The present invention relates to anti-tumor lymphocytes, and a variant cyclic GMP-AMP synthase (cGAS) carrying an amino acid substitution of one or both arginines at amino acid positions 255 and 236 and/or an amino acid substitution of one or both lysines at amino acid positions 254 and 258; or a nucleic acid molecule encoding said variant cGAS for use in the treatment of a tumor in a subject.