Study Evaluating SC291 in Subjects With r/r B-cell Malignancies (ARDENT)

Inclusion Criteria: * Male or female subjects aged 18-80 years at the time of signing informed consent. * Diagnosis of NHL (WHO 2016 criteria) or CLL (iwCLL criteria), including: * Large B-cell lymphoma, including diffuse large B-cell lymphoma (DLBCL) not otherwise - - specified (including DLBCL arising from indolent lymphoma), primary mediastinal large -- - B-cell lymphoma, high grade B-cell lymphoma, follicular lymphoma grade 3B * Follicular lymphoma (dose escalation only except for follicular lymphoma grade 3B) * Marginal zone lymphoma (dose escalation only) * Mantle cell lymphoma (dose escalation only) * CLL or SLL * Relapsed/refractory disease after at least 2 prior systemic regimens per standard of care or after autologous stem cell transplant * ECOG performance status of 0 or 1. * At least one measurable lesion per Lugano Classification (NHL); CLL subjects must meet iwCLL treatment criteria * Life expectancy ≥12 weeks Exclusion Criteria: * Prior anti-CD19 therapy including CD19-directed CAR T treatment or other CD19-directed antibody or cell therapy (e.g., NK cell). (Part 2 dose expansion only - prior approved CD19-directed CAR T therapy required) * History of primary central nervous system (CNS) lymphoma or presence of CNS metastases * Systemic anticancer therapy (including platinum-based chemotherapies and I/O therapies) or radiotherapy within 14 days of SC291 (28 days for biologics) * Autologous HSCT within 6 weeks of treatment with SC291 (or allogeneic HSCT at any time). * Active autoimmune disease or any other diseases requiring immunosuppressive therapy or corticosteroid therapy (defined as \>20 mg/day prednisone or equivalent). * History or presence of cardiac or CNS disorders as defined in the protocol