Prophylactic IFN-γ blockade drives axi-cel expansion without preventing refractory toxicities: caution against pre-emptive use.

Cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS) affect most patients receiving axicabtagene ciloleucel (axi-cel) for relapsed or refractory large B-cell lymphoma (LBCL). Based on pre-clinical data, we hypothesized that prophylactic IFN-γ blockade could prevent toxicity without impairing efficacy. We initiated an open-label phase 2 trial (NCT06550141) evaluating single-dose emapalumab one day before axi-cel. Here, we report the first two patients to caution against the pre-emptive emapalumab use prior axi-cel: Both developed treatment-refractory toxicities including high-grade ICANS and overlapping CRS-IEC-HS requiring multiple immunomodulatory agents. CAR T-cell expansion exceeded levels reported in ZUMA-1 and a standard-of-care axi-cel cohort at our institution. Despite therapeutic emapalumab and suppressed free IFN-γ, IL-2 and sIL-2R were markedly elevated, suggesting CRS was driven independent of IFN-γ. Both patients achieved complete responses, suggesting preserved efficacy. Given the unanticipated severity and refractoriness of toxicities, recruitment with this design was discontinued and the protocol was amended.