Yngvar Fløisand

Evidence for the involvement of galectin-3 in mesenchymal stem cell suppression of allogeneic T-cell proliferation

Human bone marrow‐derived mesenchymal stem cells (MSC) are multipotent non‐hematopoietic progenitors that have regulatory activity on immune cells. NOD‐ and Toll‐like receptors (NLR, TLR) have several roles in immunity, including those relevant to pathogen recognition and shaping the course of immune responses by controlling gene expression. We have shown that these innate immune receptors are expressed by hematopoietic CD34+ progenitors and MSC. To uncover genes critical in MSC function, first we have used microarray to screen for potential transcripts whose levels are altered in response to NOD‐1 and TLR‐2 activation, and second we validated some candidate genes using real‐time RT‐PCR, Western blots and cellular assays. Amongst the altered genes, galectin‐3 was upregulated at both mRNA and protein levels in response to TLR‐2 activation. Interestingly, MSC secreted galectin‐3, a protein known to modulate T‐cell proliferation, gene expression, cell adhesion and migration. Knockdown of galectin‐3 in MSC using small interfering RNA (siRNA) reduced the immunosuppressive effect of MSC on mixed lymphocyte cultures when compared to cells treated with an irrelevant siRNA (P < 0.05). Collectively, the data emphasize a new role of galectin‐3 in the immunomodulatory function of MSC and indicate that NOD signalling pathway is also functional in these cells.

TLR agonists induce the differentiation of human bone marrow CD34+ progenitors into CD11c+ CD80/86+ DC capable of inducing a Th1-type response

We recently reported that human bone marrow hematopoietic CD34+ progenitors express functional Toll‐like receptors (TLR) and can differentiate into myeloid cells just by stimulation with resiquimod (R848), a specific agonist for TLR7/8. However, the mechanisms by which R848 induces cell differentiation, the effects of other TLR agonists and the functionality of the differentiated cells are not known. Comparable to R848, loxoribine (a TLR7 agonist) and Pam3CSK4 (a TLR2 agonist) induced cytokine production and cell differentiation along the myeloid lineage. R848 and loxoribine were more effective than Pam3CSK4 at inducing the lineage‐negative (CD11c+ CD14–) dendritic cells (DC), whereas Pam3CSK4 was more effective at inducing CD11c+ CD14+ monocytes. Both cell subsets expressed CD80/CD86 and HLA‐DR molecules; however, they showed differential expression of CD1a, CD1b, CD1c, CD11b, CD206 and CD207 markers when compared with each other. Cell differentiation into DC was significantly inhibited by an anti‐TNF‐α nonoclonal antibody. The CD11c+ CD14– subset was isolated and shown to be more potent in stimulating an alloreaction than the CD11c+ CD14+ subset. Collectively, these data highlight the differential effects of TLR agonists on human bone marow CD34+ progenitor cells and provide a new opportunity for generating functional DC that would be useful in cancer vaccination.

Mesenchymal stem cell-mediated T cell suppression occurs through secreted galectins

Human galectins are involved in a variety of biological and pathological processes including cell adhesion, apoptosis, differentiation, immune regulation and tumour evasion. Previously, we identified galectin-3 as the first human lectin involved in the modulation of the immunosuppressive potential of mesenchymal stem cells (MSCs). In this study, we report on the expression profiles and potential activities of other galectins expressed in these cells. The data show that MSCs constitutively express galectins-1, -3 and -8 at both the mRNA and protein levels. In contrast to galectin-8, galectins-1 and -3 are secreted and found on the cell surface. MSC-mediated T cell suppression was inhibited by galectin-1-specific siRNAs but not by galectin-8-specific siRNAs. The double knockdown of galectins-1 and -3 almost abolished the immunosuppressive capacity of MSCs. The use of a competitive inhibitor for galectin binding, ß lactose, restored alloresponsiveness, implying an extracellular mechanism of action of galectins. Collectively, the data highlight the involvement of secreted galectins-1 and -3 in MSC-mediated T cell suppression. The immunosuppression by MSC-secreted galectins should facilitate the use of recombinant galectin-1 and/or -3 as a novel therapy to alleviate inflammatory reactions such as those seen in graft versus host disease (GvHD) and autoimmune disorders.

Impaired expression of indoleamine 2, 3-dioxygenase in monocyte-derived dendritic cells in response to Toll-like receptor-7/8 ligands

The effects of immunostimulatory RNAs (isRNAs) on the expression of immuno‐suppressive factors are largely unknown. Indoleamine 2,3‐dioxygenase (IDO) is a key negative regulator of immune responses and it has been implicated in hampering immunity against tumours. Here we show that the activation of Toll‐like receptors (TLR)‐7/8 with isRNAs or R848, a specific ligand for TLR7/8, can induce IDO expression in human monocytes, but not in monocyte‐derived dendritic cells (moDC). In contrast to TLR7/8 agnosists, treatment of the same moDC with interferon‐γ‐induced IDO expression. Treatment of monocytes with 2′‐O‐methyl uridine‐modified isRNAs alone does not induce IDO, but totally abrogated the effects of unmodified isRNAs. Like isRNAs, synthetic viral RNAs and cytomegalovirus (CMV) induced IDO in monocytes, whereas TLR2 ligand lipopeptide Pam3Cys exhibited no effect. Furthermore, IDO positive monocytes suppressed autologous T‐cell activation. Collectively, these data indicate for first time that the potency of TLR7/8 signalling pathways to induce IDO expression in monocytes is silenced when the cells are programmed to differentiate into dendritic cells. The immunosuppressive properties of IDO might confer an advantage to CMV‐infected monocytes to escape T‐cell responses. The findings that 2′‐O‐methyl modified RNAs can block isRNA‐induced IDO expression would facilitate the design of new TLR inhibitors.

Similar Properties of Chondrocytes from Osteoarthritis Joints and Mesenchymal Stem Cells from Healthy Donors for Tissue Engineering of Articular Cartilage

Lesions of hyaline cartilage do not heal spontaneously, and represent a therapeutic challenge. In vitro engineering of articular cartilage using cells and biomaterials may prove to be the best solution. Patients with osteoarthritis (OA) may require tissue engineered cartilage therapy. Chondrocytes obtained from OA joints are thought to be involved in the disease process, and thus to be of insufficient quality to be used for repair strategies. Bone marrow (BM) derived mesenchymal stem cells (MSCs) from healthy donors may represent an alternative cell source. We have isolated chondrocytes from OA joints, performed cell culture expansion and tissue engineering of cartilage using a disc-shaped alginate scaffold and chondrogenic differentiation medium. We performed real-time reverse transcriptase quantitative PCR and fluorescence immunohistochemistry to evaluate mRNA and protein expression for a range of molecules involved in chondrogenesis and OA pathogenesis. Results were compared with those obtained by using BM-MSCs in an identical tissue engineering strategy. Finally the two populations were compared using genome-wide mRNA arrays. At three weeks of chondrogenic differentiation we found high and similar levels of hyaline cartilage-specific type II collagen and fibrocartilage-specific type I collagen mRNA and protein in discs containing OA and BM-MSC derived chondrocytes. Aggrecan, the dominant proteoglycan in hyaline cartilage, was more abundantly distributed in the OA chondrocyte extracellular matrix. OA chondrocytes expressed higher mRNA levels also of other hyaline extracellular matrix components. Surprisingly BM-MSC derived chondrocytes expressed higher mRNA levels of OA markers such as COL10A1, SSP1 (osteopontin), ALPL, BMP2, VEGFA, PTGES, IHH, and WNT genes, but lower levels of MMP3 and S100A4. Based on the results presented here, OA chondrocytes may be suitable for tissue engineering of articular cartilage.

Age and stress related phenotypical changes in bone marrow CD34+ cells

Objective. Phenotypical changes in the human bone marrow (BM) due to age and stress have not so far been properly addressed in the literature. In the present study, we compared CD34+ BM cells between older and young volunteers. The influence of stress on CD34+ cell phenotype in older patients was investigated in an age‐matched group with acute myocardial infarction (AMI). Cytokines thought to influence BM CD34+ cell homeostasis were also analysed. Material and methods. BM mononuclear cells of 10 older volunteers and of 7 young volunteers (18–25 years), as well as 22 AMI patients, were analysed by flow cytometry for the following markers: CD34, CD38, CD117 (c‐kit) and CD133. Blood samples were analysed for CRP, IL‐6, MCP‐1, IL‐8, MMP‐9, TIMP‐1 and TNFα by ELISA methods. Results. Significantly higher numbers of CD34+ CD38− cells (both absolute and relative) were observed in older volunteers than in young volunteers and AMI patients. Higher numbers of immature progenitors, namely CD34+CD38− cells and CD34+CD38−CD117+CD133+ cells, were observed among older volunteers compared to the other groups. However, the relative number of CD34+ cells lacking CD38 expression or expressing CD133 was higher in the old volunteers and AMI patients. None of the circulating factors investigated correlated with any of the cell population yields. Conclusion. In this study, we found that the absolute and relative numbers of BM CD34+CD38− progenitor cells increase with age. The increment is attenuated in patients with AMI.

Homeostatic chemokines CCL19 and CCL21 promote inflammation in human immunodeficiency virus‐infected patients with ongoing viral replication

CCL19 and CCL21 and their receptor CCR7 are expressed constitutively within lymphoid organs, regulating lymphocyte homing. Recent studies suggest that these chemokines may have inflammatory properties. We hypothesized a role of CCL19/CCL21 in human immunodeficiency virus (HIV) infection by promoting inflammation. We examined the expression of CCL19 and CCL21 in mononuclear cells from peripheral blood mononuclear cells (PBMC) and bone marrow mononuclear cells (BMMC) in HIV‐infected patients before and during highly active anti‐retroviral therapy (HAART). We also examined the ability of CCL19/CCL21 to promote inflammatory responses in these patients. PBMC from untreated HIV‐infected patients (n = 29) released enhanced levels of CCL19 spontaneously compared with cells from controls (n = 20), particularly in those with symptomatic disease (n = 15, P < 0·01 versus controls). During HAART (n = 9), there was a decrease in the spontaneous CCL19 release and an increase in the phytohaemagglutinin‐stimulated CCL19 release in both PBMC (P < 0·01) and BMMC (P < 0·05). In patients with enhanced HIV replication there was an increased proportion of inflammatory CD8+CCR7‐CD45RA‐ T cells in peripheral blood [P < 0·01 and P < 0·05 versus controls, untreated (n = 9) and treatment failure (n = 8), respectively]. In vitro, CCL19/CCL21 promoted an inflammatory response in PBMC when accompanied by high viral load, irrespective of HAART. The HIV‐tat protein significantly boosted the inflammatory effect of CCL19/CCL21 in PBMC. These findings link a dysregulated CCL19/CCL21/CCR7 system in HIV‐infected patients to persistent inflammation and HIV replication, not only in untreated HIV infection, but also in treatment failure during HAART.

NOD2/CARD15 on bone marrow CD34+ hematopoietic cells mediates induction of cytokines and cell differentiation

Human bone marrow (BM) hematopoietic cells were found recently to express functional TLRs and TLR signaling‐induced cytokine production and cell differentiation. Here, we have asked whether signals other than those from TLRs could instruct BM CD34+ cells to produce cytokines and differentiate by uncovering the role of nucleotide oligomerization domain (Nod)‐like receptor (NLR) family members, NOD1 and NOD2. We show that NOD2 is expressed by freshly isolated human BM CD34+ cells, whereas the expression of its close homologue NOD1 is very weak. Stimulation of the cells by the muramyl dipeptide (MDP), but not its inactive D–D enantiomer, is sufficient to trigger the expression of TNF‐α, GM‐CSF, CD11c, CD14, CD206, and the transcription factor PU.1, which is indispensable for cell differentiation toward the myeloid lineage. MDP differentiated CD11c+ cell subset‐activated T cells in MLR. Furthermore, NOD2 stimulation enhanced the CD34+ response to TLR ligands (e.g., LPS, palmitoyl‐3‐cysteine‐serine‐lysine‐4) and increased intracellular α‐defensin protein levels. Although the best‐known function of NLRs involves mature cells, our data highlight for the first time the functionality of these receptors in human BM CD34+ hematopoietic cells.

Relationship between clinical and BK virological response in patients with late hemorrhagic cystitis treated with cidofovir : a retrospective study from the European Group for Blood and Marrow Transplantation

To investigate the relationship between clinical response and modification of BK viremia, we assessed retrospectively 32 cases of hemorrhagic cystitis (HC) after allogeneic hematopoietic SCT that were treated with i.v. cidofovir (CDV). They were 22 men (69%) and 10 women (31%) with a median age of 24 years, range 3–62. The median number of CDV doses was 3, range 1–8, and the treatment lasted for a median of 3 weeks, range 1–10. Clinical improvement of HC was observed in 27 patients (84%). In 12 of 32 episodes (37.5%), BK viremia was determined before every CDV administration and a complete clinical response was observed in 10 of 12 patients (83%), the reduction of BK viremia load being ⩾1 log by 2 weeks after starting CDV. Nephrotoxicity related to CDV was observed in nine patients. Among 26 patients with 100-day follow-up, 4 of 4 patients who had a complete clinical response by 30 days were alive vs 16 of 22 (73%) who did not have the resolution of HC in this time frame. We conclude that in patients with HC, the response to CDV treatment is usually associated with a significant reduction of BK viremia load.

Lung transplantation for bronchiolitis obliterans syndrome after allo-SCT

Chronic GVHD (cGVHD) associated bronchiolitis obliterans syndrome (BOS) is a serious complication after allo-SCT, and lung transplantation (LTx) may be the ultimate treatment option. To evaluate this treatment, data on all patients with LTx after allo-SCT ever performed in Sweden, Norway, Denmark and Finland were recorded and compared with survival data from the Scandiatransplant registry. In total, LTx after allo-SCT had been performed in 13 patients. Allo-SCT was done because of AML (n=6), CML (n=3), ALL (n=2), immunodeficiency (n=1) and aplastic anemia (n=1). All developed clinical cGVHD, with median interval from allo-SCT to LTx of 8.2 (0.7–16) years. Median age at LTx was 34 (16–55) years, and the median postoperative observation time was 4.2 (0.1–15) years. Two patients died, one due to septicemia, the other of relapsing leukemia, after 2 and 14 months, respectively. Four developed BOS, one of these was retransplanted. The survival did not significantly differ from the survival in matched LTx controls, being 90% 1 year and 75% 5 years after LTx compared with 85% and 68% in the controls. We therefore suggest that LTx may be considered in carefully selected patients with BOS due to cGVHD after allo-SCT.