Rapid immune recovery and low TRM in haploidentical stem cell transplantation in children and adolescence using CD3/CD19-depleted stem cells

Post-transplant cyclophosphamide or cell selection in haploidentical allogeneic hematopoietic cell transplantation?

BACKGROUND

One major limitation for broader applicability of allogeneic hematopoietic cell transplantation (allo-HCT) in the past was the lack of HLA-matched histocompatible donors. Preclinical mouse studies using T-cell depleted haploidentical grafts led to an increased interest in the use of ex vivo T-cell depleted (TCD) haploidentical allo-HCT. TCD grafts through negative (T-cell depletion) or positive (CD34+ cell selection) techniques have been investigated to reduce the risk of graft-versus-host disease (GVHD) given the known implications of alloreactive T cells. A more practical approach to deplete alloreactive T cells in vivo using high doses of cyclophosphamide after allografting has proved to be feasible in overcoming the HLA barrier. Such approach has extended allo-HCT feasibility to patients for whom donors could not be found in the past. Nowadays, haploidentical donors represent a common donor source for patients in need of an allo-HCT. The broad application of haploidentical donors became possible by understanding the importance of depleting alloreactive donor T cells to facilitate engraftment and reduce incidence and severity of GVHD. These techniques involve ex vivo graft manipulation or in vivo utilization of pharmacologic agents, notably post-transplant cyclophosphamide (PTCy).

DISCUSSION

While acknowledging that no randomized controlled prospective studies have been yet conducted comparing TCD versus PTCy in haploidentical allo-HCT recipients, there are two advantages that would favor the PTCy, namely ease of application and lower cost. However, emerging data on adverse events associated with PTCy including, but not limited to cardiac associated toxicities or increased incidence of post-allograft infections, and others, are important to recognize.

Efficacy and Reliability of T-Cell-Depleted Haploidentical Stem Cell Transplantation in Hematologic Disorders: A Retrospective Study

BACKGROUND

A promising recent strategy for haploidentical transplantation is the depletion of T lymphocytes based on the selective elimination of T cells by manipulation, which enables a very low incidence of nonrelapse mortality and graft-vs-host disease. It is more expensive than conventional unmanipulated methods and requires dedicated transplant centers and sufficient stem cell processing facilities. This retrospective study aimed to evaluate the relapse, survival, and clinical data of the patients and to analyze the outcomes of the technique.

METHODS

The study included 56 adult patients who underwent haploidentical stem cell transplantation via αβ T-cell depletion.

RESULTS

The median age of the patients at the time of hematopoietic stem cell transplantation was 41.5 years (range, 20-70 years); 22 patients (39.3%) were women. After the transplantation, half of the patients (50.0%) needed immunosuppressive drugs, and 17.9% of the patients experienced a post-transplant relapse. The mortality rate was 55.4%, and nonrelapse mortality was 25.0%. The 100-day mortality rate was 19.6%. The median overall days was 1101 days (142-3813 days), whereas the median progression-free overall was 302.5 days (11-2479 days). Being older (age >40), having hypertension, having acute liver graft-vs-host disease, and having systemic fungal infection were found as risk factors that significantly increased mortality (with 3.5-, 2.8-, 3.7-, and 2.7-fold increases, respectively).

CONCLUSION

To conclude, T-cell-depleted hematopoietic stem cell transplantation is an effective and reliable technique that has the potential to decrease morbidity and improve relapse-free survival, especially for young patients requiring haploidentical donor transplantation for hematologic malignancy.

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.

Antibody Response against Vaccine Antigens in Children after TCRαβ-Depleted Haploidentical Stem Cell Transplantation: Is It Similar to That in Recipients with Fully Matched Donors?

Recipients of hematopoietic stem cell transplantation (HSCT) with HLA-mismatched donors are more immune suppressed than those with fully matched donors. The immunologic response to vaccines also may differ in HLA-mismatched haploidentical HSCT recipients. In this study, we aimed to evaluate the antibody response to vaccines in pediatric TCRαβ-depleted haploidentical HSCT recipients. This longitudinal study included a study group of 21 children who underwent haploidentical HSCT without CD19 depletion and with TCRαβ depletion and a control group of 38 children who underwent fully matched donor HSCT. Antibody levels were quantified by serologic tests before vaccination and after each dose against tetanus, diphtheria, pneumococcus, hepatitis B, hepatitis A, measles, rubella, mumps, and varicella. The median recipient age was significantly lower (P = .037) and the median donor age was significantly higher (P = .000) in the haploidentical group compared with the fully matched group. At the months 1, 3, 6, 9 and 12 post-transplantation, the median CD4, CD8, and CD19 cell counts and lymphocyte counts were similar in the haploidentical and fully matched groups. The median natural killer cell count was higher in the haploidentical group at the months 1, 3, and 6 post-transplantation (P = .001, .006, and .004, respectively). The median time to first vaccination was similar in the 2 groups (12.5 [range, 11 to 14] months for the haploidentical group and 11 [range, 9 to 13] months for the fully matched group; P = .441). Seroprotection rates were 100% in both groups after the second and third doses of diphtheria vaccine, the third dose of tetanus vaccine, the third dose of hepatitis B vaccine, the second and third doses of pneumococcal conjugate vaccines (PCV13), and pneumococcal polysaccharide vaccine (PSPV23), although lower after the initial doses and before vaccination. Seroprotection for hepatitis A, rubella, and varicella was >90% in the fully matched group and 100% for the haploidentical group after the second doses. Measles and mumps seroprotection rates were >80% in the haploidentical group and approximately 70% for the fully matched group after the second dose. Antibody response and seroprotection rates against vaccine antigens were similar in the haploidentical group and the fully matched when revaccination was started at 12 months post-transplantation. These findings support the idea that TCRαβ-depleted haploidentical HSCT recipients can be revaccinated according to the same vaccination schedule as fully matched HSCT recipients. Revaccination earlier after transplantation and vaccine responses for recipients of different types of HSCT should be evaluated in future studies.

Transplant for non-malignant disorders: an International Society for Cell & Gene Therapy Stem Cell Engineering Committee report on the role of alternative donors, stem cell sources and graft engineering

Hematopoietic stem cell transplantation (HSCT) is curative for many non-malignant disorders. As HSCT and supportive care technologies improve, this life-saving treatment may be offered to more and more patients. With the development of new preparative regimens, expanded alternative donor availability, and graft manipulation techniques, there are many options when choosing the best regimen for patients. Herein the authors review transplant considerations, transplant goals, conditioning regimens, donor choice, and graft manipulation strategies for patients with non-malignant disorders undergoing HSCT.

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.

Emerging approaches to improve allogeneic hematopoietic cell transplantation outcomes for nonmalignant diseases

Many congenital or acquired nonmalignant diseases (NMDs) of the hematopoietic system can be potentially cured by allogeneic hematopoietic cell transplantation (HCT) with varying types of donor grafts, degrees of HLA matching, and intensity of conditioning regimens. Unique features that distinguish the use of allogeneic HCT in this population include higher rates of graft failure, immune-mediated cytopenias, and the potential to achieve long-term disease-free survival in a mixed chimerism state. Additionally, in contrast to patients with hematologic malignancies, a priority is to completely avoid graft-versus-host disease in patients with NMD because there is no theoretical beneficial graft-versus-leukemia effect that can accompany graft-versus-host responses. In this review, we discuss the current approach to each of these clinical issues and how emerging novel therapeutics hold promise to advance transplant care for patients with NMDs.

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.

Depletion of CD45RA+ T cells: Advantages and disadvantages of different purification methods

BACKGROUND

Recently, new advances were made regarding the depletion of CD45RA⁺ naïve T cells from haploidentical grafts as they are suspected to be the most alloreactive.

METHODS

Within this project we investigated CD45RA-depletion from G-CSF mobilized PBSC by two different purification strategies according to GMP, specifically direct depletion of CD45RA⁺ cells (one-step approach), or CD34-positive selection followed by CD45RA-depletion (two-step approach).

RESULTS

With log -3.9 and - 3.8 the depletion quality of CD45RA⁺ T cells was equally for both approaches together with a close to complete CD19⁺ B cell depletion. However, due to a high expression of CD45RA the majority of NK cells were lost within both CD45RA depletion strategies. Stem cell recovery after one-step CD45RA-depletion was at median 52.0% (range: 49.7-67.2%), which was comparable to previously published recovery data received from direct CD34 positive selection. Memory T cell recovery including CD4⁺ and CD8⁺ memory T cell subsets was statistically not differing between both purification approaches. The recovery of CD4⁺ and CD8⁺ T cells was as well similar, but overall a higher amount of cytotoxic than T-helper cells were lost as indicated by an increase of the CD4/CD8 ratio.

CONCLUSIONS

CD45RA-depletion from G-CSF mobilized PBSC is feasible as one- and two-step approach and results in sufficient reduction of CD45RA⁺ T cells as well as B cells, but also to a co-depletion of NK cells. However, by gaining two independent cell products, the two-step approach enables the highest clinical flexibility in regard to individual graft composition with precise dosage of stem cells and T cells.

The Synergistic Use of IL-15 and IL-21 for the Generation of NK Cells From CD3/CD19-Depleted Grafts Improves Their ex vivo Expansion and Cytotoxic Potential Against Neuroblastoma: Perspective for Optimized Immunotherapy Post Haploidentical Stem Cell Transplantation

Neuroblastoma (NB) is the most common solid extracranial tumor in childhood. Despite therapeutic progress, prognosis in high-risk NB is poor and innovative therapies are urgently needed. Therefore, we addressed the potential cytotoxic capacity of interleukin (IL)-activated natural killer (NK) cells compared to cytokine-induced killer (CIK) cells for the treatment of NB. NK cells were isolated from peripheral blood mononuclear cells (PBMCs) by indirect CD56-enrichment or CD3/CD19-depletion and expanded with different cytokine combinations, such as IL-2, IL-15, and/or IL-21 under feeder-cell free conditions. CIK cells were generated from PBMCs by ex vivo stimulation with interferon-γ, IL-2, OKT-3, and IL-15. Comparative analysis of expansion rate, purity, phenotype and cytotoxicity was performed. CD56-enriched NK cells showed a median expansion rate of 4.3-fold with up to 99% NK cell content. The cell product after CD3/CD19-depletion consisted of a median 43.5% NK cells that expanded significantly faster reaching also 99% of NK cell purity. After 10–12 days of expansion, both NK cell preparations showed a significantly higher median cytotoxic capacity against NB cells relative to CIK cells. Remarkably, these NK cells were also capable of efficiently killing NB spheroidal 3D culture in long-term cytotoxicity assays. Further optimization using a novel NK cell culture medium and a prolonged culturing procedure after CD3/CD19-depletion for up to 15 days enhanced the expansion rate up to 24.4-fold by maintaining the cytotoxic potential. Addition of an IL-21 boost prior to harvesting significantly increased the cytotoxicity. The final cell product consisted for the major part of CD16⁻, NCR-expressing, poly-functional NK cells with regard to cytokine production, CD107a degranulation and antitumor capacity. In summary, our study revealed that NK cells have a significantly higher cytotoxic potential to combat NB than CIK cell products, especially following the synergistic use of IL-15 and IL-21 for NK cell activation. Therefore, the use of IL-15+IL-21 expanded NK cells generated from CD3/CD19-depleted apheresis products seems to be highly promising as an immunotherapy in combination with haploidentical stem cell transplantation (SCT) for high-risk NB patients.

The Evolution of T Cell Depleted Haploidentical Transplantation

Work on bone marrow transplantation from haploidentical donor has been proceeding for over 20 years all over the world and new transplant procedures have been developed. To control both graft rejection and graft vs. host disease, some centers have preferred to enhance the intensity of the conditioning regimens and the post-transplant immune suppression in the absence of graft manipulation; others have concentrated on manipulating the graft in the absence of any additional post-transplant immune suppressive agent. Due to the current high engraftment rates, the low incidence of graft-vs.-host disease and regimen related mortality, transplantation from haploidentical donors have been progressively offered even to elderly patients. Overall, survivals compare favorably with reports on transplants from unrelated donors. Further improvements will come with successful implementation of strategies to enhance post-transplant immune reconstitution and to prevent leukemia relapse.

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.

Peripheral Blood Stem Cell Mobilization in Healthy Donors by Granulocyte Colony-Stimulating Factor Causes Preferential Mobilization of Lymphocyte Subsets

Background

Allogeneic hematopoietic stem cell transplantation is associated with a high risk of immune-mediated post-transplant complications. Graft depletion of immunocompetent cell subsets is regarded as a possible strategy to reduce this risk without reducing antileukemic immune reactivity.

Study design and methods

We investigated the effect of hematopoietic stem cell mobilization with granulocyte colony-stimulating factor (G-CSF) on peripheral blood and stem cell graft levels of various T, B, and NK cell subsets in healthy donors. The results from flow cytometric cell quantification were examined by bioinformatics analyses.

Results

The G-CSF-induced mobilization of lymphocytes was a non-random process with preferential mobilization of naïve CD4⁺ and CD8⁺ T cells together with T cell receptor αβ⁺ T cells, naïve T regulatory cells, type 1 T regulatory cells, mature and memory B cells, and cytokine-producing NK cells. Analysis of circulating lymphoid cell capacity to release various cytokines (IFNγ, IL10, TGFβ, IL4, IL9, IL17, and IL22) showed preferential mobilization of IL10 releasing CD4⁺ T cells and CD3^-19^- cells. During G-CSF treatment, the healthy donors formed two subsets with generally strong and weaker mobilization of immunocompetent cells, respectively; hence the donors differed in their G-CSF responsiveness with regard to mobilization of immunocompetent cells. The different responsiveness was not reflected in the graft levels of various immunocompetent cell subsets. Furthermore, differences in donor G-CSF responsiveness were associated with time until platelet engraftment. Finally, strong G-CSF-induced mobilization of various T cell subsets seemed to increase the risk of recipient acute graft versus host disease, and this was independent of the graft T cell levels.

Conclusion

Healthy donors differ in their G-CSF responsiveness and preferential mobilization of immunocompetent cells. This difference seems to influence post-transplant recipient outcomes.

T Cell-Depleted and T Cell-Replete HLA-Haploidentical Stem Cell Transplantation for Non-malignant Disorders

PURPOSE OF REVIEW

Hematopoietic stem cell transplantation (HSCT) is a treatment option for children with malignant and non-malignant disorders as well as an expanding number of inherited disorders. However, only a limited portion of patients in the need of an allograft have an HLA-compatible, either related or unrelated, donor. Haploidentical HSCT is now considered a valid treatment option, especially in view of the recent insights in terms of graft manipulation. This review will offer an overview of clinical results obtained through the use of haploidentical HSCT in non-malignant diseases. We will analyze major advantages and drawbacks of both T cell depleted and unmanipulated HSCT, discussing future challenges for further improving patients' outcome.

RECENT FINDINGS

T cell depletion (TCD) aims to reduce the morbidity and mortality associated with graft-versus-host disease (GvHD). However, the delayed immune recovery and the risk of graft failure still remain potential problems. In the last years, the use of post-transplant cyclophosphamide has been shown to be an alternative effective strategy to prevent GvHD in recipients of haploidentical HSCT. Recent data suggest that both T cell depleted and T cell-replete haplo-HSCT are suitable options to treat children with several types of non-malignant disorders lacking an HLA-identical donor.

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.

Treatment of relapse after allogeneic stem cell transplantation in children and adolescents with ALL: the Frankfurt experience

Therapy for post-transplant relapse of paediatric ALL is limited. Standardised curative approaches are not available. We hereby describe our local procedure in this life-threatening situation. A total of 101 ALL patients received their first allogeneic stem cell transplantation (SCT) in our institution. After relapse, our primary therapeutic goal was to cure the patient with high-dose chemotherapy or specific immunotherapy (HDCHT/SIT) followed by a second SCT from a haploidentical donor (transplant approach). If this was not feasible, low-dose chemotherapy and donor lymphocyte infusions (LDCHT+DLI) were offered (non-transplant approach). A total of 23 patients suffered a post-transplant relapse. Eight patients received HDCHT/SIT, followed by haploidentical SCT in 7/8. Ten received LDCHT+DLI. The eight patients treated with a second transplant and the ten treated with the non-transplant approach had a 4-year overall survival of 56% and 40%, respectively (P=0.232). Prerequisites for successful treatment of post-transplant relapse by either a second transplant or experimental non-transplant approaches are good clinical condition and the capacity to achieve haematological remission by the induction treatment element.

Haploidentical hematopoietic stem cell transplantation with post-transplant high-dose cyclophosphamide in high-risk children: A single-center study

Recently, haploidentical transplantations have been performed with unmanipulated BM or PBSC. This approach is becoming more widely adopted with the use of PTCY. However, there is limited evidence about this approach in children. We present 15 children who received 16 haploidentical HSCT with unmanipulated BM or PBSC using PTCY for GVHD prophylaxis. Post-transplant CY(50 mg/kg IV) was given on the third and fifth day, and CsA or tacrolimus with MMF or MP was also used for GVHD prophylaxis. All patients engrafted at a median of 16 and 18 days for neutrophil and thrombocyte recovery, respectively. Grades II-III acute GVHD developed in seven patients, and mild chronic GVHD was found in two patients. Two patients died within the first 100 days due to sepsis (TRM 12.5%). Eleven patients are currently alive, with a median follow-up of 12 months (range 6-22 months). The 12-month OS and DFS were 75 ± 10.8% and 68.8 ± 11.6%, respectively. Our results with these high-risk patients are encouraging for haploidentical HSCT in pediatric patients. Future studies should continue to assess haploidentical HSCT, including comparison of other modalities, in a primary pediatric population.

Treatment of CMV infection after allogeneic hematopoietic stem cell transplantation

Despite a remarkable reduction in the past decades, cytomegalovirus (CMV) disease in allogeneic hematopoietic stem cell transplant (HSCT) recipients remains a feared complication, still associated with significant morbidity and mortality. Today, first line treatment of CMV infection/reactivation is still based on dated antiviral compounds Ganciclovir (GCV), Foscarnet (FOS) and Cidofovir (CDF) with their burdensome weight of side effects. Maribavir (MBV), Letermovir (LMV) and Brincidofovir (BDF) are three new promising anti-CMV drugs without myelosuppressive properties or renal toxic effects that are under investigation in randomized phase II and III trials. Adoptive T-cell therapy (ATCT) in CMV infection possesses a strong rationale, demonstrated by several proof of concept studies; its feasibility is currently under investigation by clinical trials. ATCT from third-party and naïve donors could meet the needs of HSCT recipients of seronegative donors and cord blood grafts. In selected patients such as recipients of T-cell depleted grafts, ATCT, based on CMV-specific host T-cells reconstitution kinetics, would be of value in the prophylactic and/or preemptive CMV treatment. Vaccine-immunotherapy has the difficult task to reduce the incidence of CMV reactivation/infection in highly immunocompromised HSCT patients. Newer notions on CMV biology may represent the base to flush out the Troll of transplantation.

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.

Unrelated CD3/CD19-depleted peripheral stem cell transplantation for Hurler syndrome

For patients with mucopolysaccharidosis type IH (MPS1-H; Hurler syndrome), early allogeneic hematopoietic stem cell transplantation (HSCT) is the treatment of choice. One boy and one girl aged 20.5 and 22 months, respectively, with MPS1-H received a conditioning regimen consisting of thiotepa, fludarabine, treosulfan, and ATG. Grafts were peripheral blood stem cells from unrelated donors (10/12 and 11/11 matched), that were manipulated by CD3/CD19 depletion and contained 20.3 and 28.2 × 10(6) CD34+ cells/kg body weight, respectively. Both patients achieved stable hematopoietic engraftment and stable donor chimerism. Neither acute or chronic graft-versus-host disease (GVHD) nor other severe transplant-related complications occurred. At a follow-up of 48 and 37 months, both patients are alive and well with normal levels of α-L-iduronidase and have made major neurodevelopmental progress. Treosulfan-based conditioning offers the advantage of reduced toxicity; the use of unrelated CD3/CD19-depleted peripheral stem cell grafts allows transfusion of high CD34+ cell numbers together with a "tailored" number of CD3+ cells as well as engraftment facilitating cells in order to achieve rapid hematopoietic engraftment while reducing the risk of graft rejection and GVHD. This regimen might be an additional option when unrelated donor HSCT is considered for a patient with MPS1-H.

Improving cytomegalovirus-specific T cell reconstitution after haploidentical stem cell transplantation

Cytomegalovirus (CMV) infection and delayed immune reconstitution (IR) remain serious obstacles for successful haploidentical stem cell transplantation (haplo-SCT). CMV-specific IR varied according to whether patients received manipulated/unmanipulated grafts or myeloablative/reduced intensity conditioning. CMV infection commonly occurs following impaired IR of T cell and its subsets. Here, we discuss the factors that influence IR based on currently available evidence. Adoptive transfer of donor T cells to improve CMV-specific IR is discussed. One should choose grafts from CMV-positive donors for transplant into CMV-positive recipients (D+/R+) because this will result in better IR than would grafts from CMV-negative donors (D−/R+). Stem cell source and donor age are other important factors. Posttransplant complications, including graft-versus-host disease and CMV infection, as well as their associated treatments, should also be considered. The effects of varying degrees of HLA disparity and conditioning regimens are more controversial. As many of these factors and strategies are considered in the setting of haplo-SCT, it is anticipated that haplo-SCT will continue to advance, further expanding our understanding of IR and CMV infection.

Immune reconstitution after haploidentical hematopoietic stem cell transplantation

Haploidentical hematopoietic stem cell transplantation (HSCT) offers the benefits of rapid and nearly universal donor availability and has been accepted worldwide as an alternative treatment for patients with hematologic malignancies who do not have a completely HLA-matched sibling or who require urgent transplantation. Unfortunately, serious infections and leukemia relapse resulting from slow immune reconstitution remain the 2 most frequent causes of mortality in patients undergoing haploidentical HSCT, particularly in those receiving extensively T cell-depleted megadose CD34(+) allografts. This review summarizes advances in immune recovery after haploidentical HSCT, focusing on the immune subsets likely to have the greatest impact on clinical outcomes. The progress made in accelerating immune reconstitution using different strategies after haploidentical HSCT is also discussed. It is our belief that a predictive immune subset-guided strategy to improve immune recovery might represent a future clinical direction.

Highlights of the third International Conference on Immunotherapy in Pediatric Oncology

The third International Conference on Immunotherapy in Pediatric Oncology was held in Frankfurt/Main, Germany, October 1-2, 2012. Major topics of the conference included (i) cellular therapies using antigen-specific and gene-modified T cells for targeting leukemia and pediatric solid tumors; (ii) overcoming hurdles and barriers with regard to immunogenicity, immune escape, and the role of tumor microenvironment; (iii) vaccine strategies and antigen presentation; (iv) haploidentical transplantation and innate immunity; (v) the role of immune cells in allogeneic transplantation; and (vi) current antibody/immunoconjugate approaches for the treatment of pediatric malignancies. During the past decade, major advances have been made in improving the efficacy of these modalities and regulatory hurdles have been taken. Nevertheless, there is still a long way to go to fully exploit the potential of immunotherapeutic strategies to improve the cure of children and adolescents with malignancies. This and future meetings will support new collaborations and insights for further translational and clinical immunotherapy studies.

T cell depletion in paediatric stem cell transplantation

Haematopoietic stem cell transplantation (HSCT) can be a curative procedure for a growing number of paediatric diseases, but as the indications for HSCT grow, so does the need to find suitable stem cell donors. When the preferred option of a genoidentical sibling donor is not available alternative donors, including unrelated adult or umbilical cord blood donors, or haploidentical related donors may be considered. Outcome following alternative donor HSCT has improved over the past 20 years but graft-versus-host disease (GvHD) remains a significant obstacle. T cell depletion (TCD) for non-genoidentical grafts aims to reduce the morbidity and mortality associated with GvHD, but this intervention has not led directly to improved survival due to delayed immune reconstitution and increased infections, graft rejection and increased rates of disease relapse. Limited data from the paediatric population, however, suggest some encouraging results for children undergoing haploidentical HSCT: a move from positive selection of CD34(+) haematopoietic stem cells towards negative depletion of specific cell subsets in order to retain useful accessory cells within the graft appears to enhance immune reconstitution and improve disease-free survival. Here we review recent paediatric outcome data for T cell-depleted HSCT, explore the role of serotherapy in conditioning regimens and look at future possibilities to improve outcome, including novel allodepletion techniques, suicide gene therapy and pathogen-specific immunotherapy.

Negative depletion of CD3(+) and TcRαβ(+) T cells

PURPOSE OF REVIEW

In contrast to CD34(+) positive selection, negative depletion strategies retain large numbers of effector cells in allogeneic peripheral stem cell grafts, such as natural killer (NK) and other cells. This review summarizes the clinical experience obtained using negative depletion approaches of CD3(+) and T-cell receptor (TcR)αβ(+) T lymphocytes.

RECENT FINDINGS

Attempts to improve immune reconstitution and to better exploit the graft-versus-malignancy effect after transplantation of T-cell-depleted grafts through the preservation of immune effector cells led to the development of CD3-, CD3/CD19- and more recently TcRαβ/CD19-negative depletion strategies of mobilized peripheral stem cell grafts. A faster immune reconstitution has been observed in patients with negatively depleted grafts after haploidentical transplantation, although no prospective randomized trials have been reported to date. In a randomized study of matched sibling and matched unrelated transplantation, CD3/CD19-depleted peripheral stem cell grafts led to a faster recovery of NK cells compared with the CD34(+)-positive selection group.

SUMMARY

New technologies allow the large-scale graft engineering of peripheral stem cells for clinical use in matched and mismatched stem cell transplantation. Further clinical trials are necessary to decide which of these methods is associated with a faster immune reconstitution and a better outcome after transplantation.

New approaches to graft engineering for haploidentical bone marrow transplantation

Haploidentical transplantation opens the possibility to offer this treatment to a large number of patients with an otherwise incurable disease, such as some hematologic or oncologic malignancies, inborn or acquired bone marrow failure syndromes, hemoglobinopathies, immunodeficiencies, or other genetic diseases. Initial attempts at haploidentical transplantation using unmanipulated bone marrow were associated with a high transplant-related mortality. However, recent insights into the biology of haploidentical transplantation, the availability of effective in vivo large-scale graft-manipulation technology, and improved supportive care strategies have led to and are still leading to significantly better outcomes compared to previous decades. Methods for the in vitro depletion of T lymphocytes from mobilized peripheral blood stem cells (PBSC) to prevent graft-versus-host disease (GvHD) have facilitated the wider use and acceptance of haploidentical transplantation in children and adult patients. Besides in vitro T-cell depletion techniques, other methods, such as the isolation of alloreactive natural killer (NK) cells, virus-specific T lymphocytes, and other effector or regulatory cells are nowadays available to rapidly rebuild the immune system after haploidentical transplantation for the prevention of severe infections or relapses of the underlying diseases.

Haploidentical hematopoietic transplantation: current status and future perspectives

For patients with hematologic malignancies at high risk of relapse who do not have matched donors, a suitable alternative stem cell source is the HLA-haploidentical 2 or 3-loci mismatched family donor who is readily available for nearly all patients. Transplantation across the major HLA barrier is associated with strong T-cell alloreactions, which were originally manifested as a high incidence of severe GVHD and graft rejection. The present review shows how these obstacles to successful transplantation were overcome in the last 15 years, making full haplotype-mismatched transplantation a clinical reality that provides similar outcomes to transplantation from matched unrelated donors. The review also discusses the advantages and drawbacks of current options for full haplotype-mismatched transplantation and highlights innovative approaches for re-building immunity after transplantation and improving survival.