Expression and functional characterization of CD33 transcript variants in human acute myeloid leukemia

Area of Science:

• Hematology
• Immunology
• Molecular Biology

Background:

• CD33 is a validated target for acute myeloid leukemia (AML) immunotherapy, particularly with gemtuzumab ozogamicin (GO).
• Previous research identified a CD33 splice variant lacking exon 2 (CD33∆E2), impacting the V-set domain.

Purpose of the Study:

• To investigate the expression and functional characteristics of CD33 transcript variants in AML.
• To understand how different CD33 splice variants affect immunotherapy efficacy.

Main Methods:

• Analysis of CD33 splice variants in primary AML specimens.
• Engineering acute leukemia cell sublines to express individual CD33 variants.
• Assessing endocytic properties and GO cytotoxicity of CD33 variants.

Main Results:

• Identified full-length CD33 (CD33FL), CD33∆E2, CD33E7a, and CD33∆E2,E7a variants in AML specimens.
• All CD33 variants exhibited endocytic properties.
• CD33FL and CD33E7a were susceptible to GO cytotoxicity, while CD33∆E2 and CD33∆E2,E7a were not.
• Co-expression of CD33∆E2 did not affect CD33FL endocytosis or GO cytotoxicity.

Conclusions:

• CD33 expression in AML is more complex than previously understood.
• CD33 variants lacking exon 2 are not targeted by current GO therapy.
• These CD33 variants represent potential targets for future antibody-based immunotherapies.