Acute vascular rejection

Cytokine-inducible promoters to drive dynamic transgene expression: The "Smart Graft" strategy

BACKGROUND

Ubiquitous expression of T-cell regulatory transgenes such as the cytotoxic T lymphocyte-associated antigen 4 (CTLA4) or the high-affinity variant LEA29Y improves xeno graft survival. Such donor pigs are however immunocompromised and susceptible to infection. Continous high expression of CTLA4 or LEA29Y in the graft could also compromise the health status of recipients. The novel "Smart Graft" strategy is likely to avoid these problems by controlling the expression of T-cell regulatory transgenes as and when required.

METHODS

Candidate promoters inducible by inflammatory cytokines were identified by in silico screening for potential NF-κB binding sites. Basal promoter levels and responsiveness to TNFα and IL1ß were quantified by expression of secreted embryonic alkaline phosphatase in cultured cells. Promoters were modified to increase responsiveness by removing regulatory elements or adding SP-1 or NF-κB binding sites and again tested in vitro. The most promising promoters were then assessed in vivo. Porcine cells expressing inducible Renilla luciferase constructs were transplanted into immunodeficient NOD-Scid-IL2 receptor gamma^null (NSG) mice. Following engraftment, the recipient's immune system was reconstituted by splenocyte transfer raising an immune response to the porcine xenograft. The resulting induction of promoter activity was detected by in vivo bioimaging.

RESULTS

Three human (hTNFAIP1, hVCAM1 and hCCL2), and one porcine promoter (pA20) were chosen for in vitro tests. In all experiments, the semi-synthetic and inducible ELAM promoter as well as the CAG promoter were used as references. In contrast to hTNFAIP1 and hVCAM1 the ELAM, hCCL2 and pA20 promoters showed significant induction after cytokine challenge. The hCCL2 and pA20 promoters were further optimized, resulting in increased responsiveness to TNFα and IL1ß. Cytokine-dependent upregulation of promoter activity was tested in vivo, where the ELAM and the optimized hCCL2 promoters showed a 2-fold upregulation, while one of the improved A20 promoters showed almost 10-fold upregulation. Our results also revealed more than 4-fold cytokine inducibility of the CAG promoter.

CONCLUSION

This is the first in vivo comparison of existing and newly designed cytokine-inducible promoters. Optimization of promoter structure resulted in almost 10-fold inducibility of promoter activity. Such a rapid and dynamically regulated response to inflammation and cell damage could reduce initial graft rejection, making the "Smart Graft" approach a useful means of modulating the expression of immune regulatory transgenes to avoid deleterious effects on porcine and human health. Expressing transgenes in this fashion could provide a safer organ for transplantation.

Viable pigs after simultaneous inactivation of porcine MHC class I and three xenoreactive antigen genes GGTA1, CMAH and B4GALNT2

BACKGROUND

Cell surface carbohydrate antigens play a major role in the rejection of porcine xenografts. The most important for human recipients are α-1,3 Gal (Galactose-alpha-1,3-galactose) causing hyperacute rejection, also Neu5Gc (N-glycolylneuraminic acid) and Sd(a) blood group antigens both of which are likely to elicit acute vascular rejection given the known human immune status. Porcine cells with knockouts of the three genes responsible, GGTA1, CMAH and B4GALNT2, revealed minimal xenoreactive antibody binding after incubation with human serum. However, human leucocyte antigen (HLA) antibodies cross-reacted with swine leucocyte antigen class I (SLA-I). We previously demonstrated efficient generation of pigs with multiple xeno-transgenes placed at a single genomic locus. Here we wished to assess whether key xenoreactive antigen genes can be simultaneously inactivated and if combination with the multi-transgenic background further reduces antibody deposition and complement activation.

METHODS

Multiplex CRISPR/Cas9 gene editing and somatic cell nuclear transfer were used to generate pigs carrying functional knockouts of GGTA1, CMAH, B4GALNT2 and SLA class I. Fibroblasts derived from one- to four-fold knockout animals, and from multi-transgenic cells (human CD46, CD55, CD59, HO1 and A20) with the four-fold knockout were used to examine the effects on human IgG and IgM binding or complement activation in vitro.

RESULTS

Pigs were generated carrying four-fold knockouts of important xenoreactive genes. In vitro assays revealed that combination of all four gene knockouts reduced human IgG and IgM binding to porcine kidney cells more effectively than single or double knockouts. The multi-transgenic background combined with GGTA1 knockout alone reduced C3b/c and C4b/c complement activation to such an extent that further knockouts had no significant additional effect.

CONCLUSION

We showed that pigs carrying several xenoprotective transgenes and knockouts of xenoreactive antigens can be readily generated and these modifications will have significant effects on xenograft survival.

Xenotransplantation: an overview of the field

Xenotransplantation, the transplantation of cells, tissues, or organs between different species, has the potential to overcome the current shortage of human organs and tissues for transplantation. In the last decade, the progress made in the field is remarkable, suggesting that clinical xenotransplantation procedures, particularly those involving cells, may become a reality in the not-too-distant future. However, several hurdles remain, mainly immunological barriers, physiological discrepancies, and safety issues, making xenotransplantion a complex and multidisciplinary discipline.

Intravenous Immunoglobulin and Plasmapheresis in Acute Humoral Rejection: Experience in Renal Allograft Transplantation

Acute humoral rejection (AHR) in kidney transplantation is associated with higher rates of allograft loss when compared with acute cellular rejection (ACR). Treatment with intravenous immunoglobulin (IVIG) combined with plasmapheresis (PP) has been used recently in many centers. We report the incidence, clinical characteristics, and outcome of patients with AHR treated with IVIG and PP. All patients (n=519) at our institution who underwent kidney transplantation between January 1999 and August 2003 were retrospectively analyzed and classified according to biopsy results into three groups: AHR, ACR, and no rejection. AHR was diagnosed in 23 patients (4.5%) and ACR in 75 patients (15%). Mean follow-up was 844+/-23 days. Female sex, black race, and high panel-reactive antibody were risk factors for AHR. Most AHR patients (22 of 23) were treated with IVIG and PP. Two-year graft survival was numerically worse in patients with AHR versus ACR (78% vs. 85%, p=0.5) but the difference was not statistically significant. Graft survival after AHR treated with IVIG and PP is much better than it has been historically. IVIG in combination with PP is an effective treatment for AHR. Graft survival in this setting is similar to graft survival in patients with ACR.

Effect of plasma exchange in combination with deoxyspergualin on the survival of guinea-pig hearts in macrophage-depleted C6-deficient rats

The present study aimed to evaluate the effect of plasma exchange (PE) in combination with certain immunosuppressive agents on the survival of guinea-pig hearts in C6-deficient (C6-) rats. To deplete macrophages, we gave liposome-encapsulated dichloromethylene diphosphonate (Lip-Cl2MDP) intravenously (i.v.) in a dose of 10 mg/kg on day 2 before transplantation and every 5 days until rejection. Deoxyspergualin (DSG) was also given i.v. in a dose of 10 mg/kg/day from day -2 until rejection. Plasma exchange was performed 1 day before xenografting. All animals were splenectomized just before heart transplantation. Heart xenografts were evaluated twice daily and harvested at the time of rejection. The serum levels of anti-guinea-pig xenoreactive antibody (IgM, IgG) were measured using enzyme-linked immunosorbent assay (ELISA). Graft survival was 2.8 +/- 0.5 days in control rats, and 4.0 +/- 0.3 days with PE alone. A combination of PE with Lip-Cl2MDP or DSG did not improve the results (4.2 +/- 0.6 days vs. 4.8 +/- 0.6 days, respectively). While in rats treated with PE and the combination of Lip-Cl2MDP and DSG, graft survival was significantly prolonged (6.9 +/- 1.1 days, P < 0.01 vs. controls). In untreated control rats, xenoreactive antibody (IgM, IgG) levels decreased immediately after PE, but their levels rapidly returned to normal. In rats treated with DSG or DSG + Lip-Cl2MDP, the IgM levels remained low during the observation period. Immunohistochemistry showed that macrophage infiltration into the graft was suppressed in Lip-Cl2MDP-treated groups at the time of rejection. Our results demonstrate that sustained suppression of antibody levels can be achieved by PE in combination with DSG and xenograft survival is further prolonged in macrophage-depleted C6- rats. These findings suggest that strategies targeting antibody and macrophages may be useful in prolonging xenograft survival.