The purpose of this study is to evaluate the efficacy of nelarabine-based consolidation and maintenance therapy in term of relapse-free survival (RFS) in high-risk (HR) patients.

Inclusion Criteria:

1. Whose blood and bone marrow explorations have been completed before the steroids prephase
2. aged 18-59 years old with a not previously treated (including IT injection) T-ALL newly-diagnosed according to the WHO 2008 definition with > 20% bone marrow blasts
3. With Eastern Cooperative Oncology Group (ECOG) performance status < 3
4. With or without central nervous system (CNS) involvement or testis
5. Without other evolving cancer (except basal cell carcinoma of the skin and "in situ" carcinoma of the cervix) or its chemo or radio-therapy treatment finished at least since 6 months
6. Having signed a written informed consent
7. With efficient contraception for women of childbearing age (excluding estrogens and IUD)
8. Having received or being receiving steroid prephase
9. With health insurance coverage

Exclusion Criteria:

1. With lymphoblastic lymphoma and bone marrow blasts < 20%, Burkitt-type ALL or with antecedents of chronic myeloid leukemia (CML) or other myeloproliferative neoplasm

2. With contra-indication to anthracyclines or any other general or visceral contra-indication to intensive therapy except if considered related to the ALL:

   • Aspartate transaminase (AST) and/or alanine transaminase (ALT) > 5 x upper limit of normal range (ULN)
   • Total bilirubin ≥ 2.5 x upper limit of normal range (ULN)
   • Creatinine > 1.5 x upper limit of normal range (ULN) or creatinine clearance <50 mL/mn

3. Myocardial infarction within 6 months prior to inclusion in the trial, cardiomyopathy (NYHA grade III or IV), left ejection ventricle fraction (LEVF) < 50% and/or RF < 30%,

4. Active severe infection or known seropositivity for HIV or Human T cell leukemia/lymphoma virus type 1 (HTLV-1) or active hepatitis B or C

5. Other active malignancy

6. Pregnant (beta-Human Chorionic Gonadotropin (hCG) positive) or nursing woman

7. Women of childbearing potential not willing to use an effective form of contraception during participation in the study and at least three months thereafter. Patients not willing to ensure not to beget a child during participation in the study and at least three months thereafter

8. Treated with any other investigational agent or participation in another trial within 30 days prior to entering this study

9. Not able to bear with the procedures or the frequency of visits planned in the trial

10. Unable to consent, under tutelage or curators, or judiciary safeguard