679 Characterization of tumor specific CD8+ T cell responses in patients with recurrent/metastatic HPV16-positive head and neck cancer receiving HB-200 monotherapy as second or later line treatment in a phase 1 study - Siqing Fu; Rom S Leidner; Ki Chung; Jiaxin Niu; Ilian Tchakov; Debra L Richardson; Xiaoping Qing; Jorge Nieva; Douglas Adkins; Alan L Ho; Minh Phan; Alexander T Pearson; et al. (Journal for ImmunoTherapy of Cancer, 2023)