Oligonucleotide library screening for identification of virus-specific T-cell receptors.

We demonstrate an optimized oligonucleotide library-based approach for the identification of virus-reactive T-cell receptors using Epstein-Barr virus as an example. HEK293T served as antigen-presenting cells and were co-cultured with human T cells that were transduced with T-cell receptors in question. T-cell activation was detected by CD137 expression.

CD137 expression and signal function drive pleiotropic γδ T-cell effector functions that inhibit intracellular M. tuberculosis growth.

Co-activation signal that induces/sustains pleiotropic effector functions of antigen-specific γδ T cells remains unknown. Here, Mycobacteria tuberculosis (Mtb) tuberculin administration during tuberculosis (TB) skin test resulted in rapid expression of co-activation signal molecules CD137 and CD107a by fast-acting Vγ2Vδ2 T cells in TB-resistant subjects (Resisters), but not patients with active TB. And, anti-CD137 agonistic antibody treatment experiments showed that CD137 signaling enabled Vγ2Vδ2 T cells to produce more effector cytokines and inhibit intracellular Mtb growth in macrophages (Mɸ). Consistently, Mtb antigen (Ag) HMBPP stimulation induced sustainable high-level CD137 expression in fresh and activated Vγ2Vδ2 T cells from uninfected subjects, but not TB patients. CD137+Vγ2Vδ2 T-cell subtype predominantly displayed central memory phenotype and mounted better proliferative responses than CD137-Vγ2Vδ2 T-cells. In response to HMBPP, CD137+Vγ2Vδ2 T-cell subtype rapidly differentiated into greater numbers of pleiotropic effector cells producing anti-Mtb cytokines compared to CD137-Vγ2Vδ2 T subtype, with the non-canonical NF-κB pathway involved. CD137 expression in Vγ2Vδ2 T cells appeared to signal anti-Mtb effector functions leading to intracellular Mtb growth inhibition in Mɸ, and active TB disrupted such CD137-driven anti-Mtb effector functions. CD137+Vγ2Vδ2 T-cells subtype exhibited an epigenetic-driven high-level expression of GM-CSF and de novo production of GM-CSF critical for Vγ2Vδ2 T-cell controlling of Mtb growth in Mϕ. Concurrently, exosomes produced by CD137+Vγ2Vδ2 T cells potently inhibited intracellular mycobacterial growth. Furthermore, adoptive transfer of human CD137+Vγ2Vδ2 T cells to Mtb-infected SCID mice conferred protective immunity against Mtb infection. Thus, our data suggest that CD137 expression/signaling drives pleiotropic γδ T-cell effector functions that inhibit intracellular Mtb growth.

CD137+ tumor infiltrating lymphocytes predicts ovarian cancer survival.

OBJECTIVE: Ovarian cancer (OC) is the leading cause of death from gynecologic malignancy in the United States, and biomarkers of patient outcomes are limited. Data using immunohistochemical (IHC) analysis are mixed regarding whether and which tumor infiltrating lymphocytes (TILs) impact survival, and IHC does not adequately quantify rare cell populations, including CD137+ (4-1BB) tumor-reactive TILs. Our study investigates if a higher percentage of CD3+ CD137+ TILs is associated with improved overall survival (OS) in OC. METHODS: Flow cytometry was performed on viably banked OC digests. Chart review and statistical analysis were performed. Forty-seven patients were included, 40 of whom were diagnosed with high-grade serous ovarian carcinoma (HGSOC), papillary serous carcinoma, or undifferentiated histology. RESULTS: A high percentage of CD3+ CD137+ TILs correlated with improved OS (n = 40, r = 0.48, P = 0.0016). Subjects were divided into CD3+ CD137+ TIL high and low groups by the median. Subjects with high CD3+CD137+ TIL frequencies (>9.6%) had longer OS (Wilcoxon rank-sum test; P = 0.0032) and improved OS (logrank test; P = 0.007). Differences in CD3+ or CD3+ CD8+ TILs did not impact survival. CD3+ CD137+ TILs were predictive of OS regardless of germline mutation or debulking status. Analysis of subgroups including late stage HGSOC and late stage HGSOC with primary optimal cytoreduction indicated CD3+ CD137+ TILs correlated with improved OS after adjusting for age and PARP inhibitor use (P = 0.034 and P = 0.016, respectively). CONCLUSIONS: Prevalence of CD3+ CD137+ TILs in digested OC specimens is associated with improved OS, while general TIL markers are not. CD137 has the potential to be a novel biomarker for survival in OC.

Synthetic dual co-stimulation increases the potency of HIT and TCR-targeted cell therapies.

Chimeric antigen receptor T cells have dramatically improved the treatment of hematologic malignancies. T cell antigen receptor (TCR)-based cell therapies are yet to achieve comparable outcomes. Importantly, chimeric antigen receptors not only target selected antigens but also reprogram T cell functions through the co-stimulatory pathways that they engage upon antigen recognition. We show here that a fusion receptor comprising the CD80 ectodomain and the 4-1BB cytoplasmic domain, termed 80BB, acts as both a ligand and a receptor to engage the CD28 and 4-1BB pathways, thereby increasing the antitumor potency of human leukocyte antigen-independent TCR (HIT) receptor- or TCR-engineered T cells and tumor-infiltrating lymphocytes. Furthermore, 80BB serves as a switch receptor that provides agonistic 4-1BB co-stimulation upon its ligation by the inhibitory CTLA4 molecule. By combining multiple co-stimulatory features in a single antigen-agnostic synthetic receptor, 80BB is a promising tool to sustain CD3-dependent T cell responses in a wide range of targeted immunotherapies.

Development of a c-MET x CD137 bispecific antibody for targeted immune agonism in cancer immunotherapy.

BACKGROUND: Targeting the costimulatory receptor CD137 has shown promise as a therapeutic approach for cancer immunotherapy, resulting in anti-tumor efficacy demonstrated in clinical trials. However, the initial CD137 agonistic antibodies, urelumab and utomilumab, faced challenges in clinical trials due to the liver toxicity or lack of efficacy, respectively. Concurrently, c-MET has been identified as a highly expressed tumor-associated antigen (TAA) in various solid and soft tumors. METHODS: In this study, we aimed to develop a bispecific antibody (BsAb) that targets both c-MET and CD137, optimizing the BsAb format and CD137 binder for efficient delivery of the CD137 agonist to the tumor microenvironment (TME). We employed a monovalent c-MET motif and a trimeric CD137 Variable Heavy domain of Heavy chain (VHH) for the BsAb design. RESULTS: Our results demonstrate that the c-MET x CD137 BsAb provides co-stimulation to T cells through cross-linking by c-MET-expressing tumor cells. Functional immune assays confirmed the enhanced efficacy and potency of the c-MET x CD137 BsAb, as indicated by activation of CD137 signaling, target cell killing, and cytokine release in various tumor cell lines. Furthermore, the combination of c-MET x CD137 BsAb with Pembrolizumab showed a dose-dependent enhancement of target-induced T cell cytokine release. CONCLUSION: Overall, the c-MET x CD137 BsAb exhibits a promising developability profile as a tumor-targeted immune agonist by minimizing off-target effects while effectively delivering immune agonism. It has the potential to overcome resistance to anti-PD-(L)1 therapies.

Facile generation of biepitopic antibodies with intrinsic agonism for activating tumor necrosis factor receptors.

Agonist antibodies are being pursued for therapeutic applications ranging from neurodegenerative diseases to cancer. For the tumor necrosis factor (TNF) receptor superfamily, higher-order clustering of three or more receptors is key to their activation, which can be achieved using antibodies that recognize two unique epitopes. However, the generation of biepitopic (i.e., biparatopic) antibodies typically requires animal immunization and is laborious and unpredictable. Here, we report a simple method for identifying biepitopic antibodies that potently activate TNF receptors without the need for additional animal immunization. Our approach uses existing, receptor-specific IgGs, which lack intrinsic agonist activity, to block their corresponding epitopes, then selects single-chain antibodies that bind accessible epitopes. The selected antibodies are fused to the light chains of IgGs to generate human tetravalent antibodies. We highlight the broad utility of this approach by converting several clinical-stage antibodies against OX40 and CD137 (4-1BB) into biepitopic antibodies with potent agonist activity.

Design of Crosslinking Antibodies For T-Cell Activation: Experimental and Computational Analysis of PD-1/CD137 Bispecific Agents.

Bispecific and multispecific agents have become increasingly utilized in cancer treatment and immunotherapy, yet their complex design parameters present a challenge in developing successful therapeutics. Bispecifics that crosslink receptors on two opposing cells can provide specific activation of a receptor only when these cells are in close spatial proximity, such as an immune cell and cancer cell in a tumor. These agents, including T cell activating bispecifics, can avoid off-tumor toxicity through activation only in the tumor microenvironment by utilizing a tumor target to cluster T-cell receptors for a selective costimulatory signal. Here, we investigate a panel of PD-1/CD137 targeted Humabody VH domains to determine the key factors for T cell activation, such as affinity, valency, expression level, domain orientation, and epitope location. Target expression is a dominant factor determining both specificity and potency of T cell activation. Given an intrinsic expression level, the affinity can be tuned to modulate the level of activation and IC50 and achieve specificity between low and high expression levels. Changing the epitope location and linker length showed minor improvements to activation at low expression levels, but increasing the valency for the target decreased activation at all expression levels. By combining non-overlapping epitopes for the target, we achieved higher receptor activation at low expression levels. A kinetic model was able to capture these trends, offering support for the mechanistic interpretation. This work provides a framework to quantify factors for T cell activation by cell-crosslinking bispecific agents and guiding principles for the design of new agents.

Improvement of daratumumab- or elotuzumab-mediated NK cell activity by the bi-specific 4-1BB agonist, DARPin α-FAPx4-1BB: A preclinical study in multiple myeloma.

Multiple myeloma (MM) progression is closely dependent on cells in the bone marrow (BM) microenvironment, including fibroblasts (FBs) and immune cells. In their BM niche, MM cells adhere to FBs sustaining immune evasion, drug resistance and the undetectable endurance of tumor cells known as minimal residual disease (MRD). Here, we describe the novel bi-specific designed ankyrin repeat protein (DARPin) α-FAPx4-1BB (MP0310) with FAP-dependent 4-1BB agonistic activity. The α-FAPx4-1BB DARPin simultaneously binds to FAP and 4-1BB overexpressed by activated FBs and immune cells, respectively. Although flow cytometry analysis showed that T and NK cells from MM patients were not activated and did not express 4-1BB, stimulation with daratumumab or elotuzumab, monoclonal antibodies (mAbs) currently used for the treatment of MM, significantly upregulated 4-1BB both in vitro and in MM patients following mAb-based therapy. The mAb-induced 4-1BB overexpression allowed the engagement of α-FAPx4-1BB that acted as a bridge between FAP+FBs and 4-1BB+NK cells. Therefore, α-FAPx4-1BB enhanced both the adhesion of daratumumab-treated NK cells on FBs as well as their activation by improving release of CD107a and perforin, hence MM cell killing via antibody-mediated cell cytotoxicity (ADCC). Interestingly, α-FAPx4-1BB significantly potentiated daratumumab-mediated ADCC in the presence of FBs, suggesting that it may overcome the BM FBs' immunosuppressive effect. Overall, we speculate that treatment with α-FAPx4-1BB may represent a valuable strategy to improve mAb-induced NK cell activity fostering MRD negativity in MM patients through the eradication of latent MRD cells.

Orchestrating NK and T cells via tri-specific nano-antibodies for synergistic antitumor immunity.

The functions of natural killer (NK) and T cells in innate and adaptive immunity, as well as their functions in tumor eradication, are complementary and intertwined. Here we show that utilization of multi-specific antibodies or nano-antibodies capable of simultaneously targeting both NK and T cells could be a valuable approach in cancer immunotherapy. Here, we introduce a tri-specific Nano-Antibody (Tri-NAb), generated by immobilizing three types of monoclonal antibodies (mAbs), using an optimized albumin/polyester composite nanoparticle conjugated with anti-Fc antibody. This Tri-NAb, targeting PDL1, 4-1BB, and NKG2A (or TIGIT) simultaneously, effectively binds to NK and CD8+ T cells, triggering their activation and proliferation, while facilitating their interaction with tumor cells, thereby inducing efficient tumor killing. Importantly, the antitumor efficacy of Tri-NAb is validated in multiple models, including patient-derived tumor organoids and humanized mice, highlighting the translational potential of NK and T cell co-targeting.

Short-term cultured tumor fragments to study immunotherapy combinations based on CD137 (4-1BB) agonism.

Biomarkers for cancer immunotherapy are an unmet medical need. The group of Daniela Thommen at the NKI recently reported on novel methodologies based on short-term cultures of patient-derived tumor fragments whose cytokine concentrations in the supernatants and activation markers on infiltrating T cells were associated with clinical response to PD-1 blockade. We set up a similar culture technology with tumor-derived fragments using mouse tumors transplanted into syngeneic immunocompetent mice to test an agonist anti-CD137 mAb and its combinations with anti-PD-1 and/or anti-TGF-ß. Increases in IFNγ concentrations in the tissue culture supernatants were detected upon in-culture activation with the anti-CD137 and anti-PD-1 mAb combinations or concanavalin A as a positive control. No other cytokine from a wide array was informative of stimulation with these mAbs. Interestingly, increases in Ki67 and other activation markers were substantiated in lymphocytes from cell suspensions gathered at the end of 72 h cultures. In mice bearing bilateral tumors in which one was excised prior to in vivo anti-CD137 + anti-PD-1 treatment to perform the fragment culture evaluation, no association was found between IFNγ production from the fragments and the in vivo therapeutic outcome in the non-resected contralateral tumors. The experimental system permitted freezing and thawing of the fragments with similar functional outcomes. Using a series of patient-derived tumor fragments from excised solid malignancies, we showed IFNγ production in a fraction of the studied cases, that was conserved in frozen/thawed fragments. The small tumor fragment culture technique seems suitable to preclinically explore immunotherapy combinations.

ATG-101 Is a Tetravalent PD-L1×4-1BB Bispecific Antibody That Stimulates Antitumor Immunity through PD-L1 Blockade and PD-L1-Directed 4-1BB Activation.

Immune checkpoint inhibitors (ICI) have transformed cancer treatment. However, only a minority of patients achieve a profound response. Many patients are innately resistant while others acquire resistance to ICIs. Furthermore, hepatotoxicity and suboptimal efficacy have hampered the clinical development of agonists of 4-1BB, a promising immune-stimulating target. To effectively target 4-1BB and treat diseases resistant to ICIs, we engineered ATG-101, a tetravalent "2+2″ PD-L1×4-1BB bispecific antibody. ATG-101 bound PD-L1 and 4-1BB concurrently, with a greater affinity for PD-L1, and potently activated 4-1BB+ T cells when cross-linked with PD-L1-positive cells. ATG-101 activated exhausted T cells upon PD-L1 binding, indicating a possible role in reversing T-cell dysfunction. ATG-101 displayed potent antitumor activity in numerous in vivo tumor models, including those resistant or refractory to ICIs. ATG-101 greatly increased the proliferation of CD8+ T cells, the infiltration of effector memory T cells, and the ratio of CD8+ T/regulatory T cells in the tumor microenvironment (TME), rendering an immunologically "cold" tumor "hot." Comprehensive characterization of the TME after ATG-101 treatment using single-cell RNA sequencing further revealed an altered immune landscape that reflected increased antitumor immunity. ATG-101 was well tolerated and did not induce hepatotoxicity in non-human primates. According to computational semimechanistic pharmacology modeling, 4-1BB/ATG-101/PD-L1 trimer formation and PD-L1 receptor occupancy were both maximized at around 2 mg/kg of ATG-101, providing guidance regarding the optimal biological dose for clinical trials. In summary, by localizing to PD-L1-rich microenvironments and activating 4-1BB+ immune cells in a PD-L1 cross-linking-dependent manner, ATG-101 safely inhibits growth of ICI resistant and refractory tumors. SIGNIFICANCE: The tetravalent PD-L1×4-1BB bispecific antibody ATG-101 activates 4-1BB+ T cells in a PD-L1 cross-linking-dependent manner, minimizing the hepatotoxicity of existing 4-1BB agonists and suppressing growth of ICI-resistant tumors. See related commentary by Ha et al., p. 1546.