Weekly Digests
‹ Back to August

IL-2 therapy requires IL-Rα binding to stimulate tumor-specific immune responses

August 30, 2023

Recent advances in IL-2 treatment strategies have led to the development of IL-2Rβγ-biased approaches in which toxicity is expected to be lower. However, recent clinical research has shown disappointing results. Wu, Chia, et al. assessed the mode of action of various IL-2 constructs to help the future design of IL-2 treatments. Their results were recently published in Nature Cancer.

To investigate the mode of action of various forms of IL-2 treatment, the researchers tested human IL-2wt with IL-2 (which has IL-2Rα-disrupting mutations resulting in an IL-2Rβγ-biased IL-2 analog). In vitro, IL-2wt activated Tregs more efficiently than IL-2, while both versions had similar activity on resting CD8+ T, CD4+CD25- T, and NK cells (which all express IL-2Rβγ). However, in vivo, IL-2wt had stronger antitumor efficacy and resulted in lower body weight loss and fewer deaths than IL-2. This was surprising, as previous data suggested that IL-2wt would favor Tregs in the tumor microenvironment (TME), resulting in immunosuppression, and binding to IL-2Rα on endothelial cells would result in toxicity.

Treatment with IL-2 induced higher CD8+ T cell-to-Treg ratios than IL-2wt in both tumors and peripheral tissue. However, the increased numbers of CD8+ T cells did not result in better antitumor responses. As tumor-infiltrating lymphocytes (TIL) in the TME can be tumor antigen-specific effector T cells (TST) and tumor-irrelevant bystander T cells, there might be differences in the activation of TST and bystander cells by these different IL-2 constructs. IL-2wt was found to expand more CD39+CD8+ T cells or p15E-tetramer+CD8+ T cells in the TME, while IL-2 expanded CD39-PD-1- bystanders. TST cells expressed higher CD25 levels than bystander cells and were more likely to be activated by IL-2wt.

The researchers then performed single-cell RNA sequencing (scRNAseq) on immune cells isolated from tumors treated with the two constructs. Zooming in on the T cell populations, eight clusters could be observed. IL-2wt increased the number of activated CD8+ T cells and conventional CD4+ T cells, while IL-2expanded naive CD8+ T cells. Both treatments decreased the proportion of Tregs, but this was more strongly the case in the IL-2 group. Trajectory and gene expression analyses showed that IL-2wt stimulated the differentiation of CD8+ T cells into more activated, effector, and exhausted states, while IL-2 kept a less activated and naive T cell phenotype.

The researchers then created IL-2α-bias, in which IL-2-IL-2Rβ binding was interrupted. This construct could bind IL-2Rα and had activity on CD25-expressing T cells only. To test whether selective activation of CD25+CD8+ effector T cells was sufficient for antitumor activity, MC38 tumor-bearing mice were treated with IL-2α-bias. Treatment effectively inhibited tumor growth, and in B16F10-OVA tumors it increased the proportion of the OVA-tetramer+CD8+ TILs.

The researchers then assessed how treatment with IL-2α-bias affected Treg populations. In the peripheral blood, treatment increased the proportion of Tregs and downregulated the percentage of CD8+ T cells. However, in the tumor an opposite trend was observed, with an increase in the proportion of CD8+ T cells and decrease of Tregs, suggesting the effects of IL-2α-bias are context-dependent.

Given that expression of CD25 and PD-1 is regulated by TCR signaling, the researchers hypothesized that a population of tumor antigen-experienced CD8+ TILs coexpress CD25 and PD-1, and serve as the major antitumor immune cells. In CD8+ TIL from MC38 tumors, most cells expressing CD25 also expressed PD-1, while PD-1+CD25+CD8+ T cells were mostly absent in the spleen. In various tumor types, the percentage of PD-1+CD25+ cells among the total CD8+ TIL population varied. Tumors with relatively higher CD8+ T cell infiltration (MC38, B16F10, and CT26) responded better to IL-2α-bias treatment than those with lower TIL, and the percentage of PD-1+CD25+ and CD25+ cells among CD8+ TILs strongly correlated with antitumor activity in these models.

To assess whether the PD-1+CD25+CD8+ TIL subset also exists in human tumors, scRNAseq data of CD8+ T cells obtained from 14 tumor collections and matched normal tissue were compared. Coexpression of PD-1 and CD25 was detected in 0.2-5.2% of all CD8+ TIL across different tumor types and these cells were more prevalent in tumors than in healthy tissues.

To determine how anti-PD-1 treatment may affect IL-2 signaling, in vitro experiments were performed with human T cells. Anti-PD-1 treatment stimulated an increase in production of IL-2 by stimulated T cells, which was mainly coming from the PD-1+CD25+CD8+ population. Returning to mice, in MC38 tumors, treatment with anti-PD-1 stimulated IL-2 production in CD25+PD-1+ and CD25+PD-1-CD8+ T cell subsets.

To further examine how IL-2 affects response to anti-PD-1 treatment, Wu, Chia et al. reanalyzed biomarker and efficacy data from a clinical trial assessing the anti-PD-1 antibody sintilimab plus pemetrexed and platinum (chemo) in patients with non-squamous non-small cell lung carcinoma. In those treated with the combination, there was a strong positive correlation between the IL-2 pathway signature and tumor responses, with those with a higher signature having better responses and improved survival. These results were confirmed in another study with data from patients with melanoma treated with various anti-PD-1 antibodies. Therefore, the IL-2 signature may serve as a biomarker for therapy response in PD-1-targeting therapies.

To assess the effects of IL-2 signatures in tumors with T cells in exhausted states, the researchers developed mouse models with different exhaustion states. In mice with small, less exhausted tumors, anti-PD-1 resulted in tumor regression, while in large tumors with fixed dysfunctional states, the effects were limited. Bulk RNAseq showed that small tumors had higher IL-2 pathway activation, IFNγ response, and CD8+TCR activation signatures than large tumors. In both TIL-exhausted MC38 and TIL-excluded EMT6 large tumor models, IL-2α-bias had a synergistic effect when combined with anti-PD-1, resulting in eradication of most tumors, long-term survival, and protection against tumor rechallenge.

This study suggests that IL-2 targeting CD25 can specifically activate tumor-reactive T cells instead of increasing the number of bystander T cells in the tumor, and that treatment may work synergistically with anti-PD-1 treatment. Therefore, these data can inform the development of more effective IL-2 therapies.

Written by Maartje Wouters, image by Lauren Hitchings.


Wu W, Chia T, Lu J, Li X, Guan J, Li Y, Fu F, Zhou S, Feng Y, Deng J, Zou J, Sun J, Yao Y, Ling X, Wu Z, Zhang Y, Xu J, Wang F, Liang X, Wu M, Liu H, Chen B, He K. IL-2Rα-biased agonist enhances antitumor immunity by invigorating tumor-infiltrating CD25+CD8+ T cells. Nat Cancer. 2023 Aug 7. 

In the Spotlight...

Tumor immunogenicity dictates reliance on TCF1 in CD8+ T cells for response to immunotherapy

Escobar et al. showed that tumor immunogenicity determines the reliance of tumor antigen-specific CD8+ T cells on TCF1 expression for ICB response. TCF1 was dispensable for T cell priming and therapy response in highly immunogenic tumors, but was essential for optimal priming of CD8+ T cells and ICB response in poorly immunogenic tumors that accumulate TOX+ dysfunctional T cells. Loss of TCF1 destabilized the dysfunctional intratumoral CD8+ T cells that shared features with CD8+ T cells in ICB non-responder patients. In poorly immunogenic tumors, therapeutic vaccination or increase in antigen presentation overcame TCF1 dependency for ICB response.

Contributed by Shishir Pant

A major role for CD4+ T cells in driving cytokine release syndrome during CAR T cell therapy

Using an immunocompetent mouse model of aggressive B cell lymphoma, Boulch et al. showed that IV injection of anti-CD19 CD4+, but not CD8+, CAR T cells alone induced cytokine release syndrome (CRS)-like effects on body temperature, weight, and serum cytokine and chemokine levels. In patients with diffuse large B-cell lymphoma treated with anti-CD19 CAR T cells, those who experienced CRS had a higher proportion of CD4+ CAR T cells in the blood. Using an IFNγ knockout murine model and a model with variable tumor burden, it was shown that CD4+ CAR T cell-induced CRS was dependent on a high tumor burden, but not IFNγ production.

Contributed by Maartje Wouters

Everything New this Week In...

Close Modal

Small change for you. Big change for us!

This Thanksgiving season, show your support for cancer research by donating your change.

In less than a minute, link your credit card with our partner RoundUp App.

Every purchase you make with that card will be rounded up and the change will be donated to ACIR.

All transactions are securely made through Stripe.