BL22 immunotoxin (CAT-3888)

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No longer in clinical development. Related to GCR-8015/CAT-8015, which have increased affinity to CD22.

General information

Class/mechanism: Recombinant anti-CD22 immunotoxin fusion protein comprised of a murine anti-CD22 antibody fragment (disulphide-linked Fv, dsFv) and Pseudomonas exotoxin PE38. BL22 binds to CD22 positive cells and is endocytosed, resulting in intracellular release of the toxin and cell death.

The original manufacturer was acquired in 2005.[1] Development of this drug was discontinued in 2008, at which time it was superseded by the more potent and less toxic Moxetumomab pasudotox (HA22).

Preliminary data

Hairy cell leukemia

  1. Abstract: R. J. Kreitman, W. H. Wilson, M. Stetler-Stevenson, P. Noel, I. Pastan. Long term follow-up of BL22 in cladribine-resistant hairy cell leukemia. 2004 ASCO Annual Meeting abstract 6624.
  2. Abstract: R. J. Kreitman, W. H. Wilson, M. Stetler-Stevenson, P. Noel, D. J. FitzGerald, I. Pastan. Phase II trial of CAT-3888 (BL22) in chemo-resistant hairy cell leukemia. 2007 ASCO Annual Meeting abstract 7095.
  3. Kreitman RJ, Stetler-Stevenson M, Margulies I, Noel P, Fitzgerald DJ, Wilson WH, Pastan I. Phase II trial of recombinant immunotoxin RFB4(dsFv)-PE38 (BL22) in patients with hairy cell leukemia. J Clin Oncol. 2009 Jun 20;27(18):2983-90. Epub 2009 May 4. link to original article PubMed

Also known as

  • Code name: GCR-3888


  1. Cambridge Antibody Technology Group PLC (CATG) Acquires Oncology Product Candidates From Genencor International, Inc.