Photodynamic therapy (PDT) is an effective non-invasive treatment for epithelial pre-cancers, yet its efficacy in cutaneous squamous cell carcinoma (SCC) is limited by the immunosuppressive microenvironment of SCC. Vitamin D (VitD) has emerged as a potential neoadjuvant to enhance photodynamic priming in several cancers, but its immunologic effects in SCC remain poorly defined. Here, we investigated how VitD pretreatment modulates local and systemic immune responses to aminolevulinic acid-based