PD-1 or CTLA-4 blockade promotes CD86-driven Treg responses upon radiotherapy of lymphocyte-depleted cancer in mice
Elselien Frijlink, … , Inge Verbrugge, Jannie Borst
Elselien Frijlink, … , Inge Verbrugge, Jannie Borst
Published February 13, 2024
Citation Information: J Clin Invest. 2024;134(6):e171154. https://doi.org/10.1172/JCI171154.
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Research Article Immunology Oncology

PD-1 or CTLA-4 blockade promotes CD86-driven Treg responses upon radiotherapy of lymphocyte-depleted cancer in mice

Abstract

Radiotherapy (RT) is considered immunogenic, but clinical data demonstrating RT-induced T cell priming are scarce. Here, we show in a mouse tumor model representative of human lymphocyte–depleted cancer that RT enhanced spontaneous priming of thymus-derived (FOXP3+Helios+) Tregs by the tumor. These Tregs acquired an effector phenotype, populated the tumor, and impeded tumor control by a simultaneous, RT-induced CD8+ cytotoxic T cell (CTL) response. Combination of RT with CTLA-4 or PD-1 blockade, which enables CD28 costimulation, further increased this Treg response and failed to improve tumor control. We discovered that upon RT, the CD28 ligands CD86 and CD80 differentially affected the Treg response. CD86, but not CD80, blockade prevented the effector Treg response, enriched the tumor-draining lymph node migratory conventional DCs that were positive for PD-L1 and CD80 (PD-L1+CD80+), and promoted CTL priming. Blockade of CD86 alone or in combination with PD-1 enhanced intratumoral CTL accumulation, and the combination significantly increased RT-induced tumor regression and OS. We advise that combining RT with PD-1 and/or CTLA-4 blockade may be counterproductive in lymphocyte-depleted cancers, since these interventions drive Treg responses in this context. However, combining RT with CD86 blockade may promote the control of such tumors by enabling a CTL response.

Authors

Elselien Frijlink, Douwe M.T. Bosma, Julia Busselaar, Thomas W. Battaglia, Mo D. Staal, Inge Verbrugge, Jannie Borst

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Figure 7

CD86-mediated CD28 costimulation is required for PD-1–dependent eTreg expansion.

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CD86-mediated CD28 costimulation is required for PD-1–dependent eTreg ex...
(A) PD-1 expression on Ki67+CD8+ T cells (green) and eTregs (red) in the tumor as identified in Figure 5A, presented as a heatmap and a representative histogram across all experimental conditions. (B–D) TC-1 tumor–bearing mice received 0 Gy (n = 4) or 20 Gy RT on day 0 with vehicle (PBS, n = 8) or blocking mAbs against PD-1 (n = 11), CD86 (n = 10), or their combination (n = 10) on days 0, 3, and 6. CD3+ lymphocyte responses were analyzed by flow cytometry in non-TdLNs, TdLNs, and tumor on day 8. (B) UMAP visualization of the treatment response of the CD3+ T cell subpopulations. The red circle indicates eTregs, and the green circle indicates Ki67+CD8+ T cells (see also Supplemental Figure 8, B and C). (C) Frequencies of eTregs and cTregs identified in Supplemental Figure 8B among CD3+ T cells in the indicated tissues. (D) Quantification of the Ki67+CD8+ T cell population among total CD3+ T cells in the TdLN and tumor. (E) Individual tumor growth curves and (F) OS of TC-1 tumor–bearing mice receiving RT on day 0 with vehicle (n = 27), blocking mAbs against PD-1 (n = 26), CD86 (n = 26), or a combination (n = 28) on days 0, 3, and 6. Proportion of mice that fully recovered is indicated. (G) Proposed effect of combined CD86 and PD-1 blockade on Tregs. (i) PD-L1/L2 on cDCs engages PD-1, which inhibits CD28 costimulation of Tregs. (ii) PD-1 blockade enables CD28 costimulation of Tregs. (iii) CD86 blockade inhibits CD28 costimulation of Tregs, which cannot be overruled by PD-1 blockade, impeding the Treg response. Data are from 1 experiment and are representative of 2 experiments. Error bars indicate the SD. *P < 0.05, **P < 0.01, and ***P < 0.001, by ordinary 1-way ANOVA with Dunnett’s post hoc test (C), Brown-Forsythe ANOVA with Dunnett’s T3 post hoc analysis (D), and Mantel-Cox analysis (F).