Background: Immunotherapy using active immunization of tumor associated antigens has been expected to improve the prognosis of malignant tumor patients. We conducted phase I trial to investigate safety and efficacy of autologous tumor lysate-pulsed dendritic cell (DC) vaccination therapy after resection for esophageal cancer. We already reported the clinical results for enrolled 11 patients. All patients completed the protocol therapy and no treatment-related adverse events more than grade 3 was observed (primary endpoint), and recurrence rate within 2 years was 18% (n = 2). In this study, we further analyzed the immune responses in vaccinated patients. Methods: Patients with stage IIA (T2N0 or T3N0, UICC TNM classification 6^th edition) esophageal cancer after curative (R0) resection were eligible. Tumor lysate we used for DC vaccines potentially contains mutated proteins (neoantigens) derived from somatic mutations. Patients received DC vaccines (more than 5.0×10⁶ cells) 6 times every 2 weeks. We evaluated neutrophil-to-lymphocyte ratio (NLR) in each patient from CRF data. We identified candidate neoantigens by next generation sequencing and MHC class I binding prediction algorism. We screened the immune responses against those neoantigens using HLA transgenic mice and healthy human PBMCs. Results: Absolute lymphocyte counts, absolute neutrophil counts and NLR were not specifically different between patients with or without recurrence. For specific immune responses, we observed the reactivity in 6 out of 59 candidate neoepitopes identified from two patients in HLA transgenic mouse system. Two out of 6 peptides displayed reactivity in human healthy PBMCs. Conclusions: We analyzed immune responses to predicted candidate neoantigens. We are now investigating immune landscape in the tumor using RNA sequencing data and its relevance to the antigen responses. Clinical trial information: UMIN000002837.