Chemotherapy is used in the treatment of many types of cancer. Paclitaxel (PTX) is an effective chemotherapeutic but is associated with undesirable toxicity and hypersensitivity reactions. Efforts to improve effectiveness and decrease toxicity associated with PTX have included the use of nanoparticles. FID-007 consists of PTX encapsulated with polyethyloxazoline (PEOX) polymer which improves pharmacokinetics and may lead to decreased toxicity and enhanced therapeutic activity. Immunotherapy including checkpoint inhibitors has been effective for many tumor types, nonetheless favorable responses are seen in the minority of patients. Successful efforts to improve response rates have included treating with dual checkpoint inhibition or combining checkpoint inhibitors with cytotoxic chemotherapy. It is not known which chemotherapy or what dose of chemotherapy is most effective in combination with checkpoint inhibitors. PTX exerts immunomodulatory effects on the host immune system, especially when given at doses lower than the typical cytotoxic doses. PTX has been shown to increase antigen presentation by dendritic cells, induce IL-12 production, and decrease regulatory T cells and myeloid derived suppressor cells. Research in this area has been limited and has not adequately explored the impact of nanosomal encapsulated PTX on the host immune system. FID-007 is being studied in patients with solid tumors. We will add expansion cohorts to the existing study treating at the maximum tolerated dose (MTD) and a low dose to study immunomodulatory effects of FID-007 on the host immune system. Results will be used to design a study combining a checkpoint inhibitor with FID-007 at the optimum immunomodulatory dose.