Fresh Leukemic Blasts Research Articles

Abstract 5608: Deciphering role of NLRP3 inflammasome in acute myeloid leukemia microenvironment

Abstract Acute Myeloid Leukemia (AML), the most common form of leukemia in adults. Despite intensive chemotherapy regimen, approximately 60% of patients subsequently relapse. Inflammatory cells and mesenchymal stem cells (MSC) which are part of bone marrow (BM) microenvironment, play a critical role in cancer progression. Current strategies are focused on understanding cell-cell contact dependent/independent communication within the leukemic stem cell niche. NLRP3 is a part of innate immune mechanisms, resulting in the release of IL-1β and IL-18 immunomodulatory cytokines. Current study was aimed at analyzing NLRP3 pathway regulation at phenotypic and genotypic level in AML BM-MSC compared to healthy BM-MSC and their cross-talk with immune function in AML stem cell niche. MSC were isolated and cultured from AML BM that exhibited heterogenous fibroblastoid shape. Multi-color flow cytometry of AML BM-MSC revealed characteristic high expression of CD90 and minimal expression of CD45. They also expressed immune checkpoint markers TIM3, PDL-1, adenosine receptors A1R/A2BR, vimentin and NLRP3. Cultured AML BM MSC and fresh leukemic blasts demonstrated tunneling nanotubules, increased vesicles and increase in mitochondria which were of irregular shapes and sizes as seen by transmission electron microscopy. Microarray data revealed genes of NLRP3 damage-associated molecular patterns (DAMP) pathway viz. Nlrp3, NME8, Pycard and IL-18 were distinctly upregulated in AML BM-MSC compared to uninvolved BM-MSC. AML peripheral blood (PB) plasma showed immunosuppressive effect on healthy peripheral blood mononuclear cells. NK cell cytotoxicity was found to be significantly reduced in presence of culture supernatant of AML cell line and further reduced with supernatant of cells activated for NLRP3 pathway. Immunofluorescence demonstrated NLRP3 expression in AML BM-MSC and also in vesicles released from MSC. NLRP3 pathway activation was observed in AML cell line which was significantly abrogated upon treatment with NLRP3 inhibitor. NLRP3 pathway is stimulated using basic DAMP agent LPS and secondary activators ATP or Nigericin. Activation was visualized by colocalization of NLRP3 and caspase-1, in the presence/absence of NLRP3 inhibitor. Expression of IL-1β was observed using immunofluorescence and its release in culture supernatants was measured by ELISA. Inhibition of NLRP3 corroborated with decreased secretion of IL-1β in AML cell line. Thus, a positive correlation of IL-1β release was observed with expression of NLRP3. Paraffin sections of AML BM are being evaluated for NLRP3 pathway markers by immunohistochemistry. Understanding remodelling of BM-MSC, leukemia target and immune cell dynamics through NLRP3 pathway regulation in stroma microenvironment may provide crucial leads in therapeutic modulation of the immune response within the stem cell niche. Citation Format: Monalisa Sahoo, Manasi Nagare, Naythan Dcunha, Meena Patkar, Manju Sengar, Navin Khattry, Anant Gokarn, Sachin Punatar, Sridhar Epari, Tanuja Shet, Jyoti Kode. Deciphering role of NLRP3 inflammasome in acute myeloid leukemia microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5608.

Elucidating the Non-Catalytic Function of Fatty Acid Synthase and Its Autophagy-Dependent Degradation in Acute Myelocytic Leukemia Differentiation Therapy

Acute myeloid leukemia (AML) is characterized by a block in myeloid differentiation and an aberrant cell proliferation of leukemia blasts. While other AML therapies cure only 30% of the patients, acute promyelocytic leukemia (APL) is successfully treated by differentiation therapy using all-trans retinoic acid (ATRA) in combination with chemotherapy or arsenic trioxide. A better understanding of the molecular mechanisms underlying ATRA therapy in APL may offer new perspectives in the treatment of additional AML subtypes.Fatty acid synthase (FASN) is the only human lipogenic enzyme able of de novo fatty acid synthesis. Its expression is very low in healthy adult tissues, whereas increased expression is commonly found in a variety of cancerous tissues. Therefore, FASN represents an attractive potential drug target.To investigate if a similar expression pattern is found in normal versus malignant myeloid cells, we determined FASN expression in fresh leukemic blast cells from untreated AML patients obtained at the Inselspital Bern (Switzerland) (n=68) and expression data available online from the Bloodspot server (n=203). In both AML cohorts, we found that FASN expression is significantly higher in AML patients than in healthy granulocytes (p<0.05). Accordingly, FASN protein levels are reduced in NB4 and HT93 APL cells upon ATRA-induced granulocyte differentiation. Additionally, silencing FASN in NB4 cells led to an acceleration of differentiation upon ATRA treatment. Surprisingly, solely inhibiting the catalytic function of FASN using C75 or Orlistat did not affect granulocyte differentiation nor FASN expression. To validate that FASN levels and not activity attenuate granulocyte differentiation, we took advantage of the green tea polyphenol epigallocatechin-3-gallate (EGCG) that reduces FASN protein expression. Indeed, similar to knocking down FASN, EGCG treatment of NB4 cells resulted in increased differentiation paralleled by decreased FASN protein levels.We and others demonstrated the importance of autophagy for successful ATRA-induced APL differentiation. Autophagy is an intracellular degradation system that ensures a dynamic recycling of cytoplasmic contents. This process is regulated by the so-called autophagy related genes or ATGs. ATG1, or ULK1, is a key autophagy gene of the initiation complex that is inhibited by mTOR-mediated phosphorylation leading to reduced autophagy activity.FASN expression correlates with mTOR activity in several solid cancers, therefore we hypothesized that FASN activates mTOR resulting in decreased autophagy in AML cells. Indeed, lowering FASN protein expression by either shRNA or EGCG resulted in increased autophagy together with a decreased mTOR-mediated phosphorylation of ULK1.Next, we aimed at understanding how FASN expression is regulated during ATRA treatment. We found a negative correlation between KLF5 and FASN expression in both AML patient cohorts (r=-0.3) and 4 potential KLF binding sites on the FASN promoter, suggesting that KLF5 inhibits FASN transcription.However, since the protein half-life of FASN is around 24 hours, transcriptional inhibition is not sufficient to fully explain the reduced protein levels upon ATRA treatment. We therefore tested if FASN protein itself is degraded via autophagy. Co-treatment of NB4 cells with ATRA and the lysosome inhibitor Bafilomycin A1 led to a dose dependent accumulation of FASN protein suggesting that FASN is an autophagy substrate during ATRA treatment. Furthermore, using mCherry-LC3B expressing NB4 cells, we were able to show FASN and LC3B co-localization by fluorescence microscopy.Finally, we asked whether inhibiting FASN expression levels would increase ATRA sensitivity in non-APL AML cells. To this end, we treated KG-1, OCI-AML2 and MOLM-13 AML cells with EGCG in combination with ATRA. Importantly, combining ATRA with EGCG resulted in increased differentiation of these non-APL cells paralleled by reduced FASN levels, decreased mTOR activity and ULK1 phosphorylation.Together, our data suggest that EGCG treatment is beneficial for differentiation therapy of non-APL AML cells by activating autophagy via degradation of FASN and thereby inactivating mTOR. Furthermore, high FASN expression in AML is likely due to low expression of its positive transcriptional regulator KLF5 and low autophagy activity. DisclosuresNo relevant conflicts of interest to declare.

Dual-functional capability of CD3+CD56+ CIK cells, a T-cell subset that acquires NK function and retains TCR-mediated specific cytotoxicity

AbstractCD3+CD56+ cytokine-induced killer (CIK) cells display a potent cytolytic activity. The adhesion molecule lymphocyte function-associated antigen-1 plays a crucial role in binding as well as in cytolytic activity of CIK cells against tumor target cells expressing the corresponding ligands. CIK cells express activating natural killer (NK) receptors, including NKG2D, DNAX accessory molecule-1 (DNAM-1), and low levels of NKp30. Cell signaling not only through TCR/CD3 but also through NKG2D, DNAM-1, and NKp30 leads to CIK cell activation resulting in granule exocytosis, cytokine secretion, and cytotoxicity. Antibody blocking experiments showed that DNAM-1, NKG2D, and NKp30 are involved in the TCR-independent tumor cell recognition and killing. Anti–CMV-specific CIK cells could be expanded in standard CIK cultures and mediate both specific, MHC-restricted recognition and TCR-independent NK-like cytolytic activity against leukemic cell lines or fresh leukemic blasts. Antibody blocking of lymphocyte function-associated antigen-1 and DNAM-1 led to significant reduction of both CTL and NK-cell functions, whereas blocking of NKG2D and NKp30 only inhibited NK-like cytotoxicity. Their dual-effector function suggests that CIK cells, when used in a clinical setting, may control both neoplastic relapses and viral infections, 2 frequently associated complications in patients who received a transplant.

Rapid and massive expansion of cord blood-derived cytokine-induced killer cells: an innovative proposal for the treatment of leukemia relapse after cord blood transplantation

We have used a standardized 21-day expansion protocol to produce cytokine-induced killer (CIK) cells starting from very small amounts of nucleated cells (approximately 15 x 10(6) cells) isolated from cord blood. Mononuclear cells are stimulated with anti CD3 (OKT3) and IFNgamma and then expanded with IL-2. Moreover, we show that washouts of cord blood units bags (at the end of the infusion) may be sufficient to yield almost 500 x 10(6) CIK by the same expansion protocol. CIK cells show strong cytotoxic activity against a variety of tumor target cell lines including B and T lymphomas and myeloid leukemias. More importantly, expanded cord blood-derived CIK cells are cytotoxic against fresh leukemic blasts and express perforin, granzyme and NKG2D molecule at high levels. The same in vitro protocol has already been used to expand CIK cells from peripheral blood of adult donors under GMP conditions and therefore these observations open up the possibility of imagining a future clinical application of leukemia relapse following cord blood transplantation with CIK cells obtained from the same cord blood unit.

Clinical scale isolation of T cell-depleted CD56+ donor lymphocytes in children.

We present a clinical scale method for immunomagnetic separation of CD56+ donor natural killer cells for adoptive immunotherapy of pediatric leukemias after allogeneic transplantation. This time-saving and partially automated procedure employed CD56+ selection followed by CD3+ depletion, resulting in a median purity of 98.6% NK cells and a four-log depletion of T cells. The enriched NK cells demonstrated high cytotoxic activity against K562 target cells and fresh leukemic blasts with low HLA class I expression, which could be further enhanced by IL-2 stimulation. Lysis of NK-insensitive leukemic cells with high HLA class I expression could also be demonstrated via ADCC. Due to the high degree of T cell depletion, alloreactive proliferation in mixed lymphocyte cultures and response to T cell-specific mitogen stimulation was profoundly decreased. Our results suggest that, even in the case of mismatched donors, infusions of donor NK cells with extremely low T cell content may be a promising treatment option for leukemic minimal residual disease after allogeneic transplantation without risk of inducing severe GVHD.

Effects of single or split exposure of leukemic cells to temozolomide, combined with poly(ADP-ribose) polymerase inhibitors on cell growth, chromosomal aberrations and base excision repair components.

To evaluate the antitumor activity of single versus split exposure of neoplastic cells to temozolomide (TZM) and poly(ADP-ribose) polymerase (PARP) inhibitor. A leukemic Jurkat cell line and freshly isolated leukemic blasts were used. Jurkat cells are resistant to O6-methylguanine damage induced by TZM due to high levels of O6-alkylguanine-DNA alkyltransferase and to a functional defect in the mismatch repair system. Cells were treated with 3-aminobenzamide or with NU1025 to inhibit PARP activity. TZM was added to cell cultures immediately after PARP inhibitors. The concentrations of TZM used were 62.5 microM (corresponding to the peak plasma concentration in patients) or 125 microM. TREATMENT DESIGN: Cells were treated with 125 microM TZM plus PARP inhibitors (single exposure), or twice with 62.5 microM TZM plus PARP inhibitors with an interval of 24 h between treatments (split exposure). Tumor cell growth, clastogenicity and base excision repair gene transcripts or enzymatic activity were evaluated. The split exposure of Jurkat cells to TZM induced more pronounced and persistent growth inhibition and comparable chromosome damage in comparison with the single exposure. In addition, PARP inhibitors potentiated the cytotoxic effects induced by repeated treatment with TZM in fresh leukemic blasts. A marked decrease in X-ray repair cross-complementing 1 transcript and methylpurine glycosylase (MPG) transcript was detected in Jurkat cells subjected to the split exposure. In this case, a significant reduction in the corresponding enzymatic activity was also observed. Cytotoxicity induced by TZM and PARP inhibitors can be improved by a fractionated modality of drug treatment. The reduction in MPG transcript and function would presumably contribute to an increase in cell susceptibility to DNA damage induced by the methylating agent and PARP inhibitors.

Parameters involved in the recognition of fresh human leukemic blasts by tumor-specific cytolytic T cell clones: a model study

Although clinical experience and in vitro data provide evidence of an anti-leukemic activity of T cells, there are few examples of recognition of leukemic cells by tumor-specific T cells in vitro. Tumor antigens encoded by the MAGE genes are useful tools to study this recognition. We tested the sensitivity to recognition and lysis by anti-MAGE CTL clones of MAGE-A1 positive cell lines HL60 and K562, after transfection with an HLA-A1 construct, and of fresh leukemic blasts from 10 HLA-A2 patients, after incubation with a peptide encoded by gene MAGE-A3. The presentation of MAGE antigens by leukemic cell lines and fresh leukemic blasts induced TNF secretion and cytotoxicity by MAGE-specific CD8 + CTL clones. The amount of peptide presented by the leukemic blasts, more than the level of expression of HLA class I, adhesion or costimulatory molecules, was the major limiting factor for recognition. These data indicate that leukemic cells may be targeted by T cells showing specificity for a leukemia antigen.

Expression of cyclin-dependent kinase inhibitor p15 INK4B during normal and leukemic myeloid differentiation

Objective Expression of the cyclin-dependent kinase inhibitor p15 INK4B frequently is altered in myeloid malignancies. We previously demonstrated that p15 INK4B is expressed in normal myeloid cells. The aim of this study was to investigate whether p15 INK4B expression is restricted to the granulomonocytic lineage and to evaluate its modulation during normal and leukemic myeloid differentiation. Materials and Methods Normal CD34 + cells were cultured in serum-free media to obtain granulomonocytic, erythroid, or megakaryocytic unilineage differentiation. NB4 promyelocytic cell line and fresh leukemic blasts from seven patients with acute promyelocytic leukemia were cultured with all-trans retinoic acid. At different times of culture, cell samples were collected to evaluate p15 INK4B by semiquantitative reverse transcriptase polymerase chain reaction. Results p15 INK4B mRNA was found during granulomonocytic and megakaryocytic, but not erythroid, differentiation. In the granulomonocytic lineage, p15 INK4B was detectable when the majority of cells were at the promyelocytic stage and increased progressively in more mature elements. In the megakaryocytic lineage, p15 INK4B was expressed in the early phase of differentiation, before megakaryoblasts had appeared, and was mantained throughout the time of culture. NB4 cell line and five of seven leukemic samples displayed undetectable or very low level of p15 INK4B that rapidly increased during retinoic acid-induced differentiation. Two leukemic samples (both collected from two patients developing all-trans retinoic acid syndrome) showed high basal levels of p15 INK4B, which was not modified by retinoic acid treatment. Conclusions p15 INK4B upregulation occurs specifically during normal granulomonocytic and megakaryocytic commitment. In acute promyelocytic leukemic blasts, p15 INK4B, which is detectable at a very low level, is promptly increased by retinoic acid. In contrast, two acute promyelocytic leukemia samples obtained from patients who developed all-trans retinoic acid syndrome showed high basal levels of p15 INK4B that did not increase further during all-trans retinoic acid-induced differentiation.

Cytidine deaminase - the methodological relevance of AraC deamination for ex vivo experiments using cultured cell lines, fresh leukemic blasts, and normal bone marrow cells.

The clinical effects of cytosine arabinoside (AraC) are highly dependent on schedule and dose. Many regimens administered to patients are derived from artificial model systems involving permanent leukemic cell lines. The differences in pharmacokinetics between the in vivo situation and such cell lines are largely neglected. However, cytidine deaminase activity in particular has a major impact on AraC pharmacokinetics by degrading AraC to its inactive metabolite AraU, and it has been shown to be of prognostic relevance in the treatment of acute myeloid leukemia. This study therefore investigated cytidine deaminase activities and AraC deamination in a variety of the most commonly used leukemic cell lines and fresh blasts and their impact on the results of an in vitro model system. It was found that cells from different cell lines (BLIN, CEM, HL60, K562, RAJI, REH, U937) vary greatly in cytidine deaminase activity (e.g., 1.89 nmol per min/mg in K562 versus 0.01 in BLIN cells) and degrade between 18.5 (BLIN) and 96.5% (REH) of AraC to AraU in the incubation medium. This degradation results in highly different AraC exposures for different cells (e.g., AUC of 960 ng per h/ml in REH versus 4048 ng per h/ml in BLIN cells) in spite of identical starting concentrations of the drug. Formation of AraCTP as the main cytotoxic metabolite of AraC is significantly influenced by the differences in cell type-dependent cytidine deaminase activity (e.g., 35.6 ng/10(7) cells in REH versus 180.2 ng/10(7) cells in BLIN cells). In contrast to permanent cell lines, fresh leukemic blasts and normal bone marrow mononuclear cells featured low AraC degradation in the model system.

Antileukemic action of buthionine sulfoximine: evidence for an intrinsic death mechanism based on oxidative stress.

The glutathione-depleting agent buthionine sulfoximine (BSO) was found to be toxic to some AML blast populations. This toxicity was manifested as the appearance of high levels of reactive oxygen generation in GSH-depleted cells, and later by the loss of mitochondrial membrane potential and an increase in intracellular calcium. Striking heterogeneity in BSO sensitivity was observed in a series of four human AML cell lines, and in fresh leukemic blasts obtained from eight AML patients. In some cases, toxicity was seen at BSO concentrations as low as 1 microM; approximately 100-fold less than the plasma levels achieved in patients treated with BSO as a drug resistance reversing agent. Based on these results we propose that some AML blast populations are unusually dependent on GSH-based antioxidant mechanisms, due to high intrinsic rates of reactive oxygen generation. The mitochondrial respiratory chain is the most likely source of this reactive oxygen. Because toxicity is seen at clinically achievable concentrations of BSO, this agent might have antileukemic activity in patients.

Sensitivity of Acute Leukemia Cells to Cytarabine Is a Correlate of Cellular es Nucleoside Transporter Site Content Measured by Flow Cytometry With SAENTA-Fluorescein

AbstractCytarabine (araC) is converted to araC 5′-triphosphate after entering leukemia cells as a substrate for nucleoside transport processes. This study tested the relationship between araC cytotoxicity, measured in an in vitro tetrazolium dye reduction assay of cell viability, and the cellular abundance of es nucleoside transport elements, assayed by a flow cytometric method that used the es-specific stain, 5-(SAENTA-x8)-fluorescein (5-(Sx8)-F), in cultured leukemia cells and in myeloblasts and lymphoblasts (blasts) from leukemia patients. Cellular es site abundance (Bmax value for 5-(Sx8)-F binding) varied sixfold among nine leukemic myeloblast samples from patients. In cultured OCI/AML-2 myeloblasts and CCRF-CEM T-lymphoblasts, and in fresh leukemic blasts, es sites were fractionally blocked by treatment with graded concentrations of nitrobenzylthioinosine (NBMPR), an inhibitory es site ligand, to simulate the variation in es expression found in leukemic blasts from patients with acute myeloid leukemia. When the cytotoxicity of a single concentration of araC was determined in NBMPR-treated leukemia cells, cell kill correlated closely with the intensity of 5-(Sx8)-F fluorescence (r = .92 to .99), a measure of the cell surface abundance of functional es nucleoside transporter sites. Concentrations of NBMPR that achieved half-maximal reduction (4.3 to 12 nmol/L) of cellular 5-(Sx8)-F fluorescence (measured by flow cytometry) approximated IC50 values (1 to 10 nmol/L) previously found for inhibition by NBMPR of es-mediated nucleoside fluxes in several cell types, supporting the view that 5-(Sx8)-F interacted with the es transporter. The correlation of araC cytotoxicity and the Bmax for 5-(Sx8)-F binding to es sites in cultured leukemia cells and in leukemic blasts from acute leukemia patients (r = .95) suggests that the flow cytometry assay of es capacity may be useful in predicting clinical response to araC.

Sensitivity of Acute Leukemia Cells to Cytarabine Is a Correlate of Cellular es Nucleoside Transporter Site Content Measured by Flow Cytometry With SAENTA-Fluorescein

Cytarabine (araC) is converted to araC 5′-triphosphate after entering leukemia cells as a substrate for nucleoside transport processes. This study tested the relationship between araC cytotoxicity, measured in an in vitro tetrazolium dye reduction assay of cell viability, and the cellular abundance of es nucleoside transport elements, assayed by a flow cytometric method that used the es-specific stain, 5-(SAENTA-x8)-fluorescein (5-(Sx8)-F), in cultured leukemia cells and in myeloblasts and lymphoblasts (blasts) from leukemia patients. Cellular es site abundance (Bmax value for 5-(Sx8)-F binding) varied sixfold among nine leukemic myeloblast samples from patients. In cultured OCI/AML-2 myeloblasts and CCRF-CEM T-lymphoblasts, and in fresh leukemic blasts, es sites were fractionally blocked by treatment with graded concentrations of nitrobenzylthioinosine (NBMPR), an inhibitory es site ligand, to simulate the variation in es expression found in leukemic blasts from patients with acute myeloid leukemia. When the cytotoxicity of a single concentration of araC was determined in NBMPR-treated leukemia cells, cell kill correlated closely with the intensity of 5-(Sx8)-F fluorescence (r = .92 to .99), a measure of the cell surface abundance of functional es nucleoside transporter sites. Concentrations of NBMPR that achieved half-maximal reduction (4.3 to 12 nmol/L) of cellular 5-(Sx8)-F fluorescence (measured by flow cytometry) approximated IC50 values (1 to 10 nmol/L) previously found for inhibition by NBMPR of es-mediated nucleoside fluxes in several cell types, supporting the view that 5-(Sx8)-F interacted with the es transporter. The correlation of araC cytotoxicity and the Bmax for 5-(Sx8)-F binding to es sites in cultured leukemia cells and in leukemic blasts from acute leukemia patients (r = .95) suggests that the flow cytometry assay of es capacity may be useful in predicting clinical response to araC.

Vascular Endothelial Growth Factor, a Possible Paracrine Growth Factor in Human Acute Myeloid Leukemia

AbstractVascular endothelial growth factor (VEGF ) is a multifunctional cytokine involved in angiogenesis, inflammation, and wound healing. It is secreted by a variety of tumor cell lines, including hematopoietic lines. Therefore, we investigated expression of VEGF and its receptors on fresh leukemic blasts. VEGF-specific transcripts were detected by polymerase chain reaction (PCR) in 20 of 28 patients with de novo acute myeloid leukemia (AML) and in 3 of 5 patients with secondary AML. Using immunocytochemistry, we found VEGF protein in 2 leukemic cell lines and in 8 AML patients, in concordance with PCR results. Supernatants of fresh leukemic cells from 24 AML patients contained significantly more VEGF than supernatants from bone marrow cells of 9 normal donors or of CD34-enriched cells from 3 normal volunteer donors as determined by an enzyme-linked immunosorbent assay. VEGF possesses two high-affinity receptors, KDR and FLT1. Using a sensitive nested PCR assay, we detected expression of FLT1 in 10 of 20 patients with de novo AML and 3 of 5 patients with secondary AML. KDR was expressed in 4 of 22 patients with de novo AML and 1 of 4 with secondary AML. To study possible paracrine growth stimulation of AML blasts, endothelial cells from human umbilical cords were incubated with increasing concentrations of VEGF. A dose-dependent increase of granulocyte-macrophage colony-stimulating factor secretion from endothelial cells was identified.

Differentiation induction in non-lymphocytic leukemia cells upon treatment with mizoribine.

Inosine-5'-monophosphate (IMP) dehydrogenase catalyzes the rate-limiting reaction of guanine nucleotide biosynthesis and has been implicated in the reaction of cell growth and differentiation. We examined the ability of mizoribine, an IMP dehydrogenase inhibitor, to induce differentiation in HL-60 and U937 cells as well as in fresh leukemic blast cells from patients with non-lymphocytic leukemia. Treatment with mizoribine reduced intracellular GTP levels and induced morphologic and functional differentiation in these two cell lines in a dose-dependent manner. HL-60 and U937 cells developed polymorphic nuclei and macrophage-like cytoplasm, respectively, as well as expression of CD11b and CD14 antigens and the ability to oxidize NBT. These changes became evident when intracellular GTP levels decreased to approximately 30% of untreated controls and were abrogated by addition of guanosine to the media. However, in fresh leukemic cells, the cells showing maturation in response to mizoribine were limited in those derived from two of ten patients having non-lymphocytic leukemia. These findings suggest mizoribine could induce differentiation in HL-60 and U937 cells through a decrease of intracellular GTP levels. Further study is required to determine its clinical use in patients with acute non-lymphocytic leukemia.

Antibody-independent phagocytosis of tumor cells by human monocyte-derived macrophages cultured in recombinant macrophage colony-stimulating factor.

Human monocytes exposed in vitro to recombinant macrophage-colony-stimulating factor (rhMCSF) differentiate into monocyte-derived macrophages (MDM), which mediate efficient antibody-dependent cytotoxicity (ADCC) against tumor cells. We and others have shown that this form of ADCC is unusual in that phagocytosis, rather than extracellular lysis, appears to play the major role in target cell killing. In this study, we asked whether the phagocytic form of cytotoxicity seen with ADCC could occur in the absence of an opsonizing antibody. We now report that, whereas cell lines derived from solid tumors are often resistant to antibody-independent cytotoxicity, malignant cells of lymphoid origin appear particularly susceptible to such antibody-independent killing. We found that all of nine lymphocytic leukemia and lymphoma cell lines tested in a total of 35 experiments, plus all four samples of fresh leukemic blasts, were consistently susceptible to antibody-independent MDM cytotoxicity. Antibody-independent cytotoxicity against these cells was efficient (40%-63% killing) at effector: target (E:T) ratios as low as 2:1. Like ADCC, antibody-independent cytotoxicity involved phagocytosis of target cells, as demonstrated by ingestion of fluorescently labeled targets and analysis by flow cytometry. At the time of phagocytosis, the majority of target cells retained membrane integrity, as indicated by the direct transfer of intracellular [51Cr]chromate from radiolabeled targets to phagocytosing MDM, without release of the label into the medium. However, in contrast to ADCC, we found that the degree of antibody-independent cytotoxicity was not a function of the E:T ratio. Instead, a constant proportion of the available target cells were killed regardless of the E:T ratio, suggesting that target cell recognition, rather than effector cell potency, might be the limiting factor in determining cytotoxicity. In additional experiments, we have also identified a second tumor cell type, nueroblastoma, as being susceptible to antibody-independent phagocytosis (all of five cell lines tested, cytotoxicity 40%-93%, E:T = 3:1). Our data thus indicate that the cytotoxicity induced by rhMCSF is not confined to antibody-mediated killing, and that phagocytosis can play a significant role in target cell destruction even in the absence of opsonizing antibody.

Flow cytometric study of idarubicin and daunorubicin accumulation and the effect of verapamil in leukemic cell lines and fresh cells from patients with acute non-lymphoblastic leukemia

By using flow cytometry, the intracellular accumulation (Acc) of idarubicin (IDA) and daunorubicin (DNR) and the effect of verapamil (VRP) on both anthracycline accumulation (VRP) index) were studied in leukemic cell lines (K562 and HL60 and their two DNR-resistant subclones) and fresh leukemic cells. IDA accumulated more than DNR in both parental (K562: p < 0.03 and HL60: 0.09) and resistant cell lines ( p < 0.01 for both cell lines) irrespective of whether or not they were treated with VRP. VRP index was higher for DNR than for IDA ( p < 0.05). Similar results were observed in fresh leukemic blasts from 25 patients with ANLL (IDA Acc superior to DNR Acc: p < 0.0001; higher VRP index for DNR than for IDA: p < 0.01). The higher Acc of IDA than DNR seen in fresh leukemic cells could explain the better clinical efficacy of IDA reported in patients with ANLL.

Effects of human stem cell factor (c-kit ligand) on proliferation of myeloid leukemia cells: heterogeneity in response and synergy with other hematopoietic growth factors

A novel hematopoietic growth factor, the stem cell factor (SCF), for primitive hematopoietic progenitor cells has recently been purified and its gene has been cloned. In this study we tested the mitogenic activity of recombinant human SCF on myeloid leukemia cells as well as the expression of its receptor. We have investigated the proliferation of 31 myeloid leukemia cell lines as well as fresh myeloid leukemic blasts from 17 patients in a 72-hour 3H-thymidine uptake assay in the presence of various concentrations of recombinant human (rh) SCF alone or in combination with saturating concentrations of granulocyte- macrophage colony-stimulating factor (GM-CSF), G-CSF, M-CSF, interleukin-3 (IL-3), or erythropoietin (EPO). Only five of 31 lines, but fresh leukemic blasts from 12 of 17 patients with acute myeloid leukemia (AML), significantly responded to SCF. The responding cell lines were of the acute promyelocytic, chronic myeloid, megakaryoblastic, and erythroleukemia origin, the responding blast preparations of all French-American-British subtypes. Synergistic activities of SCF were found with G-CSF, GM-CSF, EPO, and IL-3. To determine the SCF binding sites on leukemic cells, we used 125I- radiolabeled SCF in Scatchard analysis and cross-linking studies. The leukemic cell lines responding to SCF expressed from 2,300 up to 29,000 binding sites per cell. The SCF receptor expression was downregulated in vitro by the presence of its ligand. Cross-linking studies demonstrated a 150-Kd SCF receptor on the surface of all responding myeloid leukemias. This study suggests that SCF may be an important factor for the growth of myeloid leukemia cells, either as a direct stimulus or as a synergistic factor for other cytokines. Furthermore, using polymerase chain reaction analysis of total RNA from the myeloid leukemia lines, we found expression of SCF-mRNA in 17 of 30 lines, suggesting autocrine mechanisms in the growth of a subgroup of leukemic cells by coexpression of SCF and its receptor.

Effects of Human Stem Cell Factor ( c-kit ligand ) on Proliferation of Myeloid Leukemia Cells: Heterogeneity in Response and Synergy With Other Hematopoietic Growth Factors

A novel hematopoietic growth factor, the stem cell factor (SCF), for primitive hematopoietic progenitor cells has recently been purified and its gene has been cloned. In this study we tested the mitogenic activity of recombinant human SCF on myeloid leukemia cells as well as the expression of its receptor. We have investigated the proliferation of 31 myeloid leukemia cell lines as well as fresh myeloid leukemic blasts from 17 patients in a 72-hour 3H-thymidine uptake assay in the presence of various concentrations of recombinant human (rh) SCF alone or in combination with saturating concentrations of granulocyte-macrophage colony-stimulating factor (GM-CSF), G-CSF, M-CSF, interleukin-3 (IL-3), or erythropoietin (EPO). Only five of 31 lines, but fresh leukemic blasts from 12 of 17 patients with acute myeloid leukemia (AML), significantly responded to SCF. The responding cell lines were of the acute promyelocytic, chronic myeloid, megakaryoblastic, and erythroleukemia origin, the responding blast preparations of all French-American-British subtypes. Synergistic activities of SCF were found with G-CSF, GM-CSF, EPO, and IL-3. To determine the SCF binding sites on leukemic cells, we used 125I-radiolabeled SCF in Scatchard analysis and cross-linking studies. The leukemic cell lines responding to SCF expressed from 2,300 up to 29,000 binding sites per cell. The SCF receptor expression was downregulated in vitro by the presence of its ligand. Cross-linking studies demonstrated a 150-Kd SCF receptor on the surface of all responding myeloid leukemias. This study suggests that SCF may be an important factor for the growth of myeloid leukemia cells, either as a direct stimulus or as a synergistic factor for other cytokines. Furthermore, using polymerase chain reaction analysis of total RNA from the myeloid leukemia lines, we found expression of SCF-mRNA in 17 of 30 lines, suggesting autocrine mechanisms in the growth of a subgroup of leukemic cells by coexpression of SCF and its receptor.

A gamma delta+ T-cell leukemia bearing a novel t(8;14)(q24;q11) translocation demonstrates spontaneous in vitro natural killer-like activity

A highly malignant human T-cell leukemia was identified by cell surface analysis as a member of the T-cell receptor (TCR) gamma delta lineage. Cytogenetic and molecular analysis showed a novel t(8;14)(q24;q11) rearrangement involving the J delta 1 gene segment on chromosome 14 and the distal end of chromosome 8 near the c-myc proto-oncogene locus. The gamma delta TCR of the leukemia blasts was functionally intact and could be activated to generate intracellular calcium flux and to target Fc receptor-mediated redirected tumor cell lysis. In addition, non-major histocompatibility complex restricted lysis of a limited target cell panel was shown by fresh leukemic blasts and by the in vitro-maintained leukemia cells that was comparable to known T-cell lines with natural killer-like activity. These data suggest that the T-cell leukemia potentially had in vivo functional cytolytic activity. However, whether this activity did contribute to the patient's clinical condition could not be determined.

A γδ+ T-Cell Leukemia Bearing a Novel t(8;14)(q24;q11) Translocation Demonstrates Spontaneous In Vitro Natural Killer-Like Activity

Abstract A highly malignant human T-cell leukemia was identified by cell surface analysis as a member of the T-cell receptor (TCR) gamma delta lineage. Cytogenetic and molecular analysis showed a novel t(8;14)(q24;q11) rearrangement involving the J delta 1 gene segment on chromosome 14 and the distal end of chromosome 8 near the c-myc proto-oncogene locus. The gamma delta TCR of the leukemia blasts was functionally intact and could be activated to generate intracellular calcium flux and to target Fc receptor-mediated redirected tumor cell lysis. In addition, non- major histocompatibility complex restricted lysis of a limited target cell panel was shown by fresh leukemic blasts and by the in vitro- maintained leukemia cells that was comparable to known T-cell lines with natural killer-like activity. These data suggest that the T-cell leukemia potentially had in vivo functional cytolytic activity. However, whether this activity did contribute to the patient's clinical condition could not be determined.