Optimization strategies for expression of a novel bifunctional anti-PD-L1/TGFBR2-ECD fusion protein

Dual anti-PD-(L)1/TGF-β inhibitors in cancer immunotherapy - Updated

Immune checkpoint inhibitor (ICI) therapy suffers from tumor resistance and relapse in majority of patients due to the suppressive tumor immune microenvironment (TIME). Advances in the field have brought about development of fusion proteins able to target two signaling simultaneously and to exert maximal anti-cancer immunity. Bispecific inhibitors of transforming growth factor (TGF)-β signaling and programmed death-1 (PD-1) or programmed death-ligand 1 (PD-L1) are developed to reduce the rate of relapse and to achieve durable anti-cancer therapy. TGF-β is well-known for its immunosuppressive activity, and it takes critical roles in promotion of all tumor hallmarks. Bispecific anti-PD-(L)1/TGF-β inhibitors reinvigorate effector activity of CD8+ T and natural killer (NK) cells, hamper regulatory T cell (Treg) expansion, and increase the density of anti-tumor type 1 macrophages (M1). Responses to the bispecific approach are higher compared with solo anti-PD-(L)1 or TGF-β targeted therapy, and are seemingly more pronounced in human papillomavirus (HPV)+ patients. High expression of PD-L1 or immune-excluded phenotype in a tumor can also be markers of better response to the bispecific strategy. Besides, anti-PD-(L)1/TGF-β inhibitor therapy can be used safely with other therapeutic modalities including vaccination, radiation and chemotherapy.

Construction of a Matrix Cancer-Associated Fibroblast Signature Gene-Based Risk Prognostic Signature for Directing Immunotherapy in Patients with Breast Cancer Using Single-Cell Analysis and Machine Learning

Cancer-associated fibroblasts (CAFs) are heterogeneous constituents of the tumor microenvironment involved in the tumorigenesis, progression, and therapeutic responses of tumors. This study identified four distinct CAF subtypes of breast cancer (BRCA) using single-cell RNA sequencing (RNA-seq) data. Of these, matrix CAFs (mCAFs) were significantly associated with tumor matrix remodeling and strongly correlated with the transforming growth factor (TGF)-β signaling pathway. Consensus clustering of The Cancer Genome Atlas (TCGA) BRCA dataset using mCAF single-cell characteristic gene signatures segregated samples into high-fibrotic and low-fibrotic groups. Patients in the high-fibrotic group exhibited a significantly poor prognosis. A weighted gene co-expression network analysis and univariate Cox analysis of bulk RNA-seq data revealed 17 differential genes with prognostic values. The mCAF risk prognosis signature (mRPS) was developed using 10 machine learning algorithms. The clinical outcome predictive accuracy of the mRPS was higher than that of the conventional TNM staging system. mRPS was correlated with the infiltration level of anti-tumor effector immune cells. Based on consensus prognostic genes, BRCA samples were classified into the following two subtypes using six machine learning algorithms (accuracy > 90%): interferon (IFN)-γ-dominant (immune C2) and TGF-β-dominant (immune C6) subtypes. Patients with mRPS downregulation were associated with improved prognosis, suggesting that they can potentially benefit from immunotherapy. Thus, the mRPS model can stably predict BRCA prognosis, reflect the local immune status of the tumor, and aid clinical decisions on tumor immunotherapy.

A novel monospecific tetravalent IgG1-(scFv)2 version shown enhanced neutralizing and Fc-mediated effector functions against SARS-CoV-2

Neutralizing monoclonal antibodies (nMABs) have been proved to be effective therapeutics in treating coronavirus disease (COVID-19). To enhance the potency of nMAB 553-15, we generated a novel monospecific tetravalent IgG1-(scFv)2 version. This was achieved by covalently fusing two forms of 553-15-derived single chain variable fragments (scFv) to the C-terminus of the hIgG1 (human Immunoglobulin G1) Fc fragment. We found that the Fc-fused VL-linker-VH format achieved similar binding affinity and neutralizing behavior as 553-15. The tetravalent versions were constructed by fusing the scFv domains to the C-terminus of nMAB 553-15. As a result, the tetravalent version 55,315-VLVH exhibited significantly higher binding activity to target spike protein variants and enhanced neutralization against VOCs (variants of concern) pseudovirus compared to 553-15. We also measured the Fc effector responses of candidates using wild-type Spike-expressing CHOK1 cells. The 55,315-VLVH enhanced the function of ADCP (antibody-dependent cellular phagocytosis) but had similar IL-6 release levels compared to the bivalent 553-15. It seemed that the novel tetravalent version avoids the pro-inflammatory effect induced by macrophage activation. However, the 55,315-VLVH displayed slightly increased potency in ADCC (antibody-dependent cell-mediated cytotoxicity) and CDC (complement-dependent cytotoxicity), which might contribute to higher systemic inflammation. Further investigation is necessary to determine whether the tetravalent version is beneficial to balance efficiency and safety against COVID-19.

Bispecific antibody targeting TGF-β and PD-L1 for synergistic cancer immunotherapy

The PD-1/PD-L1 signaling pathway plays a crucial role in cancer immune evasion, and the use of anti-PD-1/PD-L1 antibodies represents a significant milestone in cancer immunotherapy. However, the low response rate observed in unselected patients and the development of therapeutic resistance remain major obstacles to their clinical application. Accumulating studies showed that overexpressed TGF-β is another immunosuppressive factor apart from traditional immune checkpoints. Actually, the effects of PD-1 and TGF-β pathways are independent and interactive, which work together contributing to the immune evasion of cancer cell. It has been verified that blocking TGF-β and PD-L1 simultaneously could enhance the efficacy of PD-L1 monoclonal antibody and overcome its treatment resistance. Based on the bispecific antibody or fusion protein technology, multiple bispecific and bifunctional antibodies have been developed. In the preclinical and clinical studies, these updated antibodies exhibited potent anti-tumor activity, superior to anti-PD-1/PD-L1 monotherapies. In the review, we summarized the advances of bispecific antibodies targeting TGF-β and PD-L1 in cancer immunotherapy. We believe these next-generation immune checkpoint inhibitors would substantially alter the cancer treatment paradigm, especially in anti-PD-1/PD-L1-resistant patients.

Next-generation immunotherapy for solid tumors: combination immunotherapy with crosstalk blockade of TGFβ and PD-1/PD-L1

INTRODUCTION

In solid tumor immunotherapy, less than 20% of patients respond to anti-programmed cell death 1 (PD-1)/programmed cell death 1 ligand 1 (PD-L1) agents. The role of transforming growth factor β (TGFβ) in diverse immunity is well-established; however, systemic blockade of TGFβ is associated with toxicity. Accumulating evidence suggests the role of crosstalk between TGFβ and PD-1/PD-L1 pathways.

AREAS COVERED

We focus on TGFβ and PD-1/PD-L1 signaling pathway crosstalk and the determinant role of TGFβ in the resistance of immune checkpoint blockade. We provide the rationale for combination anti-TGFβ and anti-PD-1/PD-L1 therapies for solid tumors and discuss the current status of dual blockade therapy in preclinical and clinical studies.

EXPERT OPINION

The heterogeneity of tumor microenvironment across solid tumors complicates patient selection, treatment regimens, and response and toxicity assessment for investigation of dual blockade agents. However, clinical knowledge from single-agent studies provides infrastructure to translate dual blockade therapies. Dual TGFβ and PD-1/PD-L1 blockade results in enhanced T-cell infiltration into tumors, a primary requisite for successful immunotherapy. A bifunctional fusion protein specifically targets TGFβ in the tumor microenvironment, avoiding systemic toxicity, and prevents interaction of PD-1+ cytotoxic cells with PD-L1+ tumor cells.

Development of the Novel Bifunctional Fusion Protein BR102 That Simultaneously Targets PD-L1 and TGF-β for Anticancer Immunotherapy

Simple Summary

Immune checkpoint inhibitors (ICIs), such as anti-PD-1/PD-L1 antibodies, have revolutionized the therapy landscape of cancer immunotherapy. However, poor clinical response to ICIs and drug resistance are the main challenges for ICIs immunotherapy. TGF-β produced in the TME was found to confer resistance to PD-1/PD-L1-targeted immunotherapy. The independent and complementary immunosuppressive role of PD-L1 and TGF-β in cancer progression provides a rationale for simultaneously targeting TGF-β and PD-L1 to improve anti-PD-L1 therapy. Consequently, we develop and characterize a novel anti-PD-L1/TGF-β bifunctional fusion protein termed BR102. The data suggest that BR102 could simultaneously disrupt TGF-β- and PD-L1-mediated signals and display high antitumor efficacy and safety. The data support further clinical advancement of BR102 as a promising approach to cancer immunotherapy.

Abstract

Immune checkpoint inhibitors (ICIs) are remarkable breakthroughs in treating various types of cancer, but many patients still do not derive long-term clinical benefits. Increasing evidence shows that TGF-β can promote cancer progression and confer resistance to ICI therapies. Consequently, dual blocking of TGF-β and immune checkpoint may provide an effective approach to enhance the effectiveness of ICI therapies. Here, we reported the development and preclinical characterization of a novel bifunctional anti-PD-L1/TGF-β fusion protein, BR102. BR102 comprises an anti-PD-L1 antibody fused to the extracellular domain (ECD) of human TGF-βRII. BR102 is capable of simultaneously binding to TGF-β and PD-L1. Incorporating TGF-βRII into BR102 does not alter the PD-L1 blocking activity of BR102. In vitro characterization further demonstrated that BR102 could disrupt TGF-β-induced signaling. Moreover, BR102 significantly inhibits tumor growth in vivo and exerts a superior antitumor effect compared to anti-PD-L1. Administration of BR102 to cynomolgus monkeys is well-tolerated, with only minimal to moderate and reversing red cell changes noted. The data demonstrated the efficacy and safety of the novel anti-PD-L1/TGF-β fusion protein and supported the further clinical development of BR102 for anticancer therapy.