Molecular analysis of a t(11;14)(q23;q11) from a patient with null-cell acute lymphoblastic leukemia

Analysis of mutagenic V(D)J recombinase mediated mutations at the HPRT locus as an in vivo model for studying rearrangements with leukemogenic potential in children

Pediatric acute lymphocytic leukemia (ALL) is a multifactorial malignancy with many distinctive developmentally specific features that include age specific acquisition of deletions, insertions and chromosomal translocations. The analysis of breakpoint regions involved in these leukemogenic genomic rearrangements has provided evidence that many are the consequence of V(D)J recombinase mediated events at both immune and non-immune loci. Hence, the direct investigation of in vivo genetic and epigenetic features in human peripheral lymphocytes is necessary to fully understand the mechanisms responsible for the specificity and frequency of these leukemogenic non-immune V(D)J recombinase events. In this review, I will present the utility of analyzing mutagenic V(D)J recombinase mediated genomic rearrangements at the HPRT locus in humans as an in vivo model system for understanding the mechanisms responsible for leukemogenic genetic alterations observed in children with leukemia.

CD3+CD4-CD8-TCR-alphabeta+ T-cell lymphoma with clinical features of primary effusion lymphoma: an autopsy case

We report an unusual case of T-cell lymphoma presenting as ascites. A 72-year-old HIV-negative woman was admitted to our hospital for abdominal discomfort associated with increasing abdominal girth over the course of 1 month. Physical examination showed a tense and distended abdomen and edema of the lower extremities. There was no hepatosplenomegaly or lymphadenopathy. A computed tomographic scan of the abdomen and chest showed massive ascites and pleural effusions, but there was no evidence of tumor masses or lymph node enlargement. The cytospin prepared from the peritoneal fluid was hypercellular and composed of a population of monotonous, large cells containing fine chromatin. No herpesvirus-8 (HHV-8) DNA was detected by polymerase chain reaction in the cells. Immunohistochemistry showed the neoplastic cells to be CD3+, CD4, CD7+. CD8-, CD34-, CD56, and TCR-alphabeta+. Repeated cytogenetic studies showed common abnormalities of del(1) (p11p22), +i(7)(ql0), and t(11:14)(q23;q11). The morphologic and immunologic findings were suggestive of peripheral T-cell lymphoma (PTCL), unspecified. This case suggests that some PTCLs with clonal chromosomal aberrations can exhibit peculiar serosal spreading in the absence of HHV-8 infection.

Cryptic signals and the fidelity of V(D)J joining

V(D)J recombination is responsible for the de novo creation of antigen receptor genes in T- and B-cell precursors. To the extent that lymphopoiesis takes place throughout an animal's lifetime, recombination errors present an ongoing problem. One type of aberrant rearrangement ensues when DNA sequences resembling a V(D)J joining signal are targeted by mistake. This study investigates the type of sequence likely to be subject to mistargeting, the level of joining-signal function associated with these sequences, and the number of such cryptic joining signals in the genome.

Molecular basis of 11q23 rearrangements in hematopoietic malignant proliferations

Chromosomal abnormalities of the 11q23 band occur frequently in various hematopoietic malignant disorders. Because numerous partner chromosomes have been previously described, it is now important to determine the number of genes involved at 11q23 and to clarify the role of the partner genes. Recent efforts in several laboratories have identified a trithorax-related gene that is involved in most of the 11q23 abnormalities. The aim of this review is to summarize the recent data concerning these 11q23 rearrangements and the understanding of their consequences.

Rearrangement of the MLL gene in acute lymphoblastic and acute myeloid leukemias with 11q23 chromosomal translocations

BACKGROUND

Translocations involving chromosome band 11q23 are very frequent in both acute lymphoblastic and acute myeloid leukemias and are the most common genetic alteration in infants with leukemia. In all age groups and all phenotypes of leukemia, an 11q23 translocation carries a poor prognosis. A major question has been whether one or several genes on band 11q23 are implicated in these leukemias. Previously, we identified the chromosomal breakpoint region in leukemias with the common 11q23 translocations and subsequently cloned a gene named MLL that spans the 11q23 breakpoint.

METHODS

We isolated a 0.74-kb BamHI fragment from a complementary DAN (cDNA) clone of the MLL gene. To determine the incidence of MLL rearrangements in patients with 11q23 abnormalities, we analyzed DNA from 61 patients with acute leukemia, 3 cell lines derived from such patients, and 20 patients with non-Hodgkin's lymphoma and 11q23 aberrations.

RESULTS

The 0.74-kb cDNA probe detected DNA rearrangements in the MLL gene in 58 of the patients with leukemia, in the 3 cell lines, and in 3 of the patients with lymphoma. All the breaks occurred in an 8.3-kb breakpoint cluster region within the MLL gene. The probe identified DNA rearrangements in all 48 patients with the five common 11q23 translocations involving chromosomes 4, 6, 9, and 19, as well as in 16 patients with uncommon 11q23 aberrations. Twenty-one different chromosomal breakpoints involving the MLL gene were detected.

CONCLUSIONS

MLL gene rearrangements were detected with a single probe and a single restriction-enzyme digest in all DNA samples from patients with the common 11q23 translocations as well as in 16 patients or cell lines with other 11q23 anomalies. The ability to detect an MLL gene rearrangement rapidly and reliably, especially in patients with limited material for cytogenetic analysis, should make it possible to identify patients who have a poor prognosis and therefore require aggressive chemotherapy or marrow transplantation.