Isolation of naturally processed peptides recognized by cytolytic T lymphocytes (CTL) on human melanoma cells in association with HLA‐A2.1

Cytolytic T lymphocyte (CTL) clones have previously been derived from peripheral blood of melanoma patient SK29(AV). They lyse autologous melanoma cells but not autologous Epstein‐Barr virus (EBV)‐transformed B lymphocytes. Immunoselection experiments indicate that these CTL clones recognize 4 different antigens (Aa, Ab, B, C) in association with a single HLA restriction element, HLA‐A2.1. While the expression of antigens B and C appears to be confined to SK29‐melanoma cells, antigens Aa and Ab are shared by a high proportion of allogeneic HLA‐A2‐positive melanoma lines. HLA‐A2.1 and total HLA class 1 molecules have now been purified from SK29‐melanoma cells using affinity chromatography and associated peptides have been eluted. Peptide pools eluted from HLA‐A2.1 and total class 1 were separated by reversed phase high performance liquid chromatography (HPLC). Individual HPLC fractions were tested for their ability to sensitize target cells for recognition by SK29‐CTL clones. The presence of antigens Aa, Ab, B and C was detected in distinct HPLC fractions that were identical for both peptide pools. As target for detection of peptide antigens in HPLC fractions, the use of the HLA‐A2.1‐positive antigen processing mutant cell line CEM x 721.174.T2 (T2), pre‐incubated with anti‐HLA‐A2 monoclonal antibody (MAb) MA2.1, was shown to be essential. Single‐peak target‐sensitizing activity was found for antigens Ab and B, whereas multi‐peak sensitizing activity was reproducibly detected for antigens Aa and C. We reason that at least some of these melanoma peptide antigens might occur in biochemically distinct isoforms. © 1994 Wiley‐Liss, Inc.