Scientists have found a new method of suppressing the automatic rejection of donated kidneys in transplant patients, by using the donor's stem cells. In a small trial carried out at Stanford University, California, eight out of 12 patients were able to stop taking anti-rejection drugs, which are usually a lifelong necessity, following this treatment.
Soon after their transplants, each of the patients in the study underwent a procedure where their lymph nodes, spleen and thymus were given a dose of radiation to kill some of their immune system's white blood cells. This was in addition to the patient taking the standard course of two anti-rejection drugs.
About ten days after the radiation treatment, the patient was injected with stem cells from the donor's blood. They then differentiate into white blood cells and become part of the recipient's immune system, and will not attack the new kidney. If the stem cells mix favourably with the patient's own cells, the patient can be taken off the first anti-rejection drug after a month, and the second after six months.
'Those eight that we've taken off the drugs, they've had no rejection, no evidence of the kidney being damaged', said Dr Samuel Strober, the immunologist who is leading the study, which was published in the New England Journal of Medicine.
All of the eight patients treated successfully have now been off the immunosuppressant drugs completely for over a year, including one for over three years. Dr Strober, explained the other four have 'failed to meet our strict drug withdrawal criteria', but have suffered no side effects from the treatment.
Currently, all transplant patients need the drug course to prevent their body from rejecting the donor organ. This is the case even if the donor is a perfect match in terms of surface markers – called HLA (human leukocyte antigen) antigen – which reduces the risk of the donated kidney being rejected. However, they can pose problems in the long-term.
'While they help ward off rejection of the new organ by the patient's own immune system, these drugs carry their own risk of side effects, such as high blood pressure, diabetes and cancer', said Dr Strober.
All the patients in this on-going clinical trial are perfect matches with their donors, but the work is now being expanded to include patients with mismatched donors, where only 50 percent of their HLA antigens match the patient's.
'Our preclinical lab results show that we can use mismatched recipients as well as matched, and that gives us confidence to move ahead', added Dr Strober.
However, Dr Flavio Vincenti, a kidney transplant expert at the University of California, San Francisco, cautioned against over-optimism. He said it was not known whether the delicate balance of the immune system can be maintained in the long-term. 'I would caution patients and physicians that this gives us maybe an idea on a mechanism of action, but from a practical point of view, it will have very limited application', Dr Vincenti told the San Francisco Chronicle.