Impact of peptide:HLA complex stability for the identification of SARS-CoV-2-specific CD8+T cells

Induction of a lasting protective immune response is dependent on presentation of epitopes to patrolling T cells through the HLA complex. While peptide:HLA (pHLA) complex affinity alone is widely exploited for epitope selection, we demonstrate that including the pHLA complex stability as a selection parameter can significantly reduce the high false discovery rate observed with predicted affinity. In this study, pHLA complex stability was measured on three common class I alleles and 1286 overlapping 9-mer peptides derived from the SARS-CoV-2 Spike protein. Peptides were pooled based on measured stability and predicted affinity. Strikingly, stability of the pHLA complex was shown to strongly select for immunogenic epitopes able to activate functional CD8⁺T cells. This result was observed across the three studied alleles and in both vaccinated and convalescent COVID-19 donors. Deconvolution of peptide pools showed that specific CD8⁺T cells recognized one or two dominant epitopes. Moreover, SARS-CoV-2 specific CD8⁺T cells were detected by tetramer-staining across multiple donors. In conclusion, we show that stability analysis of pHLA is a key factor for identifying immunogenic epitopes.

Determination of crucial epitopes in the sperm protein calsperin employing synthetic peptides and monoclonal antibodies

The chaperone protein calsperin is exclusively expressed in the testes and is essential for sperm migration from the uterus into the oviduct. During spermatogenesis, calsperin interacts with ADAM3, a spermatozoon membrane protein required for fertilization. In this study, we characterized a calsperin epitope by using two monoclonal antibodies and resin-bound calsperin peptides, which were tested for reactivity using a modified enzyme-linked immunosorbent assay. An epitope located at the C-terminal end of calsperin corresponding to amino acids ²²⁸ WEKHFLDAS²³⁷ was identified. Three hot spot amino acids were essential for antibody binding whereas the remaining amino acids in the identified epitope appeared to be essential for bringing the critical contact residues into an α-helix structure. No notable sequence similarity was determined between the identified calsperin epitope and calreticulin, a chaperone homologue with sequence similarity, indicating that the identified epitope was specific for calsperin. Characterization of the calsperin epitope and of the two antibodies tested may be used in assays for further characterization of calsperin, where knowledge about the binding sites is necessary, for example, in sandwich assays. Moreover, studies like these may be used to study the function of calsperin during spermatogenesis and fertilization in detail and to develop new male contraception methods by targeting calsperin and mediating neutralization of its function.

Epitope Mapping of Monoclonal Antibodies to Calreticulin Reveals That Charged Amino Acids Are Essential for Antibody Binding

Calreticulin is a chaperone protein, which is associated with myeloproliferative diseases. In this study, we used resin-bound peptides to characterize two monoclonal antibodies (mAbs) directed to calreticulin, mAb FMC 75 and mAb 16, which both have significantly contributed to understanding the biological function of calreticulin. The antigenicity of the resin-bound peptides was determined by modified enzyme-linked immunosorbent assay. Specific binding was determined to an 8-mer epitope located in the N-terminal (amino acids 34–41) and to a 12-mer peptide located in the C-terminal (amino acids 362–373). Using truncated peptides, the epitopes were identified as TSRWIESK and DEEQRLKEEED for mAb FMC 75 and mAb 16, respectively, where, especially the charged amino acids, were found to have a central role for a stable binding. Further studies indicated that the epitope of mAb FMC 75 is assessable in the oligomeric structure of calreticulin, making this epitope a potential therapeutic target.

Genetic polymorphisms associated with psoriasis and development of psoriatic arthritis in patients with psoriasis

Background

Psoriasis (PsO) is a chronic inflammatory disease with predominantly cutaneous manifestations. Approximately one third of patients with PsO develop psoriatic arthritis (PsA), whereas the remaining proportion of patients has isolated cutaneous psoriasis (PsC). These two phenotypes share common immunology, but with different heredity that might in part be explained by genetic variables.

Methods

Using a candidate gene approach, we studied 53 single nucleotide polymorphisms (SNPs) in 37 genes that regulate inflammation. In total, we assessed 480 patients with PsO from DERMBIO, of whom 151 had PsC for 10 years or more (PsC10), 459 patients with PsA from DANBIO, and 795 healthy controls. Using logistic regression analysis, crude and adjusted for age and gender, we assessed associations between genetic variants and PsO, PsC10, and PsA, as well as associations between genetic variants and development of PsA in PsO.

Results

Eleven polymorphisms in 10 genes were nominally associated with PsO and/or PsC and/or PsA (P < 0.05). After correction for multiple testing with a false discovery rate of 5%, two SNPs remained significant: TNF (rs361525) was associated with PsO, PsC10, and PsA; and IL12B (rs6887695) was associated with PsO.

Conclusion

Among a cohort of Danish patients with moderate-to-severe psoriasis, two SNPs in the IL12B and TNF genes were associated with susceptibility of psoriasis. None of the SNPs were specifically associated with isolated cutaneous psoriasis or psoriatic arthritis.