Inhibition of human complement-dependent cell lysis by bovine aortic endothelial cells transfected with membrane-bound complement-regulatory factor (DAF and HRF20) gene using a retroviral vector

Medium supplementation with human, but not fetal calf serum facilitates endocytosis of PLGA nanoparticles by human primary B-lymphocytes via complement opsonization

The "biological identity" of nanoparticles (NPs) is governed by a shell consisting of various biomolecules that is formed upon exposure to biological media, the so-called biomolecule corona. Consequently, supplementation of cell culture media with e.g. different sera is likely to affect interactions between cells and NPs ex-vivo, especially endocytosis. We aimed to investigate the differential impact of human and fetal-bovine serum on the endocytosis of poly (lactic-co-glycolic acid) NPs by human peripheral blood mononuclear cells via flow cytometry. Furthermore, we employed different methods to inhibit endocytosis, providing mechanistic insights. The resulting biomolecule corona was characterized via denaturing gel electrophoresis. We found profound differences between human and fetal bovine serum regarding the endocytosis of fluorescently labeled PLGA nanoparticles by different classes of human leukocytes. Uptake by B-lymphocytes was particularly sensitive. We further present evidence, that these effects are mediated by a biomolecule corona. We demonstrate to our knowledge for the first time that the complement is an important contributor to the endocytosis of non-surface-engineered PLGA-nanoparticles prepared via emulsion solvent evaporation by human immune cells. Our data demonstrates that results obtained with xenogeneic culture supplements such as fetal bovine serum may have to be interpreted with caution.

In vitro studies regarding the feasibility of bovine erythrocyte xenotransfusion

Pigs are considered the most likely source of organs and tissues should the barriers to xenotransplantation be overcome. The use of animal blood for transfusion, xenotransfusion, would have advantages over blood from random human donors with respect to supply and infection control. Large animals such as cows would be more suitable than pigs for blood donation because of easier venous access and large volume phlebotomy. Blood from 12 Holstein cows was typed and then tested for hemagglutination assay (HA), complement mediated lysis (CML), human IgM and IgG antibody binding, anti-human globulin augmented clinical cross-match and osmotic fragility with normal human serum. Results were compared with porcine erythrocytes (pRBC) and with human type O controls (hRBC). The frequency of ultra-low xenoantigen expressors was tested in a larger herd of various breeds using HA and CML. Median HA and CML titers were one of six (no HA-one of 64) and one of 26 (no CML-one of 64), respectively for bovine erythrocytes (bRBC). Hemagglutination titer was significantly higher for pRBC at one of 170 (one of four-one of 1024). HA and CML were lowest with bovine blood group J. Repeated HA and CML were negative with bRBC from one cow that also tested negative by anti-human globulin augmented cross-match with seven of nine random human sera representing the different blood groups. However, flow cytometry showed that bRBC from all cows bound human IgM and IgG. IgM mean channel fluorescence (MCF) was positively correlated with HA titer. The mean corpuscular fragility of pRBC, bRBC, and hRBC was 0.56, 0.48 and 0.41%, respectively. The frequency of HA-negative and CML-negative cows were 20 and 35%, respectively in herds of 49 animals. Bovine RBC elicit variable in vitro responses from human serum but these are uniformly much less than those seen with pRBC. Bovine RBC is more robust than pRBC. These characteristics including the potential ease and volume of blood collection make the cow a more suitable blood donor than the pig.

Protection of MLV vector particles from human complement

Murine cell-derived MLV vector particles usually are highly sensitive to human complement-mediated lysis. Expression of the human complement inhibitor CD59 on murine packaging cells resulted in partial protection of these cells from lysis caused by human complement proteins. Furthermore, CD59 was incorporated into MLV vector particles released by these packaging cells, leading to an improved resistance of the virions against human complement-mediated inactivation.

The clinical importance of choosing the right assay for detection of HLA-specific donor-reactive antibodies

BACKGROUND

We found earlier that there is a close clinical correlation between the presence of histocompatibility leukocyte antigens (HLA) class I-specific donor-reactive antibodies in cross-match serum and a significantly higher frequency of early acute rejection episodes and graft loss during the first year after the transplant.

METHODS

Specificity determinations of donor-reactive antibodies present in the cross-match serum before allogeneic kidney transplants were performed. In the present study, we compared the suitability and efficiency of (a) platelet absorptions, (b) blocking with anti-HLA monoclonal antibodies in the microcytotoxicity assay, and (c) donor-specific HLA antigen-coated magnetic microbeads in flow cytometric assays for the definition of clinically relevant HLA antibodies and their correlation with early acute rejections and early graft loss.

RESULTS

We found that the microlymphocytoxicity test using donor splenic B lymphocytes often gave positive reactions in the absence of class I or class II antibodies; in other words, a high frequency of false positive reactions was observed. Flow cytometric tests are more sensitive than microlymphocytotoxicity, not only because they are more sensitive, but also because noncomplement-binding antibodies are detected. Platelet absorptions, which detect only reactivity against HLA class I antigens, is insufficient for use in specificity determinations of donor-reactive antibodies. We found that a positive test for HLA antibodies using paramagnetic beads coated with solubilized donor-derived HLA antigens (class I or class II) correlates with early immunological complications after a transplant (P<0.001).

CONCLUSION

Assays to determine the specificity of donor-reactive antibodies are now available for use during an acute transplant situation. The introduction of such methods is expected to enhance graft survival and to reduce significantly the frequencies of acute rejections episodes after a transplant.