Therapeutic cancer vaccination against mutant calreticulin in myeloproliferative neoplasms induces expansion of specific T cells in the periphery but specific T cells fail to enrich in the bone marrow

Front Immunol. 2023 Aug 17:14:1240678. doi: 10.3389/fimmu.2023.1240678. eCollection 2023.

Abstract

Background: Therapeutic cancer vaccination against mutant calreticulin (CALR) in patients with CALR-mutant (CALRmut) myeloproliferative neoplasms (MPN) induces strong T-cell responses against mutant CALR yet fails to demonstrate clinical activity. Infiltration of tumor specific T cells into the tumor microenvironment is needed to attain a clinical response to therapeutic cancer vaccination.

Aim: Determine if CALRmut specific T cells isolated from vaccinated patients enrich in the bone marrow upon completion of vaccination and explore possible explanations for the lack of enrichment.

Methods: CALRmut specific T cells from four of ten vaccinated patients were expanded, enriched, and analyzed by T-cell receptor sequencing (TCRSeq). The TCRs identified were used as fingerprints of CALRmut specific T cells. Bone marrow aspirations from the four patients were acquired at baseline and at the end of trial. T cells were enriched from the bone marrow aspirations and analyzed by TCRSeq to identify the presence and fraction of CALRmut specific T cells at the two different time points. In silico calculations were performed to calculate the ratio between transformed cells and effector cells in patients with CALRmut MPN.

Results: The fraction of CALRmut specific T cells in the bone marrow did not increase upon completion of the vaccination trial. In general, the T cell repertoire in the bone marrow remains relatively constant through the vaccination trial. The enriched and expanded CALRmut specific T cells recognize peripheral blood autologous CALRmut cells. In silico analyses demonstrate a high imbalance in the fraction of CALRmut cells and CALRmut specific effector T-cells in peripheral blood.

Conclusion: CALRmut specific T cells do not enrich in the bone marrow after therapeutic cancer peptide vaccination against mutant CALR. The specific T cells recognize autologous peripheral blood derived CALRmut cells. In silico analyses demonstrate a high imbalance between the number of transformed cells and CALRmut specific effector T-cells in the periphery. We suggest that the high burden of transformed cells in the periphery compared to the number of effector cells could impact the ability of specific T cells to enrich in the bone marrow.

Keywords: adaptive immunity; calreticulin; cancer vaccines; immune escape; myeloproliferative neoplasms.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bone Marrow
  • Calreticulin / genetics
  • Cancer Vaccines*
  • Humans
  • Myeloproliferative Disorders* / genetics
  • Myeloproliferative Disorders* / therapy
  • Neoplasms*
  • T-Lymphocytes
  • Vaccines, Subunit

Substances

  • Calreticulin
  • Cancer Vaccines
  • Vaccines, Subunit

Grants and funding

The authors declare that this study received funding from the BRIDGE – Translational Excellence Programme (bridge.ku.dk) at the Faculty of Health and Medical Sciences, University of Copenhagen, funded by the Novo Nordisk Foundation. Grant agreement no. NNF20SA0064340. Sundhedsstyrelsen – sagsnummer 05-0400-18. Sundhedsstyrelsen – sagsnummer 05-0400-50, Det Frie Forskningsråd – sagsnummer 0134-00072B, Kræftens Bekæmpelse– sagsnummer R149-A10159. The funders were not involved in the study design, collection, analysis, interpretation of data, the writing of this article nor the decision to submit it for publication.