Sequential Immunochemotherapy Treatment with Pembrolizumab Plus Dendritic Cell (DC) Vaccine Followed by Trifluridine/Tipiracil Plus Bevacizumab in Refractory Mismatch-repair-proficient (pMMR) or Microsatellite-stable (MSS) Metastatic Colorectal Cancer

Inclusion Criteria: * Be willing and able to provide written informed consent. * Histologically confirmed pMMR or MSS mCRC * Male or female, aged ≥ 18 years * Life expectancy greater than 12 weeks * ECOG performance status \<2 * Patient suitable for the collection of biological material from leukapheresis: negative serological tests (HIV, HBV, HCV, Treponema pallidum); normal cardiological parameters (12-lead ECG and echocardiogram); evaluation by transfusionist to exclude possible contraindications to leukapheresis; recovered (grade 1 or less by CTCAE 5.0) from all the adverse events related to previous treatments.Exclusion Criteria: * Patients must have measurable disease by RECIST v 1.1 criteria on CT (or MRI) scan of the chest, abdomen and pelvis. See section 9.2 and Appendix D for the evaluation of measurable disease. * Prior treatment with 1-2 chemotherapy regimens in an advanced setting, including (if not contraindicated) fluoropyrimidines, irinotecan, oxaliplatin, an anti-VEGF monoclonal antibody and/or anti-EGFR monoclonal antibody for RAS wild-type tumors. * Patients must have normal organ and marrow function as defined below: leukocytes \>3,000/μL, absolute neutrophil count \>1,500/μL, platelets \>100,000/μL, total bilirubin \< 1.5 X institutional upper limit of normal (ULN), AST(SGOT)/ALT(SGPT) \<2.5 X ULN, creatinine \< 1.5 X ULN OR creatinine clearance \>30 mL/min/1.73 m2 * The autologous surgical specimen needed for vaccine manufacturing must have been colle…