Abstract
<title>Abstract</title> <p>The disialoganglioside GD2 is a cell surface marker of neuroblastoma and an attractive target for chimeric antigen receptor (CAR) T-cell therapy. GD2 is also expressed in Ewing sarcoma (EwS), but more heterogeneously and often below the threshold required for CAR-mediated T-cell activation. We previously showed that pharmacological inhibition of the epigenetic regulator Enhancer of Zeste Homolog 2 (EZH2), for example with the approved drug tazemetostat, selectively upregulates GD2 expression in EwS cells in vitro. Here, we evaluated prerequisites for combining EZH2 inhibition with GD2-directed CAR T-cell therapy. Oral tazemetostat induced GD2 expression in EwS xenografts in vivo, but the effect was model-dependent and not consistently reproducible. In vitro analyses revealed a pronounced impact of EZH2 inhibition on CAR T cell biology. Tazemetostat markedly impaired T cell proliferation and expansion, while enhancing antigen-specific cytolytic activity on a per-cell basis. In contrast, tazemetostat did not measurably affect macrophage polarization under conditions promoting M2-like phenotypes characteristic of the EwS tumor microenvironment. Together, these findings argue against concomitant administration of tazemetostat with GD2-specific CAR T cells. The variable target induction capacity of tazemetostat in vivo and its recent withdrawal from the market limit the translational potential of the strategy. Systematic in vivo screening of epigenetically active compounds may identify more suitable candidates for robust, clinically relevant modulation of GD2 expression in EwS and other GD2-positive cancers.</p>