USFDA Guidance: Safety Assessment of Genome Editing in Human Gene Therapy Products Using NGS and Expanded Access to Investigational Drugs for Treatment Use-Q&A

Sharan Murugan
3 hours ago
3 min read

The regulatory landscape for advanced therapies and patient access in the United States continues to evolve, with the FDA issuing updated guidances in April 2026 that address both cutting-edge genome editing safety and patient access to investigational treatments. Together, these guidances highlight the balance between innovation, safety evaluation, and ethical access to therapies across the product lifecycle.

The guidance Safety Assessment of Genome Editing in Human Gene Therapy Products Using Next-Generation Sequencing (April 2026, Draft) and Expanded Access to Investigational Drugs for Treatment Use: Questions and Answers (April 2026, Revision 2) provide comprehensive direction for sponsors, researchers, and clinicians.

Guidance 1: Safety Assessment of Genome Editing in Human Gene Therapy Products Using Next-Generation Sequencing

Introduction

This draft guidance provides recommendations on the use of next-generation sequencing (NGS) to evaluate the safety of human gene therapy products that incorporate genome editing technologies. It focuses on identifying risks such as off-target editing and genomic instability, which are critical for supporting clinical trial initiation.

Background

Genome editing technologies such as CRISPR-Cas, TALENs, and ZFNs enable targeted modifications in DNA, but they also introduce risks of unintended genomic changes. These include off-target edits and chromosomal alterations, which may affect normal cellular function and patient safety. The FDA emphasises that safety assessments must address both intended edits and unintended genomic effects, particularly for therapies targeting genetic diseases.

Scope

This guidance applies to sponsors developing human gene therapy products involving genome editing, including those targeting the genome, epigenome, or transcriptome. It focuses on nonclinical studies using NGS and bioinformatics to evaluate safety risks before clinical trial initiation.

Considerations for Next-Generation Sequencing

NGS is a central tool for detecting genomic changes and must be applied using appropriate sequencing strategies. Sponsors should select methods based on the type and size of expected edits, such as short-read sequencing for small changes and long-read sequencing for larger genomic alterations.

Adequate sequencing depth, quality control, and bias reduction strategies are essential to detect low-frequency off-target events. Detailed reporting of sequencing methods, bioinformatics tools, and analysis parameters is required to ensure reproducibility and transparency.

On-Target Edit Site Assessment

On-target editing refers to intended modifications at specific genomic locations. Sponsors must quantify editing efficiency and report both intended and unintended edits at these sites.

Appropriate sequencing strategies and representative biological samples should be used to ensure that observed editing rates reflect those expected in the final product.

Off-Target Editing Assessment

Off-target editing represents unintended modifications elsewhere in the genome and is a major safety concern. Sponsors should use a combination of cell-based, biochemical, in silico, and NGS-based methods to identify and confirm off-target sites. Studies must include biological replicates, appropriate cell types, and scientifically justified methodologies. The choice of method should align with the mechanism of action of the genome editing technology used.

Chromosomal Integrity and Genetic Variation

The guidance highlights the importance of assessing chromosomal integrity, including structural changes such as translocations. It also requires evaluation of how human genetic variability may influence off-target editing outcomes. These assessments help ensure that therapies are safe across diverse patient populations.

Reporting Requirements

Sponsors must submit detailed study reports, including sequencing data, analysis workflows, and identified off-target sites. Results should be presented in structured formats to support regulatory review.

Guidance 2: Expanded Access to Investigational Drugs for Treatment Use: Questions and Answers

This guidance provides a detailed question-and-answer framework on FDA regulations governing expanded access to investigational drugs for treatment use under an IND. It aims to improve understanding of how patients with serious or life-threatening conditions can access investigational therapies outside clinical trials.

Expanded access is categorised into three main types:

Individual patient access, including emergency use, allows treatment for a single patient under urgent or non-urgent conditions.

Intermediate-size population access applies to groups of patients smaller than those in large treatment programs.

Treatment IND or protocol enables widespread access for larger populations when sufficient data support safety and potential benefit

Submission and Process

Expanded access requests can be submitted using different regulatory pathways depending on the situation, including Form FDA 3926 for individual patient access.

Emergency use allows rapid access with retrospective documentation, while non-emergency use typically requires prior FDA and IRB approval.

For complete official guidance, refer to: