A recombinant vaccinia virus encoding a modified peptide of the gp100 melanoma-melanocyte antigen with potential use in cancer immunotherapy. gp100 human antigen is a wild type self-antigen expressed by melanocytes, pigmented retinal cells and most melanomas. This recombinant vaccinia Mgp100 encodes a fragment epitope of gp100 bearing 2 amino acids substitution; T->M at position 210 and 288 A ->V at position 210. This modification may stimulate tumor infiltrating lymphocytes (TIL) more efficiently. [ ]