203P - Targeting IL-33 reprograms tumor microenvironment and potentiates antitumor response to anti-PD-L1 immunotherapy

Background

The immunosuppressive tumor microenvironment (TME) appears to be the main challenge against cancer patients receiving benefits from PD-1/PD-L1-targeting immune checkpoint inhibitors (ICIs), and IL-33/ST2 signaling pathway fulfills critical roles in the TME. However, it remains uncertain whether IL-33 limits the therapeutic efficacy of anti-PD-L1 treatment.

Methods

Cellular and molecular mechanisms of the IL-33/ST2 on anti-PD-L1 treatment in lung cancer were assessed using RNA-seq, scRNA-seq, IB, and IF. A sST2-Fc fusion protein was constructed to target IL-33 and combined with an anti-PD-L1 antibody atezolizumab in lung tumor models. Based on this, bifunctional fusion proteins were generated to block IL-33 in tumors specifically targeting PD-L1. The underlying mechanisms of dual targeting of IL-33 and PD-L1 were revealed using RNA-seq, scRNA-seq, FACS, and IF.

Results

After anti-PD-L1 administration, tumor-infiltrating ST2⁺ regulatory T cells (Tregs) were elevated. Blocking IL-33/ST2 signaling with sST2-Fc fusion protein potentiated the antitumor efficacy of the PD-L1 antibody by boosting CD8⁺ T cell responses. Bifunctional fusion protein anti-PD-L1-sST2 demonstrated superior antitumor efficacy compared to combination therapy, not only inhibited tumor progression and extended survival, but also provided long-term protective antitumor immunity. Mechanistically, the superior antitumor activity of targeting both IL-33 and PD-L1 was due to a reduction in immunosuppressive factors, such as Tregs and exhausted CD8+ T cells, while increasing tumor-infiltrating cytotoxic T lymphocytes.

Conclusions

This study demonstrated that IL-33/ST2 is involved in the immunosuppression mechanism of PD-L1 antibody therapy. Blockade by sST2-Fc or anti-PD-L1-sST2 could remodel the inflammatory TME and induce a potent antitumor effect. These findings highlight the potential therapeutic strategies for tumor treatment by simultaneously targeting IL-33 and PD-L1.

Legal entity responsible for the study

Fudan University.

Funding

National Natural Science Foundation of China.

Disclosure

The author has declared no conflicts of interest.