x Subjects in Cohort 2a will be directly assigned to Arm 2. x Subjects in Cohort 2b will be directly assigned to Arm 2. 3 STUDY IMPLEMENTATION STUDY DESIGN 3.1.1 Schema 3.1.2 Pre-Treatment Phase: Performed on 03-C-0277 Patients with metasta tic melanoma, gastrointestinal, or genitourinary cancers will undergo resection of the tumor and apheresis under pr otocol 03-C-0277. Whole exome sequencing will be performed under protocol 03-C-0277 to identif y all cancer mutations using our standard procedures. TIL will be grown and expanded for this trial according to Standard Operating Abbreviated Title: mRNA-Based, Cancer Vaccine Version Date: January 23, 2019 24 Procedures (SOPs) which can be found in BB -IND 17858. After a sufficient yield of TIL (5x107 cells) is expanded, immunogenic neoantigens will be identified by high throughput immunologic screening using long peptides and tandem minigenes covering all mutated epitopes to identify the exact mutations recognized by autologous T-cells. Up to 15 predicted neoantigens will be selected based on exome and RNA sequencing and their binding affinity to the patient HLA molecules (see Appendix A ). The final nucleotide sequences of the mutated 15-41mer epitopes and/or driver genes will then be transmitted electronically via Globus, a secure research data management system, to Moderna for pr oduction of the NCI-4650 drug product. 3.1.3 Treatment Phase Patients will receive a mRNA-based vaccine IM at two-week intervals for four cycles. All patients may receive one course of treatment (four vaccination cycles). Immunologic tests will be performed as per Section 5.4 to quantitate circulating T-cells reactive with the immunizing antigens. If a 3-fold increase in the precursor level of pre-existing neoantigen-specific T-cells or new reactivity appears in the blood at detectable levels, patients may be vaccinated with a second and final course of treatmen t using the same vaccine dose. The second course may start approximately four weeks (± 2 weeks) from the last vaccine dose of the first course. If the patient receives only one course of treatment (four vaccination cycles), the start date of the course will be the date of the first vaccination; the end date will be the date of the first post- treatment evaluation. If the patient receives a second course (four additional vaccination cycles), the start date of the first course will be the date of the first va ccination. The date of the fifth vaccination will be both the end date of the first course and the start date of the second course. The end date of the second cour se will be the date of the fi rst post-treatment evaluation. 3.1.4 Dose-Limiting Toxicity The dose-limiting toxicity (DLT) evaluation period for determination of the maximum tolerated vaccine dose (MTD) will occur during the 21 days af ter the first vaccination for each patient. A DLT is defined as follows: All grade 3 or gr eater toxicities related to the mRNA vaccine, with the exception of : x Grade 3 fever x Grade 3 pruritus/itching x Grade 3 fatigue x Grade 3 metabolic laboratory abnormalities without signifi cant clinical sequela that resolve to grade 2 or less within 7 days. x Grade 3 autoimmune toxicity that resolves to grade 2 or less within 7 days.