Bloody camouflage: NMR analysis assists universal tranfusion

Ezine

Published: Mar 15, 2011
Author: David Bradley
Channels: NMR Knowledge Base

thumbnail image: Bloody camouflage: NMR analysis assists universal tranfusion

Cloaking blood cells

Coating blood cells with an immunological camouflage could one day lead to a new type of blood product that avoids the problem of A,B,O,± blood typing currently required for transfusion patients. NMR spectroscopy underpins the analytical work.

Chemists have been hoping to make synthetic blood for many years; such a product could be useful when there are shortages of donor blood, particularly in emergency situations, natural disasters and on the battlefield. The same products might also circumvent the issue of blood type, which makes it impossible for some patients to receive blood from donors with another type. Generally, some people are universal donors, but universal recipients are rare and most people must receive cross-matched blood.

While progress has been made towards artificial blood, an alternative approach has now been taken by biomedical engineers in Canada who are developing the technology to "camouflage" natural blood cells from donors that means that will prevent the recipient's immune system from mounting a potentially lethal response following transfusion if they are given the "wrong" blood type. The researchers report details of their so-called immuno-camouflage technique in the journal Biomacromolecules this month.

Polymers side step blood typing

Maryam Tabrizian and Sania Mansouri of McGill University, in Montreal, together with Yahye Merhi of the Montreal Heart Institute and Francoise Winnik of the University of Montreal note that blood type matching prior to transfusion is a rather difficult proposition. There are the familiar ABO blood types with which medical staff must contend as well as the Rh (rhesus) and other factors; in total there are 29 different red blood cells types. Depending on the precise correlation between donor blood and the patient's own blood type problems can arise from simple immune reaction and shock to organ failure or death. Some blood types are rare others much more common, finding suitable donors at short notice when a rare type arises in surgery can be difficult. The issue is compounded by the high cost of blood type matching.

To develop a "universal" red blood cell, the scientists in Canada have investigated ways of encasing live and functional, individual red blood cells within a multilayered shell formed from a biocompatible polymeric material. The team has built up layer-by-layer an optimized shell comprising four bilayers of alginate (AL) and chitosan-graft-phosphorylcholine (CH-PC), which are surrounded by two bilayers of AL and poly-L-lysine-graft-polyethylene glycol (PLL-PEG). They used NMR spectroscopy to confirm the grafting ratio of the coatings. The grafting ratio is the percentage of amine functions of PLL or CH modified by PEG and PC, respectively, they explain. NMR showed it to be 12.5 mol% for PLL-PEG and 30 mol% for CH-PC.

The polymeric shell acts as a chemical cloaking device, the team says, masking the proteins and peptides on the surface of the red blood cell that would otherwise trigger an immune response in a non-matched patient. The team points out that importantly, oxygen can still penetrate the polymer shell so that the red blood cells can carry on their normal function of supplying oxygen to body cells. As the patient recuperates, they produce their own new, healthy red blood cells to displace the camouflaged cells, which are ultimately broken down and excreted as waste products.

Universal blood

"The results of this study mark an important step toward the production of universal RBCs," the researchers state. They demonstrated viability and functionality of coated red blood cells by haemolysis assay and by the RBCs ability to take up oxygen. They then confirmed that the immuno-camouflage functions as predicted by showing that ABO/D (Rh) blood group antigens present on the surface of the RBCs triggered only a muted response from their respective antibodies.

"The outstanding immuno-camouflage property of our polyelectrolyte systems has been attributed to its unique design that might provide a new paradigm toward the production of universal RBCs for medical transfusion," the team concludes.

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.