Allogeneic Natural Killer Cells

This research study is designed for patients with extensive-stage small cell lung cancer (ES-SCLC) who have already received four cycles of standard chemotherapy, with at least two cycles combined with immunotherapy, and have achieved disease control (stable disease, partial response, or complete response) at their last efficacy evaluation. In this study, participants will be randomly assigned to one of two groups: Group A will receive standard immunotherapy plus 1 to 3 courses of allogeneic natural killer (NK) cell therapy. Each course consists of six NK cell infusions given over 28 days. Group B will receive standard immunotherapy alone. All participants will continue treatment until their disease progresses or they experience unacceptable side effects. The immunotherapy agents used in this study are those recommended by major international and national clinical guidelines for extensive-stage SCLC, including but not limited to durvalumab, atezolizumab, serplulimab, and adebrelimab. The purpose of this study is to evaluate whether adding NK cell therapy to standard immunotherapy can provide additional benefits for patients with extensive-stage SCLC who have responded well to initial treatment.