# CD33

Source: https://onco.cc/targets/cd33/  
OnCo record `cd33` (Target). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

CD33 is a myeloid surface marker on the blasts of 85 to 90% of acute myeloid leukaemias and on normal myeloid cells, so drugs against it also hit healthy marrow. It is the target of gemtuzumab ozogamicin, the first ADC ever approved (2000), withdrawn in 2010 and re-approved in 2017 at a lower fractionated dose.

## Summary

CD33 (Siglec-3) is a myeloid lineage marker expressed on the blasts of roughly 85 to 90 percent of acute myeloid leukaemias and on normal myeloid cells, so drugs against it hit healthy marrow as well as leukaemia. It is the antigen behind gemtuzumab ozogamicin, the first antibody-drug conjugate ever approved: approved in 2000, withdrawn in 2010 after toxicity and lack of confirmed benefit, and re-approved in 2017 at a lower fractionated dose. That history is an object lesson in ADC development, showing that dose schedule and linker stability can decide whether a valid target succeeds. Newer CD33 approaches, including bispecifics and CAR-T, still have to solve the same on-target myelosuppression. For a newcomer, CD33 is the AML surface marker on which the ADC field first learnt its lessons.

## Fields

- Kind: Target
- Last checked: 2026-09-04
- Tags: adc-target
- Symbol: CD33
- Class: surface-antigen
- Biology: Siglec-3; expressed on AML blasts and normal myeloid cells.
- Where found: Acute myeloid leukaemia

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/CD33
- Wikipedia: https://en.wikipedia.org/wiki/CD33

## Connected records

- biomarkers: [CD33 expression (CD33-positive)](https://onco.cc/biomarkers/cd33-expression/)
- cancers: [Acute myeloid leukaemia](https://onco.cc/cancers/aml/), [Acute myeloid leukaemia in children](https://onco.cc/cancers/aml-paediatric/)
- drugs: [Gemtuzumab ozogamicin](https://onco.cc/drugs/gemtuzumab-ozogamicin/)
- companies: [Actinium Pharmaceuticals](https://onco.cc/companies/actinium-pharmaceuticals/), [Orum Therapeutics](https://onco.cc/companies/orum-therapeutics/), [Vor Biopharma](https://onco.cc/companies/vor-biopharma/)
- trials: [ALFA-0701](https://onco.cc/trials/alfa-0701/), [COG AAML0531](https://onco.cc/trials/aaml0531/)
- technologies: [Antibody-drug conjugate (ADC)](https://onco.cc/technologies/adc/), [Radio-antibody & radio-ADC](https://onco.cc/technologies/radioimmunotherapy/)
- roadmaps: [ADC roadmap: from Mylotarg to bispecific and dual-payload ADCs](https://onco.cc/roadmaps/adc-generations/)

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JSON: https://onco.cc/api/v1/entities/cd33.json