A low-dose immunotherapy targeting Fc gamma Receptors and heparan sulfate proteoglycan to impact myeloid cells and control cancers with diverse immunosuppressive profiles

Nora Kakwata-Nkor Deluce, Elodie Creton, Alexandra Savatier, Honorine Lucchi, Laureen Bardouillet, Oscar Pereira Ramos, Philippe Berthon, Michel Léonetti

Myeloid cells play a key role in cancer-associated immunosuppression because their accumulation and reprogramming inhibit antitumor responses and support tumor growth. To modulate their activity, we targeted Fcγ receptors (FcγRs), which are broadly expressed in myeloid subsets. Since low-affinity Fcγ receptor IIb (FcγRIIb) mediates inhibitory signaling, we designed an immunotherapy active at a low dose to limit binding to FcγRIIb while retaining interaction with higher-affinity FcγRs. We engineered an Fc-based fusion protein, whose activity is potentiated by its ability to engage both FcγRs and a coreceptor, Heparan Sulfate Proteoglycan (HSPGs). This immunotherapy, named Fc-T54, combines an HSPG-ligand, named T54, with human IgG1-Fc. Compared with Fc, Fc-T54 displayed superior binding to Fcγ receptor IIa (FcγRIIa), Fcγ receptor IIIa (FcγRIIIa) and enhanced interactions with human leukocytes, including neutrophils, B-lymphocytes, as well as with monocytes, and dendritic cells (DCs) within peripheral blood mononuclear cells. Functionally, Fc-T54 increased monocyte/macrophage and B-cell numbers, reduced neutrophil abundance, and boosted DC activation in both the human and murine systems. Subcutaneous administration of low-dose Fc-T54 - or its murine surrogate - inhibits tumor growth in immune-deserted and immune-excluded mouse models and synergizes with anti-PD-1 therapy in an immune-inflamed model. Tumor microenvironment analysis in the bladder cancer model revealed that the immunotherapy decreased the proportion of granulocytic myeloid-derived suppressor cells while increasing CD8+ T cells and natural killer cells, promoting a microenvironment more prone to tumor control. This FcγR/HSPG-engaging immunotherapy, administered subcutaneously, offers a novel approach to modulate the myeloid compartment and improve outcomes for ICI-resistant, deserted/excluded tumors, and for inflamed tumors when used in combination regimens.