Background: Human papillomavirus 16 (HPV16) is linked to several cancer types. Treatment options are limited for patients with HPV16 positive (HPV16+) recurrent or metastatic cancers. Generation and maintenance of HPV16+ malignant state require stable expression of HPV16-specific E7 and E6 oncoproteins, also a source of immunogenic neoantigens. HB-201 and HB-202 are replicating live-attenuated vectors based on lymphocytic choriomeningitis virus and Pichinde virus, respectively, which express the same non-oncogenic HPV16 E7E6 fusion protein to induce tumor-specific T-cell responses. This is a first-in-human phase 1/2 study of HB-201 monotherapy and HB-201 & HB-202 alternating 2-vector therapy. Dose escalation is ongoing with a 3+3 design. Methods: Phase 1 is assessing different regimens and dose levels of HB-201 monotherapy and HB-201 & HB-202 alternating 2-vector therapy given intravenously (IV) with or without an initial intratumoral administration. The patient population includes HPV16+ head and neck squamous cell carcinoma (HNSCC) and other HPV16+ cancers. Safety, tolerability, and preliminary antitumor activity by Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 or immune RECIST are assessed. Results: As of Jan 2021, 25 patients with a median of 3 prior anticancer treatments have been enrolled. All had HPV16+ confirmed genotype; the most common primary site was oropharynx (72%). No dose-limiting toxicities were reported. Treatment-emergent adverse events (TEAEs) occurred in 21 patients (84%), were generally mild or moderate, with events related to study drug reported in 14 patients (56%). TEAEs reported in >10% of patients regardless of causality included fatigue, pyrexia, nausea, decreased appetite, anemia, arthralgia, chills, constipation, diarrhea, hypertension, influenza-like illness, pneumonia, and vomiting. Serious TEAEs developed in 6 patients (24%), including 1 with grade 5 hemorrhagic shock deemed unrelated to study drug. Grade 3 fatigue was the only serious or grade ≥3 TEAE assessed as related to study drug. TEAEs caused no treatment discontinuation. There were 18 patients evaluable for efficacy. For the 16 patients on HB-201 monotherapy, assessment of target lesions showed 2 partial responses (including 1 patient with an unconfirmed immune CR) and 6 patients had stable disease (SD). For the 2 patients on HB-201 & HB-202 alternating therapy, both had SD. So far, the longest duration of response was 4.8 months (144 days) and the maximum decrease in tumor diameter was 60%, both seen in HNSCC patients receiving HB-201 IV. Conclusions: HB-201 monotherapy and HB-201 & HB-202 2-vector alternating therapy were generally well-tolerated and showed preliminary antitumor activity as monotherapy in heavily pre-treated patients with HPV16+ HNSCC and other solid tumors. Clinical trial information: NCT04180215