UBX-303061 in Subjects With Relapsed/Refractory B-Cell Malignancies

Key Inclusion Criteria * Capable of giving signed informed consent * Age ≥18 years * ECOG performance status ≤2. * Phase Ia (dose-escalation part only): Subjects with relapsed and/or refractory B-cell malignancies (CLL/SLL, DLBCL, FL, MCL, WM or MZL) who have received at least 2 prior therapies and for subjects with no available treatment options as per the Investigator's discretion. * Phase Ib (dose-expansion only): Subjects with relapsed and/or refractory B-cell malignancies who have received at least 2 prior therapies and for subjects with no available treatment options as per the Investigator's discretion, and fit into one of the following groups: CLL/SLL or DLBCL or MCL or FL, WM, MZL * All subjects must have evaluable or measurable disease based on the appropriate tumor type criteria * Adequate organ and bone marrow function Key Exclusion Criteria * For subjects with lymphoma: * Systemic antineoplastic therapy or any experimental therapy within 3 weeks or 5 half-lives, whichever is shorter, before the first dose of study treatment. * Therapy with tyrosine kinase inhibitor within 5 half-lives before the first dose of study treatment. * Unconjugated monoclonal antibody therapies \<6 weeks before the first dose of study treatment. * Subjects that have undergone autologous stem cell rescue within 100 days prior to the first dose of study treatment. * Subjects that have undergone allogeneic stem cell transplant within 6 months prior to the first dose of study treatment. * Subjects with active graft-versus-host disease (GVHD) or on anti-GVHD treatment or prophylaxis. * History of chimeric antigen receptor T cell (CAR-T) therapy within 100 days prior to start of study drug. * Any immunotherapy within 4 weeks of first dose of study drug. * The time from the last dose of the most recent chemotherapy or experimental therapy to the first dose of study drug is \<5 times the t1/2 of the previously administered agent(s). * Previously exposed to BTK degradation therapy * Malignant disease, other than that being treated in this study. * Radiotherapy within 2 weeks of the first dose of study treatment * Known hypersensitivity to BTK degraders or any of the ingredients. * Impaired cardiac function or clinically significant cardiac disease * Subjects with history of severe bleeding disorders and known/suspected other autoimmune disease * Major surgery within 4 weeks of the first dose of study treatment