Novel CD33 antibodies unravel localization, biology and therapeutic implications of CD33 isoforms

Abstract

Lay abstract CD33 is a small protein that is often present on tumor cells in acute myeloid leukemia and is therefore the focus of some research to develop targeted treatments for the disease. One such CD33-targeted treatment - gemtuzumab ozogamicin has shown promise in helping acute myeloid leukemia patients. However, some patients have a variation of this small protein, resulting in a shorter form called CD33(D2), which makes the aforementioned treatment ineffective. In this study, the authors aimed to create two antibodies that would bind to both CD33 and CD33(D2) so that we can try to develop a treatment that is effective for all patients with acute myeloid leukemia. The aim of this study was to establish the therapeutic relevance of the CD33(D2) isoform by developing novel antibodies targeting the IgC domain of CD33. Two novel IgC-targeting antibodies, HL2541 and 5C11-2, were developed, and CD33 isoforms were assessed using multiple assays in cells overexpressing either CD33(FL) or CD33(D2) isoforms, unmodified acute myeloid leukemia (AML) cell lines and primary AML specimens representing different genotypes for the CD33 splicing single nucleotide polymorphism. CD33(D2) was recognized on cells overexpressing CD33(D2) and unmodified AML cell lines; however, minimal/no cell surface detection of CD33(D2) was observed in primary AML specimens. Both isoforms were detected intracellularly using novel antibodies. Minimal cell surface expression of CD33(D2) on primary AML/progenitor cells warrants further studies on anti-CD33(D2) immunotherapeutics.