Sequential Regimen of Bendamustine-Debulking Followed by ABT-199 and GA101-Induction and -Maintenance in CLL (CLL2-BAG)

Inclusion Criteria: * documented chronic lymphocytic leukemia (CLL) requiring treatment according to International Working Group on CLL (iwCLL) criteria * adequate renal function: a creatinine clearance ≥30ml/min calculated according to the modified formula of Cockcroft and Gault or directly measured with 24 hr. urine collection * adequate hematologic function: platelets ≥ 25.000/µl, neutrophils ≥ 1.000/µl and hemoglobin ≥8.0 g/dL, unless directly attributable to the patient´s CLL (e.g. bone marrow infiltration) * adequate liver function: total bilirubin ≤2x, aspartate aminotransferase (AST) / alanin aminotransferase (ALT) ≤2.5x the institutional upper Limit of normal (ULN) value, unless directly attributable to the patient's CLL or to Gilbert's Syndrome * negative serological testing for hepatitis B, negative testing for hepatitis-C RNA and negative HIV test within 6 weeks prior to registration * age ≥ 18 years * Eastern Cooperative Oncology Group (ECOG) Performance Status 0 to 2, ECOG 3 is only permitted if related to CLL * life expectancy ≥ 6 months * ability and willingness to provide written informed consent and to adhere to the study visit schedule and other protocol requirements Exclusion Criteria: * transformation of CLL (i.e. Richter's transformation, prolymphocytic leukemia) * known central nervous system (CNS) involvement * confirmed progressive multifocal leukoencephalopathy (PML) * malignancies other than CLL currently requiring systemic therapies * uncontrolled infection requiring systemic treatment * any comorbidity or organ system impairment rated with a cumulative illness rating scale (CIRS) score of 4, excluding the eyes/ears/nose/throat/larynx organ system or any other life-threatening illness, medical condition or organ system dysfunction that - in the investigator´s opinion - could compromise the patients safety or interfere with the absorption or metabolism of the study drugs (e.g, inability to swallow tablets or impaired resorption in the gastrointestinal tract) * requirement of therapy with strong cytochrome P450 isoenzyme 3A4 (CYP3A4) inhibitors/inducers or anticoagulant with warfarin, phenprocoumon (marcumar) or other vitamin K-antagonists * use of investigational agents within 28 days prior to registration * known hypersensitivity to GA101 (obinutuzumab), ABT-199 (venetoclax, GDC-0199) or any of the excipients * pregnant women and nursing mothers * fertile men or women of childbearing potential unless surgically sterile or ≥ 2 years after the onset of menopause, or willing to use two methods of reliable contraception including one highly effective (Pearl Index \<1) and one additional effective (barrier) method during study treatment and for 18 months after end of study treatment * vaccination with a live vaccine ≤28 days prior to registration * legal incapacity * prisoners or subjects who are institutionalized by regulatory or court order * persons who are in dependence to the sponsor or an investigator Inclusion/Exclusion criteria for extended follow-up and re-treatment * Patients must have participated in the CLL2-BAG trial and must have benefitted from study treatment * Only patients with a confirmed progression of CLL who are in need of treatment according to iwCLL 2008 criteria are eligible for retreatment with venetoclax and obinutuzumab * Patients who received any subsequent treatment for CLL outside the study are ineligible