This is a Phase 1, open label, multi-center study of DSP-7888 Dosing Emulsion, administered intradermally in combination with checkpoint inhibitors (Nivolumab or Atezolizumab) in adult subjects with solid tumors, including advanced melanoma, non-small cell lung cancer (NSCLC), head and neck squamous cell carcinoma (HNSCC), renal cell carcinoma (RCC), and urothelial cancer that consists of two parts: dose search (Part 1) and expansion (Part 2).