Measurement of anti-CD154 monoclonal antibody in primate sera by competitive inhibition ELISA

Safe use of anti-CD154 monoclonal antibody in pig islet xenotransplantation in monkeys

Anti-CD154mAb is a powerful co-stimulation blockade agent that is efficacious in preventing rejection, even in xenogeneic settings. It has been used in the majority of successful long-term pig-to-non-human primate islet transplantation models. However, its clinical use was halted as a result of thromboembolic complications that were also observed in preclinical and clinical organ transplantation models. An anti-CD154mAb was administered to 14 streptozotocin-induced diabetic cynomolgus monkey recipients of porcine islets, some of which received the agent for many months. Monkeys were monitored for complications, and blood monitoring was carried out frequently. After euthanasia, multiple biopsies of all organs were examined for histological features of thromboembolism. Anti-CD154mAb prevented rejection of genetically engineered pig islets in all monkeys. No significant complications were attributable specifically to anti-CD154mAb. There was no evidence of thromboembolism in multiple histological sections from all major organs, including the brain. Our data suggest that in diabetic monkeys with pig islet grafts, anti-CD154mAb would appear to be an effective and safe therapy, and is not associated with thromboembolic complications.

Pig-to-baboon heterotopic heart transplantation--exploratory preliminary experience with pigs transgenic for human thrombomodulin and comparison of three costimulation blockade-based regimens

BACKGROUND

Three costimulation blockade-based regimens have been explored after transplantation of hearts from pigs of varying genetic backgrounds to determine whether CTLA4-Ig (abatacept) or anti-CD40mAb+CTLA4-Ig (belatacept) can successfully replace anti-CD154mAb.

METHODS

All pigs were on an α1,3-galactosyltransferase gene-knockout/CD46 transgenic (GTKO.CD46) background. Hearts transplanted into Group A baboons (n=4) expressed additional CD55, and those into Group B (n=3) expressed human thrombomodulin (TBM). Immunosuppression included anti-thymocyte globulin with anti-CD154mAb (Regimen 1: n=2) or abatacept (Regimen 2: n=2) or anti-CD40mAb+belatacept (Regimen 3: n=2). Regimens 1 and 2 included induction anti-CD20mAb and continuous heparin. One further baboon in Group B (B16311) received a modified Regimen 1. Baboons were followed by clinical/laboratory monitoring of immune/coagulation parameters. At biopsy, graft failure, or euthanasia, the graft was examined by microscopy.

RESULTS

Group A baboons survived 15 to 33 days, whereas Group B survived 52, 99, and 130 days, respectively. Thrombocytopenia and reduction in fibrinogen occurred within 21 days in Group A, suggesting thrombotic microangiopathy (TM), confirmed by histopathology. In Group B, with follow-up for >4 m, areas of myofiber degeneration and scarring were seen in two hearts at necropsy. A T-cell response was documented only in baboons receiving Regimen 2.

CONCLUSIONS

The combination of anti-CD40mAb+belatacept proved effective in preventing a T-cell response. The expression of TBM prevented thrombocytopenia and may possibly delay the development of TM and/or consumptive coagulopathy.

Utilizing ELISA to monitor protein-protein interaction

Enzyme-linked immunosorbent assay (ELISA) is a commonly used method in analyzing biomolecular interactions. As a rapid, specific, and easy-to-operate method, ELISA has been used as a research tool as well as a widely adopted diagnostic method in clinical settings and for microbial testing in various industries. Inhibition ELISA is a one-site binding analysis method, which can monitor protein-protein interactions in solution as opposed to more commonly used sandwich ELISA in which the analyte capture step is required on a solid surface either through specific capture or through passive adsorption. Here, we introduce inhibition ELISA procedures, using a recombinant viral protein as an example, with emphasis on how inhibition ELISA could be used to probe subtle protein conformational changes in solution impacting protein-protein binding affinity. Inhibition ELISA is used to probe one binding site at a time for binding partners in solution with unrestricted conformation. The assay can be performed in a quantitative manner with a serially diluted analyte in solution for solution antigenicity or binding activity assessment.

T-cell-based immunosuppressive therapy inhibits the development of natural antibodies in infant baboons

BACKGROUND

We set out to determine whether B-cell tolerance to A/B-incompatible alloantigens and pig xenoantigens could be achieved in infant baboons.

METHODS

Artery patch grafts were implanted in the abdominal aorta in 3-month-old baboons using A/B-incompatible (AB-I) allografts or wild-type pig xenografts (pig). Group 1 (Gp1) (controls, n=6) received no immunosuppressive therapy (IS) and no graft. Gp2 (n=2) received an AB-I or pig graft but no IS. Gp3 received AB-I grafts+IS (Gp3A: n=2) or pig grafts+IS (Gp3B: n=2). IS consisted of ATG, anti-CD154mAb, and mycophenolate mofetil until age 8 to 12 months. Gp4 (n=2) received IS only but no graft.

RESULTS

In Gp1, anti-A/B and cytotoxic anti-pig immunoglobulin-M increased steadily during the first year. Gp2 became sensitized to donor-specific AB-I or pig antigens within 2 weeks. Gp3 and Gp4 infants that received anti-CD154mAb made no or minimal anti-A/B and anti-pig antibodies while receiving IS.

DISCUSSION

The production of natural anti-A/B and anti-pig antibodies was inhibited by IS with anti-CD154mAb, even in the absence of an allograft or xenograft, suggesting that natural antibodies may not be entirely T-cell independent. These data are in contrast to clinical experience with AB-I allotransplantation in infants, who cease producing only donor-specific antibodies.

Generation and characterization of the human neutralizing antibody fragment Fab091 against rabies virus

AIM

To transform the human anti-rabies virus glycoprotein (anti-RABVG) single-chain variable fragment (scFv) into a Fab fragment and to analyze its immunological activity.

METHODS

The Fab gene was amplified using overlap PCR and inserted into the vector pComb3XSS. The recombinant vector was then transformed into E coli Top10F' for expression and purification. The purified Fab was characterized using SDS-PAGE, Western blotting, indirect ELISA, competitive ELISA, and the fluorescent antibody virus neutralization test (FAVN), respectively, and examined in a Kunming mouse challenge model in vivo.

RESULTS

A recombinant vector was constructed. The Fab was expressed in soluble form in E coli Top10F'. Specific binding of the Fab to rabies virus was confirmed by indirect ELISA and immunoprecipitation (IP). The neutralizing antibody titer of Fab was 10.26 IU/mL. The mouse group treated with both vaccine and human rabies immunoglobulin (HRIG)/Fab091 (32 IU/kg) showed protection against rabies, compared with the control group (P<0.05, Logrank test).

CONCLUSION

The antibody fragment Fab was shown to be a neutralizing antibody against RABVG. It can be used together with other monoclonal antibodies for post-exposure prophylaxis of rabies virus in future studies.

Long-term controlled normoglycemia in diabetic non-human primates after transplantation with hCD46 transgenic porcine islets

Xenotransplantation of porcine islets into diabetic non-human primates is characterized by (i) an initial massive graft loss possibly due to the instant blood-mediated inflammatory reaction and (ii) the requirement of intensive, clinically unfriendly immunosuppressive therapy. We investigated whether the transgenic expression of a human complement-regulatory protein (hCD46) on porcine islets would improve the outcome of islet xenotransplantation in streptozotocin-induced diabetic Cynomolgus monkeys. Immunosuppression consisted of thymoglobulin, anti-CD154 mAb for costimulation blockade, and mycophenolate mofetil. Following the transplantation of islets from wild-type pigs (n = 2) or from 1,3-galactosyltransferase gene-knockout pigs (n = 2), islets survived for a maximum of only 46 days, as evidenced by return to hyperglycemia and the need for exogenous insulin therapy. The transplantation of islets from hCD46 pigs resulted in graft survival and insulin-independent normoglycemia in four of five monkeys for the 3 months follow-up of the experiment. One normalized recipient, selected at random, was followed for >12 months. Inhibition of complement activation by the expression of hCD46 on the pig islets did not substantially reduce the initial loss of islet mass, rather was effective in limiting antibody-mediated rejection. This resulted in a reduced need for immunosuppression to preserve a sufficient islet mass to maintain normoglycemia long-term.

The innate immune response and activation of coagulation in alpha1,3-galactosyltransferase gene-knockout xenograft recipients

BACKGROUND

The role of the innate immune system in the development of thrombotic microangiopathy (TM) after alpha1,3-galactosyltransferase gene-knockout (GTKO) pig organ transplantation in primates is uncertain.

METHODS

Twelve organs (nine hearts, three kidneys) from GTKO pigs were transplanted into baboons that received no immunosuppressive therapy, partial regimens, or a full regimen based on costimulation blockade. After graft failure, histologic and immunohistologic examinations were carried out.

RESULTS

Graft survival of less than 1 day was prolonged to 2 to 12 days with partial regimens (acute humoral xenograft rejection) and to 5 and 8 weeks with the full regimen (TM). Clinical or laboratory features of consumptive coagulopathy occurred in 7 of 12 baboons. Immunohistochemistry demonstrated IgM, IgG, and complement deposition in most cases. Histopathology demonstrated neutrophil and macrophage infiltrates, intravascular fibrin deposition, and platelet aggregation (TM). Grafts showed expression of primate tissue factor (TF), with increased mRNA levels, and TF was also expressed on baboon macrophages/monocytes infiltrating the graft.

CONCLUSIONS

Our data suggest that (1) irrespective of the presence or absence of the adaptive immune response, early or late xenograft rejection is associated with activation of the innate immune system; and (2) porcine endothelial cell activation and primate TF expression by recipient innate immune cells may both contribute to the development of TM.