Homocitrullination of lysine residues mediated by myeloid derived suppressor cells in the tumour environment is a target for cancer immunotherapy

Cook, K, Xue, W, Symonds, P, Daniels, I, Gijon, M, Boocock, D ORCID: https://orcid.org/0000-0002-7333-3549, Coveney, C ORCID: https://orcid.org/0000-0001-7047-6408, Miles, A ORCID: https://orcid.org/0000-0002-5388-938X, Shah, S, Atabani, S, Choudhury, R, Vaghela, P, Weston, D, Metheringham, R, Brentville, V and Durrant, L, 2021. Homocitrullination of lysine residues mediated by myeloid derived suppressor cells in the tumour environment is a target for cancer immunotherapy. Journal for ImmunoTherapy of Cancer, 9 (7): e001910.

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Abstract

Background: Homocitrullination is the post translational modification of lysine that is recognized by T cells.

Methods: This study identified homocitrullinated peptides from aldolase, enolase, cytokeratin and Bip and used HLA transgenic mice to assess immunogenicity by ELISpot assay. Vaccine efficacy was assessed in tumour therapy studies using HLA matched B16 melanoma expressing constitutive or IFNγ inducible MHC-II as represented by most human tumours. To determine the mechanism behind the therapy, immune cell infiltrates were analysed using flow cytometry and therapy studies in the presence of MPO inhibitor and T cell depletion performed. We assessed the T cell repertoire to homocitrullinated peptides in cancer patients and healthy donors using flow cytometry.

Results: Homocitrulline peptide vaccination stimulated strong CD4 T cell responses and induced significant anti-tumour therapy in an established tumour model. The anti-tumour response was dependent upon CD4 T-cells and the effect was driven mainly via direct tumour recognition, as responses were only observed if the tumours were induced to express MHC-II. In vitro proliferation assays show that healthy donors and cancer patients have an oligoclonal CD4 T-cell repertoire recognizing homocitrullinated peptides. Inhibition of cyanate generation, which mediates homocitrullination, by myeloperoxidase (MPO) inhibition reduced tumour therapy by the vaccine induced T cells (P=0.0018). Analysis of the tumour microenvironment (TME) suggested that myeloid-derived suppressor cells (MDSCs) were a potential source of MPO. The selected B16 melanoma model showed MDSC infiltration. and was appropriate to see if the homocitrulline vaccine could overcome the immunosuppression associated with MDSCs. The vaccine was very effective (90% survival) as the induced CD4 T cells directly targeted the homocitrullinated tumour and likely reversed the immunosuppressive environment.

Conclusion: We propose that MPO, potentially produced by MDSCs, catalyses the build-up of cyanate in the TME which diffuses into tumour cells causing homocitrullination of cytoplasmic proteins which are degraded and, in the presence of IFNγ, presented by MHC-II for direct CD4 T-cell recognition. Homocitrullinated proteins are a new target for cancer vaccines and may be particularly effective against tumours containing high levels of MPO expressing MDSCs.

Item Type:	Journal article
Publication Title:	Journal for ImmunoTherapy of Cancer
Creators:	Cook, K., Xue, W., Symonds, P., Daniels, I., Gijon, M., Boocock, D., Coveney, C., Miles, A., Shah, S., Atabani, S., Choudhury, R., Vaghela, P., Weston, D., Metheringham, R., Brentville, V. and Durrant, L.
Publisher:	BMC
Date:	28 July 2021
Volume:	9
Number:	7
Identifiers:	Number Type 10.1136/jitc-2020-001910 DOI 1453240 Other
Rights:	© Author(s) (or their employer(s)) 2021. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ. This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See http://creativecommons.org/licenses/by-nc/4.0/.
Divisions:	Schools > School of Science and Technology
Record created by:	Linda Sullivan
Date Added:	22 Jul 2021 08:02
Last Modified:	13 Aug 2021 09:07
URI:	https://irep.ntu.ac.uk/id/eprint/43600

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