Functions, evolution and therapeutic potential of novel activating Siglecs

The Sialic acid binding immunoglobulin-like lectins (Siglecs) are important components of immune recognition. Comparative genomics showed that SIGLEC11 genes underwent dynamic gene duplication and conversion, forming a potentially inhibitory (SIGLEC11)/activating (SIGLEC16) receptor pair in chimpanzees and humans. I identified full-length cDNA of human SIGLEC16, previously classed as a pseudogene (SIGLECP16). A UK based polymorphism screen for the two alleles, one functional and the other a pseudogene, of SIGLEC16 indicated that they are present at a similar frequency. Using Siglec-16 specific antisera, I identified Siglec-16 protein in normal human brain, and esophageal and lung tumours. An extensive comparative genomic analysis of the CD33rSiglec cluster was carried out to understand the evolution of other activating Siglecs. The CD33rSiglec cluster could be divided into two subclusters, inverted relative to each other. Two regions of strong correspondence provided evidence for a large-scale inverse duplication over 180 million years ago. Activating Siglecs appear to have arisen rapidly in primates but subsequently underwent de-selection. SIGLEC15 is evolutionarily conserved and its sequence is distinct from those of other members of the Siglec family. I raised A9E8, a phage display monoclonal antibody specific to Siglec-15. I found low surface expression on healthy leukocytes, including T cells, monocytes, macrophages and dendritic cells. However, expression was much higher on blasts of acute myeloid leukaemia (AML) patients. I detected prominent Siglec-15 expression in an AML patient who was negative for CD33, a common target in the treatment of AML. Siglec-15 therefore has potential as a novel target for AML treatment. Experiments showed that Siglec-15 is rapidly endocytosed, suggesting that it may be exploited for introducing toxins into leukaemic cells.EThOS - Electronic Theses Online ServiceGBUnited Kingdo