Abstract 3239: Selective depletion of regulatory T cells by ALD2510, a novel IL-2-sparing anti-CD25 antibody, synergizes with PD-1 blockade in breast and gynecologic cancers
Authors: FATTORI Stéphane , Roy Aude Le , Houacine Jemila , Robert Lucie , Abes Riad , Gorvel Laurent , Granjeaud Samuel , Rouvière Marie-Sarah , Amara Amira Ben , Boucherit Nicolas , Tarpin Carole , Pakradouni Jihane , Charafe-Jauffret Emmanuelle , Barrou Julien , Houvenaeghel Gilles , Lambaudie Eric , Bertucci François , Rochigneux Philippe , Gonçalves Anthony , Foussat Arnaud , Chrétien Anne-Sophie , Olive Daniel 
Published: April 2023

Abstract
Background: PD-1 blockade (αPD-1) has shown limited efficacy in breast & gynecologic cancers. In other types of solid tumor, regulatory T cells (Tregs) harbouring markers of highly suppressive effector Tregs (eTregs) correlates with poor responses to PD-1 blockade, prompting combination therapy based on eTregs depletion. Yet, subsets of Tregs remain to be determined in breast & gynecologic cancers, in order to: (i) evaluate the role of eTregs in resistances to PD-1 blockade, (ii) identify the most selective target for eTregs depletion tailored to tumors context and combination strategy.
Methods: We collected public single-cell RNA/TCR-sequencing data from primary tumors and metastases of Triple-Negative Breast Cancer patients (TNBC, N = 28) biopsied before and after αPD-1 (pembrolizumab). Microarray data from primary TNBC (N = 124) biopsied before and after αPD-1 were quired for association with clinical responses. Deep phenotyping of Tregs from normal breast tissues (N = 4) and primary breast tumors (N = 8) or gynecologic tumors (N = 17) was performed by mass cytometry. ALD2510 (αCD25NIB, Alderaan Biotechnology) is a novel non-IL-2 blocking Fc-optimized anti-CD25 mAb (1). αPD-1 and αCD25NIB combination was evaluated using: (i) a humanized αCD25NIB in CD34+ humanized NSG mice grafted with human TNBC cell lines, (ii) a murine surrogate of αCD25NIB in a syngeneic TNBC mouse model.
Results: CD25high Tregs were accumulating in breast & gynecologic tumor tissues. In TNBC patients treated with αPD-1, fractions of CD25high Tregs were further increased. CD25high Tregs highly expressed eTregs-related molecules in primary tumors, invaded tumor-draining lymph nodes and distant metastases. Amongst the potential therapeutic targets for Treg depletion, only CD25, 4-1BB and CCR8 were largely restricted to intratumoral CD25high eTregs. Yet, CD25 was the best candidate for CD25high eTregs depletion with limited on-target off-Treg effects, as: (i) CCR8 marked a small fractions of CD25high eTregs in primary tumors and was not detected in metastasis, (ii) 4-1BB marked antigen-experienced αβCD8 T cell revigorated by PD-1 blockade, (iii) only CD25high eTregs expressed 4-1BB and CCR8, yet TCR clonotype analysis revealed that CD25high eTregs originate in part from activated CD25+ Tregs, suggesting that anti-CCR8/-4-1BB mAbs may be ineffective due to CD25high eTregs replenishment in tumors. In murine models resistant to αPD-1 alone, αCD25NIB effectively depleted intratumoral CD25high eTregs, with limited effects on peripheral Tregs, and synergized with αPD-1 by restoring a positive effector αβCD8 T cells/Tregs ratio, leading to tumor clearance without adverse effects.
Conclusions: This study supports clinical evaluation of CD25high effector Tregs depletion by ALD2510 in patients with breast or gynecologic cancers resistant to PD-1 blockade.
Citation Format: Stéphane FATTORI, Aude Le Roy, Jemila Houacine, Lucie Robert, Riad Abes, Laurent Gorvel, Samuel Granjeaud, Marie-Sarah Rouvière, Amira Ben Amara, Nicolas Boucherit, Carole Tarpin, Jihane Pakradouni, Emmanuelle Charafe-Jauffret, Julien Barrou, Gilles Houvenaeghel, Eric Lambaudie, François Bertucci, Philippe Rochigneux, Anthony Gonçalves, Arnaud Foussat, Anne-Sophie Chrétien, Daniel Olive. Selective depletion of regulatory T cells by ALD2510, a novel IL-2-sparing anti-CD25 antibody, synergizes with PD-1 blockade in breast and gynecologic cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3239.