MHC multimers, methods for their generation, labeling and use

A composition comprising a plurality of MHC multimers and a carrier, wherein each MHC multimer comprises (a-b-P)n, wherein n>1, wherein a and b together form a functional MHC protein capable of binding the peptide P, when P is present;

• wherein (a-b-P) is the MHC-peptide complex formed when the peptide P binds to the functional MHC protein;
• wherein each MHC protein or MHC-peptide complex is associated with one or more multimerization domains;
• wherein said MHC multimer comprises one or more labels;
• wherein the composition comprises groups of MHC multimers, wherein MHC multimers of some of said groups comprise one or more same labels within the group and MHC multimers of others of said groups each comprise two or more different labels within the group, wherein each group of MHC multimers presents a different peptide compared to other groups;
• wherein the MHC multimers of each group are labelled with said one or more same labels or said two or more different labels;
• wherein the composition is made by a process comprising providing a plurality of said MHC-peptide complexes and associating them with said one or more multimerization domains.