In this context, the present study shall demonstrate whether application of FSP in a vaccination approach is associated with the induction of peptide-related toxicity. Hence, the study marks the first step towards the application of FSP in humans, as it provides information on the safety of FSP as vaccination agents for the first time. Moreover, the study shall provide initial information, whether vaccination with FSP can induce FSP-specific immune responses in patients with MSI-H colorectal cancer. Thus, it shall provide information, whether FSPs AIM2(-1), HT001(-1), and TAF1B(-1) have the potential to elicit peptide-specific immune responses and therefore represent suitable targets for the induction of tumor antigen-specific immune responses in patients with MSI-H tumors.