Avoidance of On-Target Off-Tumor Activation Using a Co-stimulation-Only Chimeric Antigen Receptor

Chimeric antigen receptors (CARs) combine T cell activation with antibody-mediated tumor antigen specificity, bypassing the need for T cell receptor (TCR) ligation. A limitation of CAR technology is on-target off-tumor toxicity caused by target antigen expression on normal cells. Using GD2 as a model cancer antigen, we hypothesized that this could be minimized by using T cells expressing Vγ9Vδ2 TCR, which recognizes transformed cells in a major histocompatibility complex (MHC)-unrestricted manner, in combination with a co-stimulatory CAR that would function independently of the TCR. An anti-GD2 CAR containing a solitary endodomain derived from the NKG2D adaptor DAP10 was expressed in Vγ9Vδ2⁺ T cells. Differential ligation of the CAR and/or TCR using antibody-coated beads showed that pro-inflammatory cytokine response depended on activation of both receptors. Moreover, in killing assays, GD2-expressing neuroblastoma cells that engaged the Vγ9Vδ2 TCR were efficiently lysed, whereas cells that expressed GD2 equivalently but did not engage the Vγ9Vδ2 TCR were untouched. Differentiation between X-on tumor and X-off tumor offers potential for safer immunotherapy and broader target selection.