Association between anti-thymocyte globulin exposure and CD4+ immune reconstitution in paediatric haemopoietic cell transplantation: a multicentre, retrospective pharmacodynamic cohort analysis

Rapid reconstitution of CD4 T cells and NK cells protects against CMV-reactivation after allogeneic stem cell transplantation

BACKGROUND

Epstein-Barr virus and Cytomegalovirus reactivations frequently occur after allogeneic stem cell transplantation (SCT).

METHODS

Here we investigated the role of immune cell reconstitution in the onset and subsequent severity of EBV- and CMV-reactivation. To this end, 116 patients were prospectively sampled for absolute T cell (CD4 and CD8), B-cell (CD19) and NK-cell (CD16 and CD56) numbers weekly post-SCT during the first 3 months and thereafter monthly until 6 months post-SCT. Viral load was monitored in parallel.

RESULTS

In contrast to the general belief, we found that early T-cell reconstitution does not play a role in the onset of viral reactivation. CMV reactivation in the first 7 weeks after SCT however resulted in higher absolute CD8(+) T-cell numbers 6 months post-SCT in patients with high-level reactivation, many of which were CMV-specific. Interestingly, rapid reconstitution of CD4(+) T-cells, as well as NK cells and the presence of donor KIR3DL1, are associated with the absence of CMV-reactivation after SCT, suggestive of a protective role of these cells. In contrast, EBV-reactivations were not affected in any way by the level of immune reconstitution after SCT.

CONCLUSION

In conclusion, these data suggest that CD4(+) T-cells and NK cells, rather than CD8(+) T-cells, are associated with protection against CMV-reactivation.

Challenges in the harmonization of immune monitoring studies and trial design for cell-based therapies in the context of hematopoietic cell transplantation for pediatric cancer patients

Clinical trials aimed at improving results of hematopoietic cell transplantation (HCT) by adjuvant cell-based interventions in children have been limited by small numbers and pediatric-specific features. The need for a larger number of pediatric HCT centers to participate in trials has resulted in a demand for harmonization of disease-specific clinical trials and immune-monitoring. Thus far, most phase I/II trials select different end points evaluated at disparate time points, making inter-study comparisons difficult and, sometimes, impossible. In this review, we discuss the various aspects that are important to consider for harmonizing clinical trial design as well as the critical elements for standardized (immune)-monitoring protocols in cell-based intervention trials in the context of HCT. Comparison data from trials applying harmonized trial design will lead to optimized immunotherapeutic treatment protocols to maximize clinical efficacy while minimizing toxicity.

Children in clinical trials: towards evidence-based pediatric pharmacotherapy using pharmacokinetic-pharmacodynamic modeling

INTRODUCTION

In pediatric pharmacotherapy, many drugs are still used off-label, and their efficacy and safety is not well characterized. Different efficacy and safety profiles in children of varying ages may be anticipated, due to developmental changes occurring across pediatric life.

AREAS COVERED

Beside pharmacokinetic (PK) studies, pharmacodynamic (PD) studies are urgently needed. Validated PKPD models can be used to derive optimal dosing regimens for children of different ages, which can be evaluated in a prospective study before implementation in clinical practice. Strategies should be developed to ensure that formularies update their drug dosing guidelines regularly according to the most recent advances in research, allowing for clinicians to integrate these guidelines in daily practice. Expert commentary: We anticipate a trend towards a systems-level approach in pediatric modeling to optimally use the information gained in pediatric trials. For this approach, properly designed clinical PKPD studies will remain the backbone of pediatric research.

Impact of early CMV reactivation in cord blood stem cell recipients in the current era

Several studies have reported an association between CMV reactivation and a decreased incidence of relapse for AML after adult donor allogeneic hematopoietic cell transplantation (HCT). Limited data, however, are available on the impact of CMV reactivation on relapse after cord blood (CB) stem cell transplantation. The unique combination of higher incidence of CMV reactivation in the seropositive recipient and lower incidence of graft versus host disease (GvHD) in CB HCT permits a valuable design to analyze the impact of CMV reactivation. Data from 1684 patients transplanted with CB between 2003 and 2010 for AML and ALL were analyzed. The median time to CMV reactivation was 34 days (range: 2-287). CMV reactivation and positive CMV serology were associated with increased non-relapse mortality (NRM) among both AML and ALL CB recipients (reactivation, AML: relative risk (RR) 1.41 (1.07-1.85); ALL: 1.60 (1.14-2.23); Serology, AML: RR 1.39 (1.05-1.85), ALL: RR 1.61 (1.18-2.19)). For patients with ALL, but not those with AML, this yielded inferior overall survival (P<0.005). Risk of relapse was not influenced by CMV reactivation or positive CMV serostatus for either disease.

Antithymocyte globulin in allogeneic hematopoietic cell transplantation: benefits and limitations

Significant advances have been made in allogeneic hematopoietic cell transplantation by reducing toxicities and optimizing its efficacy. Antithymocyte globulin (ATG) is an important in vivo T-cell depletion strategy, which reduces the risk of graft-versus-host disease in HLA-matched or -mismatched donor allografting. ATG effectively targets alloreactive T cells at the expense of potentially increasing the risk of post-hematopoietic cell transplantation infections and delayed immune reconstitution. We summarize the targets, mechanisms, various preparations of ATG, the growing role of ATG in prevention of graft-versus-host disease in various transplant modalities as well as emerging data on pharmacokinetic modeling for individualized ATG dosing. Further research is needed to optimize the ATG administration while minimizing the toxicities.

Stem cell transplantation for the treatment of immunodeficiency in children: current status and hopes for the future

Primary immunodeficiencies (PID) are rare inherited disorders affecting immune function and can be life-threatening if not treated. Haematopoietic stem cell transplantation (HSCT) offers a curative approach for many of these disorders and gene therapy is increasingly used as an alternative therapeutic strategy for patients lacking a suitable donor. Early diagnosis, improved supportive care and advances in gene and cell therapies have resulted in increased survival rates and improved quality of life. This review describes current strategies employed to improve outcomes in PID, focusing on new developments in HSCT, gene and cell therapy. We also address the challenges associated with newborn screening (NBS) programmes and novel mutations identified through improved diagnostic technology.

Allogeneic stem cell transplantation for X-linked agammaglobulinemia using reduced intensity conditioning as a model of the reconstitution of humoral immunity

BACKGROUND

We herein report the first case of X-linked agammaglobulinemia (XLA) that underwent allogeneic stem cell transplantation using reduced intensity conditioning (RIC). We chronologically observed the reconstitution of humoral immunity in this case.

CASE PRESENTATION

The patient was a 28-year-old Japanese male with XLA who previously had life-threatening infectious episodes and was referred for the possible indication of allogeneic stem cell transplantation. After a thorough discussion within specialists from different backgrounds, we decided to perform allogeneic peripheral stem cell transplantation from his HLA-identical elder brother. Due to the non-malignant nature of XLA, we selected RIC consisting of fludarabine, cyclophosphamide, anti-thymocyte globulin, and 3 Gy of total body irradiation. Neutrophil engraftment was achieved on day 11 with complete donor chimerism. No major complications, except for stage 1 skin graft-versus-host disease, were observed. The patient was discharged on day 75 and has been followed as an outpatient without any infectious episodes for more than 500 days.

CONCLUSIONS

Regarding immune reconstitution, CD19(+) cells, IgA, and IgM, which were undetectable before allogeneic stem cell transplantation (allo-SCT), started to increase in number 10 days after allo-SCT and continued to increase for more than 1 year. Anti-B antibodies appeared as early as day 10. Total IgG levels decreased after the discontinuation of IgG replacement and spontaneously recovered after day 350. However, most anti-viral IgG titers, except EB virus-virus capsid antigen IgG, disappeared after the discontinuation of IgG replacement. A seasonal vaccination to influenza was performed on day 148, with neither anti-influenza type A nor type B being positive after the vaccination. The transient transfer of allergic immunity to orchard grass was observed. Similar Bruton's tyrosine kinase (BTK) expression levels in monocytes and B-cells were observed between the patient and healthy control. B-cells in the peripheral blood (PB) of the patient on day 279 showed sufficient proliferation after a CD40L and IL-21 or CD40L and CpG stimulation. Effective immunoglobulin production and class switching were also observed after a CD40L and IL-21 or CpG stimulation. Signal joint kappa-deleting recombination excision circles (sjKRECs) became positive 16 days post-SCT, increased to 6300 copies/μg DNA at 42 days, and were maintained at a high level thereafter. The recovery of T-cell receptor excision circles (TRECs) was slow, but became detectable 1 year post-hematopoietic stem cell transplantation (HSCT).

Development of a diverse human T-cell repertoire despite stringent restriction of hematopoietic clonality in the thymus

The fate and numbers of hematopoietic stem cells (HSC) and their progeny that seed the thymus constitute a fundamental question with important clinical implications. HSC transplantation is often complicated by limited T-cell reconstitution, especially when HSC from umbilical cord blood are used. Attempts to improve immune reconstitution have until now been unsuccessful, underscoring the need for better insight into thymic reconstitution. Here we made use of the NOD-SCID-IL-2Rγ(-/-) xenograft model and lentiviral cellular barcoding of human HSCs to study T-cell development in the thymus at a clonal level. Barcoded HSCs showed robust (>80% human chimerism) and reproducible myeloid and lymphoid engraftment, with T cells arising 12 wk after transplantation. A very limited number of HSC clones (<10) repopulated the xenografted thymus, with further restriction of the number of clones during subsequent development. Nevertheless, T-cell receptor rearrangements were polyclonal and showed a diverse repertoire, demonstrating that a multitude of T-lymphocyte clones can develop from a single HSC clone. Our data imply that intrathymic clonal fitness is important during T-cell development. As a consequence, immune incompetence after HSC transplantation is not related to the transplantation of limited numbers of HSC but to intrathymic events.

Cord blood T cells mediate enhanced antitumor effects compared with adult peripheral blood T cells

Unrelated cord blood transplantation (CBT) without in vivo T-cell depletion is increasingly used to treat high-risk hematologic malignancies. Following T-replete CBT, naïve CB T cells undergo rapid peripheral expansion with memory-effector differentiation. Emerging data suggest that unrelated CBT, particularly in the context of HLA mismatch and a T-replete graft, may reduce leukemic relapse. To study the role of CB T cells in mediating graft-versus-tumor responses and dissect the underlying immune mechanisms for this, we compared the ability of HLA-mismatched CB and adult peripheral blood (PB) T cells to eliminate Epstein-Barr virus (EBV)-driven human B-cell lymphoma in a xenogeneic NOD/SCID/IL2rg(null) mouse model. CB T cells mediated enhanced tumor rejection compared with equal numbers of PB T cells, leading to improved survival in the CB group (P < .0003). Comparison of CB T cells that were autologous vs allogeneic to the lymphoma demonstrated that this antitumor effect was mediated by alloreactive rather than EBV-specific T cells. Analysis of tumor-infiltrating lymphocytes demonstrated that CB T cells mediated this enhanced antitumor effect by rapid infiltration of the tumor with CCR7(+)CD8(+) T cells and prompt induction of cytotoxic CD8(+) and CD4(+) T-helper (Th1) T cells in the tumor microenvironment. In contrast, in the PB group, this antilymphoma effect is impaired because of delayed tumoral infiltration of PB T cells and a relative bias toward suppressive Th2 and T-regulatory cells. Our data suggest that, despite being naturally programmed toward tolerance, reconstituting T cells after unrelated T-replete CBT may provide superior Tc1-Th1 antitumor effects against high-risk hematologic malignancies.

Immune Reconstitution after Allogeneic Hematopoietic Cell Transplantation in Children

Allogeneic (allo) hematopoietic cell transplantation (HCT) has evolved into a potent curative treatment option for a variety of malignant and nonmalignant diseases. The occurrence of complications and mortality after allo-HCT is, however, still high and is strongly associated with immune reconstitution (IR). Therefore, detailed information on IR through immunomonitoring is crucial to improve survival chances after HCT. To date, information about the reconstituting immune system after allo-HCT in pediatric patients is mostly derived from routine standard-of-care measurements. More profound knowledge on IR may provide tools to better predict and modulate adverse reactions and, subsequently, improve survival chances. Here, we provide an overview of IR (eg, immune cell subsets and circulating chemokines/cytokines) after allo-HCT in children, taking into account different cell sources and serotherapy, and discuss strategies to enhance immunomonitoring. We conclude that available IR data after allo-HCT contain limited information on immune cell families (mostly only generic T, B, and NK cells), which would improve with more detailed information on reconstituting cell subsets or effector cell functionality at earlier time points (<1 month). In addition, secretome data (eg, multiplex cytokine/chemokine profiles) could add to the understanding of IR mechanisms and cell functionality and may even provide (early) biomarkers for individual disease outcome, such as viral reactivity, graft-versus-host disease, or graft-versus-leukemia. The present data and suggestions for more detailed, standardized, and harmonized immunomonitoring in future (pediatric) allo-HCT studies will pave the path to "precision transplantation:" an individualized HCT approach (including conditioning), based on detailed information on IR and biomarkers, aiming to reduce transplantation related mortality and relapse, and subsequently improve survival chances.

Impact of ATG-containing reduced-intensity conditioning after single- or double-unit allogeneic cord blood transplantation

We analyzed 661 adult patients who underwent single-unit (n = 226) or double-unit (n = 435) unrelated cord blood transplantation (UCBT) following a reduced-intensity conditioning (RIC) consisting of low-dose total body irradiation (TBI), cyclophosphamide, and fludarabine (Cy/Flu/TBI200). Eighty-two patients received rabbit antithymocyte globulin (ATG) as part of the conditioning regimen (ATG group), whereas 579 did not (non-ATG group). Median age at UCBT was 54 years, and diagnoses were acute leukemias (51%), myelodysplastic syndrome/myeloproliferative neoplasm (19%), and lymphoproliferative diseases (30%). Forty-four percent of patients were transplanted with advanced disease. All patients received ≥4 antigens HLA-matched UCBT. Median number of collected total nucleated cells was 4.4 × 10(7)/kg. In the ATG group, on 64 evaluable patients, ATG was discontinued 1 (n = 27), 2 (n = 20), or > 2 days before the graft infusion (n = 17). In multivariate analyses, the use of ATG was associated with decreased incidence of acute graft-versus-host disease (hazard ratio [HR], 0.31; 95% confidence interval [CI], 0.17-0.55; P < .0001), higher incidence of nonrelapse mortality (HR, 1.68; 95% CI, 1.16-2.43; P = .0009), and decreased overall survival (HR, 1.69; 95% CI, 1.19-2.415; P = .003). Collectively, our results suggest that the use of ATG could be detrimental, especially if given too close to graft infusion in adults undergoing UCBT following Cy/Flu/TBI200 regimen.

Sufficient Immunosuppression with Thymoglobulin Is Essential for a Successful Haplo-Myeloid Bridge in Haploidentical-Cord Blood Transplantation

In haploidentical (haplo)-cord blood (CB) transplantations, early haplo donor engraftment serves as a myeloid bridge to sustainable CB engraftment and is associated with early neutrophil recovery. The conditioning regimens as published for haplo-cord protocols usually contain serotherapy, such as rabbit antithymocyte globulin (ATG) (Thymoglobulin, Genzyme, Cambridge, MA). However, reducing or omitting serotherapy is an important strategy to improve early immune reconstitution after transplantation. The need for serotherapy in successful haplo-cord transplantation, defined as having a haplo-derived myeloid bridge to CB engraftment, has not been investigated before. Two consecutive cohorts of patients underwent transplantation with haplo-CB. The first group underwent transplantation with haplo-CB for active infection and/or an underlying condition with expected difficult engraftment without a conventional donor available. They received a single unit (s) CB and haplo donor cells (CD34(+) selected, 5 × 10(6) CD34(+)/kg). The second cohort included patients with poor-risk malignancies, not eligible for other treatment protocols. They received a sCB and haplo donor cells (CD19/αβTCR-depleted; 5 × 10(6) CD34(+)/kg). Retrospectively in both cohorts, active ATG (Thymoglobulin) levels were measured and post-hematopoietic cell transplantation area under the curve (AUC) was calculated. The influence of ATG exposure for having a successful haplo-myeloid bridge (early haplo donor engraftment before CB engraftment and no secondary neutropenia) and transplantation-related mortality (TRM) were analyzed as primary endpoints. Twenty patients were included (16 in the first cohort and 4 in the second cohort). In 58% of evaluable patients, there was no successful haplo-derived myeloid bridge to CB engraftment, for which a low post-transplantation ATG exposure appeared to be a predictor (P <.001). TRM in the unsuccessful haplo-bridge group was 70% ± 16% versus 12% ± 12% in the successful haplo-bridge group (P = .012). In conclusion, sufficient in vivo T depletion with ATG is required for a successful haplo-myeloid bridge to CB engraftment.

Topping it up: methods to improve cord blood transplantation outcomes by increasing the number of CD34+ cells

Cord blood is increasingly recognized for its excellent stem cell potential, lenient matching criteria, instant availability and clinical behavior in transplants when cell dose criteria can be met. However with 1-2 log fewer total (stem cell) numbers in the graft compared with other cell sources, the infused cell dose per kilogram is critical for engraftment and outcome, creating the need for development of stem cell support platforms. The co-transplant platforms of haplo cord and double unit cord blood (DUCB) transplantation are aimed toward increasing stem cell dose. Together with the optimization of reduced-intensity protocols, long-term sustained engraftment using cord blood has become available to most patients, including elderly patients. Haplo cord has a low incidence of both acute and chronic graft-versus-host disease but may require anti-thymocyte globulin ATG for effective neutrophil recovery. DUCB can be performed without anti-thymocyte globulin with excellent immune reconstitution and disease-free survival, but engraftment is considerably slower, and graft-versus-host disease incidence significant. Both haplo-cord and DUCB transplantation appear to both be valid alternatives to matched unrelated donors in adults.