A Phase I-II multicenter trial with Avelumab plus autologous dendritic cell vaccine in pre-treated mismatch repair-proficient (MSS) metastatic colorectal cancer patients; GEMCAD 1602 study

[Background]: Immune check-point blockade (ICB) has shown clinical beneft in mismatch repair-defcient/microsatellite instability high metastatic colorectal cancer (mCRC) but not in mismatch repair-profcient/microsatellite stable patients. Cancer vaccines with autologous dendritic cells (ADC) could be a complementary therapeutic approach to ICB as this combination has the potential to achieve synergistic efects. [Methods]: This was a Phase I/II multicentric study with translational sub-studies, to evaluate the safety, pharmacodynamics and anti-tumor efects of Avelumab plus ADC vaccine in heavily pre-treated MSS mCRC patients. Primary objective was to determine the maximum tolerated dose and the efcacy of the combination. The primary end-point was 40% progressionfree survival at 6 months with a 2 Simon Stage. [Results]: A total of 28 patients were screened and 19 pts were included. Combined therapy was safe and well tolerated. An interim analysis (Simon design frst-stage) recommended early termination because only 2/19 (11%) patients were disease free at 6 months. Median PFS was 3.1 months [2.1–5.3 months] and overall survival was 12.2 months [3.2–23.2 months]. Stimulation of immune system was observed in vitro but not clinically. The evaluation of basal RNA-seq noted signifcant changes between pre and post-therapy liver biopsies related to lipid metabolism and transport, infammation and oxidative stress pathways. [Conclusions]: The combination of Avelumab plus ADC vaccine is safe and well tolerated but exhibited modest clinical activity. Our study describes, for the frst-time, a de novo post-therapy metabolic rewiring, that could represent novel immunotherapyinduced tumor vulnerabilities.