We investigated the engraftment properties and impact on patient outcome of 50 pediatric acute lymphoblastic leukemia (ALL) samples transplanted into NOD/SCID mice. Time to leukemia (TTL) was determined for each patient sample engrafted as weeks from transplant to overt leukemia. Short TTL was strongly associated with high risk for early relapse, identifying an independent prognostic factor. This high-risk phenotype is reflected by a gene signature that upon validation in an independent patient cohort (n = 197) identified a high-risk cluster of patients with early relapse. Furthermore, the signature points to independent pathways, including mTOR, involved in cell growth and apoptosis. The pathways identified can directly be targeted, thereby offering additional treatment approaches for these high-risk patients.

Although treatment of childhood acute myelogenous leukemia (AML) has substantially improved in the last 15 years, in nearly half of the patients disease recurs. The aim of this study was to establish the prognosis of relapsed childhood AML and to identify prognostic factors for achievement of second remission and survival. From February 1988 to July 1996, 134 children with first relapse of AML were reported to the study center of the AML-BFM group. 102 patients treated intensively to induce second remission were prospectively followed. With various regimens, complete remission was achieved in 52 of 102 patients (51%), 27 children were alive in median 2.5 years (range, 0.4-7 years) after relapse. Disease-free survival was observed in seven of 16 patients transplanted from a matched sibling donor, one of four after matched unrelated bone marrow transplantation, 10 of 22 after autologous transplantation and five of nine patients after chemotherapy alone (two patients were lost to follow-up). Time until relapse reflecting the duration of first remission is the only variable correlating CR and survival rates. Defining early relapse as less than 1.5 years from diagnosis to relapse resulted in a 5-year survival of 10%, s.e. 5% for early relapses and 40%, s.e. 10% for late relapses (P-logrank test, 0.0001). Duration of first remission is a strong predictor for achievement of second CR and survival. It should be considered in reporting results of experimental therapies.

Summary. Repeated asparaginase treatment has been associated with hypersensitivity reactions against the bacterial macromolecule in a considerable number of patients. Immunological reactions may range from anaphylaxis without impairment of serum asparaginase activity to a very fast decline in enzyme activity without any clinical symptoms. Previous investigations on a limited number of patients have shown high interindividual variability of asparaginase activity time courses and hypersensitivity reactions in about 30% of patients during reinduction treatment. Therefore, monitoring of reinduction treatment was performed prospectively in 76 children with newly diagnosed acute lymphoblastic leukaemia (ALL). According to the ALL-Berlin±Frankfurt±Mu È nster (BFM) 95 protocol, 10 000 U/m 2 body surface area of native Escherichia coli asparaginase (Asparaginase medac) was given on d 8, 11, 15 and 18. In 45/76 children, trough and peak activities were determined with every dose, and also on d 4 and d 11 after the last administration. Data on asparaginase activity were not available from the remaining 31 patients, but information with regard to hypersensitivity reactions only was given. Eighteen out of 76 patients (24%) suffered a clinical hypersensitivity reaction; however, no silent inactivation was observed. Activity in the therapeutic range of greater than 100 U/l for at least 14 d was determined in 43 of the 45 patients who were analysed for enzyme activity.

In addition to myelosuppression, anticancer drugs cause rapid and persistent depletion of lymphocytes, possibly by direct apoptosis induction in mature T and B cells. Induction of apoptosis regulators was analyzed in peripheral blood lymphocytes from pediatric patients undergoing first-cycle chemotherapy for solid tumors. In vivo chemotherapy induced a significant increase in lymphocyte apoptosis ex vivo. The activation of initiator caspase-8 and effector caspase-3 and the cleavage of caspase substrates was detected 12 to 48 hours after the onset of therapy. Caspase inhibition by Z-VAD-fmk did not reduce ex vivo lymphocyte apoptosis in all patients, indicating the additional involvement of caspaseindependent cell death. No evidence for the involvement of activation-induced cell death was found in the acute phase of lymphocyte depletion as analyzed by activation marker expression and sensitivity for CD95 signaling. Lymphocyte apoptosis in vivo appeared to be predominantly mediated by the mitochondrial pathway because a marked decrease of mitochondrial membrane potential (⌬⌿ M ) was detected after 24 to 72 hours of treatment, preceded by the increased expression of Bax. Interestingly, despite the use of DNAdamaging agents, p53 remained completely undetectable throughout treatment. In contrast, in vitro treatment with cytarabine and etoposide induced p53 protein, CD95 receptor expression, CD95 sensitivity, and CD95 receptor-ligand interaction in stimulated cycling lymphocytes, but no such induction was seen in resting cells. These data suggest that chemotherapy-induced lymphocyte depletion involves distinct mechanisms of apoptosis induction, such as direct mitochondrial and caspase-dependent pathways in resting cells and p53-dependent pathways in cycling lymphocytes. IntroductionAnticancer drugs used in chemotherapy for tumors and leukemias inhibit proliferation and induce cell death in malignant cells. In addition to the therapeutic effect on malignant cells, chemotherapy causes severe toxicity in normal tissue, leading to side effects such as mucositis, hair loss, and myelosuppression. In addition, chemotherapy induces acute lymphopenia and chronic depletion of CD4 T cells, leading to increased susceptibility to opportunistic infection. 1,2 The molecular mechanisms by which cytotoxic drugs induce depletion of lymphocytes have not been defined and may involve proliferative arrest in lymphocyte precursor compartments or, alternatively, direct induction of apoptosis in mature cells.Regulation of apoptosis or programmed cell death involves different molecular compartments, such as death receptors, 3 Bcl-2 family member proteins, 4 mitochondria, 5 p53, and caspases. 6 In tissue culture cell lines, cytotoxic drugs induce the molecular regulators of physiologic apoptosis 7,8 Cytotoxic drug-induced apoptosis in leukemia 9 and carcinoma 28 cell lines critically depends on the activation of caspases. Caspases are activated by death receptor signaling or are a consequence of mitochondrial alterations including the release ...