• Patients in safety run in must meet the following criteria for study entry:

• A diagnosis of relapsed CD20+ Follicular Lymphoma grade 1-3a

• A diagnosis of relapsed CD20+ diffuse large B-cell lymphoma

• Patients in dose expansion must meet the following criteria for study entry:

• • A diagnosis of relapsed CD20+ diffuse large B-cell lymphoma

• Patients in each component (safety run in and dose expansion) must meet the following criteria for study entry:

⁃ Evidence of progression or lack of response following at least 1 prior treatment

⁃ Able and willing to provide written informed consent and to comply with the study protocol

⁃ Age ≥ 18 years as these drugs have not yet established safety and efficacy in pediatric patients

⁃ At least 1 node greater than 1.5cm in short axis diameter

⁃ Adequate hematologic function (unless abnormalities are related to NHL), defined as follows:

∙ Hemoglobin ≥ 9.0 g/dL

‣ Absolute neutrophil count ≥ 1.0 x 109/L

‣ Platelet count ≥ 75 x 109/L

⁃ Serum bilirubin \<1.5x ULN except in patients with Gilbert's syndrome as defined by \> 80% unconjugated bilirubin who must have a serum bilirubin of \<4x ULN; AST (SGOT) and ALT (SGPT) ≤ 3x ULN or \< 5x ULN if hepatic metastases are present

⁃ Renal function assessed by calculated creatinine clearance:

⁃ • Calculated creatinine clearance ≥ 30ml/min by Cockcroft-Gault formula. See section below, Dosing Regimen, regarding lenalidomide dose adjustment for calculated creatinine clearance ≥ 30ml/min and \< 60ml/min.

⁃ Patients must be willing to receive transfusions of blood products.

⁃ For men who are not surgically sterile, agreement to use a barrier method of contraception for ≥ 3 months after the last treatment dose. In addition, male patients must agree to request that their partners use an additional method of contraception, such as oral contraceptives, intrauterine device, barrier method of contraception, or spermicidal jelly. With female partners of childbearing potential or pregnant female partners, men must remain abstinent or use a condom during the treatment period and for 60 days after the final dose of mosunetuzumab, 6 months after the final dose of polatuzumab vedotin, and 60 days after the final dose of tocilizumab, as applicable, to avoid exposing the embryo. Men must refrain from donating sperm during this same period.

‣ For women of reproductive potential who are not surgically sterile, agreement to use two adequate methods of contraception, such as oral contraceptives, intrauterine device, or barrier method of contraception in conjunction with spermicidal jelly for≥ 12 months after the last therapeutic drug dose

‣ Females of childbearing potential (FCBP, defined as a female of childbearing potential is a sexually mature woman who: 1) has not undergone a hysterectomy or bilateral oophorectomy; or 2)has not been naturally postmenopausal for at least 24 consecutive months (i.e., has had menses at any time in the preceding 24 consecutive months). must have a negative serum pregnancy test with a sensitivity of at least 50 mIU/mL within 10 - 14 days prior to and again within 24 hours of prescribing lenalidomide and must either commit to continued abstinence from heterosexual intercourse or begin TWO acceptable methods of birth control, one highly effective method and one additional effective method AT THE SAME TIME, at least 4 weeks before she starts taking lenalidomide. FCBP must also agree to ongoing pregnancy testing. Men must agree to use a latex condom during sexual contact with a female of childbearing potential even if they have had a successful vasectomy. Should a woman become pregnant or suspect she is pregnant while she or her partner is participating in this study, she should inform her treating physician immediately. Women must refrain from donating eggs during this same period.

‣ All study participants must be registered into the mandatory Revlimid REMS® program and be willing and able to comply with the requirements of Revlimid REMS® program.

‣ Able to take aspirin (81 or 325 mg) daily as prophylactic anticoagulation (patients intolerant to ASA may use warfarin or low molecular weight heparin).