Secondary anchor polymorphism in the HA-1 minor histocompatibility antigen critically affects MHC stability and TCR recognition.
T cell recognition of minor histocompatibility antigens (mHags) underlies allogeneic immune responses that mediate graft-versus-host disease and the graft-versus-leukemia effect following stem cell transplantation. Many mHags derive from single amino acid polymorphisms in MHC-restricted epitopes, but our understanding of the molecular mechanisms governing mHag immunogenicity and recognition is incomplete. Here we examined antigenic presentation and T-cell recognition of HA-1, a prototypic autosomal mHag derived from single nucleotide dimorphism (HA-1(H) versus HA-1(R)) in the HMHA1 gene. The HA-1(H) peptide is restricted by HLA-A2 and is immunogenic in HA-1(R/R) into HA-1(H) transplants, while HA-1(R) has been suggested to be a "null allele" in terms of T cell reactivity. We found that proteasomal cleavage and TAP transport of the 2 peptides is similar and that both variants can bind to MHC. However, the His>Arg change substantially decreases the stability and affinity of HLA-A2 association, consistent with the reduced immunogenicity of the HA-1(R) variant. To understand these findings, we determined the structure of an HLA-A2-HA-1(H) complex to 1.3A resolution. Whereas His-3 is accommodated comfortably in the D pocket, incorporation of the lengthy Arg-3 is predicted to require local conformational changes. Moreover, a soluble TCR generated from HA-1(H)-specific T-cells bound HA-1(H) peptide with moderate affinity but failed to bind HA-1(R), indicating complete discrimination of HA-1 variants at the level of TCR/MHC interaction. Our results define the molecular mechanisms governing immunogenicity of HA-1, and highlight how single amino acid polymorphisms in mHags can critically affect both MHC association and TCR recognition.
Nicholls
Sarah
S
Cancer Research UK Institute for Cancer Studies, Edgbaston, Birmingham B15 2TT, United Kingdom.
Piper
Karen P
KP
Mohammed
Fiyaz
F
Dafforn
Timothy R
TR
Tenzer
Stefan
S
Salim
Mahboob
M
Mahendra
Premini
P
Craddock
Charles
C
van Endert
Peter
P
Schild
Hansjörg
H
Cobbold
Mark
M
Engelhard
Victor H
VH
Moss
Paul A H
PA
Willcox
Benjamin E
BE
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D001120:Arginine / Q000378:metabolism; D002469:Cell Separation; D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D000939:Epitopes / Q000737:chemistry / Q000276:immunology; D015789:HLA-A2 Antigen / Q000737:chemistry; D006801:Humans; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000276:immunology; D015778:Minor Histocompatibility Antigens / Q000737:chemistry* / Q000235:genetics*; D011110:Polymorphism, Genetic; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011485:Protein Binding; D055550:Protein Stability; D017433:Protein Structure, Secondary; D021381:Protein Transport; D011948:Receptors, Antigen, T-Cell / Q000737:chemistry / Q000276:immunology*; D020349:Surface Plasmon Resonance; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology; D014019:Tissue Donors
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters; D000939:Epitopes; D015789:HLA-A2 Antigen; D015778:Minor Histocompatibility Antigens; D011948:Receptors, Antigen, T-Cell; C073119:TAP1 protein, human; D001120:Arginine; D046988:Proteasome Endopeptidase Complex