Inclusion Criteria:
* Phase I: Patients with ES-SCLC and disease progression after one or more chemotherapy regimens (that included a platinum-based doublet chemotherapy in combination with a PD-L1 inhibitor) according to the local SOC (2L+), unless the patient was ineligible to receive such therapies or was not a candidate for any available standard therapy, according to the investigator's judgement. Prior DLL3 (Delta-like ligand 3) targeted therapy is allowed.
* Phase II: Patients with ES-SCLC who have received a platinum-based doublet chemotherapy in combination with a PD-L1 inhibitor according to local standard of care, unless the patient was ineligible to receive such therapies or was not a candidate for any available standard therapy, as determined by the investigator's judgment. Prior DLL-3 targeted therapy is not allowed.
* Male or female patients must be ≥ 18 years of age.
* Histologically or cytologically confirmed small cell lung cancer (SCLC).
* At least one measurable lesion as defined by Response Evaluation Criteria in Solid Tumors (RECIST 1.1).
* Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.
* Patients must have an archival tumor tissue available, collected within 6 months prior to screening. If an archival tumor sample, collected within 6 months prior to screening, is not available, patients must be willing to undergo a new tumor biopsy at screening; , however this specimen need not be collected prior to scheduling leukapheresis. If a new biopsy is not medically feasible, exceptions may be considered after documented discussion with the Novartis medical monitor.
* Patient must be deemed suitable by the investigator to undergo the lymphodepletion (LD) regimen.
* Patient must have an apheresis product of non-mobilized cells accepted for manufacturing.
Exclusion Criteria:
* Prior administration of a genetically modified cellular product, including prior DLL3-targeted CAR-T cell therapy.
* Unstable or symptomatic central nervous system (CNS) metastases and/or carcinomatous meningitis. Stable brain metastases may participate provided they meet the specific criteria.
* Uncontrolled seizure disorder.
* Clinically significant active infections, including Hepatitis B/C and Human Immunodeficiency Virus (HIV).
* Has a known additional malignancy that is progressing or requires active treatment, with specific exceptions as defined in the study protocol.
* History of prior solid organ transplant or allogenic hematopoietic cell transplant
* Other significant pulmonary, cardiac, hepatic, renal or neurologic disease, parameters for which are defined in the study protocol.
* Pregnant or nursing women.
Other protocol-defined inclusion/exclusion criteria may apply.