AUTHOR=Holmström Morten Orebo , Andersen Morten , Traynor Sofie , Ahmad Shamaila Munir , Lisle Thomas Landkildehus , Handlos Grauslund Jacob , Skov Vibe , Kjær Lasse , Ottesen Johnny T. , Gjerstorff Morten Frier , Hasselbalch Hans Carl , Andersen Mads Hald 

TITLE=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

JOURNAL=Frontiers in Immunology

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2023.1240678

DOI=10.3389/fimmu.2023.1240678

ISSN=1664-3224

ABSTRACT=<sec><title>Background</title><p>Therapeutic cancer vaccination against mutant calreticulin (<italic>CALR</italic>) in patients with <italic>CALR</italic>-mutant (<italic>CALR</italic>mut) 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.</p></sec><sec><title>Aim</title><p>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.</p></sec><sec><title>Methods</title><p>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. <italic>In silico</italic> calculations were performed to calculate the ratio between transformed cells and effector cells in patients with <italic>CALR</italic>mut MPN.</p></sec><sec><title>Results</title><p>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 <italic>CALR</italic>mut cells. <italic>In silico</italic> analyses demonstrate a high imbalance in the fraction of <italic>CALR</italic>mut cells and CALRmut specific effector T-cells in peripheral blood.</p></sec><sec><title>Conclusion</title><p>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 <italic>CALR</italic>mut cells. <italic>In silico</italic> 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.</p></sec>