The activation of CD8(+) T-cells requires the uptake of exogenous polypeptide antigens and proteolytic processing of these antigens to octamer or nonamer peptides, which are loaded on MHC-I complexes and presented to the T-cell. By using an azide as a bioorthogonal protecting group rather than as a ligation handle, masked antigens were generated-antigens that are not recognized by their cognate T-cell unless they are deprotected on the cell using a Staudinger reduction.

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The activation of CD8 + T-cells requires the uptake of exogenous polypeptide antigens and proteolytic processing of these antigens to octamer or nonamer peptides,w hich are loaded on MHC-I complexes and presented to the T-cell. By using an azide as abioorthogonal protecting group rather than as al igation handle,m asked antigens were generatedantigens that are not recognized by their cognate T-cell unless they are deprotected on the cell using aS taudinger reduction.

Synthetic vaccines, based on antigenic peptides that comprise MHC−I and MHC‐II T‐cell epitopes expressed by tumors, show great promise for the immunotherapy of cancer. For optimal immunogenicity, the synthetic peptides (SPs) should be adjuvanted with suitable immunostimulatory additives. Previously, we have shown that improved immunogenicity in vivo is obtained with vaccine modalities in which an SP is covalently connected to an adjuvanting moiety, typically a ligand to Toll‐like receptor 2 (TLR2). SPs were covalently attached to UPam, which is a derivative of the classic TLR2 ligand Pam3CysSK4. A disadvantage of the triply palmitoylated UPam is its high lipophilicity, which precludes universal adoption of this adjuvant for covalent modification of various antigenic peptides as it renders the synthetic vaccine insoluble in several cases. Here, we report a novel conjugatable TLR2 ligand, mini‐UPam, which contains only one palmitoyl chain, rather than three, and therefore has less impact on the solubility and other physicochemical properties of a synthetic peptide. In this study, we used SPs that contain the clinically relevant neoepitopes identified in a melanoma patient who completely recovered after T‐cell therapy. Homogeneous mini‐UPam‐SP conjugates have been prepared in good yields by stepwise solid‐phase synthesis that employed a mini‐UPam building block pre‐prepared in solution and the standard set of Fmoc‐amino acids. The immunogenicity of the novel mini‐UPam‐SP conjugates was demonstrated by using the cancer patient's T‐cells.