TCR-alpha/beta and CD19 depletion and treosulfan-based conditioning regimen in unrelated and haploidentical transplantation in children with acute myeloid leukemia

Comprehensive up-to-date analysis on TCRαβ/CD19-depleted hematopoietic stem cell transplantation in pediatric hematological malignancies

This meta-analysis assesses the efficacy of TCRαβ+/CD19+ depleted hematopoietic stem cell transplantation (HSCT) in pediatric patients with hematological malignancies, bridging the gap in the heterogeneous results of published studies. We analyzed post-HSCT complications and survival outcomes in 1068 children across 14 studies, using both aggregated and patient-level data from acute myeloid leukemia/myelodysplastic syndromes (AML/MDS) and acute lymphoblastic leukemia (ALL) studies, employing the IPDfromKM technique for time-to-event data reconstruction. The analysis reveals a 95 % engraftment success rate (95 % CI: 93-97) and 6-year overall survival and disease-free survival (DFS) rates of 67.2 % and 66.3 %, respectively, with no significant differences in DFS between haploidentical and unrelated donors (hazard ratio = 0.9, 95 % CI: 0.53-1.55). Acute graft-versus-host disease (GvHD) grades III-IV and chronic GvHD incidences were 8 % (95 % CI: 6-11) and 17 % (95 % CI: 10-27). The relapse rate was 27 % (95 % CI: 21-33), with relapse-related mortality at 21 % (95 % CI: 15-28) and HSCT-related mortality at 12 % (95 % CI: 7-19). Relapse was significantly lower in patients (mostly ALL) receiving total body irradiation (risk ratio = 0.53, P = 0.04). These findings underscore TCRαβ/CD19-depleted HSCT as a valuable option for patients without HLA-matched donors, highlighting the need for larger, multicenter studies.

The use of haploidentical stem cell transplant as an alternative donor source in patients with decreased access to matched unrelated donors

INTRODUCTION

The likelihood of finding HLA-matched unrelated donors for rare HLA types and non-white European ancestry continues to be a challenge with less than a 70% chance of finding a full match. Mismatched transplants continue to have high rates of transplant-related mortality. With the near-universal ability to find a haploidentical donor in families, haploidentical transplants have become of more critical importance in ethnic minority groups and patients with rare HLA types.

METHODS

Data was collected through clinical trials, review articles, and case reports published in the National Library of Medicine.

RESULTS

The use of improved lymphodepleting conditioning regimens, graft versus host disease (GVHD) prophylaxis using regimens such as post-transplant cyclophosphamide, mycophenolate, and tacrolimus have improved engraftment to nearly 100 percent and reduced transplant-related mortality to less than 20 percent. Attention to donor-specific antibodies (DSAs) with interventions using bortezomib, rituximab, and plasmapheresis has decreased graft failure rates.

CONCLUSION

With improved prevention of GVHD with interventions such as post-transplant cyclophosphamide and management of DSAs, haploidentical transplants continue to improve transplant-related mortality (TRM) compared to patients who received matched-related donor transplants. While TRM continues to improve, ongoing research with haploidentical transplants will focus on improving graft and donor immunosuppression and identifying the best regimens to improve TRM without compromising relapse-free survival.

Impact of Natural Killer Cell-Associated Factors on Acute Leukemia Outcomes after Haploidentical Hematopoietic Stem Cell Transplantation with αβ T Cell Depletion in a Pediatric Cohort

The technique of αβ T cell depletion (αβTCD) is a well-established method of hematopoietic stem cell transplantation (HSCT) for children with acute leukemia owing to the low rates of graft-versus-host disease and nonrelapse mortality (NRM). The graft-versus-leukemia effect is generally ascribed to natural killer (NK) cells conserved within the graft. It is not known whether NK-related factors affect the outcome of αβTCD HSCT, however. The aim of this retrospective study was to explore the impact of NK alloreactivity (based on donor-recipient killer immunoglobulin-like receptor [KIR] mismatch), graft NK cell dose, and blood NK cell recovery on day +30 post-HSCT on the incidences of leukemia relapse and NRM. The pediatric acute leukemia cohort comprised 295 patients who underwent their first HSCT from a haploidentical donor in complete remission. During post hoc analysis, the total cohort was divided into subcohorts by diagnosis (acute lymphoblastic leukemia [ALL]/acute myeloid leukemia [AML]), NK alloreactivity prediction (KIR match/KIR mismatch), graft NK cell dose (less than versus greater than the median value), and blood NK cell recovery on day +30 post-HSCT (less than versus greater than the median value). We also investigated the influence of serotherapy (antithymocyte globulin [ATG] group) versus abatacept + tocilizumab combination [aba+toci] group) on relapse risk in the context of KIR mismatch. The risks of relapse and NRM were calculated by the cumulative risk method, and groups were compared using the Gray test. Multivariate analysis revealed no apparent impact of predicted NK alloreactivity or any other studied NK cell-related factors for the entire cohort. For patients with AML, a significantly higher relapse risk associated with high NK cell graft content on the background of no predicted KIR mismatch (P = .002) was shown. Multivariate analysis confirmed this finding (P = .018); on the other hand, for the KIR-mismatched patients, there was a trend toward a lower risk of relapse associated with high NK cell dose. The use of ATG was associated with a trend toward reduced relapse risk (P = .074) in the AML patients. There was no significant impact of NK-related factors in the ALL patients. Overall, the evaluated NK-related factors did not show a clear and straightforward correlation with the key outcomes of HSCT in our cohort of children with acute leukemia. In practice, the data support prioritization of KIR-mismatched donors for patients with AML. Importantly, a potential interaction of KIR ligand mismatch and NK cell content in the graft was identified. Indirect evidence suggests that additional cellular constituents of the graft could influence the function of NK cells after HSCT and affect their role as graft-versus-leukemia effectors.

HLA-haploidentical T-cell receptor αβT/B-cell-depleted stem cell transplantation for Fanconi anemia

HLA-haploidentical stem cell transplantation (haplo-SCT) using post-transplant high-dose cyclophosphamide (PT-CY) is an alternative choice when a suitable donors is unavailable. However, PT-CY is difficult in patients with Fanconi anemia (FA) due to their high vulnerability to alkylating agents. For FA, we prefer haplo-SCT by T-cell receptor αβT-cell and B-cell depletion (αβT/B-depleted haplo-SCT), which can reduce the risks of PT-CY-related complications and graft-versus-host disease (GVHD). An 11-year-old boy with diagnosed FA (FANCG mutation) and bone marrow failure was to receive αβT/B-depleted haplo-SCT from his father (HLA 4/8 allele matched) due to absence of an HLA-matched donors. αβT/B-depleted peripheral blood stem cells (CD34 + cell count, 1.17 × 107/kg; αβ + T-cell count, 1.3 × 105/kg) were infused following conditioning consisting of fludarabine (150 mg/m2), cyclophosphamide (40 mg/kg), anti-thymocyte globulin (5 mg/kg), rituximab (375 mg/m2), and thoraco-abdominal irradiation (3 Gy). Tacrolimus was used for GVHD prophylaxis until day + 30. Neutrophil engraftment was achieved on day + 9, and complete chimerism was confirmed on days + 28 and + 96. At 12-month post-SCT, the patient was well without GVHD or any other complications. αβT/B-depleted haplo-SCT is a good choice not only for patients unsuitable for PT-CY, but also for all pediatric recipients to reduce SCT-related complications.

Cellular Strategies for Separating GvHD from GvL in Haploidentical Transplantation

GvHD still remains, despite the continuous improvement of transplantation platforms, a fearful complication of transplantation from allogeneic donors. Being able to separate GvHD from GvL represents the greatest challenge in the allogeneic transplant setting. This may be possible through continuous improvement of cell therapy techniques. In this review, current cell therapies are taken into consideration, which are based on the use of TCR alpha/beta depletion, CD45RA depletion, T regulatory cell enrichment, NK-cell-based immunotherapies, and suicide gene therapies in order to prevent GvHD and maximally amplify the GvL effect in the setting of haploidentical transplantation.

Microenvironment in acute myeloid leukemia: focus on senescence mechanisms, therapeutic interactions, and future directions

Acute myeloid leukemia (AML) is a disease with a dismal prognosis, mainly affecting the elderly. In recent years, new drugs have improved life expectancy and quality of life, and a better understanding of the genetic-molecular nature of the disease has shed light on previously unknown aspects of leukemogenesis. In parallel, increasing attention has been attracted to the complex interactions between cells and soluble factors in the bone marrow (BM) environment, collectively known as the microenvironment. In this review, we discuss the central role of the microenvironment in physiologic and pathologic hematopoiesis and the mechanisms of senescence, considered a fundamental protective mechanism against the proliferation of damaged and pretumoral cells. The microenvironment also represents a fertile ground for the development of myeloid malignancies, and the leukemic niche significantly interacts with drugs commonly used in AML treatment. Finally, we focus on the role of the microenvironment in the engraftment and complications of allogeneic hematopoietic stem cell transplantation, the only curative option in a conspicuous proportion of patients.

Treosulfan-Based Conditioning Regimen In Pediatric Hematopoietic Stem Cell Transplantation: A Retrospective Analysis on Behalf of the Spanish Group for Hematopoietic Transplantation and Cellular Therapy (GETH-TC)

Increasing data on treosulfan-based conditioning regimens before hematopoietic stem cell transplantation (HSCT) demonstrate the consistent benefits of this approach, particularly regarding acute toxicity. This study aimed to describe the results of treosulfan-based conditioning regimens in children, focusing on toxicity and outcomes when used to treat both malignant and nonmalignant diseases. This retrospective observational study of pediatric patients treated in Spain with treosulfan-based conditioning regimens before HSCT was based on data collection from electronic clinical records. We studied a total of 160 treosulfan-based conditioning HSCTs to treat nonmalignant diseases (n = 117) or malignant diseases (n = 43) in 158 children and adolescents. The median patient age at HSCT was 5.1 years (interquartile range, 2 to 10 years). The most frequent diagnoses were primary immunodeficiency (n = 42; 36%) and sickle cell disease (n = 42; 36%) in the nonmalignant disease cohort and acute lymphoblastic leukemia (n = 15; 35%) in the malignant disease cohort. Engraftment occurred in 97% of the patients. The median times to neutrophil engraftment (17 days versus 14 days; P = .008) and platelet engraftment (20 days versus 15 days; P = .002) were linger in the nonmalignant cohort. The 1-year cumulative incidence of veno-occlusive disease was 7.98% (95% confidence interval [CI], 4.6% to 13.6%), with no significant differences between cohorts. The 1-year cumulative incidence of grade III-IV acute graft-versus-host disease (GVHD) was higher in the malignant disease cohort (18% versus 3.2%; P = .011). Overall, the malignant cohort had both a higher total incidence (9% versus 3%; P < .001) and a higher 2-year cumulative incidence (16% versus 1.9%; P < .001) of total chronic GVHD. The 2-year cumulative transplantation-related mortality was 15%, with no difference between the 2 cohorts. The 5-year overall survival was 80% (95% CI, 72% to 86%) and was higher in the nonmalignant cohort (87% versus 61%; P = .01). The 2-year cumulative incidence of relapse was 25% in the malignant cohort. The 5-year cumulative GVHD-free, relapse-free survival rate was 60% (95% CI, 51% to 70%) and was higher in the nonmalignant cohort (72% versus 22%; P < .001). A treosulfan-based radiation-free conditioning regimen is feasible, achieving a high engraftment rate and 5-year overall survival, and is an emerging option for the first HSCT in nonmalignant diseases.

EBV-induced T-cell responses in EBV-specific and nonspecific cancers

Epstein-Barr virus (EBV) is a ubiquitous human tumor virus associated with various malignancies, including B-lymphoma, NK and T-lymphoma, and epithelial carcinoma. It infects B lymphocytes and epithelial cells within the oropharynx and establishes persistent infection in memory B cells. With a balanced virus-host interaction, most individuals carry EBV asymptomatically because of the lifelong surveillance by T cell immunity against EBV. A stable anti-EBV T cell repertoire is maintained in memory at high frequency in the blood throughout persistent EBV infection. Patients with impaired T cell immunity are more likely to develop life-threatening lymphoproliferative disorders, highlighting the critical role of T cells in achieving the EBV-host balance. Recent studies reveal that the EBV protein, LMP1, triggers robust T-cell responses against multiple tumor-associated antigens (TAAs) in B cells. Additionally, EBV-specific T cells have been identified in EBV-unrelated cancers, raising questions about their role in antitumor immunity. Herein, we summarize T-cell responses in EBV-related cancers, considering latency patterns, host immune status, and factors like human leukocyte antigen (HLA) susceptibility, which may affect immune outcomes. We discuss EBV-induced TAA-specific T cell responses and explore the potential roles of EBV-specific T cell subsets in tumor microenvironments. We also describe T-cell immunotherapy strategies that harness EBV antigens, ranging from EBV-specific T cells to T cell receptor-engineered T cells. Lastly, we discuss the involvement of γδ T-cells in EBV infection and associated diseases, aiming to elucidate the comprehensive interplay between EBV and T-cell immunity.

Potential value of high-throughput single-cell DNA sequencing of Juvenile myelomonocytic leukemia: report of two cases

Juvenile myelomonocytic leukemia (JMML) is a rare myeloproliferative disease of early childhood that develops due to mutations in the genes of the RAS-signaling pathway. Next-generation high throughput sequencing (NGS) enables identification of various secondary molecular genetic events that can facilitate JMML progression and transformation into secondary acute myeloid leukemia (sAML). The methods of single-cell DNA sequencing (scDNA-seq) enable overcoming limitations of bulk NGS and exploring genetic heterogeneity at the level of individual cells, which can help in a better understanding of the mechanisms leading to JMML progression and provide an opportunity to evaluate the response of leukemia to therapy. In the present work, we applied a two-step droplet microfluidics approach to detect DNA alterations among thousands of single cells and to analyze clonal dynamics in two JMML patients with sAML transformation before and after hematopoietic stem cell transplantation (HSCT). At the time of diagnosis both of our patients harbored only "canonical" mutations in the RAS signaling pathway genes detected by targeted DNA sequencing. Analysis of samples from the time of transformation JMML to sAML revealed additional genetic events that are potential drivers for disease progression in both patients. ScDNA-seq was able to measure of chimerism level and detect a residual tumor clone in the second patient after HSCT (sensitivity of less than 0.1% tumor cells). The data obtained demonstrate the value of scDNA-seq to assess the clonal evolution of JMML to sAML, response to therapy and engraftment monitoring.

αβ+ /CD19+ -depleted haploidentical stem cell transplantation for children with acute leukemia: Is there a protective effect of increased γδ+ T-cell content in the graft?

BACKGROUND

Haploidentical hematopoietic stem cell transplantation (HSCT) with depletion of αβ⁺ T cells and CD19⁺ B cells has emerged as a viable alternative to traditional donors for treating acute leukemia in children. As the use of this innovative approach continues to grow and more experience is gained, it is essential to identify and comprehend the key factors that contribute to successful transplantation and improved outcomes.

METHODS

We conducted a retrospective analysis of single-center data from 27 children with acute lymphoblastic leukemia and 11 children with acute myeloid leukemia who underwent haploidentical HSCT with depletion of αβ⁺ T cells and CD19⁺ B cells between the years 2013 and 2020.

RESULTS

Engraftment was successful in 35 out of 38 patients (92%), who were all children conditioned using either a total body irradiation-based regimen or a treosulfan, fludarabine, and thiotepa regimen engrafted successfully. The 5-year overall survival and event-free survival rates were 51% and 42%, respectively. There were no cases of grade III-IV acute graft-versus-host disease, and only two patients developed chronic graft-versus-host disease. Patients with a higher content of γδ⁺ T cells in the graft demonstrated a longer event-free survival.

CONCLUSIONS

αβ⁺ /CD19⁺ -depleted haploidentical hematopoietic stem cell transplantation can offer long-term remission for children with acute leukemia with minimal graft-versus-host disease.

Hematopoietic stem cell transplantation for inborn errors of immunity: 30-year single-center experience

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) represents an effective treatment for a variety of inborn errors of immunity (IEI). We report the experience of children affected by IEI who received allo-HSCT over a period of 32 years at IRCCS Istituto Giannina Gaslini, Genoa, Italy. HSCTs were performed in 67 children with IEI. Kaplan-Meier estimates of overall survival (OS) rate at 5 years in the whole group of patients was 83.4% after a median follow-up of 4 years. Median age at transplant was 2.5 years. Eight allo-HSCTs were complicated by either primary or secondary graft failure (GF), the overall incidence of this complication being 10.9%. Incidence of grade 3-4 acute GvHD (aGvHD) was 18.7%, significantly lower in the haploidentical transplant cohort (p = 0.005). Year of transplant (≤2006 vs. >2006) was the main factor influencing the outcome. In fact, a significant improvement in 5-year OS was demonstrated (92.5% >2006 vs. 65% ≤2006, p = 0.049). Frequency of severe aGvHD was significantly reduced in recent years (≤2006 61.5%, vs. >2006 20%, p = 0.027). A significant progress has been the introduction of the TCR αβ/CD19-depleted haploidentical platform, which was associated with the absence of severe aGvHD. However, it was associated with 23.5% incidence of GF. All but one patient experiencing GF in the this specific cohort were successfully retransplanted. In summary, allo-HSCT is confirmed to be an effective treatment for children with IEI, even in the absence of an HLA-matched donor.

Haploidentical hematopoietic stem cell transplantation as individual treatment option in pediatric patients with very high-risk sarcomas

Background

Prognosis of children with primary disseminated or metastatic relapsed sarcomas remains dismal despite intensification of conventional therapies including high-dose chemotherapy. Since haploidentical hematopoietic stem cell transplantation (haplo-HSCT) is effective in the treatment of hematological malignancies by mediating a graft versus leukemia effect, we evaluated this approach in pediatric sarcomas as well.

Methods

Patients with bone Ewing sarcoma or soft tissue sarcoma who received haplo-HSCT as part of clinical trials using CD3+ or TCRα/β+ and CD19+ depletion respectively were evaluated regarding feasibility of treatment and survival.

Results

We identified 15 patients with primary disseminated disease and 14 with metastatic relapse who were transplanted from a haploidentical donor to improve prognosis. Three-year event-free survival (EFS) was 18,1% and predominantly determined by disease relapse. Survival depended on response to pre-transplant therapy (3y-EFS of patients in complete or very good partial response: 36,4%). However, no patient with metastatic relapse could be rescued.

Conclusion

Haplo-HSCT for consolidation after conventional therapy seems to be of interest for some, but not for the majority of patients with high-risk pediatric sarcomas. Evaluation of its future use as basis for subsequent humoral or cellular immunotherapies is necessary.

Immunological recovery following HLA-matched CD3+ TCR αß+/CD19+ depleted hematopoietic stem cell transplantation in children

BACKGROUND

Allogeneic hematopoietic stem cell transplantation (HSCT) is a potentially curative option for children with both malignant and nonmalignant diseases. T-cell depletion techniques may result in reduced transplant-related mortality compared with unmanipulated grafts due to a lower incidence of GvHD.

METHODS

Immune recovery and outcome were analyzed in a cohort of 23 patients with malignant and nonmalignant diseases who received CD3+TCRαβ+ T- and B-cell-depleted allografts from matched donors after reduced-intensity or myeloablative conditioning. The median number of CD34+, CD3+TCRαβ+, and CD19+B-cells infused was 12.7 × 10⁶ /kg, 16.8 × 10³ /kg, and 96 × 10³ /kg bodyweight.

RESULTS

With a median follow-up of 36 (range 1-73) months, overall survival and disease-free survival at 3 years were 65.2% and 60.8%. Eight patients died, six due to the underlying disease and two of extended visceral cGvHD. Immune reconstitution, disease-free, and overall survivals were similar compared with a historical cohort of 23 patients transplanted with matched unmanipulated bone marrow. A significant lower rate of higher grade (III-IV) aGvHD was observed in the manipulated HSCT group (8.7% vs. 26%; p = 0.001), whereas the incidence of cGvHD was equal.

CONCLUSIONS

Our data suggest that this graft manipulation strategy could be a safe and effective alternative to conventional HSCT techniques in matched donors.

A retrospective study of treosulfan versus busulfan-based conditioning in pediatric patients

OBJECTIVES

To compare the outcomes of treosulfan-based vs. busulfan-based conditioning regimens in allogeneic hematopoietic stem cell transplantation (HSCT) in pediatric patients.

METHODS

Retrospective study of all consecutive patients (2012-2019) treated with allogenic HSCT and treosulfan- or busulfan-based conditioning regimens at a single center.

RESULTS

A total of 101 HSCT were included: 66 HSCT with busulfan and 35 with treosulfan. In malignant diseases (n=62), busulfan-based conditioning was more commonly employed than treosulfan: 82.3% vs. 17.7%. However, the use of treosulfan for malignant diseases increased over time: 6.5% of HSCT in 2012-2015 vs. 29% of HSCT in 2015-2019 (P=0.02). The cohort of treosulfan had more children under 1-year of age than the busulfan cohort (31 vs. 13%; P=0.033). The percentage of patients who received serotherapy was 73 and 89% in the non-malignant and malignant groups respectively. The engraftment, time to neutrophil, and platelet engraftment were not significantly different between the busulfan and the treosulfan cohorts. Rate of grade II-IV acute GvHD was significantly higher in the busulfan cohort than the treosulfan cohort (39% vs. 15%; P=0.016). No differences were observed in endothelial damage complications, chronic GvHD, relapse, overall survival, and transplant-related mortality.

CONCLUSIONS

Busulfan-based conditioning regimens are used more frequently for children undergoing allogenic HSCT, but treosulfan-based conditioning is gaining acceptance. Treosulfan-based conditioning is associated with lower rates of acute GvHD, and no significant differences on overall survival were observed compared with busulfan.

HAPLOIDENTICAL STEM CELL TRANSPLANTATION AFTER TCR αβ+AND CD19+ CELLS DEPLETION IN CHILDREN WITH CONGENITAL NON-MALIGNANT DISEASE

BACKGROUND

. Haploidentical hematopoietic stem cell transplantation (haplo-HSCT) represents a valuable alternative for children with non-malignant disease and ex-vivo negative selection of TCR αβ⁺-cells is an emerging graft manipulation option that carries several potential advantages in terms of reduced risk of Graft versus Host Disease (GvHD) and improved immune reconstitution.

METHODS

. We reported all consecutive patients with a diagnosis of non-malignant disease who received a TCR-αβ⁺ and CD19⁺depleted haplo-HSCT at "IRCCS Istituto Giannina Gaslini" from 2013 to 2019; the conditioning regimen was myeloablative or non-myeloablative, depending on underlying disease; all patients received anti-thymocyte globulin and rituximab. No post-transplant GvHD prophylaxis was given in presence of a TCR-αβ⁺ cell-dose in the graft lower than the threshold of 1 × 10⁵/kg of the recipient's weight.

RESULTS

. Among 20 HSCTs, engraftment occurred in 17 (85%) after a median of 14 and 12 days from graft infusion for neutrophils and platelets respectively. Primary graft failure was diagnosed in 3 (15%) patients, two (10%) experienced secondary rejection; all of these underwent a second HSCT. The cumulative incidence of a-GvHD and c-GvHD was 15% (2 grade 1, 1 grade 4) at 90 days and 5% (1 grade 1) at 7 months, respectively. Cytomegalovirus reactivation requiring pre-emptive treatment was observed in 9 patients (45%). One patient developed a JC virus-related progressive multifocal leukoencephalopathy, successfully managed with donor-derived virus-specific T-cell infusions. A complete immunological recovery was reached in most patients within 6 months. After a median follow-up of 4 years, 18 patients are alive, with a cumulative survival probability of 90%.

CONCLUSION

. Haplo-HSCT after ex-vivo TCR-αβ⁺/CD19⁺ negative selection may be considered a good option for children with non-malignant diseases since it ensures a high engraftment rate with an acceptable risk of graft failure, very low incidence of significant GvHD, and good immune reconstitution with low frequency of severe virus-related disease. However, the control of viral infection/reactivation should be kept high in order to promptly provide pre-emptive treatments and approaches of antiviral adoptive immunotherapy.

The Role of γδ T Cells as a Line of Defense in Viral Infections after Allogeneic Stem Cell Transplantation: Opportunities and Challenges

In the complex interplay between inflammation and graft-versus-host disease (GVHD) after allogeneic stem cell transplantation (allo-HSCT), viral reactivations are often observed and cause substantial morbidity and mortality. As toxicity after allo-HSCT within the context of viral reactivations is mainly driven by αβ T cells, we describe that by delaying αβ T cell reconstitution through defined transplantation techniques, we can harvest the full potential of early reconstituting γδ T cells to control viral reactivations. We summarize evidence of how the γδ T cell repertoire is shaped by CMV and EBV reactivations after allo-HSCT, and their potential role in controlling the most important, but not all, viral reactivations. As most γδ T cells recognize their targets in an MHC-independent manner, γδ T cells not only have the potential to control viral reactivations but also to impact the underlying hematological malignancies. We also highlight the recently re-discovered ability to recognize classical HLA-molecules through a γδ T cell receptor, which also surprisingly do not associate with GVHD. Finally, we discuss the therapeutic potential of γδ T cells and their receptors within and outside the context of allo-HSCT, as well as the opportunities and challenges for developers and for payers.

Optimized Conformal Total Body Irradiation Among Recipients of TCRαβ/CD19-Depleted Grafts in Pediatric Patients With Hematologic Malignancies: Single-Center Experience

Total body irradiation (TBI) in combination with chemotherapy is widely used as a conditioning regimen in pediatric and adult hematopoietic stem cell transplantation (HSCT). The combination of TBI with chemotherapy has demonstrated superior survival outcomes in patients with acute lymphoblastic and myeloid leukemia when compared with conditioning regimens based only on chemotherapy. The clinical application of intensity-modulated radiation therapy (IMRT)-based methods (volumetric modulated arc therapy (VMAT) and TomoTherapy) seems to be promising and has been actively used worldwide. The optimized conformal total body irradiation (OC-TBI) method described in this study provides selected dose reduction for organs at risk with respect to the most significant toxicity (lungs, kidneys, lenses). This study included 220 pediatric patients who received OC-TBI with subsequent chemotherapy and allogenic HSCT with TCRαβ/CD19 depletion. A group of 151 patients received OC-TBI using TomoTherapy, and 40 patients received OC-TBI using the Elekta Synergy™ linac with an Agility-MLC (Elekta, Crawley, UK) using volumetric modulated arc therapy (VMAT). Twenty-nine patients received OC-TBI with supplemental simultaneous boost to bone marrow-(SIB to BM) up to 15 Gy: 28 patients (pts)-TomoTherapy; one patient-VMAT. The follow-up duration ranged from 0.3 to 6.4 years (median follow-up, 2.8 years). Overall survival (OS) for all the patients was 63% (95% CI: 56-70), and event-free survival (EFS) was 58% (95% CI: 51-65). The cumulative incidence of transplant-related mortality (TRM) was 10.7% (95% CI: 2.2-16) for all patients. The incidence of early TRM (<100 days) was 5.0% (95% CI: 1.5-8.9), and that of late TRM (>100 days) was 5.7 (95% CI: 1.7-10.2). The main causes of death for all the patients were relapse and infection. The concept of OC-TBI using IMRT VMAT and helical treatment delivery on a TomoTherapy treatment unit provides maximum control of the dose distribution in extended targets with simultaneous dose reduction for organs at risk. This method demonstrated a low incidence of severe side effects after radiation therapy and predictable treatment effectiveness. Our initial experience demonstrates that OC-TBI appears to be a promising technique for the treatment of pediatric patients.

Results of a multicenter phase I/II trial of TCRαβ and CD19-depleted haploidentical hematopoietic stem cell transplantation for adult and pediatric patients

Hematopoietic stem cell transplantation (HSCT) from haploidentical donors is a viable option for patients lacking HLA-matched donors. Here we report the results of a prospective multicenter phase I/II trial of transplantation of TCRαβ and CD19-depleted peripheral blood stem cells from haploidentical family donors after a reduced-intensity conditioning with fludarabine, thiotepa, and melphalan. Thirty pediatric and 30 adult patients with acute leukemia (n = 43), myelodysplastic or myeloproliferative syndrome (n = 6), multiple myeloma (n = 1), solid tumors (n = 6), and non-malignant disorders (n = 4) were enrolled. TCR αβ/CD19-depleted grafts prepared decentrally at six manufacturing sites contained a median of 12.1 × 10⁶ CD34⁺ cells/kg and 14.2 × 10³ TCRαβ⁺ T-cells/kg. None of the patients developed grade lll/IV acute graft-versus-host disease (GVHD) and only six patients (10%) had grade II acute GVHD. With a median follow-up of 733 days 36/60 patients are alive. The cumulative incidence of non-relapse mortality at day 100, 1 and 2 years after HSCT was 5%, 15%, and 17% for all patients, respectively. Estimated probabilities of overall and disease-free survival at 2 years were 63% and 50%, respectively. Based on these promising results in a high-risk patient cohort, haploidentical HSCT using TCRαβ/CD19-depleted grafts represents a viable treatment option.

Repeated haploidentical allogeneic hematopoietic stem cell transplantation with TCR αβ/CD19 depletion in patient with primary myelofibrosis. Case report

Indications of allogeneic hematopoietic stem cell transplantation (allo-HSCT) in patients with primary myelofibrosis are intermediate-2 and high-risk group of DIPSS (Dynamic International Prognostic Scoring System), beginning of the disease in childhood. The other adverse factors affect engraftment and survival after allo-HSCT, example partialy matched donor. But the result of allo-HSCT from matched related donors and result of allo-HSCT from haploidentical donors are comparable. The method for haploidentical hematopoietic stem cell transplantation is T-cell-depletion. This is clinical case of T-cell-depleted haploidentical hematopoietic stem cell transplantation in patient with primary myelofibrosis, the diagnosis was established in childhood.

Graft failure after "ex-vivo" T-cell depleted haploidentical transplantation in pediatric patients with high-risk hematological malignancies. A risk factors and outcomes analysis

Risk factors and outcomes of GF after TCD haploidentical transplantation in children with hematological malignancies were analyzed. 148 TCD transplants were included. 78 patients were diagnosed of ALL and 70 patients of AML. 22 out of 148 patients developed GF. MVA showed that patient <9 years (HR: 5.0; 95% CI: 1.1-23.0; p = 0.03) and pre-transplant CD8+ ≥150/µL (HR: 12.0; 95% CI: 1.6-95.3; p = 0.01) were associated with GF. A score was assigned to each patient. The cumulative incidence of GF for patients with CD8+ ≥150/µL (2 points) was 6 ± 4% and 3 ± 2% for patients <9 years (1 point) while for patients with 3 points was 24 ± 6%, With a median follow-up of 48 months (range; 4-180 months), 14 (64%) of 22 patients with GF are alive and disease-free. DFS for GF patients was 53 ± 12%. In conclusion, patient age and pre-transplant CD3+/CD8+ are associated with GF in children undergoing TCD haploidentical transplantation.

Safety and efficacy of the low-dose memory (CD45RA-depleted) donor lymphocyte infusion in recipients of αβ T cell-depleted haploidentical grafts: results of a prospective randomized trial in high-risk childhood leukemia

Depletion of αβ T cells from the graft prevents graft-vs.-host disease (GVHD) and improves outcome of HSCT from haploidentical donors. In a randomized trial, we aimed to evaluate the safety and efficacy of low-dose memory (CD45RA-depleted) donor lymphocytes (mDLI) after HSCT with αβ T-cell depletion. A cohort of 149 children was enrolled, 76 were randomized to receive scheduled mDLI and 73 received standard care. Conditioning was based on either 12 Gy total body irradiation or treosulfan. Rabbit antithymocyte globulin was replaced by tocilizumab and abatacept. Primary end points were the incidence of acute GVHD grades II-IV and the incidence of cytomegalovirus (CMV) viremia. The incidence of grades II-IV aGVHD was 14% in the experimental arm and 12% in the control arm, p-0.8. The incidence of CMV viremia was 45% in the experimental arm and 55% in the control arm, p-0.4. Overall, in the total cohort 2-year NRM was 2%, cumulative incidence of relapse was 25%, event-free survival 71%, and overall survival 80%, without difference between the study arms. Memory DLI was associated with improved recovery of CMV-specific T-cell responses in a subcohort of CMV IgG seropositive recipients.

CD4+ T-cell reconstitution predicts survival outcomes after acute graft-versus-host-disease: a dual-center validation

Acute graft-versus-host-Disease (aGVHD) is a major cause of morbidity and mortality after allogeneic hematopoietic cell transplantation (HCT). We previously showed that early CD4+ T-cell immune reconstitution (IR; CD4+ IR) predicts survival after HCT. Here, we studied the relation between CD4+ IR and survival in patients developing aGVHD. Pediatric patients undergoing first allogeneic HCT at University Medical Center Utrecht (UMC)/Princess Máxima Center (PMC) or Memorial Sloan Kettering Cancer Center (MSK) were included. Primary outcomes were nonrelapse mortality (NRM) and overall survival (OS), stratified for aGVHD and CD4+ IR, defined as ≥50 CD4+ T cells per μL within 100 days after HCT or before aGVHD onset. Multivariate and time-to-event Cox proportional hazards models were applied, and 591 patients (UMC/PMC, n = 276; MSK, n = 315) were included. NRM in patients with grade 3 to 4 aGVHD with or without CD4+ IR within 100 days after HCT was 30% vs 80% (P = .02) at UMC/PMC and 5% vs 67% (P = .02) at MSK. This was associated with lower OS without CD4+ IR (UMC/PMC, 61% vs 20%; P = .04; MSK, 75% vs 33%; P = .12). Inadequate CD4+ IR before aGVHD onset was associated with significantly higher NRM (74% vs 12%; P < .001) and inferior OS (24% vs 78%; P < .001). In this retrospective analysis, we demonstrate that early CD4+ IR, a simple and robust marker predictive of outcomes after HCT, is associated with survival after moderate to severe aGVHD. This association must be confirmed prospectively but suggests strategies to improve T-cell recovery after HCT may influence survival in patients developing aGVHD.

Harnessing Mechanisms of Immune Tolerance to Improve Outcomes in Solid Organ Transplantation: A Review

Survival after solid organ transplantation (SOT) is limited by chronic rejection as well as the need for lifelong immunosuppression and its associated toxicities. Several preclinical and clinical studies have tested methods designed to induce transplantation tolerance without lifelong immune suppression. The limited success of these strategies has led to the development of clinical protocols that combine SOT with other approaches, such as allogeneic hematopoietic stem cell transplantation (HSCT). HSCT prior to SOT facilitates engraftment of donor cells that can drive immune tolerance. Recent innovations in graft manipulation strategies and post-HSCT immune therapy provide further advances in promoting tolerance and improving clinical outcomes. In this review, we discuss conventional and unconventional immunological mechanisms underlying the development of immune tolerance in SOT recipients and how they can inform clinical advances. Specifically, we review the most recent mechanistic studies elucidating which immune regulatory cells dampen cytotoxic immune reactivity while fostering a tolerogenic environment. We further discuss how this understanding of regulatory cells can shape graft engineering and other therapeutic strategies to improve long-term outcomes for patients receiving HSCT and SOT.

Allogeneic Stem Cell Transplantation Platforms With Ex Vivo and In Vivo Immune Manipulations: Count and Adjust

Various allogeneic (allo) stem cell transplantation platforms have been developed over the last 2 decades. In this review we focus on the impact of in vivo and ex vivo graft manipulation on immune reconstitution and clinical outcome. Strategies include anti-thymocyte globulin- and post-transplantation cyclophosphamide-based regimens, as well as graft engineering, such as CD34 selection and CD19/αβT cell depletion. Differences in duration of immune suppression, reconstituting immune repertoires, and associated graft-versus-leukemia effects and toxicities mediated through viral reactivations are highlighted. In addition, we discuss the impact of different reconstituting repertoires on donor lymphocyte infusions and post allo pharmacological interventions to enhance tumor control. We advocate for precisely counting all graft ingredients and therapeutic drug monitoring during conditioning in the peripheral blood, and for adjusting dosing accordingly on an individual basis. In addition, we propose novel trial designs to better assess the impact of variations in transplantation platforms in order to better learn from our diversity of "counts" and potential "adjustments." This will, in the future, allow daily clinical practice, strategic choices, and future trial designs to be based on data guided decisions, rather than relying on dogma and habits.

"Ex-vivo" T-cell depletion in allogeneic hematopoietic stem cell transplantation: New clinical approaches for old challenges

Allogeneic transplantation still remains as standard of care for patients with high-risk hematological malignancies at diagnosis or after relapse. However, GvHD remains yet as the most relevant clinical complication in the early post-transplant period. TCD allogeneic transplant is now considered a valid option to reduce severe GvHD and to provide a platform for cellular therapy to prevent relapse disease or to treat opportunistic infections.

αβ T-cell graft depletion for allogeneic HSCT in adults with hematological malignancies

We conducted a multicenter prospective single-arm phase 1/2 study that assesses the outcome of αβ T-cell depleted allogeneic hematopoietic stem cell transplantation (allo-HSCT) of peripheral blood derived stem cells from matched related, or unrelated donors (10/10 and 9/10) in adults, with the incidence of acute graft-versus-host disease (aGVHD) as the primary end point at day 100. Thirty-five adults (median age, 59; range, 19-69 years) were enrolled. Conditioning consisted of antithymocyte globulin, busulfan, and fludarabine, followed by 28 days of mycophenolic acid after allo-HSCT. The minimal follow-up time was 24 months. The median number of infused CD34+ cells and αβ T cells were 6.1 × 106 and 16.3 × 103 cells per kg, respectively. The cumulative incidence (CI) of aGVHD grades 2-4 and 3-4 at day 100 was 26% and 14%. One secondary graft failure was observed. A prophylactic donor lymphocyte infusion (DLI) (1 × 105 CD3+ T cells per kg) was administered to 54% of the subjects, resulting in a CI of aGVHD grades 2-4 and 3-4 to 37% and 17% at 2 years. Immune monitoring revealed an early reconstitution of natural killer (NK) and γδ T cells. Cytomegalovirus reactivation associated with expansion of memory-like NK cells. The CI of relapse was 29%, and the nonrelapse mortality 32% at 2 years. The 2-year CI of chronic GVHD (cGVHD) was 23%, of which 17% was moderate. We conclude that only 26% of patients developed aGVHD 2-4 after αβ T-cell-depleted allo-HSCT within 100 days and was associated with a low incidence of cGVHD after 2 years. This trial was registered at www.trialregister.nl as #NL4767.

Contemporary haploidentical stem cell transplant strategies in children with hematological malignancies

The barriers to HLA-mismatched or haploidentical hematopoietic stem cell transplantation (HSCT), namely GvHD and graft failure, have been overcome with novel transplant platforms. Post-transplant Cyclophosphamide (PTCy) is widely available, feasible and easy to implement. TCRαβ T and B cell depletion comes with consistent GvHD preventive benefits irrespective of age and indication. Naive T-cell depletion helps prevention of severe viral reactivations. The Beijing protocol shows promising outcomes in patients with poor remission status at the time of transplantation. For children, the toxicities and late outcomes related to these transplants are truly relevant as they suffer the most in the long run from transplant-related toxicities, especially chronic GvHD. While comparing the outcomes of different Haplo-HSCT approaches, one must understand the transplant immunobiology and factors affecting the transplant outcomes. Leukemia remission status at the time of conditioning is a consistent factor affecting the transplant outcomes using any of these platforms. Prospective comparison of these platforms lacks in a homogenous population; however, the evidence is growing, and this review highlights the areas of research gaps.

National Institutes of Health Consensus Development Project on Criteria for Clinical Trials in Chronic Graft-versus-Host Disease: I. The 2020 Etiology and Prevention Working Group Report

Preventing chronic graft-versus-host disease (GVHD) remains challenging because the unique cellular and molecular pathways that incite chronic GVHD are poorly understood. One major point of intervention for potential prevention of chronic GVHD occurs at the time of transplantation when acute donor anti-recipient immune responses first set the events in motion that result in chronic GVHD. After transplantation, additional insults causing tissue injury can incite aberrant immune responses and loss of tolerance, further contributing to chronic GVHD. Points of intervention are actively being identified so that chronic GVHD initiation pathways can be targeted without affecting immune function. The major objective in the field is to continue basic studies and to translate what is learned about etiopathology to develop targeted prevention strategies that decrease the risk of morbid chronic GVHD without increasing the risks of cancer relapse or infection. Development of strategies to predict the risk of developing debilitating or deadly chronic GVHD is a high research priority. This working group recommends further interrogation into the mechanisms underpinning chronic GVHD development, and we highlight considerations for future trial design in prevention trials.

Serotherapy-Free Regimen Improves Non-Relapse Mortality and Immune Recovery Among the Recipients of αβ TCell-Depleted Haploidentical Grafts: Retrospective Study in Childhood Leukemia

Depletion of αβ T cells from the graft prevents graft-versus-host disease (GVHD) and improves the outcome of hematopoietic stem cell transplantation (HSCT) from haploidentical donors. Delayed recovery of adaptive immunity remains a problem, which can be approached by adoptive T-cell transfer. In a randomized trial, we have assessed the safety and efficacy of low-dose memory (CD45RA-depleted) donor lymphocytes (mDLI) after HSCT with αβ T-cell depletion. Antithymocyte globulin (ATG) is viewed as an essential component of preparative regimen, critical for both prevention of graft failure and GVHD. Variable pharmacokinetics of ATG may significantly affect lymphocyte subpopulations after HSCT. To uncover the potential of mDLI, we replaced rabbit ATG with tocilizumab and abatacept. Here we compare post hoc the immune recovery and the key clinical outcomes, including nonrelapse mortality (NRM), overall- and event-free survival (OS and EFS), between the cohort enrolled in the prospective randomized trial and a historical cohort, comprised of patients grafted with a conventional ATG-based HSCT with αβ T cell depletion. A cohort of 149 children was enrolled in the prospective trial and 108 patients were selected as historical controls from a prospectively populated database. Patient population was comprised of children with high-risk hematologic malignancies, with more than 90% represented by acute leukemia. Median age at enrollment was 8.8 years. In the prospective cohort 91% of the donors were haploidentical parents, whereas in the historical cohort 72% of the donors were haploidentical. Conditioning was based on either 12Gy total body irradiation or treosulfan. Thiotepa, fludarabine, bortezomib, and rituximab were used as additional agents. Patients in the historical cohort received rabbit ATG at 5 mg/kg total dose, while prospective cohort patients received tocilizumab at 8 mg /kg on day -1 and abatacept at 10 mg/kg on days 0, 7, 14, and 28. Patients in the prospective trial cohort were randomized 1:1 to receive mDLI starting on day 0, whereas 69% of historical cohort patients received mDLI after engraftment, as part of previous trials. Primary engraftment rate was 99% in the prospective cohort and 98% in the historical cohort. The incidence of grade II-IV aGVHD was 13% in the prospective cohort and 16 % in the control group. Chronic GVHD developed among 13% (historical) and 7% (prospective) cohorts (P = .07). The incidence of cytomegalovirus viremia was 51% in the prospective cohort arm and 54% in the historical control arm (p = ns). Overall, in the prospective cohort 2-year NRM was 2%, incidence of relapse was 25%, EFS was 71%, and OS was 80%, whereas in the historical cohort 2-year NRM was 13%, incidence of relapse was 19%, EFS was 67%, and OS was 76%, difference non-significant for relapse and survival. NRM was significantly improved in the ATG-free cohort (P = .002). Recovery of both αβ- and γδ- T cells was significantly improved at days +30 and +60 after HSCT in recipients of ATG-free preparative regimens, as well as recovery of naïve T cells. Among the recipients of αβ T-cell-depleted grafts, replacement of ATG with nonlymphodepleting abatacept and tocilizumab immunomodulation did not compromise engraftment and GVHD control and was associated with significantly lower NRM and better immune recovery early after HSCT.

T-Cell-Replete Versus ex vivo T-Cell-Depleted Haploidentical Haematopoietic Stem Cell Transplantation in Children With Acute Lymphoblastic Leukaemia and Other Haematological Malignancies

Allogeneic haematopoietic stem cell transplantation (HSCT) represents a potentially curative option for children with high-risk or refractory/relapsed leukaemias. Traditional donor hierarchy favours a human leukocyte antigen (HLA)-matched sibling donor (MSD) over an HLA-matched unrelated donor (MUD), followed by alternative donors such as haploidentical donors or unrelated cord blood. However, haploidentical HSCT (hHSCT) may be entailed with significant advantages: besides a potentially increased graft-vs.-leukaemia effect, the immediate availability of a relative as well as the possibility of a second donation for additional cellular therapies may impact on outcome. The key question in hHSCT is how, and how deeply, to deplete donor T-cells. More T cells in the graft confer faster immune reconstitution with consecutively lower infection rates, however, greater numbers of T-cells might be associated with higher rates of graft-vs.-host disease (GvHD). Two different methods for reduction of alloreactivity have been established: in vivo T-cell suppression and ex vivo T-cell depletion (TCD). Ex vivo TCD of the graft uses either positive selection or negative depletion of graft cells before infusion. In contrast, T-cell-repleted grafts consisting of non-manipulated bone marrow or peripheral blood grafts require intense in vivo GvHD prophylaxis. There are two major T-cell replete protocols: one is based on post-transplantation cyclophosphamide (PTCy), while the other is based on anti-thymocyte globulin (ATG; Beijing protocol). Published data do not show an unequivocal benefit for one of these three platforms in terms of overall survival, non-relapse mortality or disease recurrence. In this review, we discuss the pros and cons of these three different approaches to hHSCT with an emphasis on the significance of the existing data for children with acute lymphoblastic leukaemia.

Infectious complications in allogeneic hematopoietic cell transplant recipients: Review of transplant-related risk factors and current state of prophylaxis

Allogeneic hematopoietic cell transplantation is a complex procedure that carries a significant risk of complications. Infections are among the most common of them. Several direct factors such as neutropenia, hypogammaglobulinemia, lymphopenia, mucosal barrier injury, and graft-versus-host disease have been shown to be associated with increased infectious risk post-transplant. Apart from direct factors, there are also indirect transplant-related factors that are the primary trigger to the formers' development. The most important of them are type of preparative regimen, graft source, donor type, graft-versus-host disease prophylaxis, and graft manipulation techniques. In this review, an attempt has been made to summarize the role of the transplant-related factors in the development of infectious complications and provide evidence underlying the current concept of infectious disease prophylaxis in patients after allogeneic hematopoietic cell transplantation.

Immune Reconstitution Following TCRαβ/CD19-Depleted Hematopoietic Cell Transplantation for Hematologic Malignancy in Pediatric Patients

TCRαβ/CD19-depleted HCT has been used with excellent outcomes in pediatric patients with hematologic malignancies, and several studies have demonstrated rapid immune reconstitution in the nonmalignant setting. However, immune recovery following TCRαβ/CD19-depleted hematopoietic cell transplantation (HCT) for malignancy remains incompletely elucidated. Furthermore, the majority of studies to date have used haploidentical and matched unrelated donors. Here we report results of immune reconstitution following TCRαβ/CD19-depleted HCT for hematologic malignancy in 51 pediatric patients with hematologic malignancies, the majority of whom received grafts from unrelated donors. Grafts were from matched unrelated (n = 20), mismatched unrelated (n = 20), and haploidentical (n = 11) donors. The median CD34⁺ cell dose was 10.2 × 10⁶/kg (range, 4.54 to 20 × 10⁶/kg), and the median TCRαβ⁺ cell dose was 2.53 × 10⁴/kg (range, 0 to 44.9 × 10⁴/kg). Conditioning was myeloablative with either busulfan or total body irradiation, cyclophosphamide, and thiotepa. Thirty-three patients also received rabbit antithymocyte globulin. No prophylactic post-transplantation immune suppression was routinely given. Forty-three patients received rituximab on day +1 for recipient positive Epstein-Barr virus serology. Forty-nine patients (96%) engrafted with a median time to neutrophil recovery of 13 days (range, 8 to 30 days). Thirty-seven patients (73%) are alive at a median follow-up of 25 months (range, 6 to 50 months). Nine patients (18%) developed grade II-IV acute graft-versus-host disease (GVHD), and 5 patients (11%) developed extensive chronic GVHD. Twenty-six patients (51%) experienced viral reactivation. T cell reconstitution was rapid with significant numbers of CD3⁺, CD4⁺, and CD8⁺ T cells present on first assessment at 4 months post-HCT, and significant numbers of naïve CD4⁺ T cells were present by 8 months post-HCT. Chronic GVHD was associated with delayed T cell recovery; however, T cell reconstitution was not affected by underlying diagnosis, donor source, TCRαβ⁺ T cell dose, conditioning regimen, or use of antithymocyte globulin. B cell recovery mirrored T cell recovery, and i.v. Ig was discontinued at a median of 8 months (range, 4 to 22 months) post-HCT in patients alive and relapse-free at last follow-up. Immune reconstitution is rapid following TCRαβ/CD19-depleted HCT in pediatric patients with hematologic malignancies. Donor graft source, haploidentical or unrelated, did not affect immune reconstitution. Viral reactivation is common in the first 100 days post-HCT, indicating that improved T cell defense is needed in the early post-HCT period.

T-cell tracking, safety, and effect of low-dose donor memory T-cell infusions after αβ T cell-depleted hematopoietic stem cell transplantation

The delayed recovery of adaptive immunity underlies transplant-related mortality (TRM) after αβ T cell-depleted hematopoietic stem cell transplantation (HSCT). We tested the use of low-dose memory donor lymphocyte infusions (mDLIs) after engraftment of αβ T cell-depleted grafts.A cohort of 131 pediatric patients (median age 9 years) were grafted with αβ T cell-depleted products from either haplo (n = 79) or unrelated donors (n = 52). After engraftment, patients received mDLIs prepared by CD45RA depletion. Cell dose was escalated monthly from 25 × 10³ to 100 × 10³/kg (haplo) and from 100 × 10³ to 300 × 10³ /kg (MUD). In a subcohort of 16 patients, T-cell receptor (TCR) repertoire profiling with deep sequencing was used to track T-cell clones and to evaluate the contribution of mDLI to the immune repertoire.In total, 343 mDLIs were administered. The cumulative incidence (CI) of grades II and III de novo acute graft-versus-host disease (aGVHD) was 5% and 2%, respectively, and the CI of chronic graft-versus-host disease was 7%. Half of the patients with undetectable CMV-specific T cells before mDLI recovered CMV-specific T cells. TCR repertoire profiling confirmed that mDLI-derived T cells significantly contribute to the TCR repertoire up to 1 year after HSCT and include persistent, CMV-specific T-cell clones.

Immune Modulation Properties of Zoledronic Acid on TcRγδ T-Lymphocytes After TcRαβ/CD19-Depleted Haploidentical Stem Cell Transplantation: An analysis on 46 Pediatric Patients Affected by Acute Leukemia

TcRαβ/CD19-cell depleted HLA-haploidentical hematopoietic stem cell transplantation (haplo-HSCT) represents a promising new platform for children affected by acute leukemia in need of an allograft and lacking a matched donor, disease recurrence being the main cause of treatment failure. The use of zoledronic acid to enhance TcRγδ+ lymphocyte function after TcRαβ/CD19-cell depleted haplo-HSCT was tested in an open-label, feasibility, proof-of-principle study. Forty-six children affected by high-risk acute leukemia underwent haplo-HSCT after removal of TcRαβ+ and CD19+ B lymphocytes. No post-transplant pharmacological graft-versus-host disease (GvHD) prophylaxis was given. Zoledronic acid was administered monthly at a dose of 0.05 mg/kg/dose (maximum dose 4 mg), starting from day +20 after transplantation. A total of 139 infusions were administered, with a mean of 3 infusions per patient. No severe adverse event was observed. Common side effects were represented by asymptomatic hypocalcemia and acute phase reactions (including fever, chills, malaise, and/or arthralgia) within 24–48 h from zoledronic acid infusion. The cumulative incidence of acute and chronic GvHD was 17.3% (all grade I-II) and 4.8% (all limited), respectively. Patients given 3 or more infusions of zoledronic acid had a lower incidence of both acute GvHD (8.8 vs. 41.6%, p = 0.015) and chronic GvHD (0 vs. 22.2%, p = 0.006). Transplant-related mortality (TRM) and relapse incidence at 3 years were 4.3 and 30.4%, respectively. Patients receiving repeated infusions of zoledronic acid had a lower TRM as compared to those receiving 1 or 2 administration of the drug (0 vs. 16.7%, p = 0.01). Five-year overall survival (OS) and disease-free survival (DFS) for the whole cohort were 67.2 and 65.2%, respectively, with a trend toward a better OS for patients receiving 3 or more infusions (73.1 vs. 50.0%, p = 0.05). The probability of GvHD/relapse-free survival was significantly worse in patients receiving 1–2 infusions of zoledonic acid than in those given ≥3 infusions (33.3 vs. 70.6%, respectively, p = 0.006). Multivariable analysis showed an independent positive effect on outcome given by repeated infusions of zoledronic acid (HR 0.27, p = 0.03). These data indicate that the use of zoledronic acid after TcRαβ/CD19-cell depleted haploHSCT is safe and may result in a lower incidence of acute GvHD, chronic GvHD, and TRM.

Treosulfan-fludarabine-thiotepa-based conditioning treatment before allogeneic hematopoietic stem cell transplantation for pediatric patients with hematological malignancies

Treosulfan-based conditioning prior to allogeneic transplantation has been shown to have myeloablative, immunosuppressive, and antineoplastic effects associated with reduced non-relapse mortality (NRM) in adults. Therefore, we prospectively evaluated the safety and efficacy of treosulfan-based conditioning in children with hematological malignancies in this phase II trial. Overall, 65 children with acute lymphoblastic leukemia (35.4%), acute myeloid leukemia (44.6%), myelodysplastic syndrome (15.4%), or juvenile myelomonocytic leukemia (4.6%) received treosulfan intravenously at a dose of 10 mg/m²/day (7.7%), 12 g/m²/day (35.4%), or 14 g/m²/day (56.9%) according to their individual body surface area in combination with fludarabine and thiotepa. The incidence of complete donor chimerism at day +28 was 98.4% with no primary and only one secondary graft failure. At 36 months, NRM was only 3.1%, while relapse incidence was 21.7%, and overall survival was 83.0%. The cumulative incidence of acute graft-vs.-host disease was 45.3% for grades I–IV and 26.6% for grades II–IV. At 36 months, 25.8% overall and 19.4% moderate/severe chronic graft-vs.-host disease were reported. These data confirm the safe and effective use of treosulfan-based conditioning in pediatric patients with hematological malignancies. Therefore, treosulfan/fludarabine/thiotepa can be recommended for myeloablative conditioning in children with hematological malignancies.

Control of graft-versus-host disease with rabbit anti-thymocyte globulin, rituximab, and bortezomib in TCRαβ/CD19-depleted graft transplantation for leukemia in children: a single-center retrospective analysis of two GVHD-prophylaxis regimens

Both acute GVHD and chronic GVHD remain the leading cause of morbidity and death after allogeneic HSCT. We conducted a retrospective analysis comparing two GVHD-prophylaxis regimens: 35 patients received "Regimen 1" (horse ATG, tacrolimus, and methotrexate) and 46 "Regimen 2" (rabbit ATG, rituximab, and peritransplant bortezomib). All 81 patients with a median age of 9 (0.6-23) years with ALL (n = 31) or AML (n = 50) in complete remission received TCRαβ/CD19-depleted transplants between May 2012 and October 2016, from 40 HLA-matched unrelated and 41 haploidentical donors. After a median follow-up of 3.9 years, the CI of acute GVHD II-IV was 15% (95% CI: 7-30) in the "Regimen 2" group and 34% (95% CI: -54) in the "Regimen 1" group, P = .05. "Regimen 2" was also more effective in the prevention of chronic GVHD; the CI at 1 year after HSCT was 7% (95% CI: 2-19) vs 31% (95% CI: 19-51), P = .005. The CI of relapse at 3 years adjusted for the GVHD-prophylaxis regimen groups 31% (95% CI: 19-51) for the "Regimen 1" vs 21% (95% CI: 11-37) for the "Regimen 2", P = .3. The retrospective observation suggests that the use of the rATG, rituximab, and bortezomib was associated with significantly lower rate of GVHD without the loss of anti-leukemic activity.

Prevention and Treatment of Acute Graft-versus-Host Disease in Children, Adolescents, and Young Adults

Acute graft-versus-host disease (GVHD) continues to be a major cause of morbidity and mortality after allogeneic hematopoietic cell transplant (HCT) in pediatric patients (ie, children and adolescent and young adults) and limits broader application of the therapy. Pediatric HCT patients have faced major obstacles to access clinical trials that test new agents for GVHD prevention and treatment. According to a recent search, only 6 clinical trials of interventions for prevention or treatment of acute GVHD were conducted specifically in pediatric patients in the United States over the past decade, with 8 internationally. In this review, we summarize the studies that were performed and specifically enrolled and reported on pediatric patients after allogeneic HCT and provide a listing of studies currently under way.

Innate Immune Responses in the Outcome of Haploidentical Hematopoietic Stem Cell Transplantation to Cure Hematologic Malignancies

In the context of allogeneic transplant platforms, human leukocyte antigen (HLA)-haploidentical hematopoietic stem cell transplantation (haplo-HSCT) represents one of the latest and most promising curative strategies for patients affected by high-risk hematologic malignancies. Indeed, this platform ensures a suitable stem cell source immediately available for virtually any patents in need. Moreover, the establishment in recipients of a state of immunologic tolerance toward grafted hematopoietic stem cells (HSCs) remarkably improves the clinical outcome of this transplant procedure in terms of overall and disease free survival. However, the HLA-mismatch between donors and recipients has not been yet fully exploited in order to optimize the Graft vs. Leukemia effect. Furthermore, the efficacy of haplo-HSCT is currently hampered by several life-threatening side effects including the onset of Graft vs. Host Disease (GvHD) and the occurrence of opportunistic viral infections. In this context, the quality and the kinetic of the immune cell reconstitution (IR) certainly play a major role and several experimental efforts have been greatly endorsed to better understand and accelerate the post-transplant recovery of a fully competent immune system in haplo-HSCT. In particular, the IR of innate immune system is receiving a growing interest, as it recovers much earlier than T and B cells and it is able to rapidly exert protective effects against both tumor relapses, GvHD and the onset of life-threatening opportunistic infections. Herein, we review our current knowledge in regard to the kinetic and clinical impact of Natural Killer (NK), γδ and Innate lymphoid cells (ILCs) IRs in both allogeneic and haplo-HSCT. The present paper also provides an overview of those new therapeutic strategies currently being implemented to boost the alloreactivity of the above-mentioned innate immune effectors in order to ameliorate the prognosis of patients affected by hematologic malignancies and undergone transplant procedures.

Improved survival rate in T-cell depleted haploidentical hematopoietic cell transplantation over the last 15 years at a single institution

T-cell depletion of an HLA-haploidentical (haplo) graft is often used to reduce the risk of graft-versus-host disease (GVHD), but the lack of donor T cells in the infused product may lead to graft failure, slow T-cell reconstitution, infections, and relapse. More selective T-cell depletion targeting CD45RA can effectively deplete naïve T cells but preserve large numbers of memory T cells leading to robust engraftment of diverse T-cell populations and reduction of viremia in the early post-transplant period. Herein, we report the outcome of 143 pediatric and young adult hematologic malignancy patients receiving a first allogeneic hematopoietic cell transplantation (HCT) on 6 consecutive ex vivo T-cell depleted haploHCT protocols over the past 15 years at a single institution - including the first 50 patients on an active CD45RA-depleted haploHCT study in which patients also received NK-cells and pharmacological GvHD prophylaxis post transplant. Our data demonstrated an increase in the 3-year overall survival and event-free survival in non-chemorefractory recipients receiving CD45RA-depleted grafts (78.9% and 77.7%, respectively) compared to historic T-cell depleted haploHCT cohorts (46.7% and 42.7%, respectively, p=0.004, and 0.003). This improvement was primarily due to a reduction in transplant related mortality without significant increase in the rates of GVHD.

Haploidentical Stem Cell Transplantation in Children With Hematological Malignancies Using αβ+ T-Cell Receptor and CD19+ Cell Depleted Grafts: High CD56dim/CD56bright NK Cell Ratio Early Following Transplantation Is Associated With Lower Relapse Incidence and Better Outcome

We prospectively analyzed outcomes of haploidentical hematopoietic stem cell transplantation using αβ⁺ T-cell receptor/CD19⁺ depleted grafts. Sixty-three transplantations were performed in 60 patients. Twenty-eight patients were diagnosed with acute lymphoblastic leukemia (ALL), 27 patients were diagnosed with acute myelogenous leukemia, and in eight other hematological malignancies were diagnosed. Twenty-three were in first complete remission (CR), 20 in second CR, 20 beyond second CR. Four patients developed graft failure. Median time to neutrophil and platelet recovery was 14 (range 9–25) and 10 days (range 7–30), respectively. The probability of non-relapse mortality (NRM) by day +100 after transplantation was 10 ± 4%. With a median follow-up of 28 months, the probability of relapse was 32 ± 6% and disease-free survival was 52 ± 6%. Immune reconstitution was leaded by NK cells. As such, a high CD56^dim/CD56^bright NK cell ratio early after transplantation was associated with better disease-free survival (DFS) (≥3.5; 77 ± 8% vs. <3.5; 28 ± 5%; p = 0.001) due to lower relapse incidence (≥3.5; 15 ± 7% vs. <3.5; 37 ± 9%; p = 0.04). T-cell reconstitution was delayed and associated with severe infections after transplant. Viral reactivation/disease and presence of venooclusive disease of liver in the non-caucasian population had a significant impact on NRM. αβ⁺ T-cell receptor/CD19⁺ cell-depleted haploidentical transplant is associated with good outcomes especially in patients in early phase of disease. A rapid expansion of “mature” natural killer cells early after transplantation resulted on lower probability of relapse, suggesting a graft vs. leukemia effect independent from graft-vs.-host reactions.

TCR α+ β+ /CD19+ cell-depleted hematopoietic stem cell transplantation for pediatric patients

TCR α⁺ β⁺ /CD19⁺ cell depletion is an emerging technique for ex vivo graft manipulation in HSCT. We report 20 pediatric patients who underwent TCR α⁺ β⁺ /CD19⁺ cell-depleted HSCT in four Australian centers. Conditioning regimen was dependent on HSCT indication, which included immunodeficiency (n = 14), Fanconi anemia (n = 3), and acute leukemia (n = 3). Donor sources were haploidentical parent (n = 17), haploidentical sibling (n = 2), or matched unrelated donor (n = 1). Mean cell dose was 8.2 × 10⁸ /kg TNC, 12.1 × 10⁶ /kg CD34⁺ cells, and 0.4 × 10⁵ /kg TCR α⁺ β⁺ cells. All patients achieved primary neutrophil and platelet engraftment, with average time to neutrophil engraftment 11 days (range 8-22) and platelet engraftment 24 days (range 12-69). TRM at 1 year was 15%. Rate of grade II-IV aGVHD at 1 year was 20% with no grade III-IV aGVHD seen. CMV reactivation occurred in 81% of CMV-positive recipients, with one patient developing CMV disease. Average time to CD4 recovery (>400 × 10⁶ /L) was 258 days. Overall survival for the cohort at 5 years was 80%. This report highlights the initial experience of TCR α⁺ β⁺ /CD19⁺ cell-depleted HSCT in Australian centers, with high rates of engraftment, low rates of aGVHD, and acceptable TRM.

Graft Engineering and Adoptive Immunotherapy: New Approaches to Promote Immune Tolerance After Hematopoietic Stem Cell Transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) is a curative therapeutic option for a wide range of immune and hematologic malignant and non-malignant disorders. Once transplanted, allogeneic cells have to support myeloid repopulation and immunological reconstitution, but also need to become tolerant to the host via central or peripheral mechanisms to achieve the desired therapeutic effect. Peripheral tolerance after allogeneic HSCT may be achieved by several mechanisms, though blocking alloreactivity to the host human leukocyte antigens while preserving immune responses to pathogens and tumor antigens remains a challenge. Recently uncovered evidence on the mechanisms of post-HSCT immune reconstitution and tolerance in transplanted patients has allowed for the development of novel cell-based therapeutic approaches. These therapies are aimed at inducing long-term peripheral tolerance and reducing the risk of graft-vs-host disease (GvHD), while sparing the graft-vs-leukemia (GvL) effect. Thus, ensuring effective long term remission in hematologic malignancies. Today, haploidentical stem cell transplants have become a widely used treatment for patients with hematological malignancies. A myriad of ex vivo and in vivo T-cell depletion strategies have been adopted, with the goal of preventing GvHD while preserving GvL in the context of immunogenetic disparity. αβ T-cell/CD19 B-cell depletion techniques, in particular, has gained significant momentum, because of the high rate of leukemia-free survival and the low risk of severe GvHD. Despite progress, better treatments are still needed in a portion of patients to further reduce the incidence of relapse and achieve long-term tolerance. Current post-HSCT cell therapy approaches designed to induce tolerance and minimizing GvHD occurrence include the use of (i) γδ T cells, (ii) regulatory Type 1 T (Tr1) cells, and (iii) engineered FOXP3+ regulatory T cells. Future protocols may include post-HSCT infusion of allogeneic effector or regulatory T cells engineered with a chimeric antigen receptor (CAR). In the present review, we describe the most recent advances in graft engineering and post-HSCT adoptive immunotherapy.

Pre-formulation investigations for establishing a protocol for treosulfan handling and activation

INTRODUCTION

Treosulfan is an alkylating agent that is used for the treatment of ovarian cancer and for conditioning prior to stem cell transplantation. It is a prodrug that is activated non-enzymatically to two active epoxides.

OBJECTIVES

To optimize a protocol for both in vivo samples handling and in vitro drug preparation. Treosulfan stability was tested in biological fluids at different conditions as well as for its cytotoxicity on cell lines.

RESULTS

Plasma samples can be safely frozen for a short period up to 8 h, however; for longer periods, samples should be acidified. Urine samples and cell culture media can be safely frozen regardless their pH. For in vitro investigations, incubation of treosulfan at 37 °C for 24 h activated 100% of the drug. Whole blood acidification should be avoided for the risk of hemolysis. Finally; treosulfan cytotoxicity on HL-60 cells has increased following pre-incubation for 24 h at 37 °C compared to K562 cell line.

CONCLUSION

The stability profiling of treosulfan provided a valuable reference for handling of biological samples for both in vivo and in vitro studies. These results can be utilized for further investigations concerning the drug kinetics and dynamics in addition to the development of new pharmaceutical formulations.

Immune reconstitution following hematopoietic stem cell transplantation using different stem cell sources

Introduction: Adequate immune reconstitution post-HSCT is crucial for the success of transplantation, and can be affected by both patient- and transplant-related factors. Areas covered: A systematic literature search in PubMed, Scopus, and abstracts of international congresses is performed to investigate immune recovery posttransplant. In this review, we discuss the pattern of immune recovery in the post-transplant period focusing on the impact of stem cell source (bone marrow, peripheral blood stem cells, and cord blood) on immune recovery and HSCT outcome. We examine the impact of serotherapy on immune reconstitution and the need to tailor dosing of serotherapy agents when using different stem cell sources. We discuss new techniques being used particularly with cord blood and haploidentical grafts to improve immune recovery in each scenario. Expert opinion: Cord blood T cells provide a unique CD4+ biased immune reconstitution. Initial studies using targeted serotherapy with cord grafts showed improved immune recovery with limited alloreactivity. Two competing haploidentical approaches have developed in recent years including TCRαβ/CD19 depleted grafts and post-cyclophosphamide haplo-HSCT. Both approaches have comparable survival rates with limited alloreactivity. However, delayed immune reconstitution is still an ongoing problem and could be improved by modified donor lymphocyte infusions from the same haploidentical donor.

αβ T Cell-Depleted Haploidentical Hematopoietic Stem Cell Transplantation without Antithymocyte Globulin in Children with Chemorefractory Acute Myelogenous Leukemia

We evaluated the outcome of αβ T cell-depleted haploidentical hematopoietic stem cell transplantation (HSCT) in a cohort of children with chemorefractory acute myelogenous leukemia (AML). Twenty-two patients with either primary refractory (n = 10) or relapsed refractory (n = 12) AML in active disease status received a transplant from haploidentical donors. The preparative regimen included cytoreduction with fludarabine and cytarabine and subsequent myeloablative conditioning with treosulfan and thiotepa. Antithymocyte globulin was substituted with tocilizumab in all patients and also with abatacept in 10 patients. Grafts were peripheral blood stem cells engineered by αβ T cell and CD19 depletion. Post-transplantation prophylactic therapy included infusion of donor lymphocytes, composed of a CD45RA-depleted fraction with or without a hypomethylating agent. Complete remission was achieved in 21 patients (95%). The cumulative incidence of grade II-IV acute graft-versus-host disease (GVHD) was 18%, and the cumulative incidence of chronic GVHD was 23%. At 2 years, transplantation-related mortality was 9%, relapse rate was 42%, event-free survival was 49%, and overall survival was 53%. Our data suggest that αβ T cell-depleted haploidentical HSCT provides a reasonable chance of long-term survival in a cohort of children with chemorefractory AML and creates a solid basis for further improvement.

Comparing the cost of preparing matched unrelated donor and TCR α+ β+ /CD19+ depleted donor material for pediatric hematopoietic stem cell transplants in Australia

Use of TCR α⁺ β⁺ /CD19⁺ depletion in a pediatric setting has improved the utility of haploidentical donor material, resulting in better rates of engraftment, lower rates of graft vs host disease (GVHD), and improved transplant-related mortality. There are currently no data available on the costs of TCR α⁺ β⁺ /CD19⁺ depletion. This study assessed the costs of acquiring and preparing TCR α⁺ β⁺ /CD19⁺ depleted haploidentical donor cells in comparison with matched unrelated donor (MUD) products for use in pediatric patients in Australia. Data from four pediatric transplant centers were used to estimate the resources required for donor work-up, graft acquisition, and laboratory procedures for graft preparation. Information on MUD work-up and graft acquisition was also acquired from these sites and from the national coordinating donor center in Australia. Australian-specific prices and fees were used to estimate total average costs for each transplant type, converted to USD. Preparation of graft material (including work-up, acquisition, and laboratory processes) costs USD 28 963 for TCR α⁺ β⁺ /CD19⁺ depleted haploidentical grafts and USD 27 297 for MUD grafts. The estimated difference of USD 1666 is largely attributed to the process and consumables to perform TCR α⁺ β⁺ /CD19⁺ depletion. Given the potential for recipients of TCR α⁺ β⁺ /CD19⁺ depleted grafts to require minimal GVHD prophylaxis and experience less transplant-related morbidity and mortality, use of TCR α⁺ β⁺ /CD19⁺ depletion appears favorable despite the higher initial cost. Research is currently ongoing to assess the clinical effectiveness and potential cost-effectiveness of TCR α⁺ β⁺ /CD19⁺ depletion over a patients' lifetime.

Allogeneic Hematopoietic Stem Cell Transplantation for Older Patients With Acute Myeloid Leukemia

OPINION STATEMENT

Acute myelogenous leukemia (AML) in the elderly is complex and has a poor prognosis, often characterized by higher risk cytogenetic and molecular features compared to that in younger patients. Rates of transplant have been limited by concern related to non-relapse mortality, as older patients have historically been considered medically unfit for the transplantation process. Reduced-intensity conditioning (RIC) for hematopoietic stem cell transplantation (HSCT) has been shown to provide similar efficacy to myeloablative methods, with decreased non-relapse mortality in the elderly and improved efficacy over non-transplant approaches with cytotoxic chemotherapy alone. Targeted non-cytotoxic and modified cytotoxic agents have emerged to further improve transplant outcomes for older AML patients. Validated comorbidity indices are useful tools to assess an individual's fitness for undergoing HSCT rather than chronological age alone. We believe HSCT is the primary curative treatment approach for many older AML patients, taking into account risk and comorbidities, particularly given the tendency of leukemia in this population to harbor an unfavorable disease profile. We use RIC and advocate for the addition of targeted agents if applicable. With continuing data in support of transplant for older AML patients, we anticipate that transplant rates in this population will continue to rise.

Unrelated donor vs HLA-haploidentical α/β T-cell- and B-cell-depleted HSCT in children with acute leukemia

Traditionally, hematopoietic stem cell transplantation (HSCT) from both HLA-matched related and unrelated donors (UD) has been used for treating children with acute leukemia (AL) in need of an allograft. Recently, HLA-haploidentical HSCT after αβ T-cell/B-cell depletion (αβhaplo-HSCT) was shown to be effective in single-center studies. Here, we report the first multicenter retrospective analysis of 127 matched UD (MUD), 118 mismatched UD (MMUD), and 98 αβhaplo-HSCT recipients, transplanted between 2010 and 2015, in 13 Italian centers. All these AL children were transplanted in morphological remission after a myeloablative conditioning regimen. Graft failure occurred in 2% each of UD-HSCT and αβhaplo-HSCT groups. In MUD vs MMUD-HSCT recipients, the cumulative incidence of grade II to IV and grade III to IV acute graft-versus-host disease (GVHD) was 35% vs 44% and 6% vs 18%, respectively, compared with 16% and 0% in αβhaplo-HSCT recipients (P < .001). Children treated with αβhaplo-HSCT also had a significantly lower incidence of overall and extensive chronic GVHD (P < .01). Eight (6%) MUD, 32 (28%) MMUD, and 9 (9%) αβhaplo-HSCT patients died of transplant-related complications. With a median follow-up of 3.3 years, the 5-year probability of leukemia-free survival in the 3 groups was 67%, 55%, and 62%, respectively. In the 3 groups, chronic GVHD-free/relapse-free (GRFS) probability of survival was 61%, 34%, and 58%, respectively (P < .001). When compared with patients given MMUD-HSCT, αβhaplo-HSCT recipients had a lower cumulative incidence of nonrelapse mortality and a better GRFS (P < .001). These data indicate that αβhaplo-HSCT is a suitable therapeutic option for children with AL in need of transplantation, especially when an allele-matched UD is not available.

TCR αβ+/CD19+ cell depletion in haploidentical hematopoietic allogeneic stem cell transplantation: a review of current data

Allogeneic hematopoietic stem cell transplantation is a curative option for patients with a variety of diseases. Transplantation from a related haploidentical donor is being increasingly utilized for patients who lack an available human leukocyte antigen matched related or unrelated donor. One of the strategies used for haploidentical transplants involves selective depletion of T cells expressing the αβ T cell receptor and CD19+ B cells prior to transplant. This allows for the removal of cells responsible for graft-versus-host disease and post-transplant lymphoproliferative disorder but maintains hematopoietic progenitor and stem cells for engraftment (CD34+ cells), as well as cells to elicit graft-versus-tumor effect and provide anti-infective activity (such as gamma-delta T cells and natural killer cells). The aim of this review article is to present and discuss the data available to date from studies utilizing this method of transplantation.