Antibodies to human adhesion molecules and von Willebrand factor: in vitro cross-species reactivity in the xenotransplantation setting

Characteristics of thrombin generation in a fulminant porcine sepsis model

INTRODUCTION

The activation of blood coagulation has been demonstrated in most cases of sepsis, however previous studies in humans could not detect hypercoagulability with global hemostasis assays. In a fulminant porcine sepsis model we analysed coagulation screening tests and thrombin generation to evaluate hemostatic alterations.

MATERIALS AND METHODS

Live Escherichia coli bacteria were inoculated to female pigs and prothrombin time, activated partial thromboplastin time, thrombin time and fibrinogen were measured by coagulometry. Platelet counts, platelet aggregates and platelet phosphatidyl serine (PS) expression were studied, furthermore in in vitro experiments the PS-inducing ability of septic and control plasmas was investigated by flow cytometry. Thrombin generation was carried out by the Ascent Fluoroscan reader and results were evaluated by the Thrombinoscope software.

RESULTS

Clotting assays showed a large variability, but no systematic changes during the 4-hour observation period. Platelet count significantly decreased and the number of platelet aggregates increased already by 2h compared to baseline values and to control animals. Although the increase in platelet PS expression was non-significant in the septic group, the septic plasma elicited PS expression on normal human red blood cells. Thrombin generation became significantly faster, but the quantity of formed thrombin demonstrated both hypo- and hypercoagulability depending on the setting of the assay.

CONCLUSIONS

Enhanced thrombin generation without activators and the PS-inducing capacity of septic plasma are signs of hemostatic activation during fulminant sepsis while the decreased amount of generated thrombin upon tissue factor and phospholipid induced activation demonstrates attenuated thrombin forming ability.

Hyperacute Lung Rejection in the Pig-to-Human Model 4: Evidence for Complement and Antibody Independent Mechanisms

BACKGROUND

We assessed whether the combination of complement regulation and depletion of xenoreactive antibodies improves the outcome of pulmonary xenografts compared with either strategy alone.

METHODS

Lungs from pigs heterozygous (hDAF(+/-)) or homozygous (hDAF(+/+)) for the human decay accelerating factor transgene (hDAF) or their nontransgenic litter mates (hDAF(-/-)) were perfused with heparinized whole human blood. In additional groups, xenoreactive natural antibodies (XNA) were depleted by pig lung perfusion (hDAF(-/-)/AbAbs, hDAF(+/-)/AbAbs) before the experiment. This combined approach was augmented by adding soluble complement receptor 1 (sCR1) to the perfusate in one further group (hDAF(+/-)/AbAbs/sCR1).

RESULTS

HDAF(-/-) lungs perfused with unmodified human blood were rejected after 32.5 min (interquartile range, IQR 5 to 210). HDAF(+/-) lungs survived for 90 min (IQR 10 to 161, P = 0.54). Both groups showed a rapid rise in pulmonary vascular resistance (PVR), which is a characteristic feature of hyperacute rejection (HAR). This phenomenon was blunted in the hDAF(+/+) group, although survival (48 min, IQR 14 to 111) was not further prolonged. Antibody depletion (AbAbs) led to a significant increase in survival time (hDAF(-/-)/AbAbs: 315 min, IQR 230 to 427; hDAF(+/-)/AbAbs: 375 min, IQR 154 to 575), reduced PVR and less complement production. Addition of sCR1 reduced complement elaboration but did not further improve survival (200 min, IQR 128 to 580) and surprisingly tended to increase PVR.

CONCLUSIONS

Depletion of xenoreactive antibodies is more effective than membrane-bound complement regulation to blunt hyperacute rejection of pulmonary xenografts, but even the combined approach including soluble-phase complement inhibition is not sufficient to reliably prevent organ failure within hours. It therefore seems likely that other factors independent of antibody and complement contribute to HAR in this model.

Hyperacute lung rejection in the pig-to-human model. 2. Synergy between soluble and membrane complement inhibition

BACKGROUND

The role of complement in hyperacute lung xenograft rejection has not been elucidated. The present study evaluates the effect of complement (C) C3/C5 convertase inhibition on hyperacute rejection of pig lung by human blood.

METHODS

In an established ex-vivo model, lungs from pigs heterozygous for human decay accelerating factor (hDAF), non-transgenic littermate control pigs, or farm-bred pigs were perfused with fresh human blood that was either unmodified or treated with soluble complement receptor type 1 (sCR1: TP10, 100 microg/ml).

RESULTS

Non-transgenic lungs from littermate controls had a median survival time of 35 min (range 5 to 210; P = 0.25 vs. farm-bred piglets: median 5 min, range 5 to 10). Lungs expressing hDAF survived for a median of 90 min (range 10 to 161; P = 0.5 and 0.01 vs. littermate and farm-bred controls, respectively), with sCR1, whereas hDAF (-) lungs failed by 35 min (range 6 to 307), hDAF (+) lungs survived for 330 min (range 39 to 577) [P = 0.002 vs. farm-bred; P = 0.08 vs. hDAF (-); P = 0.17 vs. sCR1/hDAF (-)]. The rise in pulmonary vascular resistance (PVR) at 5 min was blunted only by hDAF (+) with sCR1 (0.26 +/- 0.2 vs. 0.5 to 0.7 mmHg/ml/min for other groups). Plasma C3a and sC5b-9 and tissue deposition of C5b-9 were dramatically diminished using sCR1, and further decreased in association with hDAF. Histamine and thromboxane were produced rapidly in all groups.

CONCLUSION

Complement plays an important role in lung HAR. However, even potent inhibition of C3/C5 convertase, both membrane bound in lung and by a soluble-phase inhibitor in the blood, does not prevent activation of inflammatory responses known to be particularly injurious to the lung. Our findings implicate a role for innate immune pathways resistant to efficient complement regulation. The role of anti-species antibody, coagulation pathway dysregulation, and additional environmental or genetic influences remain to be defined.

Characterization of baboon anti-porcine IgG antibodies during acute vascular rejection of porcine kidney xenograft

In the pig-to-baboon model, the removal of anti-porcine natural antibodies abrogates hyperacute vascular rejection (HAVR), but the xenograft then undergoes an acute vascular rejection (AVR) concomitantly to the appearance of newly formed anti-porcine antibodies. The use of anti-IgM monoclonal antibody (mAb) in baboons allowed to avoid HAVR of pig-to-baboon renal xenografts, but, at post-operative day 6, AVR occurred because of a rapid return of anti-porcine antibodies. The aim of this work was to characterize the anti-porcine antibodies during AVR. Sera from anti-IgM-treated animals were assessed prior to the graft and at the time of AVR by enzyme linked immunosorbent assay (ELISA) to determine anti-porcine antibodies concentration as well as the IgG subtypes. The same sera were tested on confluent cultures of porcine aortic endothelial cells (PAECs) to assess (i) the cytolytic complement-dependent activity and (ii) the E-selectin expression. The K affinity of anti-Gal IgG antibodies was measured by ELISA. Anti-porcine (Gal and non-Gal) IgG antibodies were tested on PAECs by flow cytometry to discriminate the presence of Gal epitopes from the recognition of other porcine epitopes. We found that both anti-porcine IgM and IgG antibodies presented a significantly increased cytolytic activity and E-selectin expression on PAECs during AVR. These characteristics are related to an important increase of the antibody (Ab) titer (especially anti-galactosyl) and a switch to anti-galactosyl IgG1 subclass production, whereas the K affinity remained unchanged. The deleterious effects of both IgM and IgG antibodies observed during AVR showed the crucial need for treatment controlling the cells producing anti-porcine antibodies.

Stable expression of the alkaline phosphatase marker gene by neural cells in culture and after transplantation into the CNS using cells derived from a transgenic rat

Multipotent stem cells and more developmentally restricted precursors have previously been isolated from the developing nervous system and their properties analyzed by culture assays in vitro and by transplantation in vivo. However, the variety of labeling techniques that have been used to identify grafted cells in vivo have been unsatisfactory. In this article we describe the characteristics of cells isolated from a transgenic rat in which the marker gene human placental alkaline phosphatase (hPAP) is linked to the ubiquitously active R26 gene promoter. We show that hPAP is readily detected in embryonic neuroepithelial stem cells, neuronal-restricted precursor cells, and glial-restricted precursor cells. Transgene expression is robust and can be detected by both immunocytochemistry and histochemistry. Furthermore, the levels of hPAP on the cell surface are sufficient for live cell labeling and fluorescence-activated cell sorting. Expression of hPAP is stable in isolated cells in culture and in cells transplanted into the spinal cord for at least 1 month. We submit that cells isolated from this transgenic rat will be valuable for studies of neural development and regeneration.

Role of anti-Gal alpha13Gal and anti-platelet antibodies in hyperacute rejection of pig lung by human blood

BACKGROUND

Previous work has shown that antibodies against porcine antigens are an important trigger of hyperacute lung rejection (HALR). The relative importance of Gal alpha1,3Gal epitopes and other antigens, such as those expressed on pig platelet membranes or lung itself, has not been defined. This study compares the efficiency of three anti-pig antibody depletion strategies, and their efficacy with regard to attenuation of HALR.

METHODS

Plasma pooled from three human donors was adsorbed against Gal alpha1,3Gal disaccharide or porcine platelet extract (PPE), or passed through pig lung vasculature. Whole blood reconstituted using adsorbed plasma was then used to perfuse piglet lung, and results were compared with unmodified human blood.

RESULTS

Depletion of lung-reactive anti-Gal alpha1-3Gal antibodies was most efficient with the alphaGal column (99% +/- 0.5% vs 87% to 93% +/- 11% for PPE and 92% to 95% +/- 8% for lung, p < 0.01 vs alphaGal column). PPE column tended to be more efficient (77% to 84% +/- 12%) in removing anti-PPE antibodies than pig lung (66% to 70% +/- 14%) or the alphaGal column (56% to 63% +/- 16%, p < 0.05). Lung survival and function with each antibody depletion strategy was improved relative to unmodified controls (mean survival > or = 146 minutes vs 8 minutes for controls). Although alphaGal and lung adsorption yielded more consistent lung protection (survival beyond 2 hours) than did PPE, no approach proved significantly superior. Complement C3a elaboration at 10 minutes was attenuated > 80% by each adsorption strategy, an effect that was most pronounced in the lung adsorption group (95%, p < 0.01). Histamine elaboration was blunted significantly by PPE adsorption but not in other groups (p < 0.05). Platelet but not leukocyte sequestration was decreased with antibody depletion compared with the nondepleted group (44% to 50% vs 82%, p < 0.01).

CONCLUSIONS

Each antibody depletion strategy tested significantly prolongs lung xenograft survival and function compared with unmodified human blood, but none was sufficient to reliably prevent HALR. Depletion of antibodies against both alphaGal and additional cell membrane antigens, or control of antibody-independent pathogenic pathways, may be necessary to consistently prevent HALR.

IgG2 anti-Galalpha1-3Gal does not induce porcine aortic endothelial cell accommodation in vitro

BACKGROUND

Xenografts that have been protected from hyperacute rejection (HAR) are termed accommodated if they are not then rejected despite the presence of xenoantibody. It has been proposed that IgG may confer resistance to complement dependent cytotoxicity (CDC), a conventional in vitro marker of accommodation. We hypothesized that noncytotoxic IgG2 anti-Galalpha1-3Gal was responsible for this effect.

METHODS AND RESULTS

We purified IgG anti-Galalpha1-3Gal from pooled human normal immunoglobulin and three sera, by elution from protein G and Galalpha1-3Gal-R immunoadsorbents. The eluates were IgM free and > or =95% IgG2. They bound to Galalpha1-3Gal, porcine aortic endothelial cells (PAEC) and lymphocytes. It was not possible to block IgM binding to PAEC or lymphocytes using IgG anti-Galalpha1-3Gal (200 microg/ml). The eluates were noncytotoxic in micro-CDC assays. To investigate accommodation, PAEC were cultured with subsaturating doses of the four IgG eluates for up to 144 hr. Resistance of nontrypsinized PAEC to CDC by human serum was measured in a cell viability assay. PAEC were not rendered resistant to CDC in any of the experiments. To investigate the possibility that accommodation might be induced by non-Galalpha1-3Gal IgG, the experiments were repeated using HNIg, again with no protection demonstrated.

CONCLUSIONS

Using primary PAEC monolayers, we were unable to induce resistance to CDC with human normal immunoglobulin and its IgG2 anti-Gabeta1-3Gal subset. This contradicts previous experiments using trypsinized, immortalized cells. Although resistance to CDC is not an ideal marker of accommodation, the detrimental effects of IgG make it unlikely that it will become a useful clinical means of inducing accommodation.

Distribution of the Galalpha1-3Gal antigen in cultured adult and fetal porcine pancreatic islet cells: an immunoelectron microscopic study

The distribution of the Galalpha1-3Gal antigen (Galalpha) in cultured adult porcine islets (API) and fetal porcine pancreatic islet-like cell clusters (ICC) was studied using immunoelectron microscopy. API and ICC were cultured for 1 and 5 days, respectively, and immunogold labeled using human affinity isolated anti-Galalpha1-3Gal antibody, GS-IB4 lectin and antibodies against islet pancreatic hormones, vimentin, and von Willebrand factor. Differentiated endocrine cells were Gala-negative, but, in ICC, some immature endocrine cells were slightly Gala-positive. The Gala-expression in API was much weaker compared to ICC. In both API and ICC, the Gala antigen was expressed on duct epithelial cells, acinar cells, and endothelial cells. In ICC, strong Gala expression was observed on flattened cells covering their surfaces. These cells were identified as centroacinar cells originating from intra-islet ducts. In conclusion, although mature endocrine cells of cultured API and ICC lack the Gala-xenoantigen, several other cellular compounds are strongly Gala positive, which may contribute to xenorejection of these grafts.