ATRT-10. ANTI-B7-H3 CHIMERIC ANTIGEN RECEPTOR NK CELLS SHOW ANTIGEN SPECIFIC CYTOTOXICITY AGAINST ATYPICAL TERATOID/ RHABDOID TUMORSIN VITRO ANDIN VIVO

Abstract

Abstract BACKGROUND Atypical teratoid/rhabdoid tumors (AT/RTs) are the most common malignant CNS tumor in infants. AT/RT patients have a 5-year overall survival rate of ~35% and high rates of relapse, emphasizing a dire need for new safe and effective therapies. These therapy-resistant tumors frequently overexpress cell surface molecule B7-H3 (CD276). CAR-NK cells have several advantages over CAR-T cells. NK cells can be obtained from healthy donors and produced as an “off-the-shelf” product. NK cells also have a lower risk of inflammatory toxicity and graft-versus-host disease compared to T-cells when transferred across the HLA barrier. METHODS We have designed a library of variable affinity B7-H3-targeted CARs, produced γ-retroviral vector, and used this for generation of B7-H3 CAR-NK cells. We verified B7-H3 expression in a panel of AT/RT cell lines, and further engineered firefly luciferase expressing AT/RT (CHLA06.ffLuc, BT12.ffLuc, BT37.ffLuc) as well as a CHLA06-derived B7-H3 knockout. We developed an orthotopic CHLA06.ffLuc xenograft model. We tested CAR-NK cell functionality using in vitro co-culture and cytotoxicity assays. In vivo study was performed in our xenograft with intratumoral delivery of CAR-NK cells. RESULTS B7-H3 targeted CAR-NK cells demonstrate target-specific cytotoxicity when compared to untransduced NK cells (36.8±12.5% vs. 72.4±24.2% at effector:target ratio of 1:1, n=3). CRISPR/Cas9 mediated knockout of B7-H3 in target cells abolished the difference in CAR vs. no-CAR NK-mediated target killing. When delivered intracranially to CHLA-06 orthotopic xenograft bearing mice, B7-H3 CAR NK cells eliminate tumor cells and prolong survival, whereas unmodified NK cells did not (log-ranked median survival = 20 vs. 84 days, p<0.0001). CONCLUSIONS Targeting AT/RTs with an anti-B7-H3 CAR-NK cell therapy may provide a safe and effective treatment for patients who have extremely limited therapeutic options. Direct intracranial injections of cell therapies into pediatric patients is currently being explored in clinical trials.