Karen J. Maschke is a research scholar at the Hastings Center, a bioethics institution; Elisa J. Gordon is a professor of surgery-transplantation at Northwestern University’s Feinberg School of Medicine; Michael K. Gusmano is a professor of health policy at Lehigh University.

On Jan. 7, David Bennett, a 57-year-old man with end-stage heart disease, received a heart from a genetically modified pig at the University of Maryland Medical Center. The pig had 10 genetic alterations: one was designed to prevent the recipient’s body from rejecting the pig heart, another aimed to keep the pig’s heart from growing post-transplant. So far, this remarkable transplant has been a success.

A few months before the pig heart transplant, surgeons at NYU Langone Health attached a kidney from a genetically modified pig to the body of a deceased woman whose body was donated for research after death. The kidney came from a donor pig that was genetically modified to prevent organ rejection by the recipient’s body. For a 54-hour period following the procedure, the surgical team studied the pig kidney’s function while the recipient’s body was kept oxygenated on a ventilator, the organ produced urine at the level that is normal for a human kidney transplant.

Both procedures are providing transplant physicians with valuable information about how the human body responds to a transplanted pig organ. But such information will not be sufficient for changing national policies to allow animal organs to be used for transplantation. The need for an alternative to human organs is urgent because donor organs are chronically in short supply: More than 100,000 patients with end-stage organ disease are on the national transplant waiting list. Every day, 17 people die while waiting for a lifesaving organ because of organ scarcity.

Before xenotransplantation policies can be developed and implemented, clinical research trials — with human recipients of pig-organ transplants serving also as research participants — will need to be conducted. These trials will provide crucial information about the safety and effectiveness of the transplants.

Neither the pig heart nor the pig kidney transplant procedure was part of a clinical trial. Because Bennett was going to die without the transplant, the Food and Drug Administration, which regulates xenotransplantation, granted an emergency authorization for the transplant. But emergency authorizations won’t generate enough evidence needed for more-widespread use of animal organs.

Conducting clinical trials will raise ethical issues about equitable access to trial participation and access to animal organs: Should patients who are most likely to die before a human organ becomes available receive priority to enroll in a trial? How can doctors best protect transplant recipients in clinical trials using animal organs for the first time in humans?

For trials to proceed, the FDA will have to approve them, yet what eligibility criteria the agency might require for patients to enroll in trials remains to be established. The National Institutes of Health is funding our research study that looks into these questions in order to help the transplant field advance.

Clinical trials provide data about the safety and effectiveness of new medical interventions — data the FDA would weigh as it considers approving xenotransplantation for routine care. Even if that approval is eventually granted, there are several barriers to proceeding with the practice.

First, the current organ allocation system is based on the procurement, distribution and allocation of human organs for transplantation. But no policies exist to support organ allocation of animal organs.

Second, the costs of xenotransplantation for payers and patients will need to be sorted out to ensure equitable access to animal organs. The Centers for Medicare and Medicaid Services and private health insurers might want to see certain outcomes data (survival of the transplanted organ, survival of the recipient and recipient quality of life) from clinical trials to justify paying for xenotransplantation.

Before insurers are willing to pay for a new medical intervention, they will want to see evidence from clinical trials that the intervention would provide patients with beneficial outcomes. In cases of some new medical interventions the FDA has approved for routine care, insurers say the FDA has not required enough evidence from clinical trials about an intervention’s safety and/or effectiveness to justify insurance coverage.

Some patients might be receptive to receiving a pig organ, particularly those who are desperate for a lifesaving procedure. Other patients might be reluctant to receive an animal organ for moral reasons related to using animal organs, or if they don’t think clinical trials have provided enough evidence about xenotransplantation’s safety and its beneficial outcomes.

Xenotransplantation holds great promise as a way to overcome the organ shortage. Yet there are many steps to take before animal organs can be made available in routine medical care. With the recent news of these groundbreaking transplant developments, addressing the ethical, policy and regulatory factors involved is urgently needed: More than 6,000 people are expected to die this year for lack of an available organ.