Pathologists Anticipate Evolving Role Using Allogeneic Cell Therapies

Cell therapies continue to rise in usage across the cancer landscape, with chimeric antigen receptor (CAR) T-cell therapies, mesenchymal stem cell therapies, natural killer cell therapies, and tumor-infiltrating lymphocytes falling under this umbrella. Autologous CAR T-cell therapies derived from patients through leukapheresis have proven effective in hematologic malignancies, but limitations in this model have led to trials pursuing allogeneic CARs as well as other allogeneic cell therapies (ACTs) that have shown a great deal of promise.

As with bone marrow and hematopoietic cell transplantation (HCT), there are benefits and limitations with autologous and allogeneic approaches. With research into ACTs, though, more efforts have been made to overcome the limitations of relying on donor-derived cells.

“When you think about ACTs, we’re really talking about the next evolution of cells becoming drugs, this concept that you can potentially select a donor or multiple donors to create more of a characterized product,” said Matthew Anderson, MD, PhD, a pathologist and executive vice president/chief medical officer at Versiti/Medical Sciences Institute, in an interview with Targeted Oncology.

Anderson and other experts from the College of American Pathologists published an article discussing the potential challenges in their field as oncologists conduct trials and start prescribing ACTs in their practice.¹ They proposed that new biomarkers could be needed and suggested that improving collaboration and communication between pathologists and oncologists will be crucial with a new class of therapy with its own needs.

Comparing ACTs With Allogeneic HCT

Drawing from existing knowledge about traditional HCT can be a starting point for understanding ACTs, Anderson suggested. “If you think about traditional HCT, there are decades of literature on matching unrelated donors to recipients, and we can leverage that knowledge and expertise and apply it to this new area of ACTs,” he said.

Anderson noted that from a pathology perspective, he was concerned with the potential for a recipient of ACTs to have preexisting immune response to a third-party cell like an ACT. “We’d want to understand that, because we wouldn’t want to infuse an ACT into a patient that’s sensitized and could reject that drug, so you wouldn’t have any efficacy.”

He also anticipated that if patients receive an ACT early in the course of treatment, it could in theory affect their ability to receive traditional allogeneic HCT in later lines, making it important to monitor for allosensitization in those patients in the future.

Hematologic oncologists are familiar with histocompatibility matching, allosensitization, and the risk of graft-vs-host disease (GVHD) from HCTs. Many ACTs in development are directly addressing these problems preclinically by using gene alteration of donor cells, whereas some types of ACTs avoid histocompatibility issues based on the cell type employed. The first ACT approved in the United States, remestemcel-L (Ryoncil), is a treatment for acute GVHD using bone marrow–derived mesenchymal stromal cells. The donor-derived cells used in this therapy are nonhematopoietic cells that are negative for major histocompatibility complex class II molecules, which differentiate them from allogeneic bone marrow cells given in HCT.²

Anderson predicted that as ACTs become more common in clinical practice, pathologists may have to adjust their current state of testing to be more specific for these cell therapies and the genetic changes that they have. In cases where ACTs have been modified to be less immunogenic, he said that pathologists also need to gain a better understanding of the modification approaches such as lack of expression for human leukocyte antigen, so they know what to expect.

ACTs Advancing Through Clinical Trials

With approximately 500 different ACTs currently in preclinical or early phase clinical trials,¹ it is hard to predict where their impact will be felt most. A key area of investigation is allogeneic CAR T-cell therapy. Autologous CAR products are limited by the time, logistics, and expense of customizing them for each patient. Off-the-shelf CARs could be given much more easily, provided donor-derived products can achieve comparable efficacy and safety to those using the patient’s own cells.

Cemacabtagene ansegedleucel (cema-cel; formerly ALLO-501/A) is one of the most promising allogeneic CAR products in patients with large B-cell lymphoma (LBCL). Using a transcription activator-like effector nuclease–mediated knockout of several genes, it was designed to enable the use of donor cells compatible with any recipient, as well as removing the T-cell receptor to prevent GVHD. In the single-arm phase 1/2 ALPHA2 clinical trial (NCT04416984), it showed encouraging safety outcomes with no GVHD reported, as well as an overall response rate of 58% in patients with relapsed/refractory disease.³

The ongoing pivotal phase 2 ALPHA3 trial (NCT06500273) is enrolling patients who received frontline chemoimmunotherapy for LBCL and achieved remission but have detectable minimal residual disease (MRD) based on the high-sensitivity Foresight CLARITY platform. These patients are randomly assigned to receive cema-cel as consolidation vs observation. With a further randomization of those receiving cema-cel, investigators are assessing whether patients given the anti-CD52 antibody ALLO-647 as part of their lymphodepletion regimen will have better outcomes for CAR T-cell expansion vs standard lymphodepletion.

“Can we take these people who are likely to relapse and prevent relapse by administering this therapy when they’re in a low-MRD state?” asked John M. Burke, MD, a hematologic oncologist at Rocky Mountain Cancer Centers, in an interview with Targeted Oncology. “The hope is that this will, by eliminating that residual disease, prevent them from having a relapse and having to get a conventional autologous CAR T-cell product.”

Burke, who is an investigator on the ALPHA3 trial, said he is able to give cema-cel to patients in a community setting. “The toxicity appears to be less than what is seen with an autologous CAR,” he said, citing how no grade 3 or higher cytokine release syndrome (CRS) and no any-grade immune effector cell–associated neurotoxicity syndrome (ICANS) were reported in the phase 1 ALPHA (NCT03939026) and ALPHA2 trials.³

“It can be delivered in the outpatient setting,” said Burke. “I’m in community practice, and I don’t even give autologous CAR T-cell therapy, and yet I can deliver this product. We need to prove that it can be safely delivered in practices like mine.”

Potential Roles for ACT Biomarkers

As cema-cel and many other ACT products are being developed independently from one another, it is challenging to pinpoint which types of biomarkers will rise to prominence in assessing key aspects of their efficacy and safety in trials and in clinical practice. Monitoring T-cell engraftment, persistence, and exhaustion are key methods of determining that investigational CAR T-cell therapies are functioning as expected. Additionally, biomarkers that can predict safety outcomes like occurrence of CRS, ICANS, and long-term interactions have an important role given the diversity and potential inconsistency from cell therapies. Anderson and his coauthors identified a need for novel flow cytometry and immunohistochemistry assays, plus evaluation of the tumor microenvironment to effectively characterize the activity of ACTs.

“We in our committee, as part of the College of American Pathologists, are very interested in looking forward and trying to see what are the new therapeutic approaches that are being developed, so that we can start to educate the lab community more broadly and say this is coming,” said Anderson.

Awareness in the pathology field is crucial as monitoring cell therapies requires the coordination of different pathology subspecialties such as histocompatibility, flow cytometry, and molecular analysis. “The exciting part is the synthesis of laboratory medicine around this emerging area of medicine. It’s going to force that collaborative approach, which is what I’m personally excited about,” Anderson said.

Fabienne Lucas, MD, assistant professor at the University of Washington Department of Laboratory Medicine and Pathology in Seattle, who coauthored the College of American Pathologists’ article, said in an interview that due to the newness of these therapies, information that can guide pathologists on diagnostics and monitoring is lacking. “We know the use cases, or we can anticipate the problems, but it’s not yet fully reflected in in the literature,” she said.

“Pathologists hold this very unique position as stewarding [novel agents] and also being in very close communication with manufacturers and with the providers. This is something that is very unique to the diagnostic physician as part of the care team,” Lucas explained.

Communication and Collaborative Efforts

As oncologists and their patients enter the era of ACTs, Anderson and Lucas hope to see more sharing between developers of cell therapies, treating physicians, and pathologists. Anderson said his laboratory has sometimes been called to support clinical trials of ACTs operating nearby, but without full information about the trial design and agent, leaving gaps in the pathologist’s ability to gain experience and contribute their expertise.

“We’re typically using the tools that we have our at our disposal today to help out in these patient situations as part of these clinical trials,” Anderson said. “We look forward to having more consistency and knowledge and develop more standardized approaches for biomarkers in this space as these trials progress.”

As an example of the issues faced by pathologists with new therapies, Lucas brought up how prior immune-targeted therapies have made MRD flow interpretation more challenging by altering antigen expression in unexpected ways. In some cases, she said this led to additional unnecessary workup and anxiety for the patient that could have been avoided with better communication between the manufacturer, oncologist, and pathologist about the type of therapy being given. With the introduction of a new type of cell therapy that could produce biochemical interactions such as expansions of certain cell types or unexpected immune profiles, developing clear standards for use is essential.

“It starts with collaborative cross-communication, even in terms of participating in trials: understanding who is on these trials and what the agent is on the trial. Getting the laboratory involved early in those discussions, so we’re aware of those patients, and having knowledge of what they’re receiving helps immensely,” Anderson added.

Working with pharmaceutical companies more directly is another way they see potential to collaborate, Anderson said. He noted that regulator feedback provided to companies on which tests they require for trials and why isn’t always made public. More direct engagement from the developers of cell therapies could help disseminate the guidance to pathologists.

“The earlier that we’re able to get involved, we anticipate, the better it is for getting these cell therapies widely used, and that’s what we all want,” Anderson concluded. “At the end of the day, we see the potential of this. It’s important for patient access that we’re part of this as it gets developed, so we can help with our expertise to guide that development and make sure that…when there’s lots of these ACTs available for patient care, when they’re ready, we have the right testing and it’s available.”

REFERENCES:

1. Lucas F, Anderson M, Gandhi M, Mathur G, Zou J. Allogeneic cellular therapy – diagnostic challenges and opportunities for laboratory practice. College of American Pathologists. April 9, 2025. Accessed June 26, 2025. https://tinyurl.com/4faxx5ea

2. Kurtzberg J, Abdel-Azim H, Carpenter P, et al; MSB-GVHD001/002 Study Group. A phase 3, single-arm, prospective study of remestemcel-L, ex vivo culture-expanded adult human mesenchymal stromal cells for the treatment of pediatric patients who failed to respond to steroid treatment for acute graft-versus-host disease. Biol Blood Marrow Transplant. 2020;26(5):845-854. doi:10.1016/j.bbmt.2020.01.018

3. Locke FL, Munoz JL, Tees MT, et al. Allogeneic chimeric antigen receptor T-cell products cemacabtagene ansegedleucel/ALLO-501 in relapsed/refractory large B-cell lymphoma: phase I experience from the ALPHA2/ALPHA clinical studies. J Clin Oncol. 2025;43(14):1695-1705. doi:10.1200/JCO-24-01933