Limits...
Niche recycling through division-independent egress of hematopoietic stem cells.

Bhattacharya D, Czechowicz A, Ooi AG, Rossi DJ, Bryder D, Weissman IL - J. Exp. Med. (2009)

Bottom Line: Hematopoietic stem cells (HSCs) are thought to reside in discrete niches through stable adhesion, yet previous studies have suggested that host HSCs can be replaced by transplanted donor HSCs, even in the absence of cytoreductive conditioning.Bromodeoxyuridine (BrdU) feeding experiments demonstrated that HSCs in the peripheral blood incorporate BrdU at the same rate as do HSCs in the bone marrow, suggesting that egress from the bone marrow to the blood can occur without cell division and can leave behind vacant HSC niches.These data provide insight as to how HSC replacement can occur despite the residence of endogenous HSCs in niches, and suggest therapeutic interventions that capitalize upon physiological HSC egress.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Stem Cell Biology and Regenerative Medicine Stanford University School of Medicine Stanford, CA 94305, USA. deeptab@wustl.edu

ABSTRACT
Hematopoietic stem cells (HSCs) are thought to reside in discrete niches through stable adhesion, yet previous studies have suggested that host HSCs can be replaced by transplanted donor HSCs, even in the absence of cytoreductive conditioning. To explain this apparent paradox, we calculated, through cell surface phenotyping and transplantation of unfractionated blood, that approximately 1-5% of the total pool of HSCs enters into the circulation each day. Bromodeoxyuridine (BrdU) feeding experiments demonstrated that HSCs in the peripheral blood incorporate BrdU at the same rate as do HSCs in the bone marrow, suggesting that egress from the bone marrow to the blood can occur without cell division and can leave behind vacant HSC niches. Consistent with this, repetitive daily transplantations of small numbers of HSCs administered as new niches became available over the course of 7 d led to significantly higher levels of engraftment than did large, single-bolus transplantations of the same total number of HSCs. These data provide insight as to how HSC replacement can occur despite the residence of endogenous HSCs in niches, and suggest therapeutic interventions that capitalize upon physiological HSC egress.

Show MeSH

Related in: MedlinePlus

Phenotypic HSCs can be identified and purely isolated from peripheral blood. (A) Bone marrow and peripheral blood from 12-wk-old mice were stained with the combination of markers indicated. The plots from the peripheral blood represent pooled events collected from 25 animals, in which ∼50 HSCs were analyzed. Lineage cocktail antibodies were divided into different channels to minimize the chance of contamination of mature cells in the HSC gate. (B) CD27 is expressed on HSCs. KLS IL-7rα− cells from the bone marrow and blood were examined for CD34 and CD27 expression. CD34− cells segregated almost exclusively to the CD27+ population in the bone marrow, and thus the CD27 marker was useful for distinguishing HSCs from background events in the blood. All stains were repeated in eight independent experiments.
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
getmorefigures.php?uid=PMC2806613&req=5

fig2: Phenotypic HSCs can be identified and purely isolated from peripheral blood. (A) Bone marrow and peripheral blood from 12-wk-old mice were stained with the combination of markers indicated. The plots from the peripheral blood represent pooled events collected from 25 animals, in which ∼50 HSCs were analyzed. Lineage cocktail antibodies were divided into different channels to minimize the chance of contamination of mature cells in the HSC gate. (B) CD27 is expressed on HSCs. KLS IL-7rα− cells from the bone marrow and blood were examined for CD34 and CD27 expression. CD34− cells segregated almost exclusively to the CD27+ population in the bone marrow, and thus the CD27 marker was useful for distinguishing HSCs from background events in the blood. All stains were repeated in eight independent experiments.

Mentions: To determine which of these two models most accurately describes the source of HSCs in the peripheral blood, we first determined whether HSCs in the bloodstream are phenotypically and functionally similar to HSCs in the bone marrow. C-kit+ lineage− Sca-1+ (KLS) CD27+ IL-7Rα− CD150+ CD34− cells could be identified by flow cytometry in the blood that appeared to be virtually identical to phenotypic HSCs in the bone marrow (Fig. 2 A). In agreement with some previous studies (Allman et al., 2003), but in contrast to others (Wiesmann et al., 2000), we were unable to identify KLS CD34− cells in the bone marrow that did not express CD27, although it is worth noting that CD34− HSCs express slightly lower relative levels of CD27 than do their CD34+ MPP counterparts (Fig. 2 B). We believe these discrepancies are related to improved antibody conjugates that yield brighter fluorescent signals. This marker thus aided in the specific identification of rare HSCs in the blood and distinguishing these HSCs from background CD27− events (Fig. 2 B). Transplantation of CD27− bone marrow did not lead to multilineage reconstitution beyond 8 wk, confirming that all of the HSC activity is contained within the CD27+ fraction (Fig. S1 A).


Niche recycling through division-independent egress of hematopoietic stem cells.

Bhattacharya D, Czechowicz A, Ooi AG, Rossi DJ, Bryder D, Weissman IL - J. Exp. Med. (2009)

Phenotypic HSCs can be identified and purely isolated from peripheral blood. (A) Bone marrow and peripheral blood from 12-wk-old mice were stained with the combination of markers indicated. The plots from the peripheral blood represent pooled events collected from 25 animals, in which ∼50 HSCs were analyzed. Lineage cocktail antibodies were divided into different channels to minimize the chance of contamination of mature cells in the HSC gate. (B) CD27 is expressed on HSCs. KLS IL-7rα− cells from the bone marrow and blood were examined for CD34 and CD27 expression. CD34− cells segregated almost exclusively to the CD27+ population in the bone marrow, and thus the CD27 marker was useful for distinguishing HSCs from background events in the blood. All stains were repeated in eight independent experiments.
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2806613&req=5

fig2: Phenotypic HSCs can be identified and purely isolated from peripheral blood. (A) Bone marrow and peripheral blood from 12-wk-old mice were stained with the combination of markers indicated. The plots from the peripheral blood represent pooled events collected from 25 animals, in which ∼50 HSCs were analyzed. Lineage cocktail antibodies were divided into different channels to minimize the chance of contamination of mature cells in the HSC gate. (B) CD27 is expressed on HSCs. KLS IL-7rα− cells from the bone marrow and blood were examined for CD34 and CD27 expression. CD34− cells segregated almost exclusively to the CD27+ population in the bone marrow, and thus the CD27 marker was useful for distinguishing HSCs from background events in the blood. All stains were repeated in eight independent experiments.
Mentions: To determine which of these two models most accurately describes the source of HSCs in the peripheral blood, we first determined whether HSCs in the bloodstream are phenotypically and functionally similar to HSCs in the bone marrow. C-kit+ lineage− Sca-1+ (KLS) CD27+ IL-7Rα− CD150+ CD34− cells could be identified by flow cytometry in the blood that appeared to be virtually identical to phenotypic HSCs in the bone marrow (Fig. 2 A). In agreement with some previous studies (Allman et al., 2003), but in contrast to others (Wiesmann et al., 2000), we were unable to identify KLS CD34− cells in the bone marrow that did not express CD27, although it is worth noting that CD34− HSCs express slightly lower relative levels of CD27 than do their CD34+ MPP counterparts (Fig. 2 B). We believe these discrepancies are related to improved antibody conjugates that yield brighter fluorescent signals. This marker thus aided in the specific identification of rare HSCs in the blood and distinguishing these HSCs from background CD27− events (Fig. 2 B). Transplantation of CD27− bone marrow did not lead to multilineage reconstitution beyond 8 wk, confirming that all of the HSC activity is contained within the CD27+ fraction (Fig. S1 A).

Bottom Line: Hematopoietic stem cells (HSCs) are thought to reside in discrete niches through stable adhesion, yet previous studies have suggested that host HSCs can be replaced by transplanted donor HSCs, even in the absence of cytoreductive conditioning.Bromodeoxyuridine (BrdU) feeding experiments demonstrated that HSCs in the peripheral blood incorporate BrdU at the same rate as do HSCs in the bone marrow, suggesting that egress from the bone marrow to the blood can occur without cell division and can leave behind vacant HSC niches.These data provide insight as to how HSC replacement can occur despite the residence of endogenous HSCs in niches, and suggest therapeutic interventions that capitalize upon physiological HSC egress.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Stem Cell Biology and Regenerative Medicine Stanford University School of Medicine Stanford, CA 94305, USA. deeptab@wustl.edu

ABSTRACT
Hematopoietic stem cells (HSCs) are thought to reside in discrete niches through stable adhesion, yet previous studies have suggested that host HSCs can be replaced by transplanted donor HSCs, even in the absence of cytoreductive conditioning. To explain this apparent paradox, we calculated, through cell surface phenotyping and transplantation of unfractionated blood, that approximately 1-5% of the total pool of HSCs enters into the circulation each day. Bromodeoxyuridine (BrdU) feeding experiments demonstrated that HSCs in the peripheral blood incorporate BrdU at the same rate as do HSCs in the bone marrow, suggesting that egress from the bone marrow to the blood can occur without cell division and can leave behind vacant HSC niches. Consistent with this, repetitive daily transplantations of small numbers of HSCs administered as new niches became available over the course of 7 d led to significantly higher levels of engraftment than did large, single-bolus transplantations of the same total number of HSCs. These data provide insight as to how HSC replacement can occur despite the residence of endogenous HSCs in niches, and suggest therapeutic interventions that capitalize upon physiological HSC egress.

Show MeSH
Related in: MedlinePlus