T lymphocytes lack rearrangement of the bcr gene in Philadelphia chromosome-positive chronic myelocytic leukemia

To study the possible involvement of T lymphocytes in Philadelphia chromosome (Ph)-positive chronic myelocytic leukemia (CML) we analyzed the arrangement of the bcr gene in T cell and non-T cell samples of 12 CML patients. Although all the patients showed bcr rearrangements in non-T cell fractions, T cell populations lacked respective gene recombinations. Moreover, by Southern blot analyses using T cell receptor beta chain sequences our data indicate polyclonality of T cell samples from 11 of 12 cases; in one patient a clonal T cell population could be identified. These results suggest that T lineages of most Ph-positive CML patients are not derived from pluripotent stem cells involved in leukemogenesis and thus confirm previous investigations based on cytogenetic or glucose-6-phosphate dehydrogenase analyses. The demonstration of polyclonal T cell populations may reflect persistence of stem cells committed to differentiate only into T cells.

Novel transforming sequences in human acute myelocytic leukemia cell lines

DNA transfection analyses using the tumorigenicity assay were performed on seven human acute myelocytic leukemia (AML) cell lines. DNAs from all cell lines induced tumors in nude mice. Respective transforming sequences could be identified as activated N-ras genes in AML cell lines THP-1, KG-1 and Rc2a. We observed the transfer of five putative novel transforming sequences from DNAs of cell lines U937, ML-1, HEL and CTV-2. These sequences appear to be unrelated to each other and previously known oncogenes. Transfections containing these transforming genes show distinctive biological and morphological characteristics. Our data suggest that the transforming sequences reported here became activated during the transfection process rather than the AML cell line.

Strategy for the treatment of hairy cell leukemia

Both splenectomy and alpha-interferon are efficient treatments for hairy cell leukemia. Since interferon therapy seems to induce remissions of the disease, avoids the risks of surgery, and sustains the spleen, it should be discussed if this therapy may replace splenectomy as primary treatment for this disease. In order to make this decision the biologic relevance of complete remissions in hairy cell leukemia, the reliability of methods to confirm remission, the benefits and risks of both splenectomy and interferon therapy, and some aspects of the pathogenesis of the disease have to be considered. Based on our experimental and clinical results and data from other groups, we conclude that splenectomy should still be recommended as primary therapy in hairy cell leukemia provided that treatment is indicated and the patient is eligible for surgery.

Early T cell differentiated chronic myeloid leukemia blast crisis with rearrangement of the breakpoint cluster region but not of the T cell receptor beta chain genes

Early T cell differentiation is described in a case of Philadelphia chromosome-positive chronic myeloid leukemia (CML) in blast crisis, supporting multi-lineage differentiation potential of CML precursor cells. In the absence of myeloid markers, strong positivity for terminal deoxynucleotidyl transferase (TdT) and reactivity with T cell antibody 3A1, but lack of more mature T cell antigens, provided evidence for immature T cell differentiation. Molecular analysis of the breakpoint cluster region (bcr) in chromosome 22 revealed a rearrangement and thus confirmed the CML origin of the early T cell blasts. T cell receptor beta chain sequences were found in germline configuration and therefore suggest a very immature stage of T cell differentiation in the CML blasts.

Amplification and expression of the N-myc gene in neuroblastoma

Genomic configuration and expression of the N-myc gene was investigated by Southern and Northern blot analyses in 18 neuroblastomas of different clinical stages. We observed a 4-100-fold amplification of this oncogene in one of six stage III, two of four stage IV as well as one of five stage IVS tumours. Remarkably, an 80-fold N-myc amplification was demonstrated in a patient with stage IV neuroblastoma being in remission for more than 2 years; moreover, a 100-fold amplification could be detected in a stage IVS tumour from a newborn. These data are discussed in view of the recently postulated close association of N-myc amplification with rapid progression of neuroblastomas.

T cell receptor-CD3 complex during early T cell differentiation. Analysis of immature T cell acute lymphoblastic leukemias (T-ALL) at DNA, RNA, and cell membrane level

T cell acute lymphoblastic leukemias (T-ALL) can be regarded as the malignant counterparts of cells in various T cell differentiation stages. To study the expression of the human T cell receptor (TcR)-CD3 complex during the early stages of T cell differentiation, we have analyzed 22 T-ALL at the cell membrane level and the DNA level and 12 of them at the RNA level. According to their immunologic phenotype, the T-ALL could be divided into three main groups: 10 immature T-ALL (CD1-/CD3-), seven common thymocytic T-ALL (CD1+/CD3-or+), and five mature T-ALL (CD1-/CD3+). Among the 10 immature T-ALL three appeared to express the immunologic phenotype of the putative prothymocyte (TdT+/HLA-DR+/CD7+/CD2+/CD5-/CD1-/CD3-), whereas the other seven T-ALL appeared to be immature thymocytic (TdT+/HLA-DR-/CD7+/CD2+/CD5+/CD1-/CD3-). Transcripts of the CD3-delta and CD3-epsilon genes were present in all CD3- and CD3+ T-ALL tested, including prothymocytic T-ALL. However, prothymocytic T-ALL had germline TcR-beta genes and were not rearranged to the characterized TcR-gamma joining regions. The presence of CD3 transcripts and absence of TcR gene rearrangements in prothymocytic T-ALL supports their immature T cell character. Two immature thymocytic T-ALL also had germline TcR-gamma genes and one of them had germline TcR-beta genes. In all other T-ALL the TcR-gamma and TcR-beta genes were rearranged. The presumptive functional 1.3-kilobase TcR-beta transcripts were detected in the majority of T-ALL with rearranged TcR-beta genes. Distinct levels of TcR-gamma transcripts appeared to be present only in some thymocytic T-ALL, i.e., some immature thymocytic T-ALL and common thymocytic T-ALL. TcR-alpha mRNA could only be detected in CD3+ mature T-ALL, but was absent in all CD3+ common thymocytic T-ALL tested. Our data indicate that CD3 gene transcription is one of the earliest events during T cell differentiation and already occurs in prothymocytes. The TcR-gamma and TcR-beta genes rearrange early during thymocytic differentiation and can subsequently be transcribed. High levels of TcR-gamma gene transcription may only occur in a part of the T cells during thymic differentiation, while TcR-beta gene transcription continues during further differentiation. TcR-alpha gene transcription may be the final step in the production of the complete set of TcR and CD3 proteins, resulting in the expression of the TcR alpha beta-CD3 complex at the cell surface of mature T cells.(ABSTRACT TRUNCATED AT 400 WORDS)

T cell receptor-CD3 complex during early T cell differentiation. Analysis of immature T cell acute lymphoblastic leukemias (T-ALL) at DNA, RNA, and cell membrane level

T cell acute lymphoblastic leukemias (T-ALL) can be regarded as the malignant counterparts of cells in various T cell differentiation stages. To study the expression of the human T cell receptor (TcR)-CD3 complex during the early stages of T cell differentiation, we have analyzed 22 T-ALL at the cell membrane level and the DNA level and 12 of them at the RNA level. According to their immunologic phenotype, the T-ALL could be divided into three main groups: 10 immature T-ALL (CD1-/CD3-), seven common thymocytic T-ALL (CD1+/CD3-or+), and five mature T-ALL (CD1-/CD3+). Among the 10 immature T-ALL three appeared to express the immunologic phenotype of the putative prothymocyte (TdT+/HLA-DR+/CD7+/CD2+/CD5-/CD1-/CD3-), whereas the other seven T-ALL appeared to be immature thymocytic (TdT+/HLA-DR-/CD7+/CD2+/CD5+/CD1-/CD3-). Transcripts of the CD3-delta and CD3-epsilon genes were present in all CD3- and CD3+ T-ALL tested, including prothymocytic T-ALL. However, prothymocytic T-ALL had germline TcR-beta genes and were not rearranged to the characterized TcR-gamma joining regions. The presence of CD3 transcripts and absence of TcR gene rearrangements in prothymocytic T-ALL supports their immature T cell character. Two immature thymocytic T-ALL also had germline TcR-gamma genes and one of them had germline TcR-beta genes. In all other T-ALL the TcR-gamma and TcR-beta genes were rearranged. The presumptive functional 1.3-kilobase TcR-beta transcripts were detected in the majority of T-ALL with rearranged TcR-beta genes. Distinct levels of TcR-gamma transcripts appeared to be present only in some thymocytic T-ALL, i.e., some immature thymocytic T-ALL and common thymocytic T-ALL. TcR-alpha mRNA could only be detected in CD3+ mature T-ALL, but was absent in all CD3+ common thymocytic T-ALL tested. Our data indicate that CD3 gene transcription is one of the earliest events during T cell differentiation and already occurs in prothymocytes. The TcR-gamma and TcR-beta genes rearrange early during thymocytic differentiation and can subsequently be transcribed. High levels of TcR-gamma gene transcription may only occur in a part of the T cells during thymic differentiation, while TcR-beta gene transcription continues during further differentiation. TcR-alpha gene transcription may be the final step in the production of the complete set of TcR and CD3 proteins, resulting in the expression of the TcR alpha beta-CD3 complex at the cell surface of mature T cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Deletion of c-fms sequences in the 5q- syndrome

Southern blot analyses demonstrated hemizygosity of c-fms sequences in three cases of the 5q- syndrome, cytogenetically characterized by del(5)(q13;q35) or del(5)(q31;q35). In situ hybridization studies revealed a deletion of this oncogene from the 5q- chromosome in two cases; moreover, we localized c-fms to region 5q31-33.

Mapping of the oncogenes Myc, Sis, and int-1 to the distal part of mouse chromosome 15

Two proto-oncogenes, Myc and Sis, as well as a putative mouse oncogene, int-1, were localized by in situ hybridization to the distal third of mouse chromosome 15. The respective loci of these genes map to different cytogenetic sites with Myc in 15D2-D3, Sis in 15E, and int-1 in 15F1-F3. These data may be of considerable impact as to the correlation of mouse neoplasias with chromosomal aberrations involving chromosome 15.

Human acute unclassified leukemia with a unique t(4;17) chromosomal translocation expresses T lymphoid and myeloid surface antigens after in vitro culture

Bilineage differentiation along both the T lymphoid and the myeloid lineage while in in vivo diffusion chamber (DC) and in vitro suspension culture was observed in a case of acute unclassified leukemia (null-AL) and t(4;17). Prior to culture, the blast cells were TdT and la positive but did not express any lineage-specific antigenic markers. Furthermore, the immunoglobulin heavy chain and T cell receptor beta-chain genes were in germline configuration. Cytogenetically, all metaphases had the unique translocation t(4;17) (q25;q23) prior to and after culture, supporting the leukemic origin of the cells. During both DC culture and suspension culture with and without tetradecanoyl-phorbol-acetate (TPA), a substantial increase in the absolute and relative number of cells expressing both myeloid and T lymphoid antigenic markers occurred. Double-fluorescence analysis demonstrated the expression of antigenic markers of both lineages on the same population of cells, and electron microscopy revealed the induction of myeloperoxidase after both DC and suspension culture. Immunoglobulin heavy chain and T cell receptor beta-chain genes remained in germline configuration after treatment with TPA, when analyzed with JH and CT beta probes, respectively. These findings indicate that this case represents a null-AL with dual-lineage capabilities, which has probably arisen from the malignant transformation of a bipotential stem cell of lymphoid and myeloid progeny.

bcr rearrangement and translocation of the c-abl oncogene in Philadelphia positive acute lymphoblastic leukemia

The Philadelphia (Ph1) chromosome, the cytogenetic hallmark of chronic myeloid leukemia (CML), has also been detected in a significant number of acute lymphoblastic leukemias (ALL). Using in situ hybridization, we demonstrate that in accordance with observations in CML the Ph1 chromosome in ALL patients is the result of a consistent translocation of the c-abl oncogene to the Ph1 chromosome. Southern blot analysis using bcr probes, however, suggests that Ph1-positive ALL includes heterogeneous leukemic subtypes: six ALL patients showed bcr rearrangements as observed in CML; in three other patients recombination involving 5' bcr sequences could be demonstrated, but the corresponding translocated 3' bcr sequences were not detectable. A third group of five patients did not show any bcr rearrangements at all. Northern blot analysis using RNA from three Ph1-positive ALL patients revealed that in the leukemic cells of two patients larger c-abl mRNA transcripts were present, as in CML. In the RNA of one patient without a detectable bcr rearrangement, only the normal c-abl mRNA transcripts are present. The observed heterogeneity in bcr rearrangements of this group of Ph1-positive ALL patients is in contrast with the consistent results obtained in more than 50 Ph1-positive CML patients investigated in chronic and acute states.

Persistence of chronic myelocytic leukemia despite deletion of rearranged bcr/c-abl sequences in blast crisis

We report on a Ph+ chronic myelocytic leukemia (CML) case, cytogenetically characterized by the occurrence of a second Philadelphia (Ph) chromosome in lymphoid blast crisis of T cell lineage. In situ hybridization analyses showed a deletion of translocated c-abl sequences, present on the Ph during chronic state, from both Ph in acute state. Moreover, Southern blot analyses of blastic cells exhibited a rearrangement within bcr, but a deletion of 5' bcr sequences, and Northern blots failed to detect the hybrid 8.5 kb bcr/c-abl transcript usually observed in Ph+ CML.

Acute undifferentiated leukemia: implications for cellular origin and clonality suggested by analysis of surface markers and immunoglobulin gene rearrangement

Although B cell leukemias and, recently, T cell leukemias can be identified both by surface marker and molecular analysis, there remains a population of acute undifferentiated leukemias (AUL) that cannot be allocated definitively to a single cell lineage. AUL was diagnosed in nine patients according to stringent criteria. We combined both immunologic and molecular approaches to analyze further the ambiguous origin of AUL cells. Southern blot analysis revealed rearranged Ig heavy-chain genes in seven patients and indicated a biclonal or oligoclonal leukemic cell population in three of them, including one case of AUL with translocation (4;11). Analysis of cell surface markers showed expression of at least one early B cell-associated antigen (BA-1, BA-2, B4, UL-38) in six of these seven patients, with coexpression of a myeloid antigen (VIM-2) in three patients. Leukemic cells of two other patients neither exhibited Ig chain gene rearrangements nor expressed B cell-associated antigens. T cell receptor beta-chain genes showed germline configuration in all nine cases. Our results demonstrate heterogeneity among AUL patients based on molecular and surface marker analyses and suggest that most AUL blast cells are derived from a precursor cell that shares phenotypic and genotypic characteristics of early B cells with certain surface antigens of myeloid cells, in some cases of AUL more than one abnormal cell clone or subclone may exist, and the cellular origin, at least of some AULs exhibiting t(4;11), may be truly B cell lineage committed.

Biallelic heavy chain immunoglobulin gene rearrangement in acute nonlymphocytic leukemia

Acute nonlymphocytic leukemia (ANLL) was diagnosed in 18 patients based on morphological, cytochemical and immunological criteria. Leukemic cells of these cases were subjected to Southern blot analysis and subsequent hybridization to heavy chain immunoglobulin and T-cell-receptor gene probes. A rearrangement within the immunoglobulin joining region was detected in 2 cases, while the T-cell-receptor beta-chain gene was in germline configuration in all samples investigated. These data confirm recent reports indicating that immunoglobulin heavy chain gene rearrangements are not restricted to B-lineage neoplasms.

Conversion of acute undifferentiated leukemia phenotypes: analysis of clonal development

The cellular origin of acute undifferentiated leukemia (AUL) is still a matter of controversy. We report on two cases in which the diagnosis of AUL was established according to restricted criteria. Blast cells of both patients showed phenotypic conversion during the course of disease. In one case, within 24 days from starting treatment, the leukemic phenotype changed from AUL to acute myelomonocytic leukemia (FAB L1, TdT+ to FAB M4, TdT-). The initial phenotype of this acute leukemia was characterized by the co-expression of both B-lymphoid and myeloid markers on the same cell. Moreover, analysis of esterase isoenzyme pattern showed the whole spectrum of isoenzymes typically seen in myelomonocytic leukemias already at diagnosis, yet blast cells additionally contained all three isoenzymes of beta-hexosaminidase typically seen in AUL. However, examination of immunoglobulin (Ig) heavy chain gene rearrangement initially and after conversion revealed an identical monoclonal configuration of Ig heavy chain sequences in both samples. The second AUL patient relapsed after allogeneic bone marrow transplantation with common ALL-antigen (CALLA) positive acute leukemia. Subsequent Southern blot analysis showed a novel rearranged Ig fragment compared to the analysis before transplantation indicating that the leukemic clones prior to and after transplantation were not identical. No chromosomal abnormalities were observed in both cases. These data support the view that AUL cells originate from a pluripotent stem cell that is capable to differentiate in the myelomonocytic lineage (patient 1), and confirm the value of Ig gene analysis as marker for cellular clonality.

Additional c-abl/bcr rearrangements in a CML patient exhibiting two ph1 chromosomes during blast crisis

Recent data suggest that two human genes, c-abl on chromosome 9 and bcr on chromosome 22, are involved in the generation of Ph1-positive CML. To examine a possible role of these sequences in transition from chronic towards blastic phase, rearrangements within bcr were analysed in 4 patients with Ph1-positive CML during chronic and acute phase. In 3 patients bcr rearrangements were identical in both phases, while in a fourth patient with duplicated Ph1 an amplified additional bcr fragment was detected in acute phase. Northern blot analysis of blast cells of the latter patient showed a novel 10.3 kb RNA species that replaced the altered 8 kb RNA transcript usually found in Ph1-positive CML.

bcr Rearrangement without juxtaposition of c-abl in chronic myelocytic leukemia

Southern blot analysis detected a bcr gene rearrangement within leukemic cells of a Philadelphia chromosome-negative chronic myelocytic leukemia (CML) patient that led to transcription of a novel 7.3 kb bcr RNA species. Participation of the c-abl oncogene in this genomic recombination could be ruled out by in situ hybridization studies and Northern blot analysis.

[Philadelphia translocation and the human c-abl oncogene--relations in the light of molecular genetics]

Application of recombinant DNA techniques led to the characterization of a heterogenous group of evolutionary conserved genes with potential transforming activity, called oncogenes. Regularly they seem to be involved in normal cell proliferation and differentiation. Various mechanisms including an increased dosage of gene product as well as subtile point mutations activate these sequences to oncogenes sensu strictu. Molecular analysis of the Philadelphia translocation in leukemic cells of CML-patients revealed a consistent translocation of the human c-abl-oncogene from chromosome 9 to the Ph1-chromosome, regardless of the cytogenetic subtype. Moreover we could demonstrate individual breakpoints for every patient investigated so far. However, these breakpoints are clustered on chromosome 22 within sequences of the bcr-gene. In leukemic cells containing the rearranged-c-abl/bcr sequences a new transcript is detected which is possibly the mRNA for an altered c-abl-protein that unmasks associated tyrosine specific kinase activity. These gene rearrangements were not detected in Ph1-negative CML-patients. Another human oncogene, c-sis, is located on chromosome 22, but seems not to play a crucial role in the generation of CML. These results are discussed in the context of recent advances in oncogene-research.

C-abl and bcr are rearranged in a Ph1-negative CML patient

Chromosomal analysis of a patient with chronic myelocytic leukemia (CML) revealed a translocation (9;12) (q34;q21) without a detectable Philadelphia chromosome (Ph1). Using molecular approaches we demonstrate (i) a rearrangement within the CML breakpoint cluster region (bcr) on chromosome 22, and (ii) a joint translocation of bcr and c-abl oncogene sequences to the derivative chromosome 12. These observations support the view that sequences residing on both chromosome 9 (c-abl) and 22 (bcr) are involved in the generation of CML and suggest that a subset of Ph1-negative patients may in fact belong to the clinical entity of Ph1-positive CML.

Involvement of chromosome 9 in variant Ph1 translocation

Cytogenetic analysis of a patient with chronic myelocytic leukemia revealed a translocation (21; 22) (q 22; q 11) without a detectable involvement of chromosome 9. By in-situ hybridization studies, however, we demonstrate a reciprocal translocation of sequences from chromosome 9 (c-abl) to Ph1 and chromosome 22 (bcr) to 9, respectively. These observations suggest a consistent participation of chromosome 9 in the Ph1 translocation, regardless of the cytogenetic subtype.

[Molecular mechanisms of antibody synthesis]

Antibodies or immunoglobulins play a central part in the immune system. The basic unit of an antibody is composed of two identical light and two identical heavy chains; each chain contains two functionally and structurally distinct regions: an amino-terminal variable or antigen-binding site, and a carboxy-terminal constant region responsible for immunological effector functions. Thanks to recombinant DNA technology the paradox of a limited number of genes and a virtually unlimited capacity to generate specific antibodies has now been resolved at least in outline. Immunoglobulin chains are encoded in multiple gene segments of three unlinked gene families scattered along chromosomes 2 (kappa light chain), 14 (heavy chain) and 22 (lambda light chain). During B-cell differentiation these genes are assembled by somatic recombination mechanisms to form active genes. The enormous diversity generated by means of DNA rearrangements is supplemented by mutations somatically introduced into variable region sequences. The medical impact of these discoveries will be substantial. Possible applications include identification of B-cell precursors lacking conventional markes, a molecular classification of lymphomas and a precise distinction between monoclonal and polyclonal lymphoproliferative disorders.

Is the chromosomal region 9q34 always involved in variants of the Ph1 translocation?

Six variants of the Ph1 translocation are described. The clinical diagnoses were chronic myeloid leukemia (CML) in 5 cases (patients 1-5) and acute lymphocytic leukemia (ALL) in patient 6. Three Ph1 variants were clear complex translocations, involving chromosomes #9, #22, and a third chromosome, i.e., #16, #11, or #14. The other three Ph1 variants appeared as "simple" translocations between chromosome #22 and chromosome #19, #4, or #12 when G- or Q-banding were used. When studied with high resolution R-banding, a small deletion of the terminal part of one chromosome #9 was visible, strongly suggesting that these variants were also complex translocations, i.e., t(9;19;22)(q34;p13;q11),t(4;9;22) (p16;q34;q11), and t(9;12;22)(q34;p13;q11). In the latter two cases, using in situ hybridization techniques, we demonstrated the presence of c-abl sequences on the Ph1 chromosome. This proved the involvement of 9q34 in these two variants. Our proposal is that most, and probably all, variants of Ph1 are complex translocations involving part of 9q34 and that the conjunction of a specific region of 22q11 with a specific segment of 9q34 (carrying the c-abl protooncogene) is essential for the development of Ph1 + CML.

Localization of the human c-sis oncogene in Ph1-positive and Ph1-negative chronic myelocytic leukemia by in situ hybridization

Oncogenes are a group of evolutionary conserved cellular genes (c-onc) homologous to the transforming genes of oncogenic retroviruses (v-onc). Some of them are localized near the breakpoints of specific chromosomal aberrations occurring in various neoplasms, as for example the Philadelphia translocation, t(9;22)(q34;q11), in chronic myelocytic leukemia (CML). Recently, we localized the human c-abl oncogene to chromosome region 9q34 and demonstrated a translocation of this gene to the Philadelphia chromosome (Ph1,22q-) in various forms of Ph1-positive, but not Ph1-negative, chronic myelocytic leukemia (CML). Another human oncogene, c-sis, is located on chromosome 22 and was recently reported to be transferred to chromosome 9q+ in one CML patient. We have now studied 2 CML patients with classic and variant types of Ph1 translocation, one Ph1-negative case, and a healthy control using in situ hybridization of a c-sis probe to metaphase chromosomes. These studies show that c-sis: (1) is localized to region 22q12.3-q13.1, far away from the breakpoint region 22q11 in CML, (2) segregates with the translocated part of chromosome 22 to different chromosomes in Ph1-positive patients, and (3) remains on chromosome 22 in the Ph1-negative case. Therefore, these data give no support for an active role of the c-sis gene in the generation of CML. Thus, if either of these two oncogenes is involved in the development of Ph1-positive CML, c-abl appears to be the more important one.

Philadelphia chromosomal breakpoints are clustered within a limited region, bcr, on chromosome 22

We have identified and molecularly cloned 46 kb of human DNA from chromosome 22 using a probe specific for the Philadelphia (Ph') translocation breakpoint domain of one chronic myelocytic leukemia (CML) patient. The DNAs of 19 CML patients were examined for rearrangements on chromosome 22 with probes isolated from this cloned region. In 17 patients, chromosomal breakpoints were found within a limited region of up to 5.8 kb, for which we propose the term "breakpoint cluster region" (bcr). The two patients having no rearrangements within bcr lacked the Ph' chromosome. The highly specific presence of a chromosomal breakpoint within bcr in Ph'-positive CML patients strongly suggests the involvement of bcr in this type of leukemia.

Regional mapping of the human immunoglobulin lambda light chain to the Philadelphia chromosome in chronic myeloid leukaemia

The lambda light chain immunoglobulin constant region (C lambda) locus was mapped on human chromosome 22. A DNA probe containing part of the C lambda locus was isolated from a human chromosome 22 genomic library, and a series of rodent X human somatic cell hybrids (each of which contained different translocated parts of chromosome 22) were constructed and characterized. The hybridization of the C lambda probe to DNA from these cell hybrids was then studied by Southern blot analysis. The results demonstrates that the C lambda locus is situated very close to the translocation breakpoint on human chromosome 22 which is characteristic of chronic myeloid leukaemia, and at least part if not at all of the locus is situated on the Philadelphia chromosome.

Oncogenes: clues to carcinogenesis

Recent applications of recombinant DNA techniques in cancer research led to the detection of cellular genes with potential transforming activity, called oncogenes (c-onc). Regularly they seem to be involved in normal cell differentiation and proliferation: a number of oncogene-encoded proteins specifically phosphorylates tyrosine, a key reaction in growth control. Certain human tumors exhibit activated forms of these genes and DNA fragments isolated from these neoplasms transform nonneoplastic cells (transfection assay). Oncogenes were first discovered and defined in a number of retroviruses; these viral oncogenes (v-onc) are thought to have been derived from the cellular oncogenes (c-onc). By integration of the v-onc genes into the host genome acute neoplastic transformation of the cell may occur. Several modes of oncogene activation are discussed that lead either to an increased dosage of gene product or to the formation of an altered gene product. The localization of oncogenes in the human genome near the breakpoints of specific chromosome aberrations involved in various neoplasms like Burkitt lymphoma and several leukemias emphasizes the importance of these genes in carcinogenesis.

Translocation of c-ab1 oncogene correlates with the presence of a Philadelphia chromosome in chronic myelocytic leukaemia

The localization of cellular oncogenes near the break points of tumour-specific chromosomal aberrations suggests an involvement of these genes in the generation of neoplasms. Recently, we demonstrated the translocation of the human cellular homologue (c-ab1) of the transforming sequence of Abelson murine leukaemia virus (A-MuLV) from chromosome 9 to the Philadelphia chromosome (Ph1) in chronic myelocytic leukaemia (CML). In an attempt to investigate the significance of this translocation in the pathogenesis of CML, we have now studied two CML patients with complex translocations, t(9; 11; 22) and t(1; 9; 22), and two CML Ph1-negative patients with apparently normal karyotypes. In addition to using blot hybridization with human c-ab1 probes and DNA from rodent: CML cell hybrids as before, we have used in situ hybridization of these probes directly to metaphase chromosomes of CML patients. These studies show that the c-ab1 gene is translocated in Ph1-positive but not in Ph1-negative CML patients. CML without the Ph1 chromosome seems to be a distinct entity with a different origin, and this view is supported by clinical observations including correlations which reveal a poorer prognosis.

Localization of the c-ab1 oncogene adjacent to a translocation break point in chronic myelocytic leukaemia

The human c-ab1 oncogene maps within the region (q34-qter) of chromosome 9 which is translocated to chromosome 22, the Philadelphia (Ph') chromosome, in chronic myelocytic leukaemia (CML). The position of the Ph' chromosomal break point is shown to be variable and, in one CML patient, has been localized immediately 5' of, or within, the c-ab1 oncogene. A DNA restriction fragment corresponding to this site has been molecularly cloned and shown to represent a chimaeric fragment of DNA from chromosomes 9 and 22.

A cellular oncogene is translocated to the Philadelphia chromosome in chronic myelocytic leukaemia

The transforming genes of oncogenic retroviruses are homologous to a group of evolutionary conserved cellular onc genes. The human cellular homologue (c-abl) of the transforming sequence of Abelson murine leukaemia virus (A-MuL V) was recently shown to be located on chromosome 9. The long arm of this chromosome is involved in a specific translocation with chromosome 22, the Philadelphia translocation (Ph1), t(9; 22) (q34, q11), which occurs in patients with chronic myelocytic leukaemia (CML)3-5. Here we investigate whether the c-abl gene is included in this translocation. Using c-abl and v-abl hybridization probes on blots of somatic cell hybrids, positive hybridization is found when the 22q- (the Philadelphia chromosome), and not the 9q+ derivative of the translocation, is present in the cell hybrids. From this we conclude that in CML, c-abl sequences are translocated from chromosome 9 to chromosome 22q-. This finding is a direct demonstration of a reciprocal exchange between the two chromosomes and suggests a role for the c-abl gene in the generation of CML.

Subacute sclerosing panencephalitis in a brother and sister. Therapeutic trial of fibroblast interferon

This paper describes the very rare occurrence of subacute sclerosing panencephalitis (SSPE) in two siblings: a Turkish boy and his younger sister. The clinical picture was characteristic, and the diagnosis was confirmed in both cases by appropriate laboratory examination. The interval between the occurrence of the first neurological symptoms in the boy, and subsequently in the girl was four years. Study of HLA- and 27 other polymorphic marker-systems did not reveal linkage to one of the systems tested. Therapeutic trials in the girl included intravenous and intraventricular application of a total of 87 X 10(6) U human fibroblast interferon (Hu INF-beta) over 21 days. However, up to 3 months after the end of interferon administration there were no significant changes in the girl's condition.

Lymphocyte capping in muscular dystrophies

Since reports of lymphocyte capping in muscular dystrophies of various authors revealed controversial results, we investigated 47 patients and carriers with Duchenne or Becker-Kiener muscular dystrophy according to different methods. There was no significant reduction of cap formation compared to 64 healthy controls, both groups showing a mean of about 75% caps. Reduced numbers of caps, however, could be demonstrated in three otherwise healthy probands aged 70 years or more, two patients under interferon treatment, four patients under high dose methotrexate therapy as well as one patient with untreated chronic myeloic leukemia. Thus lymphocyte capping in our experience is far from being a valid method for carrier detection or prenatal diagnosis of muscular dystrophies.

Functional deficiency of fibroblasts heterozygous for Bloom syndrome as specific manifestation of the primary defect

The effect on the rate of sister chromatid exchanges (SCEs) in Bloom syndrome fibroblasts by cocultivation with Fanconi anemia and xeroderma pigmentosum fibroblasts and with Bloom syndrome heterozygotes was studied. Cells of Fanconi anemia and xeroderma origin reduced the rate of SCEs in Bloom cells by about 45%-50%, just as control cells do. In contrast, heterozygous Bloom cells reduced the rate of SCEs by only 16%-28%. In absolute figures, Fanconi cells reduced the mean rate of SCE in Bloom cells from 55.7 +/- 5.50- to 27.7 +/- 6.44, xeroderma cells to 30.5 +/- 5.73, and control cells to 28.3 +/- 5.35. Three different cell strains from Bloom syndrome heterozygotes reduced the rate to 40.1 +/- 8.81, 47.0 +/= 6.94, and 47.5 +/- 8.32. There was no effect on any of these cell strains by Bloom syndrome fibroblasts. We interpret the functional deficiency of heterozygous Bloom syndrome fibroblasts as a gene dosis effect. It probably represents a specific manifestation of the yet unknown primary defect, because it suggests the existence of a "corrective factor" that is inactive or absent in homozygous Bloom cells and reduced in heterozygotes. It may be identical with or closely related to the normal gene product at the Bloom locus.

Mutagen-induced sister chromatid exchange rate in Bloom syndrome remains unaltered in the presence of Bloom corrective factor

Fibroblasts of a patient with Bloom syndrome (GM-1492) were cultured in the presence of either mitomycin C, ethylmethanesulfonate, or 4-nitroquinoline-1-oxide, (4-NQ1-O) and sister chromatid exchange was determined. The mutagens enhanced the sister chromatid exchange rate to different degrees, 4-NQ1-O being the most potent substance. Bloom corrective factor, which is present in normal cell-conditioned culture medium, reduced the spontaneously increased SCE in Bloom syndrome cells by about 20 SCE per metaphase but failed to reduce the additional mutagen-induced SCE increase. These findings indicate that only spontaneously, but not mutagen-induced, SCE in Bloom syndrome fibroblasts can be decreased by the Bloom corrective factor.

Dna repair: pathways and defects

Damaged DNA can be repaired by three different mechanisms: photoreactivation, excision repair and postreplication repair. Each mechanism is regulated by a highly specific set of enzymes. Defects within these systems result in diseases which have one common feature: affected individuals are cancer prone. Recently, newly developed methods not only make it possible to diagnose affected patients but also to detect individuals at risk. Furthermore, the results obtained elucidate some mechanisms of carcinogenesis. Clinical applications are discussed.

Benzo[a]pyrene 4,5-oxide. Discrepancy between induction of sister chromatid exchange and binding to DNA in cultured human fibroblasts

Benzo[a]pyrene 4,5-oxide was covalently bound to DNA of cultured human fibroblasts and caused sister chromatid exchange. The monooxygenase inhibitor alpha-napthoflavone suppressed this induction of sister chromatic exchange, but did not affect binding to DNA. Control experiments with 4-nitroquinoline 1-oxide showed that alpha-naphthoflavone does not inhibit sister chromatid exchange in general. A more likely explanation for the discrepancy between induction of sister chromatid exchange and binding to DNA is that benzo[a]pyrene 4,5-oxide itself can bind to DNA, but this binding does not lead to a significant increase in sister chromatid exchange. However benzo[a]pyrene 4,5-oxide can be oxidized by monooxygenase to yet unknown products which are potent inducers of sister chromatid exchange. An important conclusion from this is that a biological effect such as the induction of sister chromatid exchange may correlate with the exact nature of DNA binding rather than with total binding, to the point where just measuring total binding may be completely misleading if intended to detect the causes of the biological effect.

Rate of sister chromatid exchanges in Bloom syndrome fibroblasts reduced by co-cultivation with normal fibroblasts

Six strains of Bloom syndrome (BlS) fibroblasts responded to co-cultivation with normal fibroblasts at a 1:2 ratio by a reduced rate of sister chromatid exchanges (SCE's) from a mean of 67.5 (range = 59--78) to 28.4 (range = 21--35). The response was dose-dependent in one strain tested at 1:2, 1:1, and 2:1 ratios. In addition, quadriradial exchange figures and other signs of increased chromosomal instability were not found in BlS cells following co-cultivation with control cells. Control cells did not respond to BlS cells and maintained a normal rate of SCEs. Culture medium conditioned for 48 hrs by normal fibroblasts could also reduce the rate of SCEs in BlS fibroblasts, but less than in co-cultivation. We suggest that the reduced rate of SCEs and the lack of chromosomal instability in BlS cells following co-cultivation represent a corrective effect that is related to the basic defect and not dependent on cell-to-cell contact.