Therapeutic depletion of CCR8<sup>+</sup> tumor-infiltrating regulatory T cells elicits antitumor immunity and synergizes with anti-PD-1 therapy
Helena Van Damme, Bruno Dombrecht, Máté Kiss, Heleen Roose, Elizabeth Allen, Eva Van Overmeire, Daliya Kancheva, Liesbet Martens, Aleksandar Murgaski, Pauline M. R. Bardet, Gillian Blancke, Maude Jans, Evangelia Bolli, Maria Solange Martins, Yvon Elkrim, James Dooley, Louis Boon, Julia Katharina Schwarze, Frank Tacke, Kiavash Movahedi, Niels Vandamme, Bart Neyns, Sebahat Ocak, Isabelle Scheyltjens, Lars Vereecke, Frank Aboubakar Nana, Pascal Merchiers, Damya Laoui, Jo A. Van Ginderachter
Abstract
BACKGROUND: Modulation and depletion strategies of regulatory T cells (Tregs) constitute valid approaches in antitumor immunotherapy but suffer from severe adverse effects due to their lack of selectivity for the tumor-infiltrating (ti-)Treg population, indicating the need for a ti-Treg specific biomarker. METHODS: We employed single-cell RNA-sequencing in a mouse model of non-small cell lung carcinoma (NSCLC) to obtain a comprehensive overview of the tumor-infiltrating T-cell compartment, with a focus on ti-Treg subpopulations. These findings were validated by flow cytometric analysis of both mouse (LLC-OVA, MC38 and B16-OVA) and human (NSCLC and melanoma) tumor samples. We generated two CCR8-specific nanobodies (Nbs) that recognize distinct epitopes on the CCR8 extracellular domain. These Nbs were formulated as tetravalent Nb-Fc fusion proteins for optimal CCR8 binding and blocking, containing either an antibody-dependent cell-mediated cytotoxicity (ADCC)-deficient or an ADCC-prone Fc region. The therapeutic use of these Nb-Fc fusion proteins was evaluated, either as monotherapy or as combination therapy with anti-programmed cell death protein-1 (anti-PD-1), in both the LLC-OVA and MC38 mouse models. RESULTS: T cells, but the CCR8 protein was only prominent on the highly activated and strongly T-cell suppressive ti-Treg subpopulation of mouse and human tumors, with no major CCR8-positivity found on peripheral Tregs. CCR8 expression resulted from TCR-mediated Treg triggering in an NF-κB-dependent fashion, but was not essential for the recruitment, activation nor suppressive capacity of these cells. While treatment of tumor-bearing mice with a blocking ADCC-deficient Nb-Fc did not influence tumor growth, ADCC-prone Nb-Fc elicited antitumor immunity and reduced tumor growth in synergy with anti-PD-1 therapy. Importantly, ADCC-prone Nb-Fc specifically depleted ti-Tregs in a natural killer (NK) cell-dependent fashion without affecting peripheral Tregs. CONCLUSIONS: Collectively, our findings highlight the efficacy and safety of targeting CCR8 for the depletion of tumor-promoting ti-Tregs in combination with anti-PD-1 therapy.