Abstract Membrane-bound heat shock protein 70 (mHsp70) is indicative for high-risk tumors with negative prognosis but also serves as a target for NK cells that are stimulated with Hsp70 peptide TKD and low dose IL-2 (TKD/IL-2). Herein, the efficacy of ex vivo TKD/IL-2 activated, autologous NK cells was tested in a randomized, investigator initiated phase II clinical trial in patients with mHsp70 positive advanced stage NSCLC after radiochemotherapy (RCT, 60-70 Gy, platinum-based chemotherapy). The interventional (INT) group received 4 cycles TKD/IL-2 activated, autologous NK cells every 2-6 weeks subsequent to standard RCT and the control (CTRL) group received best supportive care. The primary objective of the study was to examine whether the adjuvant treatment of NSCLC patients with TKD/IL-2 activated NK cells is feasible and effective with respect to progression-free survival (PFS). Secondary objectives were the assessment of treatment and biological responses, toxicity, quality-of-life (QoL, QLQ-LC13). Eight patients were randomized into the INT and eight into the CTRL arm. None of the patients died between randomization and final tumor assessment 18 months after randomization. In the INT group one patient had complete response (CR), one patient partial response (PR), two patients stable disease (SD) and one patient progressive disease (PD) at the last documented visit, whereas in the CTRL group only 2 patients showed clinical responses (PR, SD) and five patients had PD. The clinical response of patients in the INT group appeared to be mediated by activated NK cells whereas in the CTRL group by CD8+ T cells. The NK cell therapy after RCT was well tolerated, no differences in QoL were observed between both study groups. Citation Format: Gabriele Multhoff, Stephanie E. Combs, Sophie Seier, Stefan Stangl, Wolfgang Sievert, Maxim Shevtsov, Christiane Blankenstein, Martin Hildebrandt, Konrad Kokowski, Matthias Hautmann, Hubert Hautmann, Claus Roedel, Rainer Fietkau, Rudolf M. Huber, Bernhard Haller, Christina Ertl, Michal Devecka, Robert Offner, Norbert Ahrens. Targeted Natural Killer (NK) cell based adoptive immunotherapy for the treatment of patients with non-small cell lung cancer (NSCLC) after radiochemotherapy - results of a randomized phase II clinical trial (NSCLC-TKD/IL-2) (Eudra-CT Number 2008-002130-30) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr LB-076.