Gene Therapy: Treating the Transplanted Kidney and Beyond

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The goals for gene therapy are becoming both more ambitious and yet more practical as the field matures. The field will show continued advances in 2012.

In one line of research in mice, gene therapy shows promise in delivering agents that cannot be given systemically—either because of side effects or poor pharmacokinetic properties—to reduce chronic transplant dysfunction.

In the early days, researchers envisioned replacing defective genes to completely cure hereditary diseases, efforts that have largely come up short. But meanwhile, less heroic strategies have been progressing, using genes to treat symptoms, or provide short-term therapy rather than a long-term cure.

If there is a near-term role for gene therapy in renal disease, it may be of the latter form, according to Leo Deelman, PhD, assistant professor of medicine at the University of Groningen, the Netherlands. One strategy is to use gene therapy to provide local immune suppression for renal transplantation.

“Transplantation is the first choice for end stage renal disease,” Deelman said at Kidney Week 2011, “but it is associated with a lot of problems,” including rejection and acute lack of function. Early on, there is ischemia-reperfusion damage, contributing to loss of function and acute rejection. In the long term, nephron loss, inflammation, and fibrosis may occur, leading to chronic failure. “There are also side effects of systemic immunosuppressant therapy. Toxicity is a big problem.”

“Gene transfer could help, if we selectively express immunosuppressant molecules in the kidney to prevent rejection,” Deelman said.

Delivery of the gene to the target organ has always been a major stumbling block for gene therapy, and so the transplanted kidney is, in some ways, an ideal gene therapy target, since it can be treated in isolation before implantation.

There are multiple potential gene vectors, ranging from whole cells to viruses to naked DNA plasmids. “We thought adenovirus would be the most suitable vector for us,” Deelman said, “because it binds to its receptor at low temperatures, meaning that even when you have the transplanted kidney on ice, you could load it with adenovirus, and still get good transfection.”

The problem he encountered is that the kidney is relatively poorly stocked with the cellular receptors that the virus binds to to enter the cell. The solution, he found, was to modify the virus so that it binds to another receptor that is plentiful on kidney cells, increasing its uptake.

In an initial study meant to explore the potential of the gene transfer system, Deelman worked with mice in which the donor and recipient were the same strain, to minimize acute rejection. A kidney from the donor was removed and placed on ice, and then perfused with solution containing the virus, which carried a reporter gene. After 20 minutes, the kidney was washed with saline to remove excess virus, and then implanted in the recipient. He found that there was a high transfection rate, with interstitial fibroblasts expressing the transfected gene most strongly. Initial expression of the reporter gene was high, but dropped off after two weeks to only 7 percent of the original level. The kidney showed only mild levels of cytotoxic lymphocytes, indicating the virus was tolerated reasonably well.

Next, Deelman introduced immunomodulator genes into the virus, and used mice of different strains for donor and recipient. He first tried the gene for interleukin-13 (IL-13), “a potent anti-inflammatory molecule,” which reduces proinflammatory cytokines and inhibits macrophage function. As part of the experiment, he compared gene therapy on the kidney alone to injection of the adenovirus intramuscularly into the recipient. “The aim was to see whether this local therapy with IL-3 was as effective as systemic therapy,” he said.

Local therapy led to high expression of IL-13 in the kidney at day 8 after transfection, and some reduction of renal damage markers consistent with an immunomodulatory effect. The results were “similar or better than for intramuscular treatment,” he said. “Local gene therapy is a feasible alternative to systemic therapy.”

The second gene he tried was for 2,3-indoleamine dioxygenase, or IDO. IDO is the rate-limiting enzyme in the catabolism of tryptophan, and high expression depletes tryptophan. The enzyme is abundantly expressed in the placenta during pregnancy, and protects the fetus against rejection. It is also expressed in tumor cells, as a mechanism to escape the immune response. It inhibits naïve T cell proliferation and induces T cell apoptosis, while stimulating regulatory T cells. IDO has been used to prevent acute rejection in diverse organs, including skin, heart, and pancreatic islets, as well as to suppress airway inflammation.

“The aim was to determine whether gene therapy with IDO could have an effect on acute rejection of the transplanted kidney.” To test this, both kidneys in the recipient were removed before transplantation, in order to assess the function of the transplanted kidney alone.

The gene was expressed at high levels, and led to a “dramatic reduction” in plasma creatinine versus control, “and a complete normalization of kidney function.” Biomarkers of inflammation and renal damage were all lower in the treated mice, and there was less macrophage infiltration and less fibrosis. “This is really quite impressive,” Deelman said.

Deelman’s group is now examining IDO’s potential to reduce chronic transplant dysfunction. Their initial results indicate that at three months, treated mice have no proteinuria, lower blood pressure, and better body weight, compared to controls.

The long-term benefit was not due to continued expression of IDO, since, as before, gene expression was largely absent after two weeks. Instead, Deelman said, early treatment with IDO may protect cells from immune surveillance in the critical early period, or may induce tolerance.

Whether local therapy will prove superior to systemic therapy in humans “remains to be shown,” Deelman said.

January 2012 (Vol. 4, Number 1)