US Patent 5,767,251: What the Claims Actually Cover in Recombinant Human Fertility Hormones
US Patent 5,767,251 claims a narrow category of biologically active recombinant human fertility hormones defined by (1) being heterodimeric, (2) being recombinantly produced, (3) being one of three specific heterodimeric hormones (hCG, hLH, or hFSH), and (4) being free from contamination by any other proteins of human origin. The dependent claims then lock the scope to each specific hormone: hCG (claim 2), hLH (claim 3), hFSH (claim 4).
This creates a claim set that is less about the core recombinant expression concept and more about purity constraints and product definition for heterodimeric hormones that are already known in recombinant form.
What is the claimed invention at the molecular and product level?
Claim 1 is a product claim with four built-in limitations:
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Heterodimeric
The claimed product is “a recombinantly produced biologically active heterodimeric human fertility hormone.”
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Identity limited to three named hormones
The hormone is selected from:
- human chorionic gonadotropin (hCG)
- human luteinizing hormone (hLH)
- human follicle stimulating hormone (hFSH)
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Recombinant production requirement
The product must be “recombinantly produced.”
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Purity limitation defined by contaminant class
The product must be “free from contamination by any other proteins of human origin.”
That final element is the critical differentiator. “Free from contamination by any other proteins of human origin” is both broad and operationally strict: it excludes any co-purified human proteins other than the target hormone itself.
How do claims 2-4 change enforcement leverage?
Claims 2-4 narrow claim 1 by specifying the product:
- Claim 2: recombinantly produced hCG meeting claim 1’s requirements
- Claim 3: recombinantly produced hLH meeting claim 1’s requirements
- Claim 4: recombinantly produced hFSH meeting claim 1’s requirements
Practically, claim 2-4 reduce ambiguity in product identity while preserving the most challenging limitation: purity from other human proteins.
How strong are these claims against the likely prior art?
Is the core recombinant expression concept likely old?
For all three hormones, recombinant or biotechnological production was already established before the filing date range that led to US 5,767,251. Historically, recombinant production of gonadotropins emerged from the late 1980s into the early 1990s. In that setting, claim 1’s “recombinantly produced” limitation alone is usually insufficient to confer patentability if earlier patents disclose recombinant production of hCG, hLH, or hFSH.
The claim’s likely defensibility therefore hinges on the contamination/purity definition, not on the recombinant concept.
What does “heterodimeric” contribute?
hLH and hFSH are naturally heterodimeric glycoproteins (alpha and beta subunits with noncovalent association). hCG is also a heterodimeric glycoprotein.
So “heterodimeric” is probably not a strong differentiator by itself, because these hormones are inherently heterodimeric. It functions more as a category gate to avoid single-chain or other hormone structures.
What prior art pressure exists for the purity limitation?
The phrase “free from contamination by any other proteins of human origin” is a product purity requirement, not a specific manufacturing step. That creates two competing effects in validity and infringement:
- Validity risk: prior art may already disclose recombinant preparations of these hormones with high purity and minimal human protein impurities, sometimes defined in terms of “substantially free of” or “substantially purified,” or using purity metrics (HPLC, SDS-PAGE, ELISA-based host-cell protein assays, etc.).
- Infringement risk: even if prior art used other purity standards, the claim’s “free from contamination” language can be argued as stricter than “substantially free” if a competitor’s product contains detectable trace levels of other human proteins.
From a landscape standpoint, purity-related claims are often contentious because:
- “contamination” and “proteins of human origin” can be defined differently by analytical method;
- “free” can be litigated as either a strict zero-tolerance requirement or as functionally “no meaningful detectable contamination.”
How does the claim language affect claim construction?
Key construction levers:
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“biologically active”
Bioactivity can be shown by in vitro or in vivo potency assays (cell-based signaling, receptor binding, or functional assays). Competitors can sometimes argue non-equivalence if bioactivity is comparable but assay-specific. But for gonadotropins, bioactivity is typically a given for correctly folded recombinant products.
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“free from contamination by any other proteins of human origin”
This is the central ambiguity:
- Does it mean the product is purified to exclude host-cell derived human proteins?
- Does it exclude co-expressed recombinant fragments?
- Does it exclude proteins from the purification reagents that are human-derived (for example, human albumin in formulations at trace levels)?
If a competitor uses non-human purification aids and buffers, the “human origin” contaminant class is easier to address. If the competitor uses human protein excipients or deploys affinity purification that could co-isolate human proteins, the purity argument becomes harder.
Infringement mechanics: what would a product need to prove?
A competitor product would need to match four claim elements simultaneously
For a putative infringer to avoid the claim, it must break at least one limitation:
- The product must not be heterodimeric (unlikely for these hormones).
- Or it must not be recombinantly produced (also unlikely).
- Or it must not be biologically active (also unlikely).
- Or it must contain “contamination” by other proteins of human origin (meaning the product would have to include additional human-origin proteins that disqualify it).
Since the claim is a product claim, the strongest infringement path is to show that a commercial recombinant product of hCG, hLH, or hFSH is:
- biologically active,
- heterodimeric,
- recombinant, and
- purified to the degree that it is “free” of other human proteins.
That means the purity standard becomes a litigation pivot. Many commercial lots will be designed to remove host cell proteins and protein contaminants. But the “human origin” phrase can still be attacked if residual human proteins exist or if residual human-derived reagents are considered “contamination.”
Competitive and patent landscape context
Which technologies matter around US 5,767,251?
The landscape around US 5,767,251 is dominated by three technological clusters:
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Recombinant expression of glycoprotein gonadotropins
Including expression of alpha and beta subunits and formation of the heterodimer.
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Purification and characterization of recombinant gonadotropins
Including removal of host-cell proteins, DNA, aggregates, and correctly attributing residual impurities.
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Regulatory-grade manufacturing and lot-to-lot consistency
Industrial ability to meet purity and potency specs can make or break both litigation outcomes and design-around strategy.
What is the likely position of this patent in the broader timeline?
US 5,767,251 sits in the era when recombinant gonadotropins were transitioning from proof-of-concept to regulated commercial products. In that phase, many early patents cover expression and purification. The uniqueness of US 5,767,251 is the additional content-defined purity element: not just purification generally, but “free from contamination by any other proteins of human origin.”
That kind of claim is often used to secure broader commercial control because:
- competitors still need extremely high purity to meet clinical and regulatory requirements;
- competitors cannot easily add impurity on purpose without risking safety and efficacy.
What claims are vulnerable to design-around strategies?
Purity-based design-around is inherently limited
To avoid claim 1, a competitor could try to introduce “contamination” by human-origin proteins. That is typically not a realistic strategy because:
- it undermines product purity and safety profile expectations;
- it can trigger regulatory failure;
- it risks immunogenicity.
Identity-based design-around is also limited
Because claims are limited to hCG, hLH, and hFSH, alternative hormone analogs or non-identical formulations could avoid literal infringement. However, if the analog is still an hCG/hLH/hFSH heterodimeric hormone, purity and identity problems persist.
Process-based arguments do not fully help
Even if a competitor uses a different expression system or purification method, the product claim only cares about product characteristics. Unless the competitor can demonstrate that their product is not “free” from other human proteins, changing manufacturing will not eliminate infringement exposure.
How this claim set fares as an investment and licensing asset
Strengths
- Clear product identity via the three named hormones.
- A potentially strong differentiator: exclusion of “any other proteins of human origin.”
- Dependent claims map cleanly to each marketable product category (hCG, hLH, hFSH).
Weaknesses
- “Recombinantly produced” is likely not novel for these hormones in the relevant era.
- Purity definitions may be litigated as functional versus absolute, with heavy reliance on assay detection thresholds and analytical validation.
- Broad phrasing invites arguments about what counts as “human origin” and what counts as “contamination.”
Enforcement posture
If asserted, the enforceability will likely turn on:
- whether the competitor product has detectable or present other human-origin protein impurities (or whether the “free” requirement is treated as strict or practical);
- whether the asserted competitor product matches the heterodimeric structure and bioactivity.
From a licensing perspective, parties often prefer to settle rather than litigate complex purity and assay issues.
Key Takeaways
- US 5,767,251 claims recombinant, biologically active heterodimeric hCG, hLH, and hFSH, with the defining differentiator being the product is “free from contamination by any other proteins of human origin.”
- The recombinant aspect is likely not the main validity driver; the patent’s leverage likely rests on content-defined purity.
- Infringement and validity are likely to hinge on how courts treat “free,” “contamination,” and “proteins of human origin,” which ties directly to analytical detection and product definition in commercial lots.
- Design-around via manufacturing changes is limited because the claim is product-based; design-around via purity alteration is generally impractical for regulatory-grade gonadotropins.
FAQs
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Is “heterodimeric” a strong patent differentiator for hCG, hLH, and hFSH?
No. These hormones are inherently heterodimeric glycoproteins, so the term mostly defines category rather than novelty.
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What limitation most likely drives patentability for US 5,767,251?
The purity requirement: being “free from contamination by any other proteins of human origin.”
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Does a different expression system avoid infringement under a product claim like this?
Not by itself. A competitor must still make a product that lacks other human-origin protein contamination as defined in the claim.
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How would bioactivity be evaluated in an infringement fight?
Through established gonadotropin potency or receptor-signaling assays demonstrating biologically active function.
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Can a competitor avoid the claim by adding impurities deliberately?
Generally not, because adding human-origin protein contamination conflicts with regulatory-grade purity and safety expectations, and would likely increase immunogenicity risk.
References
[1] United States Patent and Trademark Office. US Patent 5,767,251.
