Frequency and clinical impact of CDKN2A/ARF/CDKN2B gene deletions as assessed by in-depth genetic analyses in adult T cell acute lymphoblastic leukemia.

Recurrent deletions of the CDKN2A/ARF/CDKN2B genes encoded at chromosome 9p21 have been described in both pediatric and adult acute lymphoblastic leukemia (ALL), but their prognostic value remains controversial, with limited data on adult T-ALL. Here, we investigated the presence of homozygous and heterozygous deletions of the CDKN2A/ARF and CDKN2B genes in 64 adult T-ALL patients enrolled in two consecutive trials from the Spanish PETHEMA group. Alterations in CDKN2A/ARF/CDKN2B were detected in 35/64 patients (55%). Most of them consisted of 9p21 losses involving homozygous deletions of the CDKNA/ARF gene (26/64), as confirmed by single nucleotide polymorphism (SNP) arrays and interphase fluorescence in situ hybridization (iFISH). Deletions involving the CDKN2A/ARF/CDKN2B locus correlated with a higher frequency of cortical T cell phenotype and a better clearance of minimal residual disease (MRD) after induction therapy. Moreover, the combination of an altered copy-number-value (CNV) involving the CDKN2A/ARF/CDKN2B gene locus and undetectable MRD (≤ 0.01%) values allowed the identification of a subset of T-ALL with better overall survival in the absence of hematopoietic stem cell transplantation.

Leukemia-initiating cell activity requires calcineurin in T-cell acute lymphoblastic leukemia.

Despite their initial efficient response to induction chemotherapy, relapse remains frequent in patients with T-cell acute lymphoblastic leukemia (T-ALL), an aggressive malignancy of immature T-cell progenitors. We previously reported sustained calcineurin (Cn) activation in human lymphoid malignancies, and showed that Cn inhibitors have antileukemic effects in mouse models of T-ALL. It was unclear, however, from these studies whether these effects resulted from Cn inhibition in leukemic cells themselves or were an indirect consequence of impaired Cn function in the supportive tumor microenvironment. We thus generated a Notch (intracellular Notch 1, ICN1)-induced T-ALL mouse model, in which conditional Cn genetic deletion is restricted to leukemic cells. Ex vivo, Cn deletion altered the adhesive interactions between leukemic cells and their supportive stroma, leukemic cell survival, proliferation, migration and clonogenic potential. In vivo, Cn activation was found to be critical for leukemia initiating/propagating cell activity as demonstrated by the failure of Cn-deficient leukemic cells to transplant the disease to syngeneic recipient mice. Importantly, combination of vincristine treatment with Cre-mediated Cn ablation cooperated to induce long-term remission of ICN1-induced T-ALL. These findings indicate that Cn is a promising target in T-ALL relapse prevention, and call for clinical trials incorporating Cn inhibitors during consolidation therapy.

Primary structure of the activation segment of procarboxypeptidase A from porcine pancreas.

The complete primary structure of the activation segment of monomeric procarboxypeptidase A from porcine pancreas has been determined by automated and manual Edman-like degradation methods performed on its fragments generated by enzymatic cleavage. The polypeptide consists of 94 residues, with a molecular mass of 10,768, and presents a high proportion of acidic and hydrophobic residues and a proline-rich region in the center of the molecule. Comparison of this sequence with the already reported equivalent sequence deduced from rat procarboxypeptidase A cDNA reveals a very high degree of homology between the two propeptides (up to a 81% of identities), which is even higher in certain large zones of the molecule.