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 4

CTLA-4 blockade exacerbates RT-induced eTreg expansion.

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CTLA-4 blockade exacerbates RT-induced eTreg expansion. Mice bearing 20 ...
Mice bearing 20 mm2 TC-1 tumors received RT (20 Gy, n = 9) or control (0 Gy, n = 6) on day 0. Treatment included vehicle (PBS) or a CTLA-4–blocking mAb on days 0, 3, 6, and 9, with longitudinal monitoring (A and B) and flow cytometric analysis of the non-TdLN, TdLN, and tumor on post-treatment day 8 (C–G). (A) Individual tumor growth curves and (B) OS for the treatment groups. Ratios indicate the number of mice that showed full recovery upon treatment compared with the total. (C) Percentage of total Tregs among CD3+ lymphocytes in the indicated tissues on day 8. (D–F) UMAP display of 2,500 randomly selected CD3+ T cells per sample in non-TdLN, TdLN, and tumor on day 8 for all treatment groups combined, with FlowSOM-guided clustering (see also Supplemental Figure 2B) (D) and marker visualization (E) used to highlight the eTreg response. (F) UMAP visualization of the response of the CD3+ T cell subpopulations in the TdLN and tumor to the indicated treatments. Red circles highlight the eTreg population. (G) Frequencies of eTregs and cTregs identified in D among CD3+ T cells found in the indicated tissues on post-treatment day 8. (H) TC-1 tumor–bearing mice received 20 Gy (n = 10/group) or control (0 Gy, n = 4–6), with CTLA-4 mAb blockade or vehicle on days 0, 3, and 6, with or without FTY720. Treg frequencies were measured in the TdLN and tumor on post-RT day 8 (same experiment as in Figure 3G). (I) Visual representation of how Tregs benefit from CTLA-4 blockade. Data are from 1 experiment and are representative of 2 experiments. Error bars indicate the SD. *P < 0.05, **P < 0.01, ***P < 0.001, and ****P < 0.0001, by Kruskal-Wallis with Dunn’s post hoc test (C and G) and 2-way ANOVA with Tukey’s multiple-comparison test (H).