Inclusion Criteria:
* 18 years of age, any race or sex, who have pathologically confirmed cutaneous melanoma
* ECOG performance status of 0 or 1
* Adequate hematologic, hepatic, renal and coagulation function
* Must have measurable disease and have an injectable target lymph node for intralesional therapy administration
* Primary melanoma has been resected
* Pathologically confirmed resectable stage III disease, clinically apparent. Resectability is at the discretion of the treating surgeon who is a melanoma specialist.
* Stage III disease can be at time of diagnosis of primary melanoma or a recurrence after initial treatment of stage I-II disease.
* BRAF mutant or wild type allowed (mutations status not necessary for enrollment)
* Signed, written informed consent
Exclusion Criteria:
* Cannot have metastatic (AJCC M1) disease
* No primary mucosal or uveal melanoma
* No evidence of melanoma associated with immunodeficiency state or history or other malignancies (other than non-melanoma skin cancer) within the past 3 years
* May not have been previously treated with T-VEC, any other oncolytic virus, pembrolizumab, or any other PD-1, PD-L1, or PD-L2 inhibitor
* Must not have a history or evidence of symptomatic autoimmune pneumonitis, glomerulonephritis, vasculitis, or other symptomatic autoimmune disease, document history of autoimmune disease or syndrome requiring systemic treatment in the past two years (i.e. use of disease modifying agents, steroids, or immunosuppressive agents) except vitiligo or resolved childhood asthma/atopy, or evidence of clinically significant immunosuppression
* Must not have active herpetic skin lesions or prior complications of herpetic infection and must not require intermittent or chronic treatment with an anti-herpetic drug (e.g. acyclovir) other than intermittent topical use
