The naive question: chemotherapy poisons cancer cells, but it also poisons healthy ones, which is why it's so brutal. What if you could deliver the poison only to the tumor? That is exactly the idea behind an antibody-drug conjugate — and the patents show it is less a single molecule than a system of three separately engineered parts.

Think of it like a guided missile. The antibody is the guidance system — engineered to lock onto a marker found mostly on cancer cells. The payload is the warhead, a toxin far too dangerous to inject on its own. And the linker is the tether that holds the warhead to the missile until it reaches the target.

“The present invention relates to an antibody-drug-conjugate capable of binding IGF-1R.”— U.S. Patent No. 11,661,457 source

That three-part structure is why ADCs are hard to build and why the patents cluster the way they do. Pierre Fabre's grant US11661457B2 covers an IGF-1R antibody-drug conjugate, and its lead claim is a small engineering blueprint written in shorthand: Ab-(L-D)n. "Ab" is the antibody, defined not loosely but by listing specific heavy- and light-chain variable-domain sequences (by SEQ ID number) so the guidance system is pinned down exactly. "D" is the drug — here a member of the dolastatin-10 / auristatin family, a class of extremely potent cell-killing toxins. "L" is the linker. And "n" is the drug-to-antibody ratio: a dependent claim fixes it at 2, another at 4. That single number is a real engineering dial — load too few warheads and the missile underperforms, load too many and the antibody itself starts to misbehave or clear too fast. The fact that it is claimed as a specific integer tells you how much that ratio matters.

The linker is the quiet hero, and the same Pierre Fabre claim treats it as a designed component in its own right. It is not "a chemical bond" but a defined assembly: a maleimide group to attach to the antibody, an optional cleavable amino-acid unit, and a self-immolative spacer (a "PAB" group) that releases the toxin only after the linker is cut. The logic is unforgiving. If the linker releases the payload too early, the toxin leaks into the bloodstream and you are back to chemotherapy's problem. If it never releases, the drug does nothing. So the patent specifies the exact chemistry of where and how the tether breaks — because controlling where and when the warhead goes off is the heart of the invention.

The other 2023 records show the same system engineered at different parts. Seagen's US11617798B2 covers anti-CD228 antibodies and the conjugates built from them — staking out a different guidance target (CD228) and the conjugates made from it, which is the "antibody" half of the system claimed as its own asset. And Seattle Genetics' US11795229B2 is even about methods of reducing the side effects of an anti-CD30 ADC therapy — proof that managing the consequences of payload release is a patentable problem in its own right, separate from the molecule itself.

Here's the 'so what.' An ADC is not one invention; it is a system, and every part — target antibody, payload class, linker chemistry, and the drug-to-antibody ratio — can be separately engineered and separately patented. That is why a single ADC can be wrapped in a thick stack of claims: one company can hold the antibody, another the linker-payload, another the dosing or side-effect-management method. Reading the Pierre Fabre claim alongside the two Seagen records, you can see the modality decomposed into its parts, each defended on its own terms.

The drug-to-antibody ratio claimed as a fixed integer — 2 in one dependent claim, 4 in another — deserves emphasis, because it is the parameter that most distinguishes an ADC from a plain antibody. Each toxin molecule must be chemically attached at a defined site, and the average number attached per antibody shapes everything: too few and the missile carries too small a warhead; too many and the antibody's own behavior degrades, clearing faster or aggregating. By claiming specific ratios, the Pierre Fabre patent is fencing off particular, deliberately chosen load-outs rather than a vague range — a sign of how tightly this single number is engineered.

The self-immolative spacer in the linker is the other detail worth dwelling on. The claim's "PAB" group is built so that, once the cleavable amino-acid unit is cut at the target, the spacer falls apart on its own and frees the toxin in active form. That two-step release — cut here, then auto-disassemble — is what lets the payload stay safely tethered in the bloodstream yet become fully active only at the destination. Seen alongside Seagen's separately claimed anti-CD228 antibodies and Seattle Genetics' claimed method for reducing anti-CD30 ADC side effects, it underlines the central point: the antibody, the linker-and-spacer chemistry, the payload, the load ratio, and even the management of release consequences are each their own engineering problem, each separately claimable.

One more structural point ties the three records together. Because the antibody is defined in the Pierre Fabre claim by explicit variable-domain sequences, the guidance system is itself a discrete, sequence-defined asset — which is exactly why Seagen can hold a separate estate around a different antibody target like CD228. The modality's value is distributed across its parts, and the patent filings carve it up accordingly rather than treating the conjugate as one indivisible thing.

The short version: when you read that a company has a promising ADC, picture a guided missile — and remember that the antibody is only the guidance. The toxin, the tether that releases it, and the precise number of warheads per antibody are where much of the 2023 patent work actually lives.