MASS-SPECTROMETRIC IDENTIFICATION OF A NATURALLY PROCESSED MELANOMA PEPTIDE RECOGNIZED BY CD8(-LYMPHOCYTES() CYTOTOXIC T)

We and others have previously reported that melanoma-specific, cytotox ic T lymphocytes (CTL) define a minimum of six class I-presented pepti de epitopes common to most HLA-A2(+) melanomas. Here we show that thre e of these peptide epitopes are coordinately recognized by a CTL clone obtained by limiting dilution from the peripheral blood of an HLA-A2( +) melanoma patient. Tandem mass spectrometry was used to characterize and sequence one of these three naturally processed melanoma peptides . One of the potential forms of the deduced peptide sequence (XXTVXXGV X, X = I or L) matches positions 32-40 of the recently identified mela noma gene MART-1/Melan-A. This peptide (p939; ILTVILGVL) binds to HLA- A2 with an intermediate-to-low affinity and is capable of sensitizing the HLA-A2(+) T2 cell line to lysis by CTL lines and clones derived fr om five different melanoma patients. A relative high frequency of anti -p939-specific effector cells appear to be present in situ in HLA-A2() melanoma patients, since p939 is also recognized by freshly isolated tumor infiltrating lymphocytes. p939 represents a good candidate for the development of peptide-based immunotherapies for the treatment of patients with melanoma.