The c-kit proto-oncogene in normal and malignant human hematopoiesis

Flow Cytometric Analysis of Normal and Neoplastic Mast Cells: Role in Diagnosis and Follow-Up of Mast Cell Disease

Human mast cells (MCs) are directly derived from human pluripotent CD34+ stem and progenitor hematopoietic cells with stem cell factor being a critical growth factor supporting human MC proliferation, differentiation, and survival. Because of the advantages that flow cytometry offers (it allows rapid, objective, and sensitive multiparameter analysis of high numbers of cells from a sample, with information being provided on the basis of a single cell), it has become the method of choice in the past decade for immunophenotypic identification, enumeration, and characterization of human MCs in bone marrow and other tissue specimens.

ABC transporter activities of murine hematopoietic stem cells vary according to their developmental and activation status

Primitive hematopoietic cells from several species are known to efflux both Hoechst 33342 and Rhodamine-123. We now show that murine hematopoietic stem cells (HSCs) defined by long-term multilineage repopulation assays efflux both dyes variably according to their developmental or activation status. In day 14.5 murine fetal liver, very few HSCs efflux Hoechst 33342 efficiently, and they are thus not detected as “side population” (SP) cells. HSCs in mouse fetal liver also fail to efflux Rhodamine-123. Both of these features are retained by most of the HSCs present until 4 weeks after birth but are reversed by 8 weeks of age or after a new HSC population is regenerated in adult mice that receive transplants with murine fetal liver cells. Activation of adult HSCs in vivo following 5-fluorouracil treatment, or in vitro with cytokines, induces variable losses in Rhodamine-123 and Hoechst 33342 efflux activities, and HSCs from mdr-1a/1b-/- mice show a dramatic decrease in Rhodamine-123 efflux ability. Thus, the Rhodamine-123 and Hoechst 33342 efflux properties of murine HSCs fluctuate in the same fashion as a number of other HSC markers, suggesting these are regulated by a common control mechanism that operates independently of that regulating the regenerative function of HSCs. (Blood. 2004;103:4487-4495)

Novel therapies for chronic myelogenous leukemia

The BCR-ABL oncogene is essential to the pathogenesis of chronic myelogenous leukemia, and immune mechanisms play an important role in control of this disease. Understanding of the molecular pathogenesis of chronic myelogenous leukemia has led to the development of several novel therapies, which can be broadly divided into therapies based on 1) inhibition of the BCR-ABL oncogene expression, 2) inhibition of other genes important to the pathogenesis of chronic myelogenous leukemia, 3) inhibition of BCR-ABL protein function, and 4) immunomodulation. We have systematically reviewed each of these novel therapeutic approaches in this article.

Ki-A10, a germ cell nuclear antigen retained in a subset of germ cell-derived tumors

Monoclonal antibody Ki-A10 recognizes a nuclear antigen of 25 and 22 kd apparent molecular mass, which is abundantly expressed by immature gonocytes, spermatogonia, and spermatocytes, whereas it is absent in spermatids, spermatozoa, oocytes, and normal somatic tissues. In a broad spectrum of human cancers the antibody showed no reactivity except for a small subset of malignant lymphomas. Because of this restricted expression pattern, we examined 173 germ cell tumors and 18 sex cord stromal tumors immunohistochemically to assess the distribution of the Ki-A10 antigen. A strongly positive reaction was found in classic seminomas, dysgerminomas, spermatocytic seminomas, and the germ cell component of gonadoblastomas. Yolk sac tumors presented a heterogeneous reactivity pattern ranging from overall positivity to complete lack of antigen expression, and in three of eight choriocarcinomas, a few clusters of cytotrophoblast cells were strongly labeled. All other tumors, including Leydig and Sertoli cell tumors as well as placental tissue, were negative. Our findings suggest that specific germ cell antigens can be retained in germ cell tumors along particular differentiation pathways. Ki-A10 is the first marker that consistently labels spermatocytic seminoma, further confirming its germ cell origin and suggesting a close relationship to classic seminoma. The antibody may serve for diagnostic purposes and promises new insights into the process of germ cell differentiation and the development of germ cell-derived neoplasia.

Expression of the c-kit (CD117) molecule in normal and malignant hematopoiesis

The c-kit proto-oncogen (CD 117) has been shown to be present in several cell types including normal and neoplastic hemopoietic cells. Among normal BM cells, CD117 expression has been found in about half of the CD34+ precursors including progenitors committed to the erythroid, granulo-monocytic, and megakaryocytic cell lineages. In addition, strong CD117 expression is detected in bone marrow mast cells as well as in a small subset of NK cells displaying strong reactivity for CD56, and in a relatively important proportion of CD3 /CD4 /CD8 prothymocytes. These results suggest that CD117 expression can be detected in both myeloid and lymphoid lineages although for the lymphoid lineage it would be restricted to a small NK-cell subset and early T-cell precursors. In acute leukemias CD117 expression was initially associated with AML. Nevertheless, at present it is well established that CD 117 expression may also be found in a relatively important proportion of T-ALL while it is usually absent in B-lineage ALL. Moreover, recent studies have shown that in about one-third of multiple myeloma cases and patients with monoclonal gammopathy of undetermined significance plasma cells display reactivity for CD1117. The prognostic influence of CD117 expression has not yet been clearly established. The analysis of this marker may also be of value for the investigation of minimal residual disease (MRD). It has been suggested that CD117 in combination with other antigens may be of great help for the identification of leukemia-associated phenotypes that could be used to monitor MRD in both acute myeloid leukemias and multiple myeloma patients achieving morphological complete remission.

Immunophenotype of c-kit cells in normal human bone marrow: implications for the detection of minimal residual disease in AML

In the present study, seven normal human bone marrow samples from healthy volunteers have been analysed in order to investigate the immunophenotypic characteristics of the normal CD117+ cells and their utility for the detection of minimal residual disease in 71 acute myeloid leukaemia patients. Our results show that most of normal BM CD117+ cells coexpress the HLADR and the myeloid associated CD33 antigen. In addition, almost half of CD117+ cells are CD34+, these cells displaying a different FSC/SSC distribution when compared to the CD117+/CD34- cells. No CD117+/CD15+ and CD117+/CD10+ cells were detected and very few CD117+ cells (< 1 x 10(-3) expressing the HLADR-/CD34-, CD33+/HLADR- and CD34+/HLADR- phenotypes were found to be present in normal BM. In contrast, from the 71 AML patients analysed, 34 had CD117+/CD15+ blast cells and eight had the CD117+ phenotypes detected at low frequencies (< 1 x 10(-3)) in normal BM. In summary, the present study shows that the use of the CD117 antigen in different monoclonal antibodies combinations may be of great help for the detection of minimal residual disease in a high proportion of AML cases, especially in those patients displaying the CD117+/CD15+ phenotype, because cells coexpressing both antigens in normal BM, if present, are at very low frequencies.

A reappraisal of the role of insulin-like growth factor I in the regulation of human hematopoiesis

IGF-I has been reported to increase hematopoietic progenitor cell cloning efficiency. To investigate this phenomenon, we studied the IGF-I responsiveness of human marrow cells expressing IGF-I receptor (IGF-IR), a direct strategy not used previously. IGF-IR+ and control CD34+ marrow cells were isolated using immunoaffinity methods. Then, the cells were cloned in methylcellulose containing variable amounts of serum- and lineage-appropriate growth factors supplemented with recombinant human IGF-I. In contrast to CD34+ cells, IGF-IR+ cells never gave rise to CFU-Blast, CFU-Mix, CFU-GM, BFU-E, or CFU-E. To substantiate the suggestion that CD34+ and IGF-IR+ cells were distinct populations, we used reverse transcription PCR to detect IGF-I, EpO, and KIT receptor mRNAs in these cells. The mRNA phenotype of CD34+ cells was EpO (+), KIT (+), and IGF-IR (-), while IGF-IR+ cells were IGF-IR (+), EpO (-), and KIT (-). These results suggested that IGF-IR is either not expressed or expressed at low levels on normal hematopoietic progenitor cells. Functional significance of the latter possibility was tested by exposing CD34+ cells to IGF-IR antisense oligodeoxynucleotides. Colony formation was unaffected by oligodeoxynucleotide disruption of IGF-IR, suggesting that, even if expressed at low level, the receptor's functional significance was doubtful. Nevertheless, when cultured in the presence of IGF-I, IGF-IR+ cells elaborated an activity with mild BFU-E stimulatory effects. Accordingly, if IGF-I plays a role in hematopoietic colony formation, it is probably and results from stimulation of IGF-IR-positive ancillary cells to secrete growth factors. Studies carried out with human leukemia cells yielded similar results.

c-kit ligand augments granulocyte-macrophage colony growth from patients with 5q- syndrome

In vitro studies may serve as a guide to clinical strategies with cytokines. In this study, marrows from 26 patients with myelodysplastic syndrome (MDS) were assayed for myeloid progenitor cells in agar gel. Colony stimulating activity was provided by the recombinant human colony stimulating factors granulocyte-macrophage colony stimulating factor (GM-CSF), granulocyte colony stimulating factor (G-CSF), interleukin 3 (IL-3), fusion protein (FP), c-kit ligand (KL) or GM-CSF combined with other cytokines (KL, IL-3). Decreased colony forming units granulocyte-macrophage (CFU-GM) were detected in most cases (69%) compared with normal controls. Neither FP nor the combination of GM-CSF + IL-3 produced more colonies than GM-CSF alone. The number of CFU-GM did not correlate with French American British (FAB) class. All marrows (7) from patients with 5q- showed augmentation of GM-CSF induced colonies with the addition of KL. In contrast, KL augmentation was noted in only 42% of other MDS marrows (p = 0.01). This in vitro result suggests that 5q- may predict a group of MDS patients with a likelihood to respond to the combination of GM-CSF + KL.

Oligodeoxynucleotide-based therapeutics for human leukemias

As the cell and molecular biology of hematopoietic cell development becomes known in greater detail, the roles of individual genes in regulating cell proliferation and growth also become better appreciated. Some genes appear to be of particular importance in these complex processes and are therefore potential targets for molecularly based therapeutics. The rationale for such treatment is that, if the function of critical genes can be efficiently and specifically perturbed, then the ensuing disruption might lead to preferential leukemic cell death. Several technologies for carrying out targeted gene disruption now exist. One approach, the "antisense" gene strategy, appears to be particularly well suited to the treatment of human leukemia ex vivo and perhaps in vivo as well. Herein I review the experience of my laboratory in using this approach to target the c-myb and c-kit proto-oncogenes in human leukemic cells. Our results suggest that use of oligodeoxynucleotides for disrupting the function of specific genes may prove useful for both ex vivo and in vivo treatment of patients with hematopoietic malignancies.

Anomalous plasma concentrations and impaired secretion of growth factors in Fanconi's anemia

In Fanconi's anemia, which is known to be an autosomal recessive Mendelian trait with four complementary groups. In addition to stunning phenotypic variation at clinical and cellular levels, aplastic pancytopenia is a common feature. Since either an early block of differentiation in stem cells or their insufficient support by stromal functions could be an underlying factor, levels of stem cell factor (SCF) and cytokines have been measured in blood and in supernatants of monocytes after stimulation with granulocyte-macrophage colony stimulating factor (GM-CSF). In two of three FA patients, no GM-CSF was detectable, and simultaneously SCF was decreased to 8% and 15% of normal values. The combination of low SCF and GM-CSF may be implied in the pathogenesis of marrow aplasia, since comparison with W/Sl mice shows that impairment of the SCF/c-kit function alone has different effects. Also, this explains that treatment with GM-CSF in a recent study enhanced only leukogenesis and not all three lineages. In the third patient, both factors were normal, and here a different mechanism may act. In all three FA patients, interleukin 6 (IL-6) production in stimulated monocytes was decreased, which may hamper immune defense of infections in a nonspecific way.

M-07e cell bioassay detects stromal cell production of granulocyte-macrophage colony stimulating factor and stem cell factor in normal and in Diamond-Blackfan anemia bone marrow

Ten healthy donors and four patients with Diamond-Blackfan anemia (DBA) have been investigated for granulocyte-macrophage colony stimulating factor (GM-CSF) and stem cell factor (SCF) production by bone marrow-enriched fibroblasts (BMEF) in a highly sensitive biological assay on growth factor-dependent M-07e cells. M-07e cells detected active soluble kit-ligand from normal bone marrow fibroblasts as well as from DBA BMEF which produce constitutively significant amounts of SCF. Interleukin 1 beta (IL-1 beta) induced a significant increase of soluble SCF from both normal and DBA BMEF. GM-CSF was undetectable in unstimulated cultures, while its production by bone marrow microenvironmental cells was documented for both normal and DBA patients after IL-1 beta stimulation in vitro.