Cancer immunotherapy patents often involve some of the most sequence-intensive technologies in biotechnology. Antibodies, antibody fragments, T-cell receptors, chimeric antigen receptors, cytokines, fusion proteins, nucleic acid constructs, engineered binding proteins, and other biologics can generate hundreds or even thousands of nucleotide and amino acid sequences across a single patent family.
For these applications, sequence-listing preparation is not simply a formatting exercise. The sequence listing must accurately capture the biological sequences disclosed in the application while satisfying the applicable patent-office requirements. Errors in sequence identification, numbering, annotations, or conversion can create significant prosecution and filing complications.
For applications filed on or after July 1, 2022, the relevant international standard is generally WIPO Standard ST.26, which uses an XML-based format for nucleotide and amino acid sequence listings. The USPTO has implemented ST.26 through 37 CFR 1.831–1.835.
Why Sequence Listings Matter in Cancer Immunotherapy Patents
Modern cancer immunotherapy inventions frequently depend on precise biological sequences.
An antibody invention, for example, may involve:
- Heavy-chain variable-region sequences
- Light-chain variable-region sequences
- Complementarity-determining regions (CDRs)
- Full-length heavy and light chains
- Engineered variants
- Humanized sequences
- Chimeric constructs
- Fc-engineered variants
- Antibody-drug conjugate components
A CAR-T invention may add:
- Antigen-binding domains
- ScFv sequences
- Hinge regions
- Transmembrane domains
- Costimulatory domains
- Signaling domains
- Linkers
- Nucleic acid sequences encoding the construct
Likewise, T-cell receptor technologies can involve alpha and beta chains, variable regions, engineered receptors, nucleic acid constructs, and sequence variants.
The sequence listing therefore needs to be prepared as part of the substantive patent-drafting process rather than treated as a final administrative attachment.
ST.26: The Current Sequence-Listing Standard
WIPO Standard ST.26 establishes requirements for presenting nucleotide and amino acid sequences in patent applications. It uses a structured XML format containing general application information and sequence data. For U.S. applications, the filing date determines whether ST.25 or ST.26 applies. Applications filed on or after July 1, 2022 generally require ST.26, while applications filed before that date remain subject to the applicable ST.25 requirements. For U.S. national-phase applications, the relevant date is the PCT international filing date rather than the later U.S. national-phase entry date. This distinction is especially important for older cancer-immunotherapy patent families in which continuations, divisionals, national-phase applications, and related filings may have different sequence-listing requirements.
What Should Be Captured in a Complex Biologic Sequence Listing?
A robust preparation process begins by identifying every sequence disclosed in the patent application that falls within the applicable sequence-listing requirements.
For an immunotherapy application, this may require reviewing:
- The specification
- Claims
- Sequence tables
- Figures
- Experimental examples
- Construct maps
- Antibody descriptions
- Plasmid descriptions
- Nucleic acid embodiments
- Protein variants
- Mutational studies
- Binding-domain descriptions
- Cell-engineering examples
The objective is not merely to collect the sequences that appear in the claims. Sequence-listing requirements can extend to sequences disclosed elsewhere in the application.
The USPTO explains that a sequence listing provides a standardized presentation of qualifying nucleotide and amino acid sequence data disclosed in a patent application.
Building a Sequence Inventory Before XML Generation
For complex biologics, creating a master sequence inventory before generating the ST.26 file can substantially reduce errors.
Each sequence can be tracked internally by information such as:
| Internal field | Purpose |
| Internal identifier | Tracks the sequence through drafting |
| SEQ ID NO. | Connects the sequence to the application |
| Sequence type | Nucleotide or amino acid |
| Biological component | Identifies the antibody, CAR, TCR, linker, etc. |
| Source/location | Shows where the sequence appears in the specification |
| Length | Provides a basic verification point |
| Variant relationship | Identifies mutants or related sequences |
| Feature information | Supports ST.26 annotation |
| Verification status | Records whether the sequence has been checked |
This internal inventory is particularly valuable when the application contains numerous related sequences that differ by only a few residues.
Antibody Sequence Preparation
Antibody applications create several recurring sequence-management challenges.
A single therapeutic antibody may have separate sequences for its heavy and light chains, variable domains, CDRs, engineered variants, and nucleic acids encoding the proteins.
For example, a specification might disclose:
Antibody A
- Heavy-chain variable region
- Light-chain variable region
- Full heavy chain
- Full light chain
Antibody B
- Humanized heavy-chain variable region
- Humanized light-chain variable region
- Full-length chains
- Variant sequences
Antibody C
- Affinity-matured variants
- Substitution variants
- Fc-modified versions
These sequences should be reconciled carefully before assigning final sequence identifiers.
A common practical error is treating nearly identical sequences as interchangeable. A single amino-acid substitution can be legally and scientifically significant, particularly where claims rely on sequence identity, defined substitutions, CDR sequences, or functional variants.
CAR-T and Cell-Therapy Constructs
CAR-T patents can be even more complicated because a single therapeutic construct may contain multiple functional domains.
A CAR could include an antigen-binding domain followed by a hinge, transmembrane domain, costimulatory domain, and signaling domain.
The application may disclose both the amino acid sequence of the complete CAR and the nucleotide sequence encoding it, along with sequences for individual components.
Sequence preparation should therefore distinguish between:
- Individual component sequences.
- Full-length protein constructs.
- Nucleic acid sequences encoding those constructs.
- Alternative embodiments.
- Mutant or optimized variants.
Careful mapping between these categories helps prevent accidental omission or duplication.
TCR and Other Receptor-Based Immunotherapies
T-cell receptor patents present similar challenges.
A specification may disclose alpha and beta chains, variable regions, CDRs, engineered substitutions, and nucleic acid sequences. Additional sequences may be disclosed for expression constructs or alternative receptor configurations.
Sequence identifiers should be assigned systematically so that the written specification, claims, figures, and sequence listing remain synchronized.
This is particularly important when claims use language such as “comprising a sequence having at least X% identity to SEQ ID NO: …” or define a molecule by particular CDR sequences.
Sequence Features and ST.26 Annotations
ST.26 is not merely an XML container for raw strings of residues. The standard provides structured sequence information, including feature keys and qualifiers. WIPO describes the sequence data portion as containing individual sequences together with information describing those sequences. For complex biologics, appropriate feature information can help communicate the biological organization of a sequence.
Depending on the sequence, relevant features may include functional regions, coding regions, mature peptides, signal peptides, binding regions, or other biologically meaningful portions recognized under the applicable standard.
This is one reason automated conversion without substantive review can be risky: the software can help with formatting and validation, but the underlying biological information still needs to be accurate.
Minimum-Length and Sequence-Inclusion Issues
ST.26 changed certain aspects of sequence-listing practice compared with ST.25.
For example, ST.26 addresses additional sequence types and does not treat all short sequences in the same manner as the previous standard. WIPO notes that ST.26 includes certain sequence types such as D-amino acids, linear portions of branched sequences, and nucleotide analogs, while excluding certain sequences below specified minimum lengthsFor complex biologics, this makes it important to evaluate short disclosed peptides, CDR-related sequences, linkers, primers, probes, and other small sequences rather than automatically assuming that every short sequence should be included—or excluded.
The current version of ST.26 should be consulted when determining whether a particular sequence falls within the applicable requirements.
Sequence Numbering Must Stay Consistent
Sequence numbering is one of the most important quality-control issues in a biologics patent.
If the specification identifies an antibody variable region as SEQ ID NO: 25, the sequence listing must associate that identifier with the correct sequence.
The same identifier should not inadvertently be assigned to a different sequence, and sequence identifiers should remain synchronized throughout the application.
This becomes challenging when:
- New sequences are inserted late in drafting.
- Claims are amended.
- Continuations introduce new embodiments.
- Sequence tables are reorganized.
- ST.25 data are converted into ST.26.
- Multiple inventors provide overlapping sequence sets.
A master sequence database or controlled spreadsheet can help maintain consistency.
Converting ST.25 to ST.26
Patent families containing older ST.25 sequence listings may need special attention when preparing later filings.
WIPO Sequence can import ST.25 sequence listings and assist with transformation into ST.26 format. The USPTO specifically recommends reviewing the import report carefully because transformations can occur during the conversion process
The conversion should therefore be treated as a data migration and validation exercise, not a simple file-format conversion.
A good workflow is:
- Preserve the original ST.25 sequence listing.
- Import it into an appropriate ST.26 workflow.
- Review the transformation report.
- Check sequence lengths and residue strings.
- Review sequence types.
- Review feature annotations.
- Confirm sequence identifiers.
- Compare the resulting sequences against the application disclosure.
- Validate the final ST.26 XML.
- Conduct a human-readable substantive review before filing.
Using WIPO Sequence
WIPO provides WIPO Sequence, a desktop application designed to assist applicants in creating and validating ST.26 sequence listings. The software can validate project information, generate compliant XML, import various sequence-file formats, and produce a human-readable representation for review. Applicants are not legally required to use WIPO Sequence, but WIPO and the USPTO strongly recommend using software designed specifically for ST.26 preparation. Importantly, the human-readable output is useful for review but is not itself the ST.26 XML file that should be filed.
Quality Control for Complex Cancer Immunotherapy Applications
A strong quality-control process should operate at several levels.
Scientific review
Confirm that every sequence is biologically correct.
Check:
- Residue order
- Sequence length
- Amino-acid identity
- Nucleotide identity
- Reading frames
- Translation relationships
- Variant substitutions
- Domain boundaries
Patent-drafting review
Confirm that sequence identifiers correspond correctly throughout the application.
Check:
- Specification references
- Claim references
- Tables
- Figures
- Examples
- Sequence citations
ST.26 compliance review
Confirm that the XML complies with the applicable ST.26 requirements and DTD.
Filing-data review
Confirm the bibliographic and application information contained in the sequence listing.
ST.26 sequence listings contain a general information section with application-related information as well as a sequence-data section.
Filing the ST.26 XML
For U.S. nonprovisional applications subject to ST.26, the sequence listing is submitted as an XML file. The USPTO states that the XML sequence listing may be submitted electronically through Patent Center or through permitted physical media. An incorporation-by-reference statement is also required in the specification identifying the XML filename, creation date, and file size.
The USPTO currently identifies a 100 MB limit for sequence-listing XML uploads through Patent Center; larger XML files require submission using permitted physical media.
For large immunotherapy applications, file size should therefore be considered before the final filing stage.
Common Problems to Avoid
Several problems repeatedly arise in sequence-intensive biotechnology applications.
Treating sequence preparation as an administrative task
Sequence listings contain substantive biological information. They should be reviewed by people who understand both the technology and the patent disclosure.
Copy-and-paste errors
Highly similar antibody or receptor sequences make manual copying particularly vulnerable to mistakes.
Incorrect sequence identifiers
A numbering error can propagate across the specification, claims, figures, and sequence listing.
Failing to reconcile protein and nucleic acid sequences
Where both forms are disclosed, they should be checked for appropriate correspondence rather than assumed to be correct.
Overlooking sequences outside the claims
The sequence listing analysis should consider qualifying sequences disclosed throughout the application.
Blindly converting legacy sequence listings
ST.25-to-ST.26 conversion should be validated carefully, particularly for complex biological sequences.
A Practical Preparation Workflow
For a complex cancer-immunotherapy patent, an effective workflow can look like this:
Step 1: Freeze the disclosure.
Identify the version of the specification, claims, figures, and sequence data that will support the filing.
Step 2: Build the master sequence inventory.
Collect every potentially qualifying nucleotide and amino acid sequence.
Step 3: Reconcile duplicate and related sequences.
Determine which sequences are identical, variants, fragments, domains, or full-length constructs.
Step 4: Assign sequence identifiers.
Create a controlled numbering system and map every identifier to its source disclosure.
Step 5: Review biological accuracy.
Check the sequences against experimental records and the patent specification.
Step 6: Generate the ST.26 project.
Enter the required bibliographic, sequence, and feature information.
Step 7: Validate the XML.
Use WIPO Sequence or another appropriate ST.26-compliant validation workflow.
Step 8: Perform a human-readable comparison.
Compare the generated listing against the source sequence inventory.
Step 9: Conduct a patent cross-check.
Verify that every SEQ ID NO. cited in the specification and claims maps to the intended sequence.
Step 10: Perform the final filing check.
Confirm the XML filename, creation date, file size, incorporation-by-reference language, and filing format.
Conclusion
Sequence-listing preparation for cancer immunotherapy patents requires more than converting biological data into XML. Complex biologics frequently contain interconnected antibody, receptor, protein, and nucleic acid sequences whose accuracy can be critical to the scope and prosecution of the patent.For applications subject to current requirements, ST.26 provides the standardized XML framework for presenting qualifying nucleotide and amino acid sequences. WIPO Sequence can assist with authoring, importing, transforming, and validating sequence listings, but careful scientific and patent review remains essential. The strongest approach is to treat the sequence listing as an integrated component of patent drafting: build a controlled sequence inventory, verify the underlying biology, maintain consistent sequence identifiers, validate the ST.26 XML, and cross-check the final listing against the complete patent disclosure.For oncology and immunotherapy inventions involving hundreds or thousands of sequences, that disciplined process can substantially reduce avoidable filing errors and help preserve consistency across the patent family’s future prosecution and international filings.