Guest Column | October 30, 2026

Antibody–Oligonucleotide Conjugates, Part 4: Regulatory Considerations And Future Directions

By Robert Dream, consultant to the industry

In the first, second, and third articles of this four-part article series on antibody–oligonucleotide conjugates, I covered defining the AOC development plan, including the molecular architecture and the CMC consequence of “hybrid” identity; CMC development: defining the target product profile and clinical quality attributes of AOCs; manufacturing strategy, conjugation chemistry, process development and scale-up; purification: the central manufacturing challenge; and analytical control strategy, OAR/DAR measurement, mass spectroscopy, capillary electrophoresis, peptide mapping and conjugate-site analysis, bioanalytical characterization, potency assays, and stability and formulation. In this fourth article, I cover regulatory perspective, manufacturing control strategy, beyond conventional AOCs, digital and advanced analytical opportunities, the emerging concept of “molecular quality by design,” and the currently unresolved CMC challenges to address with future work.

Regulatory Perspective

AOCs occupy an unusual regulatory position because they combine features of biologics and synthetic oligonucleotide medicines. Existing regulatory frameworks can provide important principles, but there is no single universally established AOC-specific CMC template that resolves every development question. ICH Q6B¹ provides a framework for biological products and conjugates, while oligonucleotide-specific regulatory guidance is increasingly addressing synthesis, impurities, characterization, conjugation, specifications, and analytical control.^2,3

The FDA's 2024 guidance on clinical pharmacology considerations for oligonucleotide therapeutics is also relevant to AOC development, particularly for immunogenicity, organ impairment, drug interactions, and other clinical pharmacology considerations.^4,5,6

AOC developers should expect regulatory review to focus on the scientific justification for:

CQAs
specifications
analytical methods
process controls
impurity limits
OAR distribution
biological activity
stability
bioanalytical assays
comparability.

The fundamental regulatory question is likely to be less "Which traditional category does the AOC belong to?" and more "Does the control strategy demonstrate consistent manufacture of a product with defined identity, purity, potency, safety, and stability?"

Manufacturing Control Strategy

A mature AOC control strategy can be visualized as follows.

Raw materials

(as needed for the process)

Antibody manufacture

Antibody identity
Purity
Aggregation
Charge
Glycosylation

Oligonucleotide manufacture

Sequence
Chemical modifications
Impurities
Purity
Reactive
Handle

Conjugation

Reaction stoichiometry
pH
Temperature
Reaction time
OAR

Purification

Free ON removal
Free antibody removal
Aggregates
OAR distribution

Drug substance

Identity
Purity
OAR
Site occupancy
Potency
Stability

Drug product

Formulation
Concentration
Particulate control
Sterility/endotoxin
Container closure
Stability

This integrated architecture is preferable to treating each component as an independent manufacturing program.

Beyond Conventional AOCs

The next generation of AOCs is likely to move beyond the simple antibody–linker–siRNA architecture.

Site-specific AOCs

Site-specific conjugation may reduce heterogeneity and improve reproducibility. It can also simplify OAR characterization and potentially improve the relationship between molecular structure and biological activity.

Higher-loading AOCs

Increasing payload loading may increase intracellular payload delivery but can simultaneously increase molecular weight, charge, aggregation, clearance, and steric interference with antibody binding. Recent studies have reported that higher DAR can substantially alter PK and biodistribution, highlighting the need to optimize — not simply maximize — payload loading.⁷

Chemically optimized oligonucleotides

Backbone and sugar modifications can influence:

nuclease resistance
protein binding
pharmacokinetics
tissue distribution
innate immune activation
intracellular activity.

Consequently, oligonucleotide chemistry should be considered an integral part of AOC design rather than a separate optimization exercise.

Alternative payloads

Although siRNA has been prominent in AOC development, the platform may accommodate:

ASOs
splice-switching oligonucleotides
microRNA modulators
other gene-regulatory nucleic acids.

The optimal conjugation chemistry and analytical strategy may differ substantially among these payload classes.

Multifunctional conjugates

Future architectures may combine:

targeting antibody + oligonucleotide + second functional component

Such constructs would increase therapeutic potential but also dramatically expand CMC complexity.

Digital And Advanced Analytical Opportunities

AOC characterization is particularly well suited to data-rich analytical approaches.

Potential technologies include:

high-resolution native MS
multi-attribute monitoring
automated chromatographic peak deconvolution
machine learning-assisted spectral interpretation
multidimensional chromatography
single-particle and aggregation analytics
high-content cellular potency assays.

A future AOC analytical package may evolve from a collection of discrete assays toward an integrated molecular fingerprint encompassing:

sequence + site + OAR + charge + aggregation + structural integrity + potency

This could substantially improve process understanding and comparability.

The Emerging Concept Of “Molecular Quality By Design”

The central lesson from AOC development is that the molecule itself must be designed with manufacturability and analytical control in mind.

A development program should ask, at the discovery stage:

Can the conjugation site be controlled?
Can OAR be reproducibly manufactured?
Can the OAR distribution be measured?
Can free oligonucleotide be removed?
Can aggregates be separated?
Can the conjugation site be identified?
Can the intact AOC be measured in plasma?
Can potency be linked to a measurable CQA?
Can the molecule tolerate manufacturing and storage?
Can the process be scaled?

This approach can be termed molecular quality by design (MQbD): molecular architecture, process design, analytical control, and biological function are optimized simultaneously. The concept is especially relevant because recent research has shown that relatively small changes in conjugation chemistry, site, linker, OAR, or oligonucleotide chemistry can change PK and biological activity.⁸

CMC Challenges To Address

Several issues remain unresolved across the AOC process/manufacturing field.

Defining the optimal OAR: The optimal OAR is likely molecule- and target-dependent. Increasing loading does not necessarily increase therapeutic benefit.
Controlling heterogeneity: Random conjugation creates complex molecular populations that complicate purification, analytics, comparability, and potentially clinical performance.
Establishing robust potency assays: AOC potency is multistep and may require cellular assays rather than simple biochemical measurements.
Measuring intact AOC in vivo: Reliable discrimination among intact AOC, free antibody, free oligonucleotide, and catabolites remains technically demanding.
Establishing meaningful specifications: Specifications should be linked to clinical performance and manufacturing capability rather than arbitrary analytical limits.
Scaling conjugation: A reaction that performs well at milligram scale may exhibit different mixing, mass-transfer, heat-transfer, and reaction-kinetic behavior at manufacturing scale.
Controlling long-term stability: The antibody, oligonucleotide, and linker can degrade through different mechanisms, making stability-indicating analytical strategies particularly important.

Conclusions

Antibody–oligonucleotide conjugates represent a convergence of two pharmaceutical technologies that have historically been developed using different manufacturing and analytical paradigms. Their therapeutic promise derives precisely from this combination: the antibody provides targeting and receptor-mediated delivery, while the oligonucleotide provides programmable gene regulation. That same combination creates their principal CMC challenge. An AOC cannot be adequately controlled by applying an ADC analytical package to an oligonucleotide payload, nor by treating the conjugate as simply another synthetic oligonucleotide. The product behaves simultaneously as a biologic, a nucleic acid therapeutic, and a chemically defined conjugate.

Consequently, successful AOC development requires an integrated control strategy encompassing:

molecular design → conjugation chemistry → process development → purification → orthogonal analytics → potency → bioanalysis → stability

Among the most important emerging priorities are site-specific conjugation, control of OAR distribution, scalable purification, native and high-resolution mass spectrometry, charge-based analytical methods, and quantitative measurement of intact AOC and its biological products in vivo. The field is also moving toward a broader principle: the most successful AOCs will not simply be biologically active molecules; they will be molecules whose structure, manufacturing process, analytical methods, and biological mechanism are mutually aligned. As regulatory guidance for oligonucleotide therapeutics becomes more developed and clinical experience with AOCs expands, the CMC discipline will increasingly shift from demonstrating that an AOC can be made to demonstrating that it can be made reproducibly, quantitatively characterized, and consistently linked to its intended biological performance.

References:

ICH Q6B: Specifications: Test Procedures and Acceptance Criteria for Biotechnological/Biological Products. FDA/ICH. Provides principles for characterization, specifications, identity, purity, quantity, and biological activity of biological products and conjugates.
Guideline on the Development and Manufacture of Oligonucleotides. European Medicines Agency, draft guideline, 2024. Addresses synthetic oligonucleotide manufacturing, characterization, specifications, analytical control, impurities, and conjugation.
ICH Q11: Development and Manufacture of Drug Substances. International Council for Harmonisation. Provides principles for process understanding, impurity control, and drug-substance manufacturing development.
Clinical Pharmacology Considerations for the Development of Oligonucleotide Therapeutics. U.S. Food and Drug Administration, Guidance for Industry, June 2024
Clinical Pharmacology Considerations for the Development of Oligonucleotide Therapeutics. U.S. Food and Drug Administration, Guidance for Industry, June 2024
U.S. Food and Drug Administration. Q6B Specifications: Test Procedures and Acceptance Criteria for Biotechnological/Biological Products. Final guidance, August 1999.
Neutral Backbone Modifications Enhance the Pharmacokinetics and Biodistribution of Antibody–Oligonucleotide Conjugates with High Drug-to-Antibody Ratios. Journal of Medicinal Chemistry. 2026. This recent study illustrates the relationship among backbone chemistry, DAR, PK, biodistribution, and analytical characterization.
Structure–Activity Relationship of Antibody–Oligonucleotide Conjugates: Evaluating Bioconjugation Strategies for Antibody–siRNA Conjugates for Drug Development. Journal of Medicinal Chemistry. 2024.
Structure–Activity Relationship of Antibody–Oligonucleotide Conjugates: Evaluating Bioconjugation Strategies for Antibody–Phosphorodiamidate Morpholino Oligomer Conjugates for Drug Development. 2024.

About The Author:

Robert Dream is a recognized industry leader with over 35 years of experience in the life sciences sector, including executive leadership roles. He has successfully led projects, optimized processes, and scaled products by leveraging operational excellence and deep technological expertise. Business-minded and strategically focused, Dream brings functional knowledge across manufacturing, supply chain, and regulatory domains. His background includes extensive hands-on and senior executive experience in therapeutic biotechnology and biological product manufacturing at world-leading organizations. A prolific contributor to the industry, Dream has authored numerous articles, industry guidances, and delivered many presentations.