PLACERVILLE, CALIF. — StemExpress, a tiny biomedical company in this foothill town east of Sacramento, has emerged at the heart of the contentious national debate over abortion and the scientific use of human fetal tissue. FBI agents say its floor-to-ceiling windows are security hazards, a potential line of sight for snipers. The backdrop of pine trees and hills provides cover, employees say, to strangers who crouch with cameras.

Inside, Melanie Rose, a laboratory technician, knows anyone could be watching. One recent May morning, she opened a foam box with fetal tissue packed in ice — a donation for medical research.

Rose, who is working toward a master’s degree in stem cell treatment, is one of 24 employees here thrust into view after antiabortion activists released a series of videos last year.

The videos shed light on an uncomfortable aspect of a little-known industry. They targeted Planned Parenthood, which provides abortions and, for a time, StemExpress paid a nominal fee to obtain the fetal tissue. The tissue, which is in limited supply, is a vital component in stem cell research — a great hope for medical breakthroughs. StemExpress collects the tissue and extracts the stem cells for researchers worldwide. Most of it is from adult sources — drawn from blood and bone marrow — but a small amount is from fetal tissue.

That work, with fetal tissue, has catapulted the small biotech firm out from under the radar. It is now the target of loiterers, protesters and death threats and the subject of a congressional inquiry.

At the heart of the issue is whether the work is done for profit. The exchange of fetal tissue for research is legal, so long as neither party makes money in the deal.

House Republicans and antiabortion advocates assert that firms such as StemExpress do profit illegally and that that profit fuels a demand for abortions.

StemExpress chief executive Cate Dyer says profit is not a factor.

“We lose money doing this,” Dyer said about working with fetal tissue. “We don’t have to do this, and we won’t stop doing this.”

The consequences of this supercharged debate transcend one firm. Scientists and doctors across the country say the political turmoil on Capitol Hill has stalled lifesaving work and imperiled progress toward, among other treatments, a Zika virus vaccine.

“We want to accelerate lifesaving research,” Dyer said. “That’s what it’s all about. That is my passion.”

Dyer once worked as an emergency medical technician at Santa Barbara Cottage Hospital’s trauma center. Watching people die every day at the Southern California facility, she said, inspired her to search for ways to prevent death. She started the company in 2010 with $9,000 in savings. In 2015, StemExpress said it posted roughly $5 million in revenue.

Her company’s innovation, as she describes it, is isolating the stem cells from donor tissue from the clinic, which extends their lifespan for research. Otherwise, she said, a researcher in New York who wanted an adult liver in California would lose a substantial number of its usable cells during the cross-country flight.

Before the videos came out, Dyer said, StemExpress had never had so much as a threat. Hundreds have since hit the StemExpress inbox. She said a recent message was typical of what they’d received: “We know that you use aborted fetuses in your ‘research.’ Repent now before it is too late.”

Dyer said the company provides the samples to researchers at a financial loss to expedite the creation of medicines and vaccines — and that fetal tissue represents less than 1 percent of the business.

“I want to be able to focus on saving people’s lives,” Dyer said, “and instead I have to deal with death threats.”

“Sometimes,” she said, “people cut the letters out of magazines and send us messages.”

A fateful dinner meeting

David Daleiden, an activist who leads an outfit he calls the Center for Medical Progress, secretly shot the videos. He started looking into StemExpress after seeing a Craigslist posting for a contract job to collect tissue from a women’s health clinics.

StemExpress is a business, and that’s clear from the list of products and bioservices on its website. He found it disturbing.

“The big problem, when we talk about the harvesting and sale of fetal tissue from abortion, is you’re creating a market,” he said. “You’re introducing this extra new level of demand for abortion.”

The video shows a dinner meeting with Dyer last May at an upscale restaurant in El Dorado Hills, Calif. Daleiden and his colleague posed as biotech busi­ness­ owners who wanted to partner with StemExpress.

Daleiden asked for details about StemExpress’s interest in fetal tissue, where it comes from, how it’s procured, issues with shipping it and the growing demand for it. Daleiden also asked about StemExpress’s relationship with Planned Parenthood.

Dyer’s description of Planned Parenthood as a “high-volume institution” later drew scrutiny from House Republicans.

The conversation, which Dyer says lasted about two hours, was edited down to less than 10 minutes. Any talk of money, she said, was taken out of context in the editing. She says that her business grew quickly because of the research community’s high demand for adult tissue and blood, and that’s what she was referring to when profit was discussed.

The company’s records indicate that roughly 1 percent of the tissue StemExpress collects is fetal. StemExpress typically gave Planned Parenthood $55 per sample, paying mostly for use of its rooms, storage and staffers.

Last year, a StemExpress catalog advertised a vial of two million “fresh” stem cells from a fetal liver for $1,932, and $1,840 for the same amount "cryopreserved," or frozen. Company records show they charge researchers a flat fee of $595 for each sample of fetal tissue, which costs an average $732 to prepare. In addition to compensating staffers who collect the tissue, the company pays for mileage, shipping, packaging, lab equipment, screening the sample for diseases and general upkeep.

In 2015, revenue from the transfer of fetal tissue to researchers totaled roughly $26,000. The cost of preparing the tissue, the company said, was about $33,000 — resulting in a $7,000 financial loss.

Congressional demands

The House Energy Committee’s Select Investigative Panel on Infant Lives has demanded that ­StemExpress and other biomedical players hand over thousands of pages of financial records and the names of their employees, issuing 36 subpoenas since March.

Its mission, according to its website, is to compile information about abortion providers and the biotech companies who “sell baby body parts.” The members plan to send their findings to Congress at the end of the year. On Tuesday, 180 of 188 House Democrats urged Speaker Paul D. Ryan (R-Wis.) to dissolve the panel, accusing it of harassment and McCarthyism.

Medical authorities have warned lawmakers that stigmatizing fetal tissue research could jeopardize public health. In March, the Association of American Medical Colleges — a group that includes the American Congress of Obstetricians and Gynecologists, Harvard University, and the Stanford University School of Medicine — sent a letter to congressional investigators.

“From therapies for end-stage breast cancer, diabetes and Parkinson’s disease to a promising vaccine for Ebola,” they said, “vital medical research depends on continued use of fetal tissue under current laws and regulations.”

Allowing people to donate the tissue for research, the authors stressed, is not linked to an increase in abortions, which have declined in the United States as birth control grows more accessible.

Researchers say the toll is material. During the investigation, one lab, Novogenix Laboratories in Los Angeles, has gone out of business. Dyer said the subpoenas and travel to Washington have halted her business’s expansion.

After the videos came out, she said, the supply of fetal tissue quickly dwindled. The company recorded 76 samples in 2013, 72 in 2014 and 39 in 2015. Now, on average, it gets four samples a month.

StemExpress says it has provided more than 2,000 pages of documents to Congress, including five years of banking records.

Rep. Marsha Blackburn (R-Tenn.), the chair of the House panel who describes herself as “pro-life,” said she wants to see further proof — a precise breakdown of each expense that goes into procuring and purifying fetal tissue — that StemExpress does not turn a profit. Company estimates about the cost of procuring tissue, she said, are not enough. The panel has issued a subpoena to StemExpress’s bank.

Rep. Jan Schakowsky (Ill.), the panel’s ranking Democrat, said StemExpress has been cooperative.

“This is really dangerous stuff,” she said, “and it seems to me that the real goal of this so-called investigation — I prefer the term witch hunt — is they’re hellbent on putting them out of business.”

Dyer said she has strived to respond to the panel’s requests for evidence but has resisted demands to hand over employees’ names, fearing it would threaten their security. Blackburn has said that getting employees’ names is necessary for investigators to set up interviews and that the names will not be made public.

Dyer’s security fears are not unfounded. In November, about four months after Daleiden released the first undercover video of Planned Parenthood officials, Robert L. Dear Jr. killed three people and wounded nine at a Planned Parenthood clinic in Colorado. He later told authorities, “No more baby parts.”

The next month, Scott Orton, a 57-year-old Washington state resident, was arrested after he blogged about killing StemExpress employees and, specifically, Dyer.

“She will have to face the souls of the babies she’s bought and sold when she arrives on the other side,” he wrote, according to an FBI affidavit. “I’m sending her there early.”

Chilling effects on research

Those kinds of threats and the growing political pressure have chilled stem cell research at laboratories across the country.

Steven Goldman, a neurologist at the University of Rochester Medical Center in New York, said the outrage — and anxiety over becoming a target of it — has delayed his research on multiple sclerosis.

In 2012, Goldman’s team received a $12.1 million grant from the Empire State Stem Cell Board to develop a cure. The team extracted stem cells from fetal tissue — collected from abortions performed at local hospitals — to see whether they could regenerate myelin, the insulating sheath around nerve fibers, in mouse brains.

It worked, Goldman said. He and his colleagues planned to start clinical trials on late-stage multiple sclerosis patients this year. Since Daleiden’s first video, however, the researchers’ supply of fetal tissue dried up.

“Hospitals seemed less willing” to donate, Goldman said. “We’d never had significant rejections by patients, and all of the sudden they were turning down consent forms.”

Goldman has pushed his multiple sclerosis research schedule back to 2019.

“This kind of delay,” he said, “results in the additional deaths of people who could have been rescued.”

Although the National Institutes of Health has expanded funding for fetal tissue research in recent years — federal grant money for the work jumped from $67 million in 2013 to $84 million in 2016 — scientists who receive the money say the projects have become harder to complete.

Progress has stalled at Stanford University, for example, which received more than $1.3 million in the funding in 2015.

For four years, Steven Sloan, a PhD student in neuroscience, has studied fetal tissue to better understand brain development and the types of cells that might contribute to disorders such as autism.

In 2014 and 2015, the school, a client of StemExpress and local hospitals, received tissue within a week of requesting a sample. But as the congressional investigation heated up, Sloan said, the scientists started waiting longer than a month. “All of a sudden,” he said, “getting tissue was like pulling teeth.”

Sloan, who graduates this month and plans to pursue a medical degree, said he probably will stick with adult tissue in future research.

“The backlash,” he said, “makes you think twice about proceeding with this kind of work.”

Other institutions have received more direct political pressure. Following demands from Rep. Doug Lamborn (R-Colo.), Colorado State University, a former client of StemExpress, stopped ordering fetal tissue for a project to cure HIV/AIDS. The university decided to “seek alternatives to aborted fetal tissue sources,” spokesman Mike Hooker said.

As summer — and mosquito season — approaches, Rita Driggers says, her research is particularly urgent. The medical director of the Maternal-Fetal Medicine Program at Washington’s Sibley Memorial Hospital said doctors need such tissue to defeat the Zika virus. Her study, published in the New England Journal of Medicine, suggests that Zika lingers in pregnant women long after symptoms fade.

A patient of Driggers’s had returned from Mexico, Guatemala and Belize with Zika and learned her baby’s brain wasn’t developing. When she terminated the pregnancy, she asked whether the tissue could be studied. “She wanted her misfortune to benefit other people,” Driggers said.

Even if all goes well, Driggers said, a Zika vaccine is at least two years away.

“If researchers are threatened, it’s going to make us think twice about continuing research,” she said, adding that her former boss has received death threats for her stem cell work. “Ultimately, the patients that could benefit from the research won’t.”

At the StemExpress lab, Dyer has hired armed guards, installed security cameras and put her staff through active-shooter training.

Rose, the 27-year-old lab technician, wears a silver Saint Christopher pendant for protection.

She cried when protesters first surrounded StemExpress, waving Bibles and photos of fetuses. Now she tries to make eye contact through the windows. To smile.

When Rose sets to work, she breaks the tissue apart, then soaks it in enzymes and counts the number of stem cells on a grid under a microscope. She pours the cells into two-milliliter vials, which are stored in liquid nitrogen tanks until they are shipped to a researcher at a university or major health institution.

“This tissue,” she said, “would be thrown away if we didn’t send it to researchers who are truly trying to save lives. I want them to see what I’m doing. That something good can come of it.”

This story has been updated.