Abstract:
This invention relates to a method of reducing residual white blood cells in an apheresed platelet product. The method includes the steps of adding to the platelet product a solution comprising sodium chloride and magnesium and inducing degradation of the residual white blood cells.

Description:
PRIORITY CLAIM 
       [0001]    This application claims priority from U.S. Provisional Application No. 61/101,693, filed Oct. 1, 2008. 
     
    
     BACKGROUND 
       [0002]    Human blood contains a number of components, including plasma, platelets, and red blood cells. Blood also contains components such as various types of white blood cells, and proteins of the complement system, that provide for combating infection. 
         [0003]    Blood components may be separated from each other, and further processed, for a variety of uses, particularly as transfusion products. Illustratively, red blood cells (typically concentrated as packed red blood cells), plasma, and platelets (typically concentrated as platelet concentrate), can be separately administered to different patients. Some components, e.g., plasma and/or platelets, can be pooled before administration, and plasma can be fractionated to provide enriched protein components to treat diseases. 
         [0004]    Typically, donated platelets are separated from other blood components using a centrifuge. The centrifuge rotates whole blood to separate components including platelets using centrifugal force. In use, blood enters the centrifuge while it is rotating at a very rapid speed and centrifugal forces stratifies the blood components so that particular components may be separately removed according to their densities. Centrifuges are effective at separating platelets from whole blood, however, they are typically unable to separate all of the white blood cells from the platelets to produce a platelet product that meets the “leukopoor” standard of less than 5×10 6  white blood cells for at least 3×10 11  platelets collected. 
         [0005]    Because typical centrifuge platelet collection processes are unable to completely separate white blood cells from platelets, other processes have been added to improve results. In one procedure, after centrifugation, platelets are passed through a porous woven or non-woven media filter, which may have a modified surface, to remove white blood cells. However, use of the porous filter introduces its own set of problems. Conventional porous filters may be inefficient because they may permanently remove or trap approximately 5-20% of the platelets. These conventional filters may also reduce “platelet viability,” meaning that once passed through a filter a percentage of the platelets cease to function properly and may become partially or fully activated. In addition, porous filters may cause platelets to release bradykinin, which may lead to hypotensive episodes in a patient. Porous filters are also expensive and often require additional time consuming manual labor to perform a filtration process. 
         [0006]    Another separation process known as centrifugal elutriation, separates cells suspended in a liquid medium without the use of a membrane filter. In one common form of elutriation, cells are introduced into a flow of liquid elutriation buffer. This liquid which carries the cells in suspension, is then introduced into a funnel-shaped chamber located in a spinning centrifuge. As additional liquid buffer solution flows through the chamber, the liquid sweeps smaller sized, slower-sedimenting cells toward an elutriation boundary within the chamber, while larger, faster-sedimenting cells migrate to an area of the chamber having the greatest centrifugal force. 
         [0007]    When the centrifugal force and force generated by the fluid flow are balanced, the fluid flow is increased to force slower-sedimenting cells from an exit port in the chamber, while faster-sedimenting cells are retained in the chamber. If fluid flow through the chamber is increased, progressively larger, faster-sedimenting cells may be removed from the chamber. 
         [0008]    Thus, centrifugal elutriation separates particles having different sedimentation velocities. Stoke&#39;s law describes sedimentation velocity (SV) of a spherical particle as follows: 
         [0000]    
       
         
           
             sv 
             = 
             
               
                 2 
                 9 
               
                
               
                 
                   
                     
                       r 
                       2 
                     
                      
                     
                       ( 
                       
                         
                           ρ 
                           p 
                         
                         - 
                         
                           ρ 
                           m 
                         
                       
                       ) 
                     
                   
                    
                   g 
                 
                 η 
               
             
           
         
       
     
         [0009]    where,
       r is the radius of the particle,   ρ p  is the density of the particle,   ρ m  is the density of the liquid medium,   η is the viscosity of the medium; and   g is the gravitational or centrifugal acceleration.       
 
         [0015]    Because the radius of a particle is raised to the second power in the Stoke&#39;s equation and the density of the particle is not, it is the size of a cell, rather than its density, which greatly influences its sedimentation rate. This explains why larger particles generally remain in a chamber during centrifugal elutriation, while smaller particles are released, if the particles have similar densities. 
         [0016]    Another method of leukoreduction includes a process for forming a saturated fluidized particle bed as described in U.S. Pat. No. 5,939,319. 
         [0017]    However, in all of these leukoreduction procedures, there is usually some small percentage of white blood cells which are not captured by one of the leukoreduction mediums, and are carried over into a separated platelet component. 
         [0018]    Carryover of white blood cells into platelet products is undesirable because white blood cells may transmit infections to recipients of the platelet products such as HIV and CMV, and cause other transfusion-related complications such as transfusion-associated Graft vs. Host Disease (TA-GVHD), alloimmunization and microchimerism. White blood cells may also become activated during storage and release cytokines. Cytokine accumulation during storage of platelet concentrates may mediate nonhemolytic febrile transfusion reactions in the recipient. 
         [0019]    Since the problem arises from the presence of white cells in the donated platelet products, an additional process to remove or kill the residual white blood cells from separated platelets would be desirable. It is to this additional process that the present invention is directed. 
       SUMMARY OF THE INVENTION 
       [0020]    This invention relates to a method of reducing residual white blood cells in an apheresed platelet product. The method includes the steps of adding to the platelet product a solution comprising sodium chloride and magnesium; and inducing degradation of the residual white blood cells. Degradation of the residual white blood cells caused by the addition of the solution reduces any residual white blood cells which may be contained in the platelet product. 
         [0021]    This invention also relates to a method for further leukoreducing leukoreduced apheresed platelets suitable for transfusion into a patient. This method includes the steps of providing hyperconcentrated apheresed leukoreduced platelets and resuspending the platelets in a solution containing at least sodium chloride and magnesium and lacking citrate. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a perspective view of one embodiment of an apheresis system which can be used with the present invention. 
           [0023]      FIG. 2A-B  illustrate an extracorporeal tubing circuit and cassette assembly for the system of  FIG. 1 . 
           [0024]      FIG. 3  is an exploded, perspective view of the channel assembly for the system of  FIG. 1 . 
           [0025]      FIG. 4  is a top view of the channel housing from the channel assembly of  FIG. 1  illustrating various dimensions. 
           [0026]      FIG. 5  is a perspective view of the blood processing vessel of the channel assembly of  FIG. 8  in a disassembled view. 
           [0027]      FIG. 6  is a cross-sectional view of the blood processing vessel taken along lines  18 - 18  in  FIG. 5 . 
           [0028]      FIG. 7  is a front view of a pump/valve/sensor assembly for the system of  FIG. 1 . 
           [0029]      FIG. 8  is a partial schematic view of the apparatus of the blood processing vessel of  FIG. 1  illustrating a detailed view of components of the apparatus. 
           [0030]      FIG. 9  is a graph comparing rWBC from apheresed platelets in various storage solutions over time. 
           [0031]      FIG. 10  is a graph comparing rWBC from separated whole blood in various storage solutions over time. 
           [0032]      FIG. 11  is a graph comparing the permeability of the membranes of apheresed WBC. 
           [0033]      FIG. 12  is a graph comparing Annexin V expression on platelets stored in a platelet additive solution containing moderate amounts of magnesium and plasma. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    A blood apheresis system  2  for use in and/or with the present invention is schematically illustrated in  FIG. 1 . System  2  provides for a continuous blood component separation process. Generally, whole blood is withdrawn from a donor  4  and is substantially continuously provided to a blood component separation device  6  where the blood is continuously separated into various component types. One or more of the separated blood components may then either be collected for subsequent transfusion or may be uncollected and returned to the donor  4 . 
         [0035]    In the blood apheresis system  2 , blood is withdrawn from the donor  4  and directed through a preconnected bag and tubing set  8  which includes an extracorporeal tubing circuit  10  and a blood processing vessel  352  which together define a closed, sterile and disposable system. The set  8  is adapted to be mounted on and/or in the blood component separation device  6 . The separation device  6  preferably includes a pump/valve/sensor assembly  1000  for interfacing with the extracorporeal tubing circuit  10 , and a channel assembly  200  for interfacing with the disposable blood processing vessel  352 . 
         [0036]    The channel assembly  200  may include a channel housing  204  which is rotatably interconnected with a rotatable centrifuge rotor assembly  568  which provides the centrifugal forces required to separate blood into its various blood component types by centrifugation. The blood processing vessel  352  may then be interfitted within the channel housing  204 . When connected as described, blood can then be flowed substantially continuously from the donor  4 , through the extracorporeal tubing circuit  10 , and into the rotating blood processing vessel  352 . The blood within the blood processing vessel  352  may then be continuously separated into various blood component types and at least one of these blood component types (e.g., platelets, plasma, or red blood cells) is continually removed from the blood processing vessel  352 . Blood components which are not being retained for collection are also removed from the blood processing vessel  352  and returned to the donor  4  via the extracorporeal tubing circuit  10 . 
         [0037]    Operation of the blood component separation device  6  is controlled by one or more processors included therein, and may comprise a plurality of embedded computer processors to accommodate interface with ever-increasing PC user facilities (e.g., CD ROM, modem, audio, networking and other capabilities). Relatedly, in order to assist the operator of the apheresis system  2  with various aspects of its operation, the blood component separation device  6  includes a graphical interface  660  with an interactive touch screen  664 . 
         [0038]    A plurality of other known apheresis systems may also be useful herewith, as for example, the Baxter CS3000 and/or AMICUS and/or AUTOPHERESIS-C systems, and/or the Haemonetics MCS or MCS+ and/or the Fresenius COM.TEC or AS-104 and/or the CaridianBCT TRIMA ACCEL System. 
       Disposable Set: Extracorporeal Tubing Circuit 
       [0039]    By way of example only, and not meant to be limiting, a dual stage apheresis system (the Trima System, available from CaridianBCT, Inc., Lakewood, Colo., USA) is described below. Further descriptions of the duel stage may be found in U.S. Pat. No. 6,200,287 herein incorporated by reference. It should be noted that a single stage apheresis system (the Trima Accel System, also available from CaridianBCT, Inc. Lakewood, Colo., USA) may also be used to carry out the present invention without departing from the spirit and scope of the invention. Exemplary descriptions of the single stage system may be found in U.S. Pat. Nos. 6,053,856 and 7,549,956 herein incorporated by reference. 
         [0040]    As illustrated in  FIGS. 2A-2B , blood-primable extracorporeal tubing circuit  10  comprises a cassette assembly  110  and a number of tubing assemblies  20 ,  50 ,  60 ,  80 ,  90 ,  100  interconnected therewith. Generally, blood removal/return tubing assembly  20  provides a single needle interface between a donor/patient  4  and cassette assembly  110 , and blood inlet/blood component tubing subassembly  60  provides the interface between cassette assembly  110  and blood processing vessel  352 . An anticoagulant tubing assembly  50 , platelet collection tubing assembly  80 , plasma collection tubing assembly  90 , red blood cell collection assembly  950  and vent bag tubing subassembly  100  are also interconnected with cassette assembly  110 . As will be appreciated, the extracorporeal tubing circuit  10  and blood processing vessel  352  are interconnected to combinatively yield a closed disposable for a single use. 
         [0041]    The blood removal/return tubing assembly  20  includes a needle subassembly  30  interconnected with blood removal tubing  22 , blood return tubing  24  and anticoagulant tubing  26  via a common manifold  28 . The needle subassembly  30  includes a needle  32  having a protective needle sleeve  34  and needle cap  36 , and interconnect tubing  38  between needle  32  and manifold  28 . Needle subassembly  30  further includes a D sleeve  40  and tubing clamp  42  positioned about the interconnect tubing  38 . Blood removal tubing  22  may be provided with a Y-connector  44  interconnected with a blood sampling subassembly  46 . 
         [0042]    Cassette assembly  110  includes front and back molded plastic plates (not shown) that are hot-welded together to define a rectangular cassette member  115  having integral fluid passageways. The cassette assembly  110  further includes a number of outwardly extending tubing loops interconnecting various integral passageways. The integral passageways are also interconnected to the various tubing assemblies. 
         [0043]    Specifically, cassette assembly  110  includes a first integral anticoagulant passageway  120   a  interconnected with the anticoagulant tubing  26  of the blood removal/return tubing assembly  20 . The cassette assembly  110  further includes a second integral anticoagulant passageway  120   b  and a pump-engaging, anticoagulant tubing loop  122  between the first and second integral anticoagulant passageways  120   a ,  120   b . The second integral anticoagulant passageway  120   b  is interconnected with anticoagulant tubing assembly  50 . The anticoagulant tubing assembly  50  includes a spike drip chamber  52  connectable to an anticoagulant source, anticoagulant feed tubing  54  and a sterilizing filter  56 . During use, the anticoagulant tubing assembly  50  supplies anticoagulant to the blood removed from a donor/patient  4  to reduce or prevent any clotting in the extracorporeal tubing circuit  10 . 
         [0044]    Cassette assembly  110  also includes a first integral blood inlet passageway  130   a  interconnected with blood removal tubing  22  of the blood removal/return tubing assembly  20 . The cassette assembly  110  further includes a second integral blood inlet passageway  130   b  and a pump-engaging, blood inlet tubing loop  132  between the first and second integral blood inlet passageways  130   a ,  130   b . The first integral blood inlet passageway  130   a  includes a first pressure-sensing module  134  and inlet filter  136 , and the second integral blood inlet passageway  130   b  includes a second pressure-sensing module  138 . The second integral blood inlet passageway  130   b  is interconnected with blood inlet tubing  62  of the blood inlet/blood component tubing assembly  60 . 
         [0045]    Blood inlet tubing  62  is also interconnected with input port  392  of blood processing vessel  352  to provide whole blood thereto for processing. To return separated blood components to cassette assembly  110 , the blood inlet/blood component tubing assembly  60  further includes red blood cell (RBC)/plasma outlet tubing  64 , platelet outlet tubing  66  and plasma outlet tubing  68  interconnected with corresponding outlet ports  492  and  520 ,  456 , and  420  of blood processing vessel  352 . The RBC/plasma outlet tubing  64  includes a Y-connector  70  to interconnect tubing spurs  64   a  and  64   b . The blood inlet tubing  62 , RBC/plasma outlet tubing  64 , plasma outlet tubing  68  and platelet outlet tubing  66  all pass through first and second strain relief members  72  and  74  and a braided bearing member  76  therebetween. 
         [0046]    Platelet outlet tubing  66  of the blood input/blood component tubing assembly  60  includes a cuvette  65  (not shown) for use in the detection of red blood cells (via an interfacing RBC spillover detector provided on blood component separation device  6 ) and interconnects with a first integral platelet passageway  140   a  of cassette assembly  110 . Platelet outlet tubing  66  also includes a chamber  67 , positioned in close proximity to platelet collect port  420  of blood processing vessel  352 . As will be described in more detail below, during operation a saturated bed of platelets will form within chamber  67  to retain white blood cells contaminating the separated platelets within chamber  67 . 
         [0047]    The cassette assembly  110  further includes a pump-engaging, platelet tubing loop  142  interconnecting the first integral platelet passageway  140   a  and a second integral platelet passageway  140   b . The second integral platelet passageway  140   b  includes first and second spurs  144   a  and  144   b , respectively. The first spur  144   a  is interconnected with platelet collection tubing assembly  80 . 
         [0048]    The platelet collection tubing assembly  80  can receive separated platelets during operation and includes platelet collector tubing  82  and platelet collection bags  84  interconnected thereto via a Y-connector  86 . Slide clamps  88  are provided on platelet collector tubing  82 . 
         [0049]    The second spur  144   b  of the second integral platelet passageway  140   b  is interconnected with platelet return tubing loop  146  of the cassette assembly  110  to return separated platelets to a donor/patient  4 . For such purpose, platelet return tubing loop  146  is interconnected to the top of a blood return reservoir  150  integrally formed by the molded front and back plates of cassette member  115 . One or more types of uncollected blood components, collectively referred to as return blood, will cyclically accumulate in and be removed from reservoir  150  during use. Back plate  114  (not shown) of the cassette member  115  also includes an integral frame corner  116  defining a window  118  through a corner of cassette member  115 . The frame corner  116  includes keyhole recesses  119  for receiving and orienting the platelet collector tubing  82  and platelet return tubing loop  146  in a predetermined spaced relationship within window  118 . 
         [0050]    The plasma outlet tubing  68  of blood inlet/blood component tubing assembly  60  interconnects with a first integral plasma passageway  160   a  of cassette assembly  110 . Cassette assembly  110  further includes a pump-engaging, plasma tubing loop  162  interconnecting the first integral plasma passageway  160   a  and a second integral plasma passageway  160   b . The second integral plasma passageway  160   b  includes first and second spurs  164   a  and  164   b . The first spur  164   a  is interconnected to the plasma collection tubing assembly  90 . 
         [0051]    The plasma collection tubing assembly  90  may be employed to collect it, plasma during use and includes plasma collector tubing  92  and plasma collection bag  94 . A slide clamp  96  is provided on plasma collector tubing  92 . 
         [0052]    The second spur  164   b  of the second integral plasma passageway  160   b  is interconnected to a plasma return tubing loop  166  to return plasma to donor/patient  4 . For such purpose, the plasma return tubing loop  166  is interconnected to the top of the blood return reservoir  150  of the cassette assembly  110 . Again, keyhole recesses  119  in the frame  116  of cassette assembly  110  are utilized to maintain the plasma collector tubing  92  and plasma return tubing loop  166  in a predetermined spaced relationship within window  118 . 
         [0053]    The RBC/plasma outlet tubing  64  of the blood inlet/blood component tubing assembly  60  is interconnected with integral RBC/plasma passageway  170  of cassette assembly  110 . The integral RBC/plasma passageway  170  includes first and second spurs  170   a  and  170   b , respectively. The first spur  170   a  is interconnected with RBC/plasma return tubing loop  172  to return separated RBC/plasma to a donor/patient  4 . For such purpose, the RBC/plasma return tubing loop  172  is interconnected to the top of blood return reservoir  150  of the cassette assembly  110 . The second spur  170   b  may be closed off, or may be connected with an RBC/plasma collection tubing assembly  950  for collecting RBC/plasma during use. RBC collection tubing assembly  950  includes RBC collector tubing  952 , an RBC collection reservoir, or bag  954 , and sterile barrier filter/drip spike assembly  956 . The RBC/plasma return tubing loop  172  and RBC/plasma collector tubing  952  is maintained in a desired orientation within window  118  by keyhole recesses  119  of the frame  116 . 
         [0054]    Vent bag tubing assembly  100  is also interconnected to the top of blood return reservoir  150  of cassette assembly  110 . The vent bag tubing assembly  100  includes vent tubing  102  and a vent bag  104 . During use, sterile air present since packaging within cassette assembly  110 , and particularly within blood return reservoir  150 , cyclically passes into and back out of vent tubing  102  and vent bag  104 . 
         [0055]    The platelet return tubing loop  146 , plasma return tubing loop  166  and RBC/plasma return tubing loop  172  are interconnected in a row to the top of blood return reservoir  150  immediately adjacent to forwardly projecting sidewalls  152  so that the blood components returned thereby will flow down the inner walls of the blood return reservoir  150 . The blood return reservoir  150  includes an enlarged, forwardly projecting mid-section  154 , a reduced top section  156  and reduced bottom section  158 . A filter  180  is disposed in a bottom cylindrical outlet  182  of the blood return reservoir  150 . 
         [0056]    A first integral blood return passageway  190   a  is interconnected to the outlet  182  of blood return reservoir  150 , and is further interconnected to a second integral blood return passageway  190   b  via a pump-engaging, blood return tubing loop  192 . The second integral blood return passageway  190   b  is interconnected with the blood return tubing  24  of the blood removal/return tubing assembly  20  to return blood to the donor/patient  4  via needle assembly  30 . 
         [0057]    Pump-engaging tubing loops  122 ,  132 ,  142 ,  162  and  192  extend from cassette member  115  to yield an asymmetric arrangement thereby facilitating proper mounting of cassette assembly  110  on blood component separation device  6  for use. 
       Channel Housing 
       [0058]    The channel assembly  200  is illustrated in  FIG. 3  and includes a channel housing  204  which is disposed on the rotatable centrifuge rotor assembly  568  ( FIG. 1 ) and which receives a disposable blood processing vessel  352 . 
         [0059]    The blood processing vessel  352  is disposed within the channel  208 . Generally, the channel  208  allows blood to be provided to the blood processing vessel  352  during rotation of the channel housing  204 , to be separated into its various blood component types by centrifugation, and to have various blood component types removed from the blood processing vessel  352  during rotation of the channel housing  204 . 
         [0060]    As illustrated in  FIG. 3 , a RBC dam  232  in the channel  208  is disposed in a clockwise direction from the blood inlet slot  224  and whose function is to preclude RBCs and other large cells such as WBCs from flowing in a clockwise direction beyond the RBC dam  232 . At least in that portion of the channel  208  between the blood inlet port  224  and the RBC dam  232 , blood is separated into a plurality of layers of blood component types including, from the radially outermost layer to the radially innermost layer, red blood cells (“RBCs”), white blood cells (“WBCs”), platelets, and plasma. The majority of the separated RBCs are removed from the channel  208  through an RBC outlet port assembly  516  which is disposed in an RBC outlet slot  272  associated with the channel  208 , although at least some RBCs may be removed from the channel  208  through a control port assembly  488  which is disposed in a control port slot  264  associated with the channel  208 . 
         [0061]    As shown in  FIG. 4 , separated RBCs and other large cells as noted above are removed from the first stage  312  utilizing the above-noted configuration of the outer channel wall  216  which induces the RBCs and other large cells as noted to flow in a counterclockwise direction (e.g., generally opposite to the flow of blood through the first stage  312 ). Specifically, separated RBCs and other large cells as noted, flow through the first stage  312  along the outer channel wall  216 , past the blood inlet slot  224  and the corresponding blood inlet port assembly  388  on the blood processing vessel  352 , and to an RBC outlet slot  272 . In order to reduce the potential for counterclockwise flows other than separated RBCs being provided to the control port assembly  488  disposed in the control port slot  264  a control port dam  280  of the channel  208  is disposed between the blood inlet slot  224  and the RBC outlet slot  272 . That is, preferably neither WBCs nor any portion of a buffy coat, disposed radially adjacent to the separated RBCs, is allowed to flow beyond the control port dam  280  and to the control port slot  264 . The “buffy coat” includes primarily WBCs, lymphocytes, and the radially outwardmost portion of the platelet layer. As such, substantially only the separated RBCs and plasma are removed from the channel  208  via the RBC control slot  264 . 
       Disposable Set: Blood Processing Vessel 
       [0062]    As shown in more detail in  FIG. 3 , the blood processing vessel  352  is disposed within the channel  208  of channel assembly  204  for directly interfacing with and receiving a flow of blood in an apheresis procedure. The use of the blood processing vessel  352  alleviates the need for sterilization of the channel assembly  204  after each apheresis procedure and the vessel  352  may be discarded to provide a disposable system. 
         [0063]    Referring primarily to  FIG. 5 , the blood processing vessel  352  includes a first end  356  and a second end  364  which overlaps with the first end  356  and is radially spaced therefrom. A first connector  360  is disposed proximate the first end  356  and a second connector  368  is disposed proximate the second end  364 . When the first connector  360  and second connector  368  are engaged (typically permanently), a continuous flow path is available through the blood processing vessel  352 . 
         [0064]    The blood processing vessel  352  includes an inner sidewall  372  and an outer sidewall  376 . In the embodiment illustrated in  FIG. 6 , the blood processing vessel  352  is formed by sealing two pieces of material together (e.g., RF welding). More specifically, the inner sidewall  372  and outer sidewall  376  are connected along the entire length of the blood processing vessel  352  to define an upper seal  380  and a lower seal  384 . Seals are also provided on the ends of the vessel  352 . 
         [0065]    Blood is introduced into the interior of the blood processing vessel  352  through a blood inlet port assembly  388 . The blood inlet port assembly  388  includes a blood inlet port  392  and a blood inlet tube  412  which is fluidly interconnected therewith exteriorly of the blood processing vessel  352 . The blood inlet port  392  extends through and beyond the inner sidewall  372  of the blood processing vessel  352  into an interior portion of the blood processing vessel  352 . 
         [0066]    Separated RBCs flow along the outer sidewall  376  of the blood processing vessel  352  adjacent the outer channel wall  216 , past the blood inlet port  392 , and to the RBC outlet port assembly  516 . 
         [0067]    The RBC outlet port assembly  516  generally includes an RBC outlet port  520  and an RBC outlet tube  540  fluidly interconnected therewith exteriorly of the blood processing vessel  352 . The RBC outlet port  520  extends through and beyond the inner sidewall  372  of the blood processing vessel  352  into an interior portion of the blood processing vessel  352 . 
         [0068]    Separated platelets are allowed to flow beyond the RBC dam  232  and into the second stage  316  (see  FIG. 4 ) of the channel  208  in platelet-rich plasma. The blood processing vessel  352  includes a platelet collect port assembly  416  to continually remove these platelets from the vessel  352  throughout an apheresis procedure. Generally, the platelet collect port assembly  416  is disposed in a clockwise direction from the blood inlet port assembly  388 , as well as from the RBC dam  232  when the blood processing vessel  352  is loaded into the channel  208 . Moreover, the platelet collect port assembly  416  interfaces with the outer sidewall  376  of the blood processing vessel  352 . 
         [0069]    The platelet collect port assembly  416  generally includes a platelet collect port  420  and a platelet collect tube  66  (see  FIG. 8 ) which is fluidly interconnected with fluid chamber  67 . 
         [0070]    As illustrated in  FIG. 8 , the fluid chamber  67  is formed by joining a first chamber section  242  having inlet  240  to a second chamber section  244  having outlet  3246 . 
         [0071]    The volume of the fluid chamber  67  should be at least large enough to accommodate enough platelets to provide a saturated fluidized particle bed (described below) for a particular range of flow rates, particle sizes and centrifuge rotor  200  speeds. 
         [0072]    The fluid chamber interior has a maximum cross-sectional area  248  located at a position intermediate the inlet  240  and outlet  246  where sections  242 ,  244  join. The cross-sectional area of the fluid chamber interior decreases, or tapers from the maximum cross-sectional area  248  as shown in  FIG. 8 . Although the fluid chamber  67  is depicted with two sections  242 ,  244  having frustoconical interior shapes, the interior shapes may be paraboloidal, or of any other shape having a major cross-sectional area greater than the inlet or outlet area. The fluid chamber  67  may be constructed from a unitary piece of plastic rather than from separate sections. 
       Pump/Valve/Sensor Assembly 
       [0073]    As noted, cassette assembly  110  is mounted upon and operatively interfaces with the pump/valve/sensor assembly  1000  of blood component separation device  6  during use. The pump/valve/sensor assembly  1000  as illustrated in  FIG. 7  includes a cassette mounting plate  1010 , and a number of peristaltic pump assemblies, flow divert valve assemblies, pressure sensors and ultrasonic level sensors interconnected to face plate  6   a  of blood collection device  6  for pumping, controlling and monitoring the flow of blood/blood components through extracorporeal tubing circuit  10  during use. 
         [0074]    More particularly, anticoagulant pump assembly  1020  is provided to receive anticoagulant tubing loop  122 , blood inlet pump assembly  1030  is provided to receive blood inlet tubing loop  132 , platelet pump assembly  1040  is provided to receive platelet tubing loop  142 , plasma pump assembly  1060  is provided to receive plasma tubing loop  162 , and blood return pump assembly  1090  is provided to receive blood return tubing loop  192 . 
         [0075]    Each of the peristaltic pump assemblies  1020 ,  1030 ,  1040 ,  1060 , and  1090  includes a rotor  1022 ,  1032 ,  1042 ,  1062  and  1092 , and raceway  1024 ,  1034 ,  1044 ,  1064 , and  1094  between which the corresponding tubing loop is positioned to control the passage and flow rate of the corresponding fluid. 
         [0076]    Platelet divert valve assembly  1100  is provided to receive platelet collector tubing  82  and platelet return tubing loop  146 , plasma divert valve assembly  1110  is provided to receive plasma collector tubing  92  and plasma return tubing loop  166 , and RBC/plasma divert valve assembly  1120  is provided to receive RBC/plasma return tubing loop  172  and RBC/plasma collector tubing  952 . 
       Operation of Extracorporeal Tubing Circuit and Pump/Valve/Sensor Assembly 
       [0077]    In an initial blood prime mode of operation, blood return pump  1090  is operated in reverse to transfer whole blood through blood removal/return tubing assembly  20 , integral blood return passageway  190 , blood return tubing loop  192  and into reservoir  150 . Contemporaneously and/or prior to the reverse operation of blood return pump  1090 , anticoagulant peristaltic pump  1020  is operated to prime and otherwise provide anticoagulant from anticoagulant tubing assembly  50 , through anticoagulant integral passageways  120   a ,  120   b  and into blood removal tubing  22  and blood return tubing  24  via manifold  28 . 
         [0078]    In the blood processing mode, the blood inlet peristaltic pump  1030 , platelet peristaltic pump  1040  and plasma peristaltic pump  1060  are operated continuously. 
         [0079]    In normal operation, whole blood will pass through needle assembly  30 , blood removal tubing  22 , cassette assembly  110  and blood inlet tubing  62  to processing vessel  352 . The whole blood will then be separated in vessel  352 . A separated platelet stream will pass out of port  420  of the vessel, through platelet tubing  66 , through chamber  67 , back through cassette assembly  110 , through tubing  82  to be collected in collector assembly  80 . Similarly, separated plasma will exit vessel  352  through port  456  to plasma tubing  68  back through cassette assembly  110 , and will then either be collected in plasma tubing assembly  90  or diverted to reservoir  150 . Further, separated red blood cells and plasma may pass through ports  492  and  520  of vessel  352  through RBC/plasma tubing  64 , through cassette assembly  110  and either into reservoir  150  or into RBC/plasma collector tubing assembly  950  for collection. 
       Platelet Collection and Purification 
       [0080]    The blood separation control device  6  provides control signals to pump/valve/sensor assembly  1000  so that platelet divert valve assembly  1100  diverts the flow of separated platelets pumped through platelet outlet tubing  66  into chamber  67  for further purification and finally into platelet collection tubing  82  for collection in bag  84 . 
         [0081]    To separate contaminating white blood cells from platelets in chamber  67 , plasma, the least dense blood component, flows within the separation vessel  352  along the top surface of the buffy coat layer  58  (see  FIG. 8 ). When the height of the buffy coat layer  58  approaches the top of RBC dam  232 , the flowing plasma washes the platelets and some white blood cells of the buffy coat layer  58  over the RBC dam  232  into the platelet collect well  236 . 
         [0082]    Plasma then carries platelets and white blood cells from the platelet collect well  236  (see  FIG. 8 ) into the fluid chamber  67 , which is filled with a priming fluid, so that a saturated fluidized particle bed may be formed. The processor maintains the rotation speed of the rotor  200  within a predetermined rotational speed range to facilitate formation of this saturated fluidized bed. In addition, the processor regulates platelet pump  1040  to convey plasma, platelets, and white blood cells at a predetermined flow rate through the tubing segment  66  and into inlet  28  of the fluid chamber  67 . These flowing blood components displace the priming fluid from the fluid chamber  67 . 
         [0083]    When the platelet and white blood cell particles enter the fluid chamber  67 , they are subjected to two opposing forces. Plasma flowing through the fluid chamber with the aid of pump  1040  establishes a first viscous drag force when plasma flowing through the fluid chamber  67  urges the particles toward the outlet  32  in the direction “D”, shown in  FIG. 7 . A second centrifugal force created by rotation of the rotor  200  and fluid chamber  67  acts in the direction “C” to urge the particles toward the inlet  28 . 
         [0084]    The processor regulates the rotational speed of the rotor  200  and the flow rate of the pump  1040  to collect platelets and white blood cells in the fluid chamber  67 . As plasma flows through the fluid chamber  67 , the flow velocity of the plasma decreases as the plasma flow approaches the maximum cross-sectional area  33 . This flow reaches a minimum velocity at this maximum cross-sectional area  33 . Because the rotating centrifuge rotor  200  creates a sufficient gravitational field in the fluid chamber  67 , the platelets accumulate near the maximum cross-sectional area  33  rather than flowing from the fluid chamber  67  with the plasma. The white blood cells accumulate somewhat below the maximum cross-sectional area  33 . However, density inversion tends to mix these particles slightly during this initial establishment of the saturated fluidized particle bed. 
         [0085]    The larger white blood cells accumulate closer to the chamber inlet  28  than the smaller platelet cells, because of their different sedimentation velocities. Preferably, the rotational speed and flow rate are controlled so that very few platelets and white blood cells flow from the fluid chamber  67  during formation of the saturated fluidized particle bed. 
         [0086]    The platelets and white blood cells continue to accumulate in the fluid chamber  67  while plasma flows through the fluid chamber  67 . As the concentration of platelets increases, the interstices between the particles become reduced and the viscous drag force from the plasma flow gradually increases. Eventually the platelet bed becomes a saturated fluidized particle bed within the fluid chamber  67 . Since the bed is now saturated with platelets, for each new platelet that enters the saturated bed in the fluid chamber  67 , a single platelet must exit the bed. Thus, the bed operates at a steady state condition with platelets exiting the bed at a rate equal to the rate additional platelets enter the bed after flowing through inlet  28 . 
         [0087]    Although the bed is saturated with platelets, a small number of white blood cells may be interspersed in the platelet bed. These white blood cells, however will tend to “fall” or settle out of the platelet bed toward inlet  28  due to their higher sedimentation velocity. Most white blood cells generally collect within the fluid chamber  67  between the saturated platelet bed and the inlet  28 . Thus, the bed effectively filters white blood cells from the blood components continuously entering the fluid chamber  67 , while allowing plasma and platelets released from the saturated bed to exit the chamber  67 . 
         [0088]    However, because cells in chamber  67  are separated based on size, the white cells having a smaller than average size may escape the platelet bed and contaminate the concentrated platelets. Although the number of WBCs which escape the chamber  67  are small, (an average of less than 10 5  rWBC end up in the platelet product, compared to 5×10 9  being retained within the chamber  67 ) as discussed in the background above, even this small number of WBC can cause undesirable side effects in the recipient of the platelet product. 
         [0089]    As discussed above, after further purification of the platelets in chamber  67 , the purified platelets flow out of chamber  67 , through tubing  82  and into platelet collect bag(s)  84 . The purified platelets in bag(s)  84  may then be resuspended in a liquid which enables the platelets to be stored over time. Resuspension/storage liquid could be added directly to the platelets contained in bag  84 , or the platelets could be transferred out of bag  84  into a bag containing the resuspension/storage fluid. Resuspension/storage fluid could also be in bag  84  before the platelets are added. 
         [0090]    One fluid which may be used as a resuspension fluid/platelet storage solution is Isolyte S (available from B Braun). Isolyte S is commonly used as an intravenous electrolyte solution. This multi-electrolyte injection solution has a well-characterized safety profile in the United States, and contains ingredients known to support platelet storage. 100 mL of Isolyte S pH 7.4 contains 0.53 g sodium chloride, 0.5 g sodium gluconate, 0.37 g sodium acetate trihydrate, 0.037 g potassium chloride and 0.03 g magnesium chloride hexahydrate and is made by processing the constituents in water. The solution has an osmolarity of around 295 mOsm. Isolyte S is not commonly used as a platelet additive solution. However, when used as an additive solution for platelet storage, it appears to have the added benefit of disintegrating contaminating white blood cells which escaped the saturated fluidized particle bed within chamber  67  and are contained in apheresed platelets. 
         [0091]    As discussed above, it is undesirable to have even a small amount of white blood cells contaminating a platelet concentrate, whether they escaped through a leukoreduction filter or a saturated fluidized particle bed within chamber  67 . The below experiments demonstrate that if Isolyte S is used as a platelet additive solution, residual white blood cells contaminating an apheresed platelet concentrate are disintegrated. 
       Results 
     Example 1 
       [0092]    A single hyperconcentrated platelet product was collected on the TRIMA apheresis machine  6 , purified in chamber  67 , and stored in platelet bag  84 . The content of platelet bag  84  was divided into 7 small (50 mL) bags. Plasma or the following constituents were added to each small bag (the platelets included a 37.5% plasma carryover): saline, saline+Mg 2+ , SSP + , Isolyte S, Isolyte S+Citrate and Isolyte S−Mg 2+ . The concentrations of Mg 2+  or citrate added were comparable to what is found in current PAS solutions (see Table 1 below). The primary differences between Isolyte S and the below listed PAS solutions are that Isolyte S lacks citrate and contains twice the amount of magnesium. Note: Plasmalyte A has the same constituents as Isolyte S, it merely has a different manufacturer. 
         [0093]    Residual WBC (rWBC) samples were taken and measured at approximately 2 hour intervals for 4 hours and then again on Day 1 (after overnight storage on a flatbed rotator). The initial (T 0 ) time point was taken immediately after mixing. The results are shown in  FIG. 9 . 
         [0094]    As seen in  FIG. 9 :
       rWBC counts decrease by ˜30% by Day 1 in plasma.   rWBC counts decrease by ˜30% by Day 1 in SSP + .   rWBC counts decrease by &lt;30% by Day 1 in saline.   rWBC counts decrease by ˜100% by Day 1 in Isolyte S.   rWBC counts decrease by ˜100% by Day 1 in saline+Mg 2+ .   rWBC counts decrease by ˜30% by Day 1 in Isolyte S+citrate.   rWBC counts decrease by ˜80% by Day 1 in Isolyte S−Mg 2+ .       
 
         [0102]    Although rWBC decrease as a function of time regardless of the storage medium, rWBC counts decreased at a much faster rate when stored in a medium containing a moderate amount of magnesium compared to plasma or other platelet additive solutions. 
         [0103]    Using Isolyte S as a platelet additive solution may help to reduce the number of residual WBC in apheresed platelet products. 
         [0104]    The above experiment appears to suggest that the lack of citrate and inclusion of approximately at least a moderate amount of Mg 2+  in Isolyte S as compared to the amount present in the other solutions in Table 1 may be responsible for the observed decrease in rWBC counts in Isolyte S-stored hyperconcentrated platelets collected using apheresis. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Concentration of Electrolytes 
               
             
          
           
               
                   
                   
                   
                 PAS-2 
                 PAS-3 
                   
                 PAS-3M 
               
               
                 (mEq/L) 
                 Plasmalyte A 
                 Isolyte S 
                 T-sol 
                 Intersol 
                 Composol 
                 SSP+ 
               
               
                   
               
             
          
           
               
                 Sodium 
                 140 
                 141 
                 176 
                 191.9 
                 173 
                 183.9 
               
               
                 Potassium 
                 5 
                 5 
                 — 
                 — 
                 5 
                 5 
               
               
                 Magnesium 
                 3 
                 3 
                 — 
                 — 
                 1.5 
                 1.5 
               
               
                 Chloride 
                 98 
                 98 
                 116 
                 77.3 
                 98 
                 77.2 
               
               
                 Acetate 
                 27 
                 27 
                 30 
                 32.5 
                 27 
                 32.5 
               
               
                 Gluconate 
                 23 
                 23 
                 — 
                 — 
                 23 
                 — 
               
               
                 Phosphate 
                 — 
                 1 
                 — 
                 28.2 
                 — 
                 28.2 
               
               
                 Citrate 
                 — 
                 — 
                 10 
                 10.8 
                 11 
                 10.8 
               
               
                 pH 
                 7.4 
                 7.4 
                 7.2 
                 7.2 
                 7.0 
                 7.2 
               
               
                   
               
             
          
         
       
     
       Example 2 
       [0105]    This study looked at the effects of platelet additive solution containing moderate amounts of magnesium on residual white blood cells contained in hyperconcentrated platelet products. Hyperconcentrated platelet products are platelets which are collected at a high enough concentration that they require dilution in a storage solution. A concentration greater than or equal to 2100×10 3 /μl is considered a hyperconcentrated platelet product. Because of the lack of plasma in a hyperconcentrated platelet product, platelet quality degrades after 48 hours of storage. Therefore, hyperconcentrated platelets must be diluted in a platelet additive solution to allow for seven days of storage. 
         [0106]    Table 2 shows rWBC data for paired hyperconcentrated platelet products collected on the Trima Accel System. The first column represents rWBC counts for individual platelet products before addition of a platelet storage solution containing moderate amounts of magnesium; the second column represents rWBC counts for individual platelet products after addition of a platelet additive solution containing moderate amounts of magnesium. The data in Table 2 demonstrates that the rWBC concentration decreases by 70% on average with the addition of platelet additive solution containing moderate amounts of magnesium. Decrease in rWBC concentration indicates that WBCs are being disintegrated by a platelet additive solution containing moderate amounts of magnesium. 
         [0000]    
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 rWBC concentration data for paired platelet products. 
               
             
          
           
               
                 Pre-Isolyte 
                 Post-Isolyte 
                 Change in 
               
               
                 rWBC 
                 rWBC 
                 rWBC 
               
               
                 WBC/uL 
                 WBC/uL 
                 % 
               
               
                   
               
             
          
           
               
                 3.36 
                 1 †    
                 70% 
               
               
                 3.42 
                  1.82 
                 47% 
               
               
                 3.84 
                 1 †    
                 74% 
               
               
                 3.99 
                 1 †    
                 75% 
               
               
                 4.59 
                 1 †    
                 78% 
               
               
                 5.67 
                 1 †    
                 82% 
               
               
                 5.76 
                 1 †    
                 83% 
               
               
                 7.95 
                 1 †    
                 87% 
               
               
                 42.09 
                 20.51 
                 51% 
               
               
                 192.36 
                 93.5  
                 51% 
               
               
                   
                 Avg 
                 70% 
               
               
                   
               
               
                   † Value of 1 represents the lower detection limit of the assay 
               
             
          
         
       
     
       Example 3 
       [0107]    One hypothesis for the unexpected results using an additive solution containing moderate amounts of magnesium as a platelet additive solution is that the population of WBC that escapes the saturated fluidized particle bed in chamber  67  or a leukoreduction filter media, are not representative of the WBC population as a whole. In order to escape the saturated fluidized particle bed in the chamber  67  and leukoreduction media, this subpopulation of WBC may be smaller and less dense than the average WBC. Internal studies have shown that WBCs carried over in standard platelet products are enriched in B lymphocytes. 39% of the WBCs found in platelets apheresed using a Trima apheresis machine are B lymphocytes, as compared to the 3.3% found in whole blood. Moreover, lymphocytes make up 28% of WBC in whole blood but make up 98% of WBC found in platelets separated using the Trima apheresis system. This smaller, denser subpopulation of WBCs from apheresed blood may be more sensitive to the residual amount of Ca +2  remaining (originating from the initial whole blood) in the apheresed platelets in combination with the Mg +2  ions found in an additive solution containing moderate amounts of magnesium, and therefore more susceptible to apoptosis or lysis. 
         [0108]    To determine whether the rWBCs contaminating the platelet concentrates differ from normal lymphocytes in their response to exposure to an additive solution containing moderate amounts of magnesium, mononuclear cells were isolated from a whole blood buffy coat preparation using Leukocyte Separation Medium (LSM® Lymphocyte Separation Medium commercially available from MP Biomedicals, Solon, Ohio, USA). The buffy coats were separated from whole blood using an automated whole blood separation system (the Atreus System, available from CaridianBCT, Inc., Lakewood, Colo.). These cells are considered to be normal, unselected mononuclear cells. The cells were then suspended at a concentration of 10/μl in anticoagulated plasma and in anticoagulated plasma plus additive solution at a ratio of 1:2, using SSP+ and Isolyte S as the additive solutions. As seen in  FIG. 10 , over 24 hours there was no significant decrease in WBC concentration as determined by flow cytometry in the plasma or in either of the plasma-additive solution products. “Normal” mononuclear cells, then, in plasma: additive solution containing moderate amounts of magnesium at a volume ratio of 1:2, differ from rWBC in the platelet concentrates in that they do not show the rapid decreases in concentration seen with the rWBC from apheresed platelets. 
         [0109]    In the BD Leucocount (commercially available kit from Becton Dickinson, Franklin Lakes, N.J., USA) flow cytometric assay the rWBCs are labeled with propidium iodide (PI), a DNA dye. In order to allow the PI to enter the nuclei of the leukocytes, the sample preparation includes treatment with detergent (EDTA) to make the cell and nuclear membranes permeable. The Leucocount assay was carried out on platelet products in the presence and absence of detergent. In theory, only WBCs whose membranes were compromised or “leaky” would be stained by PI in the absence of detergent treatment. The percent of WBC with permeable membranes was calculated according to: 
         [0000]    
       
         
           
             
               
                 W 
                  
                 
                     
                 
                  
                 B 
                  
                 
                     
                 
                  
                 C 
                  
                 
                     
                 
                  
                 s 
                  
                 
                     
                 
                  
                 stained 
                  
                 
                     
                 
                  
                 by 
                  
                 
                     
                 
                  
                 PI 
                  
                 
                     
                 
                  
                 without 
                  
                 
                     
                 
                  
                 detergent 
               
               
                 W 
                  
                 
                     
                 
                  
                 B 
                  
                 
                     
                 
                  
                 C 
                  
                 
                     
                 
                  
                 s 
                  
                 
                     
                 
                  
                 stained 
                  
                 
                     
                 
                  
                 using 
                  
                 
                     
                 
                  
                 the 
                  
                 
                     
                 
                  
                 standard 
                  
                 
                     
                 
                  
                 
                   assay 
                    
                   
                     
                         
                     
                      
                     
                         
                     
                   
                   ( 
                   
                     with 
                      
                     
                       
                           
                       
                        
                       
                           
                       
                     
                      
                     detergent 
                   
                   ) 
                 
               
             
             × 
             100 
           
         
       
     
         [0110]    Two controls were tested; in one, WBCs had been stored for 19 days in EDTA tubes and were seriously compromised by the detergent. For this sample, 100% of WBCs stained by the standard assay were stained in the absence of detergent. In comparison, only 61% of WBCs stored in EDTA for two days were stained. Ninety two percent (92%) of the rWBCs from apheresis platelet products collected on the Trima Accel system were stained in the absence of detergent treatment, while only 3% of WBCs that were isolated from the saturated fluidized particle bed in chamber  67  in the same collection were stained. This is shown in  FIG. 11 . Those WBCs isolated from chamber  67  had not “escaped” to become rWBCs, and were representative of the “normal” population of retained leukocytes. 
         [0111]    The lack of effect of platelet additive solution containing moderate amounts of magnesium on “normal” WBCs and the demonstration that the rWBC in platelet concentrates collected on the Trima Accel System have permeable membranes, supports the hypothesis that the rWBCs in platelet concentrates collected on the Trima and Trima Accel Systems represent a subpopulation of leukocytes that are compromised, perhaps in the early stages of apoptosis, and may be susceptible to rapid disintegration in the presence of mediators, such as ionized magnesium. 
       Example 4 
       [0112]    If the rWBC stored in an additive solution containing moderate amount of magnesium with 35% plasma carryover undergo accelerated apoptosis due to the presence of moderate concentrations of ionized magnesium, the question can arise as to whether this additive/storage medium has similar effects on the platelets. This is answered, in part, by the observation that the platelet concentrations are maintained throughout the storage period, and that in vitro platelet quality data of the additive solution containing moderate amounts of magnesium-stored platelets differ little from those stored in plasma alone. To investigate this further, the differences in Annexin V expression in paired platelet products stored in plasma and in additive solution containing moderate amounts of magnesium with 35% plasma carryover were studied. Annexin V binds to phosphatidyl serine exposed on the outside of cell membranes. It detects membrane changes that are early signs of apoptosis in leukocytes and platelets.  FIG. 12  shows the results of seven paired studies that demonstrate no significant differences in Annexin V expression between plasma-stored and 35% plasma carryover-additive solution containing moderate amounts of magnesium-stored platelets. This observation shows that the storage conditions do not induce measurable apoptosis in the platelets. 
       Example 5 
       [0113]    This study focused on providing in vitro quality data to support additive solution containing moderate amounts of magnesium as a platelet additive solution. 
         [0114]    This was a paired study in which subjects donated platelet products by apheresis on the Trima Accel system. Each subject underwent a Control, standard single platelet unit collection (standard platelet collected on Trima Accel and stored in plasma) and a Test, single unit collection (hyperconcentrated platelet collected on Trima Accel in significantly less plasma, diluted and stored in additive solution containing moderate amount of magnesium) on the same day, separated by at least 90 minutes. In other words, Test platelets were collected in a hyperconcentrated state and diluted with additive solution containing moderate amount of magnesium prior to storage, whereas Control platelets are collected and stored at standard concentration. 
         [0115]    The order of Test and Control collections was randomized. The Control platelet units mirrored the Test platelet units in terms of yield and final concentration. 
         [0116]    The hyperconcentrated platelet (Test) products were resuspended in additive solution containing moderate amounts of magnesium to a plasma carryover (=plasma volume/[plasma volume+P.A.S. volume]) of 35%. Plasma volume collected by apheresis includes a minor amount (16-20% of total volume) of ACD-A, which is the anticoagulant mixed with donor blood entering the Trima disposable tubing set during an apheresis procedure. Therefore, the actual plasma volume at 35% plasma carryover is 28-29% of the volume of the stored platelet concentrate. All platelet products were stored at 20-24° C. with agitation for seven days. Samples were taken from the stored platelet products on days  1 ,  5 , and  7  of storage. 
         [0117]    The primary outcome for this study was that 95% or more of the Test units have Day 5 pH at 22° C. greater than 6.2 with one-sided confidence limit of 95% (0/60 failures) in accordance with the FDA Guidance for Industry and FDA Review Staff: Collection of Platelets by Automated Methods, December 2007. This is shown in Table 3. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Test 
                 Control 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Average 
                 7.4 
                 7.5 
               
               
                   
                 St Dev 
                 0.2 
                 0.1 
               
               
                   
                 Min 
                 6.7 
                 7.2 
               
               
                   
                 Max 
                 7.6 
                 7.7 
               
               
                   
                 N 
                 67 
                 67 
               
               
                   
                   
               
             
          
         
       
     
         [0118]    Table 4 represents the average values of other measures of in vitro platelet quality during storage of Test and Control platelets. p-selectin, ESC, HSR, and morphology were measured after 5 Day storage. These values are within expected ranges for both Test and Control platelet products. 
         [0000]    
       
         
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 P-selectin 
                 ESC 
                 HSR 
                 Morphology 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Test 
               
             
          
           
               
                   
                 Average 
                 22.8 
                 23.2 
                 53.2 
                 290 
               
               
                   
                 St Dev 
                 15.4 
                 4.9 
                 12.4 
                 49 
               
               
                   
                 Min 
                 1.7 
                 14.2 
                 16.5 
                 200 
               
               
                   
                 Max 
                 72.0 
                 39.1 
                 72.0 
                 385 
               
               
                   
                 N 
                 67 
                 67 
                 67 
                 67 
               
             
          
           
               
                 Control 
               
             
          
           
               
                   
                 Average 
                 15.1 
                 24.9 
                 55.6 
                 293 
               
               
                   
                 St Dev 
                 9.7 
                 6.0 
                 10.9 
                 48 
               
               
                   
                 Min 
                 2.0 
                 11.8 
                 29.5 
                 205 
               
               
                   
                 Max 
                 52.0 
                 44.4 
                 77.0 
                 388 
               
               
                   
                 N 
                 67 
                 67 
                 67 
                 67 
               
               
                   
                   
               
             
          
         
       
     
         [0119]    The results of these investigations of the effects of 35% plasma carryover-additive solution containing moderate amounts of magnesium-storage on the rWBCs contained in platelet concentrates collected on the Trima Accel System strongly suggest that the rWBCs consist primarily of membrane permeable, possibly early apoptotic, lymphocytes. The low citrate concentration in the storage medium, coupled with moderate concentrations of magnesium, a known mediator of lymphocyte apoptosis, results in rapid disintegration of the initial low numbers of contaminating leukocytes. The rapid disappearance of intact leukocytes in platelet concentrates collected on the Trima Accel System and stored in 35% plasma carryover and additive solution containing moderate amounts of magnesium has no detectable effects on the platelets. The plasma-additive solution containing moderate amounts of magnesium does not induce apoptosis in the platelets or degradation in platelet quality over the period of storage. 
         [0120]    The foregoing description of the present invention has been presented for purposes of illustration and description. Furthermore, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the above teachings, and skill and knowledge of the relevant art, are within the scope of the present invention.