The biologic medicines have revolutionized the way several complicated and chronic diseases are treated. The monoclonal antibodies, therapeutic proteins, enzymes, and other biologic treatments could offer highly effective and focused ways of managing the diseases. However, some of these medications are made from proteins or protein-based materials and could be seen by the body as foreign material.

This phenomenon is referred to as immunogenicity, although not all the immune reactions will cause any trouble. Nevertheless, the issue of immunogenicity has several implications for patient safety and treatment efficacy.

The knowledge about how immunogenicity arises, how it is identified, and what its consequences for the patients might be is thus an important aspect of biologic drugs.

What Happens When the Immune System Recognizes a Biologic Drug?

Upon administration to a patient, the therapeutic molecule may be recognized by the body's immune system as a foreign substance. In some cases, the presence of certain biologics triggers the development of anti-drug antibodies (ADAs) in some patients.

Anti-drug antibodies can vary in their properties and clinical implications. Some ADAs may bind to the biologic drug molecule but without any impact on its activity, whereas other ADAs, called neutralizing antibodies (NAbs), prevent the drug from performing its biological function.

The mere presence of ADAs in a patient's body does not automatically translate into a possible adverse event. What is clinically important is the nature of the immune reaction, the drug used, and other patient-specific parameters.



How Can Immunogenicity Affect Patient Safety?

1. Hypersensitivity and Infusion-Related Reactions

One of the major safety risks related to immune response to biologic medicines is that of hypersensitivity or infusion reaction.

The reaction may vary from minor symptoms, including:

• Rash
• Itchiness
• Fever
• Headache
• Chills

to severe reactions involving difficulties in breathing, low blood pressure, or generalized allergic reaction.

It is not always that all infusion reactions are due to the development of antibodies against the drug and there are various biological mechanisms involved in infusion reactions. Immunogenicity is one of the important parameters for assessing safety of biologic drugs.

2. Reduced Treatment Effectiveness
   
   
   

The indirect effects of immunogenicity on the safety of patients may occur when antibodies compromise the efficacy of the medicine in use.

For instance, the neutralization of a biological drug by antibodies may lead to its decreased efficacy. Other types of antibodies are capable of affecting the pharmacokinetics of the drug.

In the case of decreased exposure to the drug, the patient will not obtain the expected therapeutic effect. This may even worsen the condition of the patient.

This problem is especially significant for medications that control severe and chronic conditions.

3. Changes in Drug Pharmacokinetics
   
   
   

Antibodies against drugs have the potential to modify the pharmacokinetics of a biological.

This can be due to the following reasons:

• Clearance of the drug
• Exposure of the drug
• Half-life of the drug
• Circulation of the drug

This could make it even harder to achieve the desired drug concentration.

There is variability across products in terms of the clinical effect. Thus, an immune response does not necessarily lead to treatment failure.

4. Immune Complex-Related Effects
   
   

Sometimes, antibodies may combine with the therapeutic agent, leading to immune complexes.

Depending on their nature and behavior within the body, immune complexes may have inflammatory or immunogenic effects.

Various things determine the effects, such as the size and persistence of the complex, its biological activity, and the patients immune system.

This is just one of the many reasons why it is critical to analyze the nature of the immune reaction rather than just the presence of antibodies.

5. Neutralizing Antibodies and Loss of Biological Activity
   
   
   

One reason why neutralizing antibodies play such a critical role is that they can affect the biological activity of a therapeutic protein.

To give one example, if a biologic protein is used to inhibit a particular signaling pathway, the neutralizing antibodies could prevent the protein from fulfilling its intended task.

The outcome of such an interaction could be impaired therapeutic efficacy, or even total lack of efficacy.

In some therapies, such an outcome might be detrimental, which makes it very important to monitor and characterize immunogenicity.

Why Do Some Patients Develop Stronger Immune Responses?

Immunogenicity is affected by product-related and patient-related characteristics.

Some product-related characteristics might be:

• Protein sequence and conformation
• Aggregation
• Post-translational modifications
• Contamination
• Formulation
• Production process
• Route of administration

Some patient-related characteristics might be:

• Genetic variability
• Immune system status
• Prior experience with the same therapeutic proteins
• The underlying condition
• Comorbidities
• Medications
• Length and regimen of treatment

This means that two different patients taking the same biologic drug can have entirely different immune responses.

How Is Immunogenicity Monitored?

Immunogenicity can have a considerable effect on the safety and efficacy of these drugs; therefore, its assessment is carried out throughout the development of biologic drugs.

For example, assessment of immunogenicity could consist of the detection of anti-drug antibodies in patient samples. Should antibodies be detected, further testing may be conducted to define their nature and clinical relevance.
Some examples of such testing include:


Are antibodies present?

Is there any specificity toward the therapeutic agent?

Can they affect the drug's biological activity?

Do they affect the exposure, efficacy, or safety of the drug?

This approach will enable scientists to distinguish between the presence of clinically relevant and insignificant antibodies.

Immunogenicity Does Not Always Mean Danger


It should be emphasized that the existence of immunogenicity does not necessarily imply the harmfulness of a particular therapy.

Patients can produce anti-drug antibodies without any clinical significance of such a phenomenon. Certain types of responses by the immune system may be temporary, weak, or have no impact on the pharmacological properties of the therapy.

Consequently, immunogenicity must be assessed in light of other clinical data, including:

• adverse reactions
• drug concentration in patients
• pharmacodynamic effects
• therapy efficacy
• disease state
• antibody properties

The goal is not simply to eliminate every detectable immune response, but to understand whether the response has a meaningful impact on the patient's treatment.

Reducing Immunogenicity Risk During Drug Development

Issues regarding patient safety start way back before the biological medicine enters the clinic.


There are several methods by which developers can explore the immunogenicity risks associated with drug development, such as:

• Protein engineering
• Controlling protein aggregation
• Formulation
• Manufacturing impurities control
• Product characterization
• Routes of administration
• Sensitive immunogenicity assay development
• Monitoring patients in clinical trials

These approaches could help identify any possible risk earlier on.

The Importance of a Comprehensive Safety Assessment

Immunogenicity should never be considered alone.

A positive ADA test does not mean that there is going to be an adverse outcome, just like a negative ADA test does not mean that there will be no immune-mediated response.

Instead, immunogenicity information needs to be combined with clinical safety information, PK/PD and efficacy information.

This way, it will become clear whether the immune response is clinically meaningful or not.



Looking Ahead

In line with the advances made in biologic treatments, immunogenicity knowledge and management will continue to play a critical role in ensuring the safety of patients.

Some of the areas of advancement in biologics that could aid in identifying immune-related issues early in the development of a drug include protein engineering, analytics, immunogenicity assays, computational predictions, and data analysis techniques.

The ultimate goal of developing a biologic should not only be its effectiveness but its safety to patients as well.

Conclusion

Immunogenicity may pose risks to patient safety through ways such as allergic reactions, drug exposure changes, therapeutic failure, and many others. However, the mere fact of having an immune response does not always mean that there is a safety issue.

The crucial thing is knowing when an immune response translates into a risk.

By developing products properly, performing thorough immunogenicity tests and monitoring, and continually studying the impact of immunogenicity on patients' health, one may achieve great results in risk management.

By Shara Najimudeen, Digital Marketing Executive, GLC Europe, Colombo Office, Sri Lanka.