Acute promyelocytic leukemia (APL) is a well-defined entity among acute leukemia, cytogenetically characterized by a t(15;17) (q22;q11–12) translocation. In vitro and in vivo studies suggest that all-trans retinoic acid (RA) treatment restores cell maturation. We have isolated the first permanent cell line with t(15;17), derived from the marrow of a patient with APL in relapse. The establishment of the cell line, its morphologic, karyotypic, and immunohistochemical features are reported. RA induced cell line maturation. Cells strongly expressed myeloid markers, but also some T-cell markers. Additional karyotypic abnormalities, a 12p rearrangement and the possible presence of a homogeneous staining region (HSR) on 19q+ are discussed both in relation to T-cell (CD2, CD4) and monocyte (CD9) markers, and to the acquired cell growth autonomy. The cell line represents a remarkable tool for biomolecular studies.

Twenty-two patients with acute promyelocytic leukemia were treated with all-trans retinoic acid (RA, 45 mg/m2 per day) for 90 days. Of the 22, four patients were previously untreated, two were resistant after conventional chemotherapy, and 16 were in first (n = 11), second (n = 4), or third (n = 1) relapse. We observed 14 complete response, four transient responses, one failure, and three early deaths. Length of hospitalization and number of transfusions were notably reduced in complete responders. Correction of coagulation disorders and an increase of WBCs were the first signs of all-trans RA efficacy. Morphologic analysis performed at days 0, 15, 30, 45, 60, and 90 showed that complete remissions were obtained without bone marrow (BM) hypoplasia. Presence of Auer rods in the maturing cells confirmed the differentiation effect of the treatment. At remission, the t(15;17) initially present in 20 patients was not found. The in vitro studies showed a differentiation in the presence of all-trans RA in 16 of the 18 tested cases. The single nonresponder to all trans RA in vitro did not respond in vivo. Adverse effects of RA therapy--skin and mucosa dryness, hypertriglyceridemia, and increase of hepatic transaminases-- were frequently noted. We also observed bone pain in 11 patients and hyperleukocytosis in four patients. Whether maintenance treatment consisted of low-dose chemotherapy or all-trans RA, early relapses were observed. Five patients are still in complete remission (CR) at 4 to 13 months. Our study confirms the major efficacy of all-trans RA in M3, even in relapsing patients. Remissions are obtained by a differentiation process.

The human TEL gene is involved in several 12p13 chromosomal abnormalities present in various human hematological malignancies, the most frequent being the t(12;21)(p13;q22), speci®c for childhood acute lymphoblastic leukemia. The predicted product of TEL harbours an amino acid region similar to the ETS DNA binding domain. We now report the isolation of the murine TEL cDNA and the characterization of the human TEL proteins. Human and murine TEL proteins are particularly homologous within their aminoterminal regions and their ETS domains. TEL proteins are nuclear and display speci®c DNA binding activity toward classical ETS binding sites. In addition, we show that TEL mRNAs initiate translation at either of the two ®rst inframe ATGs (codon 1 and 43) to encode 50 kDa and 57 kDa TEL proteins. In vivo, each of these primary translational products is modi®ed by multiple phosphorylation events.