By Hendra Lukman 
A groundbreaking advancement at Stanford Medicine is set to transform the landscape of stem cell transplantation, offering a less toxic and more accessible path for patients with debilitating genetic disorders. A novel antibody therapy, developed through extensive research, has demonstrated the ability to prepare patients for life-saving stem cell transplants without the need for the harsh and often debilitating effects of traditional chemotherapy or radiation. This innovation, highlighted by the successful outcomes of a phase 1 clinical trial, marks a significant leap forward in making these critical procedures safer and more widely available.
A Paradigm Shift in Stem Cell Transplant Preparation
The initial focus of this pioneering study was on individuals suffering from Fanconi anemia, a rare and severe inherited blood disorder. Fanconi anemia compromises the body’s ability to repair DNA damage, leading to a progressive failure of the bone marrow to produce essential blood cells. This deficiency can result in life-threatening complications such as bleeding and infections. For these patients, stem cell transplantation is often the only curative option. However, the conventional conditioning regimens required to eliminate the patient’s own faulty stem cells – typically high-dose chemotherapy or radiation – pose substantial risks, including secondary cancers and severe organ damage, making the transplant process itself extremely perilous.
The Stanford team’s innovative approach bypasses these toxic treatments. Instead, they utilized an antibody targeting CD117, a protein prevalent on the surface of blood-forming stem cells. This antibody, known as briquilimab, effectively depletes the patient’s own stem cells, creating a receptive environment for the donor cells without the collateral damage associated with radiation and genotoxic chemotherapy agents like busulfan.
"We were able to treat these really fragile patients with a new, innovative regimen that allowed us to reduce the toxicity of the stem cell transplant protocol," stated Dr. Agnieszka Czechowicz, MD, PhD, assistant professor of pediatrics and co-senior author of the study. "Specifically, we could eliminate the use of radiation and genotoxic chemotherapy called busulfan, with exceptional outcomes."
The findings, published in the prestigious journal Nature Medicine, detail the successful transplantation of three young children with Fanconi anemia. These children have now been followed for two years post-transplant and are reportedly thriving. This remarkable achievement suggests that the antibody-based conditioning regimen could have broad applicability for individuals with a spectrum of inherited diseases necessitating stem cell transplants.
The Genesis of an Innovative Therapy
The roots of this breakthrough therapy can be traced back over two decades to the foundational research conducted at Stanford Medicine. Dr. Czechowicz began investigating blood-forming stem cells in 2004 as an undergraduate student under the guidance of Dr. Irving Weissman, MD, then director of Stanford’s Institute for Stem Cell Biology and Regenerative Medicine. Their early work in animal models revealed that blocking CD117 with antibodies could effectively eliminate stem cells without the need for radiation or chemotherapy. This critical insight laid the groundwork for developing a human-compatible antibody. Through persistent research and collaboration with other scientists at Stanford, a version of the antibody suitable for clinical use was identified, culminating in the recent phase 1 trial.
Dr. Rajni Agarwal, MD, professor of pediatric stem cell transplantation and co-first author of the study, emphasized the urgency and significance of finding safer transplant alternatives. "If they don’t get a transplant in time, Fanconi anemia patients’ bodies eventually will not make blood, so they die of bleeding or infections," she explained. "The reason I am so excited about this trial is that it is a novel approach to help these patients, who are very vulnerable."
Addressing the Donor Match Challenge
Beyond mitigating the toxicity of the conditioning regimen, the Stanford team also addressed another significant bottleneck in stem cell transplantation: the scarcity of fully matched donors. Historically, an estimated 40% of patients requiring a transplant faced insurmountable hurdles due to the inability to find a compatible donor. This often led to delayed or forgone life-saving treatments.
To broaden the pool of potential donors, the researchers implemented a sophisticated modification of the donor bone marrow. This process involved enriching the donated marrow for CD34+ cells – the actual blood-forming stem cells – while meticulously removing immune cells known as alpha/beta T-cells. These T-cells are notorious for triggering graft-versus-host disease (GVHD), a potentially life-threatening complication where the donor’s immune system attacks the recipient’s body. This innovative approach, pioneered by Dr. Alice Bertaina, MD, PhD, enables safe and effective stem cell transplants from half-matched donors, including parents.
"We are expanding the donors for stem cell transplantation in a major way, so every patient who needs a transplant can get one," Dr. Agarwal stated, underscoring the profound impact of this donor flexibility.
A Child’s Journey to Recovery: The Story of Ryder Baker
The transformative potential of this new therapy was vividly illustrated by the experience of Ryder Baker, an 11-year-old from Seguin, Texas. Ryder was the first patient to undergo the antibody-based transplant procedure at Lucile Packard Children’s Hospital Stanford in early 2022. His journey before the transplant was marked by the debilitating symptoms of Fanconi anemia, including profound fatigue and a lack of stamina.
"He was so tired, he didn’t have stamina. It’s completely different now," recounted his mother, Andrea Reiley, reflecting on Ryder’s remarkable recovery. She added that her son’s Fanconi anemia "doesn’t slow him down like it used to." Today, Ryder is a picture of renewed vitality. He has regained his energy, successfully completed fifth grade, actively participates in sports, and even earned an "Up and Coming Player" award from his school soccer team. His mother shared that Ryder takes pride in knowing his participation in the trial is helping pave the way for other children.
Broader Implications and Future Directions
The success of this phase 1 trial has ignited optimism for a wider application of this antibody-based approach. While stem cell transplants are most frequently employed in the treatment of blood cancers, where the bone marrow is infiltrated by malignant cells, the improved safety profile of this new method opens doors for patients with a broader range of conditions.
"Bone marrow or stem cell transplants are most commonly used in blood cancers, in which the bone marrow is full of malignant cells and patients have no other options," Dr. Czechowicz explained. "But as we’re making these transplants better and safer, we can expand them to more patients including those with many different diseases."
Fanconi anemia, characterized by the body’s impaired ability to repair DNA, typically manifests in childhood with symptoms like fatigue, stunted growth, recurrent infections, and easy bruising or bleeding. By the age of 12, approximately 80% of affected individuals develop progressive bone marrow failure, a condition that is often fatal without intervention. The irony is stark: while transplants offer a cure, the traditional pre-transplant treatments carry a significant risk of inducing secondary cancers, with nearly all patients developing them by age 40. The Stanford team’s antibody-based strategy aims to drastically mitigate this long-term risk.
The phase 1 trial involved three young participants, all under the age of 10, each with distinct genetic variations of Fanconi anemia. They each received a single intravenous dose of briquilimab 12 days prior to their transplant. Crucially, they did not receive busulfan or radiation; their conditioning consisted solely of the antibody and standard immune-suppressing medications. The donated stem cells, sourced from a parent and meticulously processed to remove harmful immune cells, were administered. Within a fortnight, the new stem cells had engrafted successfully in the patients’ bone marrow. None experienced graft rejection, and within one month post-transplant, donor cells had almost entirely replaced their own. The research team’s initial goal was a mere 1% presence of donor cells, a target they far surpassed, with all three children achieving nearly 100% donor cell chimerism two years later.
"We’ve been surprised by how well it’s worked," Dr. Czechowicz admitted. "We were optimistic that we would get here, but you never know when you’re trying a new regimen."
Even with the enhanced safety of this new protocol, stem cell transplants remain a demanding medical intervention. Ryder, for instance, spent over a month in the hospital and experienced temporary side effects such as exhaustion, nausea, and hair loss. "It was heartbreaking to see him go through things like that — I’d rather go through it than my child," Ms. Reiley shared, her voice filled with emotion. "I felt the heartbreak for him, and now he doesn’t have to."
Since his recovery, Ryder has experienced significant physical improvements, including growth and weight gain, and is no longer plagued by constant illness. "It used to be huge hits when he would get sick at all, and I really don’t have to worry about that anymore," Ms. Reiley said.
The Road Ahead: Expanding Access and Refining Treatments
The success of the phase 1 trial has propelled Stanford Medicine to initiate a phase 2 clinical trial involving a larger cohort of children with Fanconi anemia. Furthermore, the researchers are actively exploring the potential of this antibody approach for patients with other rare bone marrow failure disorders, such as Diamond-Blackfan anemia.
While chemotherapy and radiation remain essential for eliminating cancer cells in most leukemia patients, the Stanford team is investigating whether the antibody therapy can benefit elderly cancer patients who are too frail to tolerate traditional conditioning regimens. "That population is often at a disadvantage," Dr. Agarwal noted. "It may provide us with a way to treat them with less intensity so it’s possible for them to get a transplant."
The research efforts are also focused on developing next-generation antibody-based treatments, aiming to further refine outcomes and improve the efficacy for Fanconi anemia and similar conditions.
Collaboration and Support Fueling Innovation
This transformative research represents a collaborative endeavor involving numerous experts and institutions. Key contributors include Dr. Czechowicz, Dr. Agarwal, Dr. Bertaina, and co-senior author Dr. Matthew Porteus, MD, PhD. The study also benefited from the expertise of researchers from the University of California, San Francisco; Kaiser Permanente Bernard J. Tyson School of Medicine; St. Jude Children’s Research Hospital; Memorial Sloan Kettering Cancer Center; and Jasper Therapeutics Inc.
The research received crucial funding from anonymous donors, the California Institute of Regenerative Medicine, and the Fanconi Cancer Foundation. Jasper Therapeutics generously provided the briquilimab antibody, and the Stanford Clinical Trial Program was instrumental in supporting the study’s implementation.
The development of this antibody therapy signifies a monumental shift in stem cell transplantation, offering a beacon of hope for patients who were previously limited by the toxicities of conventional treatments. By minimizing harm and expanding donor options, Stanford Medicine is charting a course toward a future where life-saving transplants are more accessible and less burdensome for those in need.