Key Inclusion Criteria:

          -  Histologically confirmed locally advanced or metastatic cutaneous squamous cell
             carcinoma

          -  Patients with locally advanced disease who are not suitable candidates for surgical or
             radiological treatment of lesions or have refused those treatments

          -  At least 1 lesion that is measurable and injectable by study criteria

          -  Eastern Cooperative Oncology Group (ECOG) performance status ≤1

          -  Anticipated life expectancy >12 weeks

          -  All patients must consent to provide archived or newly obtained tumor material for
             central pathology review for confirmation of diagnosis of CSCC.

        Key Exclusion Criteria:

          -  Prior treatment with an oncolytic therapy

          -  Patients with active significant herpetic infections or prior complications of HSV-1
             infection (e.g. herpetic keratitis or encephalitis)

          -  Patients who require intermittent or chronic use of systemic (oral or intravenous)
             anti-virals with known anti-herpetic activity (e.g. acyclovir)

          -  Ongoing or recent (within 5 years) evidence of significant autoimmune disease that
             required treatment with systemic immunosuppressive treatments

          -  Prior treatment with an agent that blocks the PD-1/PD-L1 pathway.

          -  Prior treatment with other immune modulating agents other than as adjuvant or
             neoadjuvant therapy within 3 years.

          -  Untreated brain metastasis(es) that may be considered active.

          -  Acute or chronic active hepatitis B or known history of hepatitis B or hepatitis C or
             human immunodeficiency virus (HIV) infection

          -  History of ILD/pneumonitis within the last 5 years or a history of ILD/pneumonitis
             requiring treatment with systemic steroids.

          -  Any major or surgical procedure ≤ 28 days before randomization

          -  Administration of live vaccines ≤ 28 days before randomization

        Note: Other protocol defined Inclusion/Exclusion criteria apply.