Investigation of lymphocyte depletion and repopulation using alemtuzumab (Campath-1H) in cynomolgus monkeys.

As the target CD52 molecule is expressed on erythrocytes of most nonhuman primate strains, using alemtuzumab in these species would cause massive hemolysis. Six cynomolgus monkeys of Indonesian origin, screened by agglutination assay for absence of CD52 on erythrocytes, were administered alemtuzumab in a cumulative dose to a maximum of 60 mg/kg. In two monkeys, mycophenolate mofetil (MMF) was added as maintenance therapy. Complete depletion of T and B lymphocytes (>99.5%) was achieved with 20 mg/kg alemtuzumab and was more profound than in monkeys treated with antithymocyte globulin (n = 5), as quantified by flow cytometry. Repopulation was suppressed by weekly injections of 10 mg/kg. Without MMF, repopulation of CD20(+)B cells and CD8(+)T cells was complete within 2 and 3 months, respectively, and repopulation of CD4(+)T cells was 67% after 1 year. MMF significantly delayed CD4(+)T-cell repopulation. Among repopulating CD4(+) and CD8(+) T cells, a phenotypic shift was observed from CD45RA(hi)CD62L(hi) naïve cells toward CD45RA(lo)CD62L(lo) effector memory cells. In lymph nodes, the depletion of naïve cells was more profound than of memory cells, which may have initiated a proliferation of memory cells. This model offers opportunities to investigate lymphocyte depletion/repopulation phenomena, as well as the efficacy of alemtuzumab in preclinical transplantation models.

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.

Metabolic aspects of pig-to-monkey (Macaca fascicularis) islet transplantation: implications for translation into clinical practice.

AIMS/HYPOTHESIS: Attempts to use an alternative source of islets to restore glucose homeostasis in diabetic patients require preclinical islet xenotransplantation models to be tested. These models raise questions about metabolic compatibility between species and the most appropriate metabolic parameters to be used to monitor graft function. The present study investigated and compared relevant gluco-metabolic parameters in pigs, monkeys and the pig-to-monkey islet transplantation model to gain insight into the potential clinical outcome of pig-to-human islet transplantation. METHODS: Basal and IVGTT-stimulated blood glucose, C-peptide, insulin and glucagon levels were assessed in non-diabetic pigs and monkeys. The same parameters were used to evaluate the performance of porcine islet xenografts in diabetic monkeys. RESULTS: Non-diabetic cynomolgus monkeys showed lower levels of fasting and stimulated blood glucose but higher levels of C-peptide and insulin than non-diabetic pigs. The reported levels in humans lie between those of monkeys and pigs, and differences in metabolic parameters between pigs and humans appear to be smaller than those between pigs and cynomolgus monkeys. The transplantation data indicated that the degree of graft function (evaluated by the measurement of C-peptide levels) necessary to normalise blood glucose in the recipient was determined by the recipient levels rather than by the donor levels. CONCLUSIONS/INTERPRETATION: The differences between donor and recipient species may affect the transplantation outcome and need to be considered when assessing graft function in xenotransplantation models. Given the differences between monkeys and humans as potential recipients of pig islets, it should be easier to reach glucose homeostasis in pig-to-human than in pig-to-non-human primate islet xenotransplantation.

Living donor renal transplantation using alemtuzumab induction and tacrolimus monotherapy.

Alemtuzumab was used as an induction agent in 205 renal transplant recipients undergoing 207 living donor renal transplants. All donor kidneys were recovered laparoscopically. Postoperatively, patients were treated with tacrolimus monotherapy, and immunosuppression was weaned when possible. Forty-seven recipients of living donor renal transplants prior to the induction era who received conventional triple drug immunosuppression without antibody induction served as historic controls. The mean follow-up was 493 days in the alemtuzumab group and 2101 days in the historic control group. Actuarial 1-year patient and graft survival were 98.6% and 98.1% in the alemtuzumab group, compared to 93.6% and 91.5% in the control group, respectively. The incidence of acute cellular rejection (ACR) at 1 year was 6.8% in the alemtuzumab group and 17.0% (p < 0.05) in the historic control group. Most (81.3%) episodes of ACR in the alemtuzumab group were Banff 1 (a or b) and were sensitive to steroid pulses for the treatment of rejection. There was no cytomegalovirus disease or infection. The incidence of delayed graft function was 0%, and the incidence of posttransplant insulin-dependent diabetes mellitus was 0.5%. This study represents the largest series to date of live donor renal transplant recipients undergoing alemtuzumab induction, and confirms the short-term safety and efficacy of this approach.

The ethics debate in relation to xenotransplantation.

Xenotransplantation is the transplantation of organs and cells from one species to another: it has enormous potential to increase the supply of organs and tissues to alleviate human disease. Recent scientific progress has eliminated the obstacle of hyperacute rejection, which is the massive destruction of the transplanted organ within 24 h. Despite this progress and the tremendous clinical potential, a number of ethical issues require careful consideration. These issues involve the human recipients, source animals, biotechnology companies and ultimately, the general public. One of the greatest concerns is the potential risk that an infectious agent will be transferred with the organ to the recipient, from whom it may spread, leading to a possible epidemic. However, there is no current evidence that porcine endogenous retrovirus, which is the agent of greatest concern, will be pathogenic. Using modern biotechnology, it may be possible to generate pigs that are free of this virus in the near future. Addressing these issues deliberately and in a scientific manner, with public involvement and education, will result in a greater understanding of the risks and benefits of xenotransplantation. This knowledge can then be utilised to fulfil the increasing demand for transplantable organs, with minimal risk.