Megadose transplantation of purified peripheral blood CD34(+) progenitor cells from HLA-mismatched parental donors in children

Immune reconstitution after transplantation of autologous peripheral stem cells in children: a comparison between CD34+ selected and nonmanipulated grafts

BACKGROUND AND AIMS

High-dose chemotherapy (HDC) followed by autologous stem cell transplantation (ASCT) improves the prognosis in pediatric patients with several solid tumors and lymphomas. Little is known about the reconstitution of the immune system after ASCT and the influence of CD34+ cell selection on the reconstitution in pediatric patients.

METHODS

Between 1990 and 2001, 94 pediatric patients with solid tumors and lymphomas received autologous CD34+ selected or unmanipulated peripheral stem cells after HDC. CD34+ selection was carried out with magnetic microbeads. The absolute numbers of T cells, B cells and natural killer (NK) cells were measured and compared in both groups at various time points post-transplant.

RESULTS

Recovery of T cells was significantly faster in the unmanipulated group at day 30, with no significant difference later on. Reconstitution of B and NK cells was similar in both groups without significant differences at any time. The CD34+-selected group was divided into patients receiving less or more than 5.385 × 106/kg CD34+ cells. Patients in the CD34+ high-dose group displayed significantly faster reconstitutions of neutrophiles and lymphocyte subsets than the CD34+ low-dose group.

CONCLUSIONS

Engraftment and reconstitution of leukocytes, B cells and NK cells after transplantation of CD34+ selected stem cells were comparable to that in patients receiving unmanipulated grafts. T-cell recovery was faster in the unmanipulated group only within the first month. However, this delay could be compensated by transplantation of >5.385 × 106 CD34+ cells/kg. Especially for patients receiving immunotherapy after HDC large numbers of immune effector cells such as NK and T cells are necessary to mediate antibody-dependent cellular cytotoxicity. Therefore, in patients receiving autologous CD34+-selected grafts, our data emphasize the need to administer high stem cell counts.

Case Series Using Salvage Haplo-Identical Stem Cells for Secondary Transplantation

In order to expand the donor pool and accessibility of the transplant procedure, it was necessary to introduce haplo-identical stem cell transplants in the Fundeni Clinical Institute from 2015. Even if the Romanian population is an ethnically compact white population, many of the patients referred for bone marrow transplant lack a suitable donor. Hematopoietic stem cell transplant from a haplo-identical donor is an alternative option for those patients without an HLA (Human Leucocyte Antigen)-matched donor (sibling or matched unrelated). This procedure was used also as a salvage option for those who experienced engraftment failure or the rejection of the first stem cell graft. In this case series, we present three such cases, with a haplo-transplant used as a salvage protocol (after an engraftment failure or rejection of the first transplanted cells). The patients we present were diagnosed with AML (acute myeloid leukemia) with MDS (myelodysplastic syndrome), MDS-RAEB 2 (myelodysplastic syndrome-refractory anemia with excess blasts 2), and SAA (severe aplastic anemia). In two of the three cases, the engraftment failure may have been due to the conditioning Fludarabine/Busulfan/Cyclophosphamide (Flu/Bu/CFA) used, combined with marrow grafts. In all three cases, the second transplant was of haplo-identical peripheral blood stem cells using Melphalan/Fludarabine (Mel/Flu) conditioning, the cells engrafted properly and the patients experienced complete chimerism, and two of them are alive with an excellent quality of life.

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.

Ex vivo and in vivo T-cell depletion in allogeneic transplantation: towards less or non-cytotoxic conditioning regimens

INTRODUCTION

Although tremendous progress has been made since the introduction of allogeneic hematopoietic stem cell transplantation (HSCT) decades ago, there are still many obstacles to overcome. A major obstacle is the presence of T-lymphocytes in the recipient and in the donor. Recipient-derived T-lymphocytes not eliminated by the conditioning regimen are a major barrier and can lead to mixed chimerism or to complete rejection of the graft. Donor-derived T-lymphocytes can induce severe acute and chronic Graft-versus-Host Disease (GvHD).

AREAS COVERED

Currently published strategies for in vivo depletion of recipient-derived T-lymphocytes are discussed including the increase of the intensity of the conditioning regimen, the addition of anti-thymocyte globulin (ATG) or the anti-CD52 monoclonal antibody Campath. For the depletion or tolerization of the donor-derived T-lymphocytes, ex vivo-T-cell depletion methods, such as positive selection of CD34+ stem cells, negative depletion of CD3+ or TcRαβ+ T-lymphocytes or the use of post-transplant cyclophosphamide (PTCy) have been developed.

EXPERT COMMENTARY

All these currently used approaches have their disadvantages and new approaches should be investigated. In this review, we discuss current and propose new possible strategies to overcome the HLA barrier by using more specific T-cell directed therapies and/or by the combinations of current methods.

Early intestinal microbial features are associated with CD4 T-cell recovery after allogeneic hematopoietic transplant

Low intestinal microbial diversity is associated with poor outcomes after allogeneic hematopoietic cell transplantation (HCT). Using 16S rRNA sequencing of 2067 stool samples and flow cytometry data from 2370 peripheral blood samples drawn from 894 patients who underwent allogeneic HCT, we have linked features of the early post-HCT microbiome with subsequent immune cell recovery. We examined lymphocyte recovery and microbiota features in recipients of both unmodified and CD34-selected allografts. We observed that fecal microbial diversity was an independent predictor of CD4 T-cell count 3 months after HCT in recipients of a CD34-selected allograft, who are dependent on de novo lymphopoiesis for their immune recovery. In multivariate models using clinical factors and microbiota features, we consistently observed that increased fecal relative abundance of genus Staphylococcus during the early posttransplant period was associated with worse CD4 T-cell recovery. Our observations suggest that the intestinal bacteria, or the factors they produce, can affect early lymphopoiesis and the homeostasis of allograft-derived T cells after transplantation.

Co-transplantation of mesenchymal stromal cell and haploidentical hematopoietic stem cell with TCR αβ depletion in children with primary immunodeficiency syndromes

BACKGROUND

Haploidentical HSCT is a good option for children with PIDs lacking an HLA-matched donor. Co-transplantation of MSCs during haploidentical HSCT in patients with PIDs may enhance engraftment, decrease the risk of GVHD, and ensure stable donor chimerism.

METHODS

Twenty-seven pediatric patients (median age, 1.4 years; range, .3-10.9) with PIDs undergoing thirty haploidentical HSCT with TCR αβ depletion and co-transplantation of MSCs were enrolled to study. Most patients (73.3%) received myeloablative conditioning consisting of treosulfan or busulfan, fludarabine, and thiotepa. The median duration of follow-up was 14.3 months (range, 1-69 months).

RESULTS

Acute GVHD occurred in 7 patients (grade I-II n = 5, grade III-IV n = 2). Chronic GVHD was observed in only one patient. Twenty-one patients (70.2%) had 100% donor chimerism in all cell lines including T-cell and B-cell lineages. Primary graft failure was observed in 7 patients (25.9%). The cumulative incidences of TRM were 20% at day 100, and 26.7% at one year and five years. Probabilities of OS were 80% at day 100, and 71.9% at 1 year and 5 years. Infants transplanted younger than 6 months of age had the highest 5-year survival rate (85.7%).

CONCLUSION

We conclude that use of TCR αβ depleted haploidentical transplantation with MSCs may ensure a rapid engraftment rate, low incidence of significant acute and chronic GVHD, and acceptable post-transplantation morbidity, especially in patients diagnosed with SCID and may be considered in children with PIDs. In younger patients (≤6 months), survival is comparable between HLA-matched graft and CD3+ TCRαβ depleted HLA-mismatched graft recipients.

CD3/CD19 Depletion for T-cell Reduction of Allogeneic Transplants: Mostly Efficient, but not Robust

Aggressive T-cell depletion, in vitro or in vivo, is a prerequisite for survival of haplo-identical stem cell transplantation. The classical T-cell-depleted transplant, immunomagnetically enriched CD34+ cells, is very safe with respect to graft-versus-host reactivity, but associated with very high transplant-related and relapse mortality with an overall probability of survival of only 20%. Protocols for T- and B-cell depletion were therefore developed, reasoning that transplantation of the majority of Natural Killer (NK) cells and the substantial dose of residual T-cells might improve survival, which was, in principle, confirmed. Anecdotal reports of frequent failure to achieve adequate T-cell depletion prompted review of the aggregate data for transplant quality at our center. The first observation is the relative paucity of combined CD3/CD19 depletion processes as PTCy protocols have made inroads, 13 depletions in 8 years. Median T- and B-cell log-depletion were -3.89 and -1.92, respectively; instead of, CD34+ cell recovery was generally high (median 92%), as was NK-cell recovery (median 52%). However, the process failed to yield satisfactory T- and B-cell depletion in two out of 13 preparations, of which one product could be rescued by a second round of depletion, at the expense of CD34+ cell recovery. In our hands, the process is thus insufficiently robust for routine clinical use. Assuming similar observations in other centers, this may explain implementation of alternative protocols, such as TCRαβ/CD19 depletion or transplantation of unmanipulated grafts with subsequent in vivo depletion.

Comparison of haploidentical and umbilical cord blood transplantation after myeloablative conditioning

Three-year survival is similar after PTCy haplo- and UCB transplant.

Lower relapse but higher nonrelapse mortality in ≤5/8 matched UCB as compared with haplo- and 6-8/8 UCB transplant.

Haploidentical hematopoietic stem cell transplantation (haplo-HSCT) has emerged as an important treatment modality. Most reports comparing haplo-HSCT with posttransplant cyclophosphamide (PTCy) and other donor sources have focused on outcomes in older adults treated with reduced intensity conditioning. Therefore, in the current study, we evaluated outcomes in patients with hematological malignancy treated with myeloablative conditioning prior to haplo- (n = 375) or umbilical cord blood (UCB; n = 333) HSCT. All haplo recipients received a 4 of 8 HLA-matched graft, whereas recipients of UCB were matched at 6-8/8 (n = 145) or ≤5/8 (n = 188) HLA antigens. Recipients of 6-8/8 UCB transplants were younger (14 years vs 21 and 29 years) and more likely to have lower comorbidity scores compared with recipients of ≤5/8 UCB and haplo-HSCT (81% vs 69% and 63%, respectively). UCB recipients were more likely to have acute lymphoblastic leukemia and transplanted in second complete remission (CR), whereas haplo-HSCT recipients were more likely to have acute myeloid leukemia in the first CR. Other characteristics, including cytogenetic risk, were similar. Survival at 3 years was similar for the donor sources (66% haplo- and 61% after ≤5/8 and 58% after 6-8/8 UCB). Notably, relapse at 3 years was lower in recipients of ≤5/8 UCB (21%, P = .03) compared with haplo- (36%) and 6-8/8 UCB (30%). However, nonrelapse mortality was higher in ≤5/8 UCB (21%) compared with other groups (P < .0001). These data suggest that haplo-HSCT with PTCy after myeloablative conditioning provides an overall survival outcome comparable to that after UCB regardless HLA match group.

Post Transplantation Cyclophosphamide Improves Outcome of Autologous Hematopoietic Stem Cell Transplantation in Animal Model of Multiple Sclerosis

Experimental allergic encephalomyelitis (EAE) is the animal model of multiple sclerosis (MS). Autologous hematopoietic stem cell transplantation (AHSCT) has recently been recognized as the standard treatment for MS. The aim of our experiment was to investigate the effect of AHSCT with the addition of low-dose post-transplantation cyclophosphamide (Cy) on EAE in rats. Low dose post-transplantation Cy is used in haploidentical HSCT to reduce the risk of graft versus host disease. We hypothesized that it could bring additional benefit in autologous HSCT in autoimmune diseases. Rats with evoked EAE were treated with high dose (125 mg/kg) Cy, followed by AHSCT or high dose (125 mg/kg) Cy followed by AHSCT followed by low dose (20 mg/kg) Cy in two-time schedules—with the therapy applied during the pre-symptomatic or symptomatic phase of the disease. Both AHSCT and AHSCT with post-transplantation Cy in accordance with both time schedules reduce the intensity of the inflammatory response in the CNS, in comparison with non-treated EAE rats. The reduction of clinical symptoms was present in all AHSCT treatment protocols, however, it was significantly stronger when post-transplantation Cy was given during the symptomatic phase of the disease. AHSCT with the addition of post HSCT low dose Cy improved the results of AHSCT by not only reducing the intensity of inflammation in the CNS but also by significantly reducing the clinical symptoms in treated animals when compared to AHSCT alone. We provide an experimental rationale that the addition of post-transplantation Cy may improve the outcome of HSCT in MS.

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.

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.

Preclinical platform for long-term evaluation of immuno-oncology drugs using hCD34+ humanized mouse model

BACKGROUND

Well-characterized preclinical models are essential for immune-oncology research. We investigated the feasibility of our humanized mouse model for evaluating the long-term efficacy of immunotherapy and biomarkers.

METHODS

Humanized mice were generated by injecting human fetal cord blood-derived CD34+ hematopoietic stem cells to NOD-scid IL2rγnull (NSG) mice myeloablated with irradiation or busulfan. The humanization success was defined as a 25% or higher ratio of human CD45+ cells to mice peripheral blood mononuclear cells.

RESULTS

Busulfan was ultimately selected as the appropriate myeloablative method because it provided a higher success rate of humanization (approximately 80%) and longer survival time (45 weeks). We proved the development of functional T cells by demonstrating the anticancer effect of the programmed cell death-1 (PD-1) inhibitor in our humanized mice but not in non-humanized NSG mice. After confirming the long-lasting humanization state (45 weeks), we further investigated the response durability of the PD-1 inhibitor and biomarkers in our humanized mice. Early increase in serum tumor necrosis factor α levels, late increase in serum interleukin 6 levels and increase in tumor-infiltrating CD8+ T lymphocytes correlated more with a durable response over 60 days than with a non-durable response.

CONCLUSIONS

Our CD34+ humanized mouse model is the first in vivo platform for testing the long-term efficacy of anticancer immunotherapies and biomarkers, given that none of the preclinical models has ever been evaluated for such a long duration.

Identification of dual positive CD19+/CD3+ T cells in a leukapheresis product undergoing CAR transduction: a case report

Background

Chimeric antigen receptor (CAR) therapy and hematopoietic stem cell transplantation (HSCT) are therapeutics for relapsed acute lymphocytic leukemia (ALL) that are increasingly being used in tandem. We identified a non-physiologic CD19+/CD3+ T-cell population in the leukapheresis product of a patient undergoing CAR T-cell manufacturing who previously received a haploidentical HSCT, followed by infusion of a genetically engineered T-cell addback product. We confirm and report the origin of these CD19+/CD3+ T cells that have not previously been described in context of CAR T-cell manufacturing. We additionally interrogate the fate of these CD19-expressing cells as they undergo transduction to express CD19-specific CARs.

Main body

We describe the case of a preteen male with multiply relapsed B-ALL who was treated with sequential cellular therapies. He received an αβ T-cell depleted haploidentical HSCT followed by addback of donor-derived T cells genetically modified with a suicide gene for iCaspase9 and truncated CD19 for cell tracking (RivoCel). He relapsed 6 months following HSCT and underwent leukapheresis and CAR T-cell manufacturing. During manufacturing, we identified an aberrant T-cell population dually expressing CD19 and CD3. We hypothesized that these cells were RivoCel cells and confirmed using flow cytometry and PCR that the identified cells were in fact RivoCel cells and were eliminated with iCaspase9 activation. We additionally tracked these cells through CD19-specific CAR transduction and notably did not detect T cells dually positive for CD19 and CD19-directed CARs. The most likely rationale for this is in vitro fratricide of the CD19+ ‘artificial’ T-cell population by the CD19-specific CAR+ T cells in culture.

Conclusions

We report the identification of CD19+/CD3+ cells in an apheresis product undergoing CAR transduction derived from a patient previously treated with a haploidentical transplant followed by RivoCel addback. We aim to bring attention to this cell phenotype that may be recognized with greater frequency as CAR therapy and engineered αβhaplo-HSCT are increasingly coupled. We additionally suggest consideration towards using alternative markers to CD19 as a synthetic identifier for post-transplant addback products, as CD19-expression on effector T cells may complicate subsequent treatment using CD19-directed therapy.

The impact of donor type on the outcome of pediatric patients with very high risk acute lymphoblastic leukemia. A study of the ALL SCT 2003 BFM-SG and 2007-BFM-International SG

Allogeneic HSCT represents the only potentially curative treatment for very high risk (VHR) ALL. Two consecutive international prospective studies, ALL-SCT-(I)BFM 2003 and 2007 were conducted in 1150 pediatric patients. 569 presented with VHR disease leading to any kind of HSCT. All patients >2 year old were transplanted after TBI-based MAC. The median follow-up was 5 years. 463 patients were transplanted from matched donor (MD) and 106 from mismatched donor (MMD). 214 were in CR1. Stem cell source was unmanipulated BM for 330 patients, unmanipulated PBSC for 135, ex vivo T-cell depleted PBSC for 62 and cord-blood for 26. There were more advanced disease, more ex vivo T-cell depletion, and more chemotherapy based conditioning regimen for patients transplanted from MMD as compared to those transplanted from MSD or MD. Median follow up (reversed Kaplan Meier estimator) was 4.99 years, median follow up of survivals was 4.88, range (0.01–11.72) years. The 4-year CI of extensive cGvHD was 13 ± 2% and 17 ± 4% (p = NS) for the patients transplanted from MD and MMD, respectively. 4-year EFS was statistically better for patients transplanted from MD (60 ± 2% vs. 42 ± 5%, p < 0.001) for the whole cohort. This difference does not exist if considering separately patients treated in the most recent study. There was no difference in 4-year CI of relapse. The 4-year NRM was lower for patients transplanted from MD (9 ± 1% vs. 23 ± 4%, p < 0.001). In multivariate analysis, donor-type appears as a negative risk-factor for OS, EFS, and NRM. This paper demonstrates the impact of donor type on overall results of allogeneic stem cell transplantation for very-high risk pediatric acute lymphoblastic leukemia with worse results when using MMD stem cell source.

GRFS and CRFS in alternative donor hematopoietic cell transplantation for pediatric patients with acute leukemia

We report graft-versus-host disease (GVHD)-free relapse-free survival (GRFS) (a composite end point of survival without grade III-IV acute GVHD [aGVHD], systemic therapy-requiring chronic GVHD [cGVHD], or relapse) and cGVHD-free relapse-free survival (CRFS) among pediatric patients with acute leukemia (n = 1613) who underwent transplantation with 1 antigen-mismatched (7/8) bone marrow (BM; n = 172) or umbilical cord blood (UCB; n = 1441). Multivariate analysis was performed using Cox proportional hazards models. To account for multiple testing, P < .01 for the donor/graft variable was considered statistically significant. Clinical characteristics were similar between UCB and 7/8 BM recipients, because most had acute lymphoblastic leukemia (62%), 64% received total body irradiation-based conditioning, and 60% received anti-thymocyte globulin or alemtuzumab. Methotrexate-based GVHD prophylaxis was more common with 7/8 BM (79%) than with UCB (15%), in which mycophenolate mofetil was commonly used. The univariate estimates of GRFS and CRFS were 22% (95% confidence interval [CI], 16-29) and 27% (95% CI, 20-34), respectively, with 7/8 BM and 33% (95% CI, 31-36) and 38% (95% CI, 35-40), respectively, with UCB (P < .001). In multivariate analysis, 7/8 BM vs UCB had similar GRFS (hazard ratio [HR], 1.12; 95% CI, 0.87-1.45; P = .39), CRFS (HR, 1.06; 95% CI, 0.82-1.38; P = .66), overall survival (HR, 1.07; 95% CI, 0.80-1.44; P = .66), and relapse (HR, 1.44; 95% CI, 1.03-2.02; P = .03). However, the 7/8 BM group had a significantly higher risk for grade III-IV aGVHD (HR, 1.70; 95% CI, 1.16-2.48; P = .006) compared with the UCB group. UCB and 7/8 BM groups had similar outcomes, as measured by GRFS and CRFS. However, given the higher risk for grade III-IV aGVHD, UCB might be preferred for patients lacking matched donors.

Key Aspects of the Immunobiology of Haploidentical Hematopoietic Cell Transplantation

Hematopoietic stem cell transplantation from a haploidentical donor is increasingly used and has become a standard donor option for patients lacking an appropriately matched sibling or unrelated donor. Historically, prohibitive immunological barriers resulting from the high degree of HLA-mismatch included graft-vs.-host disease (GVHD) and graft failure. These were overcome with increasingly sophisticated strategies to manipulate the sensitive balance between donor and recipient immune cells. Three different approaches are currently in clinical use: (a) ex vivo T-cell depletion resulting in grafts with defined immune cell content (b) extensive immunosuppression with a T-cell replete graft consisting of G-CSF primed bone marrow and PBSC (GIAC) (c) T-cell replete grafts with post-transplant cyclophosphamide (PTCy). Intriguing studies have recently elucidated the immunologic mechanisms by which PTCy prevents GVHD. Each approach uniquely affects post-transplant immune reconstitution which is critical for the control of post-transplant infections and relapse. NK-cells play a key role in haplo-HCT since they do not mediate GVHD but can successfully mediate a graft-vs.-leukemia effect. This effect is in part regulated by KIR receptors that inhibit NK cell cytotoxic function when binding to the appropriate HLA-class I ligands. In the context of an HLA-class I mismatch in haplo-HCT, lack of inhibition can contribute to NK-cell alloreactivity leading to enhanced anti-leukemic effect. Emerging work reveals immune evasion phenomena such as copy-neutral loss of heterozygosity of the incompatible HLA alleles as one of the major mechanisms of relapse. Relapse and infectious complications remain the leading causes impacting overall survival and are central to scientific advances seeking to improve haplo-HCT. Given that haploidentical donors can typically be readily approached to collect additional stem- or immune cells for the recipient, haplo-HCT represents a unique platform for cell- and immune-based therapies aimed at further reducing relapse and infections. The rapid advancements in our understanding of the immunobiology of haplo-HCT are therefore poised to lead to iterative innovations resulting in further improvement of outcomes with this compelling transplant modality.

Haploidentical transplantation in high-risk pediatric leukemia: A retrospective comparative analysis on behalf of the Spanish working Group for bone marrow transplantation in children (GETMON) and the Spanish Grupo for hematopoietic transplantation (GETH)

A total of 192 pediatric patients, median age 8.6 years, with high-risk hematological malignancies, underwent haploidentical stem cell transplantation (haplo-HSCT) using post-transplantation cyclophosphamide (PT-Cy), or ex vivo T cell-depleted (TCD) graft platforms, from January 1999 to December 2016 in 10 centers in Spain. Some 41 patients received an unmanipulated graft followed by PT-Cy for graft-vs-host disease (GvHD) prophylaxis. A total of 151 patients were transplanted with CD3-depleted peripheral blood stem cells (PBSCs) by either CD34⁺ selection, CD3⁺ CD19⁺ depletion, TCRαβ⁺ CD19⁺ depletion or CD45RA⁺ depletion, added to CD34⁺ selection for GvHD prophylaxis. The PBSCs were the only source in patients following ex vivo TCD haplo-HSCT; bone marrow was the source in 9 of 41 patients following PT-CY haplo-HSCT. Engraftment was achieved in 91.3% of cases. A donor younger than 30 years, and the development of chronic GvHD were positive factors influencing survival, whereas positive minimal residual disease (MRD) before transplant and lymphoid disease were negative factors. The probability of relapse increased with lymphoid malignancies, a donor killer-cell immunoglobulin-like receptor (KIR) haplotype A and positive MRD pretransplant. No difference was found in overall survival, disease-free survival or relapse incidence between the two platforms. Relapse is still of concern in both platforms, and it should be the focus of future efforts. In conclusion, both platforms for haplo-HSCT were effective and could be utilized depending on the comfort level of the center.

Partially CD3+-Depleted Unrelated and Haploidentical Donor Peripheral Stem Cell Transplantation Has Favorable Graft-versus-Host Disease and Survival Rates in Pediatric Hematologic Malignancy

Most children who may benefit from stem cell transplantation lack a matched related donor. Alternative donor transplantations with an unrelated donor (URD) or a partially matched related donor (PMRD) carry an increased risk of graft-versus-host-disease (GVHD) and mortality compared with matched related donor transplantations. We hypothesized that a strategy of partial CD3⁺/CD19⁺ depletion for URD or PMRD peripheral stem cell transplantation (PSCT) would attenuate the risks of GVHD and mortality. We enrolled 84 pediatric patients with hematologic malignancies at the Children's Hospital of Philadelphia and the Children's Hospital of Wisconsin between April 2005 and February 2015. Two patients (2.4%) experienced primary graft failure. Relapse occurred in 23 patients (27.4%; cumulative incidence 26.3%), and 17 patients (20.2%) experienced nonrelapse mortality (NRM). Grade III-IV acute GVHD was observed in 18 patients (21.4%), and chronic GVHD was observed and graded as limited in 24 patients (35.3%) and extensive in 8 (11.7%). Three-year overall survival (OS) was 61.8% (95% confidence interval [CI], 50.2% to 71.4%) and event-free survival (EFS) was 52.0% (95% CI, 40.3% to 62.4%). Age ≥15 years was associated with decreased OS (P= .05) and EFS (P= .05). Relapse was more common in children in second complete remission (P = .03). Partially CD3⁺-depleted alternative donor PSCT NRM, OS, and EFS compare favorably with previously published studies of T cell-replete PSCT. Historically, T cell-replete PSCT has been associated with a higher incidence of extensive chronic GVHD compared with limited chronic GVHD, which may explain the comparatively low relapse and NRM rates in our study cohort despite similar overall rates of chronic GVHD. Partial T cell depletion may expand donor options for children with malignant transplantation indications lacking a matched related donor by mitigating, but not eliminating, chronic GVHD.

Evaluation of tenogenic differentiation potential of selected subpopulations of human adipose-derived stem cells

Identification of a suitable cell source and bioactive agents guiding cell differentiation towards tenogenic phenotype represents a prerequisite for advancement of cell-based therapies for tendon repair. Human adipose-derived stem cells (hASCs) are a promising, yet intrinsically heterogenous population with diversified differentiation capacities. In this work, we investigated antigenically-defined subsets of hASCs expressing markers related to tendon phenotype or associated with pluripotency that might be more prone to tenogenic differentiation, when compared to unsorted hASCs. Subpopulations positive for tenomodulin (TNMD+ hASCs) and stage specific early antigen 4 (SSEA-4+ hASCs), as well as unsorted ASCs were cultured up to 21 days in basic medium or media supplemented with TGF-β3 (10 ng/ml), or GDF-5 (50 ng/ml). Cell response was evaluated by analysis of expression of tendon-related markers at gene level and protein level by real time RT-PCR, western blot, and immunocytochemistry. A significant upregulation of scleraxis was observed for both subpopulations and unsorted hASCs in the presence of TGF-β3. More prominent alterations in gene expression profile in response to TGF-β3 were observed for TNMD+ hASCs. Subpopulations evidenced an increased collagen III and TNC deposition in basal medium conditions in comparison with unsorted hASCs. In the particular case of TNMD+ hASCs, GDF-5 seems to influence more the deposition of TNC. Within hASCs populations, discrete subsets could be distinguished offering varied sensitivity to specific biochemical stimulation leading to differential expression of tenogenic components suggesting that cell subsets may have distinctive roles in the complex biological responses leading to tenogenic commitment to be further explored in cell based strategies for tendon tissues.

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.

Review of Haploidentical Hematopoietic Cell Transplantation

Use of haploidentical (haplo) donors for hematopoietic cell transplantation (HCT) has significantly increased in the last decade. The major advantage with this strategy is universal availability and faster acquisition of the donor, along with affordability and provision of immunotherapy in post-transplantation period. Historically, haplo-HCT was associated with compromised outcomes because of high rates of graft-versus-host disease and graft failure, but after the development of a post-transplantation high-dose cyclophosphamide strategy, which results in selective T-cell depletion, these issues have been addressed to a large extent. Nevertheless, graft failure, high treatment-related mortality due to graft-versus-host disease, infections, delayed immune reconstitution, and disease relapse remain significant concerns. As the experience with haplo-HCTs grows, the clinical outcomes are becoming more at par with those seen with fully matched unrelated donor allogeneic HCTs.

New graft manipulation strategies improve the outcome of mismatched stem cell transplantation in children with primary immunodeficiencies

BACKGROUND

Mismatched stem cell transplantation is associated with a high risk of graft loss, graft-versus-host disease (GvHD), and transplant-related mortality. Alternative graft manipulation strategies have been used over the last 11 years to reduce these risks.

OBJECTIVE

We investigated the outcome of using different graft manipulation strategies among children with primary immunodeficiencies.

METHODS

Between 2006 and 2017, 147 patients with primary immunodeficiencies received 155 mismatched grafts: 30 T-cell receptor (TCR) αβ/CD19-depleted grafts, 43 cord blood (CB) grafts (72% with no serotherapy), 17 CD34⁺ selection with T-cell add-back grafts, and 65 unmanipulated grafts.

RESULTS

The estimated 8-year survival of the entire cohort was 79%, transplant-related mortality was 21.7%, and the graft failure rate was 6.7%. Posttransplantation viral reactivation, grade II to IV acute graft-versus-host disease (aGvHD), and chronic graft-versus-host disease (cGvHD) complicated 49.6%, 35%, and 15% of transplantations, respectively. Use of TCRαβ/CD19 depletion was associated with a significantly lower incidence of grade II to IV aGvHD (11.5%) and cGvHD (0%), although with a greater incidence of viral reactivation (70%) in comparison with other grafts. T-cell immune reconstitution was robust among CB transplants, although with a high incidence (56.7%) of grade II to IV aGvHD. Stable full donor engraftment was significantly greater at 80% among TCRαβ⁺/CD19⁺-depleted and CB transplants versus 40% to 60% among the other groups.

CONCLUSIONS

Rapidly accessible CB and haploidentical grafts are suitable alternatives for patients with no HLA-matched donor. Cord transplantation without serotherapy and TCRαβ⁺/CD19⁺-depleted grafts produced comparable survival rates of around 80%, although with a high rate of aGvHD with the former and a high risk of viral reactivation with the latter that need to be addressed.

Joint Modeling of Immune Reconstitution Post Haploidentical Stem Cell Transplantation in Pediatric Patients With Acute Leukemia Comparing CD34+-Selected to CD3/CD19-Depleted Grafts in a Retrospective Multicenter Study

Rapid immune reconstitution (IR) following stem cell transplantation (SCT) is essential for a favorable outcome. The optimization of graft composition should not only enable a sufficient IR but also improve graft vs. leukemia/tumor effects, overcome infectious complications and, finally, improve patient survival. Especially in haploidentical SCT, the optimization of graft composition is controversial. Therefore, we analyzed the influence of graft manipulation on IR in 40 patients with acute leukemia in remission. We examined the cell recovery post haploidentical SCT in patients receiving a CD34⁺-selected or CD3/CD19-depleted graft, considering the applied conditioning regimen. We used joint model analysis for overall survival (OS) and analyzed the dynamics of age-adjusted leukocytes; lymphocytes; monocytes; CD3⁺, CD3⁺CD4⁺, and CD3⁺CD8⁺ T cells; natural killer (NK) cells; and B cells over the course of time after SCT. Lymphocytes, NK cells, and B cells expanded more rapidly after SCT with CD34⁺-selected grafts (P = 0.036, P = 0.002, and P < 0.001, respectively). Contrarily, CD3⁺CD4⁺ helper T cells recovered delayer in the CD34 selected group (P = 0.026). Furthermore, reduced intensity conditioning facilitated faster immune recovery of lymphocytes and T cells and their subsets (P < 0.001). However, the immune recovery for NK cells and B cells was comparable for patients who received reduced-intensity or full preparative regimens. Dynamics of all cell types had a significant influence on OS, which did not differ between patients receiving CD34⁺-selected and those receiving CD3/CD19-depleted grafts. In conclusion, cell reconstitution dynamics showed complex diversity with regard to the graft manufacturing procedure and conditioning regimen.

Approaches to the removal of T-lymphocytes to minimize graft-versus-host disease in patients with primary immunodeficiencies who do not have a matched sibling donor

PURPOSE OF REVIEW

Since the advent of T-lymphocyte depletion in hematopoietic stem cell transplantation (HSCT) for primary immunodeficiency, survival following this procedure has remained poor compared to results when using matched sibling or matched unrelated donors, over the last 40 years. However, three new techniques are radically altering the approach to HSCT for those with no matched donor, particularly those with primary immunodeficiencies which are not severe combined immunodeficiency.

RECENT FINDINGS

Three main techniques of T-lymphocyte depletion are altering donor choice for patients with primary immunodeficiencies and have improved transplant survival for primary immunodeficiencies to over 90%, equivalent to that for matched sibling and matched unrelated donor transplants. CD3 T cell receptor (TCR)αβ CD19 depletion, CD45RA depletion and use of posttransplant cyclophosphamide give similar overall survival of 90%, although viral reactivation remains a concern. Further modification of CD3 TCRαβ CD19 depletion by adding back inducible caspase-9 suicide gene-modified CD3 TCRαβ T-lymphocytes may further improve outcomes for patients with systemic viral infection.

SUMMARY

Over the last 5 years, the outcomes of HSCT using new T-lymphocyte depletion methods have improved to the extent that they are equivalent to outcomes of matched sibling donors and may be preferred in the absence of a fully matched sibling donor, over an unrelated donor to reduce the risk of graft versus host disease.

Infusion of Alloanergized Donor Lymphocytes after CD34-selected Haploidentical Myeloablative Hematopoietic Stem Cell Transplantation

Purpose: Allogeneic hematopoietic stem-cell transplantation (HSCT) is a curative treatment for many hematologic cancers. Use of haploidentical (mismatched) donors increases HSCT availability but is limited by severe graft-versus-host disease (GvHD) and delayed immune reconstitution. Alloanergization of donor T cells is a simple approach to rebuild immunity while limiting GvHD after haploidentical HSCT, but the optimal T-cell dose and impact on immune reconstitution remain unknown.Patients and Methods: We performed a multicenter phase I trial of alloanergized donor lymphocyte infusion (aDLI) after CD34-selected myeloablative haploidentical HSCT. The primary aim was feasibility and safety with secondary aims of assessing the less frequently addressed issue of impact on immune reconstitution.Results: Nineteen patients with high-risk acute leukemia or myelodysplasia were enrolled. Engraftment occurred in 18 of 19 patients (95%). Pre-aDLI, 12 patients (63%) had bacteremia, nine of 17 at-risk patients (53%) reactivated CMV, and one developed acute GvHD. Sixteen patients received aDLI at dose levels 1 (10³ T cells/kg, n = 4), 2 (10⁴, n = 8), and 3 (10⁵, n = 4). After aDLI, five patients developed clinically significant acute GvHD, and four of 14 at-risk patients (29%) reactivated CMV. T-cell recovery was significantly greater, and functional virus- and tumor-associated antigen-specific T cells were detectable earlier in patients receiving dose level 2 or 3 versus dose level 1/no aDLI. Alloanergization of donor cells expanded the CD4⁺ T-regulatory cell frequency within aDLI, which increased further in vivo without impeding expansion of virus- and tumor-associated antigen-specific T cells.Conclusions: These data demonstrate safety and a potential role for aDLI in contributing to immune reconstitution and expanding tolerogenic regulatory T cells in vivo after CD34-selected myeloablative haploidentical HSCT. Clin Cancer Res; 24(17); 4098-109. ©2018 AACR.

Allogeneic Stem Cell Transplantation from HLA-Mismatched Donors for Pediatric Patients with Acute Lymphoblastic Leukemia Treated According to the 2003 BFM and 2007 International BFM Studies: Impact of Disease Risk on Outcomes

Allogeneic hematopoietic stem cell transplantation (HSCT) is beneficial for pediatric patients with relapsed or (very) high-risk acute lymphoblastic leukemia (ALL) in remission. A total of 1115 consecutive patients were included in the ALL SCT 2003 BFM study and the ALL SCT 2007 I-BFM study and were stratified according to relapse risk (standard versus high versus very high risk of relapse) and donor type (matched sibling versus matched donor versus mismatched donor). A total of 148 patients (60% boys; median age, 8.7 years; B cell precursor ALL, 75%) were transplanted from mismatched donors, which was defined as either less than 9/10 HLA-compatible donors or less than 5/6 unrelated cord blood after myeloablative conditioning regimen (total body irradiation based, 67%) for high relapse risk (HRR; n = 42) or very HRR (VHRR) disease (n = 106). The stem cell source was either bone marrow (n = 31), unmanipulated peripheral stem cells (n = 28), T cell ex vivo depleted peripheral stem cells (n = 59), or cord blood (n = 25). The median follow-up was 5.1 years. The 4-year rates of overall survival (OS) and event-free survival were 56% ± 4% and 52% ± 4%, respectively, for the entire cohort. Patients transplanted from mismatched donors for HRR disease obtained remarkable 4-year OS and event-free survival values of 82% ± 6% and 80% ± 6%, respectively, whereas VHRR patients obtained values of 45% ± 5% and 42% ± 5% (P < .001), respectively. The cumulative incidence of relapse was 29% ± 4% and that of nonrelapse mortality 19% ± 3%. The cumulative incidence of limited and extensive chronic graft-versus-host disease was 13% ± 3% and 15% ± 4%, respectively, among the 120 patients living beyond day 100. Multivariate analysis showed that OS was lower for transplanted VHRR patients (P = .002; hazard ratio [HR], 3.62; 95% confidence interval [CI], 1.60 to 8.20) and for patients beyond second complete remission (CR2) versus first complete remission (P < .001; HR, 3.68; 95% CI, 1.79 to 7.56); relapse occurred more frequently in patients with VHRR disease (P = .026; HR, 3.30; 95% CI, 1.16 to 9.60) and for those beyond CR2 (P = .005; HR, 4.16; 95% CI, 1.52 to 10.59). Nonrelapse mortality was not significantly higher for cytomegalovirus-positive recipients receiving cytomegalovirus-negative grafts (P = .12; HR, 1.96; 95% CI, .84 to 4.58). HSCT with a mismatched donor is feasible in pediatric ALL patients but leads to inferior results compared with HSCT with better matched donors, at least for patients transplanted for VHRR disease. The results are strongly affected by disease status. The main cause of treatment failure is still relapse, highlighting the urgent need for interventional strategies after HSCT for patients with residual leukemia before and/or after transplantation.

Comparison of two cytoreductive regimens for αβ-T-cell-depleted haploidentical HSCT in pediatric malignancies: Improved engraftment and outcome with TBI-based regimen

BACKGROUND

Graft manipulation using selective depletion of αβ-T cells provides a source of haploidentical hematopoietic stem cell transplantation (haplo-HSCT) enriched in effector cells. We report our experience implementing this haplo-HSCT for high-risk malignancies in pediatric patients focusing on the conditioning regimen.

PROCEDURE

We performed a retrospective study of patients who underwent T-cell receptor αβ-depleted haplo-HSCT for high-risk pediatric malignancies.

RESULTS

Eighteen patients underwent haplo-HSCT using this method. The initial reduced-toxicity chemotherapy-based conditioning regimen was given to eight patients, and resulted in a high rate of graft rejections (six of eight patients). Thus, total body irradiation (TBI) based regimen was introduced in the following 10 patients and resulted in engraftment in all patients. Neutrophil and platelet engraftment were rapid (median time to engraft, 10 days and 12 days, respectively). Significant treatment-related complications for both cohorts were all due to graft failure in patients receiving chemotherapy-based conditioning, with a treatment-related mortality rate of 17%. None of the patients developed hepatic sinusoidal-obstruction syndrome, and no grade III-IV acute graft versus host disease (GVHD) was observed. The majority of patients were free of immunosuppression in the first 100 days post-HSCT, and only two patients developed chronic GVHD. The cumulative incidence of relapse was 39%. Compared to patients conditioned with chemotherapy, patients conditioned with TBI had superior actuarial overall survival (66% vs. 37%, P = 0.05) and event-free survival (61% vs. 33%, P = 0.04).

CONCLUSIONS

A TBI-based conditioning for haplo-HSCT using αβ-T-cell depletion for malignant diseases ensured engraftment and resulted in acceptable outcomes.

Donor lymphocyte infusion and methotrexate for immune recovery after T-cell depleted haploidentical transplantation

CD34+ cell selection minimizes graft-versus-host disease (GVHD) after haploidentical donor stem cell transplant but is associated with slow immune recovery and infections. We report a Phase I/II study of prophylactic donor lymphocyte infusion (DLI) followed by methotrexate (MTX) GVHD prophylaxis after CD34-selected haploidentical donor transplant. A prophylactic DLI was given between day +30 and +42. Rituximab was given with DLI for the last 10 patients. The goal of the study was to determine a DLI dose that would result in a CD4+ cell count > 100/µL at Day +120 in ≥ 66% of patients with ≤ 33% grade II-III, ≤ 17% grade III, and no grade IV acute GVHD by Day +180. Thirty-five patients with malignant (n = 25) or nonmalignant disease (n = 10) were treated after CD34-selected haploidentical donor peripheral blood stem cell transplant. The DLI dose of 5 × 10⁴ /kg met the CD4/GVHD goal with 67% of patients having CD4+ cells > 100/µL and 11% grade II-IV acute GVHD. The cumulative incidence of chronic GVHD was 16%. Fatal viral and fungal infections occurred in 11%. The 2 year estimated overall survival was 69% and the relapse rate was 14% for patients in remission at transplant. There was no effect of NK alloreactivity on relapse. Nine of ten patients at the target DLI dose cohort of 5 × 10⁴ /kg are alive with median follow-up of 18 mos (range 6-29). Delayed prophylactic DLI and MTX was associated with promising outcomes at the target DLI dose. This trial was registered at clinicaltrials.gov, # NCT01027702.

NK cell therapy for hematologic malignancies

Natural killer (NK) cells are part of the innate immune system and represent the first line of defense against infections and tumors. In contrast to T cells, NK cells do not require prior antigen sensitization to induce cytotoxicity and do not cause graft-versus-host disease. These, along with other advantages, make NK cells an attractive candidate for adoptive cellular therapy. Herein, we describe the mechanisms of NK cell cytotoxicity, which is governed by an intricate balance between various activating and inhibitory receptors, including the killer cell immunoglobulin-like receptors (KIRs). We illustrate the advantages of NK alloreactivity as demonstrated in various types of hematopoietic stem cell transplants (HSCT), such as haploidentical, human leukocyte antigen-matched related or unrelated donor and umbilical cord blood transplant. We elaborate on different models used to predict NK cell alloreactivity in these studies, which are either based on the absence of the ligands for inhibitory KIRs, presence of activating NK cell receptors and KIR genes content in donors, or a combination of these. We will review clinical studies demonstrating anti-tumor efficacy of NK cells used either as a stand-alone immunotherapy or as an adjunct to HSCT and novel genetic engineering strategies to improve the anti-tumor activity of NK cells.

Transient apoptosis inhibition in donor stem cells improves hematopoietic stem cell transplantation

During hematopoietic stem cell transplantation, a substantial number of donor cells are lost because of apoptotic cell death. Transplantation-associated apoptosis is mediated mainly by the proapoptotic BCL-2 family proteins BIM and BMF, and their proapoptotic function is conserved between mouse and human stem and progenitor cells. Permanent inhibition of apoptosis in donor cells caused by the loss of these BH3-only proteins improves transplantation outcome, but recipients might be exposed to increased risk of lymphomagenesis or autoimmunity. Here, we address whether transient inhibition of apoptosis can serve as a safe but efficient alternative to improve the outcome of stem cell transplantation. We show that transient apoptosis inhibition by short-term overexpression of prosurvival BCL-XL, known to block BIM and BMF, is not only sufficient to increase the viability of hematopoietic stem and progenitor cells during engraftment but also improves transplantation outcome without signs of adverse pathologies. Hence, this strategy represents a promising and novel therapeutic approach, particularly under conditions of limited donor stem cell availability.

In-vivo or ex-vivo T cell depletion or both to prevent graft-versus-host disease after hematopoietic stem cell transplantation

INTRODUCTION

Hematopoietic stem cell transplantation (HSCT) represents a widely accepted therapeutic strategy for the treatment of hematologic disorders which are otherwise considered incurable. Alloreactive T cells infused with the stem cell inoculum may generate graft-versus-host disease (GVHD) representing one the most relevant obstacles to the successful outcome of patients receiving allogeneic HSCT. Areas covered: In this review, the authors provide an overview of the most recent approaches of T-cell depletion (TCD) including ex-vivo αβ+ TCD and in-vivo TCD with anti-thymocyte globulin (ATG). Expert opinion: Ex vivo depletion of donor T-cells prevents both acute and chronic GVHD without the need for any additional posttransplant immunological prophylaxis either in haploidentical HSCT and HLA matched transplants. Three prospective trials evaluating the efficacy of ATG in matched unrelated donor transplant recipients demonstrated that ATG reduces the incidence of both acute and chronic GVHD without a significant increase of relapse rate, and similar results have been reported in the setting of blood stem cell grafts from matched sibling donors.

T Cell-Mediated Rejection of Human CD34+ Cells Is Prevented by Costimulatory Blockade in a Xenograft Model

A xenograft model of stem cell rejection was developed by co-transplantating human CD34⁺ and allogeneic CD3⁺ T cells into NOD-scid ɣ-chain^null mice. T cells caused graft failure when transplanted at any CD34/CD3 ratio between 1:50 and 1:.1. Kinetics experiments showed that 2 weeks after transplantation CD34⁺ cells engrafted the marrow and T cells expanded in the spleen. Then, at 4 weeks only memory T cells populated both sites and rejected CD34⁺ cells. Blockade of T cell costimulation was tested by injecting the mice with abatacept (CTLA4-IgG1) from day -1 to +27 (group A), from day -1 to +13 (group B), or from day +14 to +28 (group C). On day +56 groups B and C had rejected the graft, whereas in group A graft failure was completely prevented, although with lower stem cell engraftment than in controls (P = .03). Retransplantation of group A mice with same CD34⁺ cells obtained a complete reconstitution of human myeloid and B cell lineages and excluded latent alloreactivity. In this first xenograft model of stem cell rejection we showed that transplantation of HLA mismatched CD34⁺ cells may be facilitated by treatment with abatacept and late stem cell boost.

Alternative donor hematopoietic stem cell transplantation for sickle cell disease

Most patients who could be cured of sickle cell disease (SCD) with stem cell transplantation do not have a matched sibling donor. Successful use of alternative donors, including mismatched family members, could provide a donor for almost all patients with SCD. The use of a reduced-intensity conditioning regimen may decrease late adverse effects. Ten patients with symptomatic SCD underwent CD34⁺ cell-selected, T-cell-depleted peripheral blood stem cell transplantation from a mismatched family member or unrelated donor. A reduced-intensity conditioning regimen including melphalan, thiotepa, fludarabine, and rabbit anti-thymocyte globulin was used. Patients were screened for a companion study for immune reconstitution that included a donor lymphocyte infusion given 30-42 days after transplant with intravenous methotrexate as graft-versus-host disease (GVHD) prophylaxis. Seven eligible patients were treated on the companion study. Nine of 10 patients are alive with a median follow-up of 49 months (range, 14-60 months). Surviving patients have stable donor hematopoietic engraftment (mean donor chimerism, 99.1% ± 0.7%). There were no sickle cell complications after transplant. Two patients had grade II-IV acute GVHD. One patient had chronic GVHD. Epstein-Barr virus-related posttransplant lymphoproliferative disorder (PTLD) occurred in 3 patients, and 1 patient died as a consequence of treatment of PTLD. Two-year overall survival was 90%, and event-free survival was 80%. A reduced-intensity conditioning regimen followed by CD34⁺ cell-selected, T-cell-depleted alternative donor peripheral blood stem cell transplantation achieved primary engraftment in all patients with a low incidence of GVHD, although PTLD was problematic. This trial was registered at clinicaltrials.gov as #NCT00968864.

Evaluation of bone marrow mononuclear cells as an adjunct therapy to minced muscle graft for the treatment of volumetric muscle loss injuries

BACKGROUND

The delivery of alternative myogenic cell sources to enhance the efficacy of minced muscle grafts (MG) for the treatment of volumetric muscle loss (VML) injuries is a promising strategy to overcome the demand on muscle-derived donor tissue that currently limits the translation of this therapy.

METHODS

Using a rat model of VML, bone marrow mononuclear cells (BMNCs) were evaluated for their ability to directly contribute to de novo muscle fiber regeneration by transplanting MG in a collagen carrier at a dose of 50% of the VML injury both with and without concomitant delivery of 5 million BMNCs derived via density gradient centrifugation from the bone marrow of a syngeneic green fluorescent protein (GFP)⁺ donor.

RESULTS

Histological, molecular, and functional analyses revealed that BMNCs can engraft with co-delivered MG and contribute to nascent myofiber, but do so at a low magnitude without resulting in significant changes to transcription of key myogenic genes or gains in whole muscle force generation relative to MG alone.

CONCLUSION

As such, co-delivery of BMNCs with MG is a promising treatment paradigm to VML that will require further investigation to identify the phenotype and therapeutic dosing of the bone marrow-derived cell populations which engraft most efficiently.

Incorporation of high-dose 131 I-metaiodobenzylguanidine treatment into killer immunoglobulin-like receptor/HLA-ligand mismatched haploidentical stem cell transplantation for children with neuroblastoma who failed tandem autologous stem cell transplantation

BACKGROUND

We performed a pilot study (NCT 00793351) to evaluate the effectiveness and feasibility of a strategy incorporating high-dose ¹³¹ I-metaiodobenzylguanidine (HD-MIBG) treatment into killer immunoglobulin-like receptor (KIR)/HLA-ligand mismatched haploidentical stem cell transplantation (haplo-SCT) in improving the survival of children with neuroblastoma who failed previous tandem autologous SCT.

PROCEDURE

If the patient remained progression free with salvage treatment, HD-MIBG treatment (18 mCi/kg) was given prior to reduced-intensity conditioning (cyclophosphamide + fludarabine + antithymocyte globulin). Grafts from KIR/HLA-ligand mismatched, preferably BX haplotype, haploidentical donors were transplanted to enhance the graft-versus-tumor (GVT) effect.

RESULTS

A total of seven patients were enrolled and three donors had a BX haplotype. Toxicities during HD-MIBG treatment and reduced-intensity conditioning were mild. Neutrophil recovery and complete or near complete donor chimerism were rapidly achieved. Six patients experienced acute graft-versus-host disease (GVHD; grade I in five and grade III in one), and four of six evaluable patients experienced chronic GVHD (two mild and two severe). Four patients died from tumor progression, one died from sepsis without progression, and the other two remained alive in complete response during 34 and 48 months posttransplant. All three patients remained progression free after BX haplotype SCT, whereas the other four experienced progression after AA haplotype SCT.

CONCLUSIONS

Our results suggest that the incorporation of HD-MIBG treatment in haplo-SCT and the use of BX haplotype donors might improve outcome, but this approach is currently limited by unacceptable GVHD. Further work focused on enhancement of GVT effects in relapsed neuroblastoma should be coupled with efforts to reduce GVHD.

Haploidentical hematopoietic transplantation for the cure of leukemia: from its biology to clinical translation

The present review describes the biology of human leukocyte antigen haplotype mismatched ("haploidentical") transplantation, its translation to clinical practice to cure leukemia, and the results of current transplantation protocols. The 1990s saw what had been major drawbacks of haploidentical transplantation, ie, very strong host-versus-graft and graft-versus-host alloresponses, which led respectively to rejection and graft-versus-host disease (GVHD), being overcome through transplantation of a "mega-dose" of T cell-depleted peripheral blood hematopoietic progenitor cells and no posttransplant pharmacologic immunosuppression. The absence of posttransplant immunosuppression was an opportunity to discover natural killer cell alloreactions that eradicated acute myeloid leukemia and improved survival. Furthermore, it also unveiled the benefits of transplantation from mother donors, a likely consequence of the mother-to-child interaction during pregnancy. More recent transplantation protocols use unmanipulated (without ex vivo T-cell depletion) haploidentical grafts combined with enhanced posttransplant immunosuppression to help prevent GVHD. Unmanipulated grafts substantially extended the use of haploidentical transplantation with results than even rival those of matched hematopoietic transplantation. In T cell-depleted haploidentical transplantation, recent advances were made by the adoptive transfer of regulatory and conventional T cells.

Recent advances in haploidentical hematopoietic stem cell transplantation using ex vivo T cell-depleted graft in children and adolescents

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 ex vivo depletion of T cells or unmanipulated in vivo regulation of T cells, better supportive care, and optimal conditioning regimens have significantly improved the outcomes of haploidentical HSCT. The ex vivo techniques used to remove T cells have evolved from the selection of CD34⁺ hematopoietic stem cell progenitors to the depletion of CD3⁺ cells, and more recently to the depletion of αβ⁺ T cells. The recent emerging evidence for ex vivo T cell-depleted haploidentical HSCT has provided additional therapeutic options for pediatric patients with diseases curable by HSCT but has not found a suitable related or unrelated donor. This review discusses recent advances in haploidentical HSCT, focusing on transplant using ex vivo T cell-depleted grafts. In addition, our experiences with this novel approach for the treatment of pediatric patients with malignant and non-malignant diseases are described.

Haploidentical Transplantation in Children with Acute Leukemia: The Unresolved Issues

Allogeneic hematopoietic stem cell transplantation (HSCT) remains a curative option for children with high risk and advanced acute leukemia. Yet availability of matched family donor limits its use and although matched unrelated donor or mismatched umbilical cord blood (UCB) are viable options, they fail to meet the global need. Haploidentical family donor is almost universally available and is emerging as the alternate donor of choice in adult patients. However, the same is not true in the case of children. The studies of haploidentical HSCT in children are largely limited to T cell depleted grafts with not so encouraging results in advanced leukemia. At the same time, emerging data from UCBT are challenging the existing paradigm of less stringent HLA match requirements as perceived in the past. The use of posttransplantation cyclophosphamide (PTCY) has yielded encouraging results in adults, but data in children is sorely lacking. Our experience of using PTCY based haploidentical HSCT in children shows inadequacy of this approach in younger children compared to excellent outcome in older children. In this context, we discuss the current status of haploidentical HSCT in children with acute leukemia in a global perspective and dwell on its future prospects.

Improved immune recovery after transplantation of TCRαβ/CD19-depleted allografts from haploidentical donors in pediatric patients

Immune recovery was retrospectively analyzed in a cohort of 41 patients with acute leukemia, myelodysplastic syndrome and nonmalignant diseases, who received αβ T- and B-cell-depleted allografts from haploidentical family donors. Conditioning regimens consisted of fludarabine or clofarabine, thiotepa, melphalan and serotherapy with OKT3 or ATG-Fresenius. Graft manipulation was carried out with anti-TCRαβ and anti-CD19 Abs and immunomagnetic microbeads. The γδ T cells and natural killer cells remained in the grafts. Primary engraftment occurred in 88%, acute GvHD (aGvHD) grades II and III-IV occurred in 10% and 15%, respectively. Immune recovery data were available in 26 patients and comparable after OKT3 (n=7) or ATG-F (n=19). Median time to reach >100 CD3+ cells/μL, >200 CD19+ cells/μL and >200 CD56+ cells/μL for the whole group was 13, 127 and 12.5 days, respectively. Compared with a historical control group of patients with CD34+ selected grafts, significantly higher cell numbers were found for CD3+ at days +30 and +90 (267 vs 27 and 397 vs 163 cells/μL), for CD3+4+ at day +30 (58 vs 11 cells/μL) and for CD56+ at day +14 (622 vs 27 cells/μL). The clinical impact of this accelerated immune recovery will be evaluated in an ongoing prospective multicenter trial.

Correlation of rabbit antithymocyte globulin serum levels and clinical outcomes in children who received hematopoietic stem cell transplantation from an alternative donor

We analyzed the correlation between rabbit ATG (rATG) serum levels and clinical outcomes in 37 children who received rATG at a total dose of 10 or 15 mg/kg during HSCT conditioning from an alternative donor. Fourteen patients had advanced malignant diseases, 13 had severe AA, and 10 had inherited disorders. Complete engraftment was achieved in all patients, and no rejection occurred. The cumulative incidence of grades II-IV acute GVHD and extensive chronic GVHD was 27% (95% CI, 12.5-39.6%) and 8.1% (95% CI, 0-23.1%), respectively. Multivariate analysis identified lower rATG levels at week 4 as an independent risk factor in the development of grades II-IV acute GVHD (p = 0.037). Serious infections were not observed in any patient following HSCT. No correlation was found between EBV reactivation and rATG levels at week 2 and week 4 after HSCT. Furthermore, no correlation was found between relapse and rATG levels two and four wk post-transplantation. The probability of five-yr OS among patients was 70.3% (95% CI, 59.8-79.2%). Our results suggest that targeted rATG administration may protect patients from severe acute GVHD without increasing the risk of EBV reactivation or relapse.

Novel treatment of severe combined immunodeficiency utilizing ex-vivo T-cell depleted haploidentical hematopoietic stem cell transplantation and CD45RA+ depleted donor lymphocyte infusions

BACKGROUND

Allogeneic hematopoietic stem cell transplantation (HSCT) is the only curative treatment available for severe combined immunodeficiency (SCID); although, there is a high incidence of severe infections and an increased risk of graft-versus host-disease (GvHD) with HSCT. Early intervention is a crucial prognostic factor and a HLA-haploidentical parental donor is often available. Haploidentical HSCT protocols utilizing extensively ex vivo T-cell depleted grafts (CliniMACs system) have proven efficient in preventing GvHD, but cause a delay in early T-cell recovery that increases the risk of viral infections. Here, we present a novel approach for treating SCID that combines selective depletion of GvHD-inducing alpha/beta (α/β) T-cells from the haploidentical HSCT graft with a subsequent donor lymphocyte infusion (DLI) enriched for CD45RO+ memory T-cells.

RESULTS

Our patient was diagnosed with SCID (T-B + NK+ phenotype). At 9 months of age, he received a T cell receptor(TCR)α/β-cell depleted graft from his haploidentical mother, following a reduced intensity conditioning regimen with no additional GvHD prophylaxis. Engraftment was rapid with complete donor chimerism and no signs of GvHD. However, at 12 weeks post HSCT, the patient was still T-cell lymphopenic with clinical symptoms of multiple severe viral infections. Consequently, therapeutic DLIs were initiated for enhanced anti-viral immunity. The patient was treated with CD45RA+ depleted haploidentical maternal donor lymphocytes enriched from unmobilized whole blood, and a total T-cell dose of no more than 25 x10(3) CD3+ cells/kg with >99.9% purity of CD3 + CD45RO+ memory T-cells was transferred. Following the DLI, a prompt increase in CD3 + CD4+ and CD3 + CD8+ counts was observed with a subsequent clearance of viral infections. No acute or chronic GvHD was observed.

CONCLUSIONS

Automated depletion of CD45RA+ naïve T-cells from unmobilized whole blood is a simple and rapid strategy to provide unmanipulated DLIs, with a potentially broad repertoire of pathogen specific memory T-cells. In the haploidentical setting, CD45RA+ depleted DLIs can be safely administered at low T-cell doses for efficient enhancement of viral immunity and limited risk of GvHD. We demonstrate the successful use of this approach following TCR-α/β-cell depleted HSCT for the treatment of SCID.

The evolution of T-cell depletion in haploidentical stem-cell transplantation

T-cell depletion (TCD) can prevent the onset of graft-versus-host disease (GvHD) in animal models of bone marrow transplantation; this manipulation enabled the successful application in the 1980s of T-cell depleted bone marrow (BM) for the treatment of babies with severe combined immune deficiency (SCID). However, in leukaemia patients, implementation of T-cell depletion has been more difficult, especially due to high rate of graft-rejection, leukaemia relapse and delayed immune reconstitution. These hurdles were gradually overcome by modifying the cell composition of the graft, and by reducing the toxicities associated with conditioning protocols. Although no 'gold standard' TCD method exists, T-cell depletion in its modern forms could offer clinical benefit, even for patients with a matched sibling donor.

Adipose-derived stem cells: selecting for translational success

We have witnessed a rapid expansion of in vitro characterization and differentiation of adipose-derived stem cells, with increasing translation to both in vivo models and a breadth of clinical specialties. However, an appreciation of the truly heterogeneous nature of this unique stem cell group has identified a need to more accurately delineate subpopulations by any of a host of methods, to include functional properties or surface marker expression. Cells selected for improved proliferative, differentiative, angiogenic or ischemia-resistant properties are but a few attributes that could prove beneficial for targeted treatments or therapies. Optimizing cell culture conditions to permit re-introduction to patients is critical for clinical translation.

Is there a stronger graft-versus-leukemia effect using HLA-haploidentical donors compared with HLA-identical siblings?

Haploidentical hematopoietic stem cell transplants (HSCTs) are increasingly used, but it is unknown whether they have a stronger graft-versus-leukemia (GVL) effect. We analyzed 10 679 acute leukemia patients who underwent HSCT from an HLA-matched sibling donor (MSD, n=9815) or a haploidentical donor (⩾2 HLA-antigen disparity, n=864) between 2007 and 2012, reported to the European Group for Blood and Marrow Transplantation. In a Cox regression model, acute and chronic graft-versus-host disease (GVHD) was added as time-dependent variables. There was no difference in probability of relapse between recipients of haploidentical and MSD grafts. Factors of importance for relapse after T-cell-replete grafts included remission status at HSCT, Karnofsky score ⩽80, acute GVHD of grade II or higher and chronic GVHD (P<10(-5)). Patients with post-transplant cyclophosphamide (n=194) had similar outcome as other T-cell-replete haploidentical transplants (n=369). Non-relapse mortality was significantly higher in the haploidentical group compared with that in MSD patients (P<10(-5)). Leukemia-free survival was superior in the MSD patients receiving T-cell-replete (P<10(-5)) or T-cell-depleted grafts (P=0.0006). The risk of relapse was the same in acute leukemia patients who received haploidentical donor grafts as in those given MSD transplants, suggesting a similar GVL effect.