Personalized Neoantigen Cancer Vaccine + Pembrolizumab After Rituximab for Follicular Lymphoma

This research study is studying a novel type of FL vaccine as a possible treatment for follicular lymphoma (FL). The agents involved in this study are: * Rituximab * Personalized NeoAntigen vaccine * Poly-ICLC * Pembrolizumab

This research study is a Pilot Study, which is the first time investigators are examining the Personalized Neoantigen Vaccine (NeoVax) in patients diagnosed with follicular lymphoma. The FDA (the U.S. Food and Drug Administration) has not approved the Personalized Neoantigen Vaccine as a treatment for any disease. Patients will receive 4 weekly doses rituximab (a CD20 monoclonal antibody) during NeoVax manufacturing (see below). Patients who have stable disease or achieve a response with rituximab therapy will next receiving NeoVax alone (first 5 patients) or NeoVax in combination with pembrolizumab (a PD-1 monoclonal antibody). The purpose of this study is to determine if it is possible to make and safely administer a vaccine against FL by using information gained from specific genetic characteristics of the participant's own FL cells. The investigators plan to analyze the specific genetic characteristics of the participant's own FL cells and use that information to produce proteins that may help the participant's immune system recognize and fight FL cells. This vaccine has already been tested in clinical trials in patients with advanced melanoma (a type of skin cancer) and glioblastoma (a type of brain cancer). The current study will examine the ability of the vaccine to stimulate the participant's immune system when given at several different timepoints, and will examine the participant's blood cells for signs that the FL has changed or decreased. FL cells will be obtained from a tumor biopsy. The genetic material contained in the FL cells will be examined for the presence of tumor-specific mutations. This information will be used to prepare small protein fragments, which are called "peptides." The vaccine will consist of up to 20 of these peptides as well as a drug called Poly-ICLC. A peptide from the tetanus vaccine will also be included to boost the immune response. Poly-ICLC (also called Hiltonol) is an experimental "viral mimic" and an activator of immunity. Poly-ICLC binds proteins on the surface of certain immune cells to make it appear as if a virus is present. When the cells detect the vaccine, they think it is a virus and turn on the immune system. Poly-ICLC will be mixed with NeoAntigen peptides and administered as an injection given underneath the skin. Poly-ICLC is an investigational drug, meaning the FDA has not approved it as a treatment for any disease.