Preprint Club
A cross-institutional Journal Club Initiative

Keywords

• CAR T cell

• Tumour escape

• Antigen spreading

Main Findings

Loss of the targeted antigen is a major obstacle to the success of therapy with chimeric antigen receptor (CAR) T cells, particularly for solid tumours. Antigen spreading (expansion of the immune response to secondary epitopes) to prime endogenous T cells against non-CAR-targeted tumour antigens could overcome this limitation and ensure long-lasting effects of CAR T cell therapies. However, the mechanism of antigen spreading in CAR T cell therapy remains poorly understood.

In 2019, Ma et al. (1) reported a vaccine-boosted CAR T cell approach that made use of a phospholipid polymer attached to the target antigen of the CAR (amph-ligand) in a tumour model. When injected, this amph-ligand integrates into the membrane of dendritic cells (DCs) in lymph nodes and promotes DC interactions with CAR T cells, resulting in improved anti-tumoral effect.

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In this preprint (not peer-reviewed), the authors examined the mechanism of antigen spreading induced by the amph-ligand vaccine-boosted CAR T cell therapy. They report that this approach markedly elicits priming of endogenous CD4+and CD8+Tcells against tumour antigens, resulting in the eradication of and long-term complete response in heterogeneous glioblastoma and melanoma tumours (presenting both CAR-targeted and non-targeted antigens). The authors observed phenotypical changes in tumour-infiltrating endogenous T cells in vaccine-boosted mice compared with mice treated with CAR T cells alone, including increased production of IFNγ,TNF, granzyme B and CCL3, CCL4 and CCL5 chemokines in CD8+T cells and increased transcripts associated with a TH1-type response in CD4+ T cells. These changes correlated with increased proliferation and effector functions of vaccine-boosted CAR T cells, and their upregulation of major metabolic pathways leading to the increased production of IFNγ and TNF as previously observed. Whereas blocking TNF had limited effect, the authors found that blocking IFNγ or knockout of its receptor IFNGR1 on vaccine-boosted CAR T cells abrogated the observed antigen spreading. Overexpressing IFNγ in CAR T cells recapitulated the vaccine-boosted CAR T cell-associated antigen spreading and anti-tumoral effect.

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In addition to its autocrine effect on CAR T cells, the authors found that secreted IFNγ increased the expression of CCL3–CCL5 in the tumour microenvironment, resulting in an increase in DC recruitment and antigen uptake. Furthermore, knockout of the IL-12 receptor on CAR T cells ablated the antigen spreading induced by vaccine-boosting and inhibited the anti-tumoral effects. Together, the results suggest that the CAR T cell phenotype observed after vaccine-boosting is dependent on DC-derived IL-12.

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Limitations​

• The effect of IFNg secreted by CAR T cells on antigen presentation by the tumour cells is not addressed, albeit being an essential element for antigen spreading to convert into tumour regression. In recently published paper by Sanchez-Paulete et al. (2), the authors indeed observed that IFNg secreted by CAR T cells mediates tumour immuno-editing, associated with upregulated MHC I on tumour cells and the clonal expansion of T cell specific to tumour antigens.

• The role of macrophage in the TME, and the potential change in their phenotype induced by the vaccine-boosting CAR T therapy, could be explored.

• The contribution (or feedback loop) of endogenous T cell phenotype shifts in the antigen spreading mechanism could be further clarified.

• The study is very rich in findings and the authors could perhaps have concentrated on deep diving on fewer items. For instance, they could focus less on the metabolism shift, and more on the interplay between cytokines released by the broad array of cells impacted by the IFNg secreted by the CAR T.

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Significance/Novelty

This study provides a novel perspective of antigen spreading mechanisms in the context of CAR T cell therapy, in particular the central role of the interplay between CAR T secreted IFN-γ and DC derived IL-12. These cytokines lead to phenotypical changes in endogenous T cells and enhanced DC priming, which in turn enables a longer-lasting response with CAR T cell therapy for heterogenous solid tumors. This work lays the foundation for future strategies to enhance CAR T cell therapy and overcome the challenges associated with antigen heterogeneity or loss as a tumour-resistance mechanism.

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References​

(1) Ma, L. et al. Enhanced CAR-T cell activity against solid tumors by vaccine boosting through the chimeric receptor. Science 365, 162-168 (2019)

(2) Sanchez-Paulete, A. et al. Targeting Macrophages with CAR T cell Delays Solid Tumor Progression and Enhances Antitumor Immunity. Cancer Immunology Research https://doi.org/10.1158/2326-6066.CIR-21-1075 (2022)

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Credit

Reviewed by Jaime Mateus-Tique as part of the cross-institutional journal club of the Immunology Institute of the Icahn School of Medicine, Mount Sinai (U.S.A.) and the Kennedy Institute of Rheumatology, University of Oxford.