Nemtabrutinib and Lisocabtagene Maraleucel for the Treatment of Relapsed/Refractory Chronic Lymphocytic Leukemia/Small Lymphocytic Lymphoma

Inclusion Criteria: * Confirmed diagnosis of CLL/SLL per International Workshop on Chronic Lymphocytic Leukemia (iwCLL) classification * Measurable disease by imaging (lymph node \[LN\] \> 1.5cm) or absolute lymphocyte count (ALC) (\> 5000/μL) or marrow involvement of at least 30% by flow cytometry * Eligible for lisocabtagene maraleucel (liso-cel) as standard-of-care per Food and Drug Administration (FDA) label for CLL/SLL * At least 18 years of age at time of study enrollment * Have an Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 2 * The ability to swallow and retain oral medication * NOTE: Administration of nemtabrutinib is not permitted through a percutaneous endoscopic gastro-jejunal (J PEG) tube * Participants who are hepatitis B surface antigen (HBsAg) positive are eligible if they have received hepatitis B virus (HBV) antiviral therapy for at least 4 weeks and have undetectable HBV viral load prior to randomization * Note: Participants should remain on anti-viral therapy throughout study intervention and follow local guidelines for HBV anti-viral therapy post completion of study intervention. Hepatitis B screening tests should include HBsAg and anti-HBV. Hepatitis B screening tests are not required unless: * Known history of HBV infection, * As mandated by local health authority * Absolute neutrophil count (ANC) ≥750/μL (or ≥500/μL in participants with documented bone marrow involvement) * Growth factor and/or transfusion support is permissible to stabilize participant prior to study treatment if needed * Hemoglobin ≥ 8 g/dL * Growth factor and/or transfusion support is permissible to stabilize participant prior to study treatment if needed * Platelets ≥50 000/μL (or ≥30 000/μL in participants with documented bone marrow involvement) * Growth factor and/or transfusion support is permissible to stabilize participant prior to study treatment if needed * Creatinine ≤ 1.5 × upper limit of normal (ULN) OR measured or calculated creatinine clearance (glomerular filtration rate \[GFR\] can also be used in place of creatinine or CrCl) ≥ 30 mL/min for participant with creatinine levels \> 1.5 × institutional ULN * Creatinine clearance (CrCl) should be calculated per institutional standard * Total bilirubin ≤ 1.5 × ULN OR direct bilirubin ≤ ULN for participants with total bilirubin levels \> 1.5 × ULN * Aspartate aminotransferase (AST) (serum glutamic oxaloacetic transaminase \[SGOT\]) and alanine aminotransferase (ALT) (serum glutamic pyruvate transaminase \[SGPT\]) ≤ 2.5 × ULN (≤ 5 × ULN for participants with liver metastases) * International normalized ratio (INR) OR prothrombin time (PT) ≤ 1.5 × ULN unless participant is receiving anticoagulant therapy as long as PT or partial thromboplastin time (PTT) is within therapeutic range of intended use of anticoagulants * Activated partial thromboplastin time (aPTT) ≤ 1.5 × ULN unless participant is receiving anticoagulant therapy as long as PT or PTT is within therapeutic range of intended use of anticoagulants * Cardiac (echocardiogram \[Echo\] or multi-gated acquisition scan \[MUGA\]) ejection fraction ≥ 40% Exclusion Criteria: * Diagnosis of Richter Transformation * Clinically significant (symptomatic) central nervous system (CNS) involvement at time of study enrollment. Previously treated CNS disease is allowed if the participant is asymptomatic. Incidental findings including positive cerebral spinal fluid (CSF) studies are not exclusionary * Active infection and uncontrolled infection * Active HBV/hepatitis C virus (HCV) infection * Participants must have completed curative anti-viral therapy for HCV at least 4 weeks prior to study enrollment * Participants who are HBsAg positive are eligible if they have received HBV antiviral therapy for at least 4 weeks and have undetectable HBV viral load prior to study enrollment * Note: Participants should remain on anti-viral therapy throughout study intervention and follow local guidelines for HBV anti-viral therapy post completion of study intervention * HIV with a detectable viral load or a CD4 count ≤ 350 cells/µL at time of screening * Participants with HIV who do not meet the above criteria are eligible if they are on a stable antiretroviral therapy (ART) regimen (ART must not be strong CYP3A4 inducers) for at least 4 weeks prior to study entry and are compliant with ART are eligible * Patients with an AIDS defining opportunistic infection in the past 12 months prior to screening * Gastrointestinal dysfunction that may affect drug absorption (e.g., gastric bypass surgery, gastrectomy) * History or current evidence of any condition, therapy, or laboratory abnormality that might confound the results of the study, interfere with the participant's participation for the full duration of the study, or is not in the best interest of the participant to participate, in the opinion of the treating investigator * Corrected QT interval (QTc) prolongation (defined as a QTc \> 450 msecs) or other significant electrocardiogram (ECG) abnormalities including second degree atrioventricular (AV) block type II, third degree AV block, or bradycardia (ventricular rate less than 50 beats/min) * Known allergy/sensitivity to nemtabrutinib or any of the excipients * Known prior progressive disease while on nemtabrutinib * NOTE: Refer to the investigator's brochure (IB) for details regarding prior recipients of nemtabrutinib * History of severe bleeding disorder defined as an ongoing congenital or acquired condition that leads to an increased likelihood of bleeding * Known additional malignancy that is progressing or has required active treatment within the past 2 years * NOTE: Participants with basal cell carcinoma of the skin, squamous cell carcinoma of the skin, or carcinoma in situ, excluding carcinoma in situ of the bladder, that have undergone potentially curative therapy are not excluded. Participants with low-risk, early-stage prostate ca