Background: CIAO (Checkpoint Inhibitors Assessment in Oropharynx cancer) was a window of opportunity trial evaluating the anti-PD-L1 durvalumab (durva) with or without the anti-CTLA-4 tremelimumab (treme) prior to surgery in 28 oropharynx squamous cell carcinoma (OPC) patients (pts). Here we report correlative analyses and long-term survival outcomes. Methods: A total of 28 OPC pts were randomized to receive durva (n=14) or durva plus treme (n=14) for 2 cycles prior to surgery. Adjuvant radiotherapy with or without concomitant chemotherapy was recommended based on pathology findings, per standard of care. Efficacy and safety results have been previously reported. Whole exome sequencing (WES), RNA sequencing (seq), and TCR-seq were performed on available pre- and post-treatment primary tumor specimens. Circulating HPV was quantified pre-treatment and longitudinally. Associations with objective response (OR) to therapy per RECIST were determined using either Fisher’s exact test (binary variables) or rank-sum test (continuous variables). Multiple comparisons were corrected for by the Benjamini and Hochberg method. Disease-free survival (DFS) was defined as the time from surgery to recurrence or death. Results: Of the 28 enrolled pts, 20 were newly diagnosed and 8 had locoregional recurrent disease; 25 were HPV-positive. The OR rate per RECIST was 43%. Efficacy was equivalent in both arms. Responders tended to be of younger age (p=0.02). At the DNA level, baseline tumor mutation burden was not associated with response, but mutational contraction post-treatment was more often observed among responders (p=0.02). There were no statistically significant differentially expressed genes between responders and non-responders, however, immune deconvolution revealed that a low inferred tumor neutrophil-to-leukocyte ratio was associated with response (p=0.01). TCR-seq revealed 8 TCR motifs enriched in responders at 25% false discovery rate. Serum HPV levels significantly decreased in responders after treatment (p=0.02). With a median follow-up from surgery of 59.6 months (range 14.9-71.5 months; data cut-off 1/19/24), none of the 20 patients with newly diagnosed OPC had recurrence and all remain alive at the last contact date (DFS=100%). Of the 9 patients with recurrent OPC, 3 had subsequent distant recurrence and died of disease (median DFS=5.7 years, overall DFS=66.7%). Conclusions: Responses to neoadjuvant checkpoint inhibitors was associated with tumor mutational contraction and a low baseline neutrophil-to-leukocyte ratio in OPC. Eight TCR motifs were enriched in responders. Serum HPV level dynamics was associated with tumor burden and may be useful in response monitoring. DFS outcomes were favorable in both newly diagnosed and recurrent cohorts.