Immature Hematopoietic Stem Cells Research Articles

Effect of Ultraviolet-B Light on Lymphocyte Activity at Doses at Which Normal Bone Marrow Stem Cells Are Preserved

Ultraviolet B (UVB) light is known to be immunosuppressive, but, probably because of a small UVC component in the emission spectra of some of the UVB lamps used, reports vary on effective dose levels. To prevent potentially lethal graft-versus-host disease (GVHD) after allogeneic bone marrow transplantation, alloreactive donor T-cell activity must be suppressed. In this study, a narrow wavelength UVB lamp (TL01, 312 nm peak emission) was used to determine what doses of UVB were required to abolish rat lymphocyte proliferation while simultaneously preserving rat bone marrow progenitor cell and primitive hematopoietic stem cell viability. Lymphocyte proliferation, as measured by 3H-Thymidine incorporation, in response to lectin stimulation was abolished below detection at doses greater than 3,500 J/m2. When T-cell clonogenicity was measured in a limiting dilution assay, a small fraction (0.6%) was maintained at doses up to 4,000 J/m2. Cytotoxic T-lymphocyte (CTL) activity was reduced after treatment with 4,000 J/m2, but a significant level of cytotoxicity was still maintained. Natural killer cell cytolytic activity was not affected by doses up to 4,000 J/m2. At 4,000 J+m2 there was a 10% survival of colony-forming units-granulocyte-macrophage; a 1% and 4% survival of day-8 and day-12 colony-forming units-spleen, respectively; and 11% survival of marrow repopulating ability cells. Up to 25% of late cobblestone area forming cells (4 to 5 weeks), reflecting the more immature hematopoietic stem cells, were preserved in bone marrow treated with 4,000 J/m2, indicating that early stem cells are less sensitive to UVB damage than are more committed progenitor cells. Thus, a potential therapeutic window was established at approximately 4,000 J/m2 using this light source, whereby the potentially GVHD-inducing T cells were suppressed, but a sufficient proportion of the cells responsible for engraftment was maintained.

Umbilical cord blood as a rich source of immature hematopoietic stem cells

To investigate immaturity of hematopoietic progenitor cells in umbilical cord blood mononuclear cells (CB-MNC), the formation of macroscopic colonies and mixed-cell colonies was assayed by methylcellulose culture with various combinations of cytokines (stem cell factor [SCF], interleukin [IL]-3, IL-6, granulocyte-colony stimulating factor [G-CSF], erythropoietin [EPO]) and compared with bone marrow (BM)-MNC. Moreover, distribution of the subpopulations divided by CD34, CD38, HLA-DR and CD33 was compared by flow-cytometry. Colonies derived from CB-MNC were so large that they could be observed with the naked eye and consisted of a variety of types of hematopoietic cells. Mixed-cell colonies were formed to a much greater extent in CB-MNC than in BM-MNC. Addition of EPO, IL-3, and SCF had rapid effects on the growth of mixed-cell colonies. The subpopulations of immature hematopoietic progenitor cells (CD34+, CD38-, HLA-DR-), which are supposed to be able to differentiate into hematopoietic precursors and stromal cells, were significantly higher in CB-MNC (8.7 +/- 6.6%) than in BM-MNC (0.0 +/- 0.1%; P < 0.001). These results suggest that CB is a rich source of immature hematopoietic progenitor cells compared to BM.

Differing Stem Cell Self-Renewal of Lectin-Separated Murine Bone Marrow Fractions&lt;xref ref-type="fn" rid="fn2"&gt;2&lt;/xref&gt;&lt;xref ref-type="fn" rid="fn3"&gt;3&lt;/xref&gt;

The success of bone marrow transplantation depends not only on the engraftment of adequate numbers of hematopoietic stem cells but also on their self-renewal capacity, which must be sufficient to provide lifetime hematopoiesis. The lectin peanut agglutinin (PNA), when exposed to bone marrow, causes separation into two distinct fractions. The agglutinated fraction not only is enriched with colony-forming units--spleen but also is devoid of graft-versus-host (GVH) activity when injected into allogeneic lethally irradiated recipients, and therefore, it is considered to be an ideal source for bone marrow transplantation. The absence of GVH activity is presumably due to the separation of mature thymocytes into the nonagglutinated fraction and functionally immature thymocytes into the agglutinated fraction. Although there has been speculation that immature hematopoietic stem cells also selectively bind to PNA, other evidence suggests that the relationship of lectin binding specificity to level of maturity varies in different tissues. This study was performed to assess the self-renewal capacity of lectin-separated bone marrow stem cells. Results indicate that the self-renewal of the agglutinated fraction is significantly lower than that of the unfractionated bone marrow; such self-renewal of the nonagglutinated fraction is higher. This is further evidence for the heterogeneity of the stem cell pool. Stem cell enrichment should not be the goal in bone marrow transplantation; rather, the goal should be utilization of stem cells with the greatest self-renewal potential.