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Interleukin 10 gene transfection of donor lungs ameliorates posttransplant cell death by a switch from cellular necrosis to apoptosis

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Interleukin 10 gene transfection of donor lungs ameliorates posttransplant cell death by a switch from cellular necrosis to apoptosis
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  CardiothoracicTransplantation Interleukin 10 gene transfection of donor lungs amelioratesposttransplant cell death by a switch from cellularnecrosis to apoptosis Stefan Fischer, MD, MScMarc de Perrot, MD, MScMingyao Liu, MDAlexandra A. MacLean, MDJonathan A. Cardella, MScYumiko Imai, MDMichiharu Suga, MDShaf Keshavjee, MD, MSc, FRCSC, FACS Background:  We have previously shown that cell death is a pathophysiologicconsequence of ischemia-reperfusion and that interleukin-10 gene therapy improvesthe function of transplanted lungs. Interleukin-10 downregulates the inflammatoryresponse and can inhibit apoptosis. The objective was to determine whether donorlung transfection with the interleukin-10 gene ameliorates lung dysfunction bydecreasing cell death after transplantation. Methods:  Single lung transplants were performed in 3 groups of rats (n  5 each):AdhIL-10, transtracheal administration of Ad5E1RSVhIL-10 (5    10 9 pfu); EV,empty vector; and VD, vector diluent (3% sucrose). After in vivo transfection, donorlungs were excised, stored at 4°C for 24 hours, and then transplanted. After 2 hoursofreperfusion,lungswereflushedwithtrypanblueandfixed.TUNELstainingwasusedforthedetectionofapoptosis.Thiscombinedstainingtechniqueallowsonetodeterminethe mode of cell death by distinguishing apoptotic dead cells from necrotic dead cells. Results:  Lung function was superior in the interleukin-10 group ( P  .0001) vs theEV and VD group (Pa O 2 : 240  31 mm Hg vs 98  17 mm Hg vs 129  11 mmHg, respectively). Although the total number of dead cells (as percent of total cells)was similar in all groups (32.7%    3.2%, 30.2%    2.5%, and 30.3%    3.8%),interestingly, apoptosis was highest in interleukin-10 lungs (9.7    1.9 vs 2    1.9and 1.8  2,  P  .0001), and necrosis was lowest in the interleukin-10 group (20.6  5.7 vs 28.3  3.1 and 30.3  4.2,  P  .01). Conclusions:  AdhIL-10 gene transfection improves function of transplanted lungs.Although the total number of cells dying as a result of the transplant process did notchange, the  mode  of cell death appears to have been modified. It is possible thatAdhIL-10, by decreasing proinflammatory cytokine production, ameliorates theoverall injury and preserves the ability of damaged cells to undergo a more quiescentand less tissue-damaging mode of cell death—apoptosis, rather than necrosis. From the Thoracic Surgery Research Lab-oratory, Toronto General Hospital ResearchInstitute, University Health Network, Uni-versity of Toronto, Toronto, Ontario,Canada.Read during the C. Walton Lillehei Resi-dent Forum at the Eighty-second AnnualMeeting of The American Association forThoracic Surgery, Washington, DC, May5-8, 2002.This work was supported by grants fromthe National Sanitarium Association of Canada, the Canadian Cystic FibrosisFoundation, and the Canadian Institutes of Health Research.Address for reprints: Shaf Keshavjee, MD,Director, Toronto Lung Transplant Pro-gram, Division of Thoracic Surgery, To-ronto General Hospital, 200 Elizabeth St,EN 10-224, Toronto, Ontario, Canada M5G2C4 (E-mail: shaf.keshavjee@uhn.on.ca).J Thorac Cardiovasc Surg 2003;126:1174-80Copyright © 2003 by The American Asso-ciation for Thoracic Surgery0022-5223/2003 $30.00  0doi:10.1016/S0022-5223(03)00114-4 1174 The Journal of Thoracic and Cardiovascular Surgery  ● October 2003 T   X    L ung transplantation is now accepted as astandard treatment modality for patientswith a number of end-stage lung diseases. 1 The long-term outcome after clinical lungtransplantation, however, is still not satisfac-tory, with a current 5-year survival of onlyapproximately 55%. 2 It is clear that an improved understanding of the under-lying mechanisms of the injury that is inflicted on pulmo-nary grafts by ischemia, the transplant process itself, andreperfusion of the transplanted lung—referred to as isch-emia-reperfusion (IR) injury—is required. In examiningprocesses related to the induction of cell death in humanlungs during the transplantation period, we have previouslyshown that approximately 30% of graft cells die within thefirst 2 hours after graft reperfusion by “programmed celldeath” or apoptosis, whereas almost no signs of apoptosisoccurred in same lungs neither during 1 to 6 hours of coldischemia before the transplant nor during the implantationprocess. 3 This degree of cell death was seen even in patientswho did very well after lung transplantation.Having discovered this remarkable loss of cells in trans-planted lungs, which has also been described to variousdegrees in other solid organs after transplantation, such as the liver, 4 kidney, 5 and the heart, 6 in a second study weattempted to answer the question of what determines themode of cell death after IR injury in transplanted lungs andhow various factors such as ischemic time might influencethe amount of cell death that occurs. In a rat lung transplantmodel, we determined that apoptosis is the predominantmode of cell death in transplanted and reperfused lungs aftershort and clinically relevant ischemic times (6-12 hours),whereas in transplanted lungs after extended cold ischemicperiods (18 and 24 hours) necrosis is the predominant modeof cell death with almost no apoptosis. The total amount of dead cells in grafts, however, was similar in all study lungs. 7 Interestingly, the amount of necrotic cells negatively corre-lated with posttransplant graft function, but the degree of apoptosis did not. 7 From this study we learned that severe graft injury,experimentally induced by a prolonged pretransplant graftischemic period, appears to be associated with severe celldamage with no ability for the damaged cell to recover. Theseverely injured cells undergo an uncontrolled and undi-rected pathway to death, which is necrosis. The cell mem-branes disrupt, intracellular proteins are released in thesurrounding tissue, and a massive inflammatory response isinitiated that affects neighboring healthy cells, which maybe secondarily injured and may also undergo cell death. Incase of milder IR injury, such as in lungs after short isch-emic times, however, the injured cells appear to have pre-served their ability to either recover or, if unable to recover,to undergo the more quiescent mode of cell death—apopto-sis—by initiating internal genetic suicide programs, whichfollow complex pathways. 8 In another study, we transfected donor rat lungs transtra-cheally in vivo with adenoviral vectors carrying the genethat encodes for the human anti-inflammatory cytokine in-terleukin 10 (IL-10), also named  cytokine release inhibitor  factor.  Indeed, we were able to demonstrated that IR injuryin IL-10-transfected lungs was significantly improved com-pared with lungs that were transfected with the emptyvehicle or the vehicle diluent only. 9 This positive effect wasseen in physiologic lung function, histologic examination,and the expression of the proinflammatory cytokines inter-feron-    (IFN-   ) and tumor necrosis factor-   (TNF-  ),which are early-onset mediators of IR injury. 9 The fact thatIL-10 gene therapy improves the function of the trans-planted lung having been demonstrated, the goal of thecurrent study was to determine whether this interventionhad any effect on the degree or mode of cell death associ-ated with IR injury in lung transplantation. Methods Animals Experiments were performed in male inbred (250-350 g) Lewisrats (Charles River Inc, Montreal, Quebec, Canada). All animalsreceived care in compliance with the Principles of LaboratoryAnimal Care formulated by the National Society for MedicalResearch, the Guide for the Care and Use of Laboratory Animals(NIH Publication No. 85-23, Revised 1985, US Government Print-ing Office, Washington, DC 20402-9325), and the Guide to theCare and Use of Experimental Animals formulated by the Cana-dian Council on Animal Care. The experimental protocol wasapproved by the Animal Care Committee of the Toronto GeneralHospital Research Institute. In Vivo Transfection Procedure For the in vivo gene transfection procedure, donor animals wereanesthetized in a halothane chamber, orotracheally intubated witha 14-gauge intravenous cannula, and connected to a volume-controlled ventilator (Harvard Rodent Ventilator, model 683,South Natick, Mass). All animals were ventilated with an inspiredoxygen fraction (F IO 2 ) of 1.0 and a tidal volume of 10 mL/kg at 80breaths/min.A 1-mL syringe containing 0.5 mL of the transfection solutionwas connected to the lateral outlet of a 3-way stopcock placed inthe circuit at the endotracheal catheter. For intratracheal injection,the ventilator outlet of the 3-way stopcock was closed and thesolution was injected. Ventilation was then continued until theanimal resumed spontaneous breathing (approximately 60 to 90seconds after intratracheal injection). All transfected animals werekept in microisolators for 24 hours until graft retrieval. Food andwater was supplied ad libitum. Lung Transplantation Procedure  Harvest and storage.  We used a rat left single lung transplantmodel. Donor rats were anesthetized by an intraperitoneal injectionof 1 mL of sodium pentobarbital (Somnotol, MTC Pharmaceuti- Fischer et al Cardiothoracic Transplantation The Journal of Thoracic and Cardiovascular Surgery  ● Volume 126, Number 4 1175        T       X  cals, Cambridge, Ontario, Canada) and intubated through a trache-ostomy with a 14-gauge intravenous catheter. The tracheostomytube was then connected to a volume-controlled ventilator (Har-vard Rodent Ventilator, model 683) and the animals were venti-lated at a rate of 70 breaths/min, tidal volume of 10 mL/kg, F IO 2  of 1.0, and a positive end-expiratory pressure (PEEP) of 2 cm H 2 O.After this, a median laparo-sternotomy was performed and 300USP units of heparin (Hepalean, Organon Teknika, Toronto, On-tario, Canada) was injected into the inferior vena cava (IVC). Aftera period of 5 minutes, 0.5 mL of arterial blood was taken from theabdominal aorta for baseline blood gas analysis.For the retrieval of the heart-lung block, the IVC was incised,the left atrial appendage was excised, and a 14-gauge intravenouscatheter was placed into the main pulmonary artery (PA) throughan anterior incision in the right ventricular outflow tract. The lungswere then flushed through this catheter with 20 mL of low-potassium dextran glucose (LPDG) preservation solution (Perfa-dex, Biophausia, Uppsala, Sweden) containing 500   g/L of pros-taglandin E 1  (PGE-1, Prostin VR, Upjohn, Don Mills, Ontario,Canada) from a height of 30 cm. This is the same preservationprotocol that is currently used in our clinical lung transplantprogram. 9 Immediately after the lungs were flushed, the tracheos-tomy tube was clamped after inspiration to preserve the lungs inthe inflated state. The heart-lung block was then removed andplaced in iced LPDG at 4°C. The left lung was prepared fortransplantation with the placement of three 14-gauge cuffs into theleft PA, left pulmonary vein (PV), and the left main bronchus(MB), respectively. Left lungs were placed into 40 mL of LPDG at4°C for 24 hours before transplantation. Transplantation.  Recipient animals were anesthetized and atracheostomy was performed as described for the donor animals.The recipient animals were ventilated with a gas mixture of 75%oxygen and 25% room air at a rate of 70 breaths/min and tidalvolume 10 mL/kg. A left thoracotomy was performed through thefifth intercostal space. The left lung was mobilized by dividing thepulmonary ligament. The hilar structures were then dissected free.The left PA, PV, and MB were identified and clamped withmicrosurgical aneurysm clamps. A ventral incision was made ineach of these structures. The cuffs on the donor lung structureswere placed into the corresponding recipient structures througheach incision. The anastomoses were secured with 7-0 polypro-pylene ties. The implantation time, or warm ischemia time, wasstandardized at 20 minutes; this is the period when the deflateddonor lung is in the chest at body temperature and the anastomoticprocedure is underway. After the standardized 20-minute period of warm ischemia, the transplanted lung was reinflated after removalof the MB clamp and blood was reintroduced by unclamping firstthe PV, then the PA. The animal was ventilated with an FiO 2  of 1.0at a rate of 70 breaths/min, tidal volume of 10 mL/kg, and PEEPof 2 cm H 2 O during the 2 hours of the reperfusion period. Oneminute into the reperfusion period, each animal received 1 mL of 0.9% normal saline solution intraperitoneally for volume replace-ment. Heparin was not given to the recipient animals, because it isnot routinely administered to lung transplant patients before graftreperfusion. Each animal was covered during the reperfusion pe-riod to prevent hypothermia. Two hours after graft reperfusion, 0.5mL of blood was taken from the left PV of the transplanted lungdistal to the cuff anastomosis for blood gas analysis. Tissue Treatment All study lungs were flushed for 5 minutes with 20 mL of a 500  mol/L trypan blue (Sigma Chemical Co, St. Louis, Mo) solutionthrough the main PA, followed by 20 mL of 0.9% normal salinesolution and 10 mL of 4% paraformaldehyde. Trypan blue wasdissolved in Krebs-Henseleit buffer (pH 7.4; Sigma Chemical Co).The lungs were then fixed in 10% formalin. The middle third of theleft lungs was used for histologic examination as that section isrepresentative of peripheral and central parenchymal areas. Histologic Evaluation and Viability Assessment: TripleStaining Technique The triple staining technique for the quantification of apoptotic andnecrotic cells as compared to all nucleated graft cells (dead andalive) in the same microscopic section has been previously de-scribed. 7 In brief, formalin-fixed lung tissues were embedded in paraffinand cut into 4-  m tissue slices. These were mounted onto saline-treated glass slides for histologic assessment.Apoptosis detection by in situ terminal deoxynucleotidyl trans-ferase (TdT)-mediated dUTP nick end-labeling (TUNEL) wasundertaken using the ApopTag Kit (Oncor, Gaithersburg, Md)according to the manufacturer’s instructions. Sections were depar-affinized and rehydrated. Protein digestion was carried out byapplication of proteinase K (20  g/mL) to the slides for 15 minutesat room temperature followed by 4 washes in distilled water for 2minutes each. Equilibration buffer was applied to the sections andthese were incubated in a humidified chamber for 3 minutes. Thesections were then incubated with TdT enzyme in a humidifiedchamber at 37°C for 1 hour. This method is based on the enzymaticability of TdT to catalyze a template-independent addition of deoxyribonucleotide triphosphate to the 3'-OH ends of double- orsingle-stranded DNA. Anti-digoxigenin-fluorescein was applied tothe sections and these were then incubated in a humidified cham-ber for 30 minutes at room temperature. The sections were thenwashed with phosphate-buffered saline, and antifade containingpropidium iodide (PI) (Oncor, Gaithersburg, Md) was applied fornuclear staining.TUNEL-stained tissue sections were examined with fluorescentmicroscopy. First, the PI staining (red) was examined through a520-nm filter at a magnification of 100  . PI stains (red) allnucleated cells (alive, necrotic, and apoptotic) in the same manner.The magnification was increased to 400   and a color photomi-crograph was taken. Then, the  same  area viewed for the PI stainingwas similarly examined for apoptotic staining (bright green) usinga 590-nm filter at a magnification of 400  . After a color photomi-crograph was taken through this filter system, the filters and theultraviolet light were turned off and a third picture of the  same  areawas taken to detect the trypan blue stain (dead cells) with standardlight microscopy. Two randomly chosen areas from each slidewere examined using this triple staining method.The cell counts were performed by 2 researchers in a blindedfashion. The slides were projected onto a grid comprised of 12fields so that the cells could be counted. Six randomly chosenfields were used. These 6 fields were used for all study slidecounts. PI-stained cells were counted first, followed by TUNEL-positive cells, and finally the trypan blue–stained cells. Only cellsthat could clearly be identified as individual cells were counted as Cardiothoracic Transplantation Fischer et al 1176 The Journal of Thoracic and Cardiovascular Surgery  ● October 2003 T   X    cells. If they did not fulfill this criterion, they were considered tobe background staining.The PI-stained count represents the total number of nucleatedgraft cells (total cells: alive  necrotic  apoptotic). The TUNEL-positive count represents the number of apoptotic cells. The trypanblue count identifies the number of dead cells (necrotic  apopto-tic). Therefore, the trypan blue count (necrotic  apoptotic) minusthe TUNEL-positive count (apoptotic) equals the number of ne-crotic cells. The numbers of necrotic and apoptotic cells are givenas percentages of the total number of cells (PI-stained count). Optimization of hIL-10 Gene Transfection andExpression in Donor Lungs IL-10 gene transfection of donor lungs and expression of thetransfected protein were optimized in our previous studies on invivo adenovirus-mediated gene transfection through the transtra-cheal route. 9-12 Generation of Recombinant Adenovirus ExpressingHuman IL-10 Adenoviral vectors (serotype 5) containing the human IL-10 genewith an RSV promoter (Ad5RSVhIL-10) and “empty” vectors(Ad5BGL2) were constructed at the Gene Transfer Vector Core of the University of Iowa College of Medicine, Iowa City, Iowa. ThehIL-10 adenoviral construct will be referred to as “AdhIL-10” andthe Ad5BGL2 will be referred to as “empty vector.”Human IL-10 (hIL-10) cDNA was obtained by polymerasechain reaction (PCR) with 5' and 3' flanking primers (5'-hIL-10  Bam HI:5'-CGCGGATCCCATGCACAGCT-CAGCACTG-3';3'-hIL-10  Bam HI:5'-CGCGGATCCGCCACCCTGATGTCTCAGT-3'), using the clone pSR  hIL-10 as template (kindly provided by E.Field, University of Iowa). The PCR product was cloned, using the  Bam HI restriction-site tails added to the oligonucleotide sequences, ina shuttle plasmid (pAdRSV4). This shuttle plasmid contains the Roussarcoma virus promoter, the SV40-poly A signal, and the genomicadenoviral sequences from 0 to 1 and 9 to 16 map units of humanadenovirus type 5. Recombinant adenovirus expressing IL-10 wasgenerated by homologous recombination between pAdRSVhIL-10and human adenovirus serotype 5 derivative d1309, using standardmethods. 13 AdBGL2 has the same viral backbone as AdRSVhIL-10. In Vitro and in Vivo Evaluation of hIL-10 Bioactivityafter Ad5RSVhIL-10 Gene Transfer An in vitro functional assay for hIL-10 was performed by Gud-mundsson and colleagues at the University of Iowa College of Medicine to test the activity of Ad5RSVhIL-10 on the basis of theability of IL-10 to inhibit the synthesis of IFN-    by lectin-stimu-lated spleen cells. 13 The in vitro study showed thatAd5RSVhIL-10 is bioactive in vitro, and inhibits IFN-   expressionin lectin-stimulated murine spleen cells in a dose-dependent man-ner. To test the bioactivity of Ad5RSVhIL-10 in vivo, IL-10knockout (KO) mice were injected with 5    10 8 pfu of Ad5RSVhIL-10 or AdRSVLacZ via a tail vein. Six days laterhIL-10 levels in blood were detected by ELISA. In a separateexperiment, IL-10 KO mice that received intravenous administra-tion of Ad5RSVhIL-10 survived after intravenous lipopolysaccha-ride injection, whereas IL-10 KO mice that received AdRSVLacZdied of the endotoxin, which demonstrates the bioactivity of Ad5RSVhIL-10 in vivo. Measurement of Lung Graft Function Graft function was assessed by Pa O 2  levels in blood taken from thegraft pulmonary vein at the completion of the 2-hour reperfusionperiod under direct vision with a heparinized syringe. Statistical Analysis All data are expressed as mean    SD. A 1-way analysis of variance (ANOVA) was used to determine statistical significance.When the test of equal variance or the normality test failed aKruskal-Wallis 1-way ANOVA on ranks was performed. Whenstatistical significance was reached, it was followed by a post hocanalysis using the Student-Newman-Keul method. The SigmaStatsoftware package version 1.0 (Jandel Scientific, San Rafael, Calif)was used for all statistical analyses. Results Graft Function Donor and recipient rats were size-matched in study groups.All animals in this study survived for the individual studyperiods. At the completion of the 2-hour reperfusion period,blood samples were taken from the pulmonary graft veinand analyzed for the partial pressure of oxygen (Pa O 2 ). Theability of a transplanted lung to oxygenate blood remains acritical measurement for the evaluation of posttransplantpulmonary graft function.The mean Pa O 2  level in arterial blood from donors in all3 study groups was 572    41 mm Hg. The donor Pa O 2 levels were not significantly different among the individualstudy groups. After the completion of the 2-hour reperfusionperiod, Pa O 2  levels in IL-10 lungs were significantly higher( P    .0001) than in empty vector (EV) and vector diluent(VD) lungs (240    31 vs 98    17 mm Hg and 129    11mm Hg, respectively, Figure 1). Figure 1. In vivo transtracheal adenoviral mediated IL-10 gene transfection of donor lungs improves posttransplant lung function.Study groups: EV, empty vector; VD, vector diluent; IL-10, adeno-virus-mediated interleukin-10. * P   .0001 versus other groups.Fischer et al Cardiothoracic Transplantation The Journal of Thoracic and Cardiovascular Surgery  ● Volume 126, Number 4 1177        T       X  Cell Death We have previously described the time course of apoptosisinduction in transplanted lungs during ischemia and in theearly phase after transplantation. 3 We have further shownthat the mode of cell death (apoptosis/necrosis) in lungsafter transplantation is dependent on the length of the coldischemic graft preservation time (CIT) before transplanta-tion in that apoptosis appears after transplantation andreperfusion in lungs that have been stored for relativelyshort periods of CIT, whereas necrosis is the predominantmode of cell death in lungs after extended CIT. 7 We alsodemonstrated that necrosis, but not apoptosis, correlateswith posttransplant lung function. 7 Cox has previously dem-onstrated that IL-10 enhances the resolution of pulmonaryinflammation in vivo by promoting apoptosis of neutro-phils. 14 Furthermore, IL-10 has an inhibitory effect on TNF-  –induced programmed cell death, as shown by Rojas andassociates. 15 Apoptosis levels in the EV (1.8%  2%) and VD (2.0%   1.9%) group in this study were as low as seen in ourprevious study after similar CIT, when necrosis was thepredominant mode of cell death. 7 In the IL-10 group, how-ever, apoptosis levels reached 9.7%    1.9% of total graftcells, which was significantly different than the other 2study groups ( P  .0001). This in fact does not necessarilysupport a proapoptotic effect of IL-10. Rather, it suggeststhat IL-10 reduced the injury in lungs after prolonged pres-ervation and transplantation and preserved the ability of damaged graft cells to undergo a less tissue destructivemode of cell death (apoptosis) as compared with necrosis,which causes further inflammation and tissue injury. Notethat the total number of cell that died (through apoptosis ornecrosis) was constant in all groups (32.7%  3.2% in EV,30.2%  2.5% in VD and 30.3%  3.8% in IL-10 lungs) asdepicted in Figure 2. The number of necrotic cells waslowest in IL-10 lungs (20.6%  5.7%) compared with VDlungs (28.3%  3.1%) and EV lungs (30.3%  4.2%), ( P  .01). Discussion IR injury remains a significant problem and can result inpulmonary failure, multiorgan failure, and death after lungtransplantation. Clinical and experimental studies haveidentified many of the mediators that are involved in theregulation of pulmonary IR injury. 16,17 We have previously described the role that apoptosisplays in lung transplantation. 8 Ischemia has been shown tobe a potential inducer of apoptosis. 18 Because apoptoticcells in an organ system are usually phagocytosed by mac-rophages before their membranes break down and intracel-lular enzymes are released, this mode of cell death does notlead to significant tissue inflammation, which is character-istically prominent with necrosis. 18 In human lungs, wehave previously shown that apoptosis does not occur ingrafts during cold or warm ischemia. In the early phase aftergraft reperfusion, however, the number of apoptotic graftcells increased to 34% of cells. 3 As a consequence of thisnovel observation in lung transplantation, we have chosento focus our efforts on the regulatory mechanisms that areinvolved in this dramatic loss of cells in lung grafts with theultimate hope to develop strategies to prevent cell death inthis setting.However, we have demonstrated that, in addition toapoptosis, cellular necrosis also plays a very important, if not more important, role in posttransplant graft function andthat the mode of cell death (apoptosis or necrosis) aftertransplantation is dependent on the length of ischemic graftpreservation before lung transplantation. 7 Interestingly, theamount of necrotic cells in transplanted lungs negativelycorrelated with posttransplant graft function, whereas theamount of apoptosis did not. This intriguing finding sug-gests that the 2 different modes of cell death differentiallyaffect overall graft function. This is consistent with thegeneral understanding that apoptosis is a relatively “quies-cent” form of cell death as compared with necrosis, whichinduces significant inflammation and cytokine release. Ob-viously, organ transplantation at this stage is not possiblewithout some injury to the graft or graft cells. Modernpreservation strategies in clinical lung transplantation con-tinue to focus on the reduction of graft preservation injury. 19 However, our experimental and clinical observations sug-gest that graft cell injury still remains a significant problem.Ideally, we strive to minimize  all  cell death related to theinjury of transplantation. However, if the process of trans-plantation inflicts a degree of injury such that an inevitableamount of cell death must occur, it would seem to be Figure 2. IL-10 in vivo donor lung transfection leads to a switchfrom necrosis to apoptosis in transplanted and reperfused lungs.Note that the total number of dead cells is similar in all groups,but that the AdIL-10 group has significantly less necrosis andmore apoptosis (* P     .0001; # P     .01) compared with the othergroups.Cardiothoracic Transplantation Fischer et al 1178 The Journal of Thoracic and Cardiovascular Surgery  ● October 2003 T   X  
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