Characterization of myeloid leukemias with monoclonal antibodies 3C5 and MY9

Alterations in the bone marrow microenvironment may elicit defective hematopoiesis: a comparison of aplastic anemia, chronic myeloid leukemia, and normal bone marrow

Hematopoiesis involves complex interactions between hematopoietic cells and the bone marrow (BM) microenvironment. The specific causes and mechanisms underlying dysregulated hematopoiesis are unknown. Here, BM biopsy specimens from patients with aplastic anemia (AA) and chronic myeloid leukemia (CML) and normal marrow were analyzed by semiquantitative immunohistochemistry to determine changes in the hematopoietic stem cell (HSC) compartment and BM microenvironment. HSC levels were lowest in AA and highest in CML. T and B lymphocytes were decreased in AA (p < 0.01) and CML (p < 0.01). Natural killer cells were observed in AA, but were absent in CML and healthy controls (p < 0.01). Macrophages and mast cells were absent in CML. There were significant differences between AA and CML stromal cell components. No nestin⁺ cells were observed in CML and the mean number of stromal cell-derived factor-1-positive cells was lowest in CML. Osteopontin⁺ cells were higher in AA than in CML (p < 0.01); osteonectin⁺ cells were higher in CML than in AA (p < 0.01). There was no significant difference in the expression of osteocalcin between AA and CML. The number of endothelial cells was highest in CML and lowest in AA (p < 0.01). Our findings suggest that changes in BM microenvironment components might be related to defective hematopoiesis leading to AA and/or CML.

Immunotherapy targets in pediatric cancer

Immunotherapy for cancer has shown increasing success and there is ample evidence to expect that progress gleaned in immune targeting of adult cancers can be translated to pediatric oncology. This manuscript reviews principles that guide selection of targets for immunotherapy of cancer, emphasizing the similarities and distinctions between oncogene-inhibition targets and immune targets. It follows with a detailed review of molecules expressed by pediatric tumors that are already under study as immune targets or are good candidates for future studies of immune targeting. Distinctions are made between cell surface antigens that can be targeted in an MHC independent manner using antibodies, antibody derivatives, or chimeric antigen receptors versus intracellular antigens which must be targeted with MHC restricted T cell therapies. Among the most advanced immune targets for childhood cancer are CD19 and CD22 on hematologic malignancies, GD2 on solid tumors, and NY-ESO-1 expressed by a majority of synovial sarcomas, but several other molecules reviewed here also have properties which suggest that they too could serve as effective targets for immunotherapy of childhood cancer.

Expression of an anti-CD33 single-chain antibody by Pichia pastoris

CD33 is a cell surface glycoprotein expressed on cells of myelomonocytic lineage, leukaemic cells, but not haematopoietic stem cells. By virtue of its expression pattern, CD33 has become a popular target for new immunotherapeutic approaches to treat acute myeloid leukaemia. The methylotrophic yeast Pichia pastoris strain KM71H was used to produce an anti-CD33 single chain variable fragment (scFv), with the intention of conjugation to a radioisotope, for therapeutic use. To direct secreted expression of the anti-CD33-scFv the alpha-mating factor secretory signal sequence (alpha-MF) was used, with constructs containing a complete (CS) and incomplete (INCS) cleavage site to accommodate the potential outcomes of dibasic endopeptidase, Kex2, and dipeptidyl amino peptidase, Ste13, processing. The anti-CD33-scFv was expressed in BMMY cultures using both constructs, with a final yield of 48 mg/l (CS) and 11 mg/l (INCS). N-terminal sequencing showed that the CS-scFv had not been cleaved by Ste13, leaving amino acids EAEA at the N-terminus. The INCS-scFv construct produced a mixture of 50% authentic scFv and 50% with 11 amino acids from the alpha-MF remaining at the N-terminus. Despite the aberrations in alpha-MF processing, the anti-CD33-scFv's produced from both constructs were found to be functional. Flow cytometry and Biacore analysis demonstrated binding to target antigen CD33 on the surface of human leukaemic cell line HL-60, and to recombinant soluble CD33 respectively.

Identification of the CD33-related Siglec receptor, Siglec-5 (CD170), as a useful marker in both normal myelopoiesis and acute myeloid leukaemias

Sialic acid-binding immunoglobulin-like lectin (Siglec)-5 or CD170 is a CD33-related receptor, containing cytoplasmic immune receptor-based tyrosine signalling motifs, that has previously been reported to be myeloid-specific like CD33 and thus may be useful in the characterization of both normal and malignant haemopoiesis. This study showed that Siglec-5 had a distinct expression pattern to CD33 both on normal myeloid cells and in acute myeloid leukaemia (AML). In normal bone marrow and cord blood, myeloid cells predominantly expressed Siglec-5 at the later stages of granulocytic differentiation. Siglec-5 was not expressed at significant levels by CD34+ progenitors either from bone marrow or mobilized peripheral blood. During in vitro myeloid differentiation of cord blood purified CD34+ cells, Siglec-5 was upregulated later than CD33. Siglec-5 expression remained absent or very low on cultured CD34+ cells, unlike CD33, which was present on almost all CD34+ cells by day 4. However, analysis of blasts from 23 patients with AML revealed aberrant expression of Siglec-5 with CD34 in 50% (seven of 14) of patients with CD34+ AML; 61% (14 of 23) of AML cases were positive for Siglec-5 with an increased frequency in the French-American-British subtypes M3-5 (80%) compared with M0-2 (25%). All 13 acute lymphoblastic leukaemic (ALL) samples tested, including a CD33+ ALL, were Siglec-5 negative. These results support the further evaluation of Siglec-5 antibodies in the diagnosis and monitoring of AML.

Immunoblot analysis of CD34 expression in histologically diverse neoplasms

CD34 is a heavily glycosylated transmembrane protein of approximately 110 kd whose function is essentially uncharacterized. First identified in a myeloid leukemia cell line, immunohistological reactivity with anti-CD34 antibodies is also encountered in a histologically diverse subset of nonhematolymphoid neoplasms including angiosarcoma, solitary fibrous tumors, epithelioid sarcomas, spindle cell lipomas, dermatofibrosarcoma protuberans, and myofibroblastomas. Immunohistological reactivity for CD34 in hematopoietic stem cells and endothelial cells has been shown to correspond to the expression of the CD34 protein. With the exception of gastrointestinal stromal tumors, CD34 protein expression has not been investigated in other CD34 immunohistologically reactive nonhematolymphoid neoplasms. We undertook this study to examine whether the observed reactivity for anti-CD34 antibodies in apparently unrelated tumors is due to the expression of the same protein or whether shared epitopes elaborated by other proteins could account for this reactivity. Immunoblot analyses with anti-CD34 antibodies of six different CD34 immunohistologically reactive lesions show the same approximately 110-kd molecular weight protein. In addition, two cases of dermatofibrosarcoma protuberans show double bands at approximately 110 kd. Laser-capture microdissection of CD34 immunohistologically reactive epithelioid sarcoma and nonreactive epidermal cells illustrates that this reactivity is specific to tumor cells. These results show that the observed immunohistological reactivity with anti-CD34 antibodies is due to the expression of the CD34 protein and not to shared epitopes on unrelated proteins.

The myeloid-specific sialic acid-binding receptor, CD33, associates with the protein-tyrosine phosphatases, SHP-1 and SHP-2

The myeloid restricted membrane glycoprotein, CD33, is a member of the recently characterized "sialic acid-binding immunoglobulin-related lectin" family. Although CD33 can mediate sialic acid-dependent cell interactions as a recombinant protein, its function in myeloid cells has yet to be determined. Since CD33 contains two potential immunoreceptor tyrosine-based inhibition motifs in its cytoplasmic tail, we investigated whether it might act as a signaling receptor in myeloid cells. Tyrosine phosphorylation of CD33 in myeloid cell lines was stimulated by cell surface cross-linking or by pervanadate, and inhibited by PP2, a specific inhibitor of Src family tyrosine kinases. Phosphorylated CD33 recruited both the protein-tyrosine phosphatases, SHP-1 and SHP-2. CD33 was dephosphorylated in vitro by the co-immunoprecipitated tyrosine phosphatases, suggesting that it might also be an in vivo substrate. The first CD33 phosphotyrosine motif is dominant in CD33-SHP-1/SHP-2 interactions, since mutating tyrosine 340 in a CD33-cytoplasmic tail fusion protein significantly reduced binding to SHP-1 and SHP-2 in THP-1 lysates, while mutation of tyrosine 358 had no effect. Furthermore, the NH2-terminal Src homology 2 domain of SHP-1 and SHP-2, believed to be essential for phosphatase activation, selectively bound a CD33 phosphopeptide containing tyrosine 340 but not one containing tyrosine 358. Finally, mutation of tyrosine 340 increased red blood cell binding by CD33 expressed in COS cells. Hence, CD33 signaling through selective recruitment of SHP-1/SHP-2 may modulate its ligand(s) binding activity.

Molecular cloning and functional analysis of the CD33 promoter

CD33 is a leucocyte differentiation antigen restricted to myeloid cells in blood and bone marrow. Two mRNA transcripts encoding CD33 are observed in leukaemic cell lines. The smaller transcript of 1.5 kb is comparable in size to the isolated CD33 cDNA but the origin of the larger 1.8 kb transcript is unknown. To study the regulation of human CD33 expression, a 5' genomic clone from the CD33 gene was isolated and studied for promoter activity. The clone, although lacking a TATAA box, exhibits other sequences characteristic of a promoter. Two transcriptional start sites were identified, 414 and 527 nucleotides 5' of the ATG initiation codon, suggesting that these sites are used to generate the 1.8 kb transcript observed in CD33+ cell lines. The CD33 genomic sequence directed high expression of a luciferase reporter gene in myeloid cell lines. Using deletion mutants of the promoter sequence, maximal expression was localized to the first 220 bp 5' of the ATG initiation codon. Site-directed mutagenesis of an Sp-1 and PU.1 binding site within this region showed that the PU.1, but not Sp-1, was critical for CD33 expression in myeloid lines. Given the restricted expression of CD33 on haemopoietic cells, the identification of the CD33 promoter may be useful for the study of transcription factors that regulate gene expression during early myeloid differentiation.

The diagnostic and prognostic value of immunophenotyping in acute leukemia

Immunophenotyping with monoclonal antibodies to leucocyte differentiation antigens has an established diagnostic role in the laboratory investigation of acute leukemia. In the vast majority of cases, a hemopoietic lineage can be confidently assigned; namely, acute myeloid leukemia (AML), or the precursor-B and precursor-T variants of acute lymphoblastic leukemia (ALL). The areas of greatest practical importance are in morphologically difficult or undifferentiated cases, and in distinguishing between the major variants of precursor-B and T-ALL. Cases with aberrant patterns of marker expression (acute mixed lineage leukemia, lineage infidelity) are frequently encountered in both ALL and AML, and can lead to diagnostic confusion. However, correlation with morphology and other clinicopathologic features, and careful consideration of the weight of phenotyping evidence almost always allows the correct lineage to be identified. The prognostic value of phenotypic information in acute leukemia is generally limited. Recognition of the major variants of ALL is still of clinical importance, but the significance of myeloid antigen positivity in ALL is controversial, and may not have prognostic value. Patterns of myeloid antigen expression in AML have limited prognostic significance, while the relationship between lymphoid antigen expression and treatment response in AML remains highly controversial. Careful evaluation of the predictive power of immunophenotype in large controlled clinical trials in acute leukemia is still required.

Expression of an early myelopoietic antigen (CD33) on a subset of human umbilical cord blood-derived natural killer cells

A new subset of natural killer (NK) cells was identified in human umbilical cord blood. This subset of CD56+/CD3- NK cells co-expressed the CD33 antigen, which is present on early hematopoietic progenitors confined to the myeloid lineage. The percentage of the CD56+/CD33+ cells among the CD56+/CD3- NK cells was 7.9 +/- 6.6% (n = 27) with a range of 1.4-25.5% and a considerable individual variability. Additionally, the majority of freshly isolated CD56+/CD33+ cells co-expressed the CD2 and CD7 antigen, a minor proportion co-expressed the CD8 antigen but essentially all of the cells stained negative for CD16 and CD57. Morphological analysis of the CD56+/CD33+ cells showed the features of large agranular lymphocytes. From some of the samples, the CD56+/CD33+ NK cells were cultivated and expanded in vitro by incubation of the cells with interleukin 2 (IL-2) for up to 50 days. Morphological analysis of the cultured CD56+/CD33+ cells showed the features of large granular lymphocytes (LGL). The IL-2-expanded CD56+/CD33+ NK cells showed only a low cytolytic activity against K562 target cells, whereas most of the NK activity of the expanded cells was contributed by the CD56+/CD33- NK cells.

Comparison of two methods for concentrating CD34+ cells from patients with acute non-lymphocytic leukemia

The aim of the present study was to compare two different methods for obtaining CD34+ cells from the peripheral blood or the bone marrow of patients with acute non-lymphocytic leukemia (ANLL). Twenty-two samples, obtained from 19 patients, were density cut (Ficoll-Hypaque 1.077) and, after incubation with My10 antibody, separated by panning or by immunomagnetic beads. Immunomagnetic beads provided a significantly better separation than panning, either in terms of concentration of CD34+ cells (85.5 +/- 11.6% vs. 55.7 +/- 25.0%, p = 0.003) or in terms of depletion of CD34+ cells (3.9 +/- 8.0% vs. 30.9 +/- 26.3%, p = 0.008). This was consistent with the virtually complete depletion of colony forming cells (CFC) in the CD34 negative fraction and the recovery of virtually all the CFC in the positive fraction in the samples separated by immunomagnetic beads. In conclusion, separation by immunomagnetic beads can allow collection of nearly pure CD34+ and CD34- cell populations from patients with ANLL, thereby facilitating the study of the biological characteristics of these cell populations. Moreover the method is less time consuming than panning and is not toxic to the CFC.

Anti-CD34 immunoperoxidase staining in paraffin sections of acute leukemia: Comparison with flow cytometric immunophenotyping

Anti-CD34 is a monoclonal antibody that reacts with bone marrow progenitor cells and leukemic blasts, and is expressed on 30% to 50% of all acute leukemias. Detection of CD34 has previously been restricted to flow cytometric studies. To expand the utility of CD34, we immunostained 46 paraffin-embedded bone marrow specimens with acute leukemia; results were compared with flow cytometric studies. CD34 reactivity was also evaluated in nine chronic leukemia cases, 27 malignant lymphoma cases (Hodgkin's disease and non-Hodgkin's lymphoma), six normal bone marrow specimens, and three benign, hyperplastic lymph node specimens. All cases that were CD34 positive by flow cytometry (11 of 19 B-cell precursor acute lymphoblastic leukemia cases, one of six T-cell acute lymphoblastic leukemia cases, and seven of 21 acute myeloblastic leukemia cases) were also CD34 positive in paraffin sections. Both cell membrane and cytoplasmic staining was seen. The positivity percentage and fluorescence intensity by flow cytometry correlated with the estimated number of stained cells and the intensity of immunoperoxidase staining in 18 of 19 CD34-positive cases. The remaining bone marrow and lymph node cases studied were CD34 negative; prominent endothelial cell staining, however, was noted. This is the first report of anti-CD34 staining of acute leukemia in paraffin-embedded sections. In contrast to other monoclonal antibodies reactive in bone marrow paraffin sections with leukemia, anti-CD34 immunoperoxidase staining is limited to leukemic blasts and may provide useful diagnostic information when flow cytometric studies are not available.

Isolation and characterization of the CD34+ hematopoietic progenitor cells from the peripheral blood of patients with chronic myeloid leukemia

A modified version of the original reported panning technique was used to separate CD34+ cells from the peripheral blood of patients with chronic myeloid leukemia (CML). In 13 out of 23 separations, populations of cells were obtained in which CD34+ cells constituted greater than 50% of the cells present. The best recovery and enrichment of the CD34+ cells was achieved when cells were obtained from patients in the accelerated phase of CML, when the cells were processed on the same day they were obtained from patients, and when adherence to soybean agglutinin flasks was used as a pre-enrichment step. In suspension culture, the CD34+ cells were capable of extensive proliferation and differentiation. In semi-solid culture, the number of colony-forming units (CFUs) directly correlated with CD34 positivity. The number of clonogenic cells/CD34+ cells was highest at the time of initial diagnosis of CML, fell during the chronic phase (CP) of the disease, and rose at the time of disease acceleration. This observation suggests that therapy during the CP of the disease produces a greater reduction in clonogenic cells than in the number of CD34+ cells. This effect disappears at the time of disease acceleration, presumably because of the development of drug resistance in the clonogenic cells.

Expression of hematopoietic progenitor cell associated antigen CD34 in chronic myeloid leukemia

The expression of progenitor cell associated antigen CD34 was investigated in cells from 28 patients with chronic myeloid leukemia (CML). The CD34 positivity varied from 0-26% in patients with chronic phases CML (n = 17); from 6-64% in patients with accelerated phase CML (n = 4); and from 27-97% in the patients with blastic crisis of CML (n = 8). The difference in CD34 positivity between chronic (mean 10.1 +/- 2.3%), accelerated (37.7 +/- 13.3%) and blastic (58.0 +/- 7.3%) phases of CML is statistically significant (p less than 0.05), however, the number of patients studied, especially in accelerated and blastic phases is very small. There was no difference in the CD34 positivity of the cells in the peripheral blood and in the bone marrow. CD34 positivity was higher in patients with chronic phase CML at diagnosis (untreated patients) than in those who were studied during treatment. The possible importance of serially studying CD34 positivity in patients with CML is discussed in the paper.

Clinicopathological features of acute undifferentiated leukaemia with a stem cell phenotype

Over a 4 1/2-year period, 141 patients with acute leukaemia had morphologic, immunophenotypic and cytochemical studies performed at King's College Hospital. Seven cases were noted to have blast cells which did not express myeloid or lymphoid antigens or cytochemical staining indicative of differentiation but were HLA DR and CD 34 positive. Based on these criteria we have used the term stem cell acute leukaemia to denote these patients. There were five women and two men with a median age of 61 years (16-86). Presentation marrows were heavily infiltrated with blasts (greater than 95% in 6/7) which were usually pleomorphic. Type 2 blasts. Auer rods and dysplastic features were absent. Two of six cases studied showed clonal karyotypic abnormalities. Four patients were treated with high dose chemotherapy. Three of these achieved a complete remission but relapsed at 3, 6 and 7 months respectively. The median survival of the group was 7 months (2-12). We conclude that the stem cell acute leukaemias are a distinct clinicomorphological group which appear to have a poor prognosis with conventional chemotherapy.

Immunophenotype of blast cells in acute myelofibrosis

The immunophenotype of peripheral blood blast cells from six patients with acute myelofibrosis was studied using a panel of monoclonal antibodies directed against granulocytic, erythroid, megakaryocytic and lymphoid antigenic determinants. In all patients most of the blast cells were labeled with anti-HLA-DR and with the early myelomonocytic antibodies My7 (CD13), My9 (CD33) and B1-3C5 (CD34) (3/3). In three cases, platelet antibodies Edu3 (CD41) and GPIIIa (CD61) reacted with about 30% of blast cells. TdT was positive in two out of six samples studied. Lymphoid markers T3 (CD3), Leu9 (CD7), J5 (CD10), B4 (CD19) and B1 (CD20) were negative in all cases. These results suggest that blast cells are mainly of immature myelocytic origin. However, the coexistence of megakaryoblasts cannot be ruled out in the cases with a proportion of cells that are positive with Edu3 and GPIIIa antibodies.

Production and characterization of monoclonal antibodies to human myeloperoxidase

Monoclonal antibodies (mAbs) against human myeloperoxidase (MPO) have been derived for immunopurifying MPO and immunophenotyping acute leukemias. Eight antibodies were obtained from a fusion of the P3 plasmacytoma cell line with splenic lymphocytes from mice immunized with purified human MPO. Hybridoma supernatant culture fluids were screened for antibody to MPO by an enzyme-linked immunosorbent assay. The specificity of the mAbs was characterized by immunoblotting, immunoprecipitation, and reactivity against various hematopoietic cells, cell lines, and leukemic blast cells. The eight mAbs generated were of the IgG1 isotype. One of these mAbs was successfully used to develop a one-step immunoaffinity chromatographic purification procedure for MPO. Immunoblotting and immunoprecipitation experiments suggested that the eight mAbs were reactive with at least three antigenic determinants on the MPO molecule. Immunofluorescent studies showed that these mAbs reacted specifically with cells of granulocytic-monocytic lineage and were negative with lymphoid cells. Our results suggest that these mAbs should be useful reagents for immunophenotyping hematopoietic cells.

Expression of haematopoietic progenitor cell-associated antigen BI-3C5/CD34 in leukemia

The expression of progenitor cell-associated antigen CD34, defined with monoclonal antibody BI-3C5, was investigated in cells from 109 patients with leukaemia. No reactivity was found in chronic leukaemias, whereas 31% of acute myelogenous leukaemia (AML) and most non-T, non-B acute lymphoblastic leukaemia (ALL) expressed CD34. Examples of BI-3C5+ AML included M1 and M2 FAB types only; all but one were myeloperoxidase positive. In combination with pan-myeloid markers, BI-3C5 is useful for identification of immature myeloid cells.

Terminal deoxynucleotidyl transferase positive acute myeloid leukaemia: an association with immature myeloblastic leukaemia

The morphology, membrane markers and ultrastructural cytochemistry of 39 cases of acute myeloid leukaemia (AML) with variable proportion (10-99%) of terminal deoxynucleotidyl transferase (TdT) positive blasts was compared with that of 134 cases of TdT negative AML. The incidence of TdT positive AML was 22.5% and this was significantly higher in poorly differentiated myeloblastic (M0 and M1) types (54%) than in all other FAB subtypes (10%; P less than 0.001). Our findings suggest heterogeneity among TdT positive cases. Whilst the majority correspond to genuine TdT positive AML in which evidence for exclusive myeloid nature was demonstrated by phenotypic, cytochemical and ultrastructural markers, a distinct minority (22%) of cases had mixtures of lymphoid and myeloid blasts. A change in phenotype occurred in three out of six cases studied in relapse. There was no difference in the incidence of immunoglobulin (Ig) gene rearrangement between TdT positive (two out of 12) and TdT negative (one out of 11) cases, although published data suggests that Ig gene rearrangement is significantly more common in TdT positive cases. The determination of TdT in AML allows the identification of cases of mixed acute leukaemia which probably represent proliferations of multipotent progenitor cells. The majority of TdT positive cases, nevertheless, correspond to immature types of myeloblastic leukaemia which may constitute a clinically distinct subgroup.

Immunophenotype of clonogenic cells in myeloid leukaemia

Leukaemic clonogenic cells, capable of forming colonies of blast cells in an in-vitro assay, were examined for surface antigen expression using a panel of monoclonal antibodies (Mabs) to stem cell and myeloid differentiation antigens in nine cases of acute myeloid leukaemia (AML) and four cases of chronic myeloid leukaemia in myeloid blast crisis (CML-MBC). Clonogenic cells were found to be most frequently positive with anti-HLA-DR (positive in 100% cases) and RFB-1 (71%) Mabs, with significant reactivity also being seen with CD-33 (69%) and CD-13 (61%) myeloid specific antibodies. CD-11b and CD-15 antigens, expressed predominantly on mature leucocytes, were not significantly expressed on the clonogenic population. Interestingly, the CD-34 antigen, detected by MY-10 Mab on normal myeloid progenitor cells, was demonstrated on the clonogenic fraction of only one of seven cases tested. A discrepancy between antigen expression of clonogenic cells and immunophenotype of the total leukaemic population was frequently seen, with "early" markers (CD-33, HLA-DR, RFB-1) expressed on a higher proportion of the clonogenic fraction than the overall population, while the converse was the case for the "later" marker, CD-11b. Based on the known normal distribution of differentiation antigens, particularly the CD-13 antigen, cases could be ranked according to clonogenic phenotype into immature (CD-13- HLA-DR+ CD-33+ or CD-33-; five cases), and mature (CD-13+ HLA-DR+ CD-33+; eight cases), levels. However, there was no correlation between these maturation levels and the morphology according to the FAB classification. Of note, the mature group included three CML-MBC, as well as two AML cases with a history of myelodysplasia or myeloproliferative disorder. These immunophenotypic findings indicate a heterogeneity in the level of maturation of the clonogenic population, not only in cases of de-novo AML, but also in AML thought to derive from multipotential stem cells.

'Pseudo-lymphoid' leukaemia with unusual features: ultrastructural, immunological, cytogenetic and molecular studies

An unusual case of 'pseudo-lymphoid' leukaemia is described. The leukaemic cells resembled small, mature lymphocytes but lacked B- and T-cell membrane markers as well as immunoglobulin (Ig) and T-cell receptor gene rearrangements. They showed, instead, features of early myeloid cells since they expressed 2 myeloid antigens, CDW13 and My9, and displayed peroxidase activity demonstrable by electron microscopy (EM) on unfixed cells. Cytogenetic studies showed monosomy 5, t(4;17) (p12;p11), t(2;3)(p23;q14) and an abnormal chromosome 12. Abnormalities of chromosomes 4 and 5 have been previously associated with 'pseudo-lymphoid' leukaemias. This case illustrates the value of sensitive methods for the characterization of blast cells and for the precise diagnosis of leukaemias with apparent 'lymphoid' morphology.

Purification of haemopoietic progenitor cells from patients with chronic granulocytic leukaemia using percoll density gradients and elutriation

Purification of haemopoietic progenitor cells from chronic granulocytic leukaemia buffy coat preparations requires a multistep approach using complementary cell separation techniques. In this study Percoll density gradient centrifugation and centrifugal elutriation were used to isolate large numbers of immature progenitor cells. Percoll density gradients were valuable as a first separation step: CFU-GM and CFU-GEMM could be enriched 75-fold in a light density fraction of d less than 1.056 g/ml and the technique could be adapted to cope with more than 10(10) buffy coat leucocytes. Progenitors cells were concentrated 3-fold by elutriation used as single method to separate buffy coat cells or when used to purify further light density Percoll fractions. When Percoll gradients and elutriation were used sequentially, undifferentiated mononuclear cells were enriched to more than 90% purity and between 5% and 40% of these cells formed CFU-GM or BFU-E colonies consisting of more than 40 cells. The enriched fractions were further characterized with monoclonal antibodies. The density and elutriation profiles of these colony forming cells resembled corresponding profiles of cells that reacted with the monoclonal antibody BI-3C5, which recognizes an antigen on primitive haemopoietic progenitor cells. Physical separation methods are a valuable first stage in the attempt to procure relatively pure myeloid progenitor cell populations, whose characteristics can then be further studied at a cellular or molecular level.