Method for the detection, preparation and depletion of CD4+ t lymphocytes

1. An isolated complex of:

a Major Histocompatibility Complex (MHC) class II molecule and

a peptide consisting essentially of (i) an MHC class II restricted CD4+ T cell epitope of an antigenic protein and (ii) a redox motif of [CST]-X-X-C (SEQ ID NO: 11) or C-X-X-[CST] (SEQ ID NO: 12), which are immediately adjacent to each other or separated by a linker of at most 7 amino acids, wherein X is any amino acid, C is cysteine and [CST] is an amino acid selected from cysteine, serine and threonine.

2. The complex according to claim 1 , wherein said redox motif is C-X-X-C (SEQ ID NO: 13).

3. The complex according to claim 1 , wherein said MHC class II restricted CD4+ T-cell epitope and redox motif are separated by a linker of at most 4 amino acids.

4. The complex according to claim 1 , wherein said complex between said peptide and said MHC class II molecule is a covalently bound complex.

5. The complex according to claim 4 , wherein said covalently bound complex is a fusion protein of said MHC class II molecule with said peptide.

6. The complex according to claim 1 , wherein said complex is attached to a bead or a plate.

7. An in vitro method for detecting class II restricted CD4+ T cells in a sample comprising the steps of:

providing a sample comprising cells;

contacting the sample with a complex according to claim 1 ; and

measuring the binding of said complex with cells in said sample, wherein the binding of said complex to said cells is indicative of CD4+ T cells being present in said sample.

8. The method according to claim 7 , wherein said redox motif is C-X-X-C (SEQ ID NO: 13).

9. The method according to claim 7 , wherein said MHC class II restricted CD4+ T-cell epitope and redox motif are separated by a linker of at most 4 amino acids.

10. The method according to claim 7 , wherein said peptide occurs in a non-covalent complex with the MHC class II molecule and has a length of between 12 and 20 amino acids.

11. The method according to claim 7 , wherein said complex is a fusion protein of said MCH class II molecule with said peptide.

12. The method according to claim 7 , wherein the sample is a blood sample or a tissue sample.

13. The method according to claim 12 , wherein the tissue sample is synovial fluid from a rheumatoid arthritis patient or pleural fluid of a patient with infectious pneumonia.

14. The method according to claim 12 , wherein said complex is attached to an insoluble carrier or a substrate.

15. The method according to claim 12 , further comprising the step of detecting or isolating subpopulations of detected CD4+ T cells.

16. The method according to claim 7 , wherein said CD4+ T cells are one or more selected from the group consisting of Tregs, induced Tregs such as Tr1 or Th3, naïve CD4+ T cells, polarised CD4+ T cells, and cytolytic CD4+ T cells.

17. The method according to claim 7 , wherein said sample comprises one or more cells selected from the group consisting of naïve CD4+ T cells, antigen-exposed CD4+ T cells, CD4+ T cells obtained during therapy or during vaccination, and CD4+ T cells in a tissue.

18. The method according to claim 7 , wherein said epitope sequence of said peptide is identical to the epitope sequence of said antigenic protein or wherein, the MHC class II anchoring residues of the epitope sequence of said peptide are modified compared to the epitope sequence of said antigenic protein in order to modulate the binding affinity of an epitope to CD4+ cells.

19. The method according to claim 7 , wherein said MHC class II molecule in the complex is a multimer.

20. The method according to claim 7 , wherein said complex is a soluble complex.

21. The method according to claim 7 , further comprising the step of isolating CD4+ T cells which are bound to said complex.