The present invention discloses the identification and isolation of novel MHC class II epitopes derived from the cancer antigen, NY ESO-1. The novel MHC class II epitopes from NY-EsO-1 are recognized by CD4.sup.+ T lymphocytes in an HLA class II restricted manner, in particular HLA-DR or HLA-DP restricted. The products of the gene are promising candidates for immunotherapeutic strategies for the prevention, treatment and diagnosis of patients with cancer.