Evidence for the maintenance of hematopoiesis in a large animal by the sequential activation of stem-cell clones.

Abstract

To test if hematopoiesis can be maintained by the sequential activation of stem-cell clones, we performed autologous marrow transplantations with limited numbers of cells in cats heterozygous for the X chromosome-linked enzyme glucose-6-phosphate dehydrogenase (G6PD) and observed the G6PD phenotypes of erythroid and granulocyte/macrophage progenitors over time. The animals were the female offspring of Geoffroy male and domestic female cats. In repeated studies of marrow from control animals (n = 5) or experimental animals prior to transplantation (n = 3), the percent of progenitors with domestic-type G6PD did not vary. After transplantation, the peripheral blood counts, marrow morphologies, frequencies of progenitors, and progenitor cell cycle kinetics returned to normal. However, abrupt and significant fluctuations were seen in the G6PD type of progenitors from each cat during the 1-1.5 years of observation. These data cannot be explained if there were either a large or constant population ofactive stem cells and thus imply, in a large-animal system, that hematopoiesis was maintained through clonal succession. A stochastic model was developed to estimate the numbers of active clones and their mean lifetimes.Two theories describe early hematopoietic stem-cell differentiation. The first states that stem cells may contribute indefinitely to hematopoiesis. The second theory, the theory of clonal succession, initially proposed by Kay (1), states that hematopoiesis is maintained by a subset of active stem cells and a dormant reserve. As clones are depleted, perhaps through terminal differentiation, reserve cells become active. These theories have been difficult to test experimentally and transplantation studies in mice with enzymatically or retrovirally marked cells present evidence both for (2-5) or against (6-8) clonal succession. Many murine experiments are limited by difficulties obtaining samples for repeated analysis over time. Also, when the infection of marrow cells with retroviral vectors is used to mark clonal origin, it is difficult to distinguish the contribution of the earliest stem cells from that of cells with a more restricted proliferative potential. In addition, the growth characteristics of a stem cell may change during in vitro incubation (9). For these reasons and to extend the observations to a large-animal system, we studied cats heterozygous for isotypes of the X chromosome-linked enzyme glucose-6-phosphate dehydrogenase (G6PD).Geoffroy cats (Leopardus geoffroyi, South American origin) and domestic cats (Felis catus, Euroasian origin) have evolved independently for 12 million years (10) and have electrophoretically distinct G6PD types (11). These animals were bred to produce female F1 (Safari) cats that were obligate G6PD heterozygotes. In previous studies, we demonstrated that individual colonies derived from erythroid progenitors (burst-forming units-erythroid; BFU-E) or granulocyte/macrophage progenitors (colony-forming unitsgranulocyte/macrophage, CFU-GM) contained domestictype G6P...

Polyclonal hematopoiesis maintained in patients with bone marrow failure harboring a minor population of paroxysmal nocturnal hemoglobinuria–type cells

“…7 The difference in the incidence of clonality between PNH ϩ and PNH Ϫ patients could be attributable to differences in the severity of BM failure or in the disease duration; more severe or prolonged depletion of stem cells due to extrinsic factors may lead to a higher incidence of clonal dominance in PNH Ϫ than in PNH ϩ patients. [20][21][22] However, these mechanisms are unlikely because the hematologic parameters such as leukocyte counts and disease duration did not significantly differ between PNH ϩ and PNH Ϫ patients. Our previous study 7 showed that the response to CyA therapy was significantly lower by PNH Ϫ than PNH ϩ RA patients.…”

“…Several studies have emphasized the importance of longitudinal analysis when clonality is assessed because XCIP of granulocytes can vary from time to time 20 and may be affected by IST. 12 However, a recent study of elderly individuals presents evidence against such variance of XCIP over time.…”

“…[12][13][14][15][16] If a PNH Ϫ AA or RA patient has a pathophysiology similar to that of RA with excess of blasts (RAEB) or will tend to evolve into RAEB or AML, complete or partial clonal granulopoiesis should be detected by recognizing skewed inactivation of the human androgen receptor (HUMARA) gene. [17][18][19] Whereas clonal hematopoiesis is considered to reflect not only the presence of defective stem cells, but also hematopoietic stem cell depletion, [20][21][22] it has predicted evolution to RAEB or AML in some AA patients. 23,24 If an increase of PNH-type cells in patients with AA or RA represents a benign type of BM failure, then clonal granulopoiesis may be less frequent in PNH ϩ than in PNH Ϫ patients.…”

Compartmentalized organization: a common and required feature of stem cell niches?

“…For example, in long-lived large animals, the activation of HSC clones is successive and stochastic (Abkowitz et al, 1990). In addition, HSCs in G0 possess much higher long-term engraftment ability, indicating that phenotypically similar stem cells can differ in their function depending on the exact time-point when they are assayed (Fleming et al, 1993;Passegue et al, 2005).…”

Hematopoiesis and its disorders: a systems biology approach

“…on April 27, 2019. by guest www.bloodjournal.org From feline, and nonhuman primate models of early hematopoiesis. 38,[47][48][49][50][51][52][53] In this approach, telomere shortening is used as a cellular clock to measure the rate at which hematopoietic stem cells divide. 51 This group's results suggest that the number of hematopoietic stem cells across different mammalian species is approximately evolutionarily conserved, a claim that has implications for our current understanding of human hematopoietic stem cell concentrations.…”