Protein secretion is an essential process of mammalian cells. In biomanufacturing, this process can be optimized to enhance production yields and biotherapeutic quality. While cell line engineering and bioprocess optimization have yielded high protein titers for some recombinant proteins, many remain difficult to express. Here, we investigated factors influencing protein expression in Chinese hamster ovary (CHO) cells, expressing 2,135 Human Secretome Project proteins. While the abundance of mRNA from recombinant proteins explained less than 1% of observed variation in secretion titers, analysis of 218 biochemical and biophysical descriptors uncovered intrinsic protein features that account for ~15% of secretion variability, pinpointing key drivers such as molecular weight, cysteine content, and N-linked glycosylation, and establishing a roadmap for rational design of difficult-to-express proteins. We subsequently analyzed RNA-Seq data from 95 CHO cell cultures, each expressing a distinct recombinant protein, spanning a wide range of titers. Host cell transcriptomic signatures showed strong correlations with titer, thereby providing insights into cellular processes that covary with expression. Cells failing to produce proteins exhibited increased ubiquitin-mediated proteasomal degradation, including ER-associated degradation; whereas high-producing cells demonstrated enhanced lipid metabolism and a stronger response to oxidative stress, suggesting these factors may support successful recombinant protein productions. Together, using this resource, we quantified the contributions of various protein and cellular factors that correlate with the expression of diverse recombinant human proteins in a heterologous host, thereby providing insights for next-generation CHO cell engineering.

In vitro methods for developing binding domains have been well-established for many years, owing to the cost-efficient synthesis of DNA and high-throughput selection and screening technologies. However, generating high-affinity binding domains often requires the development of focused maturation libraries for a second selection, which typically demands a detailed understanding of the binding surfaces from the initial selection, a process that can be time-consuming. In this study, we accelerated this process by using deep sequencing data from the first selection to guide the design of the maturation library. Additionally, we employed a high-throughput screening system using flow cytometry based on Escherichia coli display to identify conditional binding domains from the selection output. This approach enabled the development of a high-affinity binder targeting the cancer biomarker HER3, with a binding affinity of 3.3 nM at extracellular pH 7.4, 100 times higher than the first-generation binding domain. Notably, the binding domain features a pH-dependent release mechanism, enabling rapid release in slightly acidic environments (pH ≈6), which resemble endosomal conditions. When conjugated to the cytotoxin mertansine (DM1), the binding domain demonstrated specific cytotoxic activity against HER3-expressing cell lines, with an IC50 of 2–5 nM. The presented approach enables the efficient development of conditional binding domains which hold promise for therapeutic applications.

Recombinant adeno-associated virus (rAAV) vectors are widely used in gene therapies, but the rapidly increasing global demand has created a significant challenge for rAAV manufacturing, where production capacity remains a critical bottleneck. To address this, strategies to enhance production yields are urgently needed. This study presents an innovative approach to rAAV production using high cell density (HCD) stirred tank perfusion culture. rAAV1 and rAAV9 vectors carrying GFP cargo were used as models, with triple-plasmid transfection performed in suspension HEK293 cells at a high viable cell density of 50 million cells/mL in culture then maintained at >= 30 million cells/mL throughout production. Transfection and production parameters were first optimized in a 5 mL pseudo-perfusion spin tube screening system at HCD. A proof-of-concept was then demonstrated by scaling up to a 200 mL stirred tank bioreactor (STR) in perfusion mode. This intensified process achieved rAAV9 production levels per cell comparable to those observed in reference shake flask cultures at 1 million cells/mL. By implementing transfection at very HCD in a perfusion-based STR, this approach has the potential to significantly enhance rAAV volumetric production capacity, providing a promising solution to meet the growing demand for gene therapies.

Current antibody-based immunotherapy depends on tumor antigen shedding for proper T cell priming. Here we select a novel human CD40 agonistic drug candidate and generate a bispecific antibody, herein named BiA9*2_HF, that allows for rapid antibody-peptide conjugate formation. The format is designed to facilitate peptide antigen delivery to CD40 expressing cells combined with simultaneous CD40 agonistic activity. In vivo, the selected bispecific antibody BiA9*2_HF loaded with peptide cargos induces improved antigen-specific proliferation of CD8+ (10-15 fold) and CD4+ T cells (2-7 fold) over control in draining lymph nodes. In both virus-induced and neoantigen-based mouse tumor models, BiA9*2_HF demonstrates therapeutic efficacy and elevated safety profile, with complete tumor clearance, as well as measured abscopal impact on tumor growth. The BiA9*2_HF drug candidate can thus be utilized to tailor immunotherapeutics for cancer patients.

Cancer immunotherapy, where a patient's immune system is harnessed to eradicate cancer cells selectively, is a leading strategy for cancer treatment. However, successes with immune checkpoint inhibitors (ICI) are hampered by reported systemic and organ-specific toxicities and by two-thirds of the patients being non-responders or subsequently acquiring resistance to approved ICIs. Hence substantial efforts are invested in discovering novel targeted immunotherapies aimed at reduced side-effects and improved potency. One way is utilizing the dual targeting feature of bispecific antibodies, which have made them increasingly popular for cancer immunotherapy. Easy and predictive screening methods for activation ranking of candidate drugs in tumor contra non-tumor environments are however lacking. Herein, we present a cell-based assay mimicking the tumor microenvironment by co-culturing B cells with engineered human embryonic kidney 293 T cells (HEK293T), presenting a controllable density of platelet-derived growth factor receptor β (PDGFRβ). A target density panel with three different surface protein levels on HEK293T cells was established by genetic constructs carrying regulatory elements limiting RNA translation of PDGFRβ. We employed a bispecific antibody-affibody construct called an AffiMab capable of binding PDGFRβ on cancer cells and CD40 expressed by B cells as a model. Specific activation of CD40-mediated signaling of immune cells was demonstrated with the two highest receptor-expressing cell lines, Level 2/3 and Level 4, while low-to-none in the low-expressing cell lines. The concept of receptor tuning and the presented co-culture protocol may be of general utility for assessing and developing novel bi-specific antibodies for immuno-oncology applications.

Precise epitope determination of therapeutic antibodies is of great value as it allows for further comprehension of mechanism of action, therapeutic responsiveness prediction, avoidance of unwanted cross reactivity, and vaccine design. The golden standard for discontinuous epitope determination is the laborious X-ray crystallography method. Here, we present a combinatorial method for rapid mapping of discontinuous epitopes by mammalian antigen display, eliminating the need for protein expression and purification. The method is facilitated by automated workflows and tailored software for antigen analysis and oligonucleotide design. These oligos are used in automated mutagenesis to generate an antigen receptor library displayed on mammalian cells for direct binding analysis by flow cytometry. Through automated analysis of 33930 primers an optimized single condition cloning reaction was defined allowing for mutation of all surface-exposed residues of the receptor binding domain of SARS-CoV-2. All variants were functionally expressed, and two reference binders validated the method. Furthermore, epitopes of three novel therapeutic antibodies were successfully determined followed by evaluation of binding also towards SARS-CoV-2 Omicron BA.2. We find the method to be highly relevant for rapid construction of antigen libraries and determination of antibody epitopes, especially for the development of therapeutic interventions against novel pathogens.

Rare diseases are, despite their name, collectively common and millions of people are affected daily of conditions where treatment often is unavailable. Sulfatases are a large family of activating enzymes related to several of these diseases. Heritable genetic variations in sulfatases may lead to impaired activity and a reduced macromolecular breakdown within the lysosome, with several severe and lethal conditions as a consequence. While therapeutic options are scarce, treatment for some sulfatase deficiencies by recombinant enzyme replacement are available. The recombinant production of such sulfatases suffers greatly from both low product activity and yield, further limiting accessibility for patient groups. To mitigate the low product activity, we have investigated cellular properties through computational evaluation of cultures with varying media conditions and comparison of two CHO clones with different levels of one active sulfatase variant. Transcriptome analysis identified 18 genes in secretory pathways correlating with increased sulfatase production. Experimental validation by upregulation of a set of three key genes improved the specific enzymatic activity at varying degree up to 150-fold in another sulfatase variant, broadcasting general production benefits. We also identified a correlation between product mRNA levels and sulfatase activity that generated an increase in sulfatase activity when expressed with a weaker promoter. Furthermore, we suggest that our proposed workflow for resolving bottlenecks in cellular machineries, to be useful for improvements of cell factories for other biologics as well.