the efficacy of a xenograft demineralized and deantigenated bone matrix is here assessed with respect to osteoconductive , potential osteoinductive and immunological properties and characteristics . initial assessment of immunology uses ∝- galactosidase treated porcine cortical struts in a primate femoral onlay study . final assessment uses decalcified bone particulate that has been treated with ∝- galactosidase to eliminate ∝- gal epitopes . the biocompatibility , osteoconductive and osteoinductive potential of the demineralized matrix are assessed in a rat cranial defect model using radiography and histology . the overall unifying concept of the invention is that processed xenogeneic porcine demineralized bone treated with ∝- galactosidase is osteoconductive , osteoinductive and immunocompatible . the xenogeneic porcine demineralized bone treated with ∝- galactosidase is also biocompatible , porous , resorbable , and space maintaining . the term “ xenograft ” is synonymous with the term “ heterograft ” and refers to a graft transferred from an animal of one species to one of another species . stedman &# 39 ; s medical dictionary , williams & amp ; wilkins , baltimore , md . ( 1995 ). the term “ xenogeneic ”, as in , for example , xenogeneic soft tissue refers to soft tissue transferred from an animal of one species to one of another species . id . once implanted in an individual , a xenograft provokes immunogenic reactions such as chronic and hyperacute rejection of the xenograft . the term “ chronic rejection ”, as used herein refers to an immunological reaction in an individual against a xenograft being implanted into the individual . typically , chronic rejection is mediated by the interaction of igg natural antibodies in the serum of the individual receiving the xenograft and carbohydrate moieties expressed on cells , and / or cellular matrices and / or extracellular components of the xenograft . for example , transplantation of cartilage xenografts from non - primate mammals ( e . g ., porcine or bovine origin ) into humans is primarily prevented by the interaction between the igg natural anti - gal antibody present in the serum of humans with the carbohydrate structure galα1 - 3galβ1 - 4glcnac - r ( α - galactosyl or α - gal epitope ) expressed in the xenograft . k . r . stone et al ., porcine and bovine cartilage transplants in cynomolgus monkey : i . a model for chronic xenograft rejection , 63 transplantation 640 - 645 ( 1997 ); u . galili et al ., porcine and bovine cartilage transplants in cynomolgus monkey : ii . changes in anti - gal response during chronic rejection , 63 transplantation 646 - 651 ( 1997 ). in chronic rejection , the immune system typically responds within one to two weeks of implantation of the xenograft . in contrast with “ chronic rejection ”, “ hyper acute rejection ” as used herein , refers to the immunological reaction in an individual against a xenograft being implanted into the individual , where the rejection is typically mediated by the interaction of igm natural antibodies in the serum of the individual receiving the xenograft and carbohydrate moieties expressed on cells . this interaction activates the complement system causing lysis of the vascular bed and stoppage of blood flow in the receiving individual within minutes to two to three hours . the following examples are presented in order to more fully illustrate the preferred embodiments of the invention . these examples should in no way be construed as limiting the scope of the invention , as defined solely by the appended claims . in this example , methods have been developed for decreasing the immune response against porcine tissue implanted in monkeys , by eliminating the α - gal epitopes ( galα1 - 3galβ1 - 4glcnac - r ) with recombinant α - galactosidase , and mild glutaraldehyde fixation . results using non - decalcified bone struts provide supporting evidence for the use of bone particulates for bone repair . background . previously , crosscart inc . ( san francisco , calif ., usa ) has extensively characterized a porcine bone patellar tendon bone anterior cruciate ligament ( acl ) reconstruction device . this composite device consists of a sterile and biocompatible collagen tendon with cortical / cancellous bone plugs on each end . an irradiation - processing step significantly reduces viral agents from spiked samples . in previous primate bone testing , crosscart used porcine bone grafts in the femur of primates to evaluate solid bony fusion to screen process variables for new bone formation and fusion of implants with host tissue . methods : in this example , eighteen adult male rhesus monkeys weighing 9 - 18 . 5 kg were used to characterize cortical bone healing and graft incorporation . the anesthetized monkeys received bilateral cortical on - lay strut grafts that were secured to the mid - femur held in place with proximal and distal wires , and cancellous defects , 8 mm in diameter by 8 mm deep were created in the distal femur and proximal tibia . the screening groups consisted of xenograft cortical struts ( table i ) or cancellous bone ( table ii ) material treated as follows : ( a ) freeze only ( b ) alcohol + freeze ( c ) α - galactosidase + gluteraldehyde and α - galactosidase + gluteraldehyde + hydrogen peroxide . twelve animals received two bilateral on - lay xenograft strut grafts approximately 5 cm in length and 0 . 5 cm wide on the lateral and posterior surfaces of the femur . cortical bone healing was evaluated at 6 and 26 weeks post - implantation . cancellous bone healing with xenograft cancellous cylindrical plugs was evaluated in bilateral defects created in the metaphyseal region of the distal femur and / or proximal tibia . a total of 36 cancellous bone defects in 14 animals were evaluated with the addition of xenograft plugs at 6 , 12 , and 26 weeks post - implantation . eight control ( empty ) cancellous defects were evaluated in the distal femurs of eight animals at 26 weeks post - implantation . six animals were necropsied at 6 weeks , one at 12 weeks , and 11 at 26 weeks post - implantation . plain film radiographs were taken at intervals to test the progression of healing of the femurs and tibias . all sections were then histologically examined by preparing undecalcified histological sections to determine tissue response , residual implant material , quality and amount of new bone formation , graft incorporation and remodeling . each cortical strut and cancellous defect site was observed for gross appearance . the cortical strut grafts were manually determined to be stable or unstable prior to removing the wires . if a strut was very unstable , the wires were left in place . presence of fibrous tissue and degree of bone contact between the strut graft and femur cortex was noted . the length , width and height in millimeters of each strut graft were measured and noted . visual observation of the overall incorporation and remodeling of the strut graft was made and recorded as well as any other notable findings related to the gross appearance . similarly , the cancellous defect sites were observed for the presence of graft material , fibrous tissue , incorporation with the host bone , and visual changes in or around the defect . two struts were placed on each femur . a summary of implanted graft materials for cortical strut on - lay graft model by treatment type is depicted in table i below . a summary of implanted graft materials for cancellous bone defect graft model by treatment type is shown in table ii below . one cylindrical plug graft was placed per defect site . no animals experienced adverse clinical reaction related to the implanted materials or surgical procedures . all animals were fully weight bearing by the end of the second post - operative week . the in vivo analysis included the administration of oxytetracycline hydrochloride ( 20 mg / kg body weight ) and fluorochrome at 14 and 7 days prior to the scheduled necropsy . bilateral antero - posterior and lateral radiographs of the lower limbs were obtained immediate post - operative , at 3 months and at necropsy . all radiographs were taken within three days of the scheduled radiograph date . blood samples were intermittently taken for anti - gal activity . results : the treated xenograft material displayed improved biological performance when implanted into the non - human primate model . only the results of the 26 - week test are presented here . specifically the α - galactosidase and gluteraldehyde treatment of porcine and cortical and cancellous bone grafts demonstrated less inflammatory reaction as compared to untreated xenograft cortical and cancellous bone graft controls . furthermore , this test group also showed increased remodeling , graft incorporation and new bone formation in the in the cortical strut graft compared to untreated controls . the cancellous plug grafts placed in the distal femur and proximal tibia similarly showed increased graft incorporation and remodeling compared to untreated xenograft controls . the data is shown in the table iii below represents the summed response for both axial and longitudinal bone . the histological data of cancellous bone defects is shown in table iv below : histological analysis : the photomicrographs of undecalcified histological sections from untreated ( freezing only ) cortical strut grafted sites at 26 weeks post - operatively are shown in fig1 a and fig1 b . in fig1 a , graft incorporation was approximately 20 % to 30 % on the left femur . mineralizing cartilage is observed between the graft and host bone . residual graft is shown at the top of figure and the femur cortex is shown at the bottom ( 1 × magnification , basic fuchsin ). graft incorporation on the right femur ( fig1 b ) was considerably lower due to fibrous tissue interposition and a significant gap . note the resorption of graft distally to the right of the image . the micrographs are at 1 × magnification , stained using basic fuchsin . the photomicrographs of undecalcified histological sections from two treated ( α - galactosidase + glutaraldehyde ) cortical strut grafted sites at 26 weeks post - operatively are shown in fig2 a and fig2 b . in fig2 a , graft incorporation was approximately 55 % in this site . new bone is seen bridging from the femur cortex to the residual graft . in fig2 b , significant contact between host femur cortex , new bone bridge and strut graft was observed . the micrographs are at 1 × magnification , stained using basic fuchsin . discussion : the α - galactosidase and gluteraldehyde treated cortical strut grafted sites exhibited minimal graft resorption , limited new bone formation and no inflammatory response at 6 weeks post - operatively . at 26 weeks post - operative , there was minimal graft resorption with a significant amount of new bone formation and bony incorporation along the host cortex bridging to the graft . some fibrous tissue was present in the gap interfaces between strut and host cortex and the inflammatory reaction minimal in all cases . the inflammatory reaction to the untreated grafts was moderate to severe characterized by osteoclastic graft resorption and the presence of foreign body giant cells in the surrounding tissues . the results of all inflammatory reactions are shown in table iii and table iv , above . histological analysis of cancellous plug grafted sites evaluated at 6 weeks post - operatively showed very early and limited new bone formation . graft incorporation was related to the degree of graft resorption that was mild to moderate in the majority of defects . the inflammatory reaction to the treated cancellous grafts at 6 weeks was none to mild in the majority of sites . at 26 weeks , the amount of new bone formation was greater for the treated cancellous plug grafted sites as compared to those evaluated at 6 weeks . in the α - galactosidase + gluteraldehyde group , graft incorporation was higher with a corresponding increase in graft resorption and a lower percentage of residual graft . the majority of cancellous graft sites had none to mild inflammatory response . conclusion : the results of this example support previous findings in which recombinant α - galactosidase treatment of porcine patellar tendons resulted in a significant reduction in anti - gal humoral response and limited cellular infiltration ( galili , science and medicine , 32 ( september / october 1998 ). this example shows that bone grafts can be similarly treated with α - galactosidase to deter the inflammatory response and promote graft incorporation . although this example i does not specifically address osseus union of bone fractures , the model is , however , directly applicable to bone repair mechanisms where the union of bone is anticipated and where the infiltration of cellular materials responsible for fusion and bone reconstruction are actively recruited . this example refines the treatment regimen of example i to obtain maximum benefit in removal of α - gal epitopes from xeno - active tissues and promote accelerated osseus union . process development . diaphyseal bone is harvested from 6 to 12 month old swine from a medical grade abattoir that also supplies porcine aortic heart valves for human implantation . after dissection of soft tissue , manual periosteal stripping and marrow removal , bone pieces are subjected to consecutive hypertonic , hypotonic and alcohol rinses . the bone is then milled to sieve standardized 150 to 500 μm particle size ( zhang et al ., j . periodontal . 68 ( 11 ): 1085 - 92 ( 1997 )). after sizing , the particles are subjected to consecutive hydrogen peroxide and alcohol washes . downstream processing includes separate hydrochloric acid decalcification and enzymatic treatment . protocols have been established to characterize the α - galactosidase enzyme , as described below : assay for α - galactosidase . the enzyme α - galactosidase ( previously cloned from coffee beans and genetically expressed in the yeast pichia pastoris ) has been well - characterized ( zhu et al ., arch . biochem . biophysics 324 : 65 ( 1995 )). α - galactosidase is an exoglycosidase of molecular weight 41 kda that is diffusely distributed in nature . it functions by cleaving the terminal α - galactose residue from oligosaccharide chains from cells . the activity of recombinant enzyme is determined by reacting diluted enzyme with p - nitrophenyl - α - galactoside substrate , for 10 minutes at room temperature ( zhu et al ., arch . biochem . biophysics 827 : 324 ( 1996 )). the absorbance of p - nitrophenol in each solution is read at 405 nm . the enzyme is stable at 37 ° c ., 24 ° c ., and 4 ° c . and is affected by repeated freezing and thawing . the activity of each batch of enzyme is checked prior to use in assays . determination of α - gal epitope expression . an “ elisa inhibition ” assay was developed for the determination of α - gal epitope expression on various tissues . this assay is a modification of a radioimmunoassay solid - phase method , previously developed to measure mammalian glycoproteins . the interaction of m86 anti - gal antibody with α - gal epitopes on cells is measured by the activity of free m86 remaining in the supernatant after incubation with α - gal - bsa ( solid - phase ). with minor modifications , the assay can be used for the determination of α - gal epitope expression on bone particulate homogenates . demineralized bone particulates are incubated at various concentrations with the monoclonal anti - gal antibody designated m86 at a dilution of 1 : 100 of the antibody . after overnight incubation with constant rotation the particles and bound antibody is removed by centrifugation . the remaining anti - gal antibody in the supernatant are determined by elisa with α - gal epitope linked to bsa ( α - gal bsa ) as solid phase antigen . there is a direct correlation between the number of α - gal epitopes expressed in the bone particles and the binding of the monoclonal anti - gal antibody to these particles ( i . e . removal of the antibody from the supernatant ). bone particulates devoid of α - gal epitopes bind no anti - gal and thus does not decrease the subsequent binding of the antibody to α - gal bsa as a result of overnight incubation with the antibody . determination of enzyme protein concentration — specific activity determination . this assay employs the sigma diagnostics microprotein - pr ™ kit that quantitatively determines the amount of protein in solution . the reaction medium consists of 0 . 05 mmol / l pyrogallol red , 0 . 16 mmol / l sodium molybdate . the protein standard solution consists of human albumin ( 50 mg / 100 ml ) in saline with 0 . 1 % sodium azide as a preservative . 95 μl of the pyrogallol reagent is added into each well . deionized water is used as a blank . into the test wells are added 5 μl of enzyme solution ( 1 / 50 dilution ). the standard albumin solution is added into separate wells . the multiwell plate and contents is incubated for 3 minutes at 37 ° c . the absorbance is determined at 600 nm . the protein concentration is calculated using the formula : protein ( mg / dl )= a test − a blank / a standard − a blank × concentration of standard . procedure for epitope determination in bone particulates . this assay is a modification of a radioimmunoassay solid - phase method , previously developed to measure mammalian glycoproteins . the interaction of m86 anti - gal antibody with α - gal epitopes on cells is measured by the activity of free m86 remaining in the supernatant after incubation with α - gal - bsa . bone particulates are subjected to vigorous homogenization in pbs ph 7 . 2 / 3 . the final concentrate is then diluted to a concentration of approximately 200 mg / ml and then serially diluted with pbs containing 1 % bsa . each diluted sample ( 0 . 1 ml ) is then pipetted into a microcentrifuge tube . the monoclonal anti - gal antibody ( m86 ), at a dilution of 1 : 50 , is then also added to each tube in 0 . 1 ml aliquots . a final dilution of 1 : 100 of m86 antibody subsequently provides a 50 % maximum binding to α - gal - bsa . this dilution is suitably sensitive for determining anti - gal antibody binding to epitopes . the tubes containing the homogenate and monoclonal antibody are then maintained at 4 ° c . with continuous rotation overnight . during this period the m86 antibodies begin the binding process to the α - gal epitopes in particles of the homogenate suspension . finally , the tissue fragments that bind to antibody molecules are removed by centrifugation in an eppendorf microfuge tube at 14 , 000 rpm ( 35 , 000 × g ). hence , elisa results determine the activity of the m86 antibody remaining in the supernatant with α - gal - bsa as the solid - phase antigen and horseradish peroxidase - conjugated goat anti - mouse igm second antibody ( igm - hrp ; axcell laboratories ). color development are generated by the addition of o - phenylenediamine ( opd ) at a concentration of 1 mg / ml in peroxide buffer , ph 5 . 5 , containing 10 μl / ml of 30 % hydrogen peroxide . since particles containing α - gal epitopes remove the antibody prior to the elisa procedure , the interaction results in “ inhibition ” of the subsequent m86 binding to the solid - phase α - gal - bsa . comparison of the inhibition curves of the test homogenate m86 level with those of a standard value obtained from the m86 antibody level prior to α - gal treatment provide data that quantifies the apparent increase in antibody titer . thus , the concentration of α - galactosidase that results in complete elimination of α - gal epitopes is determined by observing no binding of m86 to the particles . procedure for determination of anti - bone matrix antibodies in sera . antibody production to bone matrix proteins is determined by elisa with particulate bone matrix as solid phase antigen . the particles are homogenized to a size of 1 - 10 μm and dried on elisa plates as 100 ug / well . hence , the procedure originally used for cartilage and ligaments is applied to bone in this test . an elisa test is performed using either untreated porcine bone particulates or α - galactosidase - treated bone particulates samples plated , dried and blocked . dilutions of serum , starting at 1 : 50 , in 50 μl amounts are then added to the wells . the plates are kept for 2 hr at room temperature , washed 4 times with pbs - tween and reacted with anti - human igg - hrp ( dako ) diluted 1 : 1000 for 1 hr at room temperature . after 5 further washes with pbs - tween , a color develops when incubated with opd for a reaction time of 3 to 5 minutes . elisa absorbance values are compared in samples of sera collected pre - and post - implantation from each animal . a stable value or increase in antibody titer provides a measure about the anti - bone immune response . determination of α - galactosidase content in bone particles . bone particulates are weighed , then dissolved in a fixed volume of pbs ( ph 7 . 0 ) plus 0 . 1 % triton x100 and homogenized . the homogenate are stored at 32 ° c . for 30 minutes followed by 10 minutes of centrifugation at 12000 g . the supernatant is decanted and millipore filtered . the α - galactosidase activities are determined in the supernatant . a similar extraction procedure is conducted in bone particulates immediately post α - galactosidase treatment . these data provide information pertaining to the precise concentration of residual α - galactosidase remaining in the tissue following processing . spiking an additional homogenates with a known amount of α - galactosidase and similarly determining the activity in the extract validates the assay . summary of protocols . enzyme optimization is conducted in groups , as described in table v . porcine graft materials treated with α - galactosidase enzyme ( 100 units / ml ) have been successfully deantigenated using a specified enzyme to gram of tissue ratio ( galili et al ., transplantation 65 : 1129 ( 1998 ); galili et al ., transplantation 63 ; 646 ( 1997 )). based on previous experience with cartilage , the enzyme should penetrate into the decalcified bone granules and destroy the ∝- gal epitopes in the bone matrix . the elimination of the ∝- gal epitopes is measured at various ∝- galactosidase concentrations by the elisa inhibition assay with a monoclonal antibody to ∝- gal epitopes as we previously described ( galili et al ., transplantation 65 : 1129 ( 1998 )) although the effective surface area of processed connective tissues has not been measured , the effective surface area of milled bone particulate ( 150 - 500 um range ) is many orders of magnitude greater . particulate processing provides vast surface area and minimal diffusional path - length , maximizing epitope presentation and resultant enzyme / product clearance . other specifics for process development include scaleable process design , implementing scaleable reactors from cell culture technology . final processing of prepared matrix materials includes lyophilization , vialing and terminal sterilization using 2 . 5 mrad ionizing radiation . once the optimization and processing has been standardized , materials for in - vivo testing are prepared . rat cranial defect model test system . the rat cranial defect model has been established as a screening assay for osteoconductive and osteoinductive properties of bone grafting materials ( hollinger & amp ; kleinschmidt , j . craniofac . surg . 1 ( 1 ): 60 - 8 ( january 1990 ); hollinger et al ., clin . orthop . ( 267 ): 255 - 63 ( june 1991 )). the long evans rats are quarantined for one - week prior to use . the rats are placed in a bell jar and subjected to inhalant anesthesia ( isofluorane ). once sedated , the rats are transferred to a sterile operating field and prepared for surgery . the animals are then injected with ketamine / xylazine cocktail ( 100 mg / 20 mg ) as an initial induction dosage followed by a maintenance dose of 50 mg / 10 mg cocktail as required . the breathing depth is monitored and the toe pinch reflex applied to evaluate the depth of anesthesia . ophthalmic ointment is applied to the eyes to prevent dehydration . the rat cranial defect model in this example uses long evans rats , in which an 8 mm trephine defect is created in the cranium ( hollinger et al ., surgery 107 ( 1 ): 50 - 4 ( january 1990 )). animals are skeletally mature with adult rats weighing between 250 - 300 gm . rat model details include a four - week assessment time point with six animals per test group ( hollinger et al ., clin . orthop . ( 267 ): 255 - 63 ( june 1991 ); schmitz et al ., acta anat ( basel ) 138 ( 3 ): 185 - 92 ( 1990 )). after the surgical site is prepared using consecutive applications of betadine and 70 % isopropyl alcohol , a linear incision is made from the nasal bone to mid - sagittal crest . soft tissues are reflected and the periosteum dissected from the exposed occipital , frontal and parietal bones . an 8 mm craniotomy defect is created with a low speed trephine under irrigation with 0 . 9 % sterile saline . final removal of the cranial piece is accomplished with a probe . pre - weighed test article is then placed uniformly in the defect and soft tissues closed with interrupted resorbable suture . care is taken not to perforate the dura and superior sagittal sinus . animals are monitored throughout the 28 - day test . animals are euthanized using i . v . 0 . 5 ml / 300 gm beuthanasia - d . craniotomy sites with 3 to 4 mm of surrounding bone are dissected from the fronto - occipital complex and immediately placed in 70 % ethanol for further analysis . after 24 hours in 70 % ethanol , specimens are radiographed using high resolution radiographic film . each roentgenogram is then digitized and radiopacity assessed within a standard 8 mm diameter circle superimposed over the defect site . the measured area of radiopacity within the standard circle is reported as a percentage of the total area . after radiomorphometry , the specimens are further dehydrated in ethanol , embedded in methacrylate and microtomed in 4 . 5 μm coronal sections . sections are prepared with trichrome stain for cellular detail and von kossa stain for newly calcified tissue . quantitative assessment of new bone formation within the defect site is assessed using von kossa stained sections after a standard gray level is established between cellular structures and newly calcified tissue within the defect site . descriptive statistics are performed on all test groups as part of the radiomorphometry and histomorphometry . additional statistical analysis is accomplished by anova with discreet comparisons evaluated by post - hoc testing and multiple comparisons using fisher analysis . porcine bone matrix assay groups in this example include decalcified , irradiated bone particles as control and decalcified particles treated with ∝- galactosidase and each of buffer , guanidine hydrochloride or glutaraldehyde , terminally sterilized as enzyme / deantigenation test groups . the selection of test groups for this analysis includes three model control groups ( a ) an unfilled defect , and demineralized human matrix treated ( b ) with and ( c ) without guanidine hydrochloride to inactivate endogenous growth factors ( shigeyama et al ., j . periodontal . 66 ( 6 ): 478 - 87 ( 1995 )). the porcine test groups mirror the guanidine extraction for endogenous growth factor removal and include a non - enzymatically treated control . previously developed deantigenation strategies have included aldehyde cross - linking and this processing variable is also included in a fourth porcine derived test group . the seven groups for this test are shown in table vi below . table vii below provides steps for one embodiment of the z - bone process : wash with wfi for 10 - 12 hours with constant agitation at 4 ° c ., repeat 2 times . wash with wfi w / 1 . 5m nacl for 10 - 12 hours with agitation with lighting mixer ( a310 inspect segments , remove any remaining soft tissue and transfer for new wfi bath for suspend resulting slurry in 70 % ipa 0 . 1 % tween 20 and pour through stacked sieves suspend bone in h 2 o 2 and stir for 4 - 6 hours at 4 ° c . decant supernatant and add . 5n hcl ( 6 l ) for 20 - 24 hours at 4 ° c . decant supernatant and add α - galactosidase solution for 4 - 12 hours at 4 - 26 ° c . in another embodiment , the pilot process differs from table vii above by one - step bulk lyophilizing with and dry particulate fill . the details of one or more embodiments of the invention are set forth in the accompanying description above . although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the invention , the preferred methods and materials are now described . other features , objects , and advantages of the invention will be apparent from the description and from the claims . in the specification and the appended claims , the singular forms include plural referents unless the context clearly dictates otherwise . unless defined otherwise , all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs . all patents and publications cited in this specification are incorporated by reference . the foregoing description has been presented only for the purposes of illustration and is not intended to limit the invention to the precise form disclosed , but by the claims appended hereto .
the invention provides for the use of an improved xenograft bone particulate with respect to osteo - integration and bone remodeling , while diminishing the primate - to - pig immunological response using established bone - processing technique . work was carried out using undecalcified bone to determine immunocompatibilty and bone remodeling potential of processed porcine bone struts following onlay graft implantation . new bone formation was evident , including the infiltration of cellular materials responsible for fusion and bone reconstruction .