This Technical Blog was written with input from Endpoint’s Ophthalmology expert Dr. Ryan Boyd, DVM, MS, DACVO.

Content has been informed by the presentation and discussion following the recent webinar “How to Plan IND-Enabling Ocular Studies”.

In ocular studies, immunosuppression is often introduced after inflammation appears—but by that point, the immune response has already been established and may no longer be controllable at the source.

In practice, this approach is frequently misaligned with how immune responses develop.

Immune activation is a predictable component of many ocular programs, particularly those involving biologics, gene therapies, or repeat dosing. These responses influence both the progression of the study and the interpretability of its endpoints.

The critical design consideration is how immune response evolves over time—and whether it is controlled before it affects the dataset.

Immune responses in ocular studies follow a temporal progression, with distinct mechanisms and treatment requirements.

Early inflammation in ocular studies is typically driven by innate immune activation within the first 48 hours and is typically responsive to local therapy, while delayed inflammation is caused by adaptive immune responses that emerge days to weeks later, are driven systemically, and often require immunosupression to achieve control.

Early-phase inflammation is typically driven by innate immune activation. This includes breakdown of the blood-ocular barrier, release of inflammatory mediators, and recruitment of immune cells into ocular compartments. These responses are generally responsive to topical or periocular treatment, but severity may require systemic treatment.

Over time, antigen-specific adaptive responses develop. These include activation of B and T lymphocytes and production of anti-drug antibodies (ADA), with immune activity driven in the spleen and peripheral lymphoid tissues and directed back to the eye.

At this stage, local treatment is insufficient. Effective control requires systemic immunosuppression to prevent continued immune activation and tissue-specific damage.

The timing of immunosuppressive intervention has a direct impact on study behavior.

Reactive treatment addresses inflammation after immune activation has occurred, but often requires higher doses of immunosuppressive medications. Whereas, prophylactic strategies target the initial immune priming phase.

Prophylactic immunosuppression targets the initial exposure window, when antigen presentation peaks and immune priming occurs. As described in the webinar, controlling this early signaling phase can reduce or prevent downstream inflammation, including longer-term responses.

This can be particularly challenging in repeat-dose studies. An initial exposure may not produce observable inflammation, while subsequent dosing can trigger an acute response driven by a primed adaptive immune system. Prolonged prophylactic immunosuppression can have adverse health effects on the animal, so careful consideration and planning are important.

Immune response directly affects both efficacy and safety interpretation.

Efficacy impact

• Immune-mediated cellular responses can target transduced or treated cells
• Reduction in therapeutic expression may occur after initial signal is observed
• Loss of therapeutic signal is incorrectly attributed to lack of efficacy when it is actually caused by immune-mediated clearance of treated cells.

Safety interpretation

• Inflammation may dominate early findings and obscure drug-related effects
• Underlying toxicity may only become apparent after immune response is controlled

Data consistency

• Adaptive immune responses introduce variability across animals
• Dose-response relationships may be obscured by immune-driven effects
• These effects are not secondary—they define whether study endpoints can be interpreted with confidence.

Effective integration of immunosuppression requires alignment between biological risk and study execution. Experienced teams define immunosuppression strategy before study initiation, align it with expected immunogenic risk, and plan both prophylactic and reactive pathways rather than relying on inflammation as a trigger for intervention.

Study design considerations

• Assess likelihood of immunogenicity based on test article properties
• Define immunosuppression strategy prior to study initiation
• Align route of administration and exposure with immune risk
• Establish both prophylactic and reactive treatment plans

Opperational considerations

• When available, use long-acting formulations to ensure consistent systemic exposure in animal models
• Combine corticosteroids with additional immunosuppressive agents when deeper suppression is required

Immune profiling considerations

• Collect ADA and/or PBMC samples at baseline and during the adaptive response window (~3–4 weeks)
• When possible, collect samples prior to initiating immunosuppression to avoid suppression-related impact on detecting a response