Re: Zymequest
I would like to share my perspective as Hematologist on the issues raised in your message.
(1) ABO-D blood grouping antigens are present on the surface membrane of Red Cells. Hemoglobin is present in the core of the Red cells and has no ABO-D antigens. A person with group O (Universal Donor) is supposed to have neither A or B antigens on the surface membrane of Red cells. Please remember there are other smaller antigens on the RBC membranes, which are not significant for most situations: Kell, Duffy etc. Any treatment of Red cells will have to eliminate AB and D antigens, and preferably all small antigens. This may be feasible, chemically or enzymatically.
However, this solves only 2 problems:(1) We donot have to croos match blood for transfusion, but it still needs to be typed initially to select which units should be convereted to O or treat all blood, regradless of group to save cost of initial typing. Certainly the process of cleansing/chemical treatment will involve costs and nullify the cost benefit of not cross matching.(2) Theoritically, with this process,we may be able to use any blood from any individual, regardless of type compatibility and save " wastage" of blood. In reality, there is always shortage of blood and so called wastage is very minimal. As you mentioned, after it is converted to) from A or B, there will have to be quality control tests to make sure that conversion is complete. This will add further costs.
This process will not solve problem of longer shelf life. With anti coagulant used today: CPDA-2, the shelf life after collection is appr. 6 weeks. This process will not solve the big problems of limited supply, need for storage of blood at 4 degree Celsius, and the BIGGEST concern today: transmission of blood borne diseases.
I still believe, after all thoughts for long time, that only viable solution is to have a Oxygen carrier, that will mimic the physiological role of normal Hemoglobin. In my opinion, there are only 2 serious contenders in the game: Somatogen with Optro-rHb 1.1 and Alliance Pharmaceuticals with Perflubro based compounds. Perflubro has demonstrated Oxygen transport abilities like Hemoglobin. The first generation Perflurocarbons product was marked by Green Gross Corporation, but has been withdrawn from market. It carried very little Oxygen and had very short half life. Alliance Pharmaceuticals (ALLP) is trying next generations Perflurocarbons: Perflubro to address these shortcomings. This copmound Perflubro is undergoing early phase clinical trials as blood substitute. It is in late phases of clinical trial as Oxygen carrier in infants and adults with ARDS-Adult Respiratory Distress Syndrome.Recent reoprts suggest very good benefits in ARDS with Perflubro.
Somatogen's rHb 1.1 is genetically engineered Hemoglobin, identical to natural hemoglobin. Since rHb 1.1 is free solution and not stored in packets of Red Cells, it has no blood group antigens to worry abour( present on Red cell membrane). However, this free solution reduces it half life to several hours, rather than 60 days with RBC containing Hemoglobin. Somatogen has long half life-modified Hemoglobins: rHb 4.11 and r Hb 4.14 in development to address short half life problem. The half life can also be prolonged by other means like combining with PEG(Poly Ethylene Glycol).
Based on available information, I still believe that Somatogen has what the Medical Science needs. It should revolutionaze the practice of Blood transfusion, just as Humulin (genetically engineered Insulin from Lilly) did to treatment of Diabetes, sending Beef and Pork derived Insulins to Annals of Medicine.
Thanks
Bharat Barai M.D.
Hematologist |
