B7H6, a stress-induced ligand for the NK-activating receptor Nkp30, is widely expressed at the surface of transformed cells yet absent in healthy tissues. This makes B7H6 an attractive target for a CAR T-cell therapy with broad clinical applicability, including colon cancer and neuroblastoma. CARs are artificial receptors comprising an extracellular antigen-binding region (often a single chain variable fragment (scFv)) fused to an intracellular T-cell activation tail (usually CD3ζ in tandem with one or two costimulatory domain(s)). Here, we report the in vitro screening of various B7H6-based CAR designs differing by either the origin of their targeting moiety (murine versus humanized scFv), the costimulatory signaling module (either CD28 or 4-1BB as a 2nd generation CAR) or a combination of CD28 and 4-1BB in a 3rd generation CAR context.
Primary human T-cell populations expressing the diverse B7H6-specific CAR constructs were compared for viability and fold expansion at the end of manufacturing as well as in vitro functionality (IFNg secretion and cytolytic activity when challenged with B7H6 expressing cell lines).
All B7H6-based CAR T-cells yielded comparable fold expansion with high viability suggesting that the CAR design has no impact on process parameters. CARs with targeting moiety of murine scFv origin were functionally superior to humanized versions in terms of killing and IFNg release potentially due to a difference in target affinity between the scFv. Second generation CARs containing CD28 endowed CAR T-cells possessed superior in vitro anti-tumor activity compared to all other constructs. Cryopreservation of these 2nd generation CAR T-cells did not significantly reduce viability and potency post-thawing.
In these studies, a B7H6-based CAR comprised of murine scFv fused to CD28-CD3ζ signaling tail represented the best choice candidate after in vitro testing warranting further investigation. Subsequent studies will include in vivo xenograft models of colon cancer and neuroblastoma as well as target profiling through immunohistochemistry assessing B7H6 expression in a wide panel of tumor and normal tissues. This work focuses upon developing a package to support the clinical testing of B7H6 targeted CAR T-cell therapy.
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B. Demoulin, L. Springuel, D. Daro, J. Bolsée, J. Houssa, F. Huberty, C. Jacques-Hespel, C. Marchand, J. Marijsse, T.L.T. Nguyen, N. Ramelot, B. Violle, C. Lonez, D.E. Gilham, V. Steenwinckel: Employee at Celyad.