Anti-CD137 monoclonal antibodies and adoptive T cell therapy: a perfect marriage?

CD137 (4-1BB)-Based Cancer Immunotherapy on Its 25th Anniversary

Twenty-five years ago, we reported that agonist anti-CD137 monoclonal antibodies eradicated transplanted mouse tumors because of enhanced CD8+ T-cell antitumor immunity. Mouse models indicated that anti-CD137 agonist antibodies synergized with various other therapies. In the clinic, the agonist antibody urelumab showed evidence for single-agent activity against melanoma and non-Hodgkin lymphoma but caused severe liver inflammation in a fraction of the patients. CD137's signaling domain is included in approved chimeric antigen receptors conferring persistence and efficacy. A new wave of CD137 agonists targeting tumors, mainly based on bispecific constructs, are in early-phase trials and are showing promising safety and clinical activity.

SIGNIFICANCE

CD137 (4-1BB) is a costimulatory receptor of T and natural killer lymphocytes whose activity can be exploited in cancer immunotherapy strategies as discovered 25 years ago. Following initial attempts that met unacceptable toxicity, new waves of constructs acting agonistically on CD137 are being developed in patients, offering signs of clinical and pharmacodynamic activity with tolerable safety profiles.

Antitumor efficacy and reduced toxicity using an anti-CD137 Probody therapeutic

Costimulation via CD137 (4-1BB) enhances antitumor immunity mediated by cytotoxic T lymphocytes. Anti-CD137 agonist antibodies elicit mild liver inflammation in mice, and the maximum tolerated dose of Urelumab, an anti-human CD137 agonist monoclonal antibody, in the clinic was defined by liver inflammation-related side effects. A protease-activated prodrug form of the anti-mouse CD137 agonist antibody 1D8 (1D8 Probody therapeutic, Pb-Tx) was constructed and found to be selectively activated in the tumor microenvironment. This construct, which encompasses a protease-cleavable linker holding in place a peptide that masks the antigen binding site, exerted antitumor effects comparable to the unmodified antibody but did not result in liver inflammation. Moreover, it efficaciously synergized with both PD-1 blockade and adoptive T-cell therapy. Surprisingly, minimal active Pb-Tx reached tumor-draining lymph nodes, and regional lymphadenectomy did not abrogate antitumor efficacy. By contrast, S1P receptor-dependent recirculation of T cells was absolutely required for efficacy. The preferential cleavage of the anti-CD137 Pb-Tx by tumor proteases offers multiple therapeutic opportunities, including neoadjuvant therapy, as shown by experiments in which the Pb-Tx is given prior to surgery to avoid spontaneous metastases.

Activating CD137 Signaling Promotes Sprouting Angiogenesis via Increased VEGFA Secretion and the VEGFR2/Akt/eNOS Pathway

Combination of antiangiogenesis and immunotherapy may be an effective strategy for treatment of solid tumors. Our previous work reported that activation of CD137 signaling promotes intraplaque angiogenesis. A number of studies have demonstrated that vascular endothelial growth factor receptor 2 (VEGFR2) is a key target for angiogenesis. However, it is unknown whether CD137-mediated angiogenesis is related to VEGFR2. In this study, we investigated the effect of CD137 on the VEGFR2 expression and explored the underlying mechanisms of CD137-mediated angiogenesis. Knock-out of CD137 in ApoE^−/− mice significantly decreased neovessel density in atherosclerotic plaques. CD137 silencing or inhibition attenuated endothelial cell (ECs) proliferation, migration, and tube formation. We found activation of CD137 signaling for increased VEGFR2 transcription and translation steadily. Moreover, CD137 signaling activated phosphorylated VEGFR2 (Tyr1175) and the downstream Akt/eNOS pathway, whereas neutralizing CD137 signaling weakened the activation of VEGFR2 and the downstream Akt/eNOS pathway. The aortic ring assay further demonstrated that CD137 signaling promoted ECc sprouting. Inhibition of VEGFR2 by siRNA or XL184 (cabozantinib) and inhibition of downstream signaling by LY294002 (inhibits AKT activation) and L-NAME (eNOS inhibitor) remarkably abolished proangiogenic effects of CD137 signaling both in vitro and ex vivo. In addition, the condition medium from CD137-activated ECs and vascular endothelial growth factor A (VEGFA) had similar effects on ECs that expressed high VEGFR2. Additionally, activating CD137 signaling promoted endothelial secretion of VEGFA, while blocking CD137 signaling attenuated VEGFA secretion. In conclusion, activation of CD137 signaling promoted sprouting angiogenesis by increased VEGFA secretion and the VEGFR2/Akt/eNOS pathway. These findings provide a basis for stabilizing intraplaque angiogenesis through VEGFR2 intervatioin, as well as cancer treatment via combination of CD137 agonists and specific VEGFR2 inhibitors.

Intratumor Adoptive Transfer of IL-12 mRNA Transiently Engineered Antitumor CD8+ T Cells

Retroviral gene transfer of interleukin-12 (IL-12) into T cells markedly enhances antitumor efficacy upon adoptive transfer but has clinically shown unacceptable severe side effects. To overcome the toxicity, we engineered tumor-specific CD8⁺ T cells to transiently express IL-12. Engineered T cells injected intratumorally, but not intravenously, led to complete rejections not only of the injected lesion but also of distant concomitant tumors. Efficacy was further enhanced by co-injection with agonist anti-CD137 mAb or by transient co-expression of CD137 ligand. This treatment induced epitope spreading of the endogenous CD8⁺ T cell immune response in a manner dependent on cDC1 dendritic cells. Mouse and human tumor-infiltrating T lymphocyte cultures can be transiently IL-12 engineered to attain marked immunotherapeutic effects.

Allergen-specific immunotherapy enhances CD8+ CD25+ CD137+ regulatory T cells and decreases nasal nitric oxide

BACKGROUND

4-1BB (CD137), a member of the inducible tumor necrosis factor receptor (TNFR) family, is expressed on regulatory T (Treg) cells and regulates Treg cells to control allergic inflammation. Pam3CSK4, a synthetic TLR2 ligand that can expand CD8⁺ Treg function, is a promising adjuvant for allergen immunotherapy (IT). We examined whether Dermatophagoides pteronyssinus (Der p) IT and Pam3CSK4 could enhance CD8⁺  CD25⁺  CD137⁺ Treg suppressive function to decrease nasal nitric oxide (nNO) levels.

METHODS

Nasal symptom scores, nNO levels, PBMCs, and inferior turbinate biopsies were obtained from 40 mite-sensitive perennial allergic rhinitis (PAR) patients before and after one year of Der p IT and 30 non-allergic control subjects. CD137 expression on CD8⁺  CD25⁺ T cells and suppressive function of CD8⁺  CD25⁺  CD137⁺ Tregs was measured using flow cytometry. Cytokine levels were analyzed by ELISA. Inducible nitric oxide synthase production by nasal epithelial cells after co-culturing with CD8⁺  CD25⁺  CD137⁺ T cells was analyzed by Western blotting.

RESULTS

Der p IT improved nasal symptom scores, decreased nNO levels, and increased CD137 expression on CD8⁺ T cells in PBMCs and nasal mucosa. Pam3CSK4 expanded the CD8⁺  CD25⁺  CD137⁺ population in PBMCs. Pam3CSK4-stimulated CD8⁺  CD25⁺  CD137⁺ Tregs induced IL-10 and TGF-β and suppressed CD4⁺  CD25- T-cell proliferation mainly by cell contact inhibition. CD8⁺  CD25⁺  CD137⁺ Tregs cultured with nasal epithelial cells suppressed Der p 2-induced iNOS production. Silencing CD137 in sorted CD8⁺  CD25⁺ T cells decreased Pam3CSK4-activated Foxp3 expression.

CONCLUSION

Der p IT expanded CD8⁺  CD25⁺  CD137⁺ Tregs and decreased nNO levels. Induced CD137 expression on CD8⁺  CD25⁺ Tregs by Pam3CSK4 stimulation may help suppress allergic inflammation during IT.

Cancer immunotherapy: broadening the scope of targetable tumours

Cancer immunotherapy has experienced remarkable advances in recent years. Striking clinical responses have been achieved for several types of solid cancers (e.g. melanoma, non-small cell lung cancer, bladder cancer and mismatch repair-deficient cancers) after treatment of patients with T-cell checkpoint blockade therapies. These have been shown to be particularly effective in the treatment of cancers with high mutation burden, which places tumour-mutated antigens (neo-antigens) centre stage as targets of tumour immunity and cancer immunotherapy. With current technologies, neo-antigens can be identified in a short period of time, which may support the development of complementary, personalized approaches that increase the number of tumours amenable to immunotherapeutic intervention. In addition to reviewing the state of the art in cancer immunotherapy, we discuss potential avenues that can bring the immunotherapy revolution to a broader patient group including cancers with low mutation burden.

Chronic retroviral infection of mice promotes tumor development, but CD137 agonist therapy restores effective tumor immune surveillance

T cell responses are crucial for anti-tumor immunity. In chronic viral infections, anti-tumor T cell responses can be compromised due to various immunological mechanisms, including T cell exhaustion. To study mechanisms of anti-tumor immunity during a chronic viral infection, we made use of the well-established Friend virus (FV) mouse model. Chronically FV-infected mice are impaired in their ability to reject FBL-3 cells-a virus-induced tumor cell line of C57BL/6 origin. Here we aimed to explore therapeutic strategies to overcome the influence of T cell exhaustion during chronic viral infection, and reactivate effector CD8+ and CD4+ T cells to eliminate tumor cells. For T cell stimulation, agonistic antibodies against the tumor necrosis factor receptor (TNFR) superfamily members CD137 and CD134 were used, because they were reported to augment the cytotoxic program of T cells. αCD137 agonistic therapy, but not αCD134 agonistic therapy, resulted in FBL-3 tumor elimination in chronically FV-infected mice. CD137 stimulation significantly enhanced the cytotoxic activity of both CD4+ and CD8+ T cells, which were both required for efficient tumor control. Our study suggests that agonistic antibodies to CD137 can efficiently enhance anti-tumor immunity even in the setting of chronic viral infection, which might have promising therapeutic applications.

Adoptive T Cell Therapy: New Avenues Leading to Safe Targets and Powerful Allies

Adoptive transfer of TCR-engineered T cells is a potent therapy, able to induce clinical responses in different human malignancies. Nevertheless, treatment toxicities may occur and, in particular for solid tumors, responses may be variable and often not durable. To address these challenges, it is imperative to carefully select target antigens and to immunologically interrogate the corresponding tumors when designing optimal T cell therapies. Here, we review recent advances, covering both omics- and laboratory tools that can enable the selection of optimal T cell epitopes and TCRs as well as the identification of dominant immune evasive mechanisms within tumor tissues. Furthermore, we discuss how these techniques may aid in a rational design of effective combinatorial adoptive T cell therapies.

Mechanisms regulating T-cell infiltration and activity in solid tumors

T-lymphocytes play a critical role in cancer immunity as evidenced by their presence in resected tumor samples derived from long-surviving patients, and impressive clinical responses to various immunotherapies that reinvigorate them. Indeed, tumors can upregulate a wide array of defense mechanisms, both direct and indirect, to suppress the ability of Tcells to reach the tumor bed and mount curative responses upon infiltration. In addition, patient and tumor genetics, previous antigenic experience, and the microbiome, are all important factors in shaping the T-cell repertoire and sensitivity to immunotherapy. Here, we review the mechanisms that regulate T-cell homing, infiltration, and activity within the solid tumor bed. Finally, we summarize different immunotherapies and combinatorial treatment strategies that enable the immune system to overcome barriers for enhanced tumor control and improved patient outcome.

Mitochondrial Morphological and Functional Reprogramming Following CD137 (4-1BB) Costimulation

T and NK lymphocytes express CD137 (4-1BB), a costimulatory receptor of the TNFR family whose function is exploitable for cancer immunotherapy. Mitochondria regulate the function and survival of T lymphocytes. Herein, we show that CD137 costimulation provided by agonist mAb and CD137L (4-1BBL) induced mitochondria enlargement that resulted in enhanced mitochondrial mass and transmembrane potential in human and mouse CD8⁺ T cells. Such mitochondrial changes increased T-cell respiratory capacities and were critically dependent on mitochondrial fusion protein OPA-1 expression. Mass and function of mitochondria in tumor-reactive CD8⁺ T cells from cancer-bearing mice were invigorated by agonist mAb to CD137, whereas mitochondrial baseline mass and function were depressed in CD137-deficient tumor reactive T cells. Tumor rejection induced by the synergistic combination of adoptive T-cell therapy and agonistic anti-CD137 was critically dependent on OPA-1 expression in transferred CD8⁺ T cells. Moreover, stimulation of CD137 with CD137 mAb in short-term cultures of human tumor-infiltrating lymphocytes led to mitochondria enlargement and increased transmembrane potential. Collectively, these data point to a critical link between mitochondrial morphology and function and enhanced antitumor effector activity upon CD137 costimulation of T cells. Cancer Immunol Res; 6(7); 798-811. ©2018 AACR.

Anti-CD137 Suppresses Tumor Growth by Blocking Reverse Signaling by CD137 Ligand

CD137 (4-1BB) is a T-cell costimulatory molecule, and agonstic CD137 antibodies are currently being evaluated in the clinic as cancer immunotherapy. Recently, it was found that CD137^-/- mice or mice injected with agonistic anti-CD137 antibodies exhibit heightened antitumor responses, contrary to expectations based on other knowledge of CD137 function. Here, we report findings related to reverse signaling by CD137 ligand (CD137L) in antigen-presenting dendritic cells (DC) in tumors that address these paradoxical results. Specifically, CD137L suppressed intratumoral differentiation of IL12-producing CD103⁺ DC and type 1 tumor-associated macrophages (TAM). Differentiation of these cell types is important because they are required to generate IFNγ-producing CD8⁺ cytotoxic T lymphocytes (Tc1). Notably, CD137L blockade increased levels of IL12 and IFNγ, which promoted intratumoral differentiation of IFNγ-producing Tc1, IL12-producing CD103⁺ DC, and type 1 TAM within tumors. Our results offer an explanation for the paradoxical effects of CD137 blockade, based on differential immunomodulatory effects of CD137 signaling and reverse signaling in T cells and DC, respectively. Further, they show how CD137L blockade can seed a forward-feedback loop for activation of CD103⁺ DC/type 1 TAM and Tc1 that can create a self-perpetuating cycle of highly effective immunosurveillance. Cancer Res; 77(21); 5989-6000. ©2017 AACR.

恶性肿瘤缺氧酸性微环境对免疫治疗影响机制的研究进展

近年来, 以免疫检查点阻断单克隆抗体和抗原受体T细胞免疫疗法细胞治疗为代表的免疫疗法在治疗恶性肿瘤方面取得突破性进展. 然而, 肿瘤通过各种不同的机制逃避免疫系统的识别和杀伤, 导致免疫治疗效果仍不理想. 由癌细胞、血管、淋巴、成纤维细胞、炎症细胞以及多种细胞外基质有机构成的肿瘤组织微环境不仅支持癌细胞的生长和转移, 也影响免疫细胞识别和杀伤癌细胞以及迁移的功能, 调控免疫效应分子的活化, 从而影响免疫治疗的效果. 实体肿瘤内异常血管网络和快速生长的癌细胞对氧过量需求导致肿瘤组织缺氧, 并加剧由于癌细胞异常代谢导致肿瘤组织的酸性微环境. 缺氧酸性微环境是肿瘤微环境最重要的组成部分, 癌细胞适应和利用这些微环境, 导致基因变异的多样性和不稳定性, 激活多种信号通路和生存因子, 造成肿瘤对包括免疫治疗在内的多种治疗方法的耐受和抵抗. 本文针对近年来肿瘤缺氧酸性微环境对免疫治疗影响机制的研究进展进行述评, 希望给从事癌症微环境和免疫治疗的临床基础科研人员提供新的思路.

Perspectives in immunotherapy: meeting report from the “Immunotherapy Bridge”, Napoli, December 5th 2015

Harnessing the immune system and preventing immune escape, the immunotherapy of cancer provides great potential for clinical application, in broad patient populations, achieving both conventional and unconventional clinical responses. After the substantial advances in melanoma, the focus of cancer immunotherapy has expanded to include many other cancers. Targeting immune checkpoints and further mechanisms used by tumors to avoid anticancer immunity, different approaches are under evaluation, including combination therapies.

The first Immunotherapy Bridge meeting focused on various cancer types including melanoma, non-small cell lung cancer, renal cell, breast and ovarian carcinoma, and discussed mechanisms of action of single agents and combination strategies, and the prediction of clinical responses.

Optimising Cancer Immunotherapy: Challenges and Opportunities

Cancer immunotherapy has moved to the forefront in the treatment of patients with cancer, providing a unique opportunity to achieve dramatic and lasting anti-tumour responses in a variety of tumour types. When it comes to patient selection and development of novel immunotherapeutic agents and combinations, so far we have merely scratched the surface of this therapeutic approach. Leading experts in the field of cancer immunotherapy gathered in Amsterdam, Netherlands, on 21st May 2016 for a Scientific Exchange to discuss the current status of immunotherapy within the field of oncology and explore the future of this evolving therapeutic strategy. Current challenges and limitations regarding the use of immunotherapy were addressed for tumour types such as melanoma, lung cancer, bladder cancer, and renal cell carcinoma (RCC). Recent advances and future directions in the areas of immunotherapy biomarkers and mechanisms of resistance were also examined. Current evidence for combination strategies with immunotherapy was highlighted, including combinations with other immunotherapies or with radiotherapy. Below is a summary of the key points discussed during this scientific exchange.