Stephen H. Benedict

T cell receptor delta gene rearrangements in acute lymphoblastic leukemia.

Using a newly isolated cDNA clone encoding the TCR-delta gene and genomic probes, we have analyzed T cell receptor (TCR) delta gene rearrangement in 19 patients with T cell acute lymphoblastic leukemia (T-ALL) and 29 patients with B-precursor ALL. Five out of seven CD3- T-ALL and 4 of 12 CD3+ T-ALL showed bi-allelic rearrangements of the TCR-delta gene. In three CD3+ patients, a single allelic TCR-delta gene rearrangement was observed with rearrangement of the TCR-alpha gene on the other allele. In five CD3+ patients with bi-allelic rearrangements of the TCR-alpha gene, the TCR-delta gene locus was deleted. Transcription of the TCR-delta gene was also analyzed in six T-ALL. Five patients expressed TCR-delta transcripts. Only one T-ALL, presumably derived from the most immature T lineage cells, did not have TCR-delta transcripts, but expressed TCR-gamma and 1.0-kb truncated TCR-beta transcripts. In B-precursor ALL, 20 patients (69%) showed rearrangements of the TCR-delta gene. The frequency of TCR-delta gene rearrangement was higher than TCR-alpha (59%), gamma (52%), or beta (31%) genes. These findings suggest that TCR-alpha gene rearrangements may take place after rearrangements of the TCR-delta gene with concomitant deletion of rearranged TCR-delta genes in T cell differentiation. Among leukemic cells of B lineage, the TCR-delta gene is the earliest rearranging TCR gene, followed by TCR-gamma and beta gene rearrangements.

T cell receptor alpha-chain gene rearrangements in B-precursor leukemia are in contrast to the findings in T cell acute lymphoblastic leukemia. Comparative study of T cell receptor gene rearrangement in childhood leukemia.

We have analyzed T cell receptor alpha-chain gene configuration using three genomic joining (J) region probes in 64 children with acute lymphoblastic leukemia (ALL). 11 out of 18 T-ALLs were T3 positive; alpha-chain gene rearrangements were demonstrated in only two of 18, indicating that the majority of T-ALLs would have rearrangements involving J alpha segments located upstream of these probes. In contrast, 15 out of 46 B-precursor ALLs showed rearrangements of the alpha-chain gene and J alpha segments located approximately 20-30 kb upstream of the constant region were involved in 13 of these patients. Nine of 15 B-precursor ALLs with rearranged alpha-chain genes had rearrangements of both gamma- and beta-chain genes, whereas the remaining six had no rearrangements of gamma- and beta-chain genes. These findings indicated that alpha-chain gene rearrangement is not specific for T lineage cells and gamma- and/or beta-chain gene rearrangement does not appear essential for alpha-chain gene rearrangement, at least in B-precursor leukemic cells.

Comparison of T cell receptor alpha, beta, and gamma gene rearrangement and expression in T cell acute lymphoblastic leukemia.

We have analyzed the configuration of the T cell receptor (TCR) alpha gene using newly developed genomic joining region (J alpha) probes, which cover approximately 80 kb of the J alpha region upstream from the constant region in 19 patients with T cell acute lymphoblastic leukemia (T-ALL) and in three CD3- leukemic T cell lines (HSB2, CEM, and MOLT4). In parallel, transcription of the TCR-alpha, beta, and gamma genes was examined in 11 of these patients and in the T cell lines. All T-ALL and the three T cell lines exhibited both TCR-gamma and beta gene rearrangements. 8 of 10 T-ALL and all T cell lines expressed TCR-gamma transcripts. All samples tested expressed both TCR-beta and CD3-gamma transcripts. TCR alpha transcripts were only observed in CD3+ T-ALL but not in CD3- T-ALL or the CD3- cell lines. Among the CD3+ T-ALL, eight had TCR-alpha gene rearrangements. In addition, TCR-alpha gene rearrangements were detected in one CD3- T-ALL and all three T cell lines. These leukemic cells may represent a transient stage between rearrangement and expression and provide an opportunity for analyzing the mechanism regulating the expression of the TCR-alpha gene.

Chapter 16 Activation of Sodium—Hydrogen Exchange by Mitogens

Publisher Summary Amiloride-sensitive Na + -H + exchange activity has been detected in the plasma membrane of virtually all mammalian cell types studied to date. The exchanger, or antiport, catalyzes the electroneutral counter transport of Na + for H + . Though the mechanism is reversible, entry of Na + in exchange for intracellular H + is the predominant transport mode under physiological conditions. This net extrusion of acid equivalents tends to offset the spontaneous tendency of the cells to become acidic, which results from metabolic acid production and from the electrodiffusive accumulation of H + (or depletion of OH - ) driven by the internally negative plasma membrane potential. The Na + -H + antiport is virtually quiescent at physiological cytosolic pH (pH i ), but is markedly activated when the cytoplasm becomes acidic. Such behavior, together with the direction of net acid transport, suggests that the antiport plays an important role in the regulation of pH i in resting (nonproliferating) cells. In addition to being activated by cytosolic acidification, the antiport can also be stimulated without prior pH i change by the addition of mitogenic or comitogenic agents such as growth factors and phorbol esters, respectively.