as noted above , the process of the invention provides a medium for the lyophilization and reconstitution of intact and biologically - active erythrocytes . while the media of the invention are novel it will be understood that apparatus and related techniques are known by those of skill in the art for the lyophilization of various materials , and cells in particular , and only the specific temperatures and apparatus employed in the examples are described herein . from this description , one of ordinary skill in the art will be capable of employing the media of the invention in a process for the freeze - drying and reconstitution of intact , viable red blood cells . packed red blood cells of variable blood type were obtained from a hospital blood donor center or drawn from healthy volunteers using heparin as an anticoagulant . repeated samples of these blood cells were washed with a phosphate buffered saline solution ( 10 mm mono - and di - basic sodium phosphate , 150 mm sodium chloride , 5 mm dextrose , and 10 mm adenosine at ph 7 . 2 ) three times with centrifugation at 14 , 000 rpm for 6 to 10 seconds to separate plasma and / or other cell types from the red blood cells . samples of the packed red blood cells were then suspended in a lyophilizing buffer containing a 2 molar concentration of glucose in pbs solution at ph 7 . 2 . the suspension was then transferred to a flask which was subsequently immersed in liquid nitrogen (- 196 ° c .) until the sample was frozen . the flask was rotated evenly in the liquid nitrogen to assure even dispersion of solution on the walls of the flask . the frozen samples were transferred to a bench top lyophilizer ( labconco model 4 . 5 ) operating at less than 100 microns of mercury vacuum with an inner chamber temperature of - 56 ° c . samples were allowed to dry thoroughly ( 6 - 24 hours ) until crystalline in appearance and brittle to touch and the flask was allowed to return to room temperature . the samples were rehydrated at 37 ° c . using a solution containing 1 m sucrose in a phosphate buffered saline solution . a volume of the rehydrating solution was added equivalent to the initial volume of the sample prior to drying . it was found upon examination of the cells with an optical microscope that about 50 % of the red blood cells had intact cell membranes . however , the hemoglobin was found not to be cell associated . nonetheless , the hemoglobin in the solution was active and if present in the cells would be effective as an oxygen carrier . repeating this procedure with fructose and ribose solutions having concentrations of from about 0 . 5 to 4 molar produced nearly equal results , as did buffered solutions of xylose and mannose at concentrations of from about 0 . 5 to 4 molar . specifically , various monosaccharides were employed in the lyophilization of rbcs as described in this example , and the distribution of the hemoglobin in the recovered solution was noted . oxyhemoglobin is capable of transporting oxygen to mammalian tissue . methemoglobin is hemoglobin which cannot bind oxygen , but can possibly be reversed to form oxyhemoglobin when found in lower concentrations by the enzyme nadh methemoglobin reductase . hemochrome is irreversibly degraded hemoglobin . in table i , the recovery of greater than 90 % oxyhemoglobin from cells lyophilized with solutions of ribose , mannose , fructose , xylose and glucose is shown . no significant variation in cell recovery is found , and oxyhemoglobin is still recovered , when the concentrations of these monosaccharides are varied from 0 . 5 to 4 . 0 molar . table i______________________________________carbohydrate % oxyhb % methb % hemochrome______________________________________2m ribose 93 . 1 5 . 4 1 . 52m mannose 94 . 2 6 . 0 02m fructose 98 . 0 1 . 3 0 . 72m sorbose 56 . 9 40 . 9 2 . 31m galactose 81 . 0 17 . 3 1 . 72m xylose 96 . 7 3 . 6 02m glucose 98 . 1 1 . 8 0 . 1______________________________________ a number of samples of packed red blood cells , obtained and washed as described in example one , were suspended in a lyophilizing buffer containing a 2 molar concentration of glucose and a concentration of either ( a ) 30 mm of 10 k or ( b ) 6 mm of 40 k polyvinylpyrrolidone in pbs at ph 7 . 2 . the suspension was then transferred to a flask which was subsequently immersed in liquid nitrogen (- 196 ° c .) until the sample was frozen . the flask was rotated evenly in the liquid nitrogen to assure even dispersion of solution on the walls of the flask . the frozen sample was transferred to a bench top lyophilizer ( labconco model 4 . 5 ) operating at less than 100 microns of mercury vacuum with an inner chamber temperature of - 56 ° c . samples were allowed to dry thoroughly ( 6 - 24 hours ) until crystalline in appearance and brittle to touch and the flask was allowed to return to room temperature . the samples were rehydrated at 37 ° c . using a solution containing 1 m sucrose in a phosphate buffered saline solution . a volume of the rehydrating solution was added equivalent to the initial volume of the sample prior to drying . the samples were centrifuged at 14 , 000 rpm in an eppendorf microcentrifuge to pellet the rehydrated red blood cells in suspension . the pelleted cells were resuspended and washed successively with solutions containing decreasing amounts of polyvinylpyrrolidone ( 10 k average molecular weight at 30 weight percent ) in phosphate buffered saline with glucose and adenosine solution . for example , cells were resuspended and washed in solutions containing 30 mm , 15 mm and 5 mm of 10 k polyvinylpyrrolidone . cells were resuspended in a phosphate buffered saline solution . the results of incorporating the polymer with the above described carbohydrate in the buffered lyophilizing solution produced surprising results not only in that the recovery of intact cells was maintained at 52 . 9 ± 7 . 9 %, but in addition the solution allowed hemoglobin retention by the cells of from 27 . 4 up to 42 . 2 % for the 10 k pvp and from 57 . 3 up to 65 . 5 % for the 40 k pvp , with greater than 80 % of the hemoglobin being oxyhemoglobin . further testing has shown that a solution with 2 m glucose , 24 k pvp at a concentration of 8 mm and glucose - 1 - phosphate at 30 mm produces even better results both in cell and hemoglobin recovery . the procedure described in example two was repeated , with various carbohydrates substituted for glucose in the lyophilizing buffer , at two different concentrations of polyvinylpyrrolidone . the results are shown in table ii . table ii______________________________________pvpmw carbohydrates % cell recovery % hb recovery______________________________________10k 1m galactose 27 . 7 10 . 3 2m mannose 57 . 6 30 . 6 2m xylose 63 . 9 32 . 3 2m fructose 54 . 6 28 . 1 2m glucose 59 . 0 28 . 624k 1m galactose 26 . 3 13 . 8 2m mannose 51 . 8 57 . 2 2m xylose 48 . 4 55 . 9 2m fructose 48 . 8 59 . 3 2m glucose 59 . 0 52 . 7______________________________________ the procedure described in example two ( using two molar glucose as the carbohydrate ) was repeated substituting polyvinylpyrrolidone of different molecular weights and concentrations for those used in the lyophilizing buffer of the previously described example . all other conditions were repeated as described in example two . the results are shown in table iii . the column headed mchc refers to the mean cell hemoglobin content of the reconstituted cells . the mchc of normal rbcs is 34 ± 2 . table iii demonstrates that pvp may be employed with molecular weights of from 10 to 40 k in concentrations of from 3 to 30 mm . the 40 kt pvp had a viscosity of about 26 to 35 poise , and the 40 k pvp had a viscosity of about 28 to 32 poise . table iii__________________________________________________________________________pvp mw molarity % conc . % hb recovery mchc__________________________________________________________________________10k 5 mm 5 13 . 6 -- 10 mm 10 15 . 0 34 . 9 20 mm 20 30 . 1 ± 4 . 1 ( n = 3 ) 20 . 9 ± 3 . 1 ( n = 3 ) 30 mm 30 36 . 5 28 . 124k 2 mm 5 24 . 7 17 . 3 4 mm 10 52 . 9 20 . 9 8 mm 20 52 . 7 ± 6 . 3 ( n = 4 ) 27 . 4 ± 4 . 3 ( n = 4 ) 12 mm 30 52 . 2 ± 6 . 9 ( n = 2 ) -- 40k 1 . 5 mm 5 17 . 7 -- 3 mm 10 31 . 0 22 . 5 6 mm 20 61 . 4 ± 4 . 1 ( n = 3 ) 25 . 7 ± 9 . 2 ( n = 3 ) 9 mm 30 52 . 0 ± 1 . 7 ( n = 2 ) 37 . 440kt 1 . 5 mm 5 17 . 7 -- 3 mm 10 31 . 8 25 . 0 6 mm 20 56 . 8 ± 0 . 4 ( n = 2 ) 36 . 3 ± 2 . 8 ( n = 2 ) 9 mm 30 50 . 0 29 . 4360k 0 . 13 mm 1 9 . 4 -- 0 . 14 mm 5 12 . 2 -- __________________________________________________________________________ the experiment described in example two was repeated using polymers other than polyvinylpyrrolidone in the lyophilizing buffer . the results are summarized in table iv . table iv______________________________________polymer mw % conc . % hb recovery______________________________________dextran 10k 5 26 . 1 10 29 . 8 20 26 . 5 30 30 . 2 40k 5 24 . 7 10 19 . 5 20 25 . 9 30 16 . 6 80k 5 15 . 2 10 26 . 5 20 20 . 2 30 18 . 7dextran 40k 10 25 . 9phosphatedextran 500k 10 11 . 4sulfateficoll 70k 5 17 . 3 10 19 . 1 400k 1 17 . 2 5 17 . 9fish gelatin 2 19 . 0 10 18 . 4dextrin 2 20 . 4 10 13 . 1albumin 2 29 . 7______________________________________ samples of packed red blood cells were obtained and washed as described in example one . these cells were suspended in a lyophilizing buffer of 20 % 24 k pvp ( 8 mm ) and 2 m glucose in phosphate buffered saline . the samples were lyophilized and reconstituted as described in example two , but with the various solutions used in the reconstitution of the cells . when water was the sole reconstituting liquid , the cells lysed within thirty minutes after reconstitution . an isotonic reconstituting solution , such as pbs or pbsga ( pbs with the addition of 5 mmol glucose and 10 mmol adenosine ) showed improvement , as did the use of reverse pbs , which employs potassium rather than sodium salts . significant improvements were shown by the use of concentrations of up to 20 % of either 10 k or 24 k pvp in the reconstitution solution . the use of a carbohydrate in a minimum concentration of at least 250 mm , preferably 0 . 05 m and most preferably at least 0 . 25 m , provides better cell morphology after reconstitution . both mono - and disaccharides may be employed for this purpose , although glucose , mannose , trehalose and sucrose are preferred with sucrose being the most preferred carbohydrate . these data are shown in table v , wherein all carbohydrate and polymer solutions are formed in pbs . table v______________________________________ % hbsolution % cell recovery recovery mchc______________________________________water 49 . 3 ± 3 . 0 37 . 4 ± 1 . 1 29 . 9 ± 1 . 8pbs 59 . 2 34 . 4 24 . 8pbsga 60 . 6 42 . 4 31 . 2reverse pbs 52 . 6 51 . 3 25 . 8glucose 1m 52 . 5 57 . 3 32 . 9mannose 1m 55 . 5 60 . 7 28 . 0trehalose 1m 65 . 7 59 . 4 24 . 9sucrose0 . 05m 61 . 7 45 . 6 24 . 40 . 10m 43 . 8 46 . 2 27 . 30 . 25m 49 . 5 52 . 8 24 . 61m 49 . 6 ± 10 . 6 51 . 4 ± 5 . 1 25 . 5 ± 2 . 15 % 10k pvp 55 . 6 ± 11 52 . 3 ± 3 . 0 23 . 5 ± 1 . 420 % 10k pvp 60 . 8 67 . 7 28 . 45 % 24k pvp 52 . 2 38 . 8 26 . 020 % 24k pvp 53 . 8 ± 9 . 4 73 . 1 ± 8 . 1 28 . 2 ± 8 . 75 % 10k pvp + 65 . 0 ± 6 . 5 59 . 0 ± 7 . 6 28 . 2 ± 8 . 71m sucrose20 % 10k pvp + 39 . 5 61 . 6 27 . 81m sucrose5 % 24k pvp + 64 . 8 59 . 3 ± 6 . 9 26 . 51m sucrose20 % 24k pvp + 77 . 7 76 . 4 ± 4 . 2 31 . 51m sucrose______________________________________ from the foregoing description , one skilled in the art can readily ascertain the essential characteristics of the invention and , without departing from the spirit and scope thereof , can adapt the invention to various usages and conditions . changes in form and substitution of equivalents are contemplated as circumstances may suggest or render expedient , and although specific terms have been employed herein they are intended in a descriptive sense and not for purposes of limitation .
a process and medium are disclosed for the lyophilization of red blood cells which comprises the use of solutions including monosaccharide hexoses and pentoses , and / or biocompatible polymers to permit the reconstitution of viable red blood cells .