Inclusion Criteria: 1. Subject is ≥18 years of age 2. Eastern Cooperative Oncology Group (ECOG) performance status of 0-2. 3. Must have a documented diagnosis of CLL/SLL requiring treatment (IwCLL Guidelines for the Diagnosis and Treatment of CLL). In addition presence of clinically measurable disease determined by at least one of the factors listed: - nodal lesion that measures ≥ 1.5 cm in longest dimension (LD) and ≥ 1.0 cm in longest perpendicular dimension (LPD), or - spleen that measures ≥ 14 cm in longest vertical dimension (LVD) with a minimum of 2 cm enlargement, or - liver that measures ≥ 20 cm in LVD with a minimum of 2 cm enlargement, or - peripheral blood B lymphocyte count > 5000/uL 4. All eligible subjects must be relapsed after or be refractory to >2 prior lines of therapy one of which must have included an approved BTK inhibitor. 5. Must meet the following laboratory parameters: 1. Absolute neutrophil count (ANC) ≥ 1,500 cells/mm^3 or ≥ 1000 cells/mm^3 if secondary to bone marrow involvement by disease, without growth factor support for 7 days (14 days if pegfilgastrim). 2. Platelet count ≥ 75,000 cells/mm^3 (100 x 10^9/L) or ≥ 50,000 cells/mm^3 (50 x 10^9/L) if secondary to bone marrow involvement by disease, without transfusion for 7 days. 3. Serum aspartate transaminase (AST/SGOT) or alanine transaminase (ALT/SGPT) < 3.0 x upper limit of normal (ULN). 4. Serum bilirubin < 1.5 x ULN unless due to Gilbert's syndrome. 5. Calculated creatinine clearance of ≥ 60 ml/min. Exclusion Criteria: 1. Presence of any significant medical condition, laboratory abnormality, or psychiatric illness that would prevent the subject from participating in the study. 2. Prior allogeneic stem cell transplant (SCT)/bone marrow transplant within 12 months of signing the ICF. Subjects who received allogeneic SCT ≥ 12 months before signing the ICF may be eligible provided there is no ongoing graft-versus-host disease and no ongoing immune suppression therapy. 3. Subject has received prior CAR-T or other T-cell targeting treatment (approved or investigational) ≤ 4 weeks prior to starting CC-99282. 4. Subject has received prior therapy with CRBN-modulating drug (eg, lenalidomide, avadomide/CC-122, pomalidomide) ≤ 4 weeks prior to starting CC-99282. 5. History of second malignancies with life expectancy of ≤ 2 years or requirement of therapy that would confound study results. 6. Peripheral neuropathy ≥ Grade 2. 7. History of hypersensitivity to lenalidomide, pomalidomide, thalidomide. 8. Impaired cardiac function or clinically significant cardiac disease. 9. Persistent diarrhea or malabsorption ≥ NCI CTCAE Grade 2, despite medical management. 10. Active disease transformation (ie, Richter's Syndrome) 11. Uncontrolled/active autoimmune hemolytic anemia or thrombocytopenia