Phenotypic and functional analysis of T-cell precursors in the human fetal liver and thymus: CD7 expression in the early stages of T- and myeloid-cell development

It has been proposed that the CD7 molecule is the first antigen expressed on the membrane of cells committed to the T-cell lineage during human fetal T-cell ontogeny. To further identify the pre-T cell subpopulation that migrates to the thymus early in ontogeny, we analyzed the phenotypic and functional characteristics of the fetal liver populations separated on the basis of CD7 expression. Three populations expressing different levels of CD7 were observed: CD7bright, CD7dull, and CD7-. A CD7bright population depleted of mature T, B, and myeloid cells (lineage negative, lin-) and mostly composed of CD56+ CD34- natural killer cells did not mature into T cells in a fetal thymic organ culture (FTOC) assay and was devoid of myeloid progenitors in a clonal colony-forming cell assay. In contrast, the CD7-/dull CD34+ lin- populations were capable of differentiating into phenotypically mature T cells after injection into FTOC and contained early myeloid progenitors. Here we phenotypically compared the fetal liver CD7 populations with the most immature fetal thymic subset that differentiated in the FTOC assay, namely the triple negative (TN, CD3-CD4-CD8-) thymocytes. Fetal TN lin- expressed high levels of CD34 marker and were further subdivided by their expression of CD1 antigen, because CD1- TN thymocytes express higher levels of CD34 antigen compared with CD1+ TN cells. CD1- lin -TN thymocytes are characterized by expressing high levels of CD2, CD7, and CD34 markers and dull levels of CD5, CD10, and CD28 molecules. We could not find fetal liver pre-T cells with a phenotype equivalent to that of TN thymocytes. Our data show that CD7 does not necessarily identify T-cell precursors during fetal T-cell development and strongly support the hypothesis that the acquisition of early T-cell markers as CD2, CD28, and CD5 molecules on the cell surface of T-cell progenitors takes place intrathymically.

Bone marrow transplantation with interleukin-1 plus kit-ligand ex vivo expanded bone marrow accelerates hematopoietic reconstitution in mice without the loss of stem cell lineage and proliferative potential

Cytokine combinations were tested for their ability to expand murine bone marrow (BM) progenitors in short-term suspension cultures (delta-cultures) with the aim of providing an enriched source of progenitors for BM transplantation (BMT). In a comparison of the efficacy of the combinations interleukin-1 (IL-1) + IL-3, IL-1 + kit-ligand (KL), and IL-1 + IL-6 + KL, BMT with IL-1 + KL expanded progenitors was found to be most effective in accelerating the recovery of peripheral blood leukocytes, platelets, and erythrocytes in lethally irradiated mice. The ex vivo expansion of BM in IL-1 + KL-stimulated delta-cultures also greatly reduced the number of transplanted cells needed to provide radioprotection. All mice survived at least 30 days when receiving 5 x 10(3) delta-cultured d1 5-fluorouracil (5-FU) BM cells (BM cells harvested 1 day after 5-FU administration), whereas complete survival of mice receiving fresh d1 5-FU BM required BMT with a 200-fold greater number of cells. BMT with expanded BM lead to predominantly donor-derived hematopoietic reconstitution for 280 days postprimary BMT and another 71 days after secondary BMT. The expansion of BM did not adversely effect the proliferative capacity and lineage potential of the stem cell compartment.

Development of a lacZ marked WEHI-3B D+ murine leukemic cell line as an in-vivo model of acute non-lymphocytic leukemia

Established leukemic cell lines have been useful models for studying the biology of leukemia. Analysis of the actions of differentiating agents on leukemic cell lines in vivo has been limited by an inability to unambiguously distinguish host hematopoietic elements from differentiated leukemic cells. In order to identify and quantify leukemic cells during in vivo studies, a derivative of the murine myelomonocytic leukemia cell line WEHI-3B D+, which stably expresses beta-galactosidase, was constructed utilizing retroviral vector gene transfer. This cell line, termed WEHI-3B D+/lacZ 2.8, demonstrated in vitro growth and differentiation properties similar to the parental cell line. WEHI-3B D+/lacZ 2.8 expressed high levels of beta-galactosidase following prolonged in vitro growth and following differentiation in suspension cultures and clonogenic assays. In vivo, WEHI-3B D+/lacZ 2.8 was leukemogenic and high level expression of beta-galactosidase was maintained. Quantification of tissue involvement with WEHI-3B D+/lacZ 2.8 leukemia was performed utilizing staining with the fluorogenic beta-galactosidase substrate fluorescein di-beta-galactoside and fluorescence-activated cell sorting analysis. In vivo differentiation efficiency following granulocyte colony-stimulating factor (G-CSF) administration was determined using a simultaneous nuclear and cytoplasmic staining procedure. Results indicate that treatment of mice inoculated with WEHI-3B D+/lacZ 2.8 cells with G-CSF administration causes detectable but limited differentiation.

Ex vivo differentiation therapy as a method of leukemic cell purging in murine bone marrow expansion cultures

We investigated the use of differentiation therapy as a method of purging bone marrow (BM) of leukemic cells in ex vivo murine BM expansion cultures (delta-cultures). In clonal cultures and in suspension cultures a combination of the differentiation-inducing agents granulocyte colony-stimulating factor (G-CSF), interleukin (IL)-6, and all-trans-retinoic acid (ATRA) was found to be most effective in inducing the differentiation of the murine myelomonocytic leukemic cell line WEHI 3B D+ LacZ clone 2.8 (clone 2.8). Furthermore, we investigated the activity of a mutant form of IL-6, mutein, and found it to have a greater specific activity in cell proliferation assays and in a clone 2.8 differentiation assay than the native form of IL-6. Coculture of clone 2.8 and BM in IL-1 and kit-ligand-stimulated delta-cultures showed that the added stimuli, G-CSF, mutein, and ATRA, decreased the expansion of leukemic cells. Mice transplanted with G-CSF, mutein, and ATRA-purged BM had an increased survival time relative to nonpurged controls. The addition of G-CSF, mutein, and ATRA to delta-cultures did not result in any impairment of hematopoietic stem cells when measured 5 wk after transplantation.

The in vitro growth of murine high proliferative potential-colony forming cells is not enhanced by growth in a low oxygen atmosphere

The growth of primitive murine hematopoietic progenitors, high proliferative potential colony-forming cells (HPP-CFC), has been reported to be improved in low O2 tension cultures. In this report we investigated the growth of HPP-CFC stimulated by combinations of interleukin (IL)-1, IL-6, kit-ligand (KL), granulocyte (G) colony-stimulating factor (CSF), macrophage-CSF (M-CSF), granulocyte-macrophage-CSF (GM-CSF) and IL-3 in clonal cultures incubated at 7% or 21% O2 tension. Neither the numbers of HPP-CFC colonies nor the number of cells per HPP-CFC colony differed significantly between cultures grown under 7% or 21% O2 tension. The mean number of cells per HPP-CFC colony was found to range from 3.9 x 10(4) to 2.2 x 10(5). The smallest HPP-CFC colonies were stimulated by the cytokine combination IL-1 + IL-6 + KL, whereas the largest colonies were stimulated by a combination of all seven cytokines tested. The growth of erythroid colonies from murine or human bone marrow did, however, show some enhancement when cultured at a lower O2 tension. These results demonstrate that the growth of murine HPP-CFC was not compromised when cultured at ambient O2 concentration.

Accelerated recovery of peripheral blood cell counts in mice transplanted with in vitro cytokine-expanded hematopoietic progenitors

Interleukin 1 (IL-1) and interleukin 3 (IL-3) act synergistically in stimulating the growth of primitive hematopoietic progenitors. Murine bone marrow (BM) harvested 24 h after 5-fluorouracil (5-FU) administration (d1 5-FU BM) was stimulated with IL-1 and IL-3 to expand its progenitor pool during 7 days of suspension culture (delta-culture), and this in vitro expanded BM was compared to fresh d1 5-FU BM in its ability to reconstitute lethally irradiated or high-dose 5-FU-treated hosts. Transplantation with expanded delta-culture BM was found to dramatically shorten the period of cytopenia following lethal irradiation as compared to animals receiving d1 5-FU BM. Recipients of delta-cultured BM demonstrated accelerated recoveries of peripheral blood leukocytes, neutrophils, platelets, and erythrocytes. Furthermore, expansion of BM in vitro reduced the number of BM cells required for engraftment following lethal irradiation. Treatment of lethally irradiated mice with IL-1 and granulocyte colony-stimulating factor (G-CSF) following transplantation with delta-cultured BM or d1 5-FU BM further improved the recovery of neutrophils in these hosts. In conjunction with G-CSF post-transplantation cytokine therapy, high-dose 5-FU-treated mice transplanted with delta-cultured BM also demonstrated improved recovery kinetics of neutrophils and erythrocytes. Five and 10 weeks after BM transplantation, a decrease in the proliferative capacity of the earliest hematopoietic progenitors, detected in assays of primary and delta-culture generated-secondary high proliferative potential colony-forming cells (HPP-CFC), was found in all transplanted mice following a chemotherapy challenge with 5-FU. However, this impairment in the early progenitor/stem cell pool was not noticeably worsened by the expansion of BM in delta-cultures. The decrease in host hematopoietic proliferative potential associated with transplantation of limiting numbers of BM cells was not reversed over the 10 weeks of this study. The expansion of BM progenitor cells without loss of long-term proliferative potential may be of clinical importance in the fields of BM transplantation and gene therapy.

Interactions among colony-stimulating factors, IL-1 beta, IL-6, and kit-ligand in the regulation of primitive murine hematopoietic cells

We have investigated the regulation of primitive murine hematopoietic progenitors by the cytokines interleukin 1 (IL-1), interleukin 6 (IL-6), and kit-ligand (KL). Individually these cytokines have a limited ability to stimulate the growth of high proliferative potential colony-forming cells (HPP-CFC) from 5-fluorouracil (5-FU)-purged bone marrow, but in combination these cytokines demonstrate synergism in promoting the growth of HPP-CFC. Furthermore, IL-1, IL-6, and KL, alone or in combination, synergized with the colony-stimulating factors (CSFs) granulocyte CSF (G-CSF), macrophage CSF (M-CSF), granulocyte-macrophage CSF (GM-CSF), or interleukin 3 (IL-3) in clonal and liquid cultures of 5-FU-purged bone marrow. The pattern of HPP-CFC growth that was observed with 40 different cytokine combinations demonstrated the unique roles of IL-1, IL-6, and KL in the regulation of HPP-CFC proliferation. Short-term liquid cultures (delta-cultures), with secondary recloning, of 5-FU-purged bone marrow were stimulated to greatly expand the numbers of progenitor cells generated in response to cytokine stimulation. The greatest expansion, over 1800-fold, of the more mature progenitor compartments took place in delta-cultures stimulated with IL-1, IL-6, and KL plus IL-3. However, the combination of IL-1 and IL-6 plus KL was optimal in expanding HPP-CFC, increasing their numbers by 700-fold. The ability to expand early progenitor cells in delta-cultures was further demonstrated by the greater than 100-fold expansions of day-12 spleen colony-forming units (CFU-S) by the synergistic interactions of IL-1 with IL-3 or KL.

Purification and partial characterization of a human hematopoietic precursor population

This study reports the development of an assay, the Pre-colony-forming unit (CFU) assay, which detects human hematopoietic precursors. The Pre-CFU assay is based on the observation that precursors to CFU-granulocyte-macrophage (CFU-GM) that are undetectable in clonogenic assays differentiate into CFU-GM preferentially following treatment in suspension culture with recombinant human interleukin-1 alpha (rhIL-1 alpha) combined with rhIL-3. Using the Pre-CFU assay, hematopoietic precursors were detected in human bone marrow depleted of CFU-GM progenitors and differentiated hematopoietic elements via 4-hydroperoxycyclophosphamide treatment coupled with selection for CD34+ cells (4-HCresistant/CD34+ marrow). Additionally, the Pre-CFU assay detected recovery of hematopoiesis substantially earlier than the CFU-GM assay in primates following myeloablation with 5-fluorouracil. The Pre-CFU assay was used to asses purification of a phenotypically defined hematopoietic precursor population, the lin-CD34+ population. The lin-CD34+ population lacks detectable surface markers for T-cell, B-cell, natural killer cell, and myeloid lineage, possesses the CD34 antigen, is devoid of CFU-GM progenitors, and yields Pre-CFU assay values comparable with 4-HCresistant/CD34+ marrow. Using a combination of phenotypic analysis and Pre-CFU assay analysis, the action of rhIL-1 alpha plus rhIL-3 treatment on lin-CD34+ cells was further characterized. The data indicate that rhIL-1 alpha plus rhIL-3 treatment induces proliferation and differentiation of early hematopoietic precursors into progenitors and terminally differentiated cells, without inducing a significant expansion of the precursor population itself.

Radioprotection by murine and human tumor-necrosis factor: dose-dependent effects on hematopoiesis in the mouse

Tumor-necrosis factor (TNF) has been shown to confer significant radioprotection in murine models. Herein, we demonstrate a dose-dependent enhancement of hematological recovery when single doses of either murine or human recombinant TNF are administered prior to irradiation. In addition to its action upon leukocytes and erythrocytes, TNF also alleviates radiation-induced thrombocytopenia in the mouse. These effects on circulating blood constituents are further reflected in increased numbers of both primitive (CFU-S) and more differentiated (CFU-GM, CFU-Mega) hematopoietic progenitors in TNF-treated animals. This suggests that TNF exerts it radioprotective effects on a pool of primitive multi-potential hematopoietic cells.