Identity

Identity is the CMC quality attribute that confirms a product contains the intended active substance, molecular construct, vector, cell type, or biological material. For biologics and advanced therapies, identity testing should demonstrate that the material has structural, molecular, immunochemical, or biological features consistent with the intended product.

Identity is an explicit specification requirement for biotechnological and biological drug substances and drug products. Identity tests are typically qualitative, highly specific, and designed to distinguish the product from closely related materials, process intermediates, incorrect constructs, or mix-up risk.

For monoclonal antibodies and recombinant proteins, identity may rely on peptide mapping, intact mass, electrophoretic profile, isoelectric focusing, immunochemical binding, or other product-specific structural assays. For AAV and other gene therapy products, identity generally requires confirmation of both the genetic payload and the vector or capsid component. For cell therapy products, identity may involve cell-surface markers, genetic modification, transgene expression, or other product-defining biological features.

Identity testing supports batch release, material traceability, comparability, mix-up investigation, and confirmation that the product tested matches the product described in the regulatory application.

Specificity: Identity assays must be highly specific to the product’s unique structure and capable of distinguishing it from related molecules and products. More than one orthogonal test may be necessary.

Method complexity under cGMP: Definitive tests (e.g., peptide mapping, genome sequencing) are multi-step and require robust SOPs and system suitability to be reliable in QC settings.

Reference standard integrity: Release testing compares to a well-characterized in-house primary reference material (and working standards) maintained for stability/traceability.

Early Development (e.g., Phase 1 IND): While few specifications may be finalized, the regulatory submission must describe adequate identity tests suited for the product and phase of development. Methods should be described with appropriate controls and system suitability criteria, and data trending is encouraged.

Mid-Development: The definitive identity method(s) are selected and optimized. Formal method qualification or validation is performed, with the extent appropriate for its intended use per ICH Q2(R2).

Late-Stage / BLA (or MAA): The identity test(s) are incorporated into the final, justified specifications. The methods must be fully validated, with specificity being the most critical validation characteristic for an identity test.

Patient risk if identity fails: Severe—wrong active or mis-identified product can negate efficacy and introduce unknown safety risks. (This is the rationale behind requiring highly specific identity tests in specifications.)

Manufacturing risk signal: Identity failure indicates a fundamental process or mix-up issue and triggers batch rejection and investigation. (Specifications serve as critical quality standards and conditions of approval.)

Monoclonal antibodies (mAbs): The primary sequence (identity) underpins higher-order structure and biological activity (potency). Charge isoform patterns (IEF/cIEF) are sensitive to PTMs and typically monitored as physicochemical heterogeneity/purity; such patterns can also support identity when demonstrated to be product-specific.

AAV gene therapy: Identity testing should distinguish genome identity from vector or capsid identity. Genome identity confirms that the packaged genetic construct contains the intended sequence or defining genetic elements. Vector or capsid identity confirms that the product contains the intended AAV capsid, serotype, or vector component. These controls help confirm that the tested product matches the intended vector and transgene cassette, while genome integrity, empty/full ratio, and potency remain related but separate quality attributes.

Required in specs: One or more highly specific identity tests are required for biotech/biological DS and DP specifications.

Method selection depends on modality:

For mAbs/therapeutic proteins, peptide mapping is frequently used for lot release to confirm structure and is widely accepted as a high-specificity identity approach.

For gene therapies, regulators expect identity to address genome + vector (e.g., sequencing/restriction mapping for genome; serotype-specific or structural assays for capsid).

ICH Q6B (Specifications): Mandates inclusion of one or more highly specific identity tests in DS/DP specifications; many characterization methods in Appendix 6.1 (e.g., peptide mapping, IEF, CE) can be adapted for identity.

ICH Q2(R2) (Validation): For identification tests, specificity is the relevant validation characteristic; other characteristics (e.g., precision, accuracy) are not normally applicable.

FDA HGT CMC IND Guidance (2020): Phase-appropriate specifications and analytical procedures are expected from early development onward; documentation should describe method performance, specificity, sensitivity, and controls.

EMA GTMP Guideline (2018): Identity & integrity of DS should be assured with tests that identify both the therapeutic sequence and the vector (e.g., DNA sequencing or restriction mapping, plus immunological assays). Identity may also be supported by transduction/expression assays.