Detection of Protein Residues in Products

Detection of Protein Residues in Products

1. Background Introduction

The rapid development of biopharmaceutical technology has revolutionized modern healthcare. Genetically modified microorganisms, leveraging their advantages such as high-efficiency expression, ease of large-scale production, and post-translational modification capabilities, have become the dominant production systems for biologics including monoclonal antibodies, recombinant proteins, vaccines, and gene therapy vectors. Host systems such as Chinese Hamster Ovary (CHO) cells, Escherichia coli (E. coli), HEK293 cells, yeast, and insect cells play an irreplaceable role in the industrial production of biopharmaceuticals [1].

However, during the manufacturing and purification of biologics, host cells inevitably release large quantities of Host Cell Proteins (HCPs)—a complex mixture of proteins including structural proteins, secreted proteins, and growth factors [2]. Despite the application of advanced purification technologies, some HCPs remain as process-related impurities in the final product. These residual HCPs pose potential immunogenic risks, which may trigger immune responses, allergic reactions, or even severe adverse events in patients [3]. Additionally, certain enzymatically active HCPs (e.g., proteases, lipases) may degrade target products or formulation excipients (e.g., polysorbates), compromising product stability and shelf life [4-5]. Therefore, HCP residue detection has become a Critical Quality Attribute (CQA) in biopharmaceutical quality control.

Stringent regulatory standards for HCP residues have been established globally. The Chinese Pharmacopoeia (2020 Edition, Volume III) explicitly stipulates: HCP residues in CHO cell-derived products shall be .05% (equivalent to   ppm), and those in E. coli-derived products shall be   ( [6]. The United States Pharmacopeia (USP)   (2015) requires the use of high-sensitivity methods for HCP detection, with residual levels typically below 100 ppm (i.e., 0 ng HCP per mg total protein) [7]; USP .1>, which will take effect in May 2025, further recommends orthogonal methods such as LC-MS/MS for HCP identification and quantification [8]. The European Pharmacopoeia (EP) 2.6.34 specifies that HCP content in biologics shall be <0.1% (000 ppm) [9]. Furthermore, regulatory authorities generally require that the antibody coverage of HCP ELISA kits be ≥70% to ensure the reliability and accuracy of detection results [10].

In 2023, the National Health Commission issued the "Requirements for Application Materials for Safety Evaluation of Genetically Modified Microorganisms Used in Food Processing (Trial)", which for the first time explicitly mandates protein residue detection for food ingredients and additives produced using genetically modified microorganisms—marking the further improvement of regulatory requirements in this field in China [11].

Beyond traditional biologics, the rapid development of Cell and Gene Therapy (CGT) products has brought new demands for protein residue detection. In CRISPR/Cas9-mediated ex vivo gene therapies (e.g., CAR-T cell therapy), genetically edited cells are infused back into patients. Both the US FDA and European EMA require the detection of residues of Cas9 nuclease, transcription factors, and other gene editing tool proteins prior to cell infusion to ensure product safety [12-13]. In response to this emerging need, Zhuhai Shutong Medical Technology Co., Ltd. has established a high-sensitivity ELISA detection platform covering HCPs, Cas9 protein, and other process-related proteins, providing comprehensive quality control technical support for the biopharmaceutical and CGT industries.

2. ELISA Detection Principle

ELISA (Enzyme-Linked Immunosorbent Assay) is currently the most mature and widely used method for protein residue detection. Based on the principle of specific antigen-antibody binding, the method amplifies signals through enzymatic reactions, enabling high-sensitivity quantitative detection of protein residues such as HCPs.

Figure 1. Schematic Diagram of ELISA Detection Principle

3. Technological Innovations and Advantages

3.1 Core Technological Innovations

3.1.1 High-Coverage Antibody Preparation Strategy

An antigen preparation method simulating actual production process conditions is adopted:

Immunogens are prepared using host cell lines and culture conditions matching the client's production process, ensuring antibodies can recognize various HCPs potentially present in actual production;

Conditioned medium is used as the antigen source, offering higher specificity and representativeness compared to cell lysates;

Antibody coverage is verified by 2D-WB or LC-MS/MS to be ≥70%, and over 80% in some cases, effectively reducing the risk of false negatives.

3.1.2 Rigorous Method Validation

All ELISA kits have completed comprehensive method validation in accordance with the Chinese Pharmacopoeia (2020 Edition, General Chapter >), ICH Q2(R2), and FDA guidelines:

Specificity: Verifies the method's ability to specifically recognize target HCPs, excluding non-specific interference;

Accuracy: Evaluated by spiked recovery tests, with recovery rates controlled within 80%-120%;

Precision: Includes assessments of repeatability, intermediate precision, and reproducibility, with a Coefficient of Variation (CV) ≤15%;

Linear Range: Standard curves cover 1-100 ng/mL, with R² ≥0.99;

Limit of Detection (LOD): As low as 1-3 ng/mL, meeting trace detection requirements;

Robustness: Evaluates the impact of key parameter changes on results to ensure method stability.

3.1.3 High-Throughput Parallel Sample Processing Capability

96-well plate design supports simultaneous detection of up to 88 samples (including standard curves and quality control samples);

Standardized operating procedures enable result output from sample preparation in just 4-6 hours per batch;

Compatible with automated microplate readers and washers, improving detection efficiency and data consistency.

3.2 Method Validation and Performance Indicators

Shutong Technology has conducted comprehensive and systematic validation of the ELISA detection platform, with all performance indicators meeting or exceeding industry standards:

4. Application Scenarios and Service Advantages

4.1 Application Scenarios

HCP detection spans the entire lifecycle of biologics, with key application scenarios including:

(1) Process Development and Optimization: Evaluate HCP clearance capabilities of different purification strategies and optimize process parameters;

(2) IND Filing Support: Provide complete method validation data and detection reports meeting regulatory requirements;

(3) In-Process Control (IPC): Monitor changes in HCP content during each purification step to ensure process stability;

(4) Product Release Testing: Ensure HCP residues in final products comply with quality standards;

(5) Process Performance Qualification (PPQ): Validate the robustness and consistency of commercial production processes;

(6) Stability Studies: Evaluate the impact of storage conditions on HCP content.

4.2 Service Advantages

(1) Multi-Host System Coverage: Supports various expression systems including CHO, E. coli, HEK293, yeast, and insect cells;

(2) Complete Method Validation: Provides a full set of validation data packages meeting IND filing requirements;

(3) Rapid Turnaround: Standard detection cycle of 5-7 working days;

(4) Quality Assurance: ISO9001 and CNAS quality management systems ensure data reliability and traceability;

(5) Technical Support: Offers IND filing technical consultation, method transfer, and validation support;

(6) Orthogonal Validation: Provides orthogonal methods such as LC-MS/MS or 2D-WB to enhance result credibility.

5. Example of ELISA HCP Detection Report

Shutong Technology provides professional HCP detection reports, including the following core content:

(1) Standard Curve and Fitting Parameters: Displays the standard curve equation, correlation coefficient R², and linear range;

(2) Quality Control Sample Results: Includes detection results of positive controls, negative controls, and quality control samples;

(3) HCP Residue Levels in Test Samples: Reports HCP content in ng/mg or ppm;

(4) Compliance Evaluation: Provides compliance conclusions by comparing with relevant regulatory limits;

(5) Method Validation Data (for IND Filings): Complete validation data including accuracy, precision, specificity, linear range, LOD, and LOQ.

6. Service Content

Shutong Technology offers end-to-end HCP detection services, including:

Service Cycle: 5-7 working days for standard detection.

7. Sample Requirements

To ensure the accuracy and reliability of detection results, please prepare samples in accordance with the following requirements:

8. References

[1] Walsh G, Walsh E. Biopharmaceutical benchmarks 2022. Nature Biotechnology. 2022;40(12):1722-1760.

[2] Wang X, Hunter AK, Mozier NM. Host cell proteins in biologics development: Identification, quantitation and risk assessment. Biotechnology and Bioengineering. 2009;103(3):446-458.

[3] Bracewell DG, Francis R, Smales CM. The future of host cell protein (HCP) identification during process development and manufacturing linked to a risk-based management for their control. Biotechnology and Bioengineering. 2015;112(9):1727-1737.

[4] Gao SX, Zhang Y, Stansberry-Perkins K, et al. Fragmentation of a highly purified monoclonal antibody attributed to residual CHO cell protease activity. Biotechnology and Bioengineering. 2011;108(4):977-982.

[5] Hall T, Sandefur SL, Frye CC, et al. Polysorbates 20 and 80 degradation by group XV lysosomal phospholipase A2 isomer X1 in monoclonal antibody formulations. Journal of Pharmaceutical Sciences. 2016;105(5):1633-1642.

[6]中国药典委员会.中华人民共和国药典（2020年版）三部通则3412、3413、3414、<9101>生物制品分析方法验证指导原则.2020.

[7] United States Pharmacopeia. USP 132> Residual Host Cell Protein Measurement in Biopharmaceuticals. 2015.

[8] United States Pharmacopeia. USP 32.1> Residual Host Cell Protein Measurement in Biopharmaceuticals by Mass Spectrometry. Official May 1, 2025.

[9] European Pharmacopoeia. EP 2.6.34 Host-Cell Protein Assays. 10th Edition. 2020.

[10] Zhu-Shimoni J, Yu C, Nishihara J, et al. Host cell protein testing by ELISAs and the use of orthogonal methods. Biotechnology and Bioengineering. 2014;111(12):2367-2379.

[11]国家卫生健康委员会.食品加工用遗传修饰微生物安全性评价申报材料要求（试行）.2023.

[12] FDA. Chemistry, Manufacturing, and Control (CMC) Information for Human Gene Therapy Investigational New Drug Applications (INDs). Guidance for Industry. 2020.

[13] EMA. Guideline on quality, non-clinical and clinical aspects of gene therapy medicinal products. EMA/CAT/80183/2014. 2018.