ID #458 Tailored gene-editing to improve B7-H3 CAR T-cell therapy for group 3 medulloblastoma
Meghan Ward, Michaela Meehl, Linda Senaoui, Jorge Ibanez, Rugile Dovidonyte, Weshely Kujur, Kelsey Bertrand, Christopher DeRenzo, Stephen Gottschalk, Martine Roussel, Benjamin Youngblood, Hongbo Chi, Giedre KrenciuteAbstract
Medulloblastoma (MB) is the most common malignant pediatric brain tumor with molecular Group 3 (G3MB) having poor prognosis with few recent advancements in treatment. Chimeric antigen receptor (CAR) T-cell therapy targeting the antigen B7-H3 is safe for pediatric brain tumor patients, including G3MB, but has had limited clinical success in eliciting durable responses in part due to poor CAR T-cell fitness. In this work, we sought to determine whether improving the capacity of B7-H3-CAR T-cells to 1) persist or 2) expand against G3MB would improve anti-tumor efficacy in patient derived xenograft (PDX) models. We used CRISPR/Cas9 to generate healthy donor-derived B7-H3-CAR T-cells with a greater potential to persist by knocking out DNMT3A or TET2 or expand by knocking out Regnase-1. As controls, we generated DNMT3A, TET2, and Regnase-1 knock out (KO) EphA2-CAR T-cells. We directly compared these CAR T-cell products against B7-H3+/EphA2+ PDX G3MB cell lines in vivo and found that only Regnase-1 KO improved the anti-tumor activity of B7-H3-CAR T-cells whereas DNMT3A or Regnase-1 KO improved the antitumor activity of EphA2-CAR T-cells. Regnase-1 KO B7-H3-CAR T-cells had a superior capacity to expand and, unexpectedly, maintained a high percentage of CD4+ CAR T-cells compared to all other KOs. Next, we validated the clinical potential of Regnase-1 KO in B7-H3-CAR T-cells generated from T cells isolated from pediatric brain tumor patients from our Loc3CAR clinical trial (NCT05835687). We show that Regnase-1 KO indeed improves the anti-tumor efficacy of patient-derived B7-H3-CAR T-cells in vivo, nominating Regnase-1 KO B7-H3 CAR-T cells as a future CAR T-cell product for clinical testing for pediatric brain tumors. Beyond the translational relevance of our work, our study highlights that the benefit of deleting negative regulators in T cells is CAR-dependent, highlighting the need to delineate underlying mechanisms going forward.