Described herein are methods for producing and utilizing an alternative signal 1 domain to construct an optimally signaling CAR. Alternative signal 1 domains of the present technology are based on alternatives to CD3ζ, including mutated ITAMs from CD3ζ (which contains 3 IT AM motifs), truncations of CD3ζ, and alternative splice variants known as CD3s, CD3 theta, and artificial constructs engineered to express fusions between CD3s or CD30 and CD3ζ. CAR polypeptides comprising alternative signal 1 domains are utilized to engineer CAR T cells. Further, this technology related to methods of treating cancer by administering to a subject in need thereof CAR T cells comprising alternative signal 1 domains.