Activation Of Cellular Proto-oncogenes Research Articles

Polymerase chain reaction-based detection of myc transduction in feline leukemia virus-infected cats.

Feline lymphomas are associated with the transduction and activation of cellular proto-oncogenes, such as c-myc, by feline leukemia virus (FeLV). We describe a polymerase chain reaction assay for detection of myc transduction usable in clinical diagnosis. The assay targets c-myc exons 2 and 3, which together result in a FeLV-specific fusion gene following c-myc transduction. When this assay was conducted on FeLV-infected feline tissues submitted for clinical diagnosis of tumors, myc transduction was detected in 14% of T-cell lymphoma/leukemias. This newly established system could become a useful diagnostic tool in veterinary medicine.

Foamy Virus Vector Carries a Strong Insulator in Its Long Terminal Repeat Which Reduces Its Genotoxic Potential

Strong viral enhancers in gammaretrovirus vectors have caused cellular proto-oncogene activation and leukemia, necessitating the use of cellular promoters in "enhancerless" self-inactivating integrating vectors. However, cellular promoters result in relatively low transgene expression, often leading to inadequate disease phenotype correction. Vectors derived from foamy virus, a nonpathogenic retrovirus, show higher preference for nongenic integrations than gammaretroviruses/lentiviruses and preferential integration near transcriptional start sites, like gammaretroviruses. We found that strong viral enhancers/promoters placed in foamy viral vectors caused extremely low immortalization of primary mouse hematopoietic stem/progenitor cells compared to analogous gammaretrovirus/lentivirus vectors carrying the same enhancers/promoters, an effect not explained solely by foamy virus' modest insertional site preference for nongenic regions compared to gammaretrovirus/lentivirus vectors. Using CRISPR/Cas9-mediated targeted insertion of analogous proviral sequences into the LMO2 gene and then measuring LMO2 expression, we demonstrate a sequence-specific effect of foamy virus, independent of insertional bias, contributing to reduced genotoxicity. We show that this effect is mediated by a 36-bp insulator located in the foamy virus long terminal repeat (LTR) that has high-affinity binding to the CCCTC-binding factor. Using our LMO2 activation assay, LMO2 expression was significantly increased when this insulator was removed from foamy virus and significantly reduced when the insulator was inserted into the lentiviral LTR. Our results elucidate a mechanism underlying the low genotoxicity of foamy virus, identify a novel insulator, and support the use of foamy virus as a vector for gene therapy, especially when strong enhancers/promoters are required.IMPORTANCE Understanding the genotoxic potential of viral vectors is important in designing safe and efficacious vectors for gene therapy. Self-inactivating vectors devoid of viral long-terminal-repeat enhancers have proven safe; however, transgene expression from cellular promoters is often insufficient for full phenotypic correction. Foamy virus is an attractive vector for gene therapy. We found foamy virus vectors to be remarkably less genotoxic, well below what was expected from their integration site preferences. We demonstrate that the foamy virus long terminal repeats contain an insulator element that binds CCCTC-binding factor and reduces its insertional genotoxicity. Our study elucidates a mechanism behind the low genotoxic potential of foamy virus, identifies a unique insulator, and supports the use of foamy virus as a vector for gene therapy.

Foamy Virus Backbone Has Insulator Properties Which Remarkably Reduce Its Genotoxicity Potential

Strong viral enhancers in γ-retrovirus vectors (GV) have caused cellular proto-oncogene activation and leukemia in gene therapy trials, necessitating the use of cellular promoters in enhancer-less integrating vectors. However, data is now emerging that inadequate transgene expression from cellular promoters may limit successful correction. Vectors derived from foamy virus (FV), a nonpathogenic retrovirus, have a higher preference for non-genic integrations than GV/lentiviral vectors (LV), and may be less genotoxic. We constructed GV, LV and FV driven either by the spleen focus forming virus (SFFV) or the murine stem cell virus (MSCV) enhancer/promoters, all driving eGFP expression, and compared their relative genotoxicity using an in vitro immortalization assay on primary hematopoietic stem/progenitor cells (HSPC). In this assay, integration near a protooncogene/gene promoting cell proliferation results in quantifiable HSPC immortalization. Strong viral enhancer/promoters from SFFV or MSCV in FV caused a remarkably low immortalization of HSPC compared to analogous LV or GV: compared to the immortalization frequency of HSPC with the SFFV-GV in this assay, SFFV-LV and MSCV-LV had 12- and 14-fold lower immortalization frequency, while the SFFV-FV and MSCV-FV showed a 155- and 414-fold lower immortalization frequency, respectively. Immortalized clones had multiple (3-10) integrated copies. Integration site analysis of FV immortalized clones revealed a majority of integrants in non-gene regions; those in genic regions targeted cell proliferation or proto-oncogenes, as previously reported. FV has been previously reported to have 2-fold higher insertions in non-genic regions and higher, but nearly half the propensity to target promoters compared to GV. However, this remarkably reduced genotoxicity with FV was not explained by the integration pattern. We therefore hypothesized that FV backbone may contain sequences that have an enhancer blocking/insulator effect. Studies on chromatin insulators have shown that enhancer-blocking property of insulators is mediated via binding of CTCF to its consensus sequences within the insulator. Indeed, an in silico analysis for CCCTC-binding factor (CTCF) binding sites in the vector backbone sequences showed more predicted CTCF binding sites in the FV than in GV or LV (26, 8, and 6, respectively). To functionally validate the enhancer-blocking effect of the FV backbone and ensure that only effects of the vector backbone would be measured, without the confounding influence of integration site or the enhancer/promoter/transgene, we inserted SFFV-GV, SFFV-LV and SFFV-FV into a clinically relevant proto-oncogene, LMO2, using CRISPR/Cas9, and assessed LMO2 expression. LMO2 upregulation has previously resulted in leukemias in the X-linked severe combined immune-deficiency and Wiscott-Aldrich syndrome (WAS) GV-mediated gene transfer trials; notably SFFV-GV was used in the WAS trial and caused leukemias in 8 of 10 patients from insertional oncogenesis. HeLa cells were transfected with the proviral donor plasmids and the guide-RNA/spCas9 plasmids and GFP+ cells sorted and cloned. Nearly all clones derived had one intact LMO2 allele, while the other alleles had GV/LV/FV proviral insertions. We next assessed LMO2 mRNA and protein expression in these clones. We found a minimal increase in LMO2 mRNA expression with SFFV-FV, in sharp contrast to significantly increased LMO2 expression with SFFV-GV and SFFV-LV by qRT-PCR (Figure 1A). Overall, the SFFV enhancer in GV demonstrated the greatest fold-increase in LMO2 expression (median increase of 280+/-23-fold over unmodified HeLa cells), followed by the SFFV enhancer in LV (median 200+/-27-fold increase). However, the same SFFV enhancer in FV only showed a 45+/-7-fold median increase in expression. Western blot analysis for LMO2 protein expression in three clones for each vector showed no detectable LMO2 expression in SFFV-FV clones, which was similar to baseline in mock (non-targeted) HeLa cells (Figure 1B). However, significantly higher LMO2 protein was detectable in GV and LV clones. Hence, the remarkably low genotoxic potential of FV, even those carrying strong viral enhancers appears to be, in large part, from an insulator property of FV sequences, making FV ideal for situations where high transgene expression, necessitating strong enhancers is required for a therapeutic effect. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Critical Variables affecting clinical-grade production of the self-inactivating gamma-retroviral vector for the treatment of X-linked severe combined immunodeficiency

Patients with X-linked severe combined immunodeficiency (SCID-X1) were successfully cured following gene therapy with a gamma-retroviral vector (gRV) expressing the common gamma chain of the interleukin-2 receptor (IL2RG). However, 5 of 20 patients developed leukemia from activation of cellular proto-oncogenes by viral enhancers in the long-terminal repeats (LTR) of the integrated vector. These events prompted the design of a gRV vector with self-inactivating (SIN) LTRs to enhance vector safety. Herein we report on the production of a clinical-grade SIN IL2RG gRV pseudotyped with the Gibbon Ape Leukemia Virus envelope for a new gene therapy trial for SCID-X1, and highlight variables that were found to be critical for transfection-based large-scale SIN gRV production. Successful clinical production required careful selection of culture medium without pre-added glutamine, reduced exposure of packaging cells to cell-dissociation enzyme, and presence of cations in wash buffer. The clinical vector was high titer; transduced 68-70% normal human CD34(+) cells, as determined by colony-forming unit assays and by xenotransplantation in immunodeficient NOD.CB17-Prkdc(scid)/J (nonobese diabetic/severe combined immunodeficiency (NOD/SCID)) and NOD.Cg-Prkdc(scid) Il2rg(tm1Wjl)/SzJ (NOD/SCID gamma (NSG))) mice; and resulted in the production of T cells in vitro from human SCID-X1 CD34(+) cells. The vector was certified and released for the treatment of SCID-X1 in a multi-center international phase I/II trial.

Physiological Promoters Reduce the Genotoxic Risk of Integrating Gene Vectors

The possible activation of cellular proto-oncogenes as a result of clonal transformation is a potential limitation in a therapeutic approach involving random integration of gene vectors. Given that enhancer promiscuity represents an important mechanism of insertional transformation, we assessed the enhancer activities of various cellular and retroviral promoters in transient transfection assays, and also in a novel experimental system designed to measure the activation of a minigene cassette contained in stably integrating retroviral vectors. Retroviral enhancer-promoters showed a significantly greater potential to activate neighboring promoters than did cellular promoters derived from human genes, elongation factor-1alpha (EF1alpha) and phosphoglycerate kinase (PGK). Self-inactivating (SIN) vector design reduced but did not abolish enhancer interactions. Using a recently established cell culture assay that detects insertional transformation by serial replating of primary hematopoietic cells, we found that SIN vectors containing the EF1alpha promoter greatly decrease the risk of insertional transformation. Despite integration of multiple copies per cell, activation of the crucial proto-oncogene Evi1 was not detectable when using SIN-EF1alpha vectors. On the basis of several quantitative indicators, the decrease in transforming activity was highly significant (more than tenfold, P < 0.01) when compared with similarly designed vectors containing a retroviral enhancer-promoter with or without a well-characterized genetic insulator core element. In this manner, the insertional biosafety of therapeutic gene vectors can be greatly enhanced and proactively evaluated in sensitive cell-based assays.

Gentherapie der SCID-X1

X-linked severe combined immunodeficiency (SCID-X1) is an inherited disease caused by inactivating mutations in the gene encoding the interleukin 2 receptor common gamma chain (IL2RG), which is located on the X-chromosome. Affected boys fail to develop two major effector cell types of the immune system (T cells and NK cells) and suffer from a functional B cell defect. Although drugs such as antibiotics can offer partial protection, the boys normally die in the first year of life in the absence of a curative therapy. For a third of the children, bone marrow transplantation from a fully matched donor is available and can cure the disease without major side effects. Mismatched bone marrow transplantation, however, is complicated by severe and potentially lethal side effects. Over the past decade, scientists worldwide have developed new treatments by introducing a correct copy of the IL2RG-cDNA. Gene therapy was highly effective when applied in young children. However, in a few patients the IL2RG-gene vector has unfortunately caused leukaemia. Activation of cellular proto-oncogenes by accidental integration of the gene vector has been identified as the underlying mechanism. In future clinical trials, improved vector technology in combination with other protocol modifications may reduce the risk of this side effect.

Hepatitis B virus infection, the immune response and hepatocellular carcinoma.

More than 250 million people worldwide are chronically infected with the hepatitis B virus (HBV) and have a 200-fold increased risk of developing hepatocellular carcinoma (HCC). This is one of the most common cancers in the world with a geographical distribution highest in areas where HBV is endemic. A number of molecular mechanisms have been proposed to explain this correlation including an acutely transforming viral oncogene; chromosomal aberrations due to HBV integration (i.e. deletions, translocations, duplications); activation of cellular proto-oncogenes; inactivation of cellular anti-oncogenes; and transactivation of cellular genes by HBV gene products. HCC usually develops only after 20-30 years of persistent HBV infection accompanied by hepatocyte necrosis, inflammation and regenerative hyperplasia. Because HBV is not directly cytopathic, liver injury must be immune mediated. Factors that predispose HBV-infected individuals to develop HCC are chronicity, an immune response and liver injury rather than a direct genetic event. Hepatic injury and continuous hepatocyte regeneration may allow an accumulation of multiple mutational events sufficient for the emergence of HCC. Pathways which lead to chronicity, the immune response during HBV infection, mechanisms of pathogenesis and methods to prevent HBV infection are all relevant to the development of HCC. Recent studies characterizing the humoral and cellular immune responses in patients chronically infected with HBV and transgenic mouse models of HBV-specific immune tolerance and pathogenesis are providing new insights into the complex association between HBV infection and HCC.

389. Testing the Oncogenic Potential of Retroviral and Lentiviral Vector Integration

Retroviral Vectors (RVs) expressing therapeutic genes have been used to transduce Hematopoietic Stem Cells (HSCs) and successfully treat hematological diseases in mice and humans. Unfortunately, RVs also triggered oncogenesis, raising concerns for the use in gene therapy. Such concerns also apply to other integrative vectors, such as Lentiviral Vectors (LVs). We have established a mouse HSC transplantation model sensitive to genotoxic stress to measure the tumorigenic potential of RVs and LVs in vivo. In mice, chronic retroviral infection triggers leukemias by insertional activation of cellular proto-oncogenes. Tumor-prone mice with specific genetic mutations develop malignancies with earlier onset after MuLV infection. We transduced HSCs from leukemia-prone Ckdn2a-/- mice with different LV and RV doses and transplanted them into lethally irradiated, syngeneic wild-type recipients. We used conventional RV expressing GFP from the LTR and a self inactivating (SIN)-LV expressing GFP from an internal PGK promoter. Three groups of mice were transplanted with BM-derived lin- Cdkn2a-/- cells, transduced with either RV or LV or untransduced. Transduction protocols were similar to those used in clinical gene therapy settings. The kinetics of tumor onset and tissue histopathology were monitored and compared for each group.

3. Effect of Retroviral and Lentiviral Vector Integrations on Transcription of Flanking Genes

In mouse, retroviral infection triggers leukemias by activation of cellular proto-oncogenes. This is usually mediated by promoter/enhancer sequences in the proviral LTR that recruit ubiquitous and/or cell type-specific transcription factors, and up-regulate expression of flanking genes, up to 300 Kb away from the integration site, and independently of orientation. Unfortunately, Retroviral Vectors (RV) used in gene therapy also triggered unwanted oncogenesis, indicating that the risk of RV insertional mutagenesis had been underestimated, and raising concerns for their further use in gene therapy. In addition RV, Lentiviral (LV) and Adeno-Associated vectors have the tendency to integrate in the proximity of expressed genes. Thus, these safety concerns apply to all integrative vectors, in particular to the closely related LV that have been proposed as improved versions of RV for several applications. The actual frequency and extent of transcriptional de-regulation occurring at randomly picked retroviral integration sites is currently unknown. In fact, integration sites retrieved from tumors are likely the result of in vivo selection for proto-oncogene activation, and it has proven very difficult to estimate the frequency of such events in unselected target cells. This information is critical to properly assess the insertional mutagenesis risk of each vector. Thus, we embarked in testing and comparing the effect of non-selected RV and LV integration on the expression of flanking genes. We generated three panels of hematopoietic cell clones, each carrying a single insertion of either a conventional RV expressing GFP from the LTR, a self inactivating (SIN)-RV expressing GFP from an internal PGK promoter, and a third-generation SIN-LV expressing GFP from the same PGK promoter. For each vector, we isolated 150 clones, and retrieved genomic DNA flanking the proviral insertion in 50 of them by linear amplification-mediated PCR. So far, sequence analysis has allowed in silico mapping of 40 single integrations. Even if our study requires a relatively small sample size, it is apparent that integration site selection differed between RV and LV; RV integrated within regions of lower gene density with respect to LV; 66% of RV insertions were intergenic, while 83 % of LV insertions were intragenic; 50% of RV insertions were found between 0.5–5kb from the closest transcription start site, as compared to only 5% of LV insertions. We then selected all the genes (SeqRef database) contained in a 600 kb interval centered on each integration site (344 up to now). We are currently comparing their relative expression levels in all cell clones by microarray technology, using custom-made microchips spotted with the selected sequences, and probing with total cDNA obtained from each clone and a pool of control untransduced ones. This analysis will indicate the frequency and extent of transcriptional perturbation around RV and LV integration. We expect to find significant differences between each vector, according to its viral origin and design. If so, our data will be critical to estimate the relative risk of oncogene activation in gene therapy applications.

Transforming Growth Factor β

Transforming growth factor β (TGFβ) has emerged as a pre-eminent negative growth factor with inhibitory effects on a range of malignant epithelial cell types. There is increasing evidence that the malignant phenotype is associated with an imbalance of growth factors within the local microenvironment of tissues. Oncogenic events promoting neoplastic progression could involve either an excess of positive growth factors or a deficiency of negative ones such as TGFβ. Whether altered levels of TGFβ are directly implicated in processes of carcinogenesis remains unresolved, but local endogenous levels of TGFβ can be manipulated pharmacologically. This may be of relevance to the mode of action of some agents with proven therapeutic efficacy. Thus, boosting of endogenous TGFβ levels could correct any pre-existing or acquired deficiency, or compensate for overproduction of positive stimulatory growth factors resulting from activation of cellular proto-oncogenes. This article reviews the evidence for modulation of TGFβ synthesis and production by several commonly used pharmacological agents, and assesses the clinical potential of this strategy both for the treatment of established tumours and prevention of malignancy.

Transplacental transfer of genotoxins and transplacental carcinogenesis.

A number of chemical compounds induce cancer in the offspring of animals treated with these compounds. The fetus is sensitive to the toxic and teratogenic effects of chemicals in the early embryonic stages, whereas it is sensitive to carcinogenic effects during late fetal stages. Carcinogens may be direct acting or may require metabolic oxidation such as those in tobacco smoke. Activation can occur in utero. Animal experiments indicate that tumors can be initiated in utero, commonly by activation of cellular proto-oncogenes, and that promotion can occur after birth by postnatal treatment with tumor promoters. This may have important implications for humans. The initial peak of cancer incidence during the first 5 years of life may be due to prenatal exposure of either parent to mutagens, but the role of paternal exposure in relation to childhood cancer is controversial. There is an increased risk of cancer in children whose fathers work in heavy industry or whose mothers work in medical or dental services. The exact etiological agents have not been unequivocally identified. Information on human transplacental exposure to carcinogens and genotoxins is limited and based on measurement of maternal plasma concentrations or analysis of cord blood. Transplacental transfer of carcinogens in smoke and smoke-related damage to fetal tissue have been demonstrated. The mycotoxin aflatoxin B1 or its metabolites have been detected in cord blood, as have metabolites of pesticides and polychlorinated biphenyls. New biomarkers may provide important information on the transplacental transfer of genotoxic compounds.(ABSTRACT TRUNCATED AT 250 WORDS)

The Chromosomes in Human Cancer and Leukemia

The past decade has witnessed significant advances in our understanding of some aspects of cancer biology, especially the genetic changes in cancer cells. During this period, the critical role of chromosome changes in the complex process of malignant transformation has received further recognition. For years, the cytogenetic database has been tapped by molecular biologists who have used the information as a starting point to tackle problems at the molecular level. Cytogenetic analysis was the key to defining two major categories of genetic rearrangements, namely, recurring chromosomal translocations and consistent deletions. These abnormalities have now been shown to contribute to the oncogenic process through either the modification and activation of cellular protooncogenes or the inactivation of tumor suppressor genes. Clinicians have also used cytogenetic information to assign prognosis in acute leukemia, lymphoma, and certain solid tumors. Thus, the karyotypic picture of any particular tumor has become of value to clinicians, biologists,

Oncogenes as clinical prognostic indicators.

Recent advances in molecular biology have enabled oncologic researchers to probe the mechanisms of neoplasm at the level of individual gene expression. Current studies of oncogenesis suggest that specific genes may induce cancer and that normal resident genes, termed proto-oncogenes, required for cellular function can be converted to oncogenes by genetic mutation [1]. Alterations in the structure or expression of certain proto-oncogenes appear to occur through a variety of mechanisms, including point mutations within the gene, rearrangements within the coding sequence of the gene or within a noncoding but functionally effective segment, amplification or overexpression of the gene, and deletion of possible ‘antioncogenes.’ Each of these mechanisms may result in the activation of cellular proto-oncogenes and are found to be associated experimentally with human cancer [2]. While it has not been proven that these genetic anomalies are directly responsible for tumorigenesis, the frequency of their presence and/or expression in some oncologic diseases suggests a biologic importance in the transformation and growth of neoplastic cells [3, 4].

Comparison of Cellular Protooncogene Activation and Transformation-Related Activity of Human Melanocytes and Metastatic Melanoma

Two cell lines (NH and HM1), established from patients with metastatic melanomas, were evaluated for the presence of activated cellular protooncogenes. Northern blot analysis demonstrated increased expression of the c-myc gene (from 9 to 14 times) in NH and HM1 cell lines by densitometric comparison with human melanocyte cell lines. Analysis of the expression of 13 additional cellular protooncogenes revealed either no detectable levels (c-fms, c-abl, v-src, c-erb A1, c-erb B, v-mos, TGF beta, and c-myb) or unaltered expression levels (cH-ras, N-ras, c-fos, and c-sis) in normal human melanocytes and metastatic melanomas. Elevated expression of the c-myc gene was also detected in two long-term cultured melanoma cell lines (RPMI 7951 and SKMEL-30). Analysis of c-myc expression by in situ hybridization in HM1 cells showed that expression was not localized to a sub-population of cycling cells and all cells were overexpressing c-myc mRNA. Differences in relative abundance of c-myc transcripts suggests a relationship with the ability of DNA from these cell lines to efficiently transform NIH 3T3 cells and form colonies on soft agar.

Avian endogenous provirus (ev-3) env gene sequencing: Implication for pathogenic retrovirus origination

The avian endogenous env gene product blocks the surface receptor and, as a result, cells become immune to related exogenous retroviruses. On the other hand, the same sequence can be included in the pathogenic retrovirus genome, as shown by oligonucleotide mapping. However, since the complete env gene sequence was not known, the comparison of genomic nucleotide sequences was not possible. Therefore an avian endogenous provirus with an intact env gene was cloned from a chicken gene bank and the regions coding for the C terminus of the gp85 and gp37 proteins were sequenced. Comparison of this sequence with those of other retroviruses proved that one of the pathogenic viruses associated with osteopetrosis is a cross between avian endogenous virus and Rous sarcoma virus. Retroviruses and, especially, endogenous retroviruses are traditionally of the most developed models of viral carcinogenesis. Many endogenous retroviruses are implicated in neoplastic transformation of the cell. For instance, endogenous mouse mammary tumor virus of some inbred lines appears to be the only causative agent in these mammary cancers. Other even nonpathogenic murine endogenous retroviruses are involved in the origination of MCF-type recombinant acute leukosis viruses. Some endogenous retroviruses are implicated in the transduction or activation of cellular protooncogenes. Our interest in endogenous viruses is based on their ability to make cells resistant to exogenous retroviruses. Expression of their major envelope glycoprotein leads to cellular surface receptor blockage and imparts immunity to infection by the related leukemia retroviruses. This problem is quite elaborated for chicken endogenous virus RAV-O (7-9).(ABSTRACT TRUNCATED AT 250 WORDS)

The Significance of Retroviruses in Oncology

Retroviruses first attracted attention as the etiological agents of tumors in various animals, including birds, rodents and primates. The retrovirus-induced tumors comprise above all T- and B-cell leukemias/lymphomas, chronic myelogenous leukemia and mammary carcinomas, and are characterized by a long latent period between infection and manifestation of the disease. Since their detection, oncogenic retroviruses have been the object of intense study contributing to our knowledge of basic mechanisms and molecular events involved in carcinogenesis in general. An essential step in the retrovirus life cycle is the covalent integration of the double-stranded DNA copy of viral RNA into the cellular genome, forming the provirus. The proviruses are quite stable and are generally a permanent acquisition for the cellular genome. Therefore, the presence of the provirus can have profound genetic implications for the host cell. There are at least three main routes that are assumed to lead to retroviral oncogenesis: Transduction of cell-derived oncogenes (v-onc) carried by some retroviruses, activation of cellular proto-oncogenes (c-onc) in cis by insertional mutation or activation of cellular genes in trans by virus encoded transcription factors.

A novel c-abl protein product in Philadelphia-positive acute lymphoblastic leukaemia.

Activation of cellular proto-oncogenes as a result of chromosomal abnormalities has been implicated in the development of some human malignancies. Perhaps one of the most striking examples of this association occurs in chronic myelogenous leukaemia, where the Philadelphia (Ph) translocation results in substitution of the 5' end of the c-abl proto-oncogene with bcr gene sequences. A unique hybrid bcr-abl message is produced. As the Ph translocation is also present in some patients with acute lymphoblastic leukaemia, we initiated studies to determine if similar genomic events occur in these two different forms of Ph-positive leukaemia. Here we report that the Ph translocation in acute lymphoblastic leukaemia can result in production of a novel aberrant c-abl protein that is distinct from the bcr-abl protein found in Ph-positive chronic myelogenous leukaemia. Our observations suggest that alternative mechanisms of activation of c-abl exist, and may be important in the development of human acute lymphoid rather than chronic myeloid malignancies.

An approach to oncological genetics.

Oncological genetics is defined as a branch of clinical cancer research dealing with the identification, description, analysis, and prevention of those human neoplasias and their related/associated syndromes in which a vertical (hereditary) transmission is assumed. The present clinical basis of this field is constituted by the 240 inherited preneoplasias and neoplasias that have been detected so far. The main hypothesis in oncological genetics might be the existence of an inherited cancer proneness phenotype (CPP), in whose determination the processes involved in the activation of cellular proto-oncogenes would presumably play a role. It is conjectured that CPP is a quantitative (random) variable with extreme values. Such indicators can be identified in small populations having a structure (i.e., tree) so that the collection of comprehensive pedigree data is indispensable.