Background: PD-1 blockade ± chemotherapy has recently become a primary systemic therapy recommended by NCCN guidelines for patients (pts) with recurrent or metastatic (R/M) head and neck squamous cell carcinoma (HNSCC). However, most pts still do not respond to treatment, indicating a large unmet need for pts with unresectable disease. CMP-001 is a toll-like receptor 9 (TLR9) agonist comprising a CpG-A oligodeoxynucleotide packaged in a virus-like particle that can induce type I interferon secretion from tumor-associated plasmacytoid dendritic cells, promoting a Th1-like chemokine milieu in the tumor microenvironment and inducing an antitumor CD8+ T-cell response. In a phase (ph) 1b study in pts with metastatic melanoma, intratumoral (IT) injection of CMP-001 + intravenous (IV) pembrolizumab (pembro) reversed PD-1 blockade resistance, induced responses in injected and noninjected lesions, and had an acceptable safety profile (Milhem et al, SITC 2020). This combination is therefore being tested in pts with HNSCC. Methods: CMP-001-007 (NCT04633278) is an open-label, multicenter, ph 2 study designed to investigate the efficacy and safety of CMP-001 + IV pembro in adult pts with histologically or cytologically confirmed R/M HNSCC considered incurable by local therapies. Eligible pts have undergone a pretreatment tumor biopsy, received no prior systemic therapy in the R/M setting, and have primary tumor locations of oropharynx, oral cavity, hypopharynx, or larynx. In addition, pts must have PD-L1-positive tumors (combined positive score ≥1), known tumor human papillomavirus (HPV) status (for oropharyngeal cancer), and measurable disease per RECIST v1.1 with ≥1 lesion amenable to IT injection. Pts with primary tumors in the nasopharynx are excluded. Enrolled pts will receive CMP-001 10 mg once weekly for 7 doses and every 3 weeks (Q3W) thereafter. The first dose may be administered subcutaneously or via IT injection, with all subsequent doses administered IT. All pts will also receive pembro 200 mg IV Q3W after the CMP-001 injection. Treatment continues until unacceptable toxicity or disease progression. The primary endpoint is investigator-assessed objective response rate (ORR) per RECIST v1.1. Secondary endpoints include safety, duration of response (DOR), progression-free survival (PFS), overall survival, and effects of HPV infection and PD-L1 expression on ORR, DOR, and PFS. Exploratory endpoints include analyses of baseline and changes from baseline in tumor or serum biomarkers related to TLR9, immune checkpoints, and potential predictors of response, as well as serum concentrations of CXCL10 and CMP-001. Refer to clinicaltrials.gov/ct2/show/NCT04633278 for the most current information on enrolling sites. Clinical trial information: NCT04633278