High mannose exposure on blood cells and development of new therapeutic modalities for sickle cell disease and cancer.

When cells reach the end of their lives, often induced by oxidative damage, they display eat me signals to macrophages. Several such signals have been described, but it is widely believed others are yet to be discovered. We have discovered that spectrin, a major constituent of the membrane skeleton is able to undergo N-glycosylation, predominantly with high mannoses. In healthy cells, mannosylated spectrin is held in microdomains just under the plasma membrane. Oxidative damage causes these domains to be ‘externalised’, so that the high mannoses are available for binding to phagocytic receptors, notably the mannose receptor (CD206) on macrophages (1). Most of this work has been performed using red blood cells. However, as spectrins are ubiquitously expressed, we think the mechanism is constitutively present in all mammalian cells. Indeed, we have data indicating this in several other nucleated cells.

The mechanism is particularly active in sickle cell disease and appears to mediate the extravascular haemolytic anaemia characteristic of the disease. In addition, it appears to be triggered relatively easily by infection with Plasmodium falciparum in sickle cell trait, thus helping to explain the well-known protection against malaria.

In the first part of this project, we will determine whether the new mechanism is active in other anaemias, particularly those associated with oxidative stress such as drug associated, G6PD deficiency and the anaemia of chronic inflammation. We also have limited data that indicate high levels of mannose display in red cells from patients who have undergone splenectomy. This failure of clearance of mannose bearing cells may provide the explanation for why septicaemia with Streptococcus pneumoniae is so common after splenectomy, as the cell walls of this organism are known to contain mannoses.

In the second part of the project, we will exploit this new mechanism to develop new treatment approaches for cancer. If macrophages can be stimulated to phagocytose red blood cells by coating their surfaces with high mannoses, then it should also be possible to get macrophages to eat cancer cells by coating their surfaces in these mannoses. This could be achieved by attaching high mannoses to antibodies against cancer cells, which should be relatively easy to achieve as antibodies produced in yeast cells have this property. We also plan to use genetic engineering to replace mannose receptors in macrophages with chimaeric receptors juxtaposing the intracytoplasmic and transmembrane portions of the mannose receptor with single chain variable fragments that recognise cancer cells. We have pilot data showing that this is indeed the case.

We envisage transducing CD34+ haematopoietic stem cells with a construct expressing the chimaeric receptor in the monocyte-macrophage lineages. Such cells should then phagocytose malignant cells bearing the relevant tumour associated antigen. It is hoped that Prof. Andy Porter will be able to supply some of the single chain antibody fragments.

The malignant part of this project will be carried out in collaboration with Prof. Anastasios Karadimitris, Hammersmith Hospital, Imperial College, London. Prof. Karadimitris is an expert in myeloma, which will be the first targeted malignancy. This is because autografting CD34+ cells is part of the routine treatment of myeloma, which should expedite an early clinical trial if the technology proves to be efficacious in vitro and in animal models.

APPLICATION PROCEDURE:
This project is advertised in relation to the research areas of MEDICAL SCIENCES. Formal applications can be completed online: https://www.abdn.ac.uk/pgap/login.php. You should apply for Degree of Doctor of Philosophy in Medical Sciences, to ensure that your application is passed to the correct person for processing.

NOTE CLEARLY THE NAME OF THE SUPERVISOR AND EXACT PROJECT TITLE ON THE APPLICATION FORM.

Candidates should contact the lead supervisor to discuss the project in advance of submitting an application, as supervisors will be expected to provide a letter of support for suitable applicants. Candidates will be informed after the application deadline if they have been shortlisted for interview. Interviews are expected to take place on 23rd or 24th July 2019.