For investors, the business of organ transplants goes well beyond checking the donor box on a driver’s license.

Federal law, of course, makes buying and selling organs illegal in the U.S. But there are investment opportunities in companies supporting the process of transplantation. They work in an area where demand exceeds supply, with more than 20 people dying each day in the U.S. because of a shortage of donated organs, according to the Department of Health and Human Services.

Historically, the organ transplant industry has not been a high growth market because it has been limited by the number of human organs available. That is changing as awareness about donation grows and researchers find ways of improving the viability of organs that might not have worked for transplant in previous years. The future may also yield breakthroughs in artificial organ development, which would also increase supply.

Organ transplants in the U.S. have increased from 19,396 in 1995 to 28,211 last year (through November 30), according to the federal Organ Procurement Transplantation Network. Beth Senko, senior analyst with Edison Investment Research, predicts that the growth in the number of transplants may accelerate as the nation’s population ages.

Investment opportunities mostly lie in companies involved in secondary aspects of the organ transplant business, such as transport, anti-rejection therapies and creating technologies to salvage previously unusable organs, Senko says.

One possibility for investors is Lifeline Scientific, which is based in Itasca, Illinois, and trades on the London Stock Exchange. Lifeline manufactures a device for transporting kidneys. The device maintains circulation through the organ so it is in optimum condition when it reaches the recipient.

Senko also suggests medical device company CryoLife (ticker: CRY), which is involved with the processing and distribution of implantable human tissues for heart and vascular procedures.

Using animals. With organs from human cadavers in short supply, a process called xenografting, or transplanting animal cells such as valves from pigs into humans, has been meeting some demand for years.

One company working on xenotransplantation technology is Revivicor, which United Therapeutics Corp. (UTHR) bought in 2011. Revivicor uses genetically engineered pigs to provide human-compatible cells to treat diabetes as well as provide organs and tissues for transplants. RTI Surgical (RTIX) is involved in processing animal tissue for implantation into humans.

Fighting rejection. Immunosuppressant drugs that help the body avoid rejection of a donated organ are key components to successful transplants, says Jeffrey Loo, health care analyst with New York-based financial information provider S&P Capital IQ.

Those drugs include Novartis’ (NVS) Neoral for liver, kidney, heart and lung transplants and Pfizer’s (PFE) Rapamune for kidney and liver transplants. But overall, the organ transplant business is “not a big market driver for most drug companies,” Loo says.

The anti-rejection arena goes beyond immunosuppressant drugs.

Now, researchers are working on developing new ways of testing whether a body is rejecting a transplanted organ that are not as expensive and invasive as biopsies, which is currently the primary way doctors test for rejection.

In 2014, Roche Holding bought Ariosa Diagnostics, a California company working on molecular diagnostics testing that would aid in transplantation. And there is CareDx (CDNA), which has a molecular blood-based test for monitoring heart transplant recipients for cellular rejection.

Building organs. While researchers are a long way off from being able to create whole, usable human organs, there has been success with growing organ-specific cells, says Caroline Corner, an analyst covering medical technology for Cantor Fitzgerald & Co.

While not directly involved in the full-organ transplant business, cell therapy technologies from companies such as StemCells (STEM) and Ocata Therapeutics (OCAT), could help pave the way for larger successes, she says.

One company working in this space is Organovo Holdings, a California company that has developed human liver tissue designed for use in drug testing. It is working on human kidney tissue for similar uses. To create the tissue, the company uses three-dimensional printing technology.

It’s still early days for Organovo, Corner says. She has a hold rating on the stock, which is traded on the NYSE MKT exchange, until the company can demonstrate it will get large pharmaceutical companies to use its cell products in toxicology studies during drug development.

While Organovo’s platform in theory has the potential to be used for “tissue-on-demand” applications, that is several years down the road, says Brandon Couillard, a health care equity analyst with Jefferies.

Organovo’s bioprinting probably won’t result in the company being able to print a kidney, he says. Rather, it will more likely be printing part of a damaged kidney, for example, that could be used to salvage that organ, he says.

Despite progress being made by mostly small-capitalization companies on a broad array of technologies, such as producing tracheas and esophaguses, growing organs remains a complicated process, Corner says.

Sometimes it behooves companies to remain private and avoid the increased scrutiny of outside investors during complicated development stages, she says. It also remains to be seen exactly what federal approval processes will look like for human-built organ tissue, she says

That’s why, Corner says, investing in the organ transplant industry remains a speculative move with a long-term time horizon.

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Organ Transplant Industry Holds Promise for Investors originally appeared on usnews.com