Weeks after suing for patent infringement, Brisbane, California-based transplant diagnostics firm CareDx Inc. has accused rival Natera Inc. in Delaware federal court of intentionally misrepresenting the accuracy of its competing kidney-transplant rejection test.

In a complaint filed Wednesday morning, attorneys for CareDx said Natera, which is based in San Carlos, California, was using a flawed study to launch a “false marketing campaign,” designed to deceive doctors, insurance companies and patients into believing that its technology was superior to CareDx's.

The lawsuit was the second in three weeks to take aim at Natera's test, branded as Prospera, which assesses kidney transplant rejection via cell-free DNA in a patient's blood. A March 26 lawsuit also filed in the U.S. District Court for the District of Delaware, accused Natera of infringing two patents underpinning CareDx's AlloSure, a noninvasive test that also assesses the health of transplanted kidneys by measuring fragments of DNA in the bloodstream.

Wednesday's complaint alleged false advertising and trademark violations under the Lanham Act, as well as the common law of unfair competition. According to the filing, Natera's public comparisons of its technology to AlloSure were based on numerous unscientific conclusions, in an “attempt to poison the marketplace.”

The suit seeks all available relief, including money damages and an injunction against Natera.

“Natera's manipulation of its test results, combined with its pattern of blatant falsehoods concerning the accuracy and veracity of Prospera as compared to AlloSure, reflects Natera's intent to unlawfully deceive and mislead consumers,” attorneys from Weil, Gotshal & Manges wrote in the 24-page filing.

Natera said Wednesday that it had not yet been served with the complaint, and declined to comment on specific allegations. However, the company stood behind its performance claims, saying they were rooted in “scientific, peer-reviewed evidence.”

“Natera's better clinical and analytic performance is documented in studies recently published in Transplantation and the Journal of Clinical Medicine,” the company said in a statement. “We believe our test will become a valuable tool in the management of kidney transplant patients and look forward to serving these patients.”

CareDx's complaint cited multiple public statements from Natera touting its test as outperforming AlloSure, which CareDx developed using two patents licenses from Stanford University. But CareDx argued that those characterizations were based on a study that was “substantially flawed” and whose methodology differed significantly from a clinical study that AlloSure had undergone.

Specifically, AlloSure alleged that Natera's study did not follow the international consensus for reporting biopses from solid organ transplants and that it analyzed samples from improperly mixed biopsy sets that were not representative of the real-world kidney transplant population. The samples, CareDx said, were taken retrospectively from a pre-existing sample archive collected from just one study center, compared to CareDx's study, which collected samples from 14 study centers with biopsies interpreted by pathologists.

“Just one of these four instances could be chalked up to innocent mistake or unintentional error,” Ed Reines, an attorney for CareDX, said in a statement. “However, together they suggest a concerted effort by Natera to mislead patients and medical personnel into thinking its study was more credible than it actually was and that it proved Natera's technology is superior to CareDx's, which it is not.”

The case, captioned CareDx v. Natera, has not yet been assigned to a judge.