For patients battling the most aggressive forms of blood cancer, a stem cell transplant often represents the final frontier of treatment\u2014a procedure with the potential to offer a life-saving cure when all other options have been exhausted. Yet, the medical community has long grappled with a persistent and sobering reality: these cancers frequently return following transplantation, leaving oncologists with a shrinking arsenal of effective secondary therapies. Now, a groundbreaking clinical trial led by researchers at the Washington University School of Medicine in St. Louis suggests a sophisticated new way forward. By genetically modifying donor stem cells before they are ever introduced into a patient, scientists believe they can make follow-up cancer treatments significantly safer and far more effective.<\/p>\n
The strategy hinges on a precise biological intervention: removing a specific protein from donor stem cells. By doing so, doctors create a \u201cshielded\u201d population of healthy blood cells that remain invisible to targeted immunotherapies. This allows clinicians to unleash powerful treatments aimed at that specific protein to hunt down residual cancer cells without inadvertently destroying the healthy, transplanted blood system that the patient relies on to survive.<\/p>\n
The study, which was conducted at Siteman Cancer Center at Barnes-Jewish Hospital and Washington University School of Medicine, along with 14 other clinical sites across the United States and Canada, has yielded results that are now sparking optimism in the oncology field. The findings were recently published in the journal Nature Medicine<\/em>.<\/p>\n According to Dr. John F. DiPersio, the Virginia E. & Sam J. Golman Professor of Medicine at Washington University and the study\u2019s corresponding author, this gene-editing approach addresses a fundamental obstacle that has historically hindered the progress of chimeric antigen receptor (CAR-T) cell therapy in certain blood cancers. While CAR-T therapy\u2014a process where a patient\u2019s own immune cells are re-engineered to recognize and kill cancer\u2014has achieved remarkable success in treating several types of blood malignancy, its utility has been notably limited when applied to diseases such as acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS).<\/p>\n The core of the problem lies in target identification. Many of the proteins expressed on the surface of AML and MDS cancer cells are not unique to the disease; they are also found on the surface of healthy myeloid cells, including the vital donor stem cells used in transplantation. When CAR-T cells are programmed to attack these shared proteins, they effectively become indiscriminate, destroying the healthy blood-forming stem cells alongside the malignant ones.<\/p>\n This unintended collateral damage creates two critical complications. First, it triggers a dangerous inflammatory response within the patient\u2019s body. Second, it fundamentally undermines the efficacy of the cancer treatment itself. Because a large proportion of the CAR-T cells are diverted to attack healthy targets, their concentration and ability to focus on the malignant cells are significantly diminished.<\/p>\n The conceptual framework for bypassing this bottleneck was first articulated by Dr. Miriam Y. Kim, currently an assistant professor of medicine at Washington University. Dr. Kim initiated this line of inquiry during her time as a postdoctoral researcher at the University of Pennsylvania and continued the work within the DiPersio lab before establishing herself as an independent investigator in the university\u2019s Division of Oncology. As a clinician at Siteman Cancer Center, she brings both a scientific and patient-centered perspective to the research.<\/p>\n In the clinical trial, researchers focused on a specific protein called CD33. Patients diagnosed with high-risk AML and MDS were treated with donor stem cells that had undergone CRISPR gene editing to permanently remove the CD33 protein. The ultimate goal was to produce a population of healthy, functional blood cells that would remain completely invulnerable to any therapeutic intervention designed to target CD33.<\/p>\n \u201cWe are encouraged by the results of this study showing that a CD33-deleted stem cell transplant looks very similar to the outcomes of standard stem cell transplantation,\u201d said Dr. DiPersio, who also serves as the director of the Center for Gene and Cellular Immunotherapy at Washington University. \u201cIn the future, we are hopeful we will be able to combine this with CD33-targeted immunotherapies, such as CAR-T cells, and improve treatment options for patients with these very aggressive blood cancers.\u201d<\/p>\n The potential of this approach was further underscored by a recent case report involving a patient with high-risk AML. Following a CD33-deleted stem cell transplant, the patient\u2019s cancer unfortunately returned. However, because their donor cells had been modified, the medical team was able to treat the recurrence with CD33-targeted CAR-T cells derived from the same original donor. The outcome was profound: the patient entered a complete remission and remained cancer-free for more than a year following the CAR-T treatment. Remarkably, the patient\u2019s bone marrow successfully produced a full array of normal blood cells, all of which lacked the CD33 protein, confirming that the engineered cells had successfully engrafted and established long-term residency. This specific case was documented in a study published in JCO Precision Oncology<\/em> in October 2025, with Dr. DiPersio serving as the senior author.<\/p>\n CD33 is an ideal candidate for this type of gene-editing strategy for several biological reasons. First, the protein is expressed almost exclusively on blood-forming cells and is notably absent from other tissues in the body, which minimizes the risk of systemic side effects. Furthermore, scientific evidence suggests that CD33 is not strictly necessary for the normal function of blood stem cells; individuals born with a natural absence of this protein do not appear to suffer from associated health problems, suggesting that its removal is well-tolerated by the human body.<\/p>\n The theoretical advantage is clear: once a patient has received a transplant of CD33-deleted stem cells, any remaining cells in the body that still express CD33 are, by definition, likely to be cancerous. This provides a clear "target" for immunotherapies. A CAR-T therapy or other antibody-based treatment can then be deployed to aggressively eliminate those specific cells while leaving the healthy, donor-derived blood system completely intact.<\/p>\n The phase 1\/2 multicenter trial enrolled 30 adult patients with AML or MDS who were categorized as having a high risk of relapse. Before the transplant procedure took place, the donor stem cells were modified using CRISPR technology to excise the CD33 protein. The resulting therapeutic product, known as tremtelectogene empogeditemcel (or "trem-cel"), was developed by Vor Biopharma, which also provided the funding for the study.<\/p>\n To evaluate whether the gene-edited stem cells could survive in the presence of a CD33-targeted agent, the trial participants received a maintenance treatment post-transplantation. The researchers utilized an engineered antibody called gemtuzumab ozogamicin, which recognizes CD33 and delivers a potent anti-cancer drug directly to cells expressing that protein.<\/p>\n While gemtuzumab ozogamicin is already FDA-approved for certain CD33-positive AML cases, its clinical utility is often hampered by significant side effects, including liver toxicity and the destruction of healthy blood cells, which can lead to dangerously low counts of white blood cells, red blood cells, and platelets. By using the gene-edited "shielded" stem cells, the researchers aimed to decouple the drug’s anti-cancer activity from its toxic impact on healthy blood production.<\/p>\n The results regarding the engraftment of these cells were highly promising. All 30 patients achieved successful engraftment by day 28, meaning the transplanted cells reached the bone marrow and began the vital process of hematopoiesis. Some patients achieved this milestone even earlier, with platelet production returning by day 16 on average. These recovery timelines are consistent with those observed in patients undergoing standard, non-edited stem cell transplants.<\/p>\n The average survival rate for participants in the trial was just over 14 months. Nineteen patients received at least one cycle of gemtuzumab ozogamicin as part of a dose-escalation protocol, which allowed the team to establish a safe and effective dose. Across these varying dose levels, patients were able to maintain stable blood cell counts\u2014a striking difference from the severe blood cell depletion typically associated with this maintenance therapy.<\/p>\n The safety profile of the procedure was largely in line with what is expected of standard stem cell transplantation. Common side effects included anemia, low platelet counts, fever, infections, and graft-versus-host disease, where donor cells recognize the recipient’s tissues as foreign. During the course of the study, seven patients passed away. Four of these deaths were attributed to the progression of their underlying cancer, while three were linked to complications stemming from the transplant procedure, such as sepsis, liver toxicity, or kidney failure.<\/p>\n Despite these challenges, Dr. DiPersio emphasized that the data establishes a strong foundation for future clinical applications. The ultimate goal is to enable a new paradigm in cancer care: one where clinicians can employ significantly more aggressive immunotherapeutic interventions without the fear of destroying the very blood system they are working to rebuild. As researchers look to the future, this strategy of "shielding" healthy cells through gene editing may prove to be a transformative tool in the ongoing effort to turn once-incurable blood cancers into manageable or curable conditions.<\/p>\n","protected":false},"excerpt":{"rendered":" For patients battling the most aggressive forms of blood cancer, a stem cell transplant often represents the final frontier of treatment\u2014a procedure with the potential to offer a life-saving cure when all other options have been exhausted. Yet, the medical community has long grappled with a persistent and sobering reality: these cancers frequently return following […]<\/p>\n","protected":false},"author":1,"featured_media":1461,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[370],"tags":[1783,1168,2683,2682,2681,2687,61,2686,2685,371,509,372,2671,2684],"class_list":["post-1462","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-science-and-nature","tag-barriers","tag-cancer","tag-cell","tag-edited","tag-gene","tag-immunotherapy","tag-nature","tag-overcoming","tag-promise","tag-science","tag-show","tag-space","tag-stem","tag-transplants"],"_links":{"self":[{"href":"https:\/\/xesi.net\/index.php?rest_route=\/wp\/v2\/posts\/1462","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/xesi.net\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/xesi.net\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/xesi.net\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/xesi.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1462"}],"version-history":[{"count":0,"href":"https:\/\/xesi.net\/index.php?rest_route=\/wp\/v2\/posts\/1462\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/xesi.net\/index.php?rest_route=\/wp\/v2\/media\/1461"}],"wp:attachment":[{"href":"https:\/\/xesi.net\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1462"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/xesi.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1462"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/xesi.net\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1462"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}A Major Challenge for CAR-T Therapy<\/h3>\n
Removing CD33 From Healthy Stem Cells<\/h3>\n
Shielding Healthy Blood Cells<\/h3>\n
Testing a CD33-Targeted Cancer Treatment<\/h3>\n
Side Effects Remained Similar to Standard Transplants<\/h3>\n