of HSPCs from BM into PB is called mobilization and may be envisioned as a danger-sensing response mechanism triggered by hypoxia or mechanical- or infection-induced tissue damage and is a part of stress response. It is unquestionable that the a-chemokine stromal derived factor-1 (SDF-1)-CXCR4 axis plays crucial role in retention of HSPCs in BM. However, all factors that direct mobilization of HSPCs into PB and homing back to the BM or their allocation to damaged organs are not characterized very well. In this chapter we will present mounting evidence that elements of innate immunity such as complement cascade (CC) cleavage fragments (e.g., C3a and C5a), granulocytes, generation of membrane attack complex (MAC) together with sphingosine-1 phosphate (S1P) orchestrate HSPC mobilization. On other hand some other bioactive lipids e.g., ceramide-1-phosphate (C1P) that is released from damaged/"leaky" cells in BM after myeloablative conditioning for transplant may play an opposite important role in homing of HSPCs to BM. Finally, the chemotactic activity of all chemoattractants for HSPCs including SDF-1, S1P and C1P is enhanced in presence of CC cleavage fragments (e.g., C3a) and MAC that is a final product of CC activation.

A novel perspective on stem cell homing and mobilization: review on bioactive lipids as potent chemoattractants and cationic peptides as underappreciated modulators of responsiveness to SDF-1 gradients

Hematopoietic stem progenitor cells (HSPCs) respond robustly to α-chemokine stromal-derived factor-1 (SDF-1) gradients, and blockage of CXCR4, a seven-transmembrane-spanning G(αI)-protein-coupled SDF-1 receptor, mobilizes HSPCs into peripheral blood. Although the SDF-1-CXCR4 axis has an unquestionably important role in the retention of HSPCs in bone marrow (BM), new evidence shows that, in addition to SDF-1, the migration of HSPCs is directed by gradients of the bioactive lipids sphingosine-1 phosphate and ceramide-1 phosphate. Furthermore, the SDF-1 gradient may be positively primed/modulated by cationic peptides (C3a anaphylatoxin and cathelicidin) and, as previously demonstrated, HSPCs respond robustly even to very low SDF-1 gradients in the presence of priming factors. In this review, we discuss the role of bioactive lipids in stem cell trafficking and the consequences of HSPC priming by cationic peptides. Together, these phenomena support a picture in which the SDF-1-CXCR4 axis modulates homing, BM retention and mobilization of HSPCs in a more complex way than previously envisioned.

Conditioning for hematopoietic transplantation activates the complement cascade and induces a proteolytic environment in bone marrow: a novel role for bioactive lipids and soluble C5b-C9 as homing factors

We have observed that conditioning for hematopoietic transplantation by lethal irradiation induces a proteolytic microenvironment in the bone marrow (BM) that activates the complement cascade (CC). As a result, BM is enriched for proteolytic enzymes and the soluble form of the terminal product of CC activation, the membrane attack complex C5b-C9 (MAC). At the same time, proteolytic enzymes induced in irradiated BM impair the chemotactic activity of α-chemokine stromal-derived factor-1 (SDF-1). As SDF-1 is considered a crucial BM chemoattractant for transplanted hematopoietic stem/progenitor cells (HSPCs), we sought to determine whether other factors that are resistant to proteolytic enzymes have a role in this process, focusing on proteolysis-resistant bioactive lipids. We found that the concentrations of sphingosine-1-phosphate (S1P) and ceramide-1-phosphate (C1P) increase in the BM after conditioning for transplantation and that both S1P and, as we show here for the first time, C1P are potent chemoattractants for HSPCs. Next, we observed that C5-deficient mice that do not generate MAC show impaired engraftment of HSPCs. In support of a role for MAC in homing and engraftment, we found that soluble MAC enhances in a CR3 (CD11b/CD18)-dependent manner the adhesion of HSPCs to BM stromal cells and increases the secretion of SDF-1 by BM stroma. We conclude that an increase in BM levels of proteolytic enzyme-resistant S1P and C1P and activation of CC, which leads to the generation of MAC, has an important and previously underappreciated role in the homing of transplanted HSPCs.

Effects of the polymorphisms of Mx1, BAT2 and CXCL12 genes on immunological traits in pigs

It is necessary that genetic markers or biomarkers can be used to predict resistance towards a wide range of infectious diseases. In the present study, we estimated the potential markers and measured their relationship with heritabilities of a wide range of immune traits. Polymorphisms in exon 13 of Mx1, intron 25 of BAT2 and intron 3 of CXCL12 were identified by sequencing, and the genotypes were analyzed by PCR-RFLP in a resource population composed of 352 pure breed Landrace piglets at days 0, 17 and 32 after birth. Associations of single-nucleotide polymorphisms (SNPs) in these genes with a variety of immunological traits and antibody levels for pig reproduction and porcine respiratory syndrome virus (PRRSV), pseudorabies virus (PRV) and classical swine fever virus (CSFV) were performed. The performance of GG genotype of BAT2 on hemoglobin concentration (HBG) and hematocrit (HCT) of piglets at day 0 was significantly higher than that of the AA and AG individuals. For Mx1, compared with CT genotype, the pigs with TT or CC generated more PRRS antibody at day 0. The piglets with CT genotype had highly significant difference of PRV antibody from those with CC and TT genotypes at day 0. And the piglets with CC genotype had higher level red blood cell count (RBC), hemoglobin concentration (HBG) and hematocrit (HCT) than those with CT and TT genotypes at day 17. For the C7462G SNP in the intron 3 of CXCL12, the PRV antibody level of piglets with the CG genotype were higher than that of piglets with CC and GG genotypes at day 17, and the mean corpuscular volume (MCV) of GG piglets were larger than that of CC and CG individuals at day 0. At the locus 7331 bp in the intron 3 of CXCL12, there were significantly differences of mean corpuscular hemoglobin concentrations (MCHC) at day 0 and white blood cell count (WBC) at day 32, which showed the trend GG or AG>AA, AA>AG or GG, respectively. The pigs with AA or GG genotype had more platelet distribution width (PDW), mean platelet volume (MPV) and platelet-large cell ratio (PLR) at day 17 than those with AG. The results of this study indicated that polymorphisms in Mx1, BAT2 and CXCL12 genes were significantly associated with the immunological traits in Landrace piglets and had potential application value for marker-assisted selection of pig breeding with disease resistance.

[CXCR4, a therapeutic target in rare immunodeficiencies?]

Currently, more than 200 primary immunodeficiency diseases have been discovered. In most cases, genetic defects affect the expression or the function of proteins involved in immune development and homeostasis. Some orphan immuno-hematological disorders are characterized by an abnormal leukocyte trafficking, a notion predictive of an anomaly of the chemokine/chemokine receptor system. In this review, we focus on recent advances in the characterization of dysfunctions of the CXCL12 (SDF-1)/CXCR4 signaling axis in two rare human immunodeficiencies, one associated with a loss of CXCR4 function, the Idiopathic CD4(+) T-cell Lymphocytopenia, and the other with a gain of CXCR4 function, the WHIM syndrome.

Idiopathic CD4+ T-cell lymphocytopenia is associated with impaired membrane expression of the chemokine receptor CXCR4

Idiopathic CD4(+) T-cell lymphocytopenia (ICL) is a rare acquired T-cell immunodeficiency of unknown pathogenic basis. Six adults with ICL who developed opportunistic infections were investigated using extensive immunophenotyping analysis and functional evaluation of the chemokine receptor CXCR4. For all 6 patients studied, a profound defect in CXCR4 expression was detected at the surface of CD4(+) T lymphocytes, in association with an abnormal intracellular accumulation of CXCR4 and of its natural ligand, the chemokine CXCL12. For all patients studied, CD4(+) T-cell chemotactic response toward CXCL12 was decreased, whereas sensitivity to CXCL8 was preserved. CXCR4 recovery after ligand-induced endocytosis was impaired in ICL CD4(+) T cells. Upon in vitro addition of interleukin-2 (IL-2), membrane expression of CXCR4 returned to normal levels in 5 of 6 patients, whereas intracellular accumulation of CXCR4 and CXCL12 disappeared. Upon therapeutic administration of IL-2, CD4(+) T-cell count and membrane CXCR4 expression and function improved over time in 3 of 4 patients treated. Therefore, our data indicate that ICL is associated with defective surface expression of CXCR4, which may be reversed by IL-2.

SDF1-3' a gene polymorphism is associated with laryngeal cancer

The SDF1-3' G801A (rs 1801157) polymorphism is associated with increased risk of various types of cancers, including those of the neck and head. Using PCR-RFLPs, we investigated the distribution of SDF1-3' G801A genotypes in patients with laryngeal cancer (n = 118) and controls (n = 250) in Poland. We found that patients with SDF1-3' A/A and G/A genotypes exhibit a 1.863-fold increased risk of laryngeal cancer (95% CI = 1.177-2.949, p = 0.0086). However, there was no significant increase in risk for the homozygous SDF1-3' A/A genotype OR = 3.235 (95% CI = 0.5330-19.633, p = 0.3329). We also did not observe a significant association between tumor characteristics and prevalence of alleles or genotypes for the SDF1-3' G801A polymorphism. Our findings suggest that the SDF1-3'A variant may be associated with an increased risk of laryngeal cancer.

SDF1-3' G801A polymorphisms in Polish patients with systemic lupus erythematosus

It has been reported that stromal cell-derived factor-1 (SDF1), currently also designated CXCL12, plays a significant role in the development of nephritis and death in the lupus mice model. Using restriction length fragment polymorphism (RFLP) analysis we assessed the frequencies of SDF1-3' G801A (rs 1801157) polymorphic variants between systemic lupus erythematosus (SLE) patients (n = 150) and controls (n = 300). There were no significant differences in the prevalence of SDF1-3' G801A polymorphic variants in SLE patients and healthy individuals. However, we observed that the SDF1-3' A/A and G/A genotypes (recessive model) contributed to renal manifestations of SLE OR = 3.042 (95% CI = 1.527-6.058, P = 0.002), and the p value stayed statistically significant after Bonferroni correction (p(corr) = 0.032) in SLE patients. We also found an association of the SDF1-3' A/A and G/A genotypes (recessive model) with dermal manifestations of SLE OR = 2.510 (95% CI = 1.247-5.052, P = 0.0122), (p(corr) = 0.1952) but this did not remain statistically significant after Bonferroni correction. Our observations suggest that the SDF1-3' G801A genotype may be associated with some clinical manifestations in patients with SLE.

NF-kappaB1 and c-Rel cooperate to promote the survival of TLR4-activated B cells by neutralizing Bim via distinct mechanisms

The nuclear factor-kappaB (NF-kappaB) pathway is crucial for the survival of B cells stimulated through Toll-like receptors (TLRs). Here, we show that the heightened death of TLR4-activated nfkb1(-/-) B cells is the result of a failure of the Tpl(2)/MEK/ERK pathway to phosphorylate the proapo-ptotic BH3-only protein Bim and target it for degradation. ERK inactivation of Bim after TLR4 stimulation is accompanied by an increase in A1/Bim and Bcl-x(L)/Bim complexes that we propose represents a c-Rel-dependent mechanism for neutralizing Bim. Together these findings establish that optimal survival of TLR4-activated B cells depends on the NF-kappaB pathway neutralizing Bim through a combination of Bcl-2 prosurvival protein induction and Tpl2/ERK-dependent Bim phosphorylation and degradation.

Inhibition of human immunodeficiency virus-1 entry using vectors expressing a multimeric hammerhead ribozyme targeting the CCR5 mRNA

Rz1–7is a multimeric hammerhead ribozyme targeting seven unique sites within the human CCR5 mRNA that is activein vitro. Mouse stem cell virus-based MGIN and human immunodeficiency virus (HIV)-1-based HEG1 vectors were used to express Rz1–7in a human CD4+T lymphoid cell line. Stable transductants expressed Rz1–7, which was further shown to be active, since CCR5 mRNA and surface CCR5 protein expression levels decreased. High levels of progeny virus were produced when the transduced cells were challenged with an X4-tropic HIV-1 (NL4-3) strain, suggesting that Rz1–7expression does not affect X4-tropic virus replication. When the transduced cells expressing Rz1–7were challenged with the R5-tropic HIV-1 (BaL) strain, 99–100 % inhibition of progeny virus production was observed for the duration of the experiment (∼2 months). When the cells were precultured for 2–3 months prior to HIV-1 infection, inhibition was more prominent in cells transduced with MGIN-Rz1–7than with HEG1-Rz1–7. Inhibition occurred at the level of viral entry, as no HIV-1 DNA could be detected. These results demonstrate that Rz1–7confers excellent inhibition of R5-tropic HIV-1 replication at the level of entry. Therefore, we anticipate that this multimeric ribozyme will be beneficial for HIV-1 gene therapy.

Nerve growth factor stimulates proliferation, adhesion and thymopoietic cytokine expression in mouse thymic epithelial cells in vitro

Thymic epithelial cells, which constitute a major component of the thymic microenvironment, provide a crucial signal for intrathymic T cell development and selection. Neuroimmune networks in the thymic microenvironment are thought to be involved in the regulation of T cell development. NGF is increasingly recognized as a potent immunomodulator, promoting "cross-talk" between various types of immune system cells. The present study clearly shows that NGF stimulates mouse thymic epithelial cell activities in vitro including cell proliferation, thymocyte adhesion to thymic epithelial cells, and the expression of cell adhesion molecules such as ICAM-1 and VCAM-1, and thymopoietic factors including IL-7, GM-CSF, SDF-1, TARC and TECK. Thus, our data are of considerable clinical importance showing that trophic NGF activity could be used to enhance the thymus regeneration and develop methods to improve host immunity when the immune function is depressed due to thymic involution.

Differential requirement for DOCK2 in migration of plasmacytoid dendritic cells versus myeloid dendritic cells

The migratory properties of dendritic cells (DCs) are important for their functions. Although several chemokines and their receptors have been implicated in DC migration, the downstream signaling molecules are largely unknown. Here we show that DOCK2, a hematopoietic cell-specific CDM family protein, is indispensable for migration of plasmacytoid DCs (pDCs), but not myeloid DCs (mDCs). Although DOCK2-deficiency did not affect development of pDCs, DOCK2-deficient (DOCK2(-/-)) mice exhibited a severe reduction of pDCs in the spleen and lymph nodes. Adoptive transfer experiments revealed that DOCK2(-/-) pDCs failed to migrate into the periarteriolar lymphoid sheaths of the spleen. In DOCK2(-/-) pDCs, chemokine-induced Rac activation was severely impaired, resulting in the reduction of motility and the loss of polarity during chemotaxis. In contrast, DOCK2(-/-) mDCs did not show any defects in Rac activation and migration. These results indicate that pDCs and mDCs use distinct molecules to activate Rac during chemotaxis.

Reduced activation of protein kinase B, Rac, and F-actin polymerization contributes to an impairment of stromal cell–derived factor-1–induced migration of CD34+ cells from patients with myelodysplasia

Patients with myelodysplasia (MDS) show a differentiation defect in the multipotent stem-cell compartment. An important factor in stem-cell differentiation is their proper localization within the bone marrow microenvironment, which is regulated by stromal cell–derived factor (SDF-1). We now show that SDF-1–induced migration of CD34+ progenitor cells from MDS patients is severely impaired. In addition, these cells show a reduced capacity to polymerize F-actin in response to SDF-1. We demonstrate a major role for Rac and phosphatidylinositol 3-kinase (PI3K) and a minor role for the extracellular signal-regulated kinase (ERK)1/2 signaling pathway in SDF-1–induced migration of normal CD34+ cells. Furthermore, SDF-1–stimulated activation of Rac and the PI3K target protein kinase B is impaired in CD34+ cells from MDS patients. Lentiviral transduction of MDS CD34+ cells with constitutive active Rac1V12 results in a partial restoration of F-actin polymerization in response to SDF-1. In addition, expression of constitutive active Rac increases the motility of MDS CD34+ cells in the absence of SDF-1, although the directional migration of cells toward this chemoattractant is not affected. Taken together, our results show a reduced migration of MDS CD34+ cells toward SDF-1, as a result of impaired activation of the PI3K and Rac pathways and a decreased F-actin polymerization.

Tumor refractoriness to anti-VEGF treatment is mediated by CD11b+Gr1+ myeloid cells

Vascular endothelial growth factor (VEGF) is an essential regulator of normal and abnormal blood vessel growth. A monoclonal antibody (mAb) that targets VEGF suppresses tumor growth in murine cancer models and human patients. We investigated cellular and molecular events that mediate refractoriness of tumors to anti-angiogenic therapy. Inherent anti-VEGF refractoriness is associated with infiltration of the tumor tissue by CD11b+Gr1+ myeloid cells. Recruitment of these myeloid cells is also sufficient to confer refractoriness. Combining anti-VEGF treatment with a mAb that targets myeloid cells inhibits growth of refractory tumors more effectively than anti-VEGF alone. Gene expression analysis in CD11b+Gr1+ cells isolated from the bone marrow of mice bearing refractory tumors reveals higher expression of a distinct set of genes known to be implicated in active mobilization and recruitment of myeloid cells. These findings indicate that, in our models, refractoriness to anti-VEGF treatment is determined by the ability of tumors to prime and recruit CD11b+Gr1+ cells.

Chemokine stromal cell-derived factor-1 induction by C/EBPβ activation is associated with all-trans-retinoic acid-induced leukemic cell differentiation

Stromal cell-derived factor-1 (SDF-1/CXCL12) is one of the essential chemokines, which mediates hematopoietic differentiations. However, the mechanism by which SDF-1 expression is regulated in granulocyte differentiation is poorly understood. Here, we suggest a novel mechanism by which all-trans-retinoic acid (ATRA) induces the expression of SDF-1 during the differentiation of promyelomonocytic leukemic U937 cells. Moreover, we also demonstrate that activation of transcription factor C/EBPbeta by ATRA regulates SDF-1 expression in U937 cells. In addition, we show that the cyclin-dependent kinase inhibitors p21(WAF1/CIP1) and Pyk2 are up-regulated by SDF-1 and increased markedly by the costimulation of ATRA and SDF-1. Furthermore, ATRA and SDF-1alpha additively induce U937 cell differentiation. Indeed, silencing the expression of SDF-1 inhibits ATRA-induced granulocyte differentiation significantly. Taken together, these results indicate that SDF-1alpha is involved in granulocyte differentiation in response to ATRA, mediated by the activation of the transcription factor C/EBPbeta.

Aberrant T-cell ontogeny and defective thymocyte and colonic T-cell chemotactic migration in colitis-prone Galphai2-deficient mice

Galphai2-deficient mice, which spontaneously develop colitis, have previously been reported to have an increased frequency of mature, single positive thymocytes compared to wild-type mice. In this study we further characterized the intrathymic changes in these mice before and during overt colitis. Even before the onset of colitis, Galphai2(-/-) thymi weighed less and contained fewer thymocytes, and this was exacerbated with colitis development. Whereas precolitic Galphai2(-/-) mice had unchanged thymocyte density compared to Galphai2(+/-) mice of the same age, this was significantly decreased in mice with colitis. Thymic atrophy in Galphai2(-/-) mice involved mainly the cortex. Using a five-stage phenotypic characterization of thymocyte maturation based on expression of CD4, CD8, TCRalphabeta, CD69 and CD62L, we found that both precolitic and colitic Galphai2(-/-) mice had significantly increased frequencies of mature single-positive CD4(+) and CD8(+) medullary thymocytes, and significantly reduced frequencies and total numbers of immature CD4(+) CD8(+) double-positive thymocytes compared to Galphai2(+/-) mice. Furthermore, cortical and transitional precolitic Galphai2(-/-) thymocytes showed significantly reduced chemotactic migration towards CXCL12, and a trend towards reduced migration to CCL25, compared to wild-type thymocytes, a feature even more pronounced in colitic mice. This impaired chemotactic migration of Galphai2(-/-) thymocytes could not be reversed by increased chemokine concentrations. Galphai2(-/-) thymocytes also showed reduced expression of the CCL25 receptor CCR9, but not CXCR4, the receptor, for CXCL12. Finally, wild-type colonic lamina propria lymphocytes migrated in response to CXCL12, but not CCL25 and, as with thymocytes, the chemokine responsiveness was significantly reduced in Galphai2(-/-) mucosal lymphocytes.

CXCL12 Limits Inflammation by Localizing Mononuclear Infiltrates to the Perivascular Space during Experimental Autoimmune Encephalomyelitis

The inflammatory response in the CNS begins with the movement of leukocytes across the blood-brain barrier in a multistep process that requires cells to pass through a perivascular space before entering the parenchyma. The molecular mechanisms that orchestrate this movement are not known. The chemokine CXCL12 is highly expressed throughout the CNS by microendothelial cells under normal conditions, suggesting it might play a role maintaining the blood-brain barrier. We tested this hypothesis in the setting of experimental autoimmune encephalomyelitis (EAE) by using AMD3100, a specific antagonist of the CXCL12 receptor CXCR4. We demonstrate that the loss of CXCR4 activation enhances the migration of infiltrating leukocytes into the CNS parenchyma. CXCL12 is expressed at the basolateral surface of CNS endothelial cells in normal spinal cord and at the onset of EAE. This polarity is lost in vessels associated with an extensive parenchymal invasion of mononuclear cells during the peak of disease. Inhibition of CXCR4 activation during the induction of EAE leads to loss of the typical intense perivascular cuffs, which are replaced with widespread white matter infiltration of mononuclear cells, worsening the clinical severity of the disease and increasing inflammation. Taken together, these data suggest a novel anti-inflammatory role for CXCL12 during EAE in that it functions to localize CXCR4-expressing mononuclear cells to the perivascular space, thereby limiting the parenchymal infiltration of autoreactive effector cells.

CXCR4 and CCR5 mediate homing of primitive bone marrow-derived hematopoietic cells to the postnatal thymus

Factors governing the entry of cells into the postnatal thymus are poorly understood. We aimed to define molecular mechanisms mediating the homing of bone marrow cells to the thymus using a sublethally irradiated in vivo murine model. Entry of unfractionated and lineage-depleted bone marrow cells to the thymus, but not bone marrow, was a Galphai-mediated phenomenon. Lineage-depleted cells that had homed to the thymus expressed abundant CXCR4 and CCR5 mRNA, alone of 17 chemokine receptors evaluated by QPCR. Thymic-homed cells were distinct from cells that had homed to bone marrow in expression of CXCR4 and CCR5 by mRNA quantification and cell-surface expression of protein. Abrogation of CXCR4 and CCR5 function by genetic, antibody, or pharmacologic means impaired homing of lineage-depleted cells to the thymus, although not in a synergistic manner, implying interdependency of these receptors in the homing process. Competitive repopulation experiments demonstrated that inhibiting CXCR4-mediated homing adversely affected the double-negative cell pool at 2 weeks, suggesting that cells with prothymocytic activity may in part home via CXCR4. Overall, our data demonstrate differential homing mechanisms governing entry of unfractionated and lineage-depleted cells to irradiated bone marrow or thymus, with thymic homing of immature cells being pertussis-sensitive and mediated by the chemokine receptors CXCR4 and CCR5.

Diverse Toll-like receptors utilize Tpl2 to activate extracellular signal-regulated kinase (ERK) in hemopoietic cells

Engaging mammalian Toll-like receptors (TLRs) activate both the NF-kappaB and mitogen-activated protein kinase signaling pathways. Here we establish that mitogen-activated protein 3 kinase Tpl2, levels of which are markedly reduced in nfkb1(-/-) cells, is required for extracellular signal-regulated kinase (ERK) activation in bone marrow-derived macrophages and B cells stimulated with diverse TLR ligands. Despite rescuing TLR-dependent ERK activation in nfkb1(-/-) bone marrow-derived macrophages by using an estrogen receptor-regulated version of the mitogen-activated protein 3 kinase, c-Raf (Raf:ER), CpG or LPS induction of IL-10 was only partially restored in nfkb1(-/-) cells expressing Raf:ER, a finding consistent with NF-kappaB1 regulating IL-10 by a combination of ERK-independent and -dependent mechanisms. Collectively, our findings indicate that the Tpl2/MEK/ERK signaling module is a master regulator of ERK-dependent gene expression downstream of TLRs in different hemopoietic cells.

Chemokine control of lymphocyte trafficking: a general overview

Chemokines are a large family of small, generally secreted polypeptides which guide lymphocyte movement throughout the body by controlling integrin avidity and inducing migration. Here, we look at recent, exciting findings on chemokine function throughout lymphocyte development and co-ordinated T and B cell migration during immune responses. Finally, we will review data on the regional control of immunity by tissue-specific chemokine receptors on effector/memory lymphocytes.

Stroke-induced Migration of Human Umbilical Cord Blood Cells: Time Course and Cytokines

The therapeutic window for treatment of individuals after stroke is narrow, regardless of the treatment regime; extension of this window would provide a major therapeutic advance. In prior reports, we demonstrated significant improvements in the behavioral defects of rats that received human umbilical cord blood (HUCB) cells 24 h after a middle cerebral arterial occlusion. These effects paralleled the recruitment of these cells to the site of tissue damage. While the administration of HUCB cells 24 h after stroke was effective, the optimal time to administer these cells after stroke has not been established. Here, we investigated the migration of HUCB cells to ischemic tissue extracts. After ischemic assault, brain tissue was homogenized, and the supernatants were assayed for their ability to attract HUCB mononuclear cells as well as for levels of several cytokines. We demonstrate increased migratory activity of HUCB cells toward the extracts harvested at 24-72 h after stroke. The extracts possessed increased levels of certain cytokines and chemokines, suggesting their participation in HUCB cell migration. The results from this study are promising in that the current 3-h therapeutic window for the treatment of stroke victims, using approved anticoagulant treatment, may be extended with the use of HUCB cell therapy 24-72 h post stroke. Last, the chemokines present in the supernatant provide a sound starting point to start examining the mechanisms responsible for the in vivo migration of HUCB cells after the induction of stroke.

Hierarchy of molecular-pathway usage in bone marrow homing and its shift by cytokines

Efficient bone marrow (BM) homing is a prerequisite for successful engraftment of transplanted hematopoietic cells (HPCs). Contradictory conclusions about the contribution of SDF-1/CXCR4 have clouded our understanding of its role within the molecular pathway cooperation needed for BM homing, particularly with the well-defined hierarchic network of adhesion molecules. In the present study we sought to unravel cooperative and compensatory molecular pathways guiding BM homing. Fresh BM-HPCs, rendered either SDF-1 unresponsive or Gi-signaling refractory, homed quite efficiently, because of compensation by alpha4-integrin interacting with VCAM-1. The contribution of SDF-1/CXCR4- or Gi-protein-mediated signals to BM homing became apparent after their blockade was combined with deletion of alpha4-integrin, leading to dramatic reduction in BM homing. Similar conclusions were revealed when VCAM-1-deficient hosts were used. Cytokine incubation changed the functional properties of BM-HPCs and hierarchy of molecular pathway usage in homing, by shifting the dominance among the homing mediators: loss of CXCR4 or Gi-signaling now significantly reduced BM homing, with only partial compensation through alpha4/VCAM-1 and endothelial selectins. These studies depict a flexible hierarchy of cooperating homing pathways, in which dominant players are repositioned with changing cytokine milieu, and possibly source of HPCs.

Pivotal function for cytoplasmic protein FROUNT in CCR2-mediated monocyte chemotaxis

Ligation of the chemokine receptor CCR2 on monocytes and macrophages with its ligand CCL2 results in activation of the cascade consisting of phosphatidylinositol-3-OH kinase (PI(3)K), the small G protein Rac and lamellipodium protrusion. We show here that a unique clathrin heavy-chain repeat homology protein, FROUNT, directly bound activated CCR2 and formed clusters at the cell front during chemotaxis. Overexpression of FROUNT amplified the chemokine-elicited PI(3)K-Rac-lamellipodium protrusion cascade and subsequent chemotaxis. Blocking FROUNT function by using a truncated mutant or antisense strategy substantially diminished signaling via CCR2. In a mouse peritonitis model, suppression of endogenous FROUNT markedly prevented macrophage infiltration. Thus, FROUNT links activated CCR2 to the PI(3)K-Rac-lamellipodium protrusion cascade and could be a therapeutic target in chronic inflammatory immune diseases associated with macrophage infiltration.

The CXCR4 agonist peptide, CTCE-0021, rapidly mobilizes polymorphonuclear neutrophils and hematopoietic progenitor cells into peripheral blood and synergizes with granulocyte colony-stimulating factor

OBJECTIVE

Mobilization of hematopoietic stem and progenitor cells (HSPC) by stromal cell-derived factor-1 (SDF-1) has been described; however, sustained adenoviral delivery or N-terminal modification was required for effect and could not be demonstrated with native protein. The aim of this study was to further investigate the SDF-1alpha/CXCR4 axis in HSPC mobilization using CTCE-0021, a cyclized CXCR4 agonist peptide, with comparable bioactivity and improved stability relative to SDF-1alpha.

METHODS

Peripheral blood cells and hematopoietic progenitor cells (HPC) were quantitated in mice administered single or multiple doses of CTCE-0021 or SDF-1alpha, or mobilized by granulocyte colony-stimulating factor (G-CSF) in combination with CTCE-0021. Proteases, cytokines, and receptors implicated in HSPC mobilization were evaluated to determine mechanism of action.

RESULTS

CTCE-0021 dose-dependently elevated blood neutrophils polymorphonuclear neutrophil [PMN] within 5 minutes that peaked after 1 hour and persisted for 24 hours. PMN mobilization could be maintained by daily dosing. CTCE-0021 mobilized colony-forming unit granulocyte macrophage (CFU-GM), burst-forming unit erythroid (BFU-E), and CFU-granulocyte-erythrocyte-monocyte-megakaryocyte (CFU-GEMM) that peaked within 1 hour after administration, and synergistically enhanced both PMN and HSPC mobilization when combined with G-CSF. Mobilization induced by CTCE-0021 was associated with rapid downregulation of CXCR4 expression on HPC. No appreciable changes in proteases implicated in HPC mobilization were observed. Significantly elevated plasma SDF-1 was detected in mobilized mice, which likely represents CTCE-0021.

CONCLUSION

These studies indicate that CTCE-0021 is an efficient and rapid mobilizer of PMN and HPC when used alone and shows synergistic activity when used in combination with G-CSF. The mobilizing effect of this peptide appears to be mediated by downregulation of the CXCR4 receptor on HPC and altered chemokine gradient.

CXCR4 mutations in WHIM syndrome: a misguided immune system?

Chemokines and their receptors are key molecules in the development and function of immune cell populations and the organization of lymphoid organs. Despite their central role in immunologic function, genetic studies exploring the intersection of chemokines or their receptors and human health have revealed few associations of unambiguous significance. The best-characterized examples have revealed striking selective advantage conferred by loss of receptors used as portals of entry by pathogens. Recently, mutations in the CXCR4 chemokine receptor gene were identified in a dominantly inherited immunodeficiency disease, WHIM syndrome. Genetic and biochemical evidences suggest that the loss of the receptor cytoplasmic tail domain results in aberrant signaling. Analyses of mutant cell responses to the receptor ligand CXCL12 have revealed enhanced chemotaxis, confirming the gain-of-function effect of the truncation mutations. The clinical features and potential mechanism of immunodeficiency in WHIM syndrome patients are discussed in this review.

The mitogen-induced increase in T cell size involves PKC and NFAT activation of Rel/NF-kappaB-dependent c-myc expression

Cell growth during the G1 stage of the cell cycle is partly controlled by inducing c-myc expression, which in B cells is regulated by the NF-kappaB1 and c-Rel transcription factors. Here, we show that c-myc-dependent growth during T cell activation requires c-Rel and RelA and that blocking this growth by inhibiting protein kinase C theta (PKCtheta) coincides with a failure to upregulate c-myc due to impaired RelA nuclear import and inhibition of NFAT-dependent c-rel transcription. These results demonstrate that different Rel/NF-kappaB dimers regulate the mitogenic growth of mature T and B cells, with a signaling pathway incorporating PKCtheta and NFAT controlling c-Rel/RelA-induced c-myc expression in activated T cells.

Evidence for recruitment of plasmacytoid dendritic cell precursors to inflamed lymph nodes through high endothelial venules

Recruitment of dendritic cells (DCs) to lymph nodes (LNs) is pivotal to the establishment of immune response. Whereas DCs have been proven to undergo afferent lymphatic pathway to enter LNs from peripheral tissues, a question remains if DCs also migrate into LNs directly from the circulation. Here we demonstrate that plasmacytoid DC (pDC) precursors can transmigrate across high endothelial venules (HEVs) of inflamed LNs in mice. Bacterial infection induces a significant number of pDC and myeloid DC (mDC) precursors into the circulation. Both subsets express a common set of chemokine receptors except CXCR3, display parallel mobilization into the blood, but show distinct trafficking pathway to the LNs. In a short-term homing assay, whereas mDC precursors migrate to peripheral tissues and subsequently to draining LNs, pDC precursors directly enter the LNs in a CXCL9 and E-selectin dependent manner. Tumor necrosis factor-alpha controls not only DC precursor mobilization into the blood but also chemokine up-regulation on LN HEVs. A similar trafficking pathway is observed also in viral infection, and CXCR3(-/-) mice-derived pDC precursors show defective trans-HEV migration. This study clarifies the inflammation-dependent, chemokine-driven distinct property of DC precursor trafficking.

Altered leukocyte response to CXCL12 in patients with warts hypogammaglobulinemia, infections, myelokathexis (WHIM) syndrome

The chemokine receptor CXCR4 and its functional ligand, CXCL12, are essential regulators of development and homeostasis of hematopoietic and lymphoid organs. Heterozygous truncating mutations in the CXCR4 intracellular tail cause a rare genetic disease known as WHIM syndrome (warts, hypogammaglobulinemia, infections, myelokathexis), whose pathophysiology remains unclear. We report CXCR4 function in 3 patients with WHIM syndrome carrying heterozygous truncating mutations of CXCR4. We show that CXCR4 gene mutations in WHIM patients do not affect cell surface expression of the chemokine receptor and its internalization upon stimulation with CXCL12. Moreover, no significant differences in calcium mobilization in response to CXCL12 are found. However, the chemotactic response of both polymorphonuclear cells and T lymphocytes in response to CXCL12 is increased. Furthermore, immunophenotypic analysis of circulating T and B lymphocytes reveals a decreased number of memory B cells and of naive T cells and an accumulation of effector memory T cells associated with a restricted T-cell repertoire. Based on our results, we suggest that the altered leukocyte response to CXCL12 may account for the pathologic retention of mature polymorphonuclear cells in the bone marrow (myelokathexis) and for an altered lymphocyte trafficking, which may cause the immunophenotyping abnormalities observed in WHIM patients.

Current mechanistic scenarios in hematopoietic stem/progenitor cell mobilization

Uncovering the molecular mechanisms governing the exit of stem/progenitor cells from bone marrow to peripheral blood at steady state or after their enforced migration has been an ongoing challenge. Recently, however, several new avenues or paradigms in mobilization have emerged from ever-expanding work in humans subjected to granulocyte colony-stimulating factor (G-CSF) mobilization, as well as from studies in normal and gene-deficient mouse models. Although these developments represent notable advances that met with considerable excitement, they have been quenched by surprising vacillations in subsequent research. This perspective highlights recent developments in mobilization along with their controversies. A full understanding of the directional cues that control the migratory behavior and the fate of stem/progenitor cells once they migrate out of bone marrow will await further experimentation, aiming to bridge our current gaps in knowledge.

Homing and mobilization of hematopoietic stem cells and hematopoietic cancer cells are mirror image processes, utilizing similar signaling pathways and occurring concurrently: circulating cancer cells constitute an ideal target for concurrent treatment with chemotherapy and antilineage-specific antibodies

Adhesion molecules and stromal cell-derived factor-1 (SDF-1)/CXCR4 signaling play key role in homing and mobilization of hematopoietic progenitor (HPC) and hematopoietic cancer clonogenic cells (HCC). High expression of VLA-4 is required for homing of HPC and HCC, whereas downregulation of these molecules is required for successful mobilization of HPC and HCC. Upregulation and activation of the SDF-1/CXCR4 signaling is required for homing of HPC and HCC, whereas disruption of the SDF-1 signaling is required for mobilization of HPC and HCC. Hence, mobilizations of HPC and HCC occur concurrently. It is proposed that drug resistance evolves as a result of repeated cycles of chemotherapy. Following each cycle of chemotherapy, HCC lose adhesion molecules and SDF-1 signaling. Surviving cells, released from tumor sites, circulate until re-expression of adhesion molecules and CXCR4 occurs, then homing to stroma of distal tissues occurs. Cytokines secreted by cells in the new microenvironment induce proliferation and drug resistance of HCC. This process is amplified in each cycle of chemotherapy resulting in disease progression. A novel model for treatment is proposed in which circulating HCC are the target for clinical intervention, and concurrent treatment with chemotherapy and antilineage-specific antibodies will result in abrogation of the 'vicious cycle' of conventional anticancer therapy.