Chemistry: molecular biology and microbiology – Enzyme – proenzyme; compositions thereof; process for... – Hydrolase
Reexamination Certificate
1998-04-30
2001-05-08
Prouty, Rebecca E. (Department: 1652)
Chemistry: molecular biology and microbiology
Enzyme , proenzyme; compositions thereof; process for...
Hydrolase
C435S200000, C435S320100, C435S325000, C435S252300, C536S023200
Reexamination Certificate
active
06228631
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a recombinant enzyme for use in the removal of type A antigens from the surface of cells in blood products, thereby converting certain sub-type A blood products to type O blood products and certain type AB blood products to type B blood products. This invention further relates to methods of cloning and expressing said recombinant enzyme. More particularly, this invention is directed to a recombinant chicken liver &agr;-N-acetylgalactosaminidase enzyme, methods of cloning and expressing said recombinant &agr;-N-acetylgalactosaminidase enzyme, and a method of removing type A antigens from the surface of cells in type A and AB blood products using said recombinant &agr;-N-acetylgalactosaminidase enzyme by contacting said enzyme with blood products so as to remove the terminal moiety of the A-antigenic determinant from the surface of cells (for example, erythrocytes) in said blood products, while allowing the structure and function of the cells in the blood products to remain intact. The recombinant &agr;-N-acetylgalactosaminidase enzyme of this invention provides a readily available and cost-efficient enzyme which can be used in the removal of type A antigens from the surface of cells in type A and AB blood products. Treatment of certain sub-type A blood products with the recombinant enzyme of this invention provides a source of cells free of the A antigen, which blood products are thereby rendered useful in transfusion therapy in the same manner of O type blood products.
BACKGROUND OF THE INVENTION
As used herein, the term “blood products” includes whole blood and cellular components derived from blood, including erythrocytes (red blood cells) and platelets.
There are more than thirty blood group (or type) systems, one of the most important of which is the ABO system. This system is based on the presence or absence of antigens A and/or B. These antigens are found on the surface of erythrocytes and on the surface of all endothelial and most epithelial cells as well. The major blood product used for transfusion is erythrocytes, which are red blood cells containing hemoglobin, the principal function of which is the transport of oxygen. Blood of group A contains antigen A on its erythrocytes. Similarly, blood of group B contains antigen B on its erythrocytes. Blood of group AB contains both antigens, and blood of group O contains neither antigen.
The blood group structures are glycoproteins or glycolipids and considerable work has been done to identify the specific structures making up the A and B determinants or antigens. It has been found that the blood group specificity is determined by the nature and linkage of monosaccharides at the ends of the carbohydrate chains. The carbohydrate chains are attached to a peptide or lipid backbone which is embedded in the lipid bi-layer of the membrane of the cells. The most important (immuno-dominant or immuno-determinant) sugar has been found to be N-acetylgalactosamine for the type A antigen and galactose for the type B antigen.
There are three recognized major sub-types of blood type A. These sub-types are known as A
1
, A intermediate (A
int
) and A
2
. There are both quantitative and qualitative differences which distinguish these three sub-types. Quantitatively, A
1
erythrocytes have more antigenic A sites, i.e., terminal N-acetylgalactosamine residues, than A
int
erythrocytes which in turn have more antigenic A sites than A
2
erythrocytes. Qualitatively, the transferase enzymes responsible for the formation of A antigens differ biochemically from each other in A
1
, A and A
2
individuals. Some A antigens found in A
1
cells contain dual A antigenic sites.
Blood of group A contains antibodies to antigen B. Conversely, blood of group B contains antibodies to antigen A. Blood of group AB has neither antibody, and blood group O has both. A person whose blood contains either (or both) of the anti-A or anti-B antibodies cannot receive a transfusion of blood containing the corresponding incompatible antigen(s). If a person receives a transfusion of blood of an incompatible group, the blood transfusion recipient's antibodies coat the red blood cells of the transfused incompatible group and cause the transfused red blood cells to agglutinate, or stick together. Transfusion reactions and/or hemolysis (the destruction of red blood cells) may result therefrom.
In order to avoid red blood cell agglutination, transfusion reactions and hemolysis, transfusion blood type is cross-matched against the blood type of the transfusion recipient. For example, a blood type A recipient can be safely transfused with type A blood which contains compatible antigens. Because type O blood contains no A or B antigens, it can be transfused into any recipient with any blood type, i.e., recipients with blood types A, B, AB or O. Thus, type O blood is considered “universal”, and may be used for all transfusions. Hence, it is desirable for blood banks to maintain large quantities of type O blood. However, there is a paucity of blood type O donors. Therefore, it is useful to convert types A, B and AB blood to type O blood in order to maintain large quantities of universal blood products.
In an attempt to increase the supply of type O blood, methods have been developed for converting certain type A, B and AB blood to type O blood. For example, U.S. Pat. No. 4,609,627 entitled “Enzymatic Conversion of Certain Sub-Type A and AB Erythrocytes” (“the '627 Patent”), which is incorporated herein by reference, is directed to a process for converting A
int
and A
2
(including A
2
B erythrocytes) to erythrocytes of the H antigen type, as well as to compositions of type B erythrocytes which lack A antigens, which compositions, prior to treatment, contained both A and B antigens on the surface of said erythrocytes. The process for converting A
int
and A
2
erythrocytes to erythrocytes of the H antigen type which is described in the '627 Patent includes the steps of equilibrating certain sub-type A or AB erythrocytes, contacting the equilibrated erythrocytes with purified chicken liver &agr;-N-acetylgalactosaminidase enzyme for a period sufficient to convert the A antigen to the H antigen, removing the enzyme from the erythrocytes and re-equilibrating the erythrocytes. As described in the '627 Patent, &agr;-N-acetylgalactosaminidase obtained from an avian liver (specifically, chicken liver) source was found to have superior activity in respect of enzymatic conversion or cleavage of A antigenic sites.
Prior to the present invention, it was necessary to purify the enzyme from an avian liver source, a process which is time consuming and can be expensive. Hence, a need has arisen to develop an enzyme source which is more readily available. In addition, a need has arisen to develop an enzyme useful in blood product conversion which enzyme is cost-efficient.
A simplified purification process is described in a related application, Ser. No. 07/964,756, filed Oct. 22, 1992, entitled “Preparation of Enzyme for Conversion of Sub-Type A and AB Erythrocytes”. This process, as described in the related application, utilizes chicken liver as a source of enzyme and, therefore, requires a number of purification steps. Despite this simplified process, it is still desirable to provide a more readily available and controlled source of enzyme, that being cloned and expressed enzyme. This would provide an enzyme source which is more consistent and which is readily purified at less cost and expense, with a still further reduced number of purification steps. Additionally, a recombinant, cloned enzyme allows for specific protein sequence modifications, which can be introduced to generate an enzyme with optimized specific activity, substrate specificity and pH range.
&agr;-N-acetylgalactosaminidase enzymes are characterized (and thereby named) by their ability to cleave N-acetylgalactosamine sugar groups. In isolating or identifying these enzymes, their activity is assessed in the laboratory by evaluating cleavage of synthetic substrates
Goldstein Jack
Zhu Alex
New York Blood Center Inc.
Prouty Rebecca E.
Wolf Greenfield & Sacks P.C.
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