Treg cells and the response to neoadjuvant chemotherapy combined with immunotherapy in resectable esophageal squamous carcinoma

e14626 Background: More and more studies focus on the neoadjuvant chemotherapy combined with immunotherapy (chemo-immunotherapy) in resectable esophageal squamous carcinoma (ESCC). Herein, we aimed to evaluate the efficacy and safety of neoadjuvant programmed cell death protein 1 inhibitors with chemotherapy and explore tumor microenvironment (TME) profiles. Methods: Patients with previously untreated, resectable, stage III ESCC in the third affiliated hospital of Soochow University were enrolled. Each patient received two-four cycles of neoadjuvant chemo-immunotherapy before surgical resection. The TME profiles of formalin-fixed paraffin-embedded tumor samples at baseline were evaluated by multiplex immunofluorescence to discover novel biomarkers of response to neoadjuvant chemo-immunotherapy. Results: Twenty patients were included, all of whom underwent R0 resection. 85% (17/20) of patients underwent 2 cycles of neoadjuvant therapy. TP53 (13/20,65%) was were high-frequency mutated gene, followed by CDKN2A (5/20,25.0%) and PIK3CA (3/20, 15.0%). PD-L1 positive (TPS≥1%) was found in only 3 patients. Postoperative pathological evaluation showed that 18 patients (90.0%) were major pathologic response (MPR), of which 5 patients (28.0%) achieved pathological complete response (pCR). Neoadjuvant therapy has acceptable side effects. TME profiles at baseline showed no significant correlation between PD-L1 and pathological response. The density of Treg cell in the tumor area was significantly lower in pCR patients than in MPR patients (P=0.0302). Conclusions: Neoadjuvant chemo-immunotherapy was well tolerated and was effective therapy for resectable ESCC. Treg cells may serve as potential predictive biomarkers.