The study is composed o f a 3-week Screening Period, the administration of multiple doses vaccine (Day 1, Week 0; Day 92, Week 13; Day 183, week 26), a 13- week Follow -up Period between the first and second vaccination and a 12- week Follow -up Period after the last vaccination. The study will be conducted on an outpatient basis. The Screening Period will occur between 21 days and 1 day prior to administration of PolyPEPI 1018 administration. Screening should be performed in parallel with the subject’s completion of the standard-of- care first-line treatment and initiation of the standard-of- care maintenance treatment. During this study period, results from a CT scan, which should be performed at the completion of the first- line treatment regimen , must be obtained. T he results from the CT scan must confirm that the subject has responded to first- line chemotherapy with documentation of cancer regression or lack of progression, according to the RECIST version 1.1 criteria. Once informed consent has been obtained , the subject will undergo a biopsy procedure in one of the accessible tumors (primary or metastasis) to check for tumor infiltrating lymphocytes (TILs). The first dose of PolyPEPI1018 will be administered on Day 1 of Week 0 and must be (1) after the subject initiates the maintenance regimen, and (2) within 3 weeks after the eligibility CT scan was performed . Vaccination will be performed at 4 anatomic sites (preferably draining to axillary or inguinal lymph nodes) and administered by SC injection . After the last injection, the subject must remain at the site for at least 1 hour to be monitored for any local and/or systemic allergic reactions. A buccal swab will be collected to determine Treos Bio ZRT OBERTO -101 Amendment 3 Product: PolyPEPI 1018 Colorectal Cancer Vaccine Page 30 of 81 CONFIDENTIAL HLA types. A subject diary will be distributed to subjects to collect local signs related to the injection sites, physical fatigue , and body temperature. Subjects will be monitored every 3 weeks for 12 weeks after first administration of PolyPEPI1018 (i.e. Weeks 3, 6, 9 and 12), then vaccinated again at week 13 and monitored every 3 weeks for 12 weeks after second administration of PolyPEPI1018 (i.e. Weeks 16, 19, 22 and 25), then vaccinated again at week 26 and monitored every 3 weeks for 12 weeks after third administration of PolyPEPI1018 (i.e. Weeks 29, 32, 35 and 38).