Differential control of human Treg and effector T cells in tumor immunity by Fc-engineered anti–CTLA-4 antibody

Abstract

Anti–CTLA-4 mAb is efficacious in enhancing tumor immunity in humans. CTLA-4 is expressed by conventional T cells upon activation and by naturally occurring FOXP3+CD4+ Treg cells constitutively, raising a question of how anti–CTLA-4 mAb can differentially control these functionally opposing T cell populations in tumor immunity. Here we show that FOXP3high potently suppressive effector Treg cells were abundant in melanoma tissues, expressing CTLA-4 at higher levels than tumor-infiltrating CD8+ T cells. Upon in vitro tumor-antigen stimulation of peripheral blood mononuclear cells from healthy individuals or melanoma patients, Fc-region–modified anti–CTLA-4 mAb with high antibody-dependent cell-mediated cytotoxicity (ADCC) and cellular phagocytosis (ADCP) activity selectively depleted CTLA-4+FOXP3+ Treg cells and consequently expanded tumor-antigen–specific CD8+T cells. Importantly, the expansion occurred only when antigen stimulation was delayed several days from the antibody treatment to spare CTLA-4+ activated effector CD8+T cells from mAb-mediated killing. Similarly, in tumor-bearing mice, high-ADCC/ADCP anti–CTLA-4 mAb treatment with delayed tumor-antigen vaccination significantly prolonged their survival and markedly elevated cytokine production by tumor-infiltrating CD8+ T cells, whereas antibody treatment concurrent with vaccination did not. Anti–CTLA-4 mAb modified to exhibit a lesser or no Fc-binding activity failed to show such timing-dependent in vitro and in vivo immune enhancement. Thus, high ADCC anti–CTLA-4 mAb is able to selectively deplete effector Treg cells and evoke tumor immunity depending on the CTLA-4–expressing status of effector CD8+ T cells. These findings are instrumental in designing cancer immunotherapy with mAbs targeting the molecules commonly expressed by FOXP3+ Treg cells and tumor-reactive effector T cells.

Targeting Treg cells in cancer immunotherapy

“…II subset) with higher levels of activation markers and FOXP3 expression than eTreg (Fr. II) cells in the blood, suggesting their contribution to poor prognosis in cancer patients (Fig. ).…”

“…Despite these promising results in experimental animals, there are several issues to consider in actual application of Treg‐cell depletion for cancer immunotherapy. For instance, both Treg and activated effector T cells share the expression of the same species of cell surface molecules, including CD25 and CTLA‐4, making it difficult to selectively deplete Treg cells without affecting effector T cells by antibodies specific for these molecules . In addition, systemic removal of Treg cells may evoke and enhance not only tumor immunity, but also autoimmunity because of their indispensable role in preventing autoimmunity.…”

“…Therefore, it is critical to understand how tumor‐infiltrating Treg cells can be specifically depleted to enhance tumor immunity while tumor‐reactive effector T cells and peripheral Treg cells (i.e., lymphoid, tissue‐resident or circulating Treg cells) be preserved to prevent autoimmunity. Recent studies have addressed this issue and shown that differential control of tumor Treg versus effector T cells or peripheral Treg cells can be achieved by selecting specific target molecules (e.g., CTLA‐4) for antibody‐mediated depletion of tumor Treg cells by considering the differences in the kinetics and the level of such Treg‐targeting molecules expression by tumor Treg cells, effector T cells, and peripheral Treg cells, and by devising the ways of Treg cell depletion via systemic or local treatment with Treg‐depleting antibody , as discussed below.…”

“…For antibody‐mediated killing of tumor Treg cells, surface molecules that are expressed on tumor Treg cells specifically or at much higher levels than other T cells are good targets. These markers include aforementioned T‐cell accessory molecules; e.g., CD25, CTLA‐4, GITR, 4‐1BB, OX‐40, LAG3, TIGIT, CCR4, and CCR8 . For example, CTLA‐4 is constitutively expressed on naïve Treg cells but its expression is higher in eTreg cells and further upregulated in tumor Treg cells, which exhibit the highest CTLA‐4 level among any tumor‐infiltrating or peripheral T cells, for example, in melanoma patients (Fig.…”

“…An anti‐CTLA‐4 mAb, which was initially considered to block CTLA‐4‐mediated negative signal into effector T cells, is able to deplete Treg cells in tumor tissues in mice by antibody dependent cell‐mediated cytotoxicity (ADCC), and thereby enhance tumor immunity . Another recent study has addressed the issue by generating anti‐CTLA‐4 mAbs that have the same epitope specificity as ipilimumab and is Fc‐engineered to possess an enhanced ADCC activity (ART‐Fc; about 1000 times higher affinity than IgG1 for the activatory FcγRIIIa) or modified to exhibit a much less or no ADCC activity (Silent‐Fc) . The ADCC‐enhanced mAb effectively augmented anti‐tumor immune responses in vitro in humans and in vivo in mice by depleting CTLA‐4‐expressing Treg cells, while mAb with much less or no ADCC activity failed to show the augmentation.…”