Taina Jaatinen

Global Gene Expression Profile of Human Cord Blood–Derived CD133+ Cells

Human cord blood (CB)–derived CD133+ cells carry characteristics of primitive hematopoietic cells and proffer an alternative for CD34+ cells in hematopoietic stem cell (HSC) transplantation. To characterize the CD133+ cell population on a genetic level, a global expression analysis of CD133+ cells was performed using oligonucleotide microarrays. CD133+ cells were purified from four fresh CB units by immunomagnetic selection. All four CD133+ samples showed significant similarity in their gene expression pattern, whereas they differed clearly from the CD133+ control samples. In all, 690 transcripts were differentially expressed between CD133+ and CD133+ cells. Of these, 393 were increased and 297 were decreased in CD133+ cells. The highest overexpression was noted in genes associated with metabolism, cellular physiological processes, cell communication, and development. A set of 257 transcripts expressed solely in the CD133+ cell population was identified. Colony‐forming unit (CFU) assay was used to detect the clonal progeny of precursors present in the studied cell populations. The results demonstrate that CD133+ cells express primitive markers and possess clonogenic progenitor capacity. This study provides a gene expression profile for human CD133+ cells. It presents a set of genes that may be used to unravel the properties of the CD133+ cell population, assumed to be highly enriched in HSCs.

The N-glycome of human embryonic stem cells

BackgroundComplex carbohydrate structures, glycans, are essential components of glycoproteins, glycolipids, and proteoglycans. While individual glycan structures including the SSEA and Tra antigens are already used to define undifferentiated human embryonic stem cells (hESC), the whole spectrum of stem cell glycans has remained unknown. We undertook a global study of the asparagine-linked glycoprotein glycans (N-glycans) of hESC and their differentiated progeny using MALDI-TOF mass spectrometric and NMR spectroscopic profiling. Structural analyses were performed by specific glycosidase enzymes and mass spectrometric fragmentation analyses.ResultsThe data demonstrated that hESC have a characteristic N-glycome which consists of both a constant part and a variable part that changes during hESC differentiation. hESC-associated N-glycans were downregulated and new structures emerged in the differentiated cells. Previously mouse embryonic stem cells have been associated with complex fucosylation by use of SSEA-1 antibody. In the present study we found that complex fucosylation was the most characteristic glycosylation feature also in undifferentiated hESC. The most abundant complex fucosylated structures were Lex and H type 2 antennae in sialylated complex-type N-glycans.ConclusionThe N-glycan phenotype of hESC was shown to reflect their differentiation stage. During differentiation, hESC-associated N-glycan features were replaced by differentiated cell-associated structures. The results indicated that hESC differentiation stage can be determined by direct analysis of the N-glycan profile. These results provide the first overview of the N-glycan profile of hESC and form the basis for future strategies to target stem cell glycans.

Optimization of immunomagnetic separation for cord blood-derived hematopoietic stem cells

BackgroundThere is a growing interest in cord blood as a source of primitive stem cells with the capacity for multilineage differentiation. Pure cell fractions are needed for the characterization and in vitro expansion of stem cells as well as for their use in preclinical research. However, enrichment of stem cells is challenging due to the lack of stem cell-specific markers and gentle protocols for the isolation of highly pure stem cell fractions. Protocols developed for the enrichment of peripheral blood-derived stem cells have been found to be suboptimal for cord blood.ResultsIn this study, immunomagnetic cell sorting protocols to purify CD34+, CD133+ and Lin- cells from fresh and cryopreserved cord blood were optimized. Reproducible purities of up to 97% were reached. The selected cells were highly viable having substantial colony-forming potential.ConclusionThe optimized protocols enable rapid enrichment of highly pure hematopoietic stem cells from both fresh and cryopreserved cord blood.

Functional Network Reconstruction Reveals Somatic Stemness Genetic Maps and Dedifferentiation‐Like Transcriptome Reprogramming Induced by GATA2

Somatic stem cell transplantation holds great promise in regenerative medicine. The best‐characterized adult stem cells are mesenchymal stem cells (MSCs), neural stem cells (NSCs), and CD133+ hematopoietic stem cells (HSCs). The applications of HSCs are hampered since these cells are difficult to maintain in an undifferentiated state in vitro. Understanding genes responsible for stem cell properties and their interactions will help on this issue. The construction of stem cell genetic networks will also help to develop rational strategies to revert somatic cells back to a stem‐like state. We performed a systemic study on human CD133+ HSCs, NSCs, MSCs, and embryonic stem cells and two different progenies of CD133+ HSCs, microvascular endothelial cells (MVECs) and peripheral blood mononuclear cells. Genes abundant in each or in all three somatic stem cells were identified. We also observed complex genetic networks functioning in postnatal stem cells, in which several genes, such as PTPN11 and DHFR, acted as hubs to maintain the stability and connectivity of the whole genetic network. Eighty‐seven HSC genes, including ANGPT1 and GATA2, were independently identified by comparing CD34+CD33−CD38− hematopoietic stem cells with CD34+ precursors and various matured progenies. Introducing GATA2 into MVECs resulted in dedifferentiation‐like transcriptome reprogramming, with HSC genes (such as ANGPT1) being up and endothelial genes (such as EPHB2) being down. This study provides a foundation for a more detailed understanding of human somatic stem cells. Expressing the newly discovered stem cell genes in matured cells might lead to a global reversion of somatic transcriptome to a stem‐like status.

Isolation of Mononuclear Cells from Human Cord Blood by Ficoll‐Paque Density Gradient

When preparing stem cell specimens from cord blood, pre-enrichment of mononuclear cells is highly recommended to improve the recovery of rare stem cells. Mononuclear cells are easily isolated by density gradient centrifugation. In Ficoll-Paque density gradient centrifugation, anticoagulant-treated and diluted cord blood is layered on the Ficoll-Paque solution and centrifuged. During centrifugation, erythrocytes and granulocytes sediment to the bottom layer. Lower density lymphocytes, together with other slowly sedimenting cells such as platelets and monocytes, are retained at the interface between the plasma and Ficoll-Paque, where they can be collected and subjected to subsequent isolation of hematopoietic stem cells or to the culture of mesenchymal stem cells.

Human CMP-N-acetylneuraminic acid hydroxylase is a novel stem cell marker linked to stem cell-specific mechanisms.

Human stem cells contain substantial amounts of the xenoantigen N‐glycolylneuraminic acid (Neu5Gc), although the levels of Neu5Gc are low or undetectable in human body fluids and most other human tissues. The lack of Neu5Gc in human tissues has been previously explained by the loss of hydroxylase activity of the human CMP‐N‐acetylneuraminic acid hydroxylase (CMAH) protein caused by a genetic error in the human Cmah gene. We thus wanted to investigate whether the human redundant Cmah gene could still function in stem cell‐specific processes. In this study, we show that CMAH gene expression is significantly upregulated in the adult stem cell populations studied, both of hematopoietic and mesenchymal origin, and identify CMAH as a novel stem cell marker. The CMAH content co‐occurs with higher levels of Neu5Gc within stem cells as measured by mass spectrometric profiling. It seems that despite being enzymatically inactive, human CMAH may upregulate the Neu5Gc content of cells by enhancing Neu5Gc uptake from exogenous sources. Furthermore, exposure to exogenous Neu5Gc caused rapid phosphorylation of β‐catenin in both CMAH overexpressing cells and bone marrow‐derived mesenchymal stem cells, thereby inactivating Wnt/β‐catenin signaling. The data demonstrate the first molecular evidence for xenoantigen Neu5Gc‐induced alteration of crucial stem cell‐specific signaling systems for the maintenance of self renewal. These results add further emphasis to the crucial need for completely xenofree culturing conditions for human stem cells. STEM CELLS 2010;28:258–267

Toll-Like Receptor Gene Polymorphisms Confer Susceptibility to Graft-Versus-Host Disease in Allogenic Hematopoietic Stem Cell Transplantation

Graft‐versus‐host disease (GvHD) is a major complication in hematopoietic stem cell transplantation (HSCT). The immune response against gut microbes is thought to be an important factor in the beginning of GvHD. Toll‐like receptors (TLR) recognize molecular structures of microbes and viruses and play central part in the innate immunity. We studied whether genetic variation in the TLR1, TLR2, TLR4, TLR5, TLR6 and TLR10 genes confers susceptibility to GvHD in 305 human leucocyte antigen‐identical sibling donor HSCTs performed in a single Finnish centre. The results showed that the genetic markers rs4833079 (P = 0.035) in TLR1, rs4837656 (P = 0.032) and rs17582214 (P = 0.029) in TLR4, rs10737416 (P = 0.048) in TLR5, rs6531656 (P = 0.035) in TLR6, and rs337629 (P = 0.005) in TLR10 were associated with the occurrence of acute GvHD. Interestingly, two markers in the TLR5 gene, rs2800230 (P = 0.010) and rs2800237 (P = 0.017), were associated with chronic GvHD. These results indicate that many genes of the TLR system are involved in the overall genetic risk for GvHD and emphasize the role of innate immunity in GvHD.

Isolation of Hematopoietic Stem Cells from Human Cord Blood

Enrichment of hematopoietic stem cells is based on the expression of certain surface antigens, such as CD34 and CD133, or on the lack of expression of lineage-specific antigens. Immunomagnetic positive selection of CD34(+) or CD133(+) cells is performed using paramagnetic microbeads conjugated to specific monoclonal antibodies (anti-human CD34 or anti-human CD133). In negative selection of lineage-negative (Lin(-)) cells, the unwanted cells are labeled with antibodies against known markers for mature hematopoietic cells (CD2, CD3, CD14, CD16, CD19, CD24, CD56, CD66b, and glycophorin A) and retained in the column. Unlabeled cells pass through the column and are collected as the Lin(-) cell fraction. Immunomagnetic cell sorting system MACS is a fast and gentle method to enrich hematopoietic stem cells. Viable and highly pure cells can be separated to be used in various downstream applications, such as flow cytometry and cell culture.

Killer-cell immunoglobulin-like receptor gene profile predicts good molecular response to dasatinib therapy in chronic myeloid leukemia

Tyrosine kinase inhibitors have greatly improved the prognosis of chronic myeloid leukemia (CML). In addition to direct kinase inhibition, their effects can also be mediated through immune modulation, such as expansion of cytotoxic T and natural-killer cells observed during dasatinib therapy. As natural-killer cell and partially CD8(+) T-cell function are regulated by killer immunoglobulin-like receptors (KIRs), we studied whether the KIR gene profile is associated with clinical therapy response in dasatinib-treated CML patients (n = 191). In first-line patients, the absence of the inhibitory KIR2DL5A (p = 0.0489), 2DL5B (p = 0.030), and 2DL5all (p = 0.0272) genes were associated with improved molecular response at the 12-month time point. In addition, the same trend was seen with two activating KIR genes, 2DS1 (p = 0.061) and 2DS2 (p = 0.071). Furthermore, when patients were clustered into two groups by their KIR gene profile, the BCR-ABL1 transcript levels differed significantly between the groups (p = 0.047), showing that patients who lacked several KIR genes had better response. The comparison of first-line and second-line patients did not show any significant differences in either KIR or human leukocyte antigen genotypes. Our results show that immunogenetic factors, such as the KIR gene profile, can play a role in tyrosine kinase inhibitor therapy response. Additional studies are warranted to elucidate the functional significance of KIR genes associated with treatment outcomes.

Characterization of a De Novo Conversion in Human Complement C4 Gene Producing a C4B5-Like Protein

Complement C4 is a highly polymorphic protein essential for the activation of the classical complement pathway. Most of the allelic variation of C4 resides in the C4d region. Four polymorphic amino acid residues specify the isotype and an additional four specify the Rodgers and Chido determinants of the protein. Rare C4 allotypes have been postulated to originate from recombination between highly homologous C4 genes through gene conversions. Here we describe the development of a de novo C4 hybrid protein with allotypic and antigenic diversity resulting from nonhomologous intra or interchromosomal recombination of the maternal chromosomes. A conversion was observed between maternal C4A3a and C4B1b genes producing a functional hybrid gene in one of the children. The codons determining the isotype, Asp1054, Leu1101, Ser1102, Ile1105 and His1106, were characteristic of C4B gene, whereas the polymorphic sites in exon and intron 28 were indicative of C4A3a sequence. The protein produced by this hybrid gene was electrophoretically similar to C4B5 allotype. It also possesses reversed antigenicity being Rodgers 1, 2, 3 and Chido-1, -2, -3, 4, -5, and -6. Our case describes the development of a rare bimodular C4B-C4B haplotype containing a functional de novo C4 hybrid gene arisen through gene conversion from C4A to C4B. Overall the data supports the hypothesis of gene conversions as an ongoing process increasing allelic diversity in the C4 locus.