Vanquish Bio is an immunotherapy company reimagining treatment of cancer with the use of unique natural killer (NK) cell derived extracellular vesicles (EVs). The goal of this STTR is to develop a therapy using natural products of the immune system for targeted destruction of myeloma tumor cells. Multiple myeloma (MM) represents ~10% of hematological cancers, and there were ~32,110 new cases and ~12,960 deaths in the U.S. in 2019. Despite treatments that include stem cell transplantation and/or chemotherapy, patients inevitably relapse. New innovations are needed that extend survival, increase durability of remission and provide options to patients ineligible for front-line therapy. We developed NK3.3, a human NK cell line derived from a healthy donor. These cells kill an array of tumor types. Using a minimal residual disease mouse model of human MM, administration of NK3.3 EVs prevented tumor recurrence for up to 100 days, versus 21 days without treatment. As NK3.3 grow in culture, they release EVs as small membrane-bound structures that are also capable of killing many different tumor cells without harming normal cells. NK3.3 EVs also kill cancer stem cells (CSC); these are resistant to standard chemotherapy and responsible for metastasis and recurrence. NK EVs can be produced in large quantities, frozen, stored and then thawed, without loss of function. Other advantages of using NK3.3 EVs include: 1) resistance to the hypoxic tumor microenvironment, 2) ability to cross the blood-brain barrier, 3) stability and 4) low toxicity. EVs are not restricted by blood group or histocompatibility and are therefore an immunotherapeutic modality that can be a universal treatment. Our goal is to develop a new infusion therapy product that will improve survival rates with less side effects for MM patients with relapsed/refractory or stable disease. Phase I is to generate NK3.3-derived EVs and demonstrate efficacy against MM and extend durability of remission, with minimal, toxic side effects. Specific Aim 1: Identify activators that maximize tumor killing activity of NK3.3 EVs. NK EVs will be isolated from NK3.3 cells cultured with activating cytokines IL-2, IL-12 and IL-15 individually and in combinations. Our goal is to prepare NK EVs that kill ≥90% of tumor cells within 72 hours of treatment, with less than 10% normal cell death. Specific Aim 2: Determine proof-of-concept efficacy with low toxicity of NK EVs in MM-bearing immunodeficient mice. We will administer different concentrations of NK EVs in MM-bearing immunodeficient mice with stable disease. The goal is to extend remission beyond 21 days in ≥50% of mice. Toxicity will be measured for qualitative visible signs and behavior, and quantitative variation in body weight, organ weight and blood chemistry. We will prove feasibility of producing more potent NK EV preparations with anti-MM activity and proof-of-concept oriented efficacy and toxicity data of NK EV therapy against MM.