Written by a parent, not a doctor. Nothing here is medical advice.

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Medicine

Inotuzumab (Besponsa)

Updated September 2026.

Also known as: Besponsa, InO

An antibody that finds the CD22 marker on leukemia cells and delivers a toxin straight inside them.

Inotuzumab (Besponsa) is an antibody with a toxin attached, given through the line. The antibody part finds CD22, a marker carried by most B-cell leukemia cells.

When the antibody locks onto CD22, the cell pulls the whole package inside, as it naturally does with that marker. Inside, the toxin (calicheamicin) is released and cuts both strands of the cell’s DNA, and the cell dies. The toxin is far too dangerous to give on its own; the antibody is what delivers it to the right cells. It is used when leukemia has come back or has not responded to the usual drugs.

I made an everyday analogy and a more scientific visualization of inotuzumab.

Everyday analogy

Inotuzumab ozogamicin is like a matching delivery that brings a cutter inside.

Inotuzumab ozogamicin is like a matching delivery that brings a cutter inside.An everyday delivery analogy in three stages. A teal delivery case travels on a powered roller lane to a building with a copper circle on its closed gate. Its diamond pass does not match, so the gate stays shut and the case stays outside. A dissolve introduces another building with a matching diamond marker. The gate opens, the whole closed case goes inside, and the gate closes behind it. Only then does the case retract its roller cover to release an uncrewed teal cutter. The view moves closer as the crawler rolls along the front lane and its jointed shears cut two timber supports behind that lane. The cut fragments fall and settle. A clearly labelled Later dissolve marks elapsed time before the weakened roof and its attached support pieces collapse and settle. No equipment drives away or moves to another building after delivery. The case and pass stand for the antibody carrier, the cutter for the released DNA-damaging payload, and the supports for DNA. The time dissolve is an editorial transition, not literal drug disappearance or reuse. Marker matching is not a guarantee that healthy cells are unaffected. 01No match. No entry.02A match. The whole case goes in.03The cutter breaks the supports.≠Different shapesGate stays shut=Matching shapesThe whole case goes inThe case opens insideCutter released insideCutting the supportsLaterThe supports are broken.The building cannot stay up.No match: the case stays outsideA match: the whole case is taken insideThe released cutter breaks the supports

1 / 3 No match: the case stays outside

No match: the case stays outside

  • Teal case and cutter = inotuzumab ozogamicin, an antibody carrying a cell-killing payload.

  • Matching pass = the antibody attaching to CD22, a marker on a cell. The whole medicine is then taken inside.

  • Case opening inside = the payload being released. Cutting the supports = damage to DNA, the cell’s instructions.

  • Building collapse = DNA damage that can cause the cell to die. The “Later” fade is a time transition, not the medicine leaving to be reused.

  • This analogy shows targeted delivery, not a perfect cancer-only lock. It does not mean that healthy cells are unaffected, show every effect, or guarantee an outcome.

Press play below for a more accurate visualization.

Interactive visual

How inotuzumab rides a leukemia cell's own recycling system to deliver a DNA-cutting payload inside it

Poster for How inotuzumab rides a leukemia cell's own recycling system to deliver a DNA-cutting payload inside it
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## From the blood to the cell In the blood vessel, inotuzumab carries a toxic payload on an antibody, so the drug travels toward the leukemia cell. ## A target that already recycles Cells recycle CD22 to reuse this surface protein; inotuzumab grips it, so the cell’s routine becomes a route inside. ## The cell brings the drug inside Because CD22 normally recycles in a membrane bubble, the cell draws the attached antibody and its payload inside too. ## Processing, release and DNA damage Inside an acidic processing compartment, the links holding the payload begin to break. The purple payload separates from the antibody, then leaves the compartment. The large antibody stays behind. The released payload reaches the nucleus, where the cell keeps its DNA. DNA has two connected strands. The payload fits into a narrow groove beside them. After activation, each payload damages nearby DNA. Breaks across both strands are difficult for this cell to repair. ## Damage starts self-destruction Because DNA damage overwhelms repair in this cell, its self-destruct program begins. Mitochondria release a signal, so more caspases activate and dismantle the cell from within. ## Sealed packets are cleared The dying cell forms small sealed packets, so a cleanup cell—a macrophage—can wrap and swallow the remains.

Side effects

The full list, kept up to date:

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