Characterization of a complex Philadelphia translocation (1p-;9q+;22q-) by gene mapping

Genomic diversity of Philadelphia-positive chronic myelogenous leukemia

The incidence of breakpoints in CML patients with variant translocations was investigated. There was no relationship between the length of various chromosomes with breakpoint frequency. However, a significantly higher (p less than 0.05) incidence of breaks were seen on the long arms as compared to the short arms due mainly to the involvement of 9q and 22q in these translocations. Chromosome 17 showed a significantly (p less than 0.005) higher involvement in these translocations, however only when 9q34-qter was not cytogenetically involved. A total of 683 breaks were found in 225 cases. 362 of these were located at c-abl and c-sis, while 110 were at other oncogenetic sites. The prognostic and hematologic features of patients with variant translocations are not significantly different from those of CML cases with the typical 9q;22q translocation. Some of these complex translocation, where the breakpoints are correlated with oncogenetic sites, are further discussed in molecular terms.

Different break-points in Philadelphia chromosome variant translocations and in constitutional and sporadic translocations

Three different samples of translocations were considered in an attempt to identify those chromosomal bands preferentially involved in variant Philadelphia chromosome (Ph1) translocations, and to compare them with bands preferentially broken in constitutional and sporadic translocations. The first sample included 204 cases of variant Ph1 translocations with 221 identified break-points (bp), the second consisted of 106 cases of non-Robertsonian constitutional translocations with 213 bp identified, and the third one of 185 bp identified in sporadic translocations found occasionally in single cells of subjects with normal karyotypes and without haematological disorders. A statistical analysis demonstrated that there are some bands preferentially broken in each of the samples, and this with a high level of significance (P less than 0.001). The analysis of the distributions of the chi 2 components permitted us to identify the 12 bands preferentially involved in variant Ph1 translocations and the 13 and 9 bands preferentially involved in constitutional and sporadic translocations, respectively. The comparison among the groups of preferential bp showed that the bands most involved in the three samples are different. Some theoretical problems related to the origin of the Ph1 chromosome are discussed.

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.

Expression of human myeloid-associated surface antigens in human-mouse myeloid cell hybrids

Hybrid cell lines were obtained after fusion of mouse myeloid cells (WEHI-TG) with leukocytes from two patients with chronic myeloid leukemia. A third fusion was carried out with leukocytes from a patient with acute lymphocytic leukemia. All three patients carried the Philadelphia chromosome (Ph1) in the leukemia cell population. Cytochemical analysis confirmed the myelo-monocytic nature of the hybrid cell lines. The presence of Ph1 translocation products could be established in most hybrids derived from the two chronic myeloid leukemic patients, which confirms that indeed human myeloid cells were fused. Several of these hybrid lines showed reactivity with monoclonal antibodies known to be specific for human myeloid cells, whereas interlineage Chinese hamster fibroblast-human chronic myeloid leukemia hybrids failed to react with these antibodies. Five independently obtained monoclonal antibodies--MI/NI, UJ-308, VIM-D5, FMC-10, and B4.3--showed very similar reactivity patterns when tested on the hybrid clones. This result substantiates the evidence obtained from other studies, that these five antibodies are directed against the same myeloid-associated antigen. The gene(s) for expression of the latter antigen could be assigned to human chromosome 11.