Pembrolizumab, Lenvatinib and IL-15 Superagonist N-803 in Combination With HER2 Targeting Autologous Dendritic Cell (AdHER2DC) Vaccine in Participants With Advanced or Metastatic Endometrial Cancer

Background: Endometrial cancer (EC) of the uterus is becoming more common in the US. Sometimes EC often has increased levels of a protein called HER2. Cancers with HER2 tend to be more aggressive and have poorer outcomes. Objective: To test 2 study drugs-a vaccine that targets HER2 (AdHER2DC) plus a drug that supercharges immune cells that kill tumor cells (N-803)-combined with 2 FDA-approved cancer treatment drugs in people with EC. Eligibility: Adults aged 18 and older with HER2-positive EC that returned or got worse after treatment. Design: AdHER2DC vaccine is made from each participant s own blood. Participants will undergo apheresis: Blood is removed from the body through a tube attached to a needle. The blood passes through a machine that separates out the target cells. The remaining blood is returned to the body through a second needle. A special catheter may be needed. The first treatment cycle is 28 days; each cycle after that will be 21 days. All participants will get the 2 approved drugs and the vaccine. One drug is a tablet taken by mouth once a day, every day. The other drug is given through a tube attached to a needle inserted into a vein. The vaccine is injected under the skin. Participants will receive the vaccine on day 1 of cycles 1, 2, and 3. Additional doses up to 3 doses will be give if possible. Some participants will receive N-803. This drug is injected under the skin of the abdomen on day 1 of each cycle. Treatment may last up to 1 year. Follow-up visits will continue up to 2 more years.

* INCLUSION CRITERIA: * Histologically confirmed endometrial cancer. * Radiographically confirmed metastatic or locally advanced disease. * Evaluable (measurable or non-measurable) disease, per RECIST 1.1. * HER2 IHC 1+, 2+ or 3+ tumor confirmed by PATHWAY HER2 (4B5) test. NOTE: The HER2 status in participants who had prior anti-HER2 therapy should be confirmed in the tumor tissue obtained after completing the anti-HER2 therapy. * Participants must have received and progressed after at least one (1) line of systemic therapy for endometrial cancer. * Age \>=18 years. * ECOG performance status \ 1,000/microliter * Platelets \> 100,000/microliter * Hemoglobin (Hgb) \> 9 g/dL (any number of transfusions within 60 days before apheresis is allowed) * Total bilirubin \