The first imSAVAR study-a-thon took place from 12 to 15 June 2023 at Fraunhofer IZI in Leipzig, Germany. 17 consortium members from ULEI, UNILU, UKW, IZI, ITEM, NVS, LABCORP, BI, PEI and LUND participated either in person or online. In three and a half dense working days, we reviewed and harmonized the CRS irAOPs for CAR T cells, Checkpoint Inhibitors and T Cell Engagers. We assigned biomarkers and test systems to the different key events and build a first version of a diagrammatic model of the harmonized CRS irAOPs. Further, we also identified ways how real world data can be integrated into the diagrammatic model of the harmonized CRS irAOP. In a breakout session with BioSci, we discussed how gender dimension can be integrated into non-clinical assessment of toxicity and formulated a task for imSAVAR. A second breakout session with Clemens Wittwehr and Laure-Alix Clerbaux (both European Commission, JRC) covered the integration of test methods into the AOP framework. After these three and a half days, all participants agreed that the spirit and drive of such an event is unique. Christina Sakellariou from LUND said: “A positive collaborative spirit and a multi-stakeholder community are key to answer big questions and drive a project forward, faster.“ This, we definitely experienced during imSAVAR’s first study-a-thon. We will carry the results of the event into the different working groups and already have plans for a second study-a-thon. Please see below more reactions from our participants and some impressions from the study-a-thon.