H4 and CTT-2 minor histocompatibility antigens: concordant genetic linkage and migration in two-dimensional peptide separation

The H4b minor histocompatibility antigen is caused by a combination of genetically determined and posttranslational modifications

Minor histocompatibility (H) Ag disparities result in graft-vs-host disease and chronic solid allograft rejection in MHC-identical donor-recipient combinations. Minor H Ags are self protein-derived peptides presented by MHC class I molecules. Most arise as a consequence of allelic variation in the bound peptide (p) that results in TCR recognizing the p/MHC as foreign. We used a combinational peptide screening approach to identify the immune dominant H2K(b)-restricted epitope defining the mouse H4(b) minor H Ag. H4(b) is a consequence of a P3 threonine to isoleucine change in the MHC-bound peptide derived from epithelial membrane protein-3. This allelic variation also leads to phosphorylation of the H4(b) but not the H4(a) epitope. Further, ex vivo CD8(+) T lymphocytes bind phosphorylated Ag tetramers with high efficiency. Although we document the above process in the minor H Ag system, posttranslational modifications made possible by subtle amino acid changes could also contribute to immunogenicity and immune dominance in tumor immunotherapeutic settings.

Immunodominance of H60 is caused by an abnormally high precursor T cell pool directed against its unique minor histocompatibility antigen peptide

The H60 minor histocompatibility (H) antigen peptide is derived from a glycoprotein that serves as a ligand for the stimulatory NKG2D receptor. We show that this peptide is remarkably immunodominant in that it competes effectively with MHC alloantigens, is efficiently crosspresented by host antigen-presenting cells (APCs), and readily elicits naive CD8 T cell responses in vitro. H60 immunodominance is neither a consequence of NKG2D engagement nor competition among minor H antigens on APCs. Instead, H60 immunodominance is a consequence of an abnormally high naive precursor frequency of H60 peptide reactive CD8 T cells. Understanding why the H60 peptide is so immunogenic has important implications in tissue transplantation and vaccine design.

Distinguishing self from nonself: immunogenicity of the murine H47 locus is determined by a single amino acid substitution in an unusual peptide

Histocompatibility (H) Ags are responsible for chronic graft rejection and graft vs host disease in solid tissue and bone marrow transplantation among MHC-matched individuals. Here we defined the molecular basis of self-nonself discrimination for the murine chromosome 7 encoded H47 histocompatibility locus, known by its trait of graft-rejection for over 40 years. H47 encodes a novel, highly conserved cell surface protein containing the SCILLYIVI (SII9) nonapeptide in its transmembrane region. The p7 isoleucine-to-phenylalanine substitution in SII9 defined the antigenic polymorphism and T cell specificity. Despite absence of the canonical consensus motif and weak binding to D(b) MHC I, both H47 peptides were presented to CTLs. However, unlike all the other known H loci, the relative immunogenicity of both H47 alleles varied dramatically and was profoundly influenced by neighboring H loci. The results provide insights into the peptide universe that defines nonself and the basis of histoincompatibility.

Immunodominant minor histocompatibility antigen peptides presented by H2Db molecules

BACKGROUND

C57BL/6 (B6) mice generate cytolytic T lymphocytes (CTLs) to a limited number of immunodominant cytotoxic T cell target (CTT) antigens and associated peptides when primed with H2-matched BALB.B spleen cells, despite multiple minor histocompatibility antigen (HA) differences. We previously showed that these CTLs recognize four Kb-bound minor HA peptides derived from CTT antigens. Here, we describe the identification of Db-bound minor HA peptides recognized by B6 anti-BALB.B CTLs.

METHODS

Peptides were extracted from Db molecules immunoprecipitated from lysates of T lymphoblasts from BALB.B mice and mice from the CXB recombinant inbred strains that express H2b and segregate minor HA from BALB/c and B6. Peptides were separated by reverse-phase high-performance liquid chromatography and tested for sensitization of targets for lysis by CTLs specific for BALB.B and the CXB strains.

RESULTS

B6 anti-BALB.B CTLs recognized a single Db-bound peptide whose distribution in CXB strains matched that of the previously reported CTT-1 minor HA. An additional Db-bound peptide (CTT-7) was recognized by B6 anti-CXBG CTLs. CTT-1 was expressed by independently derived inbred mouse strains that express H2b. CTT-1 was recognized by B6 CTLs specific for these inbred strains, except for the LP and 129 strains that stimulated CTL specific for the CTT-8 peptide expressed by these two strains.

CONCLUSIONS

These results demonstrate that B6 CTLs primed and boosted with multiple minor HA recognize a maximum of two minor HA peptides regardless of the strain of origin of H2b-matched stimulating lymphoid cells.

Brain-infiltrating cytolytic T lymphocytes specific for Theiler's virus recognize H2Db molecules complexed with a viral VP2 peptide lacking a consensus anchor residue

Mice expressing the H2b haplotype are resistant to infection with Theiler's murine encephalomyelitis virus (TMEV), which causes chronic demyelination in susceptible mice. The prominent cytolytic T-lymphocyte (CTL) response to the VP2 antigen encoded by TMEV led us to the identification of a class I-binding peptide derived from the VP2 antigen. Escherichia coli transformants overexpressing a series of 11 overlapping VP2 protein fragments were subjected to lysis and alkali digestion, and the resultant peptide pools were tested for their abilities to sensitize RMA-S targets for lysis by CTLs. The source of effector CD8+ T cells for the assays was either freshly harvested central nervous system-infiltrating lymphocytes (CNS-IL) or CNS-IL-derived VP2-specific CTL clones and lines. A 10-residue peptide at VP2 positions 121 to 130 (VP2(121-130)) (FHAGSLLVFM) was identified that sensitized targets for lysis and formed stable complexes with H2Db class I molecules. The VP2(121-130) peptide sensitized target cells for lysis by freshly harvested CNS-IL CTLs at femtomolar concentrations. Despite its relative high level of biological activity, the VP2(121-130) peptide is distinguished from other Db-binding peptides by its lack of an asparagine residue at position five, which had been previously proposed to be a requirement for Db-peptide complexing.