The t(12;21)(p13;q22) fusion gene is the most frequent genetic lesion described in precursor B cell acute lymphoblastic leukemia (ALL) of childhood occurring in a quarter of cases. This gene rearrangement is associated with a good outcome presenting a high response rate to chemotherapy. In spite of its potential clinical relevance, the t(12;21) translocation usually goes undetected with conventional cytogenetic procedures. In the present study we utilized an objective flow cytometric approach (multiparametric quantitative analysis) for the phenotypic characterization of this type of ALL. We studied a total of 74 precursor B-ALL children, including 21 t(12;21) + and 53 t(12;21) − cases. Our results show that the t(12;21)(p13;q22) + ALLs display a higher intensity of CD10 (P = 0.0016) and HLADR (P = 0.005) expression together with lower levels of the CD20 (P = 0.01), CD45 (P = 0.01), CD135 (P = 0.003) and CD34 (P = 0.03) antigens as compared to the t(12;21) − cases. Moreover, as regards CD34 expression, we observed a more heterogeneous antigen expression within individual patients with higher coefficients of variation (median of 202 vs 88, P = 0.0001). A multivariate analysis disclosed that with the immunophenotypic approach used identification of t(12;21) + cases can be achieved with a sensitivity of 86% and a specificity of 100%. We conclude that childhood precursor B-ALL carrying the t(12;21) translocation display characteristic phenotypic features which could provide a rapid, simple, sensitive and specific screening method to select for those cases that should undergo confirmatory molecular analysis. Leukemia (2000) 14, 1225-1231.

The 'promiscuous' E2A gene, at 19p13.3, is fused with two different molecular partners, PBX1 and HLF, following two chromosome translocations recurrent in childhood pre-B ALL. We have identified a novel gene, FB1, by virtue of its fusion with E2A and by a combination of molecular techniques. FB1 was localized on 19q13.4, suggesting that the novel chimera originated by a cryptic rearrangement of chromosome 19. Two FB1 transcripts, of 1.2 kb and 1.1 kb, are differentially expressed at low level in a variety of human tissues, including hemopoietic cell lines from different lineages. Accordingly, FB1 cDNA displays high homology with a number of cDNA clones from different human tissues. High homology was found also with cDNA clones from mouse and rat, suggesting that the sequence might be conserved at least among mammals. The function of the putative FB1 protein, however, is currently unknown as database sequence comparisons have failed to reveal strong homology with known proteins. The E2A/FB1 fusion appears to be a recurrent feature of pre-B ALLs, suggesting that it might have a role in the development and/or progression of leukemogenesis.

In this study we used reverse transcriptase-polymerase chain reaction (RT-PCR) for the longitudinal monitoring of minimal residual disease in 12 patients with All-1/AF-4 positive ALL. Of these, seven also showed at presentation a typical t(4;11) cytogenetic translocation. Seven patients were infants <18 months of age and five were adults. Eleven patients were treated with high-dose intensive induction and consolidation chemotherapy without bone marrow transplantation and one received conservative treatment due to poor performance status. Three had resistant disease, four relapsed within 12 months after achieving complete remission, and five are in continuous complete remission (CCR) at 32, 39, 52, 53 and 61 months from diagnosis, respectively. The sequential analysis of the ALL-1/AF-4 hybrid transcript showed a persistently negative RT-PCR in the five CCR long-term survivors. The PCR analysis resulted persistently positive in the remaining seven cases, including the four cases who relapsed after the achievement of clinical CR. These data emphasize the clinical relevance of PCR monitoring analysis in t(4;11) ALL patients and should be considered in order to better determine variable post-remission treatment according to risk prediction.

Summary:of donor origin are detectable, or as mixed chimeras if a mixture of both donor and recipient origin cells are found after BMT. With the use of increasingly sensitive techFifty-eight samples of bone marrow (31), whole peripheral blood (8) and separated fractions of circulating niques, mixed chimerism is frequently observed after allogeneic BMT. [2][3][4][5][6] Several factors related to transplant promononuclear (11) and polymorphonuclear (8) cells from 18 male patients, transplanted for hematological discedures (type of donor, conditioning regimens, T cell depletion, graft-versus-host disease (GVHD) prophylaxis) eases from related (14) or unrelated (4) female donors were analyzed for chimerism at subsequent intervals and patient features (underlying disease, age) have been shown to be associated with an increase in mixed chimer-(range, 1-72 months) following bone marrow transplantation, by means of PCR amplification of the Y-chromism (MC) after sibling BMT. [7][8][9][10][11][12] Residual male cells were shown to persist in patients grafted with T cell non-depleted osome-specific DYS14 sequence, revealed by a radiolabelled hybridization probe (dot blot technique, 0.01% marrow from an HLA-identical female donor, when clinical and hematological conditions indicated a complete sensitivity). Detection of male cells was positive in all but two of 52 samples collected within the third year engraftment and the absence of recurrent disease. 4,5,13 The need to extend the analysis of MC following BMT to a after transplantation and negative in six samples collected from three patients after the third year. In the larger series of prospectively evaluated patients with adequate follow-up, prompted us to investigate the persistfirst year after transplantation, mixed chimerism was found in all patients, apparently with no correlation ence of residual recipient cells in a series of pediatric male patients grafted from a female donor. Our findings on seriwith graft-versus-host disease. Comparable results were found in fractions of mononuclear and polymorphoally collected samples from patients in long-term continuous complete remission (CCR) establish the kinetics of the nuclear cells, when analyzed separately. The persistence of very low levels of recipient cells in patients in conresidual recipient cells, with no apparent correlation with post-transplant events. tinuous complete remission until the third year after transplantation, suggests the persistence of normal host hemopoiesis for a long period of time after the so-called myeloablative regimen. The progressive negativization, Patients and methods occurring in our patients between the second and the fourth year after transplantation, could signify the disPatients appearance of residual host hemopoiesis or its decrease to below the detection level of this highly sensitive Eighteen male patients who received a marrow graft from familial (14) or unrelated (four) female donor at the Pedimethod. Keywords: chimerism; bone marrow transplantation; dot atric Department of ...

The t(1;19) is the most frequent recurring chromosomal translocation in childhood acute lymphoblastic leukaemia (ALL). In most cases typical chimaeric E21-PBX1 transcripts are expressed as a consequence of this rearrangement, allowing the molecular detection of the t(1;19) at the RNA level. This translocations has been associated with a poor clinical outcome, although intensified chemotherapy has been reported to nullify its adverse prognostic impact. We therefore used reverse transcriptase/polymerase chain reaction (RT-PCR) to detect residual leukaemic cells at successive times during treatment and to monitor the response to chemotherapy in six t(1;19)-positive ALL pediatric patients. Five of these patients rapidly achieved molecular remission and no evidence of minimal residual disease (MRD) was found in the remission bone marrows beyond the third month of treatment. One patient still displayed residual leukaemic cells at the end of therapy, although she has been in continuous complete clinical remission (CCR) for 84 months. However, this patient is peculiar in our series in that two different types of chimaeric E2A-PBX1 transcripts were expressed in her leukaemic cells, only one being detectable in remission.