Inefficient exogenous loading of a tapasin-dependent peptide onto HLA-B*44:02 can be improved by acid treatment or fixation of target cells.
Antitumor cytolytic T lymphocytes (CTLs) recognize peptides derived from cellular proteins and presented on MHC class I. One category of peptides recognized by these CTLs is derived from proteins encoded by "cancer-germline" genes, which are specifically expressed in tumors, and therefore represent optimal targets for cancer immunotherapy. Here, we identify an antigenic peptide, which is derived from the MAGE-A1-encoded protein (160-169) and presented to CTLs by HLA-B*44:02. Although this peptide is encoded by MAGE-A1, processed endogenously and presented by tumor cells, the corresponding synthetic peptide is hardly able to sensitize target cells to CTL recognition when pulsed exogenously. Endogenous processing and presentation of this peptide is strictly dependent on the presence of tapasin, which is believed to help peptide loading by stabilizing a peptide-receptive form of HLA-B*44:02. Exogenous loading of the peptide can be dramatically improved by paraformaldehyde fixation of surface molecules or by peptide loading at acidic pH. Either strategy allows efficient exogenous loading of the peptide, presumably by generating or stabilizing a peptide-receptive, empty conformation of the HLA. Altogether, our results indicate a potential drawback of short peptide-based vaccination strategies and offer possible solutions regarding the use of problematic epitopes such as the one described here.
Ludwig Institute for Cancer Research, Brussels Branch, Brussels, Belgium.
Vincent
V
Stroobant
Nathalie
N
Demotte
Rosalie M
RM
Luiten
Ralf M
RM
Leonhardt
Peter
P
Cresswell
Aude
A
Bonehill
Alexandre
A
Michaux
Wenbin
W
Ma
Arend
A
Mulder
Benoît J
BJ
Van den Eynde
Pierre
P
van der Bruggen
Nathalie
N
Vigneron
D000818:Animals; D017951:Antigen Presentation; D019556:COS Cells; D045744:Cell Line, Tumor; D002522:Chlorocebus aethiops; D059948:HLA-B44 Antigen / Q000276:immunology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D058950:Melanoma-Specific Antigens / Q000276:immunology*; D026901:Membrane Transport Proteins / Q000502:physiology*; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*
D059948:HLA-B44 Antigen; C072011:MAGEA1 protein, human; D058950:Melanoma-Specific Antigens; D026901:Membrane Transport Proteins; C107762:tapasin