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Biomarkers for cancer immunotherapy are an unmet medical need. The group of Daniela Thommen at the NKI recently reported on novel methodologies based on short-term cultures of patient-derived tumor fragments whose cytokine concentrations in the supernatants and activation markers on infiltrating T cells were associated with clinical response to PD-1 blockade. We set up a similar culture technology with tumor-derived fragments using mouse tumors transplanted into syngeneic immunocompetent mice to test an agonist anti-CD137 mAb and its combinations with anti-PD-1 and/or anti-TGF-β. Increases in IFNγ concentrations in the tissue culture supernatants were detected upon in-culture activation with the anti-CD137 and anti-PD-1 mAb combinations or concanavalin A as a positive control. No other cytokine from a wide array was informative of stimulation with these mAbs. Interestingly, increases in Ki67 and other activation markers were substantiated in lymphocytes from cell suspensions gathered at the end of 72 h cultures. In mice bearing bilateral tumors in which one was excised prior to in vivo anti-CD137 + anti-PD-1 treatment to perform the fragment culture evaluation, no association was found between IFNγ production from the fragments and the in vivo therapeutic outcome in the non-resected contralateral tumors. The experimental system permitted freezing and thawing of the fragments with similar functional outcomes. Using a series of patient-derived tumor fragments from excised solid malignancies, we showed IFNγ production in a fraction of the studied cases, that was conserved in frozen/thawed fragments. The small tumor fragment culture technique seems suitable to preclinically explore immunotherapy combinations., Competing Interests: I. E.-S., I. R., C. H.-M., E. F.-P., A. A., S. S.-G., E. B., G. G., P. M.-G., E. C., J. A. M., S. C, F. D.-C., C. A. and A. T. declare no conflicts of interest. M. F. S. reports grants from Bristol Myers Squibb and Roche during the conduct of the study, as well as grants and personal fees from Roche and Bristol Myers Squibb, and personal fees from Numab outside the submitted work. I. M. reports grants and personal fees from Genmab during the conduct of the study, as well as grants and personal fees from Bristol Myers Squibb, Roche, AstraZeneca, and Pharmamar and personal fees from F-Star, Numab, Pieris, Boehringer Ingelheim, Gossamer, Alligator, Hotspot, Biolinerx, Bioncotech, Dompe, Highlight Therapeutics, Bright Peaks and Boston Therapeutics outside the submitted work., (© 2024 The Author(s). Published with license by Taylor & Francis Group, LLC.)