Immunotherapy

1. A composition for activating a T cell with an antigenic peptide specific for said T cell, the composition comprising:

a) a cell-expressed primary anchor protein comprising a first anchor subunit;

b) a dock protein comprising:

1) a first dock subunit that is an orthogonal binding partner of the first anchor subunit; and

2) a second dock subunit; and

c) a pMHC complex made by a process of binding an antigenic peptide to a MHC polypeptide and selecting the pMHC complex that activates a T cell, wherein the pMHC complex further comprises a second anchor subunit that is an orthogonal binding partner of the second dock subunit,

wherein the first dock subunit and the first anchor subunit are selected from the group of orthogonal binding pairs consisting of: cohesion and dockerin; SH3 ligand and SH3 domain; PDZ ligand and PDZ domain; and antigen and antibody or antigen-binding antibody fragment specific for the antigen; and

wherein the second dock subunit and the second anchor subunit are selected from the group of orthogonal binding pairs consisting of cohesion and dockerin; SH3 ligand and SH3 domain; PDZ ligand and PDZ domain; and antigen and antibody or antigen-binding antibody fragment specific for the antigen.

2. The composition of claim 1 wherein the primary anchor protein is a fusion protein comprising a protein sequence for cell surface display of the primary anchor protein.

3. The composition of claim 1 wherein the primary anchor protein is a fusion protein comprising a portion encoding a yeast mating protein.

4. The composition of claim 1 wherein the primary anchor protein is a fusion protein comprising a portion encoding yeast Aga2p.

5. The composition of claim 1 wherein the primary anchor protein comprises an epitope tag and/or the dock protein comprises an epitope tag.

6. The composition of claim 5 wherein the epitope tag is V5 or c-myc.

7. The composition of claim 1 wherein the dock protein comprises a histidine tag and/or the pMHC complex comprises a histidine tag.

8. A composition for activating a T cell with an antigenic peptide specific for said T cell, the composition comprising:

a) a cell-expressed primary anchor protein comprising a first anchor subunit, a second anchor subunit, and a third anchor subunit;

b) a first dock protein comprising:

1) a first dock subunit that is an orthogonal binding partner of the first anchor subunit; and

2) a fourth dock subunit;

c) a second dock protein comprising:

1) a second dock subunit that is an orthogonal binding partner of the second anchor subunit; and

2) a fifth dock subunit;

d) a third dock protein comprising:

1) a third dock subunit that is an orthogonal binding partner of the third anchor subunit; and

2) a sixth dock subunit;

e) a first co-stimulatory molecule comprising a fourth anchor subunit that is an orthogonal binding partner of the fourth dock subunit;

f) a second co-stimulatory molecule; or a co-inhibitory molecule that is B7-H1 (PD-L1) or Galectin-9, said second co-stimulatory molecule or said co-inhibitory molecule comprising a fifth anchor subunit that is an orthogonal binding partner of the fifth dock subunit; and

g) a pMHC complex made by a process of binding an antigenic peptide to a MCH polypeptide and selecting the pMHC complex that activates a T cell, wherein said pMHC complex further comprises a sixth anchor subunit that is an orthogonal binding partner of the sixth dock subunit,

wherein the first dock subunit and the first anchor subunit, the second dock subunit and the second anchor subunit, the third dock subunit and the third anchor subunit, the fourth dock subunit and the fourth anchor subunit, the fifth dock subunit and the fifth anchor subunit, and the sixth dock subunit and the sixth anchor subunit are each independently selected from the group of orthogonal binding pairs consisting of: cohesion and dockerin; SH3 ligand and SH3 domain; PDZ ligand and PDZ domain; and antigen and antibody or antigen-binding antibody fragment that is specific for the antigen.

9. The composition of claim 8 wherein the first co-stimulatory molecule is CD30L, CD70, TL1A, CD137L, ICAM1, CD80, CD40, CD86, ICOSL, GITRL, or OX40L.

10. The composition of claim 8 wherein the second co-stimulatory molecule is CD30L, CD70, TL1A, CD137L, ICAM1, CD80, CD40, CD86, ICOSL, GITRL, or OX40L.

11. The composition of claim 8 wherein the first co-stimulatory molecule and the pMHC complex are arranged in a bulls-eye pattern.

12. The composition of claim 8 wherein the first dock protein, the second dock protein, the third dock protein, the first co-stimulatory molecule, and the pMHC complex are expressed as soluble proteins.

13. The composition of claim 1 , further comprising a co-stimulatory molecule.

14. The composition of claim 1 , wherein the MHC is encoded by HLA-A*0201, HLA-B*0702, HLA-DR*0101, HLA-DR*0401, HLA-DR*0701, or HLA-DR*1501.

15. The composition of claim 8 , wherein the MHC is encoded by HLA-A*0201, HLA-B*0702, HLA-DR*0101, HLA-DR*0401, HLA-DR*0701, or HLA-DR*1501.