Liquid purification or separation – Processes – Separating
Reexamination Certificate
1999-12-27
2001-07-31
Kim, John (Department: 1723)
Liquid purification or separation
Processes
Separating
C210S483000, C210S488000, C210S489000, C210S490000, C210S491000, C210S503000, C210S504000, C210S505000, C210S507000, C210S508000, C264S172110, C264S172130, C264S172170, C264SDIG004, C428S297400, C435S002000
Reexamination Certificate
active
06267898
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a leukocyte-removing filter medium for removing leukocytes from a leukocyte-containing fluid, a process for producing the same, a leukocyte-removing apparatus using the same, and a method for removing leukocytes.
BACKGROUND ART
In the field of blood transfusion, in place of so-called whole blood transfusion comprising transfusing a whole blood product obtained by adding an anti-coagulant to blood collected from a blood donor, so-called component transfusion comprising separating a necessary blood component from the whole blood product and transfusing that blood component to a blood recipient is generally carried out. The component transfusion includes erythrocyte transfusion, platelet transfusion, plasma transfusion, etc., depending on the blood component necessary for a blood recipient. Blood component preparations used in these blood transfusions include red cell products, platelet products, plasma preparations, etc. In recent years, a so-called leukocyte-free blood transfusion has been developed in which a blood product is transfused after being freed of leukocytes contained therein as contaminant. Leukocyte-free blood transfusion was developed after revelation that adverse side effects accompanying blood transfusion, for example, relatively slight adverse side effects such as headache, nausea, chill, non-hemolytic pyretic reaction, etc., and serious adverse side effects such as allo-antigen sensitization, viral infection, post-transfusion GPHD, etc., which have serious influences on a blood recipient, are caused mainly by leukocytes contained as contaminants in a blood product used in transfusion.
To prevent relatively slight adverse side effects such as headache, nausea, chill, pyrexia, etc., it is sufficient that leukocytes in a blood product be removed until the remaining rate becomes less than 10
−1
-10
−2
. In addition, it is said that to prevent serious adverse side effects such as alloantigen sensitization, viral infection, etc., it is sufficient that leukocytes be removed until the remaining rate becomes less than 10
−4
-10
−6
.
Methods for removing leukocytes from a blood product are divided broadly into two categories, i.e., the centrifugation method in which leukocytes are separated and removed with a centrifuge by utilizing the difference in specific gravity among blood components, and the filter method in which leukocytes are removed by using a filter medium composed of a fibrous material or a porous element such as a porous material having interconnecting voids. The filter method is being generalized at present because it has advantages such as excellent leukocyte-removing capability, easy operations, and low cost. Of the filter method, a method of removing leukocytes by adhesion or adsorption by using non-woven fabric as a filter medium is the most widespread at present because of its especially excellent leukocyte-removing capability.
As to the mechanism of the removal of leukocytes with a filter apparatus using the above-mentioned fibrous material or porous material, removal is caused mainly because leukocytes brought into contact with the filter medium surface are adhered to or adsorbed on the filter medium surface. For example, EP-A-0155003 discloses a technique using non-woven fabric as a filter medium. In addition, WO93/01880 discloses a leukocyte-removing filter medium produced by dispersing, in a dispersion medium, a mass of a large number of small fiber pieces having a fiber diameter of 0.01 &mgr;m or less and a length of approximately 1-50 &mgr;m, and short fibers which have a fineness of approximately 0.05-0.75 d and an average length of 3-15 mm which can be spun and woven, and then removing the dispersion medium from the resulting dispersion.
Existing leukocyte-removing filters have a leukocyte-removing capability such that the number of remaining leukocytes is 1×10
5
or less. Under such circumstances, two important requirements have been imposed on leukocyte-removing filters in the market.
The first requirement is to improve the recovery of useful components and improve ease of handling by making unnecessary a procedure for recovering useful components remaining in a filter and a tube because of the presence of physiological saline and air. Improving the recovery of the useful components as compared with the existing leukocyte-removing filters is very worthwhile because blood as a starting material for blood products is often precious blood provided by well-intentioned blood donation, and unrecoverable blood remaining in a leukocyte-removing filter is wasted and discarded as it is together with the filter. It is, however, difficult to greatly improve the recovery of the useful components in a leukocyte-removing filter obtained according to prior art.
The second requirement is to completely prevent serious adverse side effects caused by leukocytes transfused into a patient, by attaining a leukocyte removal rate higher than that of the existing leukocyte-removing filters. However, in the case of a leukocyte-removing filter obtained according to prior art, it is difficult to attain such a high leukocyte removal rate so that adverse side effects can be completely prevented.
In order to satisfy the above requirements set out by the market, the present inventors earnestly investigated and consequently have accomplished the preceding invention (WO97/23266). The preceding invention is explained below in detail. Objects of the preceding invention are to provide leukocyte-removing filter medium which has a much higher leukocyte-removing capability per unit volume than do conventional filter media, and to permit satisfactory flow of a leukocyte-containing fluid; to provide a process for producing the filter medium; and to provide a filter apparatus containing the filter medium, and a method for removing leukocytes from a leukocyte-containing fluid by using the filter apparatus. The filter medium of the preceding invention is a leukocyte-removing filter medium comprising a porous element having pores with an average pore size of less than 100 &mgr;m and not less than 1.0 &mgr;m, and a fiber structure held thereby and composed of a plurality of fibers having an average fiber diameter of less than 1.0 &mgr;m and not less than 0.01 &mgr;m, wherein the void content of the filter medium is less than 95% and not less than 50%, the percentage of the fiber structure relative to the filter medium (this percentage is hereinafter referred to as holding amount) is less than 30 wt % and not less than 0.01 wt %. The ratio of the average pore size of pores of the porous element (hereinafter referred to also as the average pore size of the porous element) to the average fiber diameter of the fibers constituting the fiber structure (hereinafter referred to also as the average fiber diameter of the fiber structure) is less than 2000 and not less than 2, and the fiber structure forms a network structure.
In addition, the process for producing the leukocyte-removing filter medium of the preceding invention is, for example, a process of dispersing, in a solvent, fibers with an average fiber diameter of less than 1.0 &mgr;m and not less than 0.01 &mgr;m obtained by splitting splittable fiber, and making the resulting dispersion into paper together with a porous element having pores with an average pore size of less than 100 &mgr;m and not less than 1.0 &mgr;m (hereinafter referred to as a porous element having an average pore size of less than 100 &mgr;m and not less than 1.0 &mgr;m), to hold the fibers in the porous element.
Furthermore, in the preceding invention, a leukocyte-removing filter apparatus was found which contains a leukocyte-removing filter medium properly located therein which comprises a porous element having an average pore size of less than 100 &mgr;m and not less than 1.0 &mgr;m and a fiber structure composed of a plurality of fibers with an average fiber diameter of less than 1.0 &mgr;m and not less than 0.01 &mgr;m (hereinafter referred to as a fiber structure having an average
Fukuda Tatsuya
Tanaka Jun
Asahi Medical Co., Ltd.
Kim John
Young & Thompson
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