Any potential safety risks, such as ISRs, will be monitored closely throughout the study. Dosing will be staggered by three weeks between the first dose administered to the first patient and the first dose administered to the second patient in Dose Level 2 (starting dos e level) of the Phase I Cohort for safety monitoring purposes. Subsequent patients may begi n treatment at an interval of one week. Abbreviated Title: mRNA-Based, Cancer Vaccine Version Date: January 23, 2019 192 ELIGIBILITY ASSESSMENT AND ENROLLMENT ELIGIBILITY CRITERIA 2.1.1 Inclusion Criteria Measurable (per RECIST v1.1 criteria), meta static melanoma, ga strointestinal, or genitourinary cancer with at least one lesi on that is resectable. Only patients with metastatic gastrointestinal cancer will be eligible for enrollment on the Phase I portion of the study. Patients with metastatic melanoma, gastrointestinal, or genitourinary cancer will be eligible for enrollment on the Phase II portion of the study. Confirmation of diagnosis of metastatic cancer by the NCI Laboratory of Pathology. Patients with 3 or fewer brain metastases that are < 1 cm in diamet er and asymptomatic are eligible. Lesions that have been treated with stereotactic ra diosurgery must be clinically stable for one month after treatment for the patient to be eligible. Patients with surgically resected brain metastases are eligible. Prior therapy with at least one first-line standard of care treatment or second-line treatment of proven effectiv eness. Patients must have pr ogressive disease after prior treatment. Prior first- or second-line treatments would include the following: x Patients with metasta tic melanoma: Receipt of a chec kpoint inhibitor as first-line therapy. x Patients with metastatic melanoma with an activating mutation of KIT: Receipt of imatinib. x Patients with a BRAF V600 activating mutation: Receipt of appropriate targeted therapy. x Patients with metastatic gastrointestinal cancer: Receipt of up to two forms of approved first- and/or second-line chemotherapy regimens. x Patients with metastatic genitourinary cancers: Receipt of a first- or second-line therapy appropriate for their histologic subtype. $JH\HDUVDQG\HDUV Clinical performance status of ECOG 0 or 1 (see Appendix B ). Women of child-bearing potential must have a negative pregnancy test because of the potentially dangerous effects of the treatment on the fetus. Serology x Seronegative for HIV antibody. (The experimental treatment being evaluated in this protocol depends on an intact immune system. Patients who are HIV seropositive may have decreased immune-com petence and thus may be less responsive to the experimental treatment and more susceptible to its toxicities.) x Seronegative for hepatitis B antigen, and seronegative for hepatitis C antibody. If hepatitis C antibody test is positive, then the patient must be tested for the presence of antigen by RT-PCR and be HCV RNA negative. Abbreviated Title: mRNA-Based, Cancer Vaccine Version Date: January 23, 2019 20 Hematology x ANC > 1000/mm3 without the support of growth factors. x :%&PP3 x 3ODWHOHWFRXQWPP3 x Hemoglobin > 8.0 g/dL.