Ryan Custer was a freshman basketball player at Wright State University in Dayton, Ohio, when, in April 2017, he jumped into a pool at a house party and shattered his C5 vertebra. Paralyzed from the chest down, Custer entered a clinical trial in Chicago for an experimental stem cell therapy that could restore limited nerve function one centimeter – shoulder shrug, bicep motion, tricep use – at a time.

Cheryl Wiers, a mother in her 40s, saw her aggressive non-Hodgkin’s lymphoma return twice, with a vengeance. Chemotherapy wasn’t working, but a clinical trial for a transplant of stem cells at City of Hope medical center in Duarte, California, offered hope.

In San Francisco, Andrew Caldwell, who is HIV-positive, underwent an experimental therapy which transfused his own genetically modified stem cells back into his body; if the modified cells produced enough HIV-resistant fighter cells, known as T-cells, to suppress the virus, the treatment could functionally cure HIV.

All three are vanguards on the slowly unfolding horizon of stem cell therapies, which could offer reprieve from diseases such as certain types of cancers, Type 1 diabetes, lupus and other auto-immune disorders. And all three, along with several others, offer up their emotional, idiosyncratic, and casually radical stories in the film Ending Disease, a collection of intimate portraits of experimental medicine under the culturally fraught, politically vulnerable, and extremely promising umbrella of stem cell research.

Such research has long been a game of potentials – treatments that could cure a host of incurable diseases or conditions, from HIV to certain causes of blindness to quadriplegia; research whose funding could get kneecapped by the whims of political power, treatments that could become available to the masses but are limited to select clinical trial groups. Ending Disease, which followed several trial participants between 2016 and 2019, takes its name from the farthest reaches of said potential: “we are on the cusp of a tremendous number of cures,” said director Joe Gantz.

For each of the case studies in Ending Disease, stem cell treatments hold potential that is vague and unpredictable yet incalculably significant. For Rosie Barrero, who became legally blind from retinitis pigmentosa in her 20s, it’s the chance to see a little more clearly, to depend on her family less. For Custer, the reclamation of any movement below the neck. For Erica Billy, the opportunity to have her toddler daughter, Ava, who was born without a functional immune system, escape isolation, go to school, and avoid the harrowing treatments – chemotherapy rounds, a bone marrow transplant – that defined her infancy.

The 138-minute documentary sketches the broad outline of what stem cells are – basically, blueprint cells that could become any other type of cell in the body – and a surface-level explainer of how therapies work on a scientific level. But the portraits are hyper-specific, mundane and visceral, a clear window into the time-sensitive stakes of decades of research routinely jeopardized by political headwinds. “It’s not critical that people understand exactly how stem cells work, or exactly how CAR-T cells work,” said Gantz. Instead, the film highlights how “this is such an important moment and to follow these patients and the scientists and the doctors”, many of whom have been working on treatments for very specific diseases for decades.

As with The Race to Save the World, another Gantz film released this year, which embeds with the personal lives of several climate activists instead of macro-level arguments for change, Ending Disease captures “the tremendous emotion that these families are dealing with, hoping for a cure for their loved ones” rather than the technical explanations of how, exactly, stem cell therapies function. There are appointments, tentative conversations with doctors about scans, needle injections and families crowded around a hospital bed, a playful fight between Custer and his father over a disappointing college grade, a nurse playing with immuno-compromised Ava in a full bodysuit, Caldwell’s mother recalling his coming out, a conversation between Wiers and her husband, both Catholics, over their initial reluctance and eventual support of therapies involving embryonic stem cells.

In between, experts such as Irving Weissman, the director of the Institute for Stem Cell Biology and Regenerative Medicine at Stanford University, offer some academic context to the individual stories. Weismann, a pioneer of stem cell research for cancer treatments, attests to the heated cultural wars that have stilted scientific progress. The term “stem cell research” will likely conjure, for many, the debates of the early 2000s, when the administration of George W Bush outright banned the use of fetal tissue, such as embryonic stem cells, in scientific research. In 2004, California voters took matters into their own hands and passed state funding for its own stem cell research at the California Institute for Regenerative Medicine (CIRM).

Ryan Custer’s mother hovers over his hospital bed in Ending Disease. Photograph: Passion River Films

“Since that time, we have been able to develop purified blood-forming stem cells to rescue people from high-dose chemotherapy with their own stem cells,” Weissman said. Scientists have, for years, demonstrated that such treatment is possible, but to carry it forward to actual treatments takes years of FDA-approved clinical trials, and additional years of research, that can be jeopardized by political loyalties to anti-abortion groups opposed to the use of fetal tissue, sometimes obtained from abortions and not used in all stem cell therapies, for scientific research.

In June 2019, Donald Trump stalled federal funding for research involving fetal tissue with a shock executive order, a move that pleased the anti-abortion groups his administration sought to appease. The order, reportedly on the whims of an obscure but dogged West Wing staffer named Joe Grogan, halted trials of breakthrough treatments for HIV and forced some labs to lay off staff and abandon projects. (It also delayed efforts to investigate possible Covid-19 treatments in March 2020.)

“It would be great if we could get rid of that political and religious aspect to looking at science, and let science at least make its case and be adjudicated by the other bodies,” said Weissman, “rather than have a ban that precludes any of this scientific and medical development.” The major obstacles to the advancement and, crucially, accessibility of stem-cell treatments remains “short-term politics, not understanding what pharmaceuticals do and can do and how they must operate” from a profit motive. And, furthermore, the “valley of death” gap between discovery and actual therapy – a gap that is “our responsibility to look at, find out what the gap is, and fill the gap so that we can advance medicine for people”, said Weissman.

For the patients in Ending Disease, the gap is tangible, a tentative and real lifeline. Not all the trials were a success – the film is dedicated to Steven Sharpling, who died in 2018 after stem cell injections could not fully eradicate the brain cancer known as anaplastic astrocytoma. But even small wins are consequential for everyday life. Within months, Custer regained the ability to move his arms, and even passed a driving test using a modified car. Wiers’s treatment, which retrained her own white blood cells to recognize and destroy cancer cells, rescued her from essentially a death sentence; she’s now cancer free. Caldwell’s T-cell levels cleared a level high enough to take him off anti-viral HIV medications. Ava George’s stem cell therapy retrained her immune system enough that she can go to school with other kids. These are visions of the future; not so much silver bullets as pathways out of pure incurability – should we choose to support them.