FcγRIIB is an immune checkpoint limiting the activity of Treg-targeting antibodies in the tumor microenvironment.
Publication Title
Cancer Immunol Res
Document Type
Article
Publication Date
12-26-2023
Keywords
oregon; portland; chiles
Abstract
Preclinical murine data indicate that Fc-dependent depletion of intratumoral regulatory T cells (Tregs) is a major mechanism of action of anti-CTLA-4. However, the two main antibodies administered to patients (Ipilimumab and Tremelimumab) do not recapitulate these effects. Here, we investigate the underlying mechanisms responsible for the limited Treg depletion observed with these therapies. Using an immunocompetent murine model humanized for CTLA-4 and Fc? receptors (Fc?Rs), we show that Ipilimumab and Tremelimumab exhibit limited Treg depletion in tumors. Immune profiling of the tumor microenvironment (TME) in both humanized mice and humans revealed high expression of the inhibitory Fc receptor, Fc?RIIB, which limits antibody-dependent cellular cytotoxicity/phagocytosis (ADCC/ADCP). Blocking Fc?RIIB in humanized mice rescued the Treg-depleting capacity and antitumor activity of Ipilimumab. Furthermore, Fc engineering of antibodies targeting Treg-associated targets (CTLA-4 or CCR8) to minimize Fc?RIIB binding significantly enhanced Treg depletion, resulting in increased antitumor activity across various tumor models. Our results define the inhibitory Fc?RIIB as an immune checkpoint limiting antibody-mediated Treg depletion in the TME, and demonstrate Fc engineering as an effective strategy to overcome this limitation and improve the efficacy of Treg-targeting antibodies.
Clinical Institute
Cancer
Specialty/Research Institute
Oncology
DOI
10.1158/2326-6066.CIR-23-0389
