468 Background: The cell-based therapeutic cancer vaccine MGN1601 consists of two active pharmaceutical ingredients in fixed combination. Fourfold gene-modified, allogeneic tumor cells expressing IL-7, GM-CSF, CD80, and CD154 through MIDGE gene expression vectors are combined with the DNA-based immunomodulator dSLIMas a TLR-9 agonist. In the phase I-II clinical trial (ASET trial) heavily pre-treated patients with metastatic renal cell carcinoma (mRCC) were enrolled. Methods: TheASET study has been conducted as a multicenter, open, single-arm phase I-II study. The treatment phase (TP) consisted of 8 intradermal vaccinations, administered within 12 weeks. We analysed known mRCC prognostic factors for their predictive value, i.e. safety laboratory and immunological parameters, quality of life, local reactions and other patients’ characteristics. Results: 19 patients from the ASET study, who received at least one vaccination (ITT population), were included in the biomarker evaluation. The median overall survival (mOS) in the ITT population is currently 25 weeks. mOS of patients who discontinued TP prematurely was only 10 weeks. However, mOS of those patients who completed at least TP is not yet mature for statistical calculation (NR), but is currently estimated as 69 weeks, resulting in a highly significant difference (10 weeks vs. NR, p < 0.001). Patients with an absolute lymphocyte counts (ALC) at baseline of ≥1,000/μL had increased overall survival (mOS NR vs. 16 weeks, p = 0.013), if compared to those with an ALC <1,000/μL. Neutrophil lymphocyte ratios (NLR) at baseline of >3, bone and liver metastasis, high MSKCC score were identified as risk factors associated with lower overall survival. ALC ≥1,000/μL after three MGN1601 vaccinations (week 5) was even more significantly associated with increased overall survival (mOS NR vs. 17 weeks, p = 0.007). The NLR and quality of life improvement at week 5 as well as local reactions at injection sites seem to correlate with OS. Conclusions: MGN1601 shows promising efficacy in late stage mRCC patients. The identified parameters should be further investigated as potential biomarkers for efficacy. Clinical trial information: NCT01265368.