Reconstitution of maturating and regulatory lymphocyte subsets after cord blood and BMT in children

N-803, an IL-15 superagonist complex as maintenance therapy after allogeneic donor stem cell transplant for acute myeloid leukemia or myelodysplastic syndrome; a Phase 2 trial

Maintenance therapy may improve natural killer (NK) cell surveillance after allogeneic donor hematopoietic cell transplant (HCT) for myeloid malignancies and represents a potential approach to improve cure rates. Interleukin-15 (IL-15) enhances lymphocyte proliferation and anti-tumor activity. In a prior Phase 1 study of an IL-15 superagonist (N-803) in patients with AML who relapsed after HCT, we observed in vivo expansion of NK cells and anti-tumor responses. The primary objective of this Phase 2 trial was to determine if post-transplant N-803 could reduce relapse. We administered N-803 (n=20) (dosed 6 mcg/kg subcutaneously (SQ) at day 60 after HCT to patients with myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML) who were in complete remission (CR). N-803 treatment was planned weekly, bi-weekly or every 4 weeks in 2 sequential cohorts. The most common adverse events after administration were self-limited injection sites skin rashes (n=20). One week after an N-803 dose, we observed enhanced NK cell proliferation and improved anti-tumor cytotoxicity without inducing immune exhaustion. Five patients who developed acute graft versus host disease (aGVHD) after N-803 responded promptly to steroids and 4 patients developed chronic GVHD. Patients receiving >4 doses of N-803 had a 3-fold decrease in relapse at two years (p=0.06). These findings support the safety, immune activation, and potential efficacy of N-803 to prevent relapse of AML/MDS after HSCT.

Therapeutic Inducers of Natural Killer cell Killing (ThINKK): preclinical assessment of safety and efficacy in allogeneic hematopoietic stem cell transplant settings

BACKGROUND

Allogeneic hematopoietic stem cell transplantation (HSCT) remains the standard of care for chemotherapy-refractory leukemia patients, but cure rates are still dismal. To prevent leukemia relapse following HSCT, we aim to improve the early graft-versus-leukemia effect mediated by natural killer (NK) cells. Our approach is based on the adoptive transfer of Therapeutic Inducers of Natural Killer cell Killing (ThINKK). ThINKK are expanded and differentiated from HSC, and exhibit blood plasmacytoid dendritic cell (pDC) features. We previously demonstrated that ThINKK stimulate NK cells and control acute lymphoblastic leukemia (ALL) development in a preclinical mouse model of HSCT for ALL. Here, we assessed the cellular identity of ThINKK and investigated their potential to activate allogeneic T cells. We finally evaluated the effect of immunosuppressive drugs on ThINKK-NK cell interaction.

METHODS

ThINKK cellular identity was explored using single-cell RNA sequencing and flow cytometry. Their T-cell activating potential was investigated by coculture of allogeneic T cells and antigen-presenting cells in the presence or the absence of ThINKK. A preclinical human-to-mouse xenograft model was used to evaluate the impact of ThINKK injections on graft-versus-host disease (GvHD). Finally, the effect of immunosuppressive drugs on ThINKK-induced NK cell cytotoxicity against ALL cells was tested.

RESULTS

The large majority of ThINKK shared the key characteristics of canonical blood pDC, including potent type-I interferon (IFN) production following Toll-like receptor stimulation. A minor subset expressed some, although not all, markers of other dendritic cell populations. Importantly, while ThINKK were not killed by allogeneic T or NK cells, they did not increase T cell proliferation induced by antigen-presenting cells nor worsened GvHD in vivo. Finally, tacrolimus, sirolimus or mycophenolate did not decrease ThINKK-induced NK cell activation and cytotoxicity.

CONCLUSION

Our results indicate that ThINKK are type I IFN producing cells with low T cell activation capacity. Therefore, ThINKK adoptive immunotherapy is not expected to increase the risk of GvHD after allogeneic HSCT. Furthermore, our data predict that the use of tacrolimus, sirolimus or mycophenolate as anti-GvHD prophylaxis regimen will not decrease ThINKK therapeutic efficacy. Collectively, these preclinical data support the testing of ThINKK immunotherapy in a phase I clinical trial.

Early reversal of the lymphocyte-to-monocyte ratio after allogeneic-hematopoietic stem cell transplantation is associated with reduced relapse and improved prognosis

BACKGROUND

The early recovery of lymphocyte and monocyte cells is associated with a favorable prognosis after allogeneic stem cell transplantation (allo-HSCT); however, it is not clear whether the balance of lymphocyte and monocyte recovery affects the post-transplant prognosis.

METHODS

We examined whether the time-point at which the number of lymphocytes exceeded the number of monocytes, which we termed lymphocyte-to-monocyte ratio reversal (LMRR), affected the prognosis after allo-HSCT. We retrospectively evaluated 235 patients who underwent their first allo-HSCT at our institution.

RESULTS

The median number of days from HSCT to LMRR was 46 (range, 0-214), and the patients were divided into two groups according to the occurrence of LMRR by day 45 (LMRR45). In a multivariate analysis, early LMRR contributed favorably to overall survival (hazard ratio [HR] .519; 95% confidence interval [CI] .332-.812; p = .004) with fewer post-transplant relapses (HR .462; 95% CI, .274-.777; p = .004). Differences in the timing of LMRR did not affect non-relapse mortality (HR 1.477; 95% CI .779-2.80; p = .23) or the incidence of grade II-IV acute GVHD (LMRR45(+): 25.0% vs. LMRR45(-) 35.2%. p = .111). In subgroup analyses, LMRR45(+) was found to be a favorable factor for survival with less relapse, regardless of the disease risk, stem cell source, or the recovery of either lymphocyte or monocyte counts.

CONCLUSIONS

An early LMRR may be a novel factor that is associated with reduced relapse and improved survival after allo-HSCT.

Allogeneic stem cell transplantation in the treatment of acute myeloid leukemia: An overview of obstacles and opportunities

As an important treatment for acute myeloid leukemia, allogeneic hematopoietic stem cell transplantation (allo-HSCT) plays an important role in reducing relapse and improving long-term survival. With rapid advancements in basic research in molecular biology and immunology and with deepening understanding of the biological characteristics of hematopoietic stem cells, allo-HSCT has been widely applied in clinical practice. During allo-HSCT, preconditioning, the donor, and the source of stem cells can be tailored to the patient’s conditions, greatly broadening the indications for HSCT, with clear survival benefits. However, the risks associated with allo-HSCT remain high, i.e. hematopoietic reconstitution failure, delayed immune reconstitution, graft-versus-host disease, and post-transplant relapse, which are bottlenecks for further improvements in allo-HSCT efficacy and have become hot topics in the field of HSCT. Other bottlenecks recognized in the current treatment of individuals diagnosed with acute myeloid leukemia and subjected to allo-HSCT include the selection of the most appropriate conditioning regimen and post-transplantation management. In this paper, we reviewed the progress of relevant research regarding these aspects.

Intrabone infusion for allogeneic umbilical cord blood transplantation in children

Umbilical cord blood transplantation (UCBT) has been used to treat malignant and non-malignant diseases. UCBT offers the advantages of easy procurement and acceptable partial HLA mismatches, but also shows delayed hematopoietic and immunological recoveries. We postulated that an intrabone (IB) infusion of cord blood could provide a faster short- and long-term engraftment in a pediatric population with malignant and non-malignant hematologic diseases. We conducted this phase I-II single arm, exploratory clinical trial (NCT01711788) from 2012 to 2016 in a single center. Fifteen patients aged from 1.9 to 16.4 years received an IB UCBT. Median time to neutrophils and platelet recoveries were 18 days (range: 13-36 days) and 42 days (range: 26-107 days), respectively. Rate of severe acute GVH grade was low, with only one patient with grade III aGVH. Relapse occurred in 5 patients (38.5%) and TRM occurred in 1 patient. This leads to 6 years EFS and OS of 66.7% and 80% respectively. In conclusion, IB UCBT is safe and well-tolerated in children and hematological recovery compared similarly to the results obtained with IV UCBT.

Immune function in childhood cancer survivors: a Children's Oncology Group review

Childhood cancer and its treatment often impact the haematopoietic and lymphatic systems, with immunological consequences. Immunological assessments are not routinely included in surveillance guidelines for most survivors of childhood cancer, although a robust body of literature describes immunological outcomes, testing recommendations, and revaccination guidelines after allogeneic haematopoietic cell transplantation. Survivorship care providers might not fully consider the impaired recovery of a child's immune system after cancer treatment if the child has not undergone haematopoietic cell transplantation. We did a scoping review to collate the existing literature describing immune function after childhood cancer therapy, including both standard-dose chemotherapy and high-dose chemotherapy with haematopoietic cell rescue. This Review aims to summarise: the principles of immunology and testing of immune function; the body of literature describing immunological outcomes after childhood cancer therapy, with an emphasis on the risk of infection, when is testing indicated, and preventive strategies; and knowledge gaps and opportunities for future research.

Immune Reconstitution in Pediatric Patients Following Hematopoietic Cell Transplant for Non-malignant Disorders

Allogeneic hematopoietic cell transplant (HCT) is curative for pediatric patients with non-malignant hematopoietic disorders, including hemoglobinopathies, bone marrow failure syndromes, and primary immunodeficiencies. Early establishment of donor-derived innate and adaptive immunity following HCT is associated with improved overall survival, lower risk of infections and decreased incidence of graft failure. Immune reconstitution (IR) is impacted by numerous clinical variables including primary disease, donor characteristics, conditioning regimen, and graft versus host disease (GVHD). Recent advancements in HCT have been directed at reducing toxicity of conditioning therapy, expanding donor availability through use of alternative donor sources, and addressing morbidity from GVHD with novel graft manipulation. These novel transplant approaches impact the kinetics of immune recovery, which influence post-transplant outcomes. Here we review immune reconstitution in pediatric patients undergoing HCT for non-malignant disorders. We explore the transplant-associated factors that influence immunologic recovery and the disease-specific associations between IR and transplant outcomes.

Reconstitution of T Cell Subsets Following Allogeneic Hematopoietic Cell Transplantation

Allogeneic (allo) hematopoietic cell transplantation (HCT) is the only curative treatment option for patients suffering from chemotherapy-refractory or relapsed hematological malignancies. The occurrence of morbidity and mortality after allo-HCT is still high. This is partly correlated with the immunological recovery of the T cell subsets, of which the dynamics and relations to complications are still poorly understood. Detailed information on T cell subset recovery is crucial to provide tools for better prediction and modulation of adverse events. Here, we review the current knowledge regarding CD4+ and CD8+ T cells, γδ T cells, iNKT cells, Treg cells, MAIT cells and naive and memory T cell reconstitution, as well as their relations to outcome, considering different cell sources and immunosuppressive therapies. We conclude that the T cell subsets reconstitute in different ways and are associated with distinct adverse and beneficial events; however, adequate reconstitution of all the subsets is associated with better overall survival. Although the exact mechanisms involved in the reconstitution of each T cell subset and their associations with allo-HCT outcome need to be further elucidated, the data and suggestions presented here point towards the development of individualized approaches to improve their reconstitution. This includes the modulation of immunotherapeutic interventions based on more detailed immune monitoring, aiming to improve overall survival changes.

Rapid reconstitution of regulatory T-cell subsets is associated with reduced rates of acute graft-versus-host disease and absence of viremia after cord blood transplantation in children with reduced-intensity conditioning using alemtuzumab

Forkhead box P3 (FOXP3)+ regulatory T cell (Treg) reconstitution after unrelated donor umbilical cord blood transplantation in chemotherapy-naïve children is incompletely characterized. We studied 21 children with nonmalignant diseases receiving an identical alemtuzumab-containing regimen. We hypothesized that Treg recovery may be perturbed in patients not only by acute graft-versus-host disease (aGVHD) but also by viremia. Tregs and their memory and naïve subsets were serially monitored for proliferation and apoptosis along with conventional T cells (Tcon). A "reconstitution index" (RI) was calculated relative to pretransplantation values for each parameter. At 3 months post-UCBT, the RI of Tregs was faster compared with other immune components tested and was most rapid in patients free of aGVHD and viremia. There were significantly fewer Tregs in patients experiencing grade I-II aGVHD and/or viremia, leading to an imbalance between Tregs-Tcon ratios. Central and effector memory Tregs were most affected at this time point when they dominated in the circulation. Impaired Treg proliferation without increased apoptosis accounted for the reduced Treg-Tcon ratio. In patients affected with grade II aGVHD and viremia, the overall reduction in circulating Treg pool were associated with a more oligoclonal T-cell receptor β repertoire. Taken together, aGVHD and viremia can lead to defective Treg expansion homeostasis.

Comparative Study of Tacrolimus and Short-Term Methotrexate: 2-Day versus 3-Day Methotrexate as Graft-versus-Host-Disease Prophylaxis after Umbilical Cord Blood Transplantation in Adults

Methotrexate (MTX) in combination with a calcineurin inhibitor has been commonly used for prophylaxis of graft-versus-host disease (GVHD) following umbilical cord blood transplantation (UCBT) in Japan. However, the appropriate prophylactic MTX dosage in UCBT has not been established to date. To determine the preferential GVHD prophylaxis in UCBT, this study retrospectively investigated the administration of short-term MTX for 2 days versus 3 days. Of 103 adult patients submitted to UCBT enrolled in the study, 73 received tacrolimus (TAC) with 2 days of MTX given at 10 mg/m² on day 1 and 7 mg/m² on day 3 (very short-term [vs] MTX), whereas 30 patients received TAC with 3 days of MTX given at 10 mg/m² on day 1, 7 mg/m² on day 3, and 7 mg/m² on day 6 (short-term [s] MTX). In univariate analysis, neutrophil engraftment was shown to be significantly better (P = .039) in the vsMTX/TAC group. Among high-risk patients, the vsMTX/TAC group also exhibited earlier neutrophil engraftment (P = .042); however, the incidence of acute GVHD was higher in the vsMTX/TAC group (P = .035) on univariate analysis. In multivariate analysis, compared with sMTX/TAC, vsMTX/TAC was associated with lower risk of relapse (hazard ratio, .27; 95% confidence interval, .11 to .64; P = .003) . These results suggest that vsMTX/TAC can be appropriate GVHD prophylaxis after UCBT, especially in higher-risk patients.

Immune recovery after in vivo T-cell depletion myeloablative conditioning hematopoietic stem cell transplantation in severe beta-thalassemia children

BACKGROUND

The clinical outcome of hematopoietic stem cell transplantation (HSCT) in those with severe beta-thalassemia (β-TM) is closely related to post-transplantation immune reconstitution (IR). However, the data on the IR in these settings are scarce.

METHODS

A prospective analysis of the clinical outcome and IR in 47 children with severe β-TM who underwent in vivo T-cell depletion myeloablative conditioning and matched sibling donor HSCT was performed. Immune reconstitution, including immune cell subset counts, as well as the generation of new T and B cells assays after HSCT, was measured.

RESULTS

In the first year after HSCT, bacterial infections and cytomegalovirus (CMV) reactivation were observed in 70.2% and 36.2% of the patients, respectively. In the same period, poor CD4⁺ T-cell recovery was observed. The B cells recovered within 6 months. Natural killer (NK) cells recovered as early as 1 month, but their function was defective. Cord blood and bone marrow (CB + BM) group had slower T-cell recovery, and higher B cells and NK cells in comparison with peripheral blood and bone marrow (PB + BM) group.

CONCLUSIONS

The high incidence of infection within 1 year after in vivo T-cell depletion myeloablative conditioning HSCT in severe β-TM was consistent with poor IR.

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.

Antiviral T Cells for Adenovirus in the Pretransplant Period: A Bridge Therapy for Severe Combined Immunodeficiency

Viral infections can be life threatening in patients with severe combined immunodeficiency (SCID) and other forms of profound primary immunodeficiency disorders both before and after hematopoietic stem cell transplantation (HSCT). Adoptive immunotherapy with virus-specific T cells (VSTs) has been utilized in many patients in the setting of HSCT, but has very rarely been attempted for treatment of viral infections before HSCT. Here we describe the use of VSTs in an infant with RAG1 SCID who had developed disseminated adenovirus which failed to improve on cidofovir. Adenovirus cleared following 2 doses of VSTs and marrow infusion from a matched unrelated donor, without incidence of graft versus host disease. T cell receptor-b sequencing demonstrated expansion of adenovirus-specific T cell fraction of the VSTs, suggesting that infusion facilitated viral clearance. This report suggests that VSTs are likely safe in the pre-HSCT period, and may be a useful bridge therapy for infants with SCID and persistent viral infections.

In vitro differentiated plasmacytoid dendritic cells as a tool to induce anti-leukemia activity of natural killer cells

Acute lymphoblastic leukemia (ALL) is believed to be resistant to NK cell-mediated killing. To overcome this resistance, we developed an innovative approach based on NK cell stimulation with Toll-like receptor (TLR)-activated plasmacytoid dendritic cells (pDC). The translation of this approach into the clinic requires the production of high numbers of human pDC. Herein, we show that in vitro differentiation of cord blood CD34+ progenitors in the presence of aryl hydrocarbon receptor antagonists gives rise to clinically relevant numbers of pDC, as about 108 pDC can be produced from a typical cord blood unit. Blocking the aryl hydrocarbon receptor (AHR) pathway significantly increased the yield of pDC. When compared to pDC isolated from peripheral blood, in vitro differentiated pDC (ivD-pDC) exhibited an increased capacity to induce NK cell-mediated killing of ALL. Although ivD-pDC produced lower amounts of IFN-α than peripheral blood pDC upon TLR activation, they produced more IFN-λ2, known to play a critical role in the induction of anti-tumoral NK cell functions. Both TLR-9 and TLR-7 ligands triggered pDC-induced NK cell activation, offering the possibility to use any clinical-grade TLR-7 or TLR-9 ligands in future clinical trials. Finally, adoptive transfer of ivD-pDC cultured in the presence of an AHR antagonist cured humanized mice with minimal ALL disease. Collectively, our results pave the way to clinical-grade production of sufficient numbers of human pDC for innate immunotherapy against ALL and other refractory malignancies.

Predicting CD4 T-Cell Reconstitution Following Pediatric Hematopoietic Stem Cell Transplantation

Hematopoietic stem cell transplantation (HSCT) is an increasingly common treatment for children with a range of hematological disorders. Conditioning with cytotoxic chemotherapy and total body irradiation leaves patients severely immunocompromised. T‐cell reconstitution can take several years due to delayed restoration of thymic output. Understanding T‐cell reconstitution in children is complicated by normal immune system maturation, heterogeneous diagnoses, and sparse uneven sampling due to the long time spans involved. We describe here a mechanistic mathematical model for CD4 T‐cell immune reconstitution following pediatric transplantation. Including relevant biology and using mixed‐effects modeling allowed the factors affecting reconstitution to be identified. Bayesian predictions for the long‐term reconstitution trajectories of individual children were then obtained using early post‐transplant data. The model was developed using data from 288 children; its predictive ability validated on data from a further 75 children, with long‐term reconstitution predicted accurately in 81% of the patients.

Reconstitution of adaptive immunity after umbilical cord blood transplantation: impact on infectious complications

In comparison with allogeneic stem cell transplantation (alloHSCT) with other stem cell sources, umbilical cord blood transplantation (UCBT) was traditionally associated with increased risk of infections, particularly during the first 3 months after transplantation. Longitudinal studies of immune monitoring reported peculiar patterns of T- and B-cell recovery in the peripheral blood of UCB recipients during the first months post-transplantation. Overall, current data suggest delayed reconstitution of naive and memory CD4⁺ and CD8⁺ T-cell pools after UCBT. This is particularly true for adult recipients and for patients who received in vivo T-cell depleting approaches before the transplantation. Such delayed T-cell recovery may increase susceptibility of UCB recipients for developing opportunistic infections and viral reactivations. Regarding B-cell recovery, UCBT was associated with accelerated B-lymphopoiesis. Recent studies also reported evidence for faster functional memory B-cell recovery in UCB recipients. In this article, we briefly review T- and B-cell reconstitution after alloHSCT, with emphasis on peculiarities observed after UCBT. We further put these data in lines with risks of infections after UCBT.

Humoral Immune Reconstitution Kinetics after Allogeneic Hematopoietic Stem Cell Transplantation in Children: A Maturation Block of IgM Memory B Cells May Lead to Impaired Antibody Immune Reconstitution

Although T cell immune reconstitution after allogeneic hematopoietic stem cell transplantation (allo-HSCT) has been well studied, long-term B cell immune reconstitution remains less characterized. We evaluated humoral immune reconstitution among 71 pediatric allo-HSCT recipients. Although tetanus toxoid antibody levels were normal at 1 year after allo-HSCT, antipolysaccharide carbohydrate antibodies remained persistently low for up to 5 years. While naive B cell counts normalized by 6 months, IgM memory B cell deficiency persisted for up to 2 years (P = .01); switched memory B cell deficiency normalized by 1 year after allo-HSCT. CD4⁺ T cell immune reconstitution correlated with that of switched memory B cells as early as 6 months after allo-HSCT (r = .55, P = .002) but did not correlate with IgM memory B cells at any time point after allo-HSCT. Taken together, this suggests that allo-HSCT recipients have impaired antibody immune reconstitution, mainly due to IgM memory B cell maturation block, compared with more prompt T cell-dependent switched memory cell immune reconstitution. We further explored other factors that might affect humoral immune reconstitution. The use of total body irradiation was associated with lower naive B cells counts at 6 months after HSCT (P = .04) and lower IgM (P = .008) and switched (P = .003) memory B cells up to 2 years. Allo-HSCT recipients with extensive chronic graft-versus-host disease had lower IgM memory B cell counts (P = .03) up to 2 years after allo-HSCT. The use of cord blood was associated with better naive (P = .01), IgM (P = .0005), and switched memory (P = .006) B cells immune reconstitution. These findings may inform future prophylaxis and treatment strategies regarding risk of overwhelming infection, graft-versus-host disease, and post-allogeneic HSCT revaccination.

Relation between Acute GVHD and NK Cell Subset Reconstitution Following Allogeneic Stem Cell Transplantation

One of the major challenges of allogeneic stem cell transplantation (allo-SCT) is to reduce the risk of graft-versus-host disease (GVHD) while boosting the graft-versus-leukemia (GVL) effect. The reconstitution of natural killer (NK) cells following allo-SCT is of notable interest due to their known capability to induce GVL without GVHD. Here, in this study, we investigate the association between the incidence and severity of acute graft-versus-host disease (aGVHD) and the early reconstitution of NK cell subsets following allo-SCT. We analyzed 342 samples from 107 patients using flow cytometry, with a focus on immature CD56^high and mature cytotoxic CD56^dim NK cells. Longitudinal analysis of immune reconstitution after allo-SCT showed that the incidence of aGVHD was associated with a delayed expansion of the entire NK cell population, in particular the CD56^high subset. Notably, the disturbed reconstitution of the CD56^high NK cells also correlated with the severity of aGVHD.

Fewer Circulating Natural Killer Cells 28 Days After Double Cord Blood Transplantation Predicts Inferior Survival and IL-15 Response

Natural Killer (NK) cell immune reconstitution after double umbilical cord blood transplantation (dUCBT) is rapid and thought to be involved in graft vs. leukemia (GvL) reactions. To investigate the role of NK cell recovery on clinical outcomes, the absolute number of NK cells at Day 28 after dUCBT was determined and patients with low numbers of NK cells had inferior two year disease-free survival (hazard ratio 1.96; p=0.04). A detailed developmental and functional analysis of the recovering NK cells was performed to link NK recovery and patient survival. The proportion of NK cells in each developmental stage was similar for patients with low, medium, and high Day 28 NK cell numbers. As compared to healthy controls, patients post-transplant showed reduced NK functional responses upon K562 challenge (CD107a, IFN-γ, and TNFα); however, there were no differences based on Day 28 NK cell number. Patients with low NK numbers had 30% less STAT5 phosphorylation in response to exogenous IL-15 (p=0.04) and decreased Eomes expression (p=0.025) compared to patients with high NK numbers. Decreased STAT5 phosphorylation and Eomes expression may be indicative of reduced sensitivity to IL-15 in the low NK cell group. Incubation of patient samples with IL-15 superagonist (ALT803) increased cytotoxicity and cytokine production in all patient groups. Thus, clinical interventions, including administration of IL-15 early after transplantation may increase NK cell number and function and, in turn, improve transplantation outcomes.

TRAIL-mediated killing of acute lymphoblastic leukemia by plasmacytoid dendritic cell-activated natural killer cells

Acute lymphoblastic leukemia (ALL) still frequently recurs after hematopoietic stem cell transplantation (HSCT), underscoring the need to improve the graft-versus-leukemia (GvL) effect. Natural killer (NK) cells reconstitute in the first months following HSCT when leukemia burden is at its lowest, but ALL cells have been shown to be resistant to NK cell-mediated killing. We show here that this resistance is overcome by NK cell stimulation with TLR-9-activated plasmacytoid dendritic cells (pDCs). NK cell priming with activated pDCs resulted in TRAIL and CD69 up-regulation on NK cells and IFN-γ production. NK cell activation was dependent on IFN-α produced by pDCs, but was not reproduced by IFN-α alone. ALL killing was further enhanced by inhibition of KIR engagement. We showed that ALL lysis was mainly mediated by TRAIL engagement, while the release of cytolytic granules was involved when ALL expressed NK cell activating receptor ligands. Finally, adoptive transfers of activated-pDCs in ALL-bearing humanized mice delayed the leukemia onset and cure 30% of mice. Our data therefore demonstrate that TLR-9 activated pDCs are a powerful tool to overcome ALL resistance to NK cell-mediated killing and to reinforce the GvL effect of HSCT. These results open new therapeutic avenues to prevent relapse in children with ALL.

Neutrophil function in children following allogeneic hematopoietic stem cell transplant

HSCT is a lifesaving procedure for children with malignant and non-malignant conditions. The conditioning regimen renders the patient severely immunocompromised and recovery starts with neutrophil (PMN) engraftment. We hypothesize that children demonstrate minimal PMN dysfunction at engraftment and beyond, which is influenced by the stem cell source and the conditioning regimen. Peripheral blood was serially collected from children at 1 to 12 months following allogeneic HSCT. PMN superoxide (O2-) production, degranulation (elastase), CD11b surface expression, and phagocytosis were assessed. Twenty-five patients, mean age of 10.5 yr with 65% males, comprised the study and transplant types included: 14 unrelated cord blood stem cells (cords), seven matched related bone marrow donors, three matched unrelated bone marrow donors, and one peripheral blood progenitor cells. Engraftment occurred at 24 days. There were no significant differences between controls and patients in PMN O2- production, phagocytosis, CD11b surface expression, and total PMN elastase. Elastase release was significantly decreased <6 months vs. controls (p < 0.05) and showed normalization by six months for cords only. The conditioning regimen did not affect PMN function. PMN function returns with engraftment, save elastase release, which occurs later related to the graft source utilized, and its clinical significance is unknown.

Exploitation of natural killer cells for the treatment of acute leukemia

Natural killer (NK) cells play an important role in surveillance and elimination of malignant cells. Their spontaneous cytotoxicity was first demonstrated in vitro against leukemia cell lines, and NK cells might play a crucial role in the therapy of leukemia. NK cell activity is controlled by an array of germ line-encoded activating and inhibitory receptors, as well as modulating coreceptors. This biologic feature can be exploited in allogeneic cell therapy, and the recognition of "missing-self" on target cells is crucial for promoting NK cell-mediated graft-versus-leukemia effects. In this regard, NK cells that express an inhibitory killer immunoglobulin-like receptor (iKIR) for which the respective major histocompatibility complex class I ligand is absent on leukemic target cells can exert alloreactivity in vitro and in vivo. Several models regarding potential donor-patient constellations have been described that have demonstrated the clinical benefit of such alloreactivity of the donor-derived NK cell system in patients with adult acute myeloid leukemia and pediatric B-cell precursor acute lymphoblastic leukemia after allogeneic stem cell transplantation. Moreover, adoptive transfer of mature allogeneic NK cells in the nontransplant or transplant setting has been shown to be safe and feasible, whereas its effectivity needs further evaluation. NK cell therapy can be further improved by optimal donor selection based on phenotypic and genotypic properties, by adoptive transfer of NK cells with ex vivo or in vivo cytokine stimulation, by the use of antibodies to induce antibody-dependent cellular cytotoxicity or to block iKIRs, or by transduction of chimeric antigen receptors.

Higher Early Monocyte and Total Lymphocyte Counts Are Associated with Better Overall Survival after Standard Total Body Irradiation, Cyclophosphamide, and Fludarabine Reduced-Intensity Conditioning Double Umbilical Cord Blood Allogeneic Stem Cell Transplantation in Adults

This single-center retrospective study aimed to report the impact of early hematopoietic and immune recoveries after a standard total body irradiation, cyclophosphamide, and fludarabine (TCF) reduced-intensity conditioning (RIC) regimen for double umbilical cord blood (dUCB) allogeneic stem cell transplantation (allo-SCT) in adults. We analyzed 47 consecutive patients older than 17 years who engrafted after a dUCB TCF allo-SCT performed between January 2006 and April 2013 in our department. Median times for neutrophil and platelet recoveries were 17 (range, 6 to 59) and 37 days (range, 0 to 164), respectively. The 3-year overall (OS) and disease-free survivals, relapse incidence, and nonrelapse mortality were 65.7%, 57.2%, 27.1%, and 19%, respectively. In multivariate analysis, higher day +30 monocyte (≥615/mm(3); hazard ratio [HR], .04; 95% confidence interval [CI], .004 to .36; P < .01) and day +42 lymphocyte (≥395/mm(3); HR, .16; 95% CI, .03 to .78; P = .02) counts were independently associated with better OS. These results suggest that early higher hematopoietic and immune recovery is predictive of survival after dUCB TCF RIC allo-SCT in adults. Factors other than granulocyte colony-stimulating factor, which was used in all cases, favoring expansion of monocytes or lymphocytes, should be tested in the future as part of the UCB transplantation procedure.

Immune reconstitution after cord blood transplantation: peculiarities, clinical implications and management strategies

Umbilical cord blood (UCB) is now widely used as an alternative hematopoietic stem cell source for patients lacking closely matched related or unrelated adult donors. UCB transplantation has traditionally been associated with delayed engraftment, poor immune reconstitution and consequent increased risk of infection. More recent clinical studies, however, suggest that conditioning regimens and in particular the omission of in vivo T-cell depletion may play a crucial role in post-transplant T-cell expansion, facilitating a uniquely rapid immune recovery after UCB transplantation. The peculiar characteristics of UCB cells, the importance of thymic function and the role of conditioning regimens and graft-versus-host disease influencing immune reconstitution are described. The last part of the review reports available data on UCB, as well as third-party peripheral blood derived anti-viral cell therapy, which provides a novel approach to rescue UCB recipients with viral complications in the post-transplant period.

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.

Umbilical cord blood CD34(+) stem cells and other mononuclear cell subtypes processed up to 96 h from collection and stored at room temperature maintain a satisfactory functionality for cell therapy

BACKGROUND AND OBJECTIVES

Umbilical cord blood (UCB) is a good stem cell source for cell therapy. We recently demonstrated that cord blood mononuclear cell (MNCs) subtypes were viable and functional until 96 h after collection, even stored at room temperature. Now, we analyzed the viability and functionality of the cells before and after cryopreservation.

MATERIALS AND METHODS

Twenty UCB units were analyzed at 24 and 96 h after collection, frozen for 6 months, thawed and re-evaluated. MNCs were analyzed by flow cytometry, viability by 7-AAD and clonogenic assays (CFU) were performed.

RESULTS

After 96 h of storage, no substantial loss of MNC was found (median 7.320 × 10(6 ) × 6.05 × 10(6) ). Percentage and viability CD34(+) cells, B-cell precursors and mesenchymal stem cells were not affected. However, mature B and T lymphocytes as well as granulocytes had a substantial loss. CFU growth was observed in all samples. Prefreezing storage of 96 h was associated with a relative loss of colony formation (median 12%). Postthaw, this loss had a median of 49% (24 h samples) to 56% (96 h samples).

CONCLUSION

The delay of 96 h before UCB processing is possible, without a prohibitive impairment of CD34(+) loss in number and functionality.

Impaired interferon-alpha production by plasmacytoid dendritic cells after cord blood transplantation in children: implication for post-transplantation toll-like receptor ligand-based immunotherapy

Plasmacytoid dendritic cells (pDCs) initiate both innate and adaptive immune responses, making them attractive targets for post-transplantation immunotherapy, particularly after cord blood transplantation (CBT). Toll-like receptor (TLR) agonists are currently studied for pDC stimulation in various clinical settings. Their efficacy depends on pDC number and functionality, which are unknown after CBT. We performed a longitudinal study of pDC reconstitution in children who underwent bone marrow transplantation (BMT) and single-unit CBT. Both CBT and unrelated BMT patients received antithymocyte globulin as part of their graft-versus-host disease prophylaxis regimen. pDC blood counts were higher in CBT patients than in healthy volunteers from 2 to 9 months after transplantation, whereas they remained lower in BMT patients. We showed that cord blood progenitors gave rise in vitro to a 500-fold increase in functional pDCs over bone marrow counterparts. Upon stimulation with a TLR agonist, pDCs from both CBT and BMT recipients upregulated T cell costimulatory molecules, whereas interferon-alpha (IFN-α) production was impaired for 9 months after CBT. TLR agonist treatment is thus not expected to induce IFN-α production by pDCs after CBT, limiting its immunotherapeutic potential. Fortunately, in vitro production of large amounts of functional pDCs from cord blood progenitors paves the way for the post-transplantation adoptive transfer of pDCs.

Pharmacokinetic/pharmacodynamic modelling approaches in paediatric infectious diseases and immunology

Pharmacokinetic/pharmacodynamic (PKPD) modelling is used to describe and quantify dose-concentration-effect relationships. Within paediatric studies in infectious diseases and immunology these methods are often applied to developing guidance on appropriate dosing. In this paper, an introduction to the field of PKPD modelling is given, followed by a review of the PKPD studies that have been undertaken in paediatric infectious diseases and immunology. The main focus is on identifying the methodological approaches used to define the PKPD relationship in these studies. The major findings were that most studies of infectious diseases have developed a PK model and then used simulations to define a dose recommendation based on a pre-defined PD target, which may have been defined in adults or in vitro. For immunological studies much of the modelling has focused on either PK or PD, and since multiple drugs are usually used, delineating the relative contributions of each is challenging. The use of dynamical modelling of in vitro antibacterial studies, and paediatric HIV mechanistic PD models linked with the PK of all drugs, are emerging methods that should enhance PKPD-based recommendations in the future.

Reconstitution of regulatory T-cell subsets after allogeneic hematopoietic SCT

Previous studies on regulatory T-cell (Treg) reconstitution after allogeneic hematopoietic SCT (HSCT) have suggested that, within the GVHD process, imbalance between effector T cells and Tregs may be more important than the absolute numbers of circulating Tregs. No study has analyzed naive vs memory Treg reconstitution in a longitudinal cohort with large numbers of patients. The reconstitution of total and subsets of Treg was prospectively analyzed by flow cytometry in 185 consecutive recipients at 3, 6, 12 and 24 months after allogeneic HSCT. The levels of total, naive and memory Tregs increased, mainly within the memory subset, but remained lower than healthy controls up to 2 years after transplantation. Reduced-intensity conditioning and peripheral blood (PBSC) as the source of stem cells were associated with better 3-month reconstitution. In multivariate analysis, PBSC, recipient age ⩽25 and no anti-thymoglobulin in the conditioning regimen were associated with a better Treg reconstitution. Naive Treg long-term reconstitution was mainly influenced by recipient age. Whereas prior acute GVHD impaired Treg reconstitution, Treg subsets (absolute numbers and frequencies relative to CD4(+) T-cell subsets) at 3, 6 and 12 months after HSCT were not associated with the occurrence of a later episode of chronic GVHD.