Expert Q&A: How Is TCRαβ-Depleted Transplantation Different from Conventional HSCT, and How Do You Choose?

Summary: In this Q&A, Dr. Huaying LIU of GoBroad Chunfu Institute of Hematology & Oncology answers common questions about TCRαβ+ T-cell-depleted hematopoietic stem cell transplantation (TDH). She explains how TDH differs from the Beijing protocol, which uses ATG for in vivo T-cell depletion, and the post-transplant cyclophosphamide (PTCy) approach. TDH instead uses ex vivo immunomagnetic separation to selectively deplete αβ T cells while preserving beneficial immune cells such as γδ T cells and natural killer (NK) cells. The article also discusses potential advantages such as a lower risk of graft-versus-host disease (GVHD), reduced need for routine post-transplant immunosuppression, and earlier hematopoietic recovery, as well as strategies used to reduce relapse risk, including pre-transplant CAR-T therapy, donor lymphocyte infusion (DLI), and targeted maintenance treatment.

TCRαβ+ T-cell-depleted hematopoietic stem cell transplantation (TDH) is one of the major approaches to haploidentical transplantation and is designed to reduce the risk of graft-versus-host disease (GVHD). To address questions commonly raised by patients and families, Dr. Huaying LIU of GoBroad Chunfu Institute of Hematology & Oncology explains the key issues in a Q&A format.

Q1: A 3-year-old girl was diagnosed with high-risk B-cell acute lymphoblastic leukemia (B-ALL) in late August 2025 and is now in consolidation therapy under the SCCG-ALL-2023 high-risk protocol. Her high-risk features include NF1 and MYC mutations, p16 deletion, severe hypodiploidy (only about 26 chromosomes), and CNS3 involvement at diagnosis. Her treatment response has been very good: flow cytometry was negative by day 33 and the CNS leukemia cleared. With this combination of very high-risk genetics but a strong early treatment response, is transplantation still necessary? If MRD remains negative, could chemotherapy alone be sufficient? How do these risk factors affect long-term survival, and what are the most important decision points going forward?

Dr. Huaying Liu: Regardless of the pediatric ALL cooperative-group protocol being used, the basic treatment principle is similar: therapy is guided by risk stratification. Risk groups are defined using clinical, cytogenetic, and molecular features that are widely recognized as being closely related to prognosis, together with treatment-response indicators such as measurable residual disease (MRD).

Although this child has responded well so far, transplantation would still be the preferred option because of the prognostic significance of her high-risk features. The exact transplant strategy may differ between centers. If transplantation cannot be performed immediately for practical or clinical reasons, bone marrow MRD should be monitored closely during subsequent chemotherapy, particularly molecular and cytogenetic markers. If a marker converts from negative to positive, treatment should be adjusted promptly. Immunotherapy may be considered when appropriate, with the goal of restoring bone marrow MRD or molecular negativity before proceeding to transplantation as early as possible.

Q2: How does T-cell-depleted transplantation differ from conventional transplantation? When might TDH be considered, and what are its potential advantages?

Dr. Huaying Liu: TDH has been used extensively in Europe and the United States, and GoBroad Chunfu Institute of Hematology & Oncology has accumulated substantial experience with this approach in China. During hematopoietic stem cell transplantation, three of the major concerns for both doctors and patients are infection, graft-versus-host disease (GVHD), and relapse, especially in malignant hematologic diseases. Historically, fully matched donors were often preferred. Subsequent clinical experience has shown that haploidentical transplantation may provide a stronger graft-versus-leukemia effect in some hematologic malignancies. At the same time, haploidentical transplantation can carry higher risks, and both acute and chronic GVHD can affect quality of life, increase the risk of infection and other complications, and in severe cases become life-threatening.

There are currently three major approaches to haploidentical transplantation. The first is the Beijing protocol, which uses antithymocyte globulin (ATG) during conditioning for in vivo T-cell depletion. The second is the post-transplant cyclophosphamide (PTCy) approach, in which cyclophosphamide is given three to four days after stem cell infusion to eliminate alloreactive T cells in vivo. The third is TDH. Before the graft is infused, immunomagnetic separation is used ex vivo to remove the αβ T cells most responsible for GVHD while preserving a graft rich in CD34+ hematopoietic stem cells, γδ T cells, NK cells, monocytes, and other components.

After infusion, these retained cells can support faster hematopoietic recovery and contribute to anti-infective and antitumor immunity. Patients receiving TDH do not routinely require immunosuppressive medication for GVHD prophylaxis. Whether TDH is appropriate for an individual patient still depends on a comprehensive assessment of disease type, overall health, genetic background, tumor burden, and other clinical factors.

Q3: Compared with conventional transplantation, would a child usually spend more or less time in the hospital and in protective isolation? Does the overall treatment experience feel very different?

Dr. Huaying Liu: Conventional transplantation includes both fully matched and haploidentical approaches. For malignant hematologic diseases, our transplant strategy also takes post-transplant relapse risk into account when selecting the donor and platform. Compared with other haploidentical approaches, TDH is associated in our experience with relatively early neutrophil and megakaryocyte engraftment, a shorter period of severe neutropenia, and a lower infection risk.

Earlier platelet engraftment may also reduce bleeding risk and the need for blood product transfusions, which can shorten the time a child needs to remain in the transplant unit. One of the biggest differences between TDH and many other transplant approaches is that routine post-transplant immunosuppressive therapy is generally not required. After leaving protective isolation, children therefore take fewer oral medications and do not need regular outpatient blood tests to monitor immunosuppressant drug levels and adjust dosing.

Q4: What T-cell-depletion method does your center use? Are the stem cells processed outside the body, or are medications given to the child to remove T cells?

Dr. Huaying Liu: Our TDH approach uses ex vivo T-cell depletion. We selectively remove αβ T cells from the mobilized hematopoietic stem cell graft before infusion using immunomagnetic separation. This process is performed on the collected stem cell product, so there is no need to give the patient a special medication solely for the purpose of removing these αβ T cells in vivo.

Q5: Some families worry that removing T cells might increase the risk of leukemia relapse. What measures do you use to reduce that risk? For example, are newer drugs or targeted therapies used after transplant, or are planned donor lymphocyte infusions given?

Dr. Huaying Liu: Earlier forms of ex vivo T-cell-depleted transplantation used in China often referred to CD34-positive selection, which is different from the TCRαβ+ T-cell-depletion strategy used at our center. Recent international multicenter transplant data suggest that TCRαβ+ depletion (TDH) does not increase the risk of leukemia relapse compared with other transplant approaches.

Our center's five-year treatment data also show a relatively low relapse risk after TDH. This reflects not only the transplant platform itself, but also the comprehensive treatment strategy we use for leukemia. For each patient, we develop a full-course treatment plan that includes achieving deep MRD remission before transplant, individualizing the transplant strategy, and providing post-transplant consolidation or maintenance treatment when appropriate.

For example, immunotherapies such as blinatumomab or CAR-T may be used before transplant in selected patients. After transplant, targeted drugs may be chosen according to the patient's molecular findings, and scheduled donor lymphocyte infusions (DLI) may also be used as part of maintenance or relapse-prevention strategies. The exact plan depends on factors such as genetic test results and whether a suitable therapeutic target is available. Because routine oral immunosuppressive therapy is not required after TDH, DLI can often be started relatively early. The GVHD risk associated with this approach is generally lower and can be managed closely. At our center, dose-escalated DLI is typically started at a median of around 40 days after transplant.

Q6: Does T-cell-depleted transplantation mean a child will have almost no immune protection for a long time after transplant? How does your center monitor and prevent infections, including viruses such as CMV and EBV?

Dr. Huaying Liu: Hematopoietic stem cell transplantation is fundamentally a process of rebuilding both blood formation and the immune system, so immune recovery takes time after any transplant. The graft used in TDH contains not only large numbers of CD34+ hematopoietic stem cells, but also γδ T cells, NK cells, and other immune components.

After infusion, these cells can support relatively rapid hematopoietic recovery and contribute to infection control. As mentioned earlier, because the GVHD risk is lower after TDH, DLI can be introduced relatively early, and donor lymphocytes themselves can provide adoptive immune support. In addition to DLI, our center can also use memory T-cell infusions. Donor lymphocytes undergo CD45RA depletion so that memory T cells can be collected and cryopreserved, then infused later in gradually increasing doses when needed.

This strategy can be used to help prevent and treat common viral infections after transplant, including CMV and EBV. We also start antiviral prophylaxis early when indicated and monitor viral levels closely - for example, weekly in the early post-transplant period, then every two weeks, and later monthly as appropriate. Antiviral treatment is adjusted promptly based on the results. Cellular infusions can also be used to strengthen antiviral immunity in selected patients.

Q7: If everything goes smoothly, can TDH substantially reduce the risk of severe GVHD? Could that have meaningful long-term benefits for a child's growth and development, including height, learning, and pubertal development?

Dr. Huaying Liu: Yes. Compared with other transplant approaches, TDH is associated with a markedly lower incidence of both acute and chronic GVHD. Reducing GVHD is particularly important for children's long-term growth and development. A lower GVHD rate can substantially reduce the need for immunosuppressive therapy, and prolonged or intensive use of these medications can itself contribute to complications affecting growth, development, endocrine function, and other areas. Chronic GVHD is also an important long-term concern. Dr. Liu also cited a recent retrospective analysis from an Italian transplant team using TDH in children with relapsed/refractory leukemia (R/R ALL/AML): the 10-year GVHD-free, relapse-free survival (GRFS) was 65.1%, and among patients who were MRD-negative before transplant, 10-year disease-free survival (DFS) was 73.6%. Patients transplanted in CR1 or CR2 had better outcomes than those transplanted in CR3.

At last year's American Society of Hematology (ASH) Annual Meeting, a U.S. research team also presented a comparison of TDH and PTCy, reporting better GVHD-free, relapse-free survival (GRFS) with TDH. Our center also presented a poster at ASH last year on TDH for pediatric relapsed/refractory ALL. The two-year overall survival (OS) was 90.1%, and two-year leukemia-free survival (LFS) was 83.2%. Among patients who received TDH after CAR-T therapy, two-year OS was 90.8%, two-year LFS was 87.3%, and the relapse rate was 3.6%. The main causes of treatment failure remained relapse and infection. Our team continues to refine the strategy in an effort to further reduce both risks.

Q8: After TDH, approximately how long does immune recovery take before a child can return to school and resume more normal contact with the outside world?

Dr. Huaying Liu: Immune recovery after transplantation is complex and dynamic and involves the reconstitution of multiple immune-cell subsets. Post-transplant complications such as GVHD and infections, including CMV, as well as the use of immunosuppressive medications, can delay immune recovery. Immune function should be monitored regularly - often monthly early on, with the interval gradually extended to every three months, every six months, and eventually once a year depending on the patient's recovery.

Patients receiving TDH often achieve hematopoietic recovery relatively early. Because GVHD rates are lower and routine oral immunosuppressive therapy is generally not needed, memory T-cell infusions or dose-escalated DLI can be used earlier when appropriate to provide adoptive immune support. Patients whose B-cell function has not yet recovered may also receive immunoglobulin replacement when indicated. In many patients, immune function gradually recovers over approximately the first year after transplant. Once immune reconstitution is adequate, the child may be able to return to school and resume broader contact with the outside environment, based on the medical team's assessment.