Differentiation of natural killer (NK) cells from human primitive marrow progenitors in a stroma-based long-term culture system: identification of a CD34+7+ NK progenitor

We have recently described a marrow stroma-dependent long-term culture system that supports differentiation of CD34+ human marrow primitive progenitors into natural killer (NK) cells. We postulate that CD7 expression may be an early event in commitment of hematopoietic progenitors to the NK lineage. Here we compare the characteristics of CD34+7- and CD34+7+ marrow cells cultivated in the stroma-based NK culture system. These CD34+ populations were further compared with a marrow derived, more committed, CD34-7+ progenitor to emphasize the continuum of NK development and to highlight differences between progenitors in our assays. No progenitor proliferated when plated in media without stroma, underscoring the importance of stroma in NK differentiation. Plating progenitor populations in interleukin-2 containing media directly on preestablished, allogeneic, irradiated marrow stroma for 5 weeks resulted in CD56+CD3- NK cells; however, characteristics of the cultured populations differed. Fold expansion and cloning efficiency of the CD34+7+ population, determined by a functional limiting dilution assay was significantly higher than of the CD34+7- or CD34+7+ populations. This suggests that the CD34+7+ population is highly enriched for an NK progenitor and a possible intermediate in NK lineage differentiation. Further dividing the CD34+7+ population by the relative fluorescence of CD7 into CD34+7+dim and CD34+7+bright populations showed that the CD34+7+bright population exhibited a significantly higher cloning frequency than parallel experiments with CD34+7+dim cells (11.8% +/- 2.4% v 2.4% +/- 0.7%, n = 6; P = .005). Plating of the more primitive CD34+7- population in a transwell system (which separates progenitors from stroma by a microporous membrane) prevents differentiation into NK cells. In contrast, plating of CD34+7+ progenitors in transwells resulted in generation of NK cells. These data suggest that primitive, but not more mature NK progenitors may require direct contact with stroma for the initial differentiation steps. Finally, differentiation of the NK progenitors in this stroma-dependent model results in expression of CD2 not present on any of the starting populations. This observation suggests that marrow stroma can stimulate CD2 expression on NK progenitors in a previously undescribed fashion that may be analogous to the thymic effect on CD2 expression in immature T lymphocytes. These observations identify early steps in the commitment of primitive marrow CD34+ hematopoietic progenitors to a lymphoid lineage and underscore the importance of coexpression of CD7 with CD34 as an early lymphoid commitment characteristic and direct progenitor-stroma interactions in this process.     

Thymic stromal cells support differentiation of natural killer cells from CD34+ bone marrow cells in vitro

Abstract: Natural killer (NK) cells are CD3^? CD56⁺ lymphocytes characterized by exhibiting non-MHC restricted cytotoxicity. A developmental relationship between NK cells and T lymphocytes has been proposed, and, moreover, the thymus has been shown to contain NK cell precursors. In this study we utilized an in vitro assay, devised to study T-lymphocyte development from bone marrow progenitors, to investigate the ability of thymic stromal cells to support generation of NK cells from CD34⁺ bone marrow cells. CD34⁺ cells purified from healthy adults were seeded on adherent thymic stromal cells. The cells emerging after culture were phenotypically characterized by flow cytometry. We show that lymphocytes expressing the phenotypical characteristics of NK cells were generated from CD34⁺ bone marrow cells, and that these cells represented 1% of the cells recovered from the cultures. Furthermore, this was accomplished without supplement of exogenous interleukin 2 which is required for NK cell differentiation in bone marrow cultures.     

Characterization of natural killer cells cultured from human bone marrow cells

Human bone marrow (BM) cells, depleted of nylon wool-adherent cells, T cells, and natural killer (NK) cells, were cultured in medium containing recombinant interleukin 2 (rIL2). After 21 or 24 days in culture, numerous lymphoid cells with multiple azurophilic granules and a morphology similar to large granular lymphocytes (LGL) were found. Two-color analysis of surface phenotype showed many of these cells to be NKH1-positive and a limited number of cells had other NK markers such as CD16, CD2, or CD8. The CD3 antigen was not coexpressed with NKH1. The cultured BM cells were cytotoxic for K562, Daudi, and Raji cell lines. The NKH1+, CD2-, CD3-, CD16- cells were sorted and, in addition to having the LGL morphology, were found to be cytotoxic for K562 cells (NK [K562]). The generation of NK(K562) activity was significantly suppressed by 5-bromodeoxyuridine plus ultraviolet light treatment, indicating that DNA synthesis is required. These experiments suggest that the described culture conditions allow differentiation of progenitor cells, into immature, but functionally active, NK cells.     

Enrichment of interleukin-2-responsive natural killer progenitors in human bone marrow

Natural killer (NK) cells can be cultured in interleukin-2 (IL-2)- containing medium from selected human bone marrow (BM) cells obtained after the elimination of mature T and NK cells. To isolate and characterize IL-2-responsive NK progenitors in the selected BM cells, we investigated the expression of IL-2 receptors (IL-2R) on these cells. Neither CD25 (IL-2R alpha) nor IL-2R beta antigen was observed on the selected BM cells before culture. However, CD25+ cells without detectable levels of IL-2R beta antigen appeared 24 hours after culture in IL-2-containing medium. Cells were sorted from each fraction of the selected BM cells 24 hours after culture after staining with anti-CD33, anti-CD34, and anti-CD25 monoclonal antibodies. The generation of NK cells (CD3- CD56+ cells) and NK activity were observed only from the CD33-/CD34-/CD25+ cell fraction after culture in IL-2-containing medium. The frequency of IL-2-responsive NK progenitors relative to the fraction was 1/231 (95% confidence range, 1/156 to 1/289), which corresponded to the frequency relative to the total number of selected BM cells when the frequency relative to the CD33-/CD34-/CD25+ cell- fraction was converted according to the percentage of these cells in the total number of selected BM cells. These results indicated that IL- 2-responsive NK progenitors were enriched in the CD33-/CD34-/CD25+ cell fraction.     

Functional differences between CD38- and DR- subfractions of CD34+ bone marrow cells

Several studies have previously demonstrated enrichment in primitive progenitor cells in subfractions of CD34+ bone marrow (BM) cells not expressing CD38 or HLA-DR (DR) antigens. However, no studies have directly compared these two cell populations with regard to their content of primitive and more committed progenitor cells. Flow cytometric analysis of immunomagnetic isolated CD34+ cells demonstrated little overlap between CD34+CD38- and CD34+DR- progenitor subpopulations in that only 12% to 14% of total CD34+DR- and CD34+CD38- cells were double negative (CD34+CD38-DR-). Although the number of committed myeloid progenitor cells (colony-forming units granulocyte- macrophage) was reduced in both subpopulations, only CD34+CD38- cells were significantly depleted in committed erythroid progenitor cells (burst-forming units-erythroid). In single-cell assay, CD34+CD38- cells showed consistently poorer response to single as opposed to multiple hematopoietic growth factors as compared with unfractionated CD34+ cells, indicating that the CD34+CD38- subset is relatively enriched in primitive hematopoietic progenitor cells. Furthermore, CD34+CD38- and CD34+DR- cells, respectively, formed 3.2-fold and 1.6-fold more high proliferative potential colony-forming cell (HPP-CFC) colonies than did unfractionated CD34+ cells. Finally, CD34+CD38-DR- cells were depleted in HPP-CFCs as compared with CD34+CD38+DR+ cells. The results of the present study suggest that both the CD38- and DR- subfractions of CD34+ bone marrow cells are enriched in primitive hematopoietic progenitor cells, with the CD34+CD38- subpopulation being more highly enriched than CD34+DR- cells.     

Human mesenchymal stem cells promote human osteoclast differentiation from CD34+ bone marrow hematopoietic progenitors.

Interactions between osteoclast progenitors and stromal cells derived from mesenchymal stem cells (MSCs) within the bone marrow are important for osteoclast differentiation. In vitro models of osteoclastogenesis are well established in animal species; however, such assays do not necessarily reflect human osteoclastogenesis. We sought to establish a reproducible coculture model of human osteoclastogenesis using highly purified human marrow-derived MSCs (hMSCs) and CD34+ hematopoietic stem cells (HSCs). After 3 weeks, coculture of hMSCs and HSCs resulted in an increase in hematopoietic cell number with formation of multinucleated osteoclast-like cells (Ocls). Coculture of hMSCs with HSCs, transduced with a retroviral vector that expresses enhanced green fluorescent protein, produced enhanced green fluorescent protein+ Ocls, further demonstrating that Ocls arise from HSCs. These Ocls express calcitonin and vitronectin receptors and tartrate-resistant acid phosphatase and possess the ability to resorb bone. Ocl formation in this assay is cell contact dependent and is independent of added exogenous factors. Conditioned medium from the coculture contained high levels of interleukin (IL)-6, IL-11, leukemia inhibitory factor (LIF), and macrophage-colony stimulating factor. IL-6 and LIF were present at low levels in cultures of hMSCs but undetectable in cultures of HSCs alone. These data suggest that coculture with HSCs induce hMSCs to secrete cytokines involved in Ocl formation. Addition of neutralizing anti-IL-6, IL-11, LIF, or macrophage-colony stimulating factor antibodies to the coculture inhibited Ocl formation. hMSCs seem to support Ocl formation as undifferentiated progenitor cells, because treatment of hMSCs with dexamethasone, ascorbic acid, and beta-glycerophosphate (to induce osteogenic differentiation) actually inhibited osteoclastogenesis in this coculture model. In conclusion, we have developed a simple and reproducible assay using culture-expanded hMSCs and purified HSCs with which to study the mechanisms of human osteoclastogenesis.     

Generation of human natural killer cells from immature progenitors does not require marrow stromal cells

Human natural killer (NK) cells comprise 10% to 15% of peripheral blood mononuclear cells and have an important role in immune responses against tumors, viral infections, and graft rejection. NK cells originate in bone marrow (BM), but their progenitors and lineage development have not been completely characterized. We studied the generation of NK cells from purified CD34+HLADR- and CD34+HLADR+ BM progenitors and the influence of various cytokines on their production. We show that CD3-CD56+ cytotoxic NK cells can develop from both progenitors populations when interleukin-2 (IL-2) is present in an in vitro suspension culture system containing IL-1 alpha and stem cell factor. Up to 83.8% and 98.6% CD3-CD56+ cells were detected in CD34+HLADR- and CD34+DR+ cultures, respectively, after 5 weeks of culture; significant numbers of NK cells were first detected after 2 weeks. Cytotoxic activity paralleled NK cell numbers; up to 70% specific lysis at an effector:target ratio of 10:1 was observed at 5 weeks. IL-7 also triggered development of CD3-CD56+ cells from these immature progenitors (up to 24% and 55% appeared in CD34+HLADR- and CD34+HLADR+ cultures, respectively). Our data suggest that BM stromas are not necessary for NK cell development and that IL-2 remains essential for this lineage development and differentiation.     

CD34+/CD105+ cells are enriched in primitive circulating progenitors residing in the G0 phase of the cell cycle and contain all bone marrow and cord blood CD34+/CD38low/- precursors

A subset of circulating CD34+ cells was found to express CD105 antigen. Sorting experiments showed that most granulocyte-macrophage colony-forming units (GM-CFU) and burst-forming units - erythroid (BFU-E) were retained in the CD34+/CD105- fraction, whereas rare GM-CFU/BFU-E were generated from CD34+/CD105+ cells. Megakaryocytic aggregates were entirely retained in the CD34+/CD105+ fraction. Neutralizing doses of an anti-TGF-beta1 antibody demonstrated CD34+/CD105+ cells capable of colony-forming activity without any significant effect on CD34+/CD105- cells. Cloning of secondary colonies revealed that CD34+/CD105+ cells had a significantly higher secondary cloning efficiency than CD34+/CD105- cells. CD34+/CD105+ cells had a significantly higher long-term culture-initiating cell (LTC-IC) frequency than CD34+/CD105- cells. Kinetic analysis showed that 75% of CD34+/CD105+ cells consisted of DNA 2n G0Ki-67- cells whereas 82% of CD34+/CD105- were DNA 2n G1Ki-67+ cells, and this latter subset showed a RNA content consistently higher than CD34+/CD105+ cells. CD34+/CD105+ progenitors were CD25+, whereas CD34+/CD105- contained a small CD25+ subset. Three-colour analysis of bone marrow and cord blood CD34+ cells demonstrated that all the CD34+/CD38low/- primitive precursors were contained in CD34+/CD105+ cells. Extensive characterization of these CD105+ precursors indicated that they have biological properties associated with primitive haematopoietic precursors.     

Adherent lymphokine-activated killer cells suppress autologous human normal bone marrow progenitors

We have generated a homogeneous population of recombinant interleukin-2 (rIL-2)-stimulated effector cells termed adherent lymphokine-activated killer cells (A-LAK) from peripheral blood mononuclear cells (PBMNC) of 14 normal individuals and tested the effect of A-LAK cells on autologous hematopoietic bone marrow (BM) progenitor growth. Enrichment of A-LAK from PBMNC depended on the propensity of A-LAK precursors to adhere to plastic and proliferate in the presence of rIL-2. The resultant population had the morphologic appearance of large granular lymphocytes, and the majority of cells (73% +/- 4%) expressed the CD56+/CD3- phenotype associated with rIL-2-stimulated natural killer (NK) cells. The A-LAK population had potent lytic activity in chromium release assays against both NK-sensitive (K562) and NK-resistant (Raji) targets. When BM mononuclear cells (BMMNC) were coincubated with autologous A-LAK and rIL-2 (1,000 U/mL) added at the start of culture, dose-dependent suppression of burst-forming unit-erythroid (BFU-E) and colony-forming unit mix (CFU-MIX) colony growth was observed at effector to target ratios (E:T) ranging from 0.25:1 to 5:1 (maximal suppression BFU-E = 85% +/- 6%; CFU-MIX = 95% +/- 3%). This suppression was rIL-2 dose-dependent, and no suppression was seen in the absence of rIL-2. Depletion of BM monocytes and T lymphocytes did not alter A-LAK suppression of progenitors coincubated with A-LAK cells. Addition of polyclonal neutralizing antibodies against both interferon-gamma (IFN-gamma) and tumor necrosis facto alpha (TNF-alpha) to the coincubation culture completely abrogated the suppressive effect of A-LAK on BFU-E and CFU-MIX colony growth while each neutralizing antibody used alone had intermediate effects. In contrast to coincubation studies, 36 hours of preincubation of A-LAK cells with autologous BM (E:T 2.2:1) and rIL-2 (1,000 U/mL) followed by plating of preincubated BM cells in hematopoietic progenitor culture produced significant suppression of day 14 BFU-E (47% +/- 5%), but spared the more primitive CFU-MIX (7% +/- 9%), suggesting a divergent effect of A-LAK cells on hematopoietic progenitors at different stages of differentiation. Addition of neutralizing antibodies against IFN-gamma and TNF-alpha in preincubation failed to abrogate the suppressive effect of A-LAK on BFU-E colony growth, suggesting that this suppression occurs by a different mechanism than that seen in coincubation studies. Previous studies have demonstrated that the A-LAK population has cytotoxic and proliferative advantages over other killer cell populations.(ABSTRACT TRUNCATED AT 400 WORDS)     

Lymphokine requirement for the generation of natural killer cells from CD34+ hematopoietic progenitor cells

We have established a cell culture system without stromal cells that allows the CD34+ hematopoietic progenitor cells (HPC) to differentiate into natural killer (NK) cells. CD34+Lin (CD3, CD16, CD56)- cells were purified using fluorescence-activated cell sorting from normal adult bone marrow (BM) and cultured for 28 days in medium supplemented with interleukin-2 (IL-2) and stem cell factor (SCF). NK (CD3-CD16-CD56+) cells were generated in a dose-dependent manner in response to SCF. NK cells originated from CD34+CD33+Lin- cells, but they were barely detectable in cultures of CD34+CD33-Lin- cells. However, on addition of IL-3, an induced differentiation of NK cells from CD34+CD33-Lin- cells was observed, although at a lower frequency. Supplementing of the cell cultures with SCF alone or both SCF and IL-3 for the first 7 days followed by IL-2 for the next 21 days is essential for production of NK cells from CD34+CD33+Lin- cells and from CD34+CD33-Lin- cells, respectively. These data provide direct evidence that NK cells arise from CD34+HPC and show the minimum lymphokine requirement for their differentiation.     

CD34+/CD33- cells reselected from macrophage inflammatory protein 1 alpha+interleukin-3--supplemented "stroma-noncontact" cultures are highly enriched for long-term bone marrow culture initiating cells

Human hematopoietic stem cells are thought to express the CD34 stem cell antigen, low numbers of HLA-DR and Thy1 antigens, but no lineage commitment antigens, CD38, or CD45RA antigens. However, fluorescence- activated cell sorted CD34+ subpopulations contain not more than 1% to 5% primitive progenitors capable of initiating and sustaining growth in long-term bone marrow culture initiating cells (LTBMC-ICs). We have recently shown that culture of fresh human marrow CD34+/HLA-DR- cells separated from a stromal layer by a microporous membrane ("stroma- noncontact" culture) results in the maintenance of 40% of LTBMC-ICs. We hypothesized that reselection of CD34+ subpopulations still present after several weeks in stroma-noncontact cultures may result in the selection of cells more highly enriched for human LTBMC-ICs. Fresh marrow CD34+/HLA-DR- cells were cultured for 2 to 3 weeks in stroma- noncontact cultures. Cultured progeny was then sorted on the basis of CD34, HLA-DR, or CD33 antigen expression, and sorted cells evaluated for the presence of LTBMC-ICs by limiting dilution analysis. We show that (1) LTBMC-ICs are four times more frequent in cultured CD34+/HLA- DR- cells (4.6% +/- 1.7%) than in cultured CD34+/HLA-DR- cells (1.3% +/- 0.4%). This suggests that HLA-DR antigen expression may depend on the activation status of primitive cells rather than their lineage commitment. We then sorted cultured cells on the basis of the myeloid commitment antigen, CD33. (2) These studies show that cultured CD34+/CD33- cells contain 4% to 8% LTBMC-ICs, whereas cultured CD34+/CD33+bright cells contain only 0.1% +/- 0.03% LTBMC-ICs. Because LTBMC-ICs are maintained significantly better in stroma-noncontact cultures supplemented with macrophage inflammatory protein 1 alpha (MIP- 1 alpha) and interleukin-3 (IL-3) (Verfaillie et al, J Exp Med 179:643, 1994), we evaluated the frequency of LTBMC-ICs in CD34+/CD33- cells present in such cultures. (3) CD34+/CD33- cells present in MIP-1 alpha + IL-3-supplemented cultures contain up to 30% LTBMC-ICs. The increased frequency of LTBMC-ICs in cultured CD34+ subpopulations may be the result of terminal differentiation of less primitive progenitors, loss of cells that fail to respond to the culture conditions or recruitment of quiescent LTBMC-ICs. The capability to select progenitor populations containing up to 30% LTBMC-ICs should prove useful in studies examining the growth requirements, self-renewal, and multilineage differentiation capacity of human hematopoietic stem cells at the single-cell level.     

Reversible expression of CD34 by adult human bone marrow long-term engrafting hematopoietic stem cells

OBJECTIVE: We previously reported that CD34(-) population of bone marrow (BM) cells from adult humans contains cells capable of engraftment and multilineage differentiation. We also reported on the reversibility of CD34 expression by murine hematopoietic stem cells. Based on long-term observations in primary, secondary, and tertiary sheep recipients, we now present definitive evidence for the long-term engrafting capability of human BM CD34(-) cells, and the reversibility of CD34 expression by human BM hematopoietic stem cells (HSC) in vivo. MATERIALS AND METHODS: We used serial transplantations into primary, secondary, and tertiary preimmune fetal sheep recipients to evaluate and compare the long-term engraftment and differentiation of adult human bone marrow-derived CD34(-) and CD34(+) cells in vivo. RESULTS: In primary hosts CD34(-) or CD34(+) cells produced multilineage human cell activity that persisted for 31 months. To confirm the long-term engrafting characteristics of CD34(-) cells and determine whether CD34 expression on human HSC is reversible, we transplanted human CD34(-) and CD34(+) cells obtained from primary hosts into secondary sheep recipients. Multilineage engraftment occurred in all secondary hosts, and in tertiary hosts transplanted with CD34(-) or CD34(+) cells obtained from BM of secondary recipients. CONCLUSION: These results demonstrate that human BM CD34(-) cells are capable of long-term multilineage engraftment in vivo. The finding that both CD34(-) and CD34(+) cells from primary/secondary groups engraft secondary/tertiary hosts indicates that CD34 expression on human HSC is reversible, a process that does not impair HSC function in vivo.     

In vivo generation of decidual natural killer cells from resident hematopoietic progenitors

Decidual natural killer cells accumulate at the fetal-maternal interface and play a key role in a successful pregnancy. However, their origin is still unknown. Do they derive from peripheral natural killer cells recruited in decidua or do they represent a distinct population that originates in situ? Here, we identified natural killer precursors in decidua and uterus of pregnant mice. These precursors underwent rapid in situ differentiation and large proportions of proliferating immature natural killer cells were present in decidua and uterus as early as gestation day 4.5. Here, we investigated the origin of decidua- and uterus-natural killer cells by performing transfer experiments of peripheral mature natural killer cells or precursors from EGFP⁺ mice. Results showed that mature natural killer cells did not migrate into decidua and uterus, while precursors were recruited in these organs and differentiated towards natural killer cells. Moreover, decidua- and uterus-natural killer cells displayed unique phenotypic and functional features. They expressed high levels of the activating Ly49D receptor in spite of their immature phenotype. In addition, decidua- and uterus-natural killer cells were poorly cytolytic and produced low amounts of IFN-γ, while they released factors (GM-CSF, VEGF, IP-10) involved in neo-angiogenesis and tissue remodeling. Our data reveal in situ generation of decidual natural killer cells and provide an important correlation between mouse and human decidual natural killer cells, allowing further studies to be carried out on their role in pregnancy-related diseases.     

Characterization and phenotypic analysis of differentiating CD34+human bone marrow cells in liquid culture

Abstract: Our current understanding of human haematopoietic stem cell biology is based in part on the characterization of human CD34⁺ bone marrow cell differentiation in vitro. CD34 is highly expressed on early stem cells and haematopoietic progenitor cells with clonogenic potential and is gradually lost during differentiation and commitment. However, CD71 (transferrin receptor) is expressed at low levels on early stem cells and generally increases during haematopoietic progenitor cell proliferation. We reasoned that the combination of these surface markers would provide a useful framework for the simultaneous analysis of multiple lineage differentiation of CD34⁺ haematopoietic progenitor cells in liquid culture. In this report, we identify the phenotype of distinct subpopulations of myeloid, erythroid and lymphoid cells in liquid suspension culture using differential expression of CD34 vs. CD71 in combination with specific lineage markers. Freshly isolated human CD34⁺ bone marrow cells were introduced into suspension culture and monitored over a 6-d period using 3-colour flow cytometry. This is the first demonstration that differential expression of CD34 vs. CD71 can be used to simultaneously monitor differentiation of multiple haematopoietic cell lineages in liquid suspension culture, facilitating the study of cytokine-, drug- or chemical-induced alterations in haematopoietic progenitor cell differentiation in vitro.     

Exclusive expression of G-CSF receptor on myeloid progenitors in bone marrow CD34+ cells

Although granulocyte colony-stimulating factor (G-CSF) has been reported to act on cells of neutrophilic lineage, the administration of G-CSF to induce the mobilization of various haematopoietic progenitors into the circulation. We analysed the expression of receptors for G-CSF (G-CSFR) on human bone marrow and G-CSF-mobilized peripheral blood CD34+ cells, and examined the proliferation and differentiation capabilities of sorted CD34+G-CSFR+ and CD34+G-CSFR- cells using methylcellulose clonal culture. Flow cytometric analysis showed that G-CSFR was expressed on 14.9 +/- 4.9% of bone marrow CD34+ cells, most of which were included in CD34+CD33+ and CD34+CD38+ cell fractions. In clonal cultures, CD34+G-CSFR+ cells produced only myeloid colonies, whereas CD34+G-CSFR- cells produced erythroid bursts, megakaryocyte and multilineage colonies. When incubated with the cytokine cocktail for 5 d, CD34+G-CSFR- cells generated CD34+G-CSFR+ myeloid progenitors. In G-CSF-mobilized peripheral blood, CD34+ cells contained 10.8 +/- 5.8% of G-CSFR+ cells, most of which were also myeloid progenitors, although CD34+G-CSFR- cells contained a substantial number of myeloid progenitors. These results indicated that the expression of G-CSFR on CD34+ cells is restricted to myeloid progenitors, suggesting that the specific activity of G-CSF on myelopoiesis depends on the exclusive expression of its receptor on myeloid progenitors, and that the mobilization of various haematopoietic progenitors is not a direct effect of G-CSF in humans.     

Ex vivo expansion of CD34+/CD41+ late progenitors from enriched peripheral blood CD34+ cells

 In our experience, patients with neuroblastoma who undergo transplantation with CD34+ cells following high-dose chemotherapy have prolonged delays in platelet recovery. In vitro expansion of megakaryocyte (MK) cells may provide a complementary transplant product able to enhance platelet production in the recipient. We investigated the ability of a combination of various hematopoietic growth factors to generate ex vivo MK progenitors. Immunoselected CD34+ cells from peripheral blood stems cells (PBSCs) were cultured in media with or without serum, supplemented by IL-3, IL-6, IL-11, SCF, TPO, Flt-3 ligand, and MIP-1α. In terms of MK phenotypes, we observed a maximal expansion of CD61+, CD41+, and CD42a of 69-, 60-, and 69-fold, respectively, i.e., 8–10 times greater than the expansion of total cell numbers. Whereas the absolute increment of CD34+ cells was slightly elevated (fourfold) we showed increases of 163-, 212-, and 128-fold for CD34+/CD61+, CD34+/CD41+, and CD34+/CD42a+ cells, respectively. We obtained only a modest expansion of CFU-MKs after only 4 days of culture (fourfold) and similar levels of CFU-MKs were observed after 7 days (fivefold). Morphology and immunohistochemistry CD41+ analyses confirmed expansion of a majority of CD41+ immature cells on days 4 and 7, while on day 10 mature cells began to appear. These results show that primarily MK progenitors are expanded after 4 days of culture, whereas MK precursor expansion occurs after 7 days. When we compared the two culture media (with and without serum) we observed that increases of all specific phenotypes of the MK lineage were more elevated in serum-free culture than in medium with serum. This difference was especially marked for CD34+/CD61+ and CD34+/CD41+ (163 vs 42 and 212 vs 36, respectively). We contaminated CD34+ cells with a neuroblastoma cell line and we observed no expansion of malignant cells in our culture conditions (RT-PCR for tyrosine hydroxylase positive at day 4 and negative at day 7). With our combination of hematopoietic growth factors we are able to sufficiently expand ex vivo MK late progenitor cells to be used as complementary transplant products in neuroblastoma patients who undergo transplantation with CD34+ cells. It is possible that these committed MK late progenitors could accelerate short-term platelet recovery in the recipient until more primitive progenitor cells have had time to engraft. Received: February 1, 1999 / Accepted: June 1, 1999     

CD16- CD56+ natural killer cells after bone marrow transplantation.

Natural killer (NK) cells are phenotypically defined as lymphocytes expressing the antigens CD56 and mostly CD16 (Fc gamma RIII), but lacking CD3. A small CD3- CD16- CD56+ NK cell subset has been described in normal individuals representing less than 2% of peripheral blood lymphocytes. We analyzed here 70 patients for their reconstitution of the immune system during follow-up after autologous or allogeneic bone marrow transplantation. In 35% of these patients, two different NK cell subsets, namely CD56+dim and CD56+bright cells, were observed. The mean duration of these two subsets after transplant was 4 months. Sixty-five percent of the patients exhibited an increased number of NK cells, but only the typical CD16+ CD56+dim population. The CD56+bright subpopulation represented a particular CD3- CD16- NK subset, with posttransplant frequencies up to 70% of all NK cells and 40% of peripheral blood lymphocytes, respectively. In contrast to normal CD56+dim NK cells, CD56+bright cells coexpressed the activation antigens p75 beta-chain of interleukin-2 receptor (IL-2R), CD2R, and CD26, but were negative for CD16. NK and antibody-dependent cellular cytotoxicity activity of CD56+bright cells was low compared with CD56+dim NK cells. But using IL-2 and interferon gamma, their cytotoxicity could be enhanced even more than in CD56+dim lymphocytes. These different subsets may reflect distinct activation or differentiation steps of NK cells during reconstitution of the immune system. Their differential response to IL-2 may be of functional importance for posttransplant cytokine therapy.     

In vitro differentiation of natural killer T cells from human cord blood CD34+ cells

Natural killer T (NKT) cells are involved in innate immune defence and also in the regulation of adaptive immune responses. However, the development of NKT cells in vitro has not been fully characterized and culture conditions have not been fully optimized. In the present study, we found that an NKT cell fraction developed during the in vitro culture of cord blood (CB) CD34+ cells, and this was subsequently characterized both phenotypically and morphologically. CD34+ cells purified from 10 human CB were cultured in the presence of several cytokines and analysed by flow cytometry, light microscopy and electron microscopy. The NKT cell fraction, defined phenotypically (CD3+CD16+CD56+CD94+) as expressing the invariant T-cell receptor Valpha24 and Vbeta11, appeared in the CD56hi fractions. Intracytoplasmic staining demonstrated that interferon-gamma and interleukin 4 (IL-4) were detected in the CD56hi fractions. IL-15 was essential and, in combination with either flt3-ligand (FL) or stem cell factor (SCF), was sufficient to induce the development of NKT cells. The phenotype of the NKT cell fraction was CD45RO+CD45RA- and CD4+CD8alpha+. Morphologically, they were very large, with either round or oval nuclei, moderately condensed chromatins, voluminous weakly basophilic cytoplasm and various cytoplasmic granules such as dense core granules, multivesicular bodies, and intermediate form granules. When CD34+ cells purified from bone marrow (BM) were compared with those from CB, the latter were consistently more efficient at generating CD56hi NKT cell fractions. In conclusion, IL-15 in combination with FL and/or SCF can induce the differentiation of NKT cells from human CB CD34+ cells.