Department of Pediatrics, University of Ulsan College of Medicine, Asan Medical Center Children's Hospital, Seoul, Korea.
Allogeneic hematopoietic stem cell transplantation (HSCT) is a curative treatment for children and adolescents with various malignant and non-malignant diseases. While human leukocyte antigen (HLA)-identical sibling donor is the preferred choice, matched unrelated volunteer donor is another realistic option for successful HSCT. Unfortunately, it is not always possible to find a HLA-matched donor for patients requiring HSCT, leading to a considerable number of deaths of patients without undergoing transplantation. Alternatively, allogeneic HSCT from haploidentical family members could provide donors for virtually all patients who need HSCT. Although the early attempts at allogeneic HSCT from haploidentical family donor (HFD) were disappointing, recent advances in the effective
Allogeneic hematopoietic stem cell transplantation (HSCT) is a potentially curative treatment for children and adolescents with various malignant and non-malignant diseases. Recent progress in HSCT contributed to the improvement of outcomes for patients with diseases curable by HSCT. While human leukocyte antigen (HLA)-identical sibling donor is the preferred choice, HLA-matched unrelated volunteer donor is also a realistic option for successful HSCT. However, it is not always possible to find a HLA-matched donor for patients requiring HSCT, leading to a considerable number of deaths of patients without undergoing transplantation. The need for alternative donors has driven the development of new transplantation approaches such as transplants from HLA-haploidentical family members or umbilical cord blood.
Recent advances in the effective
Here, we review the major advances in haploidentical HSCT, focusing on the
HSCT from HFD has several advantages (Table 1): 1) virtually all patients who need HSCT can find a donor; 2) transplantation could be performed without delay, which is critical to patients with high-risk malignant disease or very severe aplastic anemia requiring urgent treatment; 3) further access to the donor for cellular therapy to treat relapse or infection or for additional transplantations is easy. In addition, HFD could rescue the patients who experienced early graft failure (GF) which is a life-threatening complication requiring prompt intervention after allogeneic HSCT .
Even though haploidentical HSCT seemed to be an attractive procedure with the added benefit of readily available donors, the early attempts at haploidentical HSCT from genetically haploidentical family members were disappointing due to the development of refractory graft-versus-host disease (GVHD) and excessively high transplant-related mortality (TRM) . A high rate of graft rejection (GR) and refractory GVHD were major drawbacks to the use of haploidentical HSCT for patients who required transplantation but lacked a suitable donor. In addition, delayed immune recovery and a high prevalence of infections were significant obstacles. Several initial trials revealed that haploidentical HSCTs had a considerably high incidence of GF and GVHD, resulting in high rates of morbidity and mortality .
T cell depletion of donor grafts to prevent fatal GVHD is crucial for successful haploidentical HSCT. The methods for T cell depletion (TCD) could be
The concept of direct depletion of T cells using an anti-CD3 monoclonal antibody with microbeads was introduced in early 2000 . Previous studies that used megadoses of CD34+ stem cells have found promising results with rapid engraftment as a possible alternative for children lacking suitable matched donors . However, haploidentical HSCTs using CD34-selected stem cells were complicated by a high rate of opportunistic infections likely related to delayed immune recovery. To overcome the limitation of CD34+ selection, a method for the negative depletion of T cells was developed. This provided T-cell-depleted grafts containing not only CD34+ stem cells, but also large numbers of NK cells and other effector cells, which were expected to reduce the risk of engraftment failure and facilitate immune reconstitution. There have been several reports on HHCT using CD3-depleted grafts in pediatric patients .
An early experiment using CD3 antibody conjugated to magnetic microbeads showed that T cells were effectively depleted with a mean log depletion of 3.4 with 82% mean recovery of CD34+ stem cells . This result suggested that a direct negative T-cell depletion method could effectively remove the CD3+ cells responsible for GVHD without negatively affecting the functions of the hematopoietic stem cells. The first published study for the clinical application of CD3-depleted grafts enrolled 22 pediatric patients with refractory hematological malignancies . Reduced-intensity conditioning (RIC) regimen consisting of fludarabine, thiotepa, melphalan and OKT3 without total body irradiation (TBI) was employed to reduce TRM. Since T-cell depletion was one of the well-established risk factors for the development of post-transplant lymphoproliferative disorder (PTLD),
With the introduction of clinically available anti-CD19 antibody, a simultaneous
In a study of 46 pediatric patients with acute leukemia and MDS, primary engraftment was achieved in 88% of the patients, and engraftment after salvage transplantation was obtained in 100% of the patients . Grade II acute GVDH and grade III-IV acute GVHD and chronic GVHD developed in 20% and 7%, and 21% of the patients, respectively. TRM was 8% at one year and 20% at 5 years. The 3-year event-free survival (EFS) was favorable (46%) for patients who were in complete remission (CR) when receiving the first haploidentical HSCT, whereas patients with leukemia and were not in CR at the time of transplantation or have received a subsequent HSCT had significantly higher risks of relapse (75% and 88%, respectively). This study showed that haploidentical HSCT using CD3/CD19-depleted allograft is a feasible treatment with low GVHD and low TRM, although the outcomes for patients with active diseases still need to be improved.
Many other studies showed that CD3/CD19 depletion could induce excellent primary engraftment rates, ranging from 83% to 100%, with acceptable GVHD and low TRM, and the survival outcomes were comparable to those of conventional HSCT .
Although donor T cells have anti-infectious and anti-tumor properties, they are responsible for GVHD in allogeneic HSCT. Gammadelta (γδ) T cells are a subset of T cells that account for 1–10% of the circulating peripheral blood T lymphocytes that express the γδ T cell receptors (TCRs) . The recently introduced method of negative depletion of αβ+ T cell is an effective strategy to dissect graft-versus-tumor effect and anti-infectious activities from GVHD. The γδ+ T cells are a small subset of T cells which can elicit both innate and adaptive immune responses to tumors and infections, while αβ+ T cells, a major subset of T cells, are the main inducers of GVHD . This manipulation removes αβ+ T cells and preserves NK cells and γδ+ T cells, which are expected to have activities against tumor and infections, thus improving the outcome of haploidentical HSCT. Although several studies have suggested beneficial roles of γδ T cells in the context of hematopoietic cell transplantation, reports of clinical experiences are still limited .
A German group reported promising results of TCRαβ/CD19-depleted haploidentical HSCT . In 41 patients with acute leukemia, MDS, solid tumors and nonmalignant disease, primary engraftment occurred in 88% of the patients. Acute GVHD grade II, III-IV, and extensive chronic GVHD were observed in 10% and 15%, and 9%, respectively. Compared with CD34+ selected haploidentical HSCT, recovery of CD3+, CD3+4+, and CD56+ cells were significantly faster with this method. Patients with leukemia and MDS who received a first haploidentical HSCT in CR1 showed a 1-year EFS of 100%, whereas no patient with active diseases survived. Owing to a short follow-up period, the clinical impact of this accelerated immune recovery remains to be clarified.
An Italian research group also reported rapid TCRγδ+ T cell reconstitution in 27 children with malignant and nonmalignant diseases after TCRαβ/CD19-depleted haploidentical HSCT . Circulating γδ+ T cells are comprised of a major subset expressing the Vδ2 chain and a minor subset expressing the Vδ1 chain. They demonstrated prompt reconstitution of Vδ1 and Vδ2 T cells post-transplantation, and showed expansion of Vδ2 cells
In a study of 22 children with nonmalignant disorders such as severe combined immunodeficiency (SCID), severe aplastic anemia (SAA), Fanconi anemia, other bone marrow failure syndrome, and immunodeficiencies, TCRαβ/CD19-depleted haploidentical HSCT showed promising outcome with favorable engraftment rates (80%), low incidence of GVHD (no visceral or chronic GVHD), and low TRM (9.3%) .
Recent studies demonstrated that αβ-depleted haploidentical HSCT is an attractive treatment option that can allow stable engraftment and has low toxicity profiles for children who lack suitable donors. Future studies should investigate whether rapid reconstitution of γδ+ T cells can translate into improved patient outcome by reducing both TRM and relapse.
Since 2008, haploidentical HSCT using
Between July 2008 and January 2013, 28 children underwent haploidentical HSCT using
Our trials with CD3-depleted haploidentical HSCT showed a rather higher incidence of GF in the early period of the study; therefore low-dose TBI (LD-TBI) was added to the conditioning regimen in an attempt to decrease GF. In addition, we modified the targeted dose of T cells by add-back of T cells from negative selection product in various ranges to improve the outcomes. Initially, targeting the infused CD3+ cell dose at 1-6×106/kg with the use of post-transplant immunosuppressants seemed to be associated with a higher incidence of severe acute GVHD and extensive chronic GVHD. A reduction of T cell dose to around 6-8×105 CD3+ cells/kg decreased the incidence of severe GVHD without increasing the incidence of GF.
Based on our previous results with CD3-depleted grafts, our recent study used αβ+ T cell-depleted grafts with a targeted dose of αβ+ cells at 1-5×105/kg by add-back of αβ+ T cells from the negative selection product after a uniform RIC with fludarabine, cyclophosphamide, r-ATG, and LD-TBI. Forty-two children and adolescents (31 with HM, 8 with NM, and 3 with solid tumors) underwent transplantations using αβ+ T cell-depleted grafts with a target of 1-5×105 αβ+ cells/kg and post-transplant immunosuppressants of tacrolimus and mycophenolate mofetil (MMF). All 42 patients achieved neutrophil engraftment at a median of 10 days (range, 9–17 d). The CIs of ≥grade II and ≥grade III acute GVHD were 31% and 12%, respectively, and the 1-year CI of chronic GVHD was 15%. One patient died of cytomegalovirus pneumonia, resulting in a TRM of 2.6%. Sixteen patients relapsed, and 11 died of disease. At a median follow-up of 19 months (range, 5–43 mo), the estimated two-year EFS for NM and HM were 88% and 50%, respectively. Our study demonstrated that haploidentical HSCT after
Pharmacologic prevention using immune-suppressive drugs such as calcineurin inhibitors, methotrexate and MMF, commonly in combination, is routine practice after the infusion of stem cells. Although advances in immunosuppressants have effectively prevented the development of acute GVHD, there are many serious toxic side effects and drug interactions requiring serial blood level monitoring . Our targeted and ranged T cell dose-strategy improved the outcomes of
Forty-six patients with HM received
Several notable reports in recent years have supported haploidentical transplant as a viable option for the treatment of acquired SAA . In our center, 25 pediatric patients with acquired SAA received haploidentical HSCT (16 with CD3-depleted graft and 9 with αβ-depleted graft) between July 2009 and January 2016. Of the 25 patients, one patient experienced primary GF and four experienced GR. All five of these patients received CD3-depleted graft and achieved sustained engraftment after salvage transplantation. Eight of the 25 patients developed acute GVHD ≥grade II (six grade II and two grade III), leading to a CI of 32%. Twenty-three of the patients survived and were transfusion-independent. At a median follow up of 40 months (range, 1–80 mo), estimated OS at 3 years was 91%. HSCT from HFD with
The recent emerging evidences for haploidentical HSCT has provided additional therapeutic options for pediatric patients with malignant and non-malignant diseases curable with HSCT but do not have a suitable related or unrelated donor. In spite of the promising results for haploidentical HSCT in pediatric patients, there are still several obstacles to overcome. Although our targeted and ranged T cell dose-strategy improved the outcomes of
Haploidentical HSCT using
Major progress in
Current haploidentical HSCT strategy for pediatric patients at AMCCH. The donor will receive G-CSF for a minimum of four consecutive days and peripheral blood mononuclear cells (PBMCs) will be collected on days -1 and 0. The αβ+ T cells will be depleted by negative depletion using the CliniMACS system (Miltenyi-BioTec, Bergisch-Gladbach, Germany). The final dose of αβ+ T cells is targeted ≤5×104/kg by adding back αβ+ T cells from the negative selection product. The patient will receive conditioning regimen consisting of fludarabine (FLU), cyclophosphamide (CY), rabbit ATG (r-ATG), and low-dose total body irradiation (LD-TBI). After that, stem cells will be infused on day 0 without any post-transplant immunosuppressants. The patient will also receive rituximab post-transplant to deplete B cells at approximately day +28 or earlier if EBV was detected with PCR. For cytomegalovirus (CMV) prophylaxis, the CMV-seropositive patient will receive ganciclovir prior to transplant and foscarnet after transplantation up until engraftment. After engraftment, ganciclovir or valganciclovir will be administered until 100 days post-transplantation with CD4+ cells at >100/µL.
Abbreviations: HSC, hematopoietic stem cells; αβ, αβ+ T cells; γδ, γδ+ T cells; DC, dendritic cells; B, B cells; HR, high-risk.