Human T, B, natural killer, and dendritic cells arise from a common bone marrow progenitor cell subset

Granulocyte-macrophage colony-stimulating factor induces the differentiation of murine erythroleukaemia cells into dendritic cells

Dendritic cells (DC) are professional antigen-presenting cells (APC) within the immune system and antigen-pulsed DC can be used as an effective vaccine for active immunotherapy of cancer. Granulocyte-macrophage colony-stimulating factor (GM-CSF) plays an important role in the generation of DC. We previously showed that GM-CSF can induce murine erythroleukaemia cells (FBL-3) to differentiate into monocyte-like cells. To develop a new vaccinating method to stimulate the host immune response to leukaemia, we further investigate whether FBL-3 cells induced by GM-CSF can differentiate into DC in the present study. After being treated with GM-CSF, FBL-3 cells expressed high levels of 33D1 and NLDC-145, which are the specific markers of DC. The expression of MHC-II, B7-1, B7-2 and vascular cell adhesion molecule-1 (VCAM-1) was up-regulated markedly; the typical morphology of DC were also observed by electron microscopy. Functionally, the GM-CSF-induced FBL-3 cells could apparently stimulate the proliferation of naive allogeneic and autologous T lymphocytes and induce the generation of specific CTL more efficiently than the wild-type FBL-3 cells. Mice immunized with GM-CSF-induced FBL-3 cells could resist the subsequent challenge with the wild-type FBL-3 cells. Collectively, these data indicate that GM-CSF differentiates murine erythroleukaemia cells into DC phenotypically, morphologically and functionally. FBL-3-derived DC can be used as a new type of vaccine. Our results may have important implications for the immunotherapy of leukaemia.

A novel surface marker (B203.13) of human haemopoietic progenitors, preferentially expressed along the B and myeloid lineages

We used a monoclonal antibody (mAb) (B203.13, IgM) generated from a mouse immunized with the human B/myeloid bi-phenotypic B1b cell line, to analyse haemopoietic cells. The antigen recognized by this mAb is expressed on most adult and umbilical cord blood CD21+ B cells, at minimal density on mature monocytes, and is undetectable on granulocytes, T, natural killer (NK) cells, and erythrocytes. Within umbilical cord blood and adult bone marrow haemopoietic progenitor cells, the B203.13 mAb recognized a surface marker, present on progenitor cells of several haemopoietic lineages, that was transiently expressed on early erythroid and T/NK progenitors, and was preferentially maintained on cells of the B and myeloid lineages. Within the CD34+ cells, B203.13 was expressed on early committed myeloid (CD33+) and erythroid (CD71dim) progenitor cells, as confirmed in colony formation assays. The mAb also reacted with cells of B and myeloid chronic leukaemias and cell lines. These data define B203.13 mAb as a novel reagent useful for the characterization of haemopoietic progenitors and leukaemias.

Neutralization of Tumor Necrosis Factor Activity Shortly After the Onset of Dendritic Cell Hematopoiesis Reveals a Novel Mechanism for the Selective Expansion of the CD14-Dependent Dendritic Cell Pathway

The CD14-dependent and -independent dendritic cell (DC) pathways are instituted simultaneously when CD34+ progenitor cells are treated with granulocyte-macrophage colony-stimulating factor (GM-CSF)/tumor necrosis factor (TNF) ± stem cell factor (SCF) (GTS). If TNF activity is neutralized within 48 hours of cytokine exposure, DC development is halted and myelogranulocytic hematopoiesis takes place. In this study, we show that disruption of TNF activity at a later time point produced a distinct alteration within the DC system. Instead of downregulating DC development, treatment of GTS cultures with antibodies to TNF (anti-TNF) on day 3 provoked the selective expansion of the CD14-dependent (monocyte) DC pathway from progenitor cell populations lacking CD14 and CD1a. After an initial decrease in proliferation, anti-TNF produced a rebound in cell growth that yielded intermediate myeloid progenitors exhibiting CD14-dependent DC differentiation potential and CD14+CD1a+ DC precursors. Cultures enriched in CD14-dependent DCs were more potent stimulators of a mixed leukocyte reaction, compared with control GTS cultures containing both types of DCs. The intermediate progenitors expanded in the presence of anti-TNF were CD115+CD33+DR+, long-lived, and displayed clonogenic potential in methylcellulose. When exposed to the appropriate cytokine combinations, these cells yielded granulocytes, monocytes, and CD14-dependent DCs. Antigen-presenting function was acquired only when DC maturation was induced from these myelodendritic progenitors with GM-CSF + interleukin-4 or GTS. These studies show a novel mechanism by which TNF regulates the DC system, as well as providing a strategy for the amplification of the CD14-dependent DC pathway from immature progenitors. Although TNF is required to ensure the institution of DC hematopoiesis from CD34+ progenitor cells, its activity on a later progenitor appears to limit the development of CD14-dependent DCs.

© 1998 by The American Society of Hematology.

Neutralization of Tumor Necrosis Factor Activity Shortly After the Onset of Dendritic Cell Hematopoiesis Reveals a Novel Mechanism for the Selective Expansion of the CD14-Dependent Dendritic Cell Pathway

The CD14-dependent and -independent dendritic cell (DC) pathways are instituted simultaneously when CD34+ progenitor cells are treated with granulocyte-macrophage colony-stimulating factor (GM-CSF)/tumor necrosis factor (TNF) ± stem cell factor (SCF) (GTS). If TNF activity is neutralized within 48 hours of cytokine exposure, DC development is halted and myelogranulocytic hematopoiesis takes place. In this study, we show that disruption of TNF activity at a later time point produced a distinct alteration within the DC system. Instead of downregulating DC development, treatment of GTS cultures with antibodies to TNF (anti-TNF) on day 3 provoked the selective expansion of the CD14-dependent (monocyte) DC pathway from progenitor cell populations lacking CD14 and CD1a. After an initial decrease in proliferation, anti-TNF produced a rebound in cell growth that yielded intermediate myeloid progenitors exhibiting CD14-dependent DC differentiation potential and CD14+CD1a+ DC precursors. Cultures enriched in CD14-dependent DCs were more potent stimulators of a mixed leukocyte reaction, compared with control GTS cultures containing both types of DCs. The intermediate progenitors expanded in the presence of anti-TNF were CD115+CD33+DR+, long-lived, and displayed clonogenic potential in methylcellulose. When exposed to the appropriate cytokine combinations, these cells yielded granulocytes, monocytes, and CD14-dependent DCs. Antigen-presenting function was acquired only when DC maturation was induced from these myelodendritic progenitors with GM-CSF + interleukin-4 or GTS. These studies show a novel mechanism by which TNF regulates the DC system, as well as providing a strategy for the amplification of the CD14-dependent DC pathway from immature progenitors. Although TNF is required to ensure the institution of DC hematopoiesis from CD34+ progenitor cells, its activity on a later progenitor appears to limit the development of CD14-dependent DCs.

© 1998 by The American Society of Hematology.

Identification of CD68+lin− Peripheral Blood Cells with Dendritic Precursor Characteristics

Expression of CD68 (macrosialin) in the absence of surface and lysosomal lineage marker molecules is a characteristic feature of T zone-associated plasmacytoid monocytes, which were recently shown to represent precursors of dendritic cells (DC). We demonstrate here a minor population of strongly CD68-positive (CD68bright) blood cells that lack all analyzed myeloid surface (CD14−, CD33−, CD13−, CD11b−, CD11c−) and lysosomal (myeloperoxidase, MPO− and lysozyme, LZ−) marker molecules (0.4 ± 2% of the total mononuclear cells). These CD68bright, lineage marker-negative (lin−) cells can be induced to proliferate in the presence of IL-3. They do not acquire myeloid features even upon stimulation with granulocyte-macrophage CSF plus IL-1, IL-3, and IL-6. Instead, these cells develop typical DC characteristics upon culture. Furthermore, these CD68brightlin− DC precursors acquire mature DC characteristics (CD86+, CD83+, CD54bright) upon stimulation with CD40 ligand plus IL-3. A second subset of DC precursor-like blood cells was found to weakly express CD68 (0.3 ± 0.2% of the total mononuclear cells) and to coexpress several myeloid lineage associated molecules (LZ+, CD11c+, CD33+, CD13+). Cells of this second subset resemble both previously described myeloid-related peripheral blood DC and germinal center DC. Analysis of peripheral blood leukocytes for CD68 thus revealed the existence of two cell subsets that phenotypically resemble lymphoid tissue-associated DC. The unique phenotype CD68brightlin− is highly reminiscent of T zone-associated plasmacytoid monocytes. CD68brightlin− blood leukocytes also functionally resemble plasmacytoid monocytes. The lack of all analyzed myeloid features by CD68brightlin− blood leukocytes suggests that these cells arise from a novel nonmyeloid human DC differentiation pathway.

Bifurcated Dendritic Cell Differentiation In Vitro From Murine Lineage Phenotype-Negative c-kit+ Bone Marrow Hematopoietic Progenitor Cells

We have recently established the culture system to generate dendritic cells (DCs) from murine Lin−c-kit+ bone marrow hematopoietic progenitor cells (HPCs) in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) + stem cell factor (SCF) + tumor necrosis factor-α (TNF-α). We present here the identification of two DC precursor subsets originated from HPCs with the phenotype of CD11b−/dullCD11c+ and CD11b+hiCD11c+ that develop independently at early time points (days 4 to 6) in the same culture conditions. Both of CD11b−/dullCD11c+ and CD11b+hiCD11c+ precursors could differentiate at day 10 to 14 into CD11b−/dullCD11c+ mature DCs with typical morphology, phenotype, and the ability to stimulate allogenic mixed leukocyte reaction (MLR). However, the endocytic capacity of fluorescein isothiocyanate-dextran was markedly reduced during the differentiation. CD11b−/dullCD11c+precursors expressed high levels of Ia, CD86, CD40, and E-cadherin molecules, but not c-fms transcript, and mature DCs derived from this precursor subset continue to express abundant E-cadherin antigen, a discernible marker for Langerhans cells. In contrast, CD11b+hiCD11c+ precursors expressed c-fms mRNA, but low levels of Ia, CD86, and E-cadherin, whereas CD40 was undetectable. CD11b−/dullCD11c+mature DCs differentiated from these precursors displayed abundant c-fms mRNA and nonspecific esterase activity. Interestingly, CD11b+hiCD11c+precursors, but not CD11b−/dullCD11c+precursors, may be bipotent cells that can be induced by M-CSF to differentiate into macrophages. All of these results suggest that CD11b−/dullCD11c+ and CD11b+hiCD11c+ cells are distinct DC precursors derived from Lin−c-kit+ HPCs, which differentiate into mature DCs through bifurcated and independent DC differentiation pathways.

Interleukin-7 Influences the Development of Thymic Dendritic Cells

Interleukin-7 (IL-7) has been shown to be a critical factor in B and T lymphopoiesis, and to influence the differentiation of myeloid cell lineages. In the present study we extend these results demonstrating that IL-7 also plays an important role in the development of thymic dendritic cells (DC). The addition of IL-7 to rat fetal thymus organ cultures (FTOC) resulted in a drastic increase in the number of CD3−CD4−CD8− cells, which mostly expressed typical DC markers, including major histocompatibility complex class II, OX-62, CD11b, CD68, and CD54. These cells exhibited morphological and ultrastructural features of DC, and were potent stimulators of the allogeneic mixed leukocyte reaction. Although increased numbers of DC were continuously generated throughout the culture period in the presence of IL-7, they were not actively dividing, indicating that DC in IL-7–treated cultures did not arise by expansion of pre-existing cells. Reduced DC numbers obtained after the addition of neutralizing anti–IL-7 antibodies to mouse FTOC confirmed the relevance of endogenously produced IL-7 on thymic DC development. Furthermore, the addition of IL-7 to FTOC derived from severe combined immunodeficient mice also generated large numbers of DC in the absence of thymocyte maturation.

The Role of Tumor Necrosis Factor α in Modulating the Quantity of Peripheral Blood-Derived, Cytokine-Driven Human Dendritic Cells and Its Role in Enhancing the Quality of Dendritic Cell Function in Presenting Soluble Antigens to CD4+ T Cells In Vitro

Because dendritic cells (DC) are critically involved in both initiating primary and boosting secondary host immune responses, attention has focused on the use of DC in vaccine strategies to enhance reactivity to tumor-associated antigens. We have reported previously the induction of major histocompatibility complex class II-specific T-cell responses after stimulation with tumor antigen-pulsed DC in vitro. The identification of in vitro conditions that would generate large numbers of DC with more potent antigen-presenting cell (APC) capacity would be an important step in the further development of clinical cancer vaccine approaches in humans. We have focused attention on identifying certain exogenous cytokines added to DC cultures that would lead to augmented human DC number and function. DC progenitors from peripheral blood mononuclear cells (PBMC) were enriched by adherence to plastic, and the adherent cells were then cultured in serum-free XVIVO-15 medium (SFM) for 7 days with added granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4). At day 7, cultures contained cells that displayed the typical phenotypic and morphologic characteristics of DC. Importantly, we have found that the further addition of tumor necrosis factor α (TNFα) at day 7 resulted in a twofold higher yield of DC compared with non–TNFα-containing DC cultures at day 14. Moreover, 14-day cultured DC generated in the presence of TNFα (when added at day 7) demonstrated marked enhancement in their capacity to stimulate a primary allogeneic mixed leukocyte reaction (8-fold increase in stimulation index [SI]) as well as to present soluble tetanus toxoid and candida albicans (10- to 100-fold increases in SI) to purified CD4+ T cells. These defined conditions allowed for significantly fewer DC and lower concentrations of soluble antigen to be used for the pulsing of DC to efficiently trigger specific T-cell proliferative responses in vitro. When compared with non–TNFα-supplemented cultures, these DC also displayed an increased surface expression of CD83 as well as the costimulatory molecules, CD80 and CD86. Removal of TNFα from the DC cultures after 2 or 4 days reduced its enhancing effect on DC yield, phenotype, and function. Thus, the continuous presence of TNFα over a 7-day period was necessary to achieve the maximum enhancing effect observed. Collectively, our findings point out the importance of exogenous TNFα added to cultures of cytokine-driven human DC under serum-free conditions, which resulted in an enhanced number and function of these APC. On the basis of these results, we plan to initiate clinical vaccine trials in patients that use tumor-pulsed DC generated under these defined conditions.

Ex Vivo Culture of CD34+/Lin−/DR− Cells in Stroma-Derived Soluble Factors, Interleukin-3, and Macrophage Inflammatory Protein-1α Maintains Not Only Myeloid But Also Lymphoid Progenitors in a Novel Switch Culture Assay

We have demonstrated that long-term culture initiating cells (LTC-IC) are maintained in a stroma noncontact (SNC) culture where progenitors are separated from stroma by a microporous membrane and LTC-IC can proliferate if the culture is supplemented with interleukin-3 (IL-3) and macrophage inflammatory protein-1α (MIP-1α). We hypothesize that the same conditions, which result in LTC-IC proliferation, may also maintain lymphoid progenitors. Natural killer (NK) cells are of lymphoid lineage and a stromal-based culture can induce CD34+/Lin−/DR−cells to differentiate along the NK cell lineage. We developed a three-step switch culture assay that was required to demonstrate the persistence of NK progenitors in CD34+/Lin−/DR− cells assayed in SNC cultures supplemented with IL-3 and MIP-1α. When CD34+/Lin−/DR− progeny from the SNC culture were plated sequentially into “NK cell progenitor switch” conditions (contact with stromal ligands, hydrocortisone-containing long-term culture medium, IL-2, IL-7, and stem cell factor [SCF]) followed by “NK cell differentiation” conditions (contact with stromal ligands, human serum, no hydrocortisone, and IL-2), significant numbers of CD56+/CD3− NK resulted, which exhibited cytotoxic activity against K562 targets. All steps are required because a switch from SNC cultures with IL-3 and MIP-1α directly to “NK cell differentiation” conditions failed to yield NK cells suggesting that critical step(s) in lymphoid commitment were missing. Additional experiments showed that CD34+/CD33− cells present after SNC cultures with IL-3 and MIP-1α, which contained up to 30% LTC-IC, are capable of NK outgrowth using the three-step switch culture. Limiting dilution analysis from these experiments showed a cloning frequency within the cultured CD34+/CD33− population similar to fresh sorted CD34+/Lin−/DR− cells. However, after addition of FLT-3 ligand, the frequency of primitive progenitors able to develop along the NK lineage increased 10-fold. In conclusion, culture of primitive adult marrow progenitors ex vivo in stroma-derived soluble factors, MIP-1α, and IL-3 maintains both very primitive myeloid (LTC-IC) and lymphoid (NK) progenitors and suggests that these conditions may support expansion of human hematopoietic stem cells. Addition of FLT-3 ligand to IL-2, IL-7 SCF, and stromal factors are important in early stages of NK development.

Ex Vivo Culture of CD34+/Lin−/DR− Cells in Stroma-Derived Soluble Factors, Interleukin-3, and Macrophage Inflammatory Protein-1α Maintains Not Only Myeloid But Also Lymphoid Progenitors in a Novel Switch Culture Assay

We have demonstrated that long-term culture initiating cells (LTC-IC) are maintained in a stroma noncontact (SNC) culture where progenitors are separated from stroma by a microporous membrane and LTC-IC can proliferate if the culture is supplemented with interleukin-3 (IL-3) and macrophage inflammatory protein-1α (MIP-1α). We hypothesize that the same conditions, which result in LTC-IC proliferation, may also maintain lymphoid progenitors. Natural killer (NK) cells are of lymphoid lineage and a stromal-based culture can induce CD34+/Lin−/DR−cells to differentiate along the NK cell lineage. We developed a three-step switch culture assay that was required to demonstrate the persistence of NK progenitors in CD34+/Lin−/DR− cells assayed in SNC cultures supplemented with IL-3 and MIP-1α. When CD34+/Lin−/DR− progeny from the SNC culture were plated sequentially into “NK cell progenitor switch” conditions (contact with stromal ligands, hydrocortisone-containing long-term culture medium, IL-2, IL-7, and stem cell factor [SCF]) followed by “NK cell differentiation” conditions (contact with stromal ligands, human serum, no hydrocortisone, and IL-2), significant numbers of CD56+/CD3− NK resulted, which exhibited cytotoxic activity against K562 targets. All steps are required because a switch from SNC cultures with IL-3 and MIP-1α directly to “NK cell differentiation” conditions failed to yield NK cells suggesting that critical step(s) in lymphoid commitment were missing. Additional experiments showed that CD34+/CD33− cells present after SNC cultures with IL-3 and MIP-1α, which contained up to 30% LTC-IC, are capable of NK outgrowth using the three-step switch culture. Limiting dilution analysis from these experiments showed a cloning frequency within the cultured CD34+/CD33− population similar to fresh sorted CD34+/Lin−/DR− cells. However, after addition of FLT-3 ligand, the frequency of primitive progenitors able to develop along the NK lineage increased 10-fold. In conclusion, culture of primitive adult marrow progenitors ex vivo in stroma-derived soluble factors, MIP-1α, and IL-3 maintains both very primitive myeloid (LTC-IC) and lymphoid (NK) progenitors and suggests that these conditions may support expansion of human hematopoietic stem cells. Addition of FLT-3 ligand to IL-2, IL-7 SCF, and stromal factors are important in early stages of NK development.

Expanding Dendritic Cells In Vivo Enhances the Induction of Oral Tolerance

The intestine is under perpetual challenge from both pathogens and essential nutrients, yet the mucosal immune system is able to discriminate effectively between harmful and innocuous Ags. It is likely that this selective immunoregulation is dependent on the nature of the APC at sites where gut Ags are processed and presented. Dendritic cells (DC) are considered the most potent of APC and are renowned for their immunostimulatory role in the initiation of immune responses. To investigate the role of DC in regulating the homeostatic balance between mucosal immunity and tolerance, we treated mice with Flt3 ligand (Flt3L), a growth factor that expands DC in vivo, and assessed subsequent systemic immune responsiveness using mouse models of oral tolerance. Surprisingly, mice treated with Flt3L to expand DC exhibited more profound systemic tolerance after they were fed soluble Ag. Most notably, tolerance could be induced in Flt3L-treated mice using very low doses of Ag that were ineffective in control animals. These findings contrast with the generally accepted view of DC as immunostimulatory APC and furthermore suggest a pivotal role for DC during the induction of tolerance following mucosal administration of Ag.

The Role of Tumor Necrosis Factor α in Modulating the Quantity of Peripheral Blood-Derived, Cytokine-Driven Human Dendritic Cells and Its Role in Enhancing the Quality of Dendritic Cell Function in Presenting Soluble Antigens to CD4+ T Cells In Vitro

Because dendritic cells (DC) are critically involved in both initiating primary and boosting secondary host immune responses, attention has focused on the use of DC in vaccine strategies to enhance reactivity to tumor-associated antigens. We have reported previously the induction of major histocompatibility complex class II-specific T-cell responses after stimulation with tumor antigen-pulsed DC in vitro. The identification of in vitro conditions that would generate large numbers of DC with more potent antigen-presenting cell (APC) capacity would be an important step in the further development of clinical cancer vaccine approaches in humans. We have focused attention on identifying certain exogenous cytokines added to DC cultures that would lead to augmented human DC number and function. DC progenitors from peripheral blood mononuclear cells (PBMC) were enriched by adherence to plastic, and the adherent cells were then cultured in serum-free XVIVO-15 medium (SFM) for 7 days with added granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4). At day 7, cultures contained cells that displayed the typical phenotypic and morphologic characteristics of DC. Importantly, we have found that the further addition of tumor necrosis factor α (TNFα) at day 7 resulted in a twofold higher yield of DC compared with non–TNFα-containing DC cultures at day 14. Moreover, 14-day cultured DC generated in the presence of TNFα (when added at day 7) demonstrated marked enhancement in their capacity to stimulate a primary allogeneic mixed leukocyte reaction (8-fold increase in stimulation index [SI]) as well as to present soluble tetanus toxoid and candida albicans (10- to 100-fold increases in SI) to purified CD4+ T cells. These defined conditions allowed for significantly fewer DC and lower concentrations of soluble antigen to be used for the pulsing of DC to efficiently trigger specific T-cell proliferative responses in vitro. When compared with non–TNFα-supplemented cultures, these DC also displayed an increased surface expression of CD83 as well as the costimulatory molecules, CD80 and CD86. Removal of TNFα from the DC cultures after 2 or 4 days reduced its enhancing effect on DC yield, phenotype, and function. Thus, the continuous presence of TNFα over a 7-day period was necessary to achieve the maximum enhancing effect observed. Collectively, our findings point out the importance of exogenous TNFα added to cultures of cytokine-driven human DC under serum-free conditions, which resulted in an enhanced number and function of these APC. On the basis of these results, we plan to initiate clinical vaccine trials in patients that use tumor-pulsed DC generated under these defined conditions.

NK cells differentiated from bone marrow, cord blood and peripheral blood stem cells exhibit similar phenotype and functions

In the present study, we investigated the differentiation of human NK cells from bone marrow, cord blood and mobilized peripheral blood purified CD34+ stem cells using a potent culture system. Elutriated CD34+ stem cells were grown for several weeks in medium supplemented with stem cell factor (SCF) and IL-15 in the presence or absence of a murine stromal cell line (MS-5). Our data indicate that IL-15 induced the proliferation and maturation of highly positive CD56+ NK cells in both types of culture, although murine stromal cells slightly increased the proliferation of NK cells. NK cells differentiated in the presence of MS-5 were mostly CD56+ CD7 and a small subset expressed CD16. These in vitro differentiated CD56+ NK cells displayed cytolytic activity against the HLA class I- target K562. The CD56+ CD16+ subset also lysed NK-resistant Daudi cells. Neither of these NK subsets were shown to express Fas ligand. Total CD56+ cells expressed high amounts of transforming growth factor-beta and granulocyte-macrophage colony-stimulating factor, but no IFN-gamma. Investigation of NK receptor expression showed that most CD56+ cells expressed membrane CD94 and NKG2-A mRNA. PCR analysis revealed that p58 was also expressed in these cells. The role of CD94 in NK cell-mediated cytotoxicity was assessed on human HLA-B7-transfected murine L cells. While a low cytotoxic activity towards HLA-B7 cells was observed, the HLA-DR4 control cells were killed with high efficiency. These studies demonstrate that cytolytic and cytokine-producing NK cells may be derived from adult and fetal precursors by IL-15 and that these cells express a CD94 receptor which may influence their lytic potential.

The role of interleukin-7 in early T-cell development

Interleukin-7 (IL-7) is a non redundant cytokine in thymic T-cell development. It binds to a dimeric receptor consisting of a specific IL-7Ralpha and a gamma-common subunit that it shares with the receptors for IL-2, 4, 9, 13 and 15. IL-7 is critical for early T-cell development but it also acts on immature B-cells and mature T-cells, and leads to secondary cytokine release. Its mechanisms of action in early T-cell development may be multiple. There is direct evidence to support a mechanistic involvement in TCR-gamma rearrangement that drives further TCR-gammadelta thymocyte commitment and maturation. There is indirect evidence for a role of IL-7 in TCR-beta rearrangement. It may however also act as a survival factor for TCR-beta rearranging thymocytes while the critical commitment selections are effected by other factors. The effects of IL-7 in fetal thymus organ culture are dose dependent, with a biphasic response: low doses of IL-7 are necessary for normal TCR-alphabeta thymocyte development but high doses block TCR-alphabeta maturation in favor of TCR-gammadelta development. A good understanding of the dose response of IL-7 in thymocyte development, mature T-cell stimulation, and of the release of secondary cytokines will be important for planning successful clinical trials with IL-7.

Developmental aspects of dendritic cells in vitro and in vivo

Dendritic cells (DC) are potent antigen presenting cells that possess the unique ability to stimulate naive T-cells. By studying DC derived from various tissues it has been shown that the morphology, phenotype and function of DC alter as they undergo a complex process of maturation. DC are derived from bone marrow progenitors and circulate in the blood as immature precursors prior to migration into the peripheral tissues. Within tissues DC are specialised in the taking up and processing of antigen so that it may be presented on MHC class II molecules. Upon appropriate stimulation tissue DC undergo further maturation and migrate to secondary lymphoid tissue where they present antigen to T-cells and induce an immune response. Studies of DC maturation in vitro have defined the cytokines regulating their development from CD34+ myelomonocytic progenitors as well as from more mature peripheral blood precursors. An alternative pathway of differentiation from thymic precursors has also been described. As a result of these studies, DC may now be generated and manipulated ex-vivo for clinical applications in oncology, autoimmune disease and transplantation.

Flt-3 Ligand Increases Microchimerism But Can Prevent the Therapeutic Effect of Donor Bone Marrow in Transiently Immunosuppressed Cardiac Allograft Recipients

C3H (H2k) mice received 50 × 106 B10 (H2b) bone marrow (BM) cells either alone or with flt-3 ligand (FL) (10 μg/day), tacrolimus (2 mg/kg/day), or both agents for 7 days. Donor MHC class II+ (IAb+) cells were quantitated in spleens by immunohistochemical analysis, and donor class II DNA detected in BM by PCR. Donor cells were rare in the BM alone and BM + FL groups, whereas there was a substantial increase in chimerism in the BM + tacrolimus group. Addition of FL to BM + tacrolimus led to a further eightfold increase in donor cells and enhanced donor DNA compared with the BM + tacrolimus group. This increase in donor cells was almost 500-fold compared with BM alone. C3H recipients of B10 heart allografts given perioperative B10 BM and tacrolimus (days 0–13) exhibited a markedly extended median graft survival time (MST, 42 days) compared with those given tacrolimus alone (MST, 22 days). Addition of FL (10 μg/day; 7 days) to BM + tacrolimus prevented the beneficial effect of donor BM (MST, 18 days). BM alone or BM + FL resulted in uniform early heart graft failure (MST < 8 days). Functional studies revealed maximal antidonor MLR and CTL activities in the BM- and BM + FL-treated groups, with minimal activity in the tacrolimus-treated groups. Thus, dramatic growth factor-induced increases in chimerism achieved under cover of immunosuppression may result in augmented antidonor T cell reactivity and reduced graft survival after immunosuppressive drug withdrawal. With FL, this may reflect striking augmentation of immunostimulatory dendritic cells.

Identification of a Common Developmental Pathway for Thymic Natural Killer Cells and Dendritic Cells

Current data support the notion that the thymus is seeded by a yet uncommitted progenitor cell able to generate T cells, B cells, natural killer (NK) cells, and dendritic cells (DCs). We assess in this report the developmental relationship of DCs and NK cells derived from a small subset of CD34+ human postnatal thymocytes that, like the earliest precursors in the fetal thymus, display low CD33 surface expression. Culture of these isolated CD34+CD33lo thymic progenitors with a mixture of cytokines, including interleukin-7 (IL-7), IL-1α, IL-6, granulocyte-macrophage colony-stimulating factor, and stem cell factor, results in predominant generation of DCs. However, the addition of IL-2 to the cytokine mixture leads to the simultaneous development of DCs and NK cells. Both developmental pathways progress through a transient population of CD34+CD44brightCD5lo/−CD33+ large-sized cells, distinct from small-sized T-lineage precursors, that contain bipotential NK/DC progenitors. These data provide evidence of linked pathways of NK cell and DC development from intrathymic precursors and suggest that NK cells and DCs branch off the T lineage through a common intermediate progenitor.

CD34+CD38−lin− Cord Blood Cells Develop into Dendritic Cells in Human Thymic Stromal Monolayers and Thymic Nodules

Thymic dendritic cells (DCs) appear to have distinct biologic and functional properties compared with DCs in other tissues. Currently, little is known about human thymic DCs because they have been difficult to isolate and culture in vitro. Here, we report that human thymic stroma can support the development of primitive human hemopoietic stem cells into mature DCs without cytokine or serum supplementation. Coculture of CD34+CD38−lineage (lin)− and CD34+CD38+lin− umbilical cord blood cells with thymic stromal monolayers induced 43 ± 17-fold and 32 ± 16-fold expansions, respectively, of umbilical cord blood progenitors and also generated large numbers of cells with the morphologic, phenotypic, and functional characteristics of mature DCs. These cells expressed class I and class II MHC, CD1a, CD2, CD4, CD11c, CD40, CD45, CD80, CD83, and CD86 and were potent stimulators of allogeneic T cell activation. Primitive hemopoietic progenitors also developed into mature DCs in a novel tissue culture system of thymic nodules wherein thymic epithelial cells and fibroblasts were grown in nodular aggregates in vitro. These results demonstrate that human thymic stroma efficiently supports the development of CD34+CD38−lin− cord blood cells into mature DCs. In addition, the culture conditions described in this report are useful systems for studying the ontogeny of human DCs in thymic microenvironments.

B-cell lymphopoiesis in mouse and man

Functional immunoglobulin gene rearrangement is a sine qua non for successful B cell development in mammalian bone marrow, but other factors are also important. Studies reported during the past year have contributed new insight into the surface receptor complexes and signaling outcomes that influence the fate of B cell precursors. Identification and characterization of secreted and membrane-associated stromal cell products, and their actions on B-cell precursors, was a parallel area of ongoing investigation.

Cytomegalovirus remains latent in a common precursor of dendritic and myeloid cells

Hematopoietic cells and their progenitors play important roles in human cytomegalovirus latency and reactivation. Latent infection has been evaluated in defined populations of myeloid-lineage-committed progenitor cells coexpressing CD33 and CD15 or CD33 and CD14 along with the dendritic cell markers CD1a and CD10. These CD33+ cell populations were found to support latency and expression of viral latency-associated transcripts and to undergo reactivation of productive viral replication when differentiated in the presence of human fibroblasts. Reactivation was also observed when myeloid cells were carried in the presence of fibroblast-conditioned medium or medium supplemented with certain cytokines (interferon gamma, tumor necrosis factor alpha, interleukin 4, or granulocyte-macrophage colony-simulating factor), suggesting that cell differentiation pathways act as determinants of reactivation. More primitive CD34+ hematopoietic cells were also found to be susceptible to viral infection and latency was maintained as these cells differentiated into CD33+-lineage-committed populations. Between 0.01% and 0.001% of CD33+ CD14+ or CD33+ CD15+ bone marrow mononuclear cells isolated from naturally infected individuals were found to express latent transcripts. Thus, cytomegalovirus is carried within a small percentage of myeloid and dendritic cell progenitors in the healthy seropositive host. Virus reactivation may be triggered by factors associated with the inflammatory response.

FLT-3 Ligand and Marrow Stroma-Derived Factors Promote CD3γ, CD3δ, CD3ζ, and RAG-2 Gene Expression in Primary Human CD34+LIN−DR− Marrow Progenitors

We hypothesize that early lymphoid commitment from primitive hematopoietic marrow progenitors is governed by signals from the marrow microenvironment leading to sequential induction of lineage-specific genes. Using expression of lymphoid genes as markers of differentiation, we characterize a highly purified population (>99.8% by double sorting) of primary human CD34+Lin−DR− progenitors. This population was then used to evaluate the effects of supplemental cytokines (interleukin-2 [IL-2], IL-3, IL-7, c-kit ligand), FLT-3 ligand (FL), and stroma-derived factors on lymphoid differentiation in vitro. CD3, RAG-1, Ikaros, CD10, and TdT transcripts were detected in the starting CD34+Lin−DR− population. By contrast, CD3γ, CD3δ, CD3ζ, and RAG-2 transcripts were not present in any samples tested. The presence of supplemental cytokines alone at culture initiation permitted stimulation of the expression of CD3ζ, but not of CD3γ or CD3δ. However, when FL and stroma-derived factors were added to cytokines, CD3 gene expression was induced in all samples. The predominant CD3 transcripts induced by optimal culture conditions were alternatively spliced isoforms lacking transmembrane sequences (CD3δ and CD3γ) and portions of the intracellular and extracellular domains (CD3γ). The combination of cytokines, FL, and stromal factors also provided a potent stimulus for RAG-2 gene expression. These findings show that FL in combination with stroma-derived factors provide important signals to promote early events required for lymphoid differentiation.

Epidermal Langerhans cell development and differentiation

Epidermal Langerhans cells (LC) play a critical role in host defense. Still we know rather little about the development and functional specialization of these bone marrow-derived dendritic cells (DC) located in the most peripheral ectodermal tissue of the mammalian organism. How LC develop from their primitive progenitors in bone marrow and to what extent LC are related in their development to other lineages of the hemopoietic system is still under debate. There are currently 3 major areas of debate: 1) which are the signals required for LC development and differentiation to occur, 2) what are the (molecular) characteristics of the intermediate stages of LC differentiation, and 3) how are LC related in their development and/or function to other cells of the hemopoietic system? A better understanding of LC development and answers to these questions can be expected from recently developed technologies which allow the in vitro generation of DC with the typical molecular, morphological and functional features of LC from purified CD34+ progenitor cells under defined serum-free culture conditions. TGF-beta 1 was found to be an absolute requirement for in vitro LC development under serum-free conditions upon stimulation with the classical DC growth and differentiation factors GM-CSF, TNF-alpha and SCF. The recently identified cytokine FLT3 ligand further dramatically enhanced in vitro LC development and even allowed efficient in vitro generation of LC colonies from serum-free single cell cultures of CD34+ hemopoietic progenitor cells.

FLT-3 Ligand and Marrow Stroma-Derived Factors Promote CD3γ, CD3δ, CD3ζ, and RAG-2 Gene Expression in Primary Human CD34+LIN−DR− Marrow Progenitors

We hypothesize that early lymphoid commitment from primitive hematopoietic marrow progenitors is governed by signals from the marrow microenvironment leading to sequential induction of lineage-specific genes. Using expression of lymphoid genes as markers of differentiation, we characterize a highly purified population (>99.8% by double sorting) of primary human CD34+Lin−DR− progenitors. This population was then used to evaluate the effects of supplemental cytokines (interleukin-2 [IL-2], IL-3, IL-7, c-kit ligand), FLT-3 ligand (FL), and stroma-derived factors on lymphoid differentiation in vitro. CD3, RAG-1, Ikaros, CD10, and TdT transcripts were detected in the starting CD34+Lin−DR− population. By contrast, CD3γ, CD3δ, CD3ζ, and RAG-2 transcripts were not present in any samples tested. The presence of supplemental cytokines alone at culture initiation permitted stimulation of the expression of CD3ζ, but not of CD3γ or CD3δ. However, when FL and stroma-derived factors were added to cytokines, CD3 gene expression was induced in all samples. The predominant CD3 transcripts induced by optimal culture conditions were alternatively spliced isoforms lacking transmembrane sequences (CD3δ and CD3γ) and portions of the intracellular and extracellular domains (CD3γ). The combination of cytokines, FL, and stromal factors also provided a potent stimulus for RAG-2 gene expression. These findings show that FL in combination with stroma-derived factors provide important signals to promote early events required for lymphoid differentiation.

FLT3: receptor and ligand. Biology and potential clinical application

Flt3 ligand (FL) is a recently identified cytokine having a central role in the proliferation, survival and differentiation of early murine and human hematopoietic precursor/stem cells. FL acts synergistically in vitro with a number of other hematopoietic growth factors such as IL-3, IL-6, IL-11, IL-12, KIT Ligand and GM-CSF. Recently, it has been shown the in vivo administration of FL results in a significant alteration of hematopoiesis in murine bone marrow (BM), spleen, peripheral blood, liver and lymph nodes. In addition, treatment with FL resulted in a significant accumulation of functionally active dendritic cells within murine lymphoid tissues. The possible applications of FL in dendritic cell-based immunotherapies are discussed.

[Dendritic cells: a complex cellular system]

Dendritic cells (DC) are the most potent antigen-presenting cells. Thus, ex vivo antigen-pulsed DC are a potentially powerful tool to induce in vivo immunity against tumor-associated or viral antigens. Therefore, culture methods to generate high numbers of DC from bone marrow or blood CD34+ hematopoietic progenitor cells have recently been developed. These methods, which use different combinations of growth factor--mainly granulocyte/macrophage colony-stimulating factor (GM-CSF), tumor necrosis factor (TNF)-alpha and interleukin (IL)-4--make the characterization of DC obtained from CD34+ cells of different origins easier and allow to assess whether DC relate to a unique or distinct differentiation pathways. Monocytes and even macrophages can also directly differentiate into DC in the presence of GM-CSF and IL-4. This has to be reconciled with evidence supporting earlier branching off of the macrophage and DC lineages, and raises questions as to the identity of the latter lineage. Apart from DC of myeloid origin, DC may also originate from lymphoid progenitors. Because the capacity of DC to capture, process and present antigens is known to vary according to their differentiation stage, and lymphoid DC might behave differently from lymphoid DC in this respect, the definition of which type of DC to use for immunotherapy must be more precise, in order to avoid detrimental side effects or results. From a practical point of view, it is also necessary to define the most appropriate cytokine combinations and schedules thereof to optimize proliferation and differentiation of DC from different origins. These conditions should then be applied to generated DC for their efficient and safe use for clinical immunotherapy.

Large granular lymphocytic leukaemia with a mixed T-cell/B-cell phenotype

We report a case of large granular lymphocytic leukaemia (LGLL) with mixed T-cell/B-cell phenotypes. The LGLL cells expressed T-cell markers such as CD1, CD2, CD3, CD5, CD7, CD8 and CD57. The CD8+ LGLL cells coexpressed B-cell markers including CD20 and PCA-1, and a fraction of purified CD8+ LGLL cells secreted double isotypes of immunoglobulins (IgG-kappa and IgA-kappa). Both TCRB and IGH genes were clonally rearranged. The LGLL cells could be divided into at least three subpopulations that were cytogenetically distinct, and all subpopulations involved the 11q23. The expression of both T- and B-cell markers on the LGLL cells suggests the involvement of a putative common lymphoid progenitor in leukaemic transformation.

Three Populations of Mouse Lymph Node Dendritic Cells with Different Origins and Dynamics

We have identified three distinct populations of mouse lymph node dendritic cells (DC) that differ in their capacity to uptake Ag delivered by different routes, and in their dynamics. The “l-DCs” are large cells that resemble the interdigitating cells and have a mature phenotype and a slow turnover. They derive from the regional tissues. The “sm-DCs” and “sl-DCs” are smaller (hence s-DC), have a more immature phenotype and a rapid turnover. The sl-DC phenotype, including CD8α expression, suggests a lymphoid-related origin. The sl-DC population is expanded 100-fold after an in vivo flt3 ligand treatment. The sm-DC phenotype suggests a myeloid-related origin. Interestingly, sm-DCs can acquire i.v. injected macromolecules in less than 30 min after injection. They may, therefore, play an important role in the immune response against blood Ags.

Retrovirally Transduced CD34++ Human Cord Blood Cells Generate T Cells Expressing High Levels of the Retroviral Encoded Green Fluorescent Protein Marker In Vitro

Human umbilical cord blood (UCB) hematopoietic stem cells (HSC) receive increased attention as a possible target for gene-transfer in gene therapy trials. Diseases affecting the lymphoid lineage, as adenosine deaminase (ADA) deficiency and acquired immunodeficiency syndrome (AIDS) could be cured by gene therapy. However, the T-cell progenitor potential of these HSC after gene-transfer is largely unknown and was up to now not testable in vitro. We show here that highly purified CD34++ Lineage marker-negative (CD34++Lin−) UCB cells generate T, natural killer (NK), and dendritic cells in a severe combined immunodeficient mouse fetal thymus organ culture (FTOC). CD34++Lin− and CD34++CD38−Lin− UCB cells express the retroviral encoded marker gene Green Fluorescent Protein (GFP) after in vitro transduction with MFG-GFP retroviral supernatant. Transduced cells were still capable of generating T, NK, and dendritic cells in the FTOC, all expressing high levels of GFP under control of the Moloney murine leukemia virus (MoMuLV) long terminal repeat promotor. We thus present an in vitro assay for thymic T-cell development out of transduced UCB HSC, using GFP as a marker gene.

Retrovirally Transduced CD34++ Human Cord Blood Cells Generate T Cells Expressing High Levels of the Retroviral Encoded Green Fluorescent Protein Marker In Vitro

Human umbilical cord blood (UCB) hematopoietic stem cells (HSC) receive increased attention as a possible target for gene-transfer in gene therapy trials. Diseases affecting the lymphoid lineage, as adenosine deaminase (ADA) deficiency and acquired immunodeficiency syndrome (AIDS) could be cured by gene therapy. However, the T-cell progenitor potential of these HSC after gene-transfer is largely unknown and was up to now not testable in vitro. We show here that highly purified CD34++ Lineage marker-negative (CD34++Lin−) UCB cells generate T, natural killer (NK), and dendritic cells in a severe combined immunodeficient mouse fetal thymus organ culture (FTOC). CD34++Lin− and CD34++CD38−Lin− UCB cells express the retroviral encoded marker gene Green Fluorescent Protein (GFP) after in vitro transduction with MFG-GFP retroviral supernatant. Transduced cells were still capable of generating T, NK, and dendritic cells in the FTOC, all expressing high levels of GFP under control of the Moloney murine leukemia virus (MoMuLV) long terminal repeat promotor. We thus present an in vitro assay for thymic T-cell development out of transduced UCB HSC, using GFP as a marker gene.

Impaired natural killer cell function as a consequence of aging

Alex Comfort wrote (1979): "... nobody needs long-lived mice." His point was, of course, that as much as possible, research should be done with humans "... who are the beneficiaries in mind ..." In this paper we hope to show that long-lived mice have been useful, if not essential, for conducting studies on the aging of innate immunity, specifically the NK cell component of the system. NK cells are activated early in the course of Trypanosoma musculi infections, which we employ as a model. We have generated evidence that the relatively severe infections of aged mice with T. musculi, are attributable, in part, to (a) functionally defective NK cells, the defect(s) being retained by LAK cells that arise from them, and (b) deficient amounts of IL-2 required to convert NK to LAK cells. Defective macrophages, which are the effector cells responsible for eliminating T. musculi, may also accumulate in aged animals. We postulate that the functionally deficient NK cells fail to generate adequate amounts of IFN gamma (and perhaps, TNF alpha) to optimally activate macrophages. This inadequacy can explain the weak ability of aged mice to control the early stage of T. musculi infection preceding the appearance of the more slowly-developing acquired immune response.

Regulated Production of Type I Collagen and Inflammatory Cytokines by Peripheral Blood Fibrocytes

We recently described a novel population of blood-borne cells, termed fibrocytes, that display a distinct cell surface phenotype (collagen+/CD13+/CD34+/CD45+), rapidly enter sites of tissue injury, and contribute to scar formation. To further characterize the role of these cells in vivo, we examined the expression of type I collagen and cytokine mRNAs by cells isolated from wound chambers implanted into mice. Five days after chamber implantation, CD34+ fibrocytes but not CD14+ monocytes or CD90+ T cells expressed mRNA for type I collagen. Fibrocytes purified from wound chambers also were found to express mRNA for IL-1β, IL-10, TNF-α, JE/MCP, MIP-1α, MIP-1β, MIP-2, PDGF-A, TGF-β1, and M-CSF. The addition of IL-1β (1–100 ng/ml), a critical mediator in wound healing, to fibrocytes isolated from human peripheral blood induced the secretion of chemokines (MIP-1α, MIP-1β, MCP-1, IL-8, and GROα), hemopoietic growth factors (IL-6, IL-10, and macrophage-CSF), and the fibrogenic cytokine TNF-α. By contrast, IL-1β decreased the constitutive secretion of type I collagen as measured by ELISA. Additional evidence for a role for fibrocytes in collagen production in vivo was obtained in studies of livers obtained from Schistosoma japonicum-infected mice. Mouse fibrocytes localized to areas of granuloma formation and connective matrix deposition. We conclude that fibrocytes are an important source of cytokines and type I collagen during both the inflammatory and the repair phase of the wound healing response. Furthermore, IL-1β may act on fibrocytes to effect a phenotypic transition between a repair/remodeling and a proinflammatory mode.

Dendritic cell development: multiple pathways to nature's adjuvants

Dendritic cells are a system of bone marrow-derived antigen-presenting cells specialized for interaction with T lymphocytes and essential for initiating primary T cell immune responses. Recent investigation indicates that dendritic cells are of diverse origin, with at least two types of myeloid precursors and a lymphoid precursor implicated in their generation. Mature dendritic cell subtypes, while sharing the capacity to activate T cells, show additional functional specialization. Some dendritic cells are equipped with additional mechanisms to regulate the response of the T cells they activate, while others are able to interact with B cells and modify B cell responses.

Pro-inflammatory cytokines and prostaglandins induce maturation of potent immunostimulatory dendritic cells under fetal calf serum-free conditions

Culture conditions for human dendritic cells (DC) have been developed by several laboratories. Most of these culture methods, however, have used conditions involving fetal calf serum (FCS) to generate DC in the presence of granulocyte-macrophage colony-stimulating factor and interleukin (IL)-4. Recently, alternative culture conditions have been described using an additional stimulation with monocyte-conditioned medium (MCM) and FCS-free media to generate DC. As MCM is a rather undefined cocktail, the yield and quality of DC generated by these cultures varies substantially. We report that a defined cocktail of tumor necrosis factor (TNF)-alpha, IL-1beta and IL-6 equals MCM in its potency to generate DC. Addition of prostaglandin (PG)E2 to the cytokine cocktail further enhanced the yield, maturation, migratory and immunostimulatory capacity of the DC generated. More importantly, culture conditions also influenced the outcome of the T cell response induced. DC cultured with TNF-alpha/IL-1/IL-6 or MCM alone induced CD4+ T cells that release intermediate levels of interferon (IFN)-gamma and no IL-4 or IL-10. Production of IFN-gamma was significantly induced by addition of PGE2, while no effect on production of IL-4 or IL-10 was observed. Even more striking differences were observed for CD8+ T cells. While MCM conditions only induced IFN-gamma(low), IL-4(neg) cells, TNF-alpha/IL-1/IL-6 promoted growth of IFN-gamma(intermediate), IL-4(neg) CD8+ T cells. Addition of PGE2 again only further polarized this pattern enhancing IFN-gamma production by alloreactive CD8+ T cells in both cultures without inducing type 2 cytokines. Taken together, the data indicate that the defined cocktail TNF-alpha/IL-1/IL-6 can substitute for MCM and that addition of PGE2 further enhances the yield and quality of DC generated. TNF-alpha/IL-1, IL-6 + PGE2-cultured DC seem to be optimal for generation of IFN-gamma-producing CD4/CD8+ T cells.

Identification of clonogenic common lymphoid progenitors in mouse bone marrow

The existence of a common lymphoid progenitor that can only give rise to T cells, B cells, and natural killer (NK) cells remains controversial and constitutes an important gap in the hematopoietic lineage maps. Here, we report that the Lin(-)IL-7R(+)Thy-1(-)Sca-1loc-Kit(lo) population from adult mouse bone marrow possessed a rapid lymphoid-restricted (T, B, and NK) reconstitution capacity in vivo but completely lacked myeloid differentiation potential either in vivo or in vitro. A single Lin(-)IL-7R(+)Thy-1(-)Sca-1loc-Kit(lo) cell could generate at least both T and B cells. These data provide direct evidence for the existence of common lymphoid progenitors in sites of early hematopoiesis.

Early Onset of Immunoglobulin Heavy Chain Gene Rearrangements in Normal Human Bone Marrow CD34+ Cells

To characterize early B-cell precursors in humans, we correlated immunoglobulin heavy chain (IgH) gene rearrangement status with the CD34, CD19, and CD10 cell surface markers. Highly purified adult bone marrow (BM) cell fractions were obtained by two successive rounds of flow cytometric cell sorting, and IgH rearrangements were analyzed by polymerase chain reaction (PCR) amplification. Complete VDJH rearrangements were observed in the CD34+ CD19+ fraction, but not in the more immature CD34+ CD19− fraction. About one quarter of these rearrangements had an open reading frame, thus potentially permitting the synthesis of a μ chain. Partial DJH rearrangements were detected in both CD34+ CD19+ and CD34+ CD19− subsets, although they were less abundant in the latter. When triple labeling was used to better characterize the CD34+ CD19− population, DJH rearrangements were found to be present in the CD34+ CD10+ CD19− fraction, but not in the more primitive CD34+ CD10− CD19−. These results indicate that IgH gene rearrangements occur in CD34+ BM cells and that they initiate in immature progenitors expressing the CD10, but not yet the CD19 surface antigen. Finally, the presence of IgH gene rearrangements in CD34+ BM cells provides a useful marker of clonality to evaluate the possible involvement of these cells in various B-cell lymphoid malignancies.

Development of Natural Killer Cells, B Lymphocytes, Macrophages, and Mast Cells From Single Hematopoietic Progenitors in Culture of Murine Fetal Liver Cells

We have recently established a clonal culture system that supports the growth of immature natural killer (NK) cells from murine fetal thymocytes. We now describe a culture system for mixed NK cell colony formation from single lymphohematopoietic progenitors. When Sca-1+c-kit+ fetal liver cells were cultured in methylcellulose media with interleukin (IL)-2, IL-7, IL-11, and steel factor (SF ), we found mixed colonies consisting of diffuse small round cells characteristic of immature NK cells and other types of cells. The single cell origin of the mixed colonies was established by micromanipulation. Individual mixed colonies derived from single cells were characterized by flow cytometric analysis and May-Grünwald Giemsa staining. All mixed colonies contained Thy-1+B220− cells, which can differentiate to mature NK cells in fetal thymus organ culture. Most of the colonies contained B220+ B-lineage cells and macrophages, and some contained mast cells. IL-1α and IL-3, which have previously been shown to inhibit the T- and B-cell potentials of blast colonies, suppressed the formation of mixed NK cell colonies. The clonal culture assay presented here may be useful in analysis of the developmental pathway and commitment of NK cells from multipotential progenitors.

Dendritic cell ontogeny: a human dendritic cell lineage of myeloid origin

Dendritic cells (DC) have been thought to represent a family of closely related cells with similar functions and developmental pathways. The best-characterized precursors are the epidermal Langerhans cells, which migrate to lymphoid organs and become activated DC in response to inflammatory stimuli. Here, we demonstrate that a large subset of DC in the T cell-dependent areas of human lymphoid organs are nonactivated cells and belong to a separate lineage that can be identified by high levels of the interleukin 3 receptor alpha chain (IL-3Ralphahi). The CD34+IL-3Ralphahi DC progenitors are of myeloid origin and are distinct from those that give rise to Langerhans cells in vitro. The IL-3Ralphahi DC furthermore appear to migrate to lymphoid organs independently of inflammatory stimuli or foreign antigens. Thus, DC are heterogeneous with regard to function and ontogeny.

Sequence analysis of rat integrin alpha E1 and alpha E2 subunits: tissue expression reveals phenotypic similarities between intraepithelial lymphocytes and dendritic cells in lymph

The integrin alpha OX-62 subunit is defined by the OX-62 monoclonal antibody that was raised against rat dendritic cells in lymph (veiled cells) and shows properties similar to those of human alpha E2 that is predominantly expressed on intraepithelial lymphocytes. To clone alpha OX-62, rat probes generated using primers specific for the human alpha E sequence were used to screen rat T cell cDNA libraries. cDNA clones encoding two similar but not identical alpha subunits that are closely related to but distinct from human alpha E were isolated. alpha E1 is predicted to be the rat homolog of mouse alpha M290 and alpha E2 corresponds to rat alpha OX-62. Immunofluorescence analysis revealed that mouse alpha E1 and rat alpha E2 are expressed in dendritic epidermal T cells in the skin, intraepithelial lymphocytes in the small intestine and in cells with a dendritic morphology present at sites where gamma delta T cells occur in lymphoid organs. Unexpectedly, alpha E2 is co-expressed with intracellular CD3-delta and a 33-kDa CD3 chain but not the T cell receptor in veiled cells. These findings suggest that veiled cells may be derived from a lymphoid precursor. Furthermore, veiled cells show phenotypic similarities to intraepithelial lymphocytes.

Natural Killer (NK) Cells Are Functionally Abnormal and NK Cell Progenitors Are Diminished in Granulocyte Colony-Stimulating Factor–Mobilized Peripheral Blood Progenitor Cell Collections

Granulocyte colony-stimulating factor (G-CSF)–mobilized peripheral blood progenitor cell (PBPC) collections are increasingly emerging as the graft of choice in many centers for autologous transplantation, and with increasing frequency for allogeneic transplantation. However, the role of myeloid cytokines in lymphoid function, lymphoid progenitors, and immune-mediated antitumor responses is not known. We studied PBPC collections from normal donors mobilized with G-CSF (10 μg/kg). CD56+/CD3− natural killer (NK) cells sorted from PBPC products exhibited a diminished ability to kill tumor targets, were less responsive in acquiring increased cytolysis with interleukin-2 (IL-2), and proliferated less than NK cells from normal unprimed peripheral blood. This abnormality was not explained by a change in phenotype of NK cells normally circulating in the blood after G-CSF administration. We could not demonstrate any direct suppressive effect on normal unprimed NK cell proliferation or cytotoxicity by culture with pharmacologic concentrations of G-CSF. We next evaluated the effects of G-CSF on CD34+ NK cell progenitors. CD34+/CD2+, CD34+/CD7+, and CD34+/CD10+ progenitors were markedly diminished in G-CSF–mobilized PBPC products. CD34+ cells cultured in limiting dilution assays showed a sixfold decrease in NK cell progenitors when derived from G-CSF–mobilized CD34+ PBPCs compared with CD34+ cells derived from unprimed marrow. The finding of decreased NK cell function, inhibited proliferation, and diminished cloning frequency after treatment with G-CSF could be mimicked in vitro by culture of primitive marrow progenitors (CD34+, lineage-negative, HLA-DR−) on stromal layers in the presence of exogenous G-CSF. The findings presented here show that G-CSF administration to normal donors decreases NK cell function and the relative frequency of NK cell progenitors within the CD34+ progenitor population. Overcoming this diminished lymphoid capacity may be important to facilitate early posttransplant immunotherapy. Our in vitro model will be used in future studies to determine the mechanism of the G-CSF–induced suppression of NK cell progenitors, which may occur early in the differentiation process.

Developing lymph nodes collect CD4+CD3- LTbeta+ cells that can differentiate to APC, NK cells, and follicular cells but not T or B cells

For a brief period during fetal lymph node organogenesis in mice, lymph node postcapillary high endothelial venules surprisingly express the Peyer's patch addressin MAdCAM-1. This expression allows initial seeding of this incipient structure by two unusual lymphocyte populations selectively expressing the Peyer's patch homing receptor integrin alpha4beta7: CD4+CD3- oligolineage progenitors and TCR gammadelta+ T cells. We show here that CD4+CD3- cells are lineage-restricted progenitors that express surface lymphotoxin-beta (LTbeta) and the chemokine receptor BLR1 and that can become natural killer cells, dendritic antigen-presenting cells, and follicular cells of unknown outcome, but these cells do not become T or B lymphocytes. Since the necessity of lymphotoxin in lymphoid organ development has been shown, we propose that the novel subset of CD4+CD3-LTbeta+ fetal cells is instrumental in the development of lymphoid tissue architecture.

Cord blood CD16+56- cells with low lytic activity are possible precursors of mature natural killer cells

Human natural killer (NK) cells are defined as being membrane CD3-, CD16+, and/or CD56+ lymphocytes; however, little is known about the ontogenic development and maturational pathways of human NK cells. The functional, phenotypic, and maturational characteristics of human umbilical cord blood (CB) NK cell subsets were studied to gain insight into the ontogenic and maturational pathways of human NK cells. We have previously shown that there is a novel subset of CD16+ CD56- NK cells present in CB. Here we further demonstrate differences in the expression of the NK-associated molecules CD2, CD7, CD8, and CD25 between CB and peripheral blood (PB) NK cells and between CB NK cell subsets. Although CB NK cell subsets were deficient in or had less lytic activity against K562 cells compared to PB NK cells, CB NK cells did possess the lytic molecules perforin and granzyme B and when artificially stimulated to secrete their granules during lytic assays, were capable of lytic activity equivalent to that of PB NK cells. Regardless of differences in phenotype and function of CB NK cell subsets, short-term and long-term incubation with cytokines induced functional (adult-like NK activity) and phenotypic (adult-like CD16+56+ or CD16-56+ surface antigen phenotype) maturation, respectively. Interleukin-2 (IL-2), IL-12, and IL-15, but not IL-7, interferon-gamma (IFN-gamma) nor tumor necrosis factor-alpha (TNF-alpha) induced functional and phenotypic maturation of CB NK cell subsets. Interestingly, culture of CB NK cell subsets with IL-2 or IL-15 led to acquisition of predominantly a CD16+56+ phenotype, while culture with IL-12 led to acquisition of both CD16+56+ and CD16-56+ phenotypes. Both functional and phenotypic maturation were not dependent upon proliferation. Studies using neutralizing anti-IFN-gamma and anti-TNF-alpha antibodies showed that survival and phenotypic maturation upon cytokine stimulation is influenced by endogenous production of TNF-alpha but not IFN-gamma. These results demonstrate that CB NK cell subsets are functionally and phenotypically immature but are capable of maturation. Additionally, CD16+56- NK cells are implicated as possible precursors of mature CD16+56+ and CD16-56+ NK cells.

Epidermal Langerhans' cells in children with primary T-cell immune deficiencies

Dendritic cells are the major antigen-presenting cells, especially for naive T lymphocytes; it is conceivable therefore that their absence or dysfunction may induce an immune deficiency (ID). Few data are available, however, concerning dendritic cells in human primary ID. Langerhans' cells (LC) are intraepidermal dendritic cells which express specific markers and may therefore be studied by immunohistochemistry on paraffin-embedded skin samples. Skin samples of nine children with primary ID were studied and compared with five age-matched controls. LC were present within the epidermis of two children with X-linked severe combined ID, a condition related to the lack of the common gamma-chain of interleukin-2 (IL-2), IL-4, IL-7, IL-9, and IL-15 receptors. LC were also present in skin samples of a child with Omenn syndrome and in three children with combined ID. By contrast, no LC were detected in the skin samples of two children with alymphocytosis and of a child with reticular dysgenesis, a condition characterized by the absence of peripheral blood leukocytes.

CD34+ Hematopoietic Progenitors From Human Cord Blood Differentiate Along Two Independent Dendritic Cell Pathways in Response to Granulocyte-Macrophage Colony-Stimulating Factor Plus Tumor Necrosis Factor α: II. Functional Analysis

In response to granulocyte-macrophage colony-stimulating factor plus tumor necrosis factor α, cord blood CD34+ hematopoietic progenitor cells differentiate along two unrelated dendritic cell (DC) pathways: (1) the Langerhans cells (LCs), which are characterized by the expression of CD1a, Birbeck granules, the Lag antigen, and E cadherin; and (2) CD14+ cell-derived DCs, characterized by the expression of CD1a, CD9, CD68, CD2, and factor XIIIa (Caux et al, J Exp Med 184:695, 1996). The present study investigates the functions of each population. Although the two populations are equally potent in stimulating naive CD45RA cord blood T cells through apparently identical mechanisms, each also displays specific activities. In particular CD14-derived DCs show a potent and long-lasting (from day 8 to day 13) antigen uptake activity (fluorescein isothiocyanate dextran or peroxidase) that is about 10-fold higher than that of CD1a+ cells, which is restricted to the immature stage (day 6). The antigen capture is exclusively mediated by receptors for mannose polymers. The high efficiency of antigen capture of CD14-derived cells is coregulated with the expression of nonspecific esterase activity, a tracer of lysosomial compartment. In contrast, the CD1a+ population never expresses nonspecific esterase activity. The most striking difference is the unique capacity of CD14-derived DCs to induce naive B cells to differentiate into IgM-secreting cells, in response to CD40 triggering and interleukin-2. Thus, although the two populations can allow T-cell priming, initiation of humoral responses might be preferentially regulated by the CD14-derived DCs. Altogether, those results show that different pathways of DC development might exist in vivo: (1) the LC type, which might be mainly involved in cellular immune responses, and (2) the CD14-derived DC related to dermal DCs or circulating blood DCs, which could be involved in humoral immune responses.

flt3 Ligand in Cooperation With Transforming Growth Factor-β1 Potentiates In Vitro Development of Langerhans-Type Dendritic Cells and Allows Single-Cell Dendritic Cell Cluster Formation Under Serum-Free Conditions

Using a recently described serum-free culture system of purified human CD34+ progenitor cells, we show here a critical cooperation of flt3 ligand (FL) with transforming growth factor-β1 (TGF-β1) in the induction of in vitro dendritic cell/Langerhans cell (DC/LC) development. The addition of FL to serum-free cultures of CD34+ cells supplemented with TGF-β1, granulocyte-macrophage colony-stimulating factor, tumor necrosis factor α, and stem cell factor strongly increases both percentages (mean, 36% ± 5% v 64% ± 4%; P = .001) and total numbers (4.4- ± 0.8-fold) of CD1a+ dendritic cells. These in vitro-generated CD1a+ cells molecularly closely resemble a particular type of DC known as an epidermal Langerhans cell. Generation of DC under serum-free conditions was found to strictly require supplementation of culture medium with TGF-β1. Upon omission of TGF-β1, percentages of CD1a+ DC decreased (to mean, 10% ± 8%; P = .001) and, in turn, percentages of granulomonocytic cells (CD1a− cells that are lysozyme [LZ+]; myeloperoxidase [MPO+]; CD14+) increased approximately threefold (P < .05). Furthermore, in the absence of TGF-β1, FL consistently promotes generation of LZ+, MPO+, and CD14+ cells, but not of CD1a+ cells. Serum-free single-cell cultures set up under identical TGF-β1– and FL-supplemented culture conditions showed that high percentages of CD34+ cells (mean, 18% ± 2%; n = 4) give rise to day-10 DC colony formation. The majority of cells in these DC-containing colonies expressed the Langerhans cell/Birbeck granule specific marker molecule Lag. Without TGF-β1 supplementation, Lag+ colony formation is minimal and formation of monocyte/macrophage-containing colonies predominates. Total cloning efficiency in the absence and presence of TGF-β1 is virtually identical (mean, 41% ± 6% v 41% ± 4%). Thus, FL has the potential to strongly stimulate DC/LC generation, but has a strict requirement for TGF-β1 to show this costimulatory effect.

flt3 Ligand in Cooperation With Transforming Growth Factor-β1 Potentiates In Vitro Development of Langerhans-Type Dendritic Cells and Allows Single-Cell Dendritic Cell Cluster Formation Under Serum-Free Conditions

Using a recently described serum-free culture system of purified human CD34+ progenitor cells, we show here a critical cooperation of flt3 ligand (FL) with transforming growth factor-β1 (TGF-β1) in the induction of in vitro dendritic cell/Langerhans cell (DC/LC) development. The addition of FL to serum-free cultures of CD34+ cells supplemented with TGF-β1, granulocyte-macrophage colony-stimulating factor, tumor necrosis factor α, and stem cell factor strongly increases both percentages (mean, 36% ± 5% v 64% ± 4%; P = .001) and total numbers (4.4- ± 0.8-fold) of CD1a+ dendritic cells. These in vitro-generated CD1a+ cells molecularly closely resemble a particular type of DC known as an epidermal Langerhans cell. Generation of DC under serum-free conditions was found to strictly require supplementation of culture medium with TGF-β1. Upon omission of TGF-β1, percentages of CD1a+ DC decreased (to mean, 10% ± 8%; P = .001) and, in turn, percentages of granulomonocytic cells (CD1a− cells that are lysozyme [LZ+]; myeloperoxidase [MPO+]; CD14+) increased approximately threefold (P < .05). Furthermore, in the absence of TGF-β1, FL consistently promotes generation of LZ+, MPO+, and CD14+ cells, but not of CD1a+ cells. Serum-free single-cell cultures set up under identical TGF-β1– and FL-supplemented culture conditions showed that high percentages of CD34+ cells (mean, 18% ± 2%; n = 4) give rise to day-10 DC colony formation. The majority of cells in these DC-containing colonies expressed the Langerhans cell/Birbeck granule specific marker molecule Lag. Without TGF-β1 supplementation, Lag+ colony formation is minimal and formation of monocyte/macrophage-containing colonies predominates. Total cloning efficiency in the absence and presence of TGF-β1 is virtually identical (mean, 41% ± 6% v 41% ± 4%). Thus, FL has the potential to strongly stimulate DC/LC generation, but has a strict requirement for TGF-β1 to show this costimulatory effect.