One patient went eight months without immunosuppressive drugs and others were switched to low doses.
The study, by Germany's University of Schleswig-Holstein, appears in Transplant International.
Currently, transplant patients must take a cocktail of powerful drugs for life to dampen down their immune system, and prevent the new organ being rejected.
But the drugs themselves can cause side effects, and may not prevent the slow rejection of the organ over time.
The new technique involves giving transplant patients an infusion of specialised cells known as a transplant acceptance-inducing cells (TAICs).
The TAICs are created by isolating a type of white blood cell from the donor, and modifying them chemically in the lab, reports BBC.
Once modified, the cells gain the ability to kill off cells in the immune system which trigger the rejection process, and to boost the action of another type of immune cell which plays a beneficial role in guarding against rejection.
The cells are then cultured alongside those from the recipient - which helps prime the immune system further - before being injected into the patient.
The technique has been tested on kidney transplant patients, some of whom were given the cells before surgery, and others after the transplant, as an additional drug therapy.
Lead researcher Dr James Hutchinson said the technique was still at a preliminary stage, but results on 17 patients were promising.
He said: "It could eventually offer patients who have had transplant surgery a much higher quality of life, free from complex drug regimes."
In the first stage of the clinical trials 12 patients received kidneys from deceased donors, and were given TAICs in addition to traditional anti-rejection drugs.
Ten patients were gradually weaned off the cocktail of conventional drugs, and six eventually took only a low dose of one particular drug, cutting the risk of side effects substantially.
In the second stage of the trial five patients who received kidneys from live donors were given an infusion of TAICs before their surgery was carried out.
One patient was able to go eight months without any immunosuppression drugs, and a further three were successfully weaned down to the single low-dose therapy.
Dr Hutchinson said: "Our research clearly shows that infusing TAICs into patients before they have a kidney transplant, or after the procedure has been carried out, is a practical and safe clinical option.
"Although this procedure is still being developed and refined, it poses an exciting possibility for clinicians and patients alike."
Keith Rigg, a transplant expert and vice president of the British Transplantation Society, said: "This is interesting work which has the potential to both reduce the risk of rejection after organ transplantation and the amount of anti-rejection drugs that are required, both of which will be good news for patients.
"As the authors say this is still early and preliminary work, and further development and refinement of the process is required, but this procedure does seem to have potential."