Integrating Allogeneic NK Cells in High-risk Advanced Stage III-IV Nasopharyngeal Cancer Patients

This clinical trial aims to determine whether Natural Killer (NK) cell therapy administered in combination with concurrent chemoradiotherapy (CRT) can reduce recurrence in patients with advanced nasopharyngeal cancer (NPC), and to identify the highest safe and tolerable dose of allogeneic NK cells. Allogeneic NK cells, derived from healthy donors, have demonstrated good tolerability in cancer patients. The primary research questions are: 1. What is the maximum tolerated dose (MTD) of allogeneic NK cells when administered with CRT in NPC patients? 2. Can the addition of allogeneic NK cells to standard CRT reduce the proportion of NPC patients with detectable plasma EBV-DNA from 30% to 10%? Phase 1: Participants will receive one of five escalating doses of allogeneic NK cells with CRT to determine the MTD. Phase 2: Participants will receive the established MTD NK dose together with CRT. Participants will undergo regular safety monitoring, side-effect assessment, measurement of plasma EBV-DNA levels, and surveillance for disease recurrence.