Stem cell engraftment and cell cycle phenotype

Abstract

Engraftment of hematopoietic stem cells in nonmyeloablated and minimally myeloablated hostsHematopoiesis is the most thoroughly characterized cell renewal, proliferation and differentiation system in biology. A central dogma is that the system is hierarchical with an orderly progression from stem cell to progenitor cell to differentiated end cell involving a progressive loss of proliferative potential linked to a gain of differentiated characteristics. A second dogma is that myeloablated treatment with radiation or chemotherapy is necessary to 'open space' in order for the transfused stem cells to engraft in marrow. A third dogma is that lymphohematopoietic stem cell is in G 0 or quiescent and that it is difficult to induce this cell to enter cell cycle and divide. These three dogmas appear to be incorrect as developed below.(1) Marrow 'space' needs to be created to allow transplanted stem cells to engraft. (2) The stem cell is quiescent and it is difficult to stimulate it to proliferate. (3) The stem cell phenotype is stable within a differentiation hierarchy. Marrow spaceFollowing on the work of others, 1-3 we have shown that virtually quantitative engraftment occurs when male BALB/c marrow cells are infused into female BALB/c hosts which have received no myeloablative treatment. [4][5][6][7][8] In this model, male cells are tracked by Southern blot or fish using Y-specific probes and the percent of male cells in female marrow, spleen or thymus determined at varying time points after marrow cell infusion. We have shown stable multilineage engraftment out to over 2 years post infusion of 200 million male BALB/c cells into female BALB/c hosts. We have shown that there is a cell dose response and that the engrafting stem cell in this model is quiescent as determined by hydroxyurea suicide. The explanation of these results appears to be based upon stem cell competition. The final engraftment phenotype would appear to be determined solely by the ratio of host to donor stem cells, rather than any treatment 'opening space'. We have extended these results to a minimally myeloablated model in which low doses of irradiation are administered and engraftment evaluated. 9 In this model, 100 cGy whole body irradiation causes mild, albeit significant, depressions of the peripheral blood platelet and white count, which recover over 2 weeks, without significant changes in marrow cellularity. These relatively mild effects are contrasted with the severe inhibition of long-term stem cell engraftment. When male BALB/c marrow cells are exposed to 100 cGy in vitro or in vivo and then evaluated 2 months after engraftment, they lose over 80% of their engrafting ability. Using this model and engrafting 40 million male cells into 100 cGy exposed mice we have shown very high levels of chimerism at times approaching 100% at 2, 5 and 8 months post engraftment. The engrafting cells here are also quiescent. These data further substantiate the hypothesis that the final phenotype after marrow cell engraftment is determined by ratios of host to...

Meeting report on an NHLBI workshop on ex vivo expansion of stem cells, July 29, 1999, Washington, D.C.

“…Decreased migration may underlay the decreased engraftment seen for progenitors cultured ex vivo prior to transplantation. Similar results were seen by Dr. Quesenberry, who showed that changes in cell cycle phase of HSC induced by ex vivo exposure to cy-tokines may in part explain decreased engraftment seen in vivo [9]. He provided further suggestive evidence that changes in adhesion receptor expression (VLA4, VLA5, PECAM, L-selectin) and function (adhesion to stroma) correlate with decreased engraftment [10].…”

Molecular mechanism of transforming growth factor β–mediated cell-cycle modulation in primary human CD34+ progenitors

“…[13][14][15] We sought to determine whether neutralization of TGF-␤, which we have demonstrated in the current studies to enhance cell-cycle progression at the molecular level, had an effect on human Immunocomplexes between cdk4 and cyclin D2 were detected only in the presence of anti-TGF-␤ antibody. After starvation in methionine-free DMEM for 4 hours, CD34 ϩ progenitors were metabolically labeled for 18 hours with 35 Smethionine/cysteine in the presence or absence of soluble TGF-␤1 or anti-TGF-␤ antibody.…”

“…It has been proposed that cycling hematopoietic stem/progenitor cells do not engraft as well as quiescent cells in bone marrow (BM) transplantation settings. [13][14][15] Because TGF-␤ is a major factor in maintaining quiescence in murine and human hematopoietic stem cells, it was possible that TGF-␤ neutralization could have adverse effects in a transplantation setting. Our goal in the current study was to elucidate the molecular pathways by which TGF-␤ alters cell-cycle progression in CD34 ϩ cells as well as the impact of TGF-␤ neutralization on primary human hematopoietic stem/progenitor cell transplantation and differentiation.…”

Aldehyde dehydrogenases are regulators of hematopoietic stem cell numbers and B-cell development

“…In the absence of sufficient ALDH activity, higher levels of ROS and related compounds lead to increased HSC activation as well as a block in G 1 to S-phase transition in order to facilitate DNA check and repair of damage caused by the reactive compounds. This model would also explain the reduced number of transplantable HSCs noted in the CRU assays we conducted as HSCs that have moved out of G 0 have an engraftment defect [27]. If this model is validated in future studies, the ALDHs could join FOXO, AKT, and other important players in cell fate decision processes impacted by the oxidative stress and redox status of HSCs [28].…”