Generation of a safe and efficacious llama single-domain antibody fragment (vHH) targeting the membrane-proximal region of 4-1BB for engineering therapeutic bispecific antibodies for cancer

Acasunlimab, an Fc-inert PD-L1×4-1BB bispecific antibody, combined with PD-1 blockade potentiates antitumor immunity via complementary immune modulatory effects

BACKGROUND

Next-generation cancer immunotherapies aim to improve patient outcomes by combining inhibitory signal blockade with targeted T-cell costimulation in tumor and lymphoid tissues. Acasunlimab (DuoBody-PD-L1×4-1BB) is an investigational, bispecific antibody designed to elicit an antitumor immune response via conditional 4-1BB activation strictly dependent on simultaneous programmed death-ligand 1 (PD-L1) binding. Since 4-1BB is coexpressed with programmed cell death protein-1 (PD-1) on CD8+ T cells, PD-1 blockade and simultaneous costimulation through 4-1BB may synergistically enhance T-cell effector functions. We hypothesized that combining acasunlimab with PD-1 blockade to fully disrupt PD-1 interactions with both PD-L1 and PD-L2 would amplify the depth and duration of antitumor immunity.

METHODS

The effect of acasunlimab and pembrolizumab combination was analyzed in vitro using functional immune cell assays, including mixed-lymphocyte reactions and antigen-specific T-cell proliferation and cytotoxicity assays. The antitumor activity of the combination was tested in vivo in (1) MC38, MB49, Pan02, and B16F10 syngeneic tumor models using acasunlimab and anti-PD-1 mouse-surrogate antibodies; and (2) triple knock-in mice expressing the human targets using an acasunlimab chimeric antibody (chi-acasunlimab) and pembrolizumab. The mechanism of action of the combination was investigated in the MC38 syngeneic model through immunohistochemistry, flow cytometry, and bulk RNA sequencing.

RESULTS

The combination reinvigorated dysfunctional T cells in vitro, while also potentiating T-cell expansion, interleukin (IL)-2 and interferon gamma secretion and cytotoxic activity. In vivo, the combination of chi-acasunlimab and pembrolizumab or mouse-surrogate antibodies potentiated antitumor activity and survival in the humanized knock-in and multiple syngeneic mouse models, leading to durable complete tumor regressions in the MC38 model consistent with therapeutic synergy. Mechanistically, the combination enhanced clonal expansion of tumor-specific CD8+ T cells in tumor-draining lymph nodes and increased the density of proliferating and cytotoxic CD8+ T cells in the tumor microenvironment. It also potentiated the IL-2 signaling pathway, increasing the proportion of granzyme B (GZMB+) stem-like CD8+ T cells thought to have superior effector function.

CONCLUSION

These preclinical results demonstrate that conditional 4-1BB stimulation combined with complete PD-1 blockade enhances antitumor immunity through complementary mechanisms. The acasunlimab and pembrolizumab combination is being evaluated in Phase 2 (NCT05117242) and pivotal Phase 3 (NCT06635824) trials in patients with metastatic non-small cell lung cancer after checkpoint inhibitor therapy failure.

Nanobodies targeting the tumor microenvironment and their formulation as nanomedicines

Among the emerging strategies for cancer theranostics, nanomedicines offer significant promise in advancing both patients' diagnosis and treatment. In combination with nanobodies, nanomedicines can potentially enhance the precision and efficiency of drug or imaging agent delivery, addressing key limitations of current approaches, such as off-target toxicities. The development of nanomedicines will be further accelerated by the creation of smart nanoparticles, and their integration with immunotherapy. Obviously, the success of nano-immunotherapy will depend on a comprehensive understanding of the tumor microenvironment, including the complex interplay of mechanisms that drive cancer-mediated immunosuppression and immune escape. Hence, effective therapeutic targeting of the tumor microenvironment requires modulation of immune cell function, overcoming resistance mechanisms associated with stromal components or the extracellular matrix, and/or direct elimination of cancer cells. Identifying key molecules involved in cancer progression and drug resistance is, therefore, essential for developing effective therapies and diagnostic tools that can predict patient responses to treatment and monitor therapeutic outcomes. Current nanomedicines are being designed with careful consideration of factors such as the choice of carrier (e.g., biocompatibility, controlled cargo release) and targeting moiety. The unique properties of nanobodies make them an effective engineering tool to target biological molecules with high affinity and specificity. In this review, we focus on the latest applications of nanobodies for targeting various components of the tumor microenvironment for diagnostic and therapeutic purposes. We also explore the main types of nanoparticles used as a carrier for cancer immunotherapies, as well as the strategies for formulating nanoparticle-nanobody conjugates. Finally, we highlight how nanobody-nanoparticle formulations can enhance current nanomedicines.

From antibodies to nanobodies: The next frontier in cancer theranostics for solid tumors

The field of cancer therapeutics has witnessed significant advancements over the past decades, particularly with the emergence of immunotherapy. This chapter traces the transformative journey from traditional antibody-based therapies to the innovative use of nanobodies in the treatment and diagnosis of solid tumors. Nanobodies are the smallest fragments of antibodies derived from camelid immunoglobulins and have redefined the possibilities in cancer theranostics due to their unique structural and functional properties. We provide an overview of the biochemical characteristics of nanobodies that make them particularly suitable for theranostic applications, such as their small size, high stability, enhanced infiltration into the complex tumor microenvironment (TME) and ability to bind with high affinity to epitopes that are inaccessible to conventional antibodies. Further, their ease of modification and functionalization has enabled the development of nanobody-based drug conjugates/toxins and radiolabeled compounds for precise imaging and targeted radiotherapy. We elucidate how nanobodies are being served as valuable tools for prognostic assessment, enabling clinicians to predict disease aggressiveness, monitor treatment response, and stratify patients for personalized therapeutic interventions.

How Biologics Have Changed the Drug Discovery Landscape

Advances in molecular biology and molecular genetics as well as major scientific breakthroughs in immunology and oncology have led to the rapid growth of biologic therapeutics. Their success has resulted in significant changes to virtually every step in the drug discovery and development process. Biologics are produced by living organisms, and screening libraries are generated by immunization or phage display. Lead optimization utilizes sophisticated protein engineering to improve drug-like properties and targeting specificity. The manufacturing process for biologics is complex and requires highly specialized facilities. Determination of pharmacology and safety must overcome the complications associated with species specificity. Initial clinical testing must proceed more slowly and carefully due to the limited predictive utility of preclinical data. In summary, the drug discovery and development process has been dramatically altered by biologic therapeutics and will continue to evolve with the introduction of messenger RNA-based therapeutics and the application of artificial intelligence.

Safety Assessment of Camelid-Derived Single-Domain Antibody as Feed Additive for Juvenile Whiteleg Shrimp (Litopenaeus vannamei) Against White Spot Syndrome Virus

A six-week feeding trial was conducted to assess the safety of single-domain antibodies (sdAbs) derived from camelids against the white spot syndrome virus (WSSV) (WSSVvp28 was used as the antigen), focusing on the whole-organism responses and molecular-level changes in juvenile whiteleg shrimp (Litopenaeus vannamei). Five experimental diets with varying levels of sdAbs were formulated: CON (no sdAb supplementation); SDA8.2 (8.20% of sdAbs); SDA16.4 (16.40% of sdAbs); SDA24.6 (24.60% of sdAbs); and SDA32.8 (32.80% of sdAbs). In the CON diet, 450 mL of water per kg of diet (45%) was used to form a feed dough, while sdAbs were used to replace the water in the treatment diets. A total of 450 shrimp, with an initial body weight of 3.27 ± 0.02 g (mean ± SEM), were randomly distributed in 15 tanks (30 shrimp per tank; three tanks per treatment). Each tank was filled with 30 L of seawater (77 L capacity) in an indoor semi-recirculating system with a constant water flow rate of 1.2 L min-1. The photoperiod was maintained at 12 h of light and 12 h of dark. The water temperature, pH, salinity, and dissolved oxygen were 27.3 ± 0.1 °C, 7.61 ± 0.01, 34 ± 1 ppt, and 5.94 ± 0.04 mg L-1, respectively. During the feeding trial, the shrimp were fed the experimental diet (40% protein and 11% lipid) three times a day for six weeks. Following the feeding trial, an acute cold-water-temperature stress test was conducted by abruptly exposing the shrimp from each treatment to 15 °C for 4 h, down from 27 °C. The results showed no significant differences in the growth performance (weight gain, feed utilization efficiency, survival, etc.), plasma metabolites (aspartate aminotransferase activity, alanine aminotransferase activity, total protein, and glucose), or antioxidant enzymes (superoxide dismutase and glutathione peroxidase) among all the experimental diets (p > 0.05). In the acute cold-temperature stress test, there was no significant interaction between sdAb supplementation and temperature stress, nor any main effect from either factor, except for the main effect of temperature stress on the glucose levels, which was significantly higher in shrimp exposed to cold-temperature stress (p < 0.05). The next-generation sequencing of differentially expressed genes (DEGs) in the hepatopancreases of shrimp fed the CON, SDA16.4, and SDA32.8 diets, followed by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses, indicated that DEGs were significantly enriched in signaling pathways associated with growth, cold stress, and antioxidant systems. Overall, the results from conventional measurements suggest that the use of sdAbs against the WSSV may be safe for juvenile whiteleg shrimp. However, findings from the sophisticated analysis indicate that further research is needed to understand the molecular mechanisms underlying the observed changes, and to evaluate the long-term effects of sdAb supplementation in shrimp diets.

Characterization of a Trispecific PD-L1 Blocking Antibody That Exhibits EGFR-Conditional 4-1BB Agonist Activity

Immune checkpoint blockade has changed the treatment paradigm for advanced solid tumors, but the overall response rates are still limited. The combination of checkpoint blockade with anti-4-1BB antibodies to stimulate tumor-infiltrating T cells has shown anti-tumor activity in human trials. However, the further clinical development of these antibodies has been hampered by significant off-tumor toxicities. Here, we generated an anti-4-1BB/EGFR/PD-L1 trispecific antibody consisting of a triple-targeting tandem trimerbody (TT) fused to an engineered silent Fc region. This antibody (IgTT-4E1-S) was designed to combine the blockade of the PD-L1/PD-1 axis with conditional 4-1BB costimulation specifically confined to the tumor microenvironment (TME). The antibody demonstrated simultaneous binding to purified EGFR, PD-L1, and 4-1BB in solution, effective blockade of the PD-L1/PD1 interaction, and potent 4-1BB-mediated costimulation, but only in the presence of EGFR-expressing cells. These results demonstrate the feasibility of IgTT-4E1-S specifically blocking the PD-L1/PD-1 axis and inducing EGFR-conditional 4-1BB agonist activity.

The enhanced antitumor activity of bispecific antibody targeting PD-1/PD-L1 signaling

The programmed cell death 1 (PD-1) signaling pathway, a key player in immune checkpoint regulation, has become a focal point in cancer immunotherapy. In the context of cancer, upregulated PD-L1 on tumor cells can result in T cell exhaustion and immune evasion, fostering tumor progression. The advent of PD-1/PD-L1 inhibitor has demonstrated clinical success by unleashing T cells from exhaustion. Nevertheless, challenges such as resistance and adverse effects have spurred the exploration of innovative strategies, with bispecific antibodies (BsAbs) emerging as a promising frontier. BsAbs offer a multifaceted approach to cancer immunotherapy by simultaneously targeting PD-L1 and other immune regulatory molecules. We focus on recent advancements in PD-1/PD-L1 therapy with a particular emphasis on the development and potential of BsAbs, especially in the context of solid tumors. Various BsAb products targeting PD-1 signaling are discussed, highlighting their unique mechanisms of action and therapeutic potential. Noteworthy examples include anti-TGFβ × PD-L1, anti-CD47 × PD-L1, anti-VEGF × PD-L1, anti-4-1BB × PD-L1, anti-LAG-3 × PD-L1, and anti-PD-1 × CTLA-4 BsAbs. Besides, we summarize ongoing clinical studies evaluating the efficacy and safety of these innovative BsAb agents. By unraveling the intricacies of the tumor microenvironment and harnessing the synergistic effects of anti-PD-1/PD-L1 BsAbs, there exists the potential to elevate the precision and efficacy of cancer immunotherapy, ultimately enabling the development of personalized treatment strategies tailored to individual patient profiles.

Enhancing anti-CD274 (PD-L1) targeting through combinatorial immunotherapy with bispecific antibodies and fusion proteins: from preclinical to phase II clinical trials

INTRODUCTION

Immune checkpoint inhibitors have achieved great success in the treatment of many different types of cancer. Programmed cell death protein ligand 1 (PD-L1, CD274) is a major immunosuppressive immune checkpoint and a target for several already approved monoclonal antibodies. Despite this, novel strategies are under development, as the overall response remains low.

AREAS COVERED

In this review, an overview of the current biomarkers for response to PD-L1 inhibitor treatment is given, followed by a discussion of potential novel biomarkers, including tumor mutational burden and circulating tumor DNA. Combinatorial immunotherapy is a potential novel strategy to increase the response to PD-L1 inhibitor treatment and currently, several interesting bispecific antibodies as well as bispecific fusion proteins are undergoing early clinical investigation. We focus on substances targeting PD-L1 and a secondary target, and a secondary immunomodulatory target like CTLA-4, TIGIT, or CD47.

EXPERT OPINION

Overall, the presented studies show anti-tumor activity of these combinatorial immunotherapeutic approaches. However, still relatively low response rates suggest a need for better biomarkers.

i-shaped antibody engineering enables conformational tuning of biotherapeutic receptor agonists

The ability to leverage antibodies to agonize disease relevant biological pathways has tremendous potential for clinical investigation. Yet while antibodies have been successful as antagonists, immune mediators, and targeting agents, they are not readily effective at recapitulating the biology of natural ligands. Among the important determinants of antibody agonist activity is the geometry of target receptor engagement. Here, we describe an engineering approach inspired by a naturally occurring Fab-Fab homotypic interaction that constrains IgG in a unique i-shaped conformation. i-shaped antibody (iAb) engineering enables potent intrinsic agonism of five tumor necrosis factor receptor superfamily (TNFRSF) targets. When applied to bispecific antibodies against the heterodimeric IL-2 receptor pair, constrained bispecific IgG formats recapitulate IL-2 agonist activity. iAb engineering provides a tool to tune agonist antibody function and this work provides a framework for the development of intrinsic antibody agonists with the potential for generalization across broad receptor classes.

Anti-PD-L1-Based Bispecific Antibodies Targeting Co-Inhibitory and Co-Stimulatory Molecules for Cancer Immunotherapy

Targeting PD-L1 via monospecific antibodies has shown durable clinical benefits and long-term remissions where patients exhibit no clinical cancer signs for many years after treatment. However, the durable clinical benefits and long-term remissions by anti-PD-L1 monotherapy have been limited to a small fraction of patients with certain cancer types. Targeting PD-L1 via bispecific antibodies (referred to as anti-PD-L1-based bsAbs) which can simultaneously bind to both co-inhibitory and co-stimulatory molecules may increase the durable antitumor responses in patients who would not benefit from PD-L1 monotherapy. A growing number of anti-PD-L1-based bsAbs have been developed to fight against this deadly disease. This review summarizes recent advances of anti-PD-L1-based bsAbs for cancer immunotherapy in patents and literatures, and discusses their anti-tumor efficacies in vitro and in vivo. Over 50 anti-PD-L1-based bsAbs targeting both co-inhibitory and co-stimulatory molecules have been investigated in biological testing or in clinical trials since 2017. At least eleven proteins, such as CTLA-4, LAG-3, PD-1, PD-L2, TIM-3, TIGIT, CD28, CD27, OX40, CD137, and ICOS, are involved in these investigations. Twenty-two anti-PD-L1-based bsAbs are being evaluated to treat various advanced cancers in clinical trials, wherein the indications include NSCLC, SNSCLC, SCLC, PDA, MBNHL, SCCHN, UC, EC, TNBC, CC, and some other malignancies. The released data from clinical trials indicated that most of the anti-PD-L1-based bsAbs were well-tolerated and showed promising antitumor efficacy in patients with advanced solid tumors. However, since the approved and investigational bsAbs have shown much more significant adverse reactions compared to PD-L1 monospecific antibodies, anti-PD-L1-based bsAbs may be further optimized via molecular structure modification to avoid or reduce these adverse reactions.

Promising Diagnostic and Therapeutic Approaches Based on VHHs for Cancer Management

The discovery of the distinctive structure of heavy chain-only antibodies in species belonging to the Camelidae family has elicited significant interest in their variable antigen binding domain (VHH) and gained attention for various applications, such as cancer diagnosis and treatment. This article presents an overview of the characteristics, advantages, and disadvantages of VHHs as compared to conventional antibodies, and their usage in diverse applications. The singular properties of VHHs are explained, and several strategies that can augment their utility are outlined. The preclinical studies illustrating the diagnostic and therapeutic efficacy of distinct VHHs in diverse formats against solid cancers are summarized, and an overview of the clinical trials assessing VHH-based agents in oncology is provided. These investigations demonstrate the enormous potential of VHHs for medical research and healthcare.

A novel single domain bispecific antibody targeting VEGF and TNF-α ameliorates rheumatoid arthritis

Anti-TNF-α therapy fails in 30% of patients, where TNF-α may not be the key causative factor in these patients. We developed a bispecific single-domain antibody block TNF-α and VEGF (V5-3).The experiments showed that V5-3 effectively activated proliferation and migration of RA-FLS and HUVEC, tube-forming role of HUVEC, and expression of inflammatory factors in vitro. Besides, the experiments indicated that the anti-RA activity of V5-3 was superior to Anbainuo in vivo. Application of V5-3 reduced the expression of inflammatory factors, extent of synovial inflammation and angiogenesis and attenuated the severity of autoimmune arthritis in collagen-induced arthritis (CIA) mice. Mechanistically, V5-3 suppressed p65, AKT and VEGFR2 phosphorylation, as well as production of TNF-α and VEGF in joint tissues. These results demonstrated that V5-3 displayed a superior effect of anti-RA, may be a new therapy to overcome the limitations of anti-TNF-α monoclonal antibody.

Small Antibodies with Big Applications: Nanobody-Based Cancer Diagnostics and Therapeutics

Monoclonal antibodies (mAbs) have exhibited substantial potential as targeted therapeutics in cancer treatment due to their precise antigen-binding specificity. Despite their success in tumor-targeted therapies, their effectiveness is hindered by their large size and limited tissue permeability. Camelid-derived single-domain antibodies, also known as nanobodies, represent the smallest naturally occurring antibody fragments. Nanobodies offer distinct advantages over traditional mAbs, including their smaller size, high stability, lower manufacturing costs, and deeper tissue penetration capabilities. They have demonstrated significant roles as both diagnostic and therapeutic tools in cancer research and are also considered as the next generation of antibody drugs. In this review, our objective is to provide readers with insights into the development and various applications of nanobodies in the field of cancer treatment, along with an exploration of the challenges and strategies for their prospective clinical trials.

Design and selection of anti-PD-L1 single-domain antibody and tumor necrosis factor superfamily ligands for an optimal vectorization in an oncolytic virus

Arming oncolytic viruses with transgenes encoding immunomodulators improves their therapeutic efficacy by enhancing and/or sustaining the innate and adaptive anti-tumoral immune responses. We report here the isolation, selection, and vectorization of a blocking anti-human PDL1 single-domain antibody (sdAb) isolated from PDL1-immunized alpacas. Several formats of this sdAb were vectorized into the vaccinia virus (VV) and evaluated for their programmed cell death protein 1 (PD1)/PD1 ligand (PDL1) blocking activity in the culture medium of tumor cells infected in vitro. In those conditions, VV-encoded homodimeric sdAb generated superior PDL1 blocking activity compared to a benchmark virus encoding full-length avelumab. The sdAb was further used to design simple, secreted, and small tumor necrosis factor superfamily (TNFSF) fusions with the ability to engage their cognate receptors (TNFRSF) only in the presence of PDL1-positive cells. Finally, PDL1-independent alternatives of TNFRSF agonists were also constructed by fusing different variants of surfactant protein-D (SP-D) oligomerization domains with TNFSF ectodomains. An optimal SP-D-CD40L fusion with an SP-D collagen domain reduced by 80% was identified by screening with a transfection/infection method where poxvirus transfer plasmids and vaccinia virus were successively introduced into the same cell. However, once vectorized in VV, this construct had a much lower CD40 agonist activity compared to the SP-D-CD40L construct, which is completely devoid of the collagen domain that was finally selected. This latest result highlights the importance of working with recombinant viruses early in the payload selection process. Altogether, these results bring several complementary solutions to arm oncolytic vectors with powerful immunomodulators to improve their immune-based anti-tumoral activity.

Single domain Camelid antibody fragments for molecular imaging and therapy of cancer

Despite innovations in cancer therapeutics, cancer remains associated with high mortality and is one of biggest health challenges worldwide. Therefore, developing precise cancer imaging and effective treatments is an unmet clinical need. A relatively novel type of therapeutics are heavy chain variable domain antibody fragments (VHHs) derived from llamas. Here, we explored the suitability of VHHs for cancer imaging and therapy through reviewing the existing literature. We searched the MEDLINE, EMBASE and Cochrane databases and identified 32 papers on molecular imaging and 41 papers on therapy that were suitable for comprehensive reviewing. We found that VHHs harbor a higher specificity and affinity compared to mAbs, which contributes to high-quality imaging and less side-effects on healthy cells. The employment of VHHs in cancer imaging showed remarkably shorter times between administration and imaging. Studies showed that 18F and 99mTc are two optimal radionuclides for imaging with VHHs and that site-specific labelling is the optimal conjugation modality for VHHs with radionuclide or fluorescent molecules. We found different solutions for reducing kidney retention and immunogenicity of VHHs. VHHs as anticancer therapeutics have been tested in photodynamic therapy, targeted radionuclide therapy, immunotherapy and molecular targeted therapy. These studies showed that VHHs target unique antigen epitopes, which are distinct from the ones recognized by mAbs. This advantage means that VHHs may be more effective for targeted anticancer therapy and can be combined with mAbs. We found that high cellular internalization and specificity of VHHs contributes to the effectiveness and safety of VHHs as anticancer therapeutics. Two clinical trials have confirmed that VHHs are effective and safe for cancer imaging and therapy. Together, VHHs seem to harbor several advantages compared to mAbs and show potential for application in personalized treatment for cancer patients. VHH-based imaging and therapy are promising options for improving outcomes of cancer patients.

4-1BB Targeting Immunotherapy: Mechanism, Antibodies, and Chimeric Antigen Receptor T

4-1BB (CD137, TNFRSF9) is a type I transmembrane protein which binds its natural ligand, 4-1BBL. This interaction has been exploited to improve cancer immunotherapy. With ligand binding by 4-1BB, the nuclear factor-kappa B signaling pathway is activated, which results in transcription of corresponding genes such as interleukin-2 and interferon-γ, as well as the induction of T cell proliferation and antiapoptotic signals. Moreover, monoclonal antibodies that target-4-1BB, for example, Urelumab and Utomilumab, are widely used in the treatments of B cell non-Hodgkin lymphoma, lung cancer, breast cancer, soft tissue sarcoma, and other solid tumors. Furthermore, 4-1BB as a costimulatory domain, for chimeric antigen receptor T (CAR-T) cells, improves T cell proliferation and survival as well as reduces T cell exhaustion. As such, a deeper understanding of 4-1BB will contribute to improvements in cancer immunotherapy. This review provides a comprehensive analysis of current 4-1BB studies, with a focus on the use of targeting-4-1BB antibodies and 4-1BB activation domains in CAR-T cells for the treatment of cancer.

Checkpoint blockade meets gene therapy: Opportunities to improve response and reduce toxicity

Immune checkpoint inhibitors (ICIs) based on monoclonal antibodies represent a breakthrough for the treatment of cancer. However, their efficacy varies among tumor types and patients, and they can lead to adverse effects due to on-target/off-tumor activity, since they are administered systemically at high doses. An alternative and attractive approach for the delivery of ICIs is the use of gene therapy vectors able to express them in vivo. This review focuses on the most recent studies using viral vectors able to express ICIs locally or systemically in preclinical models of cancer. These vectors include non-replicating viruses, oncolytic viruses able to propagate specifically in tumor cells and destroy them, and self-amplifying RNA vectors, armed with different formats of antibodies against immune checkpoints. Non-replicating vectors usually lead to long-term ICI expression, potentially eliminating the need for repeated administration. Vectors with replication capacity, although they have a shorter window of expression, can induce inflammation which enhances the antitumor effect. Finally, these engineered vectors can be used in combination with other immunostimulatory molecules or with CAR-T cells, further boosting the antitumor immune responses.

A bispecific antibody AP203 targeting PD-L1 and CD137 exerts potent antitumor activity without toxicity

BACKGROUND

Bispecific antibody has garnered considerable attention in the recent years due to its impressive preliminary efficacy in hematological malignancies. For solid tumors, however, the main hindrance is the suppressive tumor microenvironment, which effectively impedes the activation of infiltrating T cells. Herein, we designed a bispecific antibody AP203 with high binding affinity to PD-L1 and CD137 and assessed its safety and anti-tumor efficacy, as well as explored the mechanism of action.

METHODS

The optimal antibody binders against PD-L1 and CD137 were screened from the OmniMab phagemid library. The binding affinity of the constructed AP203 were evaluated using enzyme-linked immunosorbent assay (ELISA) and biolayer interferometry (BLI). T-cell stimulatory capacity was assessed using the allogeneic mixed lymphocyte reaction (MLR), antigen-specific recall response, and coculture with PD-L1-expressing cells. In vivo antitumor efficacy was evaluated using two models of tumor-xenografted humanized mice with profiling of tumor infiltrating lymphocytes (TILs). The possible toxicity of AP203 was examined using in vitro cytokine release assay by human PBMCs.

RESULTS

AP203, which simultaneously targeted PD-L1 and costimulatory CD137, elicit superior agonistic effects over parental antibodies alone or in combination in terms of T cell activation, enhanced memory recall responses, and overcoming Treg-mediated immunosuppression (P < 0.05). The agonistic activity of AP203 was further demonstrated PD-L1-dependent by coculturing T cells with PD-L1-expressing cells. In vivo animal studies using immunodeficient or immunocompetent mice both showed a dose-related antitumor efficacy superior to parental antibodies in combination (P < 0.05). Correspondingly, AP203 significantly increased tumor infiltrating CD8 + T cells, while decreased CD4 + T cells, as well as Treg cells (P < 0.05), resulting in a dose-dependent increase in the CD8 + /CD4 + ratio. Moreover, either soluble or immobilized AP203 did not induce the production of inflammatory cytokines by human PBMCs.

CONCLUSIONS

AP203 exerts potent antitumor activity not only by blocking PD-1/PD-L1 inhibitory signaling, but also by activating CD137 costimulatory signaling in effector T cells that consequently counteracts Treg-mediated immunosuppression. Based on promising preclinical results, AP203 should be a suitable candidate for clinical treatment of solid tumors.

Inside PD-1/PD-L1,2 with their inhibitors

This review summarizes current knowledge in the development of immune checkpoint inhibitors, including antibodies and small molecules.

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.

RASGRP2 is a potential immune-related biomarker and regulates mitochondrial-dependent apoptosis in lung adenocarcinoma

BACKGROUND

Ras guanine nucleotide-releasing protein 2 (RASGRP2), one of the guanine nucleotide exchange factors (GEFs), has attracted much attention in recent years. However, the correlation between RASGRP2 and immune infiltration and malignant features in lung adenocarcinoma (LUAD) has rarely been mentioned.

METHODS

The Limma package and the LASSO regression model were performed to screen for differentially expressed genes. Data from the TCGA and 5 GEO databases were used to explore the expression level of RASGRP2 in LUAD patients. A weighted co-expression network and LinkFinder module were established to find the related genes of RASGRP2. The ESTIMATE algorithm was used to analyze the correlation between RASGRP2 and immune infiltration in LUAD. Tumor-infiltrating immune cells were sorted and sequenced at the single-cell level to analyze differences in RASGRP2. Real-time PCR and immunohistochemistry were performed in the real-world cohort to verify the expression of RASGRP2 and its correlation with immune-related genes. Clone formation and EdU assays were used to verify the proliferation ability. The proportion of apoptotic cells was analyzed by flow cytometry. Observation of mitochondrial membrane potential (MMP) changes by fluorescence microscopy.

RESULTS

Our results suggested that decreased RASGRP2 was associated with worse clinical parameters and prognosis in LUAD patients. And we constructed a FLI1-HSA-miR-1976-RASGRP2 transcriptional network to support the role of RASGRP2. Enrichment analysis revealed that RASGRP2 was involved in lymphocyte activation and leukocyte adhesion. RASGRP2 was found to be positively correlated with the infiltration of most immune cells, immunoregulators, and chemokines in a subsequent study. Meanwhile, the real-world cohort confirmed that the expression levels of PDCD1, CTLA4, CD40LG, CCL14, CXCR5, and CCR7 were higher in the high-RASGRP2 expression group. Cytological experiments proved that RASGRP2 inhibited cell proliferation in LUAD by regulating mitochondrial-dependent apoptosis.

CONCLUSION

RASGRP2 was a potential immune-related biomarker of LUAD. In addition, RASGRP2 was involved in the malignant progression of LUAD through the regulation of mitochondrial-dependent apoptosis.

Nanobodies in cell-mediated immunotherapy: On the road to fight cancer

The immune system is essential in recognizing and eliminating tumor cells. The unique characteristics of the tumor microenvironment (TME), such as heterogeneity, reduced blood flow, hypoxia, and acidity, can reduce the efficacy of cell-mediated immunity. The primary goal of cancer immunotherapy is to modify the immune cells or the TME to enable the immune system to eliminate malignancies successfully. Nanobodies, known as single-domain antibodies, are light chain-free antibody fragments produced from Camelidae antibodies. The unique properties of nanobodies, including high stability, reduced immunogenicity, enhanced infiltration into the TME of solid tumors and facile genetic engineering have led to their promising application in cell-mediated immunotherapy. They can promote the cancer therapy either directly by bridging between tumor cells and immune cells and by targeting cancer cells using immune cell-bound nanobodies or indirectly by blocking the inhibitory ligands/receptors. The T-cell activation can be engaged through anti-CD3 and anti-4-1BB nanobodies in the bispecific (bispecific T-cell engagers (BiTEs)) and trispecific (trispecific T-cell engager (TriTEs)) manners. Also, nanobodies can be used as natural killer (NK) cell engagers (BiKEs, TriKEs, and TetraKEs) to create an immune synapse between the tumor and NK cells. Nanobodies can redirect immune cells to attack tumor cells through a chimeric antigen receptor (CAR) incorporating a nanobody against the target antigen. Various cancer antigens have been targeted by nanobody-based CAR-T and CAR-NK cells for treating both hematological and solid malignancies. They can also cause the continuation of immune surveillance against tumor cells by stopping inappropriate inhibition of immune checkpoints. Other roles of nanobodies in cell-mediated cancer immunotherapy include reprogramming macrophages to reduce metastasis and angiogenesis, as well as preventing the severe side effects occurring in cell-mediated immunotherapy. Here, we highlight the critical functions of various immune cells, including T cells, NK cells, and macrophages in the TME, and discuss newly developed immunotherapy methods based on the targeted manipulation of immune cells and TME with nanobodies.

The emerging landscape of novel 4-1BB (CD137) agonistic drugs for cancer immunotherapy

The clinical development of 4-1BB agonists for cancer immunotherapy has raised substantial interest during the past decade. The first generation of 4-1BB agonistic antibodies entering the clinic, urelumab (BMS-663513) and utomilumab (PF-05082566), failed due to (liver) toxicity or lack of efficacy, respectively. The two antibodies display differences in the affinity and the 4-1BB receptor epitope recognition, as well as the isotype, which determines the Fc-gamma-receptor (FcγR) crosslinking activity. Based on this experience a very diverse landscape of second-generation 4-1BB agonists addressing the liabilities of first-generation agonists has recently been developed, with many entering clinical Phase 1 and 2 studies. This review provides an overview focusing on differences and their scientific rationale, as well as challenges foreseen during the clinical development of these molecules.

Identification, binding, and structural characterization of single domain anti-PD-L1 antibodies inhibitory of immune regulatory proteins PD-1 and CD80

Programmed death-ligand 1 (PD-L1) is a key immune regulatory protein that interacts with programmed cell death protein 1 (PD-1), leading to T-cell suppression. Whilst this interaction is key in self-tolerance, cancer cells evade the immune system by overexpressing PD-L1. Inhibition of the PD-1/PD-L1 pathway with standard monoclonal antibodies has proven a highly effective cancer treatment; however, single domain antibodies (VHH) may offer numerous potential benefits. Here, we report the identification and characterization of a diverse panel of 16 novel VHHs specific to PD-L1. The panel of VHHs demonstrate affinities of 0.7 nM to 5.1 μM and were able to completely inhibit PD-1 binding to PD-L1. The binding site for each VHH on PD-L1 was determined using NMR chemical shift perturbation mapping and revealed a common binding surface encompassing the PD-1-binding site. Additionally, we solved crystal structures of two representative VHHs in complex with PD-L1, which revealed unique binding modes. Similar NMR experiments were used to identify the binding site of CD80 on PD-L1, which is another immune response regulatory element and interacts with PD-L1 localized on the same cell surface. CD80 and PD-1 were revealed to share a highly overlapping binding site on PD-L1, with the panel of VHHs identified expected to inhibit CD80 binding. Comparison of the CD80 and PD-1 binding sites on PD-L1 enabled the identification of a potential antibody binding region able to confer specificity for the inhibition of PD-1 binding only, which may offer therapeutic benefits to counteract cancer cell evasion of the immune system.

Development of therapeutic antibodies for the treatment of diseases

Since the first monoclonal antibody drug, muromonab-CD3, was approved for marketing in 1986, 165 antibody drugs have been approved or are under regulatory review worldwide. With the approval of new drugs for treating a wide range of diseases, including cancer and autoimmune and metabolic disorders, the therapeutic antibody drug market has experienced explosive growth. Monoclonal antibodies have been sought after by many biopharmaceutical companies and scientific research institutes due to their high specificity, strong targeting abilities, low toxicity, side effects, and high development success rate. The related industries and markets are growing rapidly, and therapeutic antibodies are one of the most important research and development areas in the field of biology and medicine. In recent years, great progress has been made in the key technologies and theoretical innovations provided by therapeutic antibodies, including antibody-drug conjugates, antibody-conjugated nuclides, bispecific antibodies, nanobodies, and other antibody analogs. Additionally, therapeutic antibodies can be combined with technologies used in other fields to create new cross-fields, such as chimeric antigen receptor T cells (CAR-T), CAR-natural killer cells (CAR-NK), and other cell therapy. This review summarizes the latest approved or in regulatory review therapeutic antibodies that have been approved or that are under regulatory review worldwide, as well as clinical research on these approaches and their development, and outlines antibody discovery strategies that have emerged during the development of therapeutic antibodies, such as hybridoma technology, phage display, preparation of fully human antibody from transgenic mice, single B-cell antibody technology, and artificial intelligence-assisted antibody discovery.

Current landscape and future directions of bispecific antibodies in cancer immunotherapy

Recent advances in cancer immunotherapy using monoclonal antibodies have dramatically revolutionized the therapeutic strategy against advanced malignancies, inspiring the exploration of various types of therapeutic antibodies. Bispecific antibodies (BsAbs) are recombinant molecules containing two different antigens or epitopes identifying binding domains. Bispecific antibody-based tumor immunotherapy has gained broad potential in preclinical and clinical investigations in a variety of tumor types following regulatory approval of newly developed technologies involving bispecific and multispecific antibodies. Meanwhile, a series of challenges such as antibody immunogenicity, tumor heterogeneity, low response rate, treatment resistance, and systemic adverse effects hinder the application of BsAbs. In this review, we provide insights into the various architecture of BsAbs, focus on BsAbs' alternative different mechanisms of action and clinical progression, and discuss relevant approaches to overcome existing challenges in BsAbs clinical application.

Engineering of a trispecific tumor-targeted immunotherapy incorporating 4-1BB co-stimulation and PD-L1 blockade

Co-stimulatory 4-1BB receptors on tumor-infiltrating T cells are a compelling target for overcoming resistance to immune checkpoint inhibitors, but initial clinical studies of 4-1BB agonist mAbs were accompanied by liver toxicity. We sought to engineer a tri-specific antibody-based molecule that stimulates intratumoral 4-1BB and blocks PD-L1/PD-1 signaling without systemic toxicity and with clinically favorable pharmacokinetics. Recombinant fusion proteins were constructed using scMATCH3 technology and humanized antibody single-chain variable fragments against PD-L1, 4-1BB, and human serum albumin. Paratope affinities were optimized using single amino acid substitutions, leading to design of the drug candidate NM21-1480. Multiple in vitro experiments evaluated pharmacodynamic properties of NM21-1480, and syngeneic mouse tumor models assessed antitumor efficacy and safety of murine analogues. A GLP multiple-dose toxicology study evaluated its safety in non-human primates. NM21-1480 inhibited PD-L1/PD-1 signaling with a potency similar to avelumab, and it potently stimulated 4-1BB signaling only in the presence of PD-L1, while exhibiting an EC₅₀ that was largely independent of PD-L1 density. NM21-1480 exhibited high efficacy for co-activation of pre-stimulated T cells and dendritic cells. In xenograft models in syngeneic mice, NM21-1480 induced tumor regression and tumor infiltration of T cells without causing systemic T-cell activation. A GLP toxicology study revealed no evidence of liver toxicity at doses up to 140 mg/kg, and pharmacokinetic studies in non-human primates suggested a plasma half-life in humans of up to 2 weeks. NM21-1480 has the potential to overcome checkpoint resistance by co-activating tumor-infiltrating lymphocytes without liver toxicity.

Emerging applications of nanobodies in cancer therapy

Cancer is a heterogeneous disease, requiring treatment tailored to the unique phenotype of the patient's tumor. Monoclonal antibodies (mAbs) and variants thereof have enabled targeted therapies to selectively target cancer cells. Cancer cell-specific mAbs have been used for image-guided surgery and targeted delivery of radionuclides or toxic agents, improving classical treatment strategies. Cancer cell-specific mAbs can further inhibit tumor cell growth or can stimulate immune-mediated destruction of cancer cells, a feature that has also been achieved through mAb-mediated manipulation of immune cells and pathways. Drawbacks of mAbs and their variants, together with the discovery of camelid heavy chain-only antibodies and the many advantageous features of their variable domains, referred to as V_HHs, single domain antibodies or nanobodies (Nbs), resulted in the exploration of Nbs as an alternative targeting moiety. We therefore review the state-of-the-art as well as novel exploitation strategies of Nbs for targeted cancer therapy.

Preclinical Characterization and Phase I Trial Results of a Bispecific Antibody Targeting PD-L1 and 4-1BB (GEN1046) in Patients with Advanced Refractory Solid Tumors

Checkpoint inhibitors (CPI) have revolutionized the treatment paradigm for advanced solid tumors; however, there remains an opportunity to improve response rates and outcomes. In preclinical models, 4-1BB costimulation synergizes with CPIs targeting the programmed cell death protein 1 (PD-1)/programmed cell death ligand 1 (PD-L1) axis by activating cytotoxic T-cell-mediated antitumor immunity. DuoBody-PD-L1×4-1BB (GEN1046) is an investigational, first-in-class bispecific immunotherapy agent designed to act on both pathways by combining simultaneous and complementary PD-L1 blockade and conditional 4-1BB stimulation in one molecule. GEN1046 induced T-cell proliferation, cytokine production, and antigen-specific T-cell-mediated cytotoxicity superior to clinically approved PD-(L)1 antibodies in human T-cell cultures and exerted potent antitumor activity in transplantable mouse tumor models. In dose escalation of the ongoing first-in-human study in heavily pretreated patients with advanced refractory solid tumors (NCT03917381), GEN1046 demonstrated pharmacodynamic immune effects in peripheral blood consistent with its mechanism of action, manageable safety, and early clinical activity [disease control rate: 65.6% (40/61)], including patients resistant to prior PD-(L)1 immunotherapy.

SIGNIFICANCE

DuoBody-PD-L1×4-1BB (GEN1046) is a first-in-class bispecific immunotherapy with a manageable safety profile and encouraging preclinical and early clinical activity. With its ability to confer clinical benefit in tumors typically less sensitive to CPIs, GEN1046 may fill a clinical gap in CPI-relapsed or refractory disease or as a combination therapy with CPIs. See related commentary by Li et al., p. 1184. This article is highlighted in the In This Issue feature, p. 1171.

VHH Structural Modelling Approaches: A Critical Review

VHH, i.e., VH domains of camelid single-chain antibodies, are very promising therapeutic agents due to their significant physicochemical advantages compared to classical mammalian antibodies. The number of experimentally solved VHH structures has significantly improved recently, which is of great help, because it offers the ability to directly work on 3D structures to humanise or improve them. Unfortunately, most VHHs do not have 3D structures. Thus, it is essential to find alternative ways to get structural information. The methods of structure prediction from the primary amino acid sequence appear essential to bypass this limitation. This review presents the most extensive overview of structure prediction methods applied for the 3D modelling of a given VHH sequence (a total of 21). Besides the historical overview, it aims at showing how model software programs have been shaping the structural predictions of VHHs. A brief explanation of each methodology is supplied, and pertinent examples of their usage are provided. Finally, we present a structure prediction case study of a recently solved VHH structure. According to some recent studies and the present analysis, AlphaFold 2 and NanoNet appear to be the best tools to predict a structural model of VHH from its sequence.

An Fc-inert PD-L1×4-1BB bispecific antibody mediates potent anti-tumor immunity in mice by combining checkpoint inhibition and conditional 4-1BB co-stimulation

Immune checkpoint inhibitors (ICI) targeting the PD-1/PD-L1 axis have changed the treatment paradigm for advanced solid tumors; however, many patients experience treatment resistance. In preclinical models 4-1BB co-stimulation synergizes with ICI by activating cytotoxic T- and NK-cell-mediated anti-tumor immunity. Here we characterize the mechanism of action of a mouse-reactive Fc-inert PD-L1×4-1BB bispecific antibody (mbsAb-PD-L1×4-1BB) and provide proof-of-concept for enhanced anti-tumor activity. In reporter assays mbsAb-PD-L1×4-1BB exhibited conditional 4-1BB agonist activity that was dependent on simultaneous binding to PD-L1. mbsAb-PD-L1×4-1BB further blocked the PD-L1/PD-1 interaction independently of 4-1BB binding. By combining both mechanisms, mbsAb-PD-L1×4-1BB strongly enhanced T-cell proliferation, cytokine production and antigen-specific cytotoxicity using primary mouse cells in vitro. Furthermore, mbsAb-PD-L1×4-1BB exhibited potent anti-tumor activity in the CT26 and MC38 models in vivo, leading to the rejection of CT26 tumors that were unresponsive to PD-L1 blockade alone. Anti-tumor activity was associated with increased tumor-specific CD8⁺ T cells and reduced regulatory T cells within the tumor microenvironment and tumor-draining lymph nodes. In immunocompetent tumor-free mice, mbsAb-PD-L1×4-1BB treatment neither induced T-cell infiltration into the liver nor elevated liver enzymes in the blood. Dual targeting of PD-L1 and 4-1BB with a bispecific antibody may therefore address key limitations of first generation 4-1BB-agonistic antibodies, and may provide a novel approach to improve PD-1/PD-L1 checkpoint blockade.