InVivoMAb anti-human MHC class II (HLA-DP)

To investigate the function of HLA class II molecules in B-cell activation, we generated three new anti-HLA class II monoclonal antibodies with differing specificities for DP, DQ, and DR determinants. These were tested for their ability to inhibit various B- and T-lymphocyte responses. Each of these antibodies (NB-29, DH-84, and DH-224) immunoprecipitates a heterodimer of approximately 35,000 and 28,000 mol wt from 125I-surface-labeled B-lymphoma cells, as shown by SDS-PAGE. NB-29 (IgG1) detects a polymorphic DQ determinant, while DH-224 (IgG1) is reactive with monomorphic DR determinants, and DH-84 (IgG2a) has specificity for DP, DQ, and DR. Both DH-224 and DH-84, but not NB-29, were found to inhibit significantly the stimulation of peripheral blood mononuclear cells (PBMC) by anti-mu (70%-90% inhibition) and by lipopolysaccharide (80%-90% inhibition), as measured by incorporation of tritiated thymidine. When added to highly purified populations of peripheral blood B cells, none of these anti-class II monoclonal antibodies inhibited anti-mu-induced stimulation. This suggests that the inhibitory effect that DH-224 and DH-84 have on the stimulation of unfractionated PBMC may be due to their ability to interfere with the action of accessory cells. Epstein-Barr-virus (EBV)-transformed B-cell lines, in contrast, showed substantial inhibition of growth when cultured in the presence of any of the three antibodies. With respect to T cells, DH-84 and DH-224 strongly inhibited the mixed lymphocyte response; NB-29 did not. None of these antibodies inhibited stimulation of PBMC by phytohemagglutinin (PHA). These findings suggest that DQ and DR HLA class II molecules have differing roles in B-cell activation and document a direct antiproliferative effect of anti-HLA class II monoclonal antibodies on the growth of EBV-transformed cell lines.

Accurate prediction of antigen presentation by human leukocyte antigen (HLA) class II molecules is crucial for rational development of immunotherapies and vaccines targeting CD4⁺ T cell activation. So far, most prediction methods for HLA class II antigen presentation have focused on HLA-DR because of limited availability of immunopeptidomics data for HLA-DQ and HLA-DP while not taking into account alternative peptide binding modes. We present an update to the NetMHCIIpan prediction method, which closes the performance gap between all three HLA class II loci. We accomplish this by first integrating large immunopeptidomics datasets describing the HLA class II specificity space across all loci using a refined machine learning framework that accommodates inverted peptide binders. Next, we apply targeted immunopeptidomics assays to generate data that covers additional HLA-DP specificities. The final method, NetMHCIIpan-4.3, achieves high accuracy and molecular coverage across all HLA class II allotypes.

A critical step in the immunogenicity cascade is attributed to human leukocyte antigen (HLA) II presentation triggering T cell immune responses. The liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based major histocompatibility complex (MHC) II-associated peptide proteomics (MAPPs) assay is implemented during preclinical risk assessments to identify biotherapeutic-derived T cell epitopes. Although studies indicate that HLA-DP and HLA-DQ alleles are linked to immunogenicity, most MAPPs studies are restricted to using HLA-DR as the dominant HLA II genotype due to the lack of well-characterized immunoprecipitating antibodies. Here, we address this issue by testing various commercially available clones of MHC-II pan (CR3/43, WR18, and Tü39), HLA-DP (B7/21), and HLA-DQ (SPV-L3 and 1a3) antibodies in the MAPPs assay, and characterizing identified peptides according to binding specificity. Our results reveal that HLA II receptor-precipitating reagents with similar reported specificities differ based on clonality and that MHC-II pan antibodies do not entirely exhibit pan-specific tendencies. Since no individual antibody clone is able to recover the complete HLA II peptide repertoire, we recommend a mixed strategy of clones L243, WR18, and SPV-L3 in a single immunoprecipitation step for more robust compound-specific peptide detection. Ultimately, our optimized MAPPs strategy improves the predictability and additional identification of T cell epitopes in immunogenicity risk assessments.

The identification of CD4⁺ T cell epitopes is instrumental for the design of subunit vaccines for broad protection against coronaviruses. Here, we demonstrate in COVID-19-recovered individuals a robust CD4⁺ T cell response to naturally processed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike (S) protein and nucleoprotein (N), including effector, helper, and memory T cells. By characterizing 2943 S-reactive T cell clones from 34 individuals, we found that the receptor-binding domain (RBD) is highly immunogenic and that 33% of RBD-reactive clones and 94% of individuals recognized a conserved immunodominant S346-S365 region comprising nested human leukocyte antigen DR (HLA-DR)- and HLA-DP-restricted epitopes. Using pre- and post-COVID-19 samples and S proteins from endemic coronaviruses, we identified cross-reactive T cells targeting multiple S protein sites. The immunodominant and cross-reactive epitopes identified can inform vaccination strategies to counteract emerging SARS-CoV-2 variants.