CD28 and cancer: To extend our findings for anti-cancer potential beyond the effect of spacer domain length [16], we generated L1CAM-specific CAR designs with CD28-costimulatory signaling incorporating a short (L1CAM-SS-CD28/ζ) or long (L1CAM-LS-CD28/ζ) spacer, and compared their anti-tumor activity to short (L1CAM-SS-4-1BB/ζ) and long spacer (L1CAM-SS-4-1BB/ζ) murine CAR T cells with 4-1BB-co-stimulatory signaling (Figure 1A).