This study tests the effectivity and tolerability of treatment with alemtuzumab (MabCampath) in patients with relapsed or refractory T-cell acute lymphoblastic leukemia (T-ALL) or T-lymphoblastic lymphoma. In Arm A, patients with refractory relapse receive a 2 week treatment with MabCampath followed by remission evaluation. In case of insufficient response, treatment with cladribine is added. In Arm B, patients with molecular relapse (minimal residual disease) receive a 4 week treatment with MabCampath followed by remission evaluation. In both arms, treatment is continued in case of response for up to two months.

Inclusion Criteria:

Both Arms:

• T-ALL or T-lymphoblastic lymphoma
• CD52-expression > 20%
• Aged >= 18 years
• ECOG/World Health Organization (WHO) performance status 0-2
• Life expectancy of > 2 months
• Contraception during, and for at least 6 months after, therapy
• At least a 2 week interval to the last cycle of chemotherapy (decision in individual cases if rapid progression)
• No persistent toxicity from earlier cycles
• Written informed consent

Arm 1:

• Evidence of MRD > 10(-4) with confirmation beyond week 16 in the GMALL-Study 07/2003

Arm 2:

• Relapse with failure to at least one salvage therapy or primary failure after induction therapy and at least one salvage therapy

Exclusion Criteria:

• Substantial restrictions of heart, lung, liver, or kidney function
• Active infection, HIV seropositivity or cytomegalovirus (CMV) viraemia
• Pretreatment with MabCampath®
• Known anaphylaxis to humanised antibodies
• Permanent systemic therapy with corticosteroids
• Central nervous system (CNS) involvement
• Extramedullary bulky disease
• Active secondary malignancies
• Pregnancy or nursing
• Mental disease or circumstances that prohibit compliance with the protocol procedures