NKTR-255 in Relapsed/Refractory Multiple Myeloma & Non-Hodgkin Lymphoma

Key Inclusion Criteria: * Patients must have relapsed or refractory MM or NHL with no available therapies that would confer clinical benefit for their primary disease. * For MM patients, measurable relapsed or refractory MM as defined by the IMWG Criteria (Kumar, 2016) following treatment with at least 3 lines of therapy with no other available treatment that would confer benefit. * For NHL patients, measurable or detectable disease according to International Myeloma Working Group (IMWG) and the Lugano Classification. Extranodal NHL disease that is measurable by fluorodeoxyglucose-positron emission tomography (FDG-PET) imaging only is allowed. * Estimated glomerular filtration rate (eGFR) ≥ 40 mL/min/1.73 m2. * Eastern Cooperative Oncology Group (ECOG) performance status score ≤ 2 Patient has the following laboratory test results during Screening: 1. Absolute neutrophil count (ANC) or absolute granulocyte count (AGC) ≥ 1000/µL 2. Platelets ≥ 30,000/µL 3. Hemoglobin ≥ 8g/dL 4. Absolute lymphocytes ≥ 500/µL 5. Leukocytes ≥ 3000/µL Patients are eligible who also meet all the following criteria in these cohorts of Part 2: NKTR-255 Monotherapy NHL Group Only: * Patients with NHL who received a commercially approved CD19 CAR-T product and had PD. The first dose of NKTR-255 will be administered within 30 days of the PD. NKTR-255 with Daratumumab MM Group Only : * Patients with MM must have had previous exposure to proteasome inhibitor, immunomodulatory agent (IMiD), and anti-CD38 therapy. * Patients who previously received daratumumab or other anti-CD38 therapies must have at least 3 months washout. NKTR-255 with Rituximab Group iNHL Group Only: * Patients with relapsed or refractory iNHL who previously progressed during or following 1 or more prior systemic rituximab-containing (or another treatment with an anti-CD20 antibody-containing) regimens for lymphoma. Key Exclusion Criteria: * Patients who have an active, known, or suspected autoimmune disease. * Any treatment-related neurotoxicity or cytokine release syndrome (CRS) prior to enrollment into the study should return to baseline before NKTR-255 treatment. * Active central nervous system (CNS) involvement with NHL. * Patients who have been previously treated with prior interleukin-2 or interleukin-15. * Patients who received daratumumab or other anti-CD38 therapies previously must have 3 months washout. NOTE: Other protocol defined Inclusion/Exclusion criteria may apply