Background: Colorectal Cancer (CRC) has been refractory to immune therapies. The clinical benefit of immunotherapy is thought to depend on the expansion of activated, intratumoral, tumor specific cytotoxic CD8+ T cells which are low in most CRCs. AM0010 stimulates the survival, expansion and cytotoxicity of intratumoral CD8+ T cells. Patients with CRC who have progressed on SOC first and second line of therapy have a reported 7.1 months OS with TAS-102 (Meyer et al. NEJM372;20, 2015). In this Phase 1 study the efficacy of AM0010 was studied in refractory metastatic CRC patients. Methods: CRC pts progressing on a median of 4 prior therapies (range 2-7) were treated daily with AM0010 in doses of 1 ug/kg SQ daily to 40 ug/kg in a dose escalation design. Tumor responses were assessed using irRC. Serum cytokines, activation of blood derived T cells and peripheral T cell clonality were analyzed. Pretreatment archival tissue samples were evaluated by IHC for tumor infiltration by CD8+T cells. Results: AM0010 was tolerated with reversible TrAEs. 10 pts (of 27) had a G3/4 TrAE. There were no objective responses. 11 patients were treated in dose escalation cohorts (1-10 ug/kg) and 16 pts were treated at or above RP2D (20 ug/kg or 40 ug/kg). Seven of 25 pts with at least one radiographic response evaluation had stable disease at 8 weeks. One patient had SD for 19.4 months. The mPFS (ITT n = 27 pts) was 1.6 months, mOS was 11.7 (range 2.4 – 32+) months. The median follow-up is 25.2 months (range 13-35). AM0010 increased Th1 cytokines IL-18 and IFNg in the serum of patients, while decreasing mediators of chronic, tumor promoting inflammation (Th17 cytokines) and TGFb. Tumor infiltrating granzyme B+ CD8+ T cells increased during the treatment. AM0010 induced de-novo oligoclonal expansion of T cell clones in patients. Conclusions: AM0010 is well tolerated in patients with refractory CRC. Although objective tumor responses were not seen in this very advanced CRC population, the observed immune activation including clonal T cell expansion, prolonged stable disease, and the mOS of 11.7 months is encouraging in this advanced CRC population. Future study of AM0010 in combination with FOLFOX in a second – line of therapy colorectal cancer patients is being planned. Clinical trial information: NCT02009449