Vaccine Can Induce CD4-Mediated Responses to Homocitrullinated Peptides via Multiple HLA-Types and Confer Anti-Tumor Immunity

Abstract

Homocitrullination is the post translation modification (PTM) of the amino acid lysine to homocitrulline also referred to as carbamylation. This PTM has mainly been studied in relation to autoimmune diseases including rheumatoid arthritis. Homocitrullination of lysines alters their charge which can lead to generation of neoepitopes that are differentially presented by MHC-II and induce modification-specific immune responses. Homocitrullination is often considered a process which triggers autoimmune disease by bypassing self-tolerance however, we suggest that homocitrullination may also have an alternative role in immune responses including protection against cancer. Here we demonstrate that immune responses to homocitrullinated peptides from three different proteins can be induced via multiple HLA-types. Immunization of Balb/c or HLA-transgenic DR4 and DR1 mice can induce modification-specific CD4 mediated IFNγ responses. Healthy human donors show a clear repertoire for the homocitrullinated Vimentin peptide (Vim116-135Hcit), with modification-specific and oligoclonal responses. Importantly, in vivo homocitrulline specific Vim116-135Hcit,Cyk8 371-388Hcit and Aldo 140-157Hcit responses are able to confer an anti-tumor effect in the murine B16 melanoma model. The Vim116-135Hcit anti-tumor response was dependent upon tumor expression of MHC-II suggesting the direct recognition of PTMs on tumor is an important anti-tumor mechanism. Cancer patients also have a CD4 repertoire for Vim116-135Hcit. Together these results suggest that homocitrulline-specific immune responses can be generated in healthy mice and detected in human donors through a variety of HLA-restrictions. Immunization can induce responses to Vim116-135Hcit,Aldolase 140-157Hcit and Cyk8 371-388Hcit which provide anti-tumor therapy across several HLA-types. Our results advance our understanding of homocitrulline-specific immune responses, with implications for a number of fields beyond autoimmunity, including tumor immune surveillance.

Modi-2, a vaccine stimulating CD4 mediated responses to homocitrullinated self-epitopes, as a therapy for solid cancers

“…However, responses vary between different mice strains. These results also support previous data (5,10) and confirm that responses to the Modi-2 peptides are homocitrullinespecific and mediated by CD4 T cells.…”

“…We have previously shown that homocitrullinated (Hcit) peptides derived from aldolase A (Aldo), immunoglobulin heavy chain-binding protein (BiP), cytokeratin 8 (Cyk8) and vimentin (Vim) can stimulate CD4 T cell responses through multiple MHCII alleles in standard and HLA transgenic mice including HLA-HHDII/DR1, HLA-HHDII/DP4, HLA-DR4 and Balb/c mice. We have also observed that among several peptides screened, Aldo74-93 Hcit , BiP562-579 Hcit , Cyk8 371-388 Hcit and Vim116-135 Hcit peptides induced T cell responses in the different mouse strains mentioned above (5,10). These epitopes are homologous in humans and mice.…”

“…We have previously demonstrated that targeting homocitrullinated (Hcit) peptides induces potent anti-tumour immune responses in animal models (5,10). Here, we presented the potential of a combination Modi-2 cancer vaccine as a promising therapy for solid tumours.…”

“…Vaccination targeting homocitrullinated peptides derived from self-antigens has been shown to stimulate Th1 mediated immune responses in mouse models and mediate tumour therapy (5,10).…”

Immune responses to citrullinated and homocitrullinated peptides in healthy donors are not restricted to the HLA SE shared allele and can be selected into the memory pool

“…However, if citrullination is a normal stress response, it cannot be restricted to only HLA‐DR4 +ve and HLA‐DR1 +ve individuals. We, and others, have previously demonstrated that citrullinated peptides can bind to both HLA‐DP4 [16] and HLA‐DQ alleles [17] implying a wider HLA presentation profile for citrullinated and homocitrullinated peptides [18, 19].…”