The purpose of this study is to determine whether the combination of a neoantigen vaccine targeting the DNAJB1-PRKACA fusion kinase in combination with DRP-104, Nivolumab and Ipilimumab is safe and yields a clinically compelling antitumor activity measured as based on objective response rate (ORR, assessed by RECIST 1.1). Secondary objectives include progression-free survival (PFS) and overall survival (OS).

Inclusion Criteria:

• Must have histologically confirmed FLC that is metastatic or unresectable.
• Presence of DNAJB1-PRKACA fusion transcript, assessed by RNA-sequencing, DNA-sequencing, or in situ hybridization in the archival tissue.
• Must have demonstrated radiographic progression on prior or current immunotherapy.
• Age ≥ 12 years.
• Patients < 18 years old must have a body weight ≥ 40 kg.
• ECOG (Eastern Cooperative Oncology Group) performance status of ≤2
• Patients must have adequate organ and marrow function defined by study-specified laboratory tests.
• Patients must have adequate kidney and liver function defined by study-specified laboratory tests.
• Must have measurable disease per RECIST 1.1
• Willingness to provide tissue and blood samples for mandatory translational research.
• Women of childbearing potential (WOCBP) must have a negative urine or serum pregnancy test.
• For both Women and Men, must use acceptable form of birth control while on study.
• Ability to understand and willingness to sign a written informed consent document.

Exclusion Criteria:

• Patients with a history of prior treatment with checkpoint inhibitors, such as anti-PD-1, anti-PD-L1, anti-PD-L2, anti-CD137, anti-OX-40, anti-CD40, anti-CTLA-4, or anti-LAG-3 antibodies.

• Must have had chemotherapy or other systemic therapy or radiotherapy, as follows:

  • Patients who have had chemotherapy, biological cancer therapy, or radiation 14 days prior to the first dose of study drug.
  • Patients who have had surgery within 28 days of dosing of investigational agent, excluding minor procedures.
  • Patients who have received other approved or investigational agents or device within 28 days of the first dose of study drug.

• Patients who have not recovered from acute adverse events to grade ≤1 or baseline due to agents administered, with exception of grade 2 fatigue, rash, and endocrinopathy successfully managed hormone replacement therapy, or alopecia or stable neuropathy, unless approved by the IND Sponsor.

• Patients who have received any non-oncology live vaccine therapy used for prevention of infectious diseases within 28 days of study treatment.

• Known sensitivity to or history of allergic reactions attributed to compounds of similar chemical or biologic composition of polyinosinic-polycytidylic acid (Poly-ICLC) and/or DRP-104 and/or nivolumab and/or ipilimumab.

• History of severe hypersensitivity reaction to any monoclonal antibody.

• Has an active autoimmune disease.

• Prior allogeneic stem cell transplantation or organ transplantation.

• Has a diagnosis of immunodeficiency.

• Systemic corticosteroids at immunosuppressive doses.

• Subjects with interstitial lung disease that is symptomatic or may interfere with the detection or management of suspected drug-related pulmonary toxicity.

• Has a pulse oximetry of <92% on room air or is on supplemental home oxygen.

• Active or untreated brain metastases or leptomeningeal metastases.

• Uncontrolled intercurrent active medical and/or psychiatric illness/social psychosocial problems that that would limit compliance with study requirements.

• Uncontrolled intercurrent illness including, but not limited to, uncontrolled infection, symptomatic congestive heart failure, unstable angina, cardiac arrhythmia, metastatic cancer, or psychiatric illness/social situations that would limit compliance with study requirements.

• Pregnant or breastfeeding.

• Has a known history of Human Immunodeficiency Virus (HIV)/AIDS.

• Has active hepatitis B. Patients with chronic or acute HBV infection.

• Have had evidence of active or acute diverticulitis, intra-abdominal abscess, or GI obstruction which are known risk factors for bowel perforation should be evaluated for the potential need for additional treatment before coming on study.

• Unwilling or unable to follow the study schedule for any reason.

• Patient is at the time of signing informed consent a regular user (including "recreational use") of any illicit drugs or had a recent history (within the last year) of substance abuse (including alcohol).

• Evidence of clinical ascites.

• Patients with QTc prolongation > 470 ms according to Fridericia formula.

• Patients receiving potent inducers of CYP 3A4/5 (including but not limited to apalutamide, carbamazepine, enzalutamide, mitotane, phenytoin, rifampin and St. John's Wort) who cannot safely discontinue drug at least 14 days prior to Cycle 1 Day 1.

• Have had an allergen hyposensitization therapy within 2 weeks prior to initiation of study treatment.