Abstract Background TSPP is a poly-epitope peptide vaccine to the thymidylate syntase (TS) an enzyme commonly over-expressed in replicating cancer cells and recognized as a major target of fluoropyrimidines. TSPP showed immunological and anticancer activity in preclinical models, thus in the present study we investigated its safety and immunobiological activity in advanced cancer patients. This study was designed to identify TSPP Maximum Tolerated Dose (MTD) and Optimal Biological Dose (OBD) when used alone (arm A) or in combination with GM-CSF and IL-2 according to the IG-1 regimen (arm B). Patients and methods TSPP/VAC-1 (Eudract 2009-016897-33) is a monocentric phase Ib trial including 21 pretreated advanced cancer patients (12 in arm A and 9 in arm B) enrolled between April and October 2011 (12 with colorectal, 1 with breast, 1 with gastric, 1 with biliary tract and 6 with non small cell lung cancer). All patients presented a good performance status (ECOG ≤ 1). Each patient received every 3 weeks a sc administration of TSPP diluted in motanide ISA720 (1:1) at the dosage of 100 µg (6 patients), 200 µg (6 patients), and 300 µg (9 patients). Patients enrolled in arm B also received daily sc GM-CSF (100 µg) from day 1 to 5 and sc IL-2 (0.5 MIU) bid from day 6 to 15. Results No life-threatening adverse events were recorded; 1 case of grade 3 hypothyroidism (arm B), 4 cases of poly-articular arthropaty (arm A), and 4 cases of conjuntivitis (arm A) were observed. In arm B, cytokine-related flu-like syndrome, nausea, vomiting, and dyarrhea were commonly reported. An IFN-gamma ELISPOT assay revealed an increase in TS specific CTL precursors in 5 patients in arm A and 2 in arm B. It was also observed an increase in terminal effector memory and central memory T cells in the peripheral blood in both arms. Patients enrolled in arm A showed a significant decline in peripheral immune-regulatory (CD4+CD25hi+FoxP3+) T cells (baseline vs 3 vaccinations (B vs III): 3.8 vs 1.7 %; p= 0.041) and inhibitory myeloid cells (CD11c+CD15+) [Baseline (Bs) vs III vaccinations (Vc): 5.09 vs 1.02%; p= 0.05] associated to an increase in anti-proteinase III (Bs vs III Vs:0.48 vs 1.38; p= 0.04) and anti-myeloperoxidase auto-antibodies (Bs vs III Vc: 0.76 vs 1.50; p= 0.02) and reduced level of inflammatory markers (CRP, ESR, and LDH). A quality of life analysis did not reveal significant treatment-related changes in arm A, while a detrimental effect was observed in arm B. It was recorded 1 partial response (arm A);11 disease stabilitazions (8/12 patients arm A, and 3/9 arm B) and 8 disease progressions (3/12 patients arm A and 5/9 arm B). MTD was not reached, while OBD was defined as a TSPP dosage of 300 µg. Conclusion Our results suggest that the TSPP vaccine is safe and immunologically active. On these bases we believe that TSPP deserves to be evaluated in further phase II trials in cancer patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-229. doi:1538-7445.AM2012-LB-229