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Recent experimental results in culture and in vivo are summarized that show the existence of developmental relationships between cells that build up blood vessel walls and some previously unrelated tissues and organs. It was formerly demonstrated, in lower vertebrates as well as mammals, including humans, that discrete subsets of blood-forming endothelial cells play a key role in the emergence of the definitive hematopoietic system. We have also documented the existence in human skeletal muscle of endothelium-borne, extremely potent myogenic progenitor cells. Finally, we have characterized and purified perivascular cells – or pericytes – from human tissues and demonstrated their ability to give rise to mesodermal differentiated derivatives, principally skeletal muscle. Keywords: Endothelial cell; pericyte; stem cell; blood vessel; skeletal muscle

Studies performed at RCRM have shown that hematopoietic and immune systems’ reconstitution after irradiation depends greatly on the functional abilities of the stem cells. Subset analysis and expression of CD34+ antigens on bone marrow and peripheral blood cells were studied in Chernobyl accident clean-up workers including patients with leukemia and myelodysplasia and patients exposed to the natural levels of irradiation. In myelodysplasia the elevation of early CD34+ cells was detected in bone marrow and peripheral blood. In leukemia the CD34+117+38- primitive progenitor cell counts were elevated mainly in patients with proliferation of poorly differentiated cells while in ALL’s the CD34+ counts were smaller. Circulating HSC and progenitors after radiation exposure in a wide range of doses have are preserved in a number and with proliferation potencies sufficient for the onset of clonal proliferation. In AML FLT3 mutations are the most abundant single-gene mutations. There is no difference in prevalence of FLT3 mutations in groups of radiation-associated and spontaneous AML cases. LOH/deletions at 5q and/or 7q and 7? tend to be more frequent in radiation-associated AML cases. Bone marrow and bone tissue microenvironment plays a key role in normal and neoplastic HSC changes. Differentiation to B-lineage isn’t changed and is associated with B-cell compartment growth. Keywords: stem cells; radiation; leukemia; Chernobyl

The measurement of telomere length in peripheral blood cells can give an insight into the replicative history of their respective precursor cells, the hematopoietic stem cells (HSC). Much of the observed telomere loss occurs at the stem and progenitor cell level even though these populations express the enzyme telomerase. Investigations in normal steady state hematopoiesis provided the basis for follow up studies in model disorders with increased turnover rates of HSC either due malignant transformation or due to depletion of the stem cell compartment like in defined bone marrow failure syndromes or as a consequence of reduced bone marrow reserve e.g. due to chemotherapy-induced hematological toxicity. In model scenarios like in Chronic myelogeneous leukemia (CML), the degree of telomere shortening can be correlated both with disease duration, disease stage and severity as well as with response to disease-modifying treatment strategies. Whether alterations in telomere biology are secondary phenomena or play a causal role for replicative senescence and/or the induction of genetic instability linked to disease progression in these acquired HSC disorders is under investigation. Keywords: Telomere; Telomerase; stem cell; chronic myeloid leukemia

It is generally accepted that tumor development is a multifactorial process which is caused by a sequential accumulation of different genetic alterations leading to aberrant cell cycle control, instability of genomic integrity as well as decrased recognition by the immune system. During the last decade, the tumor-host interaction has been well defined. It has been demonstrated that professional antigen presenting cells (APC), macrophages, natural killer (NK) cells, NKT cells and in particular T-lymphocytes play a key role in anti-tumor immunity. In general, immune cells monitor MHC class I-presented antigenic peptides. Presentation of self peptides by MHC class I molecules results in the generation of tolerance. In contrast, presentation of viral or tumor-derived foreign antigens leads to the induction of lysis by CD8+ cytotoxic T lymphocytes (CTL). Keywords: tumor immunology, escape mechanisms, MHC class I, CTL, NK

The RUNX1 gene, which encodes a transcription factor, is a common target of genetic mutations in acute leukemia. We propose that RUNX1 is a gatekeeper gene, the disruption of which leads to the exodus of a subset of selfrenewing “stem” cells from the normal environmental controls of homeostasis. This pool of “escaped” cells is the target of secondary mutations, accumulating over time to induce the aggressive manifestation of acute leukemia. Evidence from patient and animal studies support the concept that RUNX1 mutations are the initiating event in different leukemia subtypes, but also suggests that diverse mechanisms are used to subvert RUNX1 function. One common result is the inhibition of differentiation – but its effect impinges on different lineages and stages of differentiation, depending on the mutation. A number of different approaches have led to the identification of a few secondary events that lead to the overt acute phase, however, the majority are unknown. Finally, the concept of the “leukemic stem cell” and its therapeutic importance is discussed in light of the RUNX1 gatekeeper function. Key words: leukemic stem cell, core-binding factor, differentiation, self-renewal

The hybrid cell lines, which we have obtained, can be widely used in veterinary virology and biotechnology for preparing vaccines, test-systems for viruses. Any strains of hybrid cells are producing the biological active proteins (enzymes and others). We have obtained hybrid cell lines (P?-?К?C?, P?- ?К?H?), which are sensitive to prion protein, and also hybrid culture with β-cells of the pancreas of rabbit. Keywords: Stem cells; hybridoma; biotechnology

Institutional achievements in research of low temperature preservation of stem cells derived from fetal and adult sources are presented in the report. Special attention is attended to cryopreservation of pretenders on hemopoietic stem cells from human cord blood and fetal liver. Examining of viability of cryopreserved with DMSO fetal liver cells of specific phenotype by parallel determining with vital dye has demonstrated that CD133+ and CD34+cell candidates occurred to be more sensitive to programmed cryopreservation in comparison with more differentiated erythroid precursors (glycophorin-A – positive cells). No differences in viabilities between CD 45-, CD 133- and CD 34- positive cells after cryopreservation of primary suspension of fetal liver cells was revealed. Cryopreservation of cord blood nucleated cells with PEO-1500 allowed to obtain higher viability of hemopoietic stem CD 34+-cells in respect of CD45+-cells. Presented data demonstrated that hemopoietic cells of human fetal liver and cord blood of various phenotypes were characterized with different sensitivity to cryopreservation. Candidates to stem hemopoietic cells, obtained from two different sources: human fetal liver and cord blood, demonstrate quite a high viability after cryopreservation with various methods using cryoprotectants with different mechanisms of action. Keywords: HSC; cryopreservation; viability

Retroviral vectors are powerful tools for genetic analysis of stem cells and their progenitors. They have been used both as gene vectors, to both up or down regulate gene expression – as well as mutagens, to identify genes modulating a specific phenotype. Furthermore, their importance in the clinic is currently being tested in several on-going gene therapy trials. Understanding the basic biology of retrovirus is tantamount to developing efficacious tools for the laboratory and the clinic. Here we summarize the characterization of a novel γ-retrovirus isolate from feral mice. The M813 isolate was shown to have a unique host range and belong to a novel interference group. Our analysis also revealed the highly fusogenic potential of this virus. Finally, we were able to identify the sodium myo-inositol transporter as its receptor. The unique characteristics of this viral isolate open several venues for the development of novel research tools. Keywords: retroviruses, virus-cell interaction, cellular receptor, myo-inositol transporter, Mus cervicolor

Selectively shaping the T cell repertoire in hemopoietic stem cell transplantation and leukemia immunotherapy towards specific recognition and elimination of malignant and virus-infected cells represents a new therapeutic concept. This concept takes advantage of selectively tolerizing or depleting graft versus host disease (GvHD)-mediating T lymphocytes, while preserving or selecting cytotoxic T cell responses specific for malignant and viral disease. Two specific strategies have been extensively explored in preclinical models for this particular purpose. One strategy is to equip recipient-derived T lymphocytes with “off the shelve” available T cell antigen receptors (TCRs) specific for leukemia-associated as well as human cytomegalovirus (hCMV)- specific antigenic epitopes in order to tackle leukemic relapse and hCMV infection. This strategy is obviously as attractive in immunotherapy of malignant disease by transferring specificity and affinity of TCRs for broadspectrum tumor- and leukemia-associated antigens into T lymphocytes of patients and thus breaking their state of cancer- and leukemia-specific T cell tolerance. Another strategy is to selectively deplete the donor stem cell graft of GvHD-mediating alloreactive T lymphocytes while preserving the integrity of a leukemia- and virus-reactive T cell repertoire within the stem cell inoculum. As these strategies have been successfully developed at the preclinical level, the opportunity of transferring them into clinical application represents a possible current challenge and endeavor. Keywords: Cytotoxic T lymphocytes; T cell antigen receptor; allogeneic hemopoietic stem cell transplantation; acute myeloid leukemia

The given article gives a short overview about the development and the current structure of the bone marrow transplantation center in Kyiv. A summary on HSCT between 2001 and 2005 in relation to underlying diseases is provided. Keywords: allogeneic and autologous HSCT, Kyiv BMT center