Identification, quantification, and characterization of t cells and t cell antigens

A method for determining whether a T cell specific for a peptide is present in a population of cells, which method comprises:

• (a) introducing the peptide into an APC, which expresses a fusion protein comprising (i) a major histocompatibility complex (MHC) molecule portion and (ii) a reporter peptide portion, the peptide such that a complex forms between the fusion protein and the peptide and the peptide is displayed by the APC,
• (b) contacting the APC displaying the complex with a population of cells, such that T cells in the population of cells specific for the antigen will detectably internalize the complex,
• (c) determining T cells in the population of cells have detectably internalized the complex,
• whereupon T cells which are in the population of cells and are specific for the peptide are determined to be present.

A method for determining whether a peptide induces a T cell-mediated immune response comprising:

• (a) introducing the peptide into an APC, which expresses a fusion protein comprising (i) an MHC molecule portion and (ii) a reporter peptide portion, the peptide under conditions where a complex can form between the fusion protein and the peptide and the peptide is displayed by the APC,
• (b) contacting the APC displaying the peptide with a population of T cells, such that T cells in the population specific for the peptide detectably internalize the complex, and
• (c) detecting whether cells in the population of T cells have internalized the complex,
• whereupon the peptide is determined to induce a T cell-mediated immune response.

A method of evaluating the immunological effect of an antigen on the phenotypic or functional activity profile of a population of T cells comprising:

• (a) introducing the antigen into an APC, which expresses a fusion protein comprising (i) an MHC molecule portion and (ii) a reporter peptide portion, the antigen such that a complex forms between the fusion protein and the antigen and the antigen is displayed by the APC,
• (b) contacting the APC displaying the antigen with a population of T cells comprising T cells specific for the antigen and characterized by a phenotypic trait or functional trait, such that at least some of the T cells detectably internalize the complex, and
• (c) characterizing the population of T cells on the basis of (i) the phenotypic trait, (ii) the functional trait, (iii) a second phenotypic trait that differs from the phenotypic trait, (iv) a second functional trait that differs from the functional trait, or (v) any combination of (i)-(iv),
• whereupon the immunological effect of the antigen on the phenotypic or functional activity profile of the population of T cells is evaluated.