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Commentary Open Access | 10.1172/JCI156628
1Graduate Program in Immunology,
2Department of Surgery, and
3Department of Pathology, University of Michigan School of Medicine, Ann Arbor, Michigan, USA.
4Center of Excellence for Cancer Immunology and Immunotherapy, University of Michigan Rogel Cancer Center, Ann Arbor, Michigan, USA.
Address correspondence to: Weiping Zou, Departments of Surgery and Pathology, University of Michigan Medical School, 109 Zina Pitcher Place, Ann Arbor, Michigan 48109, USA. Phone: 734.763.6402; Email: wzou@med.umich.edu.
Find articles by Holcomb, E. in: JCI | PubMed | Google Scholar |
1Graduate Program in Immunology,
2Department of Surgery, and
3Department of Pathology, University of Michigan School of Medicine, Ann Arbor, Michigan, USA.
4Center of Excellence for Cancer Immunology and Immunotherapy, University of Michigan Rogel Cancer Center, Ann Arbor, Michigan, USA.
Address correspondence to: Weiping Zou, Departments of Surgery and Pathology, University of Michigan Medical School, 109 Zina Pitcher Place, Ann Arbor, Michigan 48109, USA. Phone: 734.763.6402; Email: wzou@med.umich.edu.
Find articles by Zou, W. in: JCI | PubMed | Google Scholar
Published February 1, 2022 - More info
PD-1 signaling on T cells is the major pathway that limits T cell immunity, but the efficacy of anti–PD-1 therapy has been limited to a small proportion of patients with advanced cancers. We fortuitously observed that anti–PD-1 therapy depends on IL-2 signaling, which raises the possibility that a lack of IL-2 limits anti–PD-1–induced effector T cell expansion. To selectively deliver IL-2 to PD-1+CD8+ tumor-infiltrating lymphocytes (TILs), we engineered a low-affinity IL-2 paired with anti–PD-1 (PD-1–laIL-2), which reduced affinity to peripheral Treg cells but enhanced avidity to PD-1+CD8+ TILs. PD-1–laIL-2 exerted better tumor control and lower toxicity than single or mixed treatments. Mechanistically, PD-1–laIL-2 could effectively expand dysfunctional and tumor-specific CD8+ T cells. Furthermore, we discovered that presumably dysfunctional PD-1+TIM3+ TILs are the dominant tumor-specific T cells responding to PD-1–laIL-2. Collectively, these results highlight that PD-1–laIL-2 can target and reactivate tumor-specific TILs for tumor regression as a unique strategy with stronger efficacy and lower toxicity.
Zhenhua Ren, Anli Zhang, Zhichen Sun, Yong Liang, Jianfeng Ye, Jian Qiao, Bo Li, Yang-Xin Fu
IL-2 is a pleiotropic cytokine. In this issue of the JCI, Ren et al. report on the development of a low-affinity IL-2 paired with anti–PD-1 (PD-1–laIL-2) that reactivates intratumoral CD8+ T cells, but not CD4+ Treg cells. PD-1–laIL-2 treatment synergized with anti–PD-L1 therapy to overcome tumor resistance to immune checkpoint blockade (ICB) in tumor-bearing mice. Rejection of rechallenged tumors following PD-1–laIL-2 therapy demonstrated the establishment of a potent T cell memory response. Furthermore, PD-1–laIL-2 therapy manifested no obvious toxicity. These findings suggest the potential of PD-1–laIL-2 therapy in treating patients with cancer.
IL-2 is produced primarily by activated CD4+ T cells and acts in a paracrine or autocrine fashion (1, 2). IL-2 receptor (IL-2R) signaling occurs through three subunits: alpha (CD25), beta (CD122), and gamma (CD132) (3). Intermediate-affinity dimeric IL-2 receptor consists of IL-2Rβ and IL-2Rγ on naive CD4+ and CD8+ T cells, memory T cells, and natural killer (NK) cells. TCR engagement or IL-2 stimulation induces the expression of IL-2Rα to form high-affinity trimeric IL-2 receptors that are highly expressed on Treg cells and recently activated effector T cells (4). IL-2 signaling has been an attractive immunotherapeutic target since IL-2 mediates effector T cell activation, including effector CD8+ T cells, which are vital for antitumor immunity. High-dose IL-2 was approved by the FDA in 1992 for treatment of certain types of cancer (5). However, IL-2 possesses a very short half-life and requires high doses to be effective, leading to toxicity and severe side effects, such as inflammation and vascular leak syndrome (6). Alternatively, low doses of IL-2 preferentially target IL-2Rα on Treg cells, restricting the immune response, and are associated with poor prognosis in patients with cancer (7, 8). Therefore, methods to target certain T cell subsets while reducing Treg cell binding have been a recent focus in the field of IL-2 therapy.
To effectively manipulate effector T cells and reduce side effects of high-dose IL-2, IL-2 variants have been developed to stimulate specific T cell subsets through selective targeting of certain IL-2R chains. One strategy has been to introduce mutations in IL-2 to create mutants with preferential IL-2R chain binding. Mutants with reduced IL-2Rβ binding have been shown to target high-affinity IL-2 receptor expressed on effector T cells (Figure 1). These mutants have also exhibited reduced toxicity, possibly due to decreased binding of intermediate-affinity receptors on NK cells that lack IL-2Rα (1, 9). STK-012, a partial IL-2 agonist produced by Synthekine, employs a similar strategy by selectively binding IL-2Rα and IL-2Rβ subunits, but not IL-2Rγ. Effector T cells that may be specific for tumor epitopes can thus expand and readily attack the tumor while avoiding NK cell stimulation (10). However, undesirable Treg cell expansion remains a concern due to high IL-2Rα expression on Treg cells (7, 8). To address this issue, IL-2 mutants with reduced binding to IL-2Rα have also been generated. The cytokine company Nektar has engineered an IL-2 mutant with a bias toward IL-2Rβ and IL-2Rγ, rather than IL-2Rα, to reduce Treg cell binding (10). H9, an IL-2 superkine (sumIL-2) with enhanced IL-2Rβ binding without the need for IL-2Rα, was shown to increase expansion of cytotoxic memory T cells and NK cells while decreasing that of Treg cells (11). Interestingly, H9T, an engineered H9-based partial agonist with further reduced binding to IL-2Rγ, was also recently shown to promote CD8+ T cell proliferation that maintained a stem-like memory state and mediated greater antitumor immunity (12).
Targeting IL-2 signaling for cancer therapy. High-dose IL-2 may preferentially target high-affinity IL-2R present on Treg cells and recently activated effector T cells. Recent strategies to target IL-2 signaling for cancer therapy include mutant IL-2 with affinity toward different IL-2R chains (alpha, or beta and gamma). Mutant IL-2 with affinity toward IL-2Rα is used to target Treg cells or recently activated effector T cells. Meanwhile, mutant IL-2 with affinity toward IL-2Rβ or IL-2Rγ subunits, rather than IL-2Rα, has been shown to target CD8+ memory T cells and NK cells with reduced binding to Treg cells. Combination of IL-2 therapy with various anti–IL-2 mAbs also differentially stimulates specific immune cell subsets. IL-2–based fusion proteins bound to antigen-specific antibodies (immunocytokines) allow for targeted delivery of IL-2 to cells/tissues expressing a protein of interest. PD-1–laIL-2, developed by Ren et al. (20), consists of low-affinity IL-2 (laIL-2) linked to an anti–PD-1 antibody. PD-1–laIL-2 selectively reactivates intratumoral PD-1+TIM-3+CD8+ T cells to enhance antitumor activity. In the future, additional IL-2–based fusion proteins may be engineered to target certain cells of interest in various disease contexts.
To enhance the activity of IL-2 in vivo and limit toxicity by reducing the necessary dose, IL-2 therapy has been combined with anti–IL-2 monoclonal antibodies (mAb). Interestingly, various anti–IL-2 mAbs differentially stimulate different immune cell subsets. Anti–mouse IL-2 mAbs S4B6 and JES6-5, as well as anti–human IL-2 mAb MAB602, complexed with recombinant IL-2, selectively stimulate memory CD8+ cells and NK cells in vivo to improve IL-2 cancer therapy (Figure 1) (13). On the other hand, anti–IL-2 mAb JES6-1 inhibits proliferation of CD8+ cells and NK cells yet maintains its ability to activate Treg cells and has been implicated as a potential treatment for autoimmune disease (14). Binding of these various mAbs to certain regions of IL-2, therefore blocking IL-2 binding to specific IL-2R chains, may explain these contrasting cell type affinities (1, 2).
IL-2–based fusion proteins are another IL-2 therapy strategy with a multitude of current preclinical and clinical trials (15, 16). Fusion of IL-2 to a fragment crystallizable (Fc) region has proven to be beneficial due to increased half-life, complement activation, and induction of antibody-dependent cellular cytotoxicity (ADCC) toward Treg cells (17–19). Furthermore, fusion of IL-2 to antigen-specific antibodies (termed an immunocytokine) allows for targeted delivery of IL-2 to cells and tissues expressing a protein of interest. Numerous IL-2 immunocytokines have been developed to target tumor-associated antigens expressed by cancer cells and their surrounding tissue (16). IL-2 is therefore honed to tumor tissues to enact its function. However, this strategy still lacks the ability to specifically target effector T cells within the tumor that are pertinent to anticancer immunity.
Ren et al. (20) addressed this intratumoral T cell targeting gap by engineering an immunocytokine fusion protein consisting of low-affinity IL-2 (laIL-2) linked to an anti–PD-1 antibody (PD-1–laIL-2). laIL-2 exhibits reduced binding to IL-2Rα and IL-2Rβ to diminish unfavorable Treg cell binding in the tumor and periphery. Meanwhile, PD-1 is highly expressed on tumor-infiltrating CD8+ T cells. As a result, PD-1–laIL-2 possessed elevated avidity toward intratumoral CD8+ T cells, rather than Treg cells or peripheral CD4+ and CD8+ T cells. This specificity not only reduced the systemic toxicity, but also enhanced tumor control in A20 and MC38 tumor models, as well as A375 tumor-bearing humanized mice. In addition, PD-1–laIL-2 in combination with anti–PD-L1 therapy overcame tumor resistance to PD-L1 blockade therapy. Notably, this effect was dependent on intratumoral CD8+ T cells, whose proliferation was selectively induced by PD-1–laIL-2. Further investigation revealed that PD-1–laIL-2 seemed to selectively target intratumoral PD-1+TIM-3+CD8+ T cells, which are usually described as a functionally exhausted and/or terminally differentiated T cell subset. Therefore, PD-1–laIL-2 could reactivate PD-1+TIM-3+CD8+ T cells to enhance antitumor activity (Figure 1). Tumor rechallenge resulted in spontaneous rejection in tumor-bearing mice previously treated with PD-1–laIL-2. This effect was also dependent on the presence of CD8+ T cells, indicating these rejuvenated T cells are tumor antigen-specific and can mediate a strong memory response. These promising results suggest that PD-1–laIL-2 therapy may bring clinical benefits to patients with cancer.
Conflict of interest: WZ serves as a scientific consultant or board member at NGM Biopharmaceuticals Inc., Roivant, NextCure, CStone, CrownBio, and Intergalactic Therapeutics.
Copyright: © 2022, Holcomb et al. This is an open access article published under the terms of the Creative Commons Attribution 4.0 International License.
Reference information: J Clin Invest. 2022;132(3):e156628. https://doi.org/10.1172/JCI156628.
See the related article at Selective delivery of low-affinity IL-2 to PD-1+ T cells rejuvenates antitumor immunity with reduced toxicity.