Phase I/II Multi-site Study Evaluating the MTD, Safety and Efficacy of the Combination Venetoclax, Lenalidomide and Rituximab in Patients With Previously Untreated Mantle Cell Lymphoma

Inclusion Criteria: * Age ≥18 years * Diagnosis of mantle cell lymphoma (MCL) established by histologic assessment * Laboratory, radiographic, physical exam findings and/or symptoms attributable to MCL * ECOG Performance Status (Eastern Cooperative Oncology Group Performance Status: an attempt to quantify cancer patients' general well-being and activities of daily life. The score ranges from 0 to 5 where 0 is asymptomatic and 5 is death) less or equal to 2 * All study participants must be registered into the mandatory Revlimid REMS® program, and be willing and able to comply with the requirements of the REMS® program * Females of reproductive potential must adhere to the scheduled pregnancy testing as required in the Revlimid REMS® program. * Men and Women of childbearing potential on appropriate contraception * Adequate organ function * Ability to understand and the willingness to sign a written informed consent. * Ability to swallow oral capsules/tablets Exclusion Criteria: * Prior treatment for MCL with chemotherapy * Pregnant or breastfeeding women * Grade 2 or higher peripheral neuropathy * Known history of CNS (Central Nervous System) or leptomeningeal by MCL prior to study enrollment * Significant cardiovascular disease * Any condition that might significantly impair drug absorption as determined by the investigator * Uncontrolled active systemic fungal, bacterial, viral, or other infection, or intravenous anti-infective treatment within 2 weeks before first dose of study drug * History of stroke or intracranial hemorrhage within 6 months of 1st dose of study drug * Concurrent participation in another clinical trial * Subject has received a moderate or strong CYP3A inhibitor or inducer within 1 week prior to treatment initiation. * Psychiatric illness or social situations that would limit compliance with study requirements * Subject has known positivity to HIV * Active infection with Hepatitis B or C virus as determined by a detectable viral load on PCR. * Prior malignancy except for adequately treated basal cell or squamous cell skin cancer, in situ cervical cancer, or any other cancer from which the subject has been disease free for ≥ 2 years or which will not limit survival to\< 2 years.