Human Gene Therapy for Rare Diseases
CONSIDERATIONS FOR PRECLINICAL STUDIES
A preclinical program that is tailored to the investigational product and the planned early-phase clinical trial contributes to the characterization of the product’s benefit/risk profile for the intended patient population. The overall objectives of a preclinical program for a GT product include:
- identification of a biologically active dose range;
- recommendations for an initial clinical dose level, dose-escalation schedule, and dosing regimen;
- establishment of feasibility and reasonable safety of the proposed clinical route of administration (ROA);
- support of patient eligibility criteria; and
- identification of potential toxicities and physiologic parameters that help guide clinical monitoring for a particular investigational product.
In addition, to justify conducting a pediatric first-in-human clinical trial that is associated with more than a minor increase over minimal risk, the preclinical program should include studies designed to demonstrate a prospect of direct benefit (21 CFR 50.52) of the investigational GT product. Preclinical evidence of a prospect of direct benefit is most important when clinical evidence of effectiveness is not available from adult subjects with the same disease. Further details for general considerations in preclinical studies are available in a separate guidance document. Although not specific to rare diseases, the following elements are recommended in the development of a preclinical program for an investigational GT product:
• Preclinical in vitro and in vivo proof-of-concept (POC) studies are recommended to establish feasibility and support the scientific rationale for administration of the investigational GT product in a clinical trial. Data derived from preclinical POC studies may guide the design of both the preclinical toxicology studies, as well as the early-phase clinical trials. The animal species and/or models selected should demonstrate a biological response to the investigational GT product that is similar to the expected response in humans.
• Biodistribution studies should be conducted to assess the distribution, persistence, and clearance of the vector from the site of administration to target and non-target tissues, including applicable biofluids (e.g., blood, lymph node fluid, cerebrospinal fluid (CSF)) as feasible. These data can determine the extent of tissue transduction and transgene expression, evaluate whether expression is transient or persistent, and guide the design of the preclinical toxicology studies as well as the early-phase clinical trials.
• Toxicology studies for an investigational GT product should incorporate elements of the planned clinical trial (e.g., dose range, ROA, dosing schedule, evaluation endpoints, etc.) to the extent feasible. Study designs should be sufficiently comprehensive to permit identification, characterization, and quantification of potential local and systemic toxicities, their onset (i.e., acute or delayed) and potential resolution, and the effect of dose level on these findings. In some cases, additional assessments may also be important to consider, such as safety and feasibility of the proposed GT delivery system and procedure, and immune response directed against the vector and the expressed transgene product.
Additional nonclinical studies may be needed to address such factors as:
1) the potential for developmental and reproductive toxicity; and
2) significant changes in the manufacturing process or formulation that may impact comparability between the product administered in clinical trials and the product intended for licensure.
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