Inclusion Criteria:

          -  Newly diagnosed stage 3 to 4B squamous cell carcinoma of the oral cavity, oropharynx,
             larynx, or hypopharynx who are candidates for surgical resection and are
             treatment-naïve. Participants must have been determined to be candidates for surgical
             resection by a multidisciplinary team including a surgeon, a medical oncologist, and a
             radiation oncologist.

          -  Has an Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 to 1 and life
             expectancy of more than 3 months.

          -  Must consent to provide the tumor tissues for analyses as described in the protocol.

          -  Must have adequate bone marrow function (without any growth factors or transfusions
             within 2 weeks prior to the first dose), kidney and liver function, with all
             laboratory values criteria detailed in the protocol.

        Exclusion Criteria:

          -  Has received live vaccine within 28 days prior to the first dose of study drug.

          -  Has a history of inflammatory bowel disease, a history of or ongoing pneumonitis or
             interstitial lung disease, had major surgery ≤ 28 days prior to the first dose of
             study drug and the surgical wound is not fully healed.

          -  Participants with hypopharyngeal or laryngeal tumors will not be candidates for Arm 4
             of the study (IT injection of ABBV-927).

          -  Requires use of an immunosuppressive medication within 14 days prior to the first dose
             of the study drug; exceptions are described in the protocol.

          -  Has a confirmed positive test results for human immunodeficiency virus, or have active
             hepatitis A, B or C.

          -  Has a history of primary immunodeficiency, allogeneic bone marrow transplantation,
             solid organ transplantation, or previous clinical diagnosis of tuberculosis.

          -  Has a history of any other malignancy within the past 3 years except for successfully
             treated non-melanoma skin cancer or localized carcinoma in situ that is considered
             cured or adequately treated by the investigator.