US Patent 9,079,949: Antibodies to Human C5 With pH-Dependent Binding, C5 Cleavage Inhibition, and FcRn-Engaging Variant Fc

What does US 9,079,949 actually claim?

US 9,079,949 is directed to isolated anti-human C5 antibodies (and fragments) that (1) bind human C5, (2) inhibit cleavage of C5 into C5a/C5b, and (3) incorporate a specific complementarity-determining region (CDR) set plus an Fc variant that engages FcRn to extend serum half-life. The claims also add functional constraints tied to pH-dependent affinity (human C5 binding at pH 7.4 vs pH 6.0) and to serum half-life in humans.

The core claim set is claims 1 and 9, which then branch into narrower embodiments (claims 2-4, 5-8, 10-12, 13-14) and downstream compositions and logistics claims (claims 15-20).

Core structural requirements (claims 1 and 9)

An antibody (or antigen-binding fragment) must satisfy all of the following:

Target and function
- Binds complement component human C5
- Inhibits cleavage of C5 into C5a and C5b (claims 1(a)-(b), 9(a)-(b))
CDR sequence constraints (exact SEQ ID NO mapping)
- Heavy chain CDR1: SEQ ID NO:23
- Heavy chain CDR2: SEQ ID NO:19
- Heavy chain CDR3: SEQ ID NO:3
- Light chain CDR1: SEQ ID NO:4
- Light chain CDR2: SEQ ID NO:5
- Light chain CDR3: SEQ ID NO:6
  (claims 1(c)(i)-(vi), 9(c)(i)-(vi))
Fc variant (FcRn binding) with CH3 substitutions in EU numbering
- Variant human IgG Fc that binds human FcRn
- CH3 domain includes substitutions:
- Met-429-Leu at residue corresponding to methionine 428
- Asn-435-Ser at residue corresponding to Asparagine 434
- EU numbering is specified; substitutions are anchored to native human IgG Fc positions.
  (claims 1(d), 9(d))
Pharmacokinetics constraint
- Human serum half-life ≥ 25 days
  (claims 5; also embedded in claim 9)

Core pH-dependent affinity constraints (claims 6-8 and 9)

The specification uses pH-dependent binding ratios and absolute Kd cutoffs to distinguish binding behavior at physiological vs acidic environments:

Claim 6: At pH 7.4 and 25°C, 0.1 nM ≤ Kd ≤ 1 nM
Claim 7: At pH 6.0 and 25°C, Kd ≥ 10 nM
Claim 8: The ratio
[ \frac{Kd(\text{pH 6.0})}{Kd(\text{pH 7.4})} > 25 ]
Claim 9: Ratio constraint: [ \frac{Kd(\text{pH 6.0})}{Kd(\text{pH 7.4})} > 24 ] plus half-life ≥ 25 days, plus the CDR set and Fc substitutions

Net effect: the patent is not limited to “anti-C5 antibodies” in general; it is limited to a narrow binding phenotype: stronger binding at pH 7.4, weaker binding at pH 6.0, paired with long persistence in serum via FcRn engagement.

How narrow are the claim boundaries?

The landscape hinge is that claim 1’s “CDR1-3” and claim 1’s Fc CH3 substitutions are both sequence-anchored and functionally constrained. This produces a layered narrowing effect:

Claim width by component

Claim element	Claim requirement type	Practical narrowing
C5 binding and C5 cleavage inhibition	functional	Eliminates non-blocking C5 binders
Exact CDR sequences (6 CDRs total)	sequence literal	Forces near-exact paratope architecture
Fc CH3 substitutions (Met-429-Leu, Asn-435-Ser; FcRn binding)	sequence literal + function	Forces specific FcRn-engaging variant
Half-life in humans	functional/PK assay	Requires Fc activity and likely manufacturability
pH-dependent Kd ratio	functional binding metric	Excludes C5 binders with flat pH response

Because the CDR sequences are specified by SEQ ID numbers, the enforceable scope is closer to a “defined paratope” patent than to a broad genus claim. Even conservative substitutions outside the listed CDR sequences can fall outside literal coverage, depending on how the “CDR comprising the amino acid sequence depicted in SEQ ID” is construed.

Where are the enforceability pressure points?

1) “Inhibits cleavage” is functional, but may be assay-specific

The claims require inhibition of cleavage of C5 into C5a/C5b. That is a functional constraint that may be satisfied by multiple antibodies, but a defendant may argue:

Inhibition measured by the claim-relevant assay is not met
Alternative mechanisms reduce cleavage readout without satisfying the exact inhibition definition

The patent’s leverage is that cleavage inhibition aligns with clinically relevant C5 blockade. The pressure point remains the mapping between claim language and assay protocol used during prosecution and later enforcement.

2) pH-dependent Kd cutoffs are highly specific

The ratio tests at pH 6.0 vs 7.4 are not generic. Claims 6-8 and 9 tie down:

Absolute Kd bounds at pH 7.4 (0.1–1 nM)
Weak binding at pH 6.0 (Kd ≥10 nM)
High ratio (>24 or >25)

These thresholds create a clear invalidity and design-around vector:

A competing antibody with different pH-binding architecture (even if it binds C5 potently at neutral pH) can fall outside the ratio/threshold claims.
A competitor can target the same pathway but tune pH response via paratope engineering or buffer/charge optimization.

3) FcRn engagement is constrained by two CH3 substitutions

The Fc variant is defined by CH3 substitutions:

Met-429-Leu
Asn-435-Ser

This is narrow. If a competitor uses a different FcRn-binding strategy (different positions or different substitutions) while maintaining long half-life, they may avoid literal coverage on Fc variant definition. Courts will typically not read in substitutes absent explicit equivalents.

4) “No detectable sialic acid residues” is a separate manufacturing constraint

Claims 13-14 tighten manufacturing and glycosylation phenotype:

Manufactured in CHO (claim 13)
Antibody does not contain detectable sialic acid residues (claim 14)

This can be a strong differentiator if a competitor makes a standard sialylated CHO product. If sialic acid is undetectable, claim 14 pulls coverage toward a deglycosylated or engineered glycoform profile.

What is the patent’s internal claim architecture (independent vs dependent coverage)?

Independent-style coverage

Claim 1: Independent, defines CDR set + Fc variant + C5 cleavage inhibition + binding + framework for half-life and pH constraints through dependent claims.
Claim 9: Independent-like second anchor; repeats most of claim 1 core but bakes in:
- pH ratio >24
- FcRn variant as defined
- serum half-life ≥25 days

Dependent claim “tighteners”

Claims 2 and 10: specify heavy and light variable regions by SEQ ID mappings
Claims 3 and 11: specify heavy chain constant region sequence by SEQ ID
Claims 4 and 12: specify full heavy and light polypeptide sequences by SEQ ID
Claims 5, 6-8: serum half-life and Kd/pH thresholds
Claims 13-14: CHO manufacturing and no detectable sialic acid
Claims 15-20: compositions, kit, syringe, article of manufacture with labeling for complement-associated condition

How does US 9,079,949 fit into the US anti-C5 antibody patent landscape?

Market context embedded in the claim design

The combination of:

anti-C5 blockade (prevents C5 cleavage into C5a/C5b)
engineered FcRn-binding variant for extended serum half-life
pH-dependent binding phenotype

maps onto the design goals of “next-generation” complement inhibitors that aim to:

retain strong target engagement at physiological pH
reduce engagement in acidic microenvironments (often endosomal)
prolong circulation via FcRn tuning

Within the broader US landscape, many anti-C5 approaches exist, including monoclonal antibodies and alternative formats. The claim set here is differentiated by:

explicit CDR sequence definition (rather than generic C5 binding)
explicit Fc CH3 substitutions (rather than generic “FcRn compatible”)
explicit pH-dependent Kd ratio constraints

Competitive claim-avoidance paths created by the claim terms

A generic anti-C5 antibody that:

binds C5 with similar potency at pH 7.4
but does not satisfy Kd ≥10 nM at pH 6.0 or ratio >24/25 may avoid claim 6-9 coverage.

An antibody with the same CDR sequences but a different FcRn variant:

can be outside claim 1(d)/9(d) if the CH3 substitutions are not the same.

An antibody with the same paratope and FcRn variant but shorter half-life:

avoids claim 5 and the embedded half-life in claim 9.

A standard sialylated CHO product:

may fall outside claim 14.

What prior art and obviousness arguments are likely to be used against these claims?

Because the claim text itself does not provide the application publication number, priority date, or the patentee’s earlier disclosures, a full, definitive prosecution-history-based assessment cannot be performed. Still, the claim structure strongly signals the standard novelty and obviousness attack pattern for this class of antibodies:

Likely novelty challenges

A novelty attack would focus on whether a single prior-art reference discloses:

an anti-human C5 antibody with the same CDR sequences (SEQ ID anchored)
plus Fc CH3 substitutions matching Met-429-Leu and Asn-435-Ser
plus pH-dependent Kd behavior thresholds

That is a high bar because it requires near match on both paratope and Fc features.

Likely obviousness challenges

Even if exact sequences are not found in one reference, obviousness is typically argued by combining:

known C5-blocking antibody scaffolds or paratope families
known FcRn-engaging Fc variants (CH3 substitutions)
known pH tuning approaches using charged residues or engineered binding kinetics

The pH ratio and Kd thresholds can be treated as optimization parameters. Examiners often view pH-dependent binding as a result-effective variable, particularly if the prior art teaches pH-dependent Fc interactions and charge-mediated antigen binding.

Where are the main invalidity/design-around vulnerabilities?

Vulnerabilities created by the pH ratio cutoffs

The pH constraints create both strength (specific phenotype) and vulnerability (parameter-driven obviousness). If prior art shows:

anti-C5 antibodies with similar binding at pH 7.4
and then shows generic methods to reduce binding in acidic pH (endosomal pH)

a challenger can argue that meeting a ratio >24/25 is within routine optimization.

Vulnerabilities created by “CDR comprising” exact sequences

The CDR sequence specificity increases enforceability against identical constructs but makes validity dependent on whether the exact CDR sequences are present or predictable. If earlier patents or papers disclose the same CDR set (or extremely close variants that still “comprise” the listed sequence), invalidity leverage rises.

Design-around that is likely to work

Three design-around levers stand out:

Keep C5 blockade but change the Fc CH3 substitutions away from Met-429-Leu/Asn-435-Ser.
Keep Fc but change the paratope so that Kd at pH 6.0 is not sufficiently weak or the Kd ratio is ≤24/25.
Keep both but reduce half-life below 25 days, if feasible without undermining clinical goals.

Claim-by-claim strategic map

Claims 1-4: sequence-locked paratope plus FcRn variant

Claim 1 sets the foundational sequence requirements.
Claims 2-4 narrow further by specifying variable and/or constant region sequences via SEQ IDs.

Claims 5-8: functional differentiation

Claim 5 (half-life ≥25 days)
Claim 6 (Kd at pH 7.4 between 0.1 and 1 nM)
Claim 7 (Kd at pH 6.0 ≥10 nM)
Claim 8 ratio >25

These claims are where competitors can most easily engineer around if they focus on pH-binding phenotype rather than C5 blockade alone.

Claim 9: bundled phenotype

Claim 9 integrates:

pH ratio >24
FcRn variant defined by CH3 substitutions
half-life ≥25 days

This “bundle” reduces flexibility in enforcement and also makes it easier to argue infringement requires satisfying multiple metrics simultaneously.

Claims 12-14: full polypeptide + manufacturing and glycoform

Claim 12 provides full heavy and light polypeptide sequences via SEQ IDs.
Claim 13 limits manufacturing to CHO.
Claim 14 limits glycoform by requiring no detectable sialic acid residues.

If a product uses different expression systems, or retains detectable sialylation, claim coverage can narrow sharply.

Claims 15-20: downstream commercial protections

Claim 15: pharmaceutical composition
Claim 16-17: therapeutic kit and syringe
Claim 18: article of manufacture with labeled intended use
Claims 19-20: composition variants tied to claim 9 and claim 12 embodiments

These claims help monetization by covering packaged products and marketed formulations, but they typically depend on proving the underlying antibody infringes.

Key takeaways for R&D and investment

US 9,079,949 is not a broad “anti-C5” patent. It is a sequence-locked paratope + Fc CH3 substitution + FcRn engagement patent with explicit pH-dependent binding cutoffs and human half-life ≥25 days.
The pH ratio and Kd thresholds are likely the single strongest differentiator against generic anti-C5 antibodies and the main avenue for design-around.
The Fc variant definition by two CH3 substitutions creates a straightforward non-infringement path if competitors select a different FcRn strategy while preserving C5 blockade.
If a program’s antibody product is a standard sialylated CHO IgG, claim 14 may be a key narrow gate that limits coverage.
For freedom-to-operate, the enforceability analysis should focus on whether candidate antibodies match: (i) the exact CDR sequences and (ii) the CH3 substitutions and (iii) the pH-dependent Kd phenotype and (iv) serum half-life threshold.

FAQs

1) What is the pH-dependent binding requirement in claim 9?

Claim 9 requires a ratio: [ Kd(\text{pH 6.0})/Kd(\text{pH 7.4}) > 24 ] with additional constraints on Fc CH3 substitutions and human serum half-life ≥25 days.

2) Which Fc changes are explicitly required?

The Fc CH3 domain must include substitutions Met-429-Leu and Asn-435-Ser (with correspondence to native positions methionine 428 and asparagine 434 in EU numbering) and must bind human FcRn.

3) Does the patent cover both antibodies and fragments?

Yes. Each claim is written to cover an isolated antibody or antigen-binding fragment thereof.

4) How do claims 13-14 narrow manufacturing scope?

Claim 13 requires manufacture in CHO cells. Claim 14 requires the antibody does not contain detectable sialic acid residues.

5) What do claims 15-20 protect commercially?

They cover pharmaceutical compositions and product packaging concepts:

composition with carrier
therapeutic kit including instructions and optionally a syringe
article of manufacture with labeled intended administration
composition embodiments tied to the underlying antibody claims

References

US Patent 9,079,949 (claims text as provided).

Applicant	Tradename	Biologic Ingredient	Dosage Form	BLA	Approval Date	Patent No.	Expiredate
Alexion Pharmaceuticals, Inc.	ULTOMIRIS	ravulizumab-cwvz	Injection	761108	December 21, 2018	⤷ Start Trial	2035-03-06
Alexion Pharmaceuticals, Inc.	ULTOMIRIS	ravulizumab-cwvz	Injection	761108	October 09, 2020	⤷ Start Trial	2035-03-06
Alexion Pharmaceuticals, Inc.	ULTOMIRIS	ravulizumab-cwvz	Injection	761108	June 22, 2022	⤷ Start Trial	2035-03-06
>Applicant	>Tradename	>Biologic Ingredient	>Dosage Form	>BLA	>Approval Date	>Patent No.	>Expiredate

Country	Patent Number	Estimated Expiration
World Intellectual Property Organization (WIPO)	2015134894	⤷ Start Trial
United States of America	9803007	⤷ Start Trial
United States of America	9663574	⤷ Start Trial
United States of America	9371377	⤷ Start Trial
United States of America	9206251	⤷ Start Trial
United States of America	9107861	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration

Summary for Patent: 9,079,949