To address on-target, off-tumor toxicity with CAR T cell therapy, Castellarin et al. developed a model in which hHER2 was stably expressed at high (hHER2-high) or low (hHER2-low) levels on normal hepatocytes to mimic clinical situations. High-affinity (HA) and low-affinity (LA) HER2 CAR T cells (CARTs) caused lethal liver toxicity in mice with hHER-high livers, but in hHER2-low mice, LA-CARTs resulted in less liver damage and lower circulating IFNγ. LA-CARTs exhibited superior antitumor efficacy against hHER2+ xenografts compared to HA-CARTs, partly due to faster trafficking from the liver into the tumor.
Contributed by Katherine Turner
ABSTRACT: Off-tumor targeting of human antigens is difficult to predict in preclinical animal studies and can lead to serious adverse effects in patients. To address this, we developed a mouse model with stable and tunable human HER2 (hHER2) expression on normal hepatic tissue and compared toxicity between affinity-tuned HER2 CAR T cells (CARTs). In mice with hHER2-high livers, both the high-affinity (HA) and low-affinity (LA) CARTs caused lethal liver damage due to immunotoxicity. Mice with hHER2-low livers, LA-CARTs exhibited less liver damage and lower systemic levels of IFN-gamma than HA-CARTs. We then compared affinity-tuned CARTs for their ability to control a hHER2-positive tumor xenograft in our model. Surprisingly, the LA-CARTs outperformed the HA-CARTs with superior antitumor efficacy in vivo. We hypothesized that this was due in part to T cell trafficking differences between LA and HA-CARTs and found that the LA-CARTs migrated out of the liver and infiltrated the tumor sooner than the HA-CARTs. These findings highlight the importance of T cell targeting in reducing toxicity of normal tissue and also in preventing off-tumor sequestration of CARTs, which reduces their therapeutic potency. Our model may be useful to evaluate various CARTs that have conditional expression of more than one scFv.