Clinical strategies to enhance posttransplant immune reconstitution

Fractionated Infusion of Hematopoietic Progenitor Cells Does Not Improve Neutrophil Recovery or Survival in Allograft Recipients

Allogeneic hematopoietic cell transplantation (HCT) offers a potentially curative therapy in patients with hematologic malignancies; however, nonrelapse mortality (NRM) remains a concern. Strategies to improve neutrophil recovery and immune reconstitution are needed to decrease NRM. Murine models of allogeneic HCT suggest that fractionated hematopoietic progenitor cell (HPC) infusion may improve engraftment through improved access of HPCs to a viable hematopoietic niche. The primary objective of the present study was to determine the impact of fractionated infusion versus unfractionated (bulk) infusion of HPCs on the time to achieve neutrophil engraftment. Secondary objectives included the effect of fractionated versus bulk infusion of HPCs on platelet engraftment, immune reconstitution, the incidence of acute graft-versus-host disease (GVHD) grade II-IV, NRM, and overall survival (OS). In this randomized phase 2 study, patients with hematologic malignancies undergoing allogeneic HCT were randomized to receive HPC infusion as a bulk (bulk arm) or in fractions (fractionated arm): 4 × 106 CD34+ cells/kg recipient weight infused on day 0, with the remaining HPCs CD34+ cell-selected then infused in equally distributed aliquots on days 2, 4, and 6 post-HCT. Randomization was stratified by type of transplant, unmodified (i.e. T cell-replete graft) versus CD34+ cell-selected (T cell-depleted graft). Patients whose donor failed to collect at least 7 × 106 CD34+ cells/kg of recipient weight received bulk HPC infusions regardless of randomization, for safety. These patients continued the HCT process on study but were replaced until each arm reached the prespecified accrual target. Per protocol, these patients were not included in this modified intention-to-treat analysis. A total of 116 patients were enrolled. Donors of 42 patients failed to mobilize the minimum CD34+ cell dose (7 × 106 cells/kg recipient weight) and were excluded from the analysis. The 74 evaluable patients included 38 randomized to the bulk arm and 36 randomized to the fractionated arm. All patients engrafted. The median time to an absolute neutrophil count of ≥0.5 × 109/L was 11 days on both arms. The day +180 median CD4+ cell count was 179 cells/µL in the bulk arm and 111 cells/µL in the fractionated arm (P = .779). The cumulative incidence of grade II-IV acute GVHD on post-transplant day +100 was 32% in the bulk arm and 17% in the fractionated arm (P = .131). Two patients in the bulk arm, but none in the fractionated arm, experienced grade III-IV GVHD. The 4-year OS was 60% in the bulk arm and 62% in the fractionated arm (P = .414), whereas the 4-year cumulative incidences of NRM and relapse were similar in the 2 arms. Fractionated infusion of HPCs in allogeneic HCT recipients did not impact neutrophil or CD4+ cell recovery, NRM, relapse, or OS when compared with bulk HPC infusion. We also observed that with current mobilization techniques, it was unlikely that more than 60% of healthy donors would be able to collect >7 × 106 CD34+ cells/kg recipient weight for adult recipients. © 2021 American Society for Transplantation and Cellular Therapy. Published by Elsevier Inc.

Immune reconstitution post allogeneic transplant and the impact of immune recovery on the risk of infection

Infection is the leading cause of non-relapse mortality after allogeneic haematopoietic cell transplantation (HCT). This occurs as a result of dysfunction to the host immune system from the preparative regimen used prior to HCT, combined with a delay in reconstitution of the donor-derived immune system after HCT. In this article, we elaborate on the process of immune reconstitution post-HCT that begins with the innate system and is followed by recovery of adaptive immunity. Simultaneously, we describe how the tempo of immune reconstitution influences the risk of various infections. We explain some of the key differences in immune reconstitution and the consequent risk of infections in recipients of peripheral blood stem cell, bone marrow or umbilical cord blood grafts. Other factors that impact on immune recovery are also highlighted. Finally, we allude to various strategies that are being tested to enhance immune reconstitution post-HCT.

FOXN1 recombinant protein enhances T-cell regeneration after hematopoietic stem cell transplantation in mice

A prolonged period of T-cell recovery is the major challenge in hematopoietic stem cell transplantation (HSCT). Thymic epithelial cells (TECs) are the major component of the thymic microenvironment for T-cell generation. However, TECs undergo degeneration over time. FOXN1 plays a critical role in TEC development and is required to maintain adult TECs for thymopoiesis. To investigate the potential application of FOXN1, we have cloned and expressed recombinant FOXN1 protein (rFOXN1) that was fused with cell-penetrating peptides. We show here that the rFOXN1 protein can translocate from the cell surface into the cytoplasm and nucleus. Administration of rFOXN1 into both congenic and allogeneic HSCT recipient mice increased the number of TECs, resulting in enhanced thymopoiesis that led to an increased number of functional T cells in the periphery. The increased number of TECs is due to the enhanced survival and proliferation of TECs. Our results suggest that rFOXN1 has the potential to be used in enhancing T-cell regeneration in patients following HSCT.

Evaluation of TCR repertoire diversity in patients after hematopoietic stem cell transplantation

T-cell receptor (TCR) repertoire analyses have been widely used to identify T cell populations of interest in cancer and autoimmunity and for characterizing immune repertoire reconstitution after hematopoietic stem cell transplantation (HSCT). Several decades of development and progress have led to the use of techniques for evaluating TCR repertoires in a more comprehensive, unbiased and fast manner, and the mechanisms of T cell immune reconstitution after HSCT and the new approaches used for recovering T cell repertoire diversity post HSCT have been more exhaustively documented to some degree. To better understand and characterize this progress, here we review recent studies on TCR repertoire diversity recovery in patients with leukemia and autoimmune disease who have received HSCT, impact factors and improvements in approaches for TCR repertoire recovery after HSCT.

Recombinant IL-7/HGFβ hybrid cytokine enhances T cell recovery in mice following allogeneic bone marrow transplantation

T cell immunodeficiency is a major complication of bone marrow (BM) transplantation (BMT). Therefore, approaches to enhance T cell reconstitution after BMT are required. We have purified a hybrid cytokine, consisting of IL-7 and the β-chain of hepatocyte growth factor (HGFβ) (IL-7/HGFβ), from a unique long-term BM culture system. We have cloned and expressed the IL-7/HGFβ gene in which the IL-7 and HGFβ genes are connected by a flexible linker to generate rIL-7/HGFβ protein. Here, we show that rIL-7/HGFβ treatment enhances thymopoiesis after allogeneic BMT. Although rIL-7 treatment also enhances the number of thymocytes, rIL-7/HGFβ hybrid cytokine was more effective than was rIL-7 and the mechanisms by which rIL-7 and rIL-7/HGFβ increase the numbers of thymocytes are different. rIL-7 enhances the survival of double negative (DN), CD4 and CD8 single positive (SP) thymocytes. In contrast, rIL-7/HGFβ enhances the proliferation of the DN, SP thymocytes, as well as the survival of CD4 and CD8 double positive (DP) thymocytes. rIL-7/HGFβ treatment also increases the numbers of early thymocyte progenitors (ETPs) and thymic epithelial cells (TECs). The enhanced thymic reconstitution in the rIL-7/HGFβ-treated allogeneic BMT recipients results in increased number and functional activities of peripheral T cells. Graft-versus-host-disease (GVHD) is not induced in the rIL-7/HGFβ-treated BMT mice. Therefore, rIL-7/HGFβ may offer a new tool for the prevention and/or treatment of T cell immunodeficiency following BMT.

Notch signaling in hematopoietic cell transplantation and T cell alloimmunity

Notch signaling can regulate both hematopoietic progenitors and alloimmune T cells in the setting of allogeneic bone marrow or hematopoietic cell transplantation (allo-HCT). Ex vivo culture of multipotent blood progenitors with immobilized Delta-like ligands induces supraphysiological Notch signals and can markedly enhance progenitor expansion. Infusion of Notch-expanded progenitors shortened myelosuppression in preclinical and early clinical studies, while accelerating T cell reconstitution in preclinical models. Notch also plays an essential role in vivo to regulate pathogenic alloimmune T cells that mediate graft-versus-host disease (GVHD), the most severe complication of allo-HCT. In mouse allo-HCT models, Notch inhibition in donor-derived T cells or transient blockade of Delta-like ligands after transplantation profoundly decreased GVHD incidence and severity, without causing global immunosuppression. These findings identify Notch in T cells as an attractive therapeutic target to control GVHD. In this review, we discuss these contrasting functions of Notch signaling with high translational significance in allo-HCT patients.

Ask the Experts: Targeting Notch signaling in graft-versus-host disease

Dr Ivan Maillard is a hematologist and a physician–scientist with an interest in the regulation of blood-forming stem cells and bone marrow transplantation. Born and raised in Switzerland, he earned his MD at the University of Lausanne (Lausanne, Switzerland) and a PhD in Immunology from the MD–PhD program of the Swiss Academy of Medical Sciences. He subsequently completed a postdoctoral fellowship at the University of Pennsylvania (PA, USA), where he also worked as an Instructor in Medicine and physician in Hematology–Oncology. Dr Maillard joined the University of Michigan (MI, USA) in 2007 where he is affiliated with the Center for Stem Cell Biology at the Life Sciences Institute, as well as with the Division of Hematology–Oncology in the Department of Medicine and the Department of Cell and Developmental Biology. Besides his research interests, Dr Maillard maintains an active clinical practice in the care of patients with cancers of the blood and lymphatic system.

Blockade of individual Notch ligands and receptors controls graft-versus-host disease

Graft-versus-host disease (GVHD) is the main complication of allogeneic bone marrow transplantation. Current strategies to control GVHD rely on global immunosuppression. These strategies are incompletely effective and decrease the anticancer activity of the allogeneic graft. We previously identified Notch signaling in T cells as a new therapeutic target for preventing GVHD. Notch-deprived T cells showed markedly decreased production of inflammatory cytokines, but normal in vivo proliferation, increased accumulation of regulatory T cells, and preserved anticancer effects. Here, we report that γ-secretase inhibitors can block all Notch signals in alloreactive T cells, but lead to severe on-target intestinal toxicity. Using newly developed humanized antibodies and conditional genetic models, we demonstrate that Notch1/Notch2 receptors and the Notch ligands Delta-like1/4 mediate all the effects of Notch signaling in T cells during GVHD, with dominant roles for Notch1 and Delta-like4. Notch1 inhibition controlled GVHD, but led to treatment-limiting toxicity. In contrast, Delta-like1/4 inhibition blocked GVHD without limiting adverse effects while preserving substantial anticancer activity. Transient blockade in the peritransplant period provided durable protection. These findings open new perspectives for selective and safe targeting of individual Notch pathway components in GVHD and other T cell-mediated human disorders.

Sending the right signal: Notch and stem cells

BACKGROUND

Notch signaling plays a critical role in multiple developmental programs and not surprisingly, the Notch pathway has also been implicated in the regulation of many adult stem cells, such as those in the intestine, skin, lungs, hematopoietic system, and muscle.

SCOPE OF REVIEW

In this review, we will first describe molecular mechanisms of Notch component modulation including recent advances in this field and introduce the fundamental principles of Notch signaling controlling cell fate decisions. We will then illustrate its important and varied functions in major stem cell model systems including: Drosophila and mammalian intestinal stem cells and mammalian skin, lung, hematopoietic and muscle stem cells.

MAJOR CONCLUSIONS

The Notch receptor and its ligands are controlled by endocytic processes that regulate activation, turnover, and recycling. Glycosylation of the Notch extracellular domain has important modulatory functions on interactions with ligands and on proper receptor activity. Notch can mediate cell fate decisions including proliferation, lineage commitment, and terminal differentiation in many adult stem cell types. Certain cell fate decisions can have precise requirements for levels of Notch signaling controlled through modulatory regulation.

GENERAL SIGNIFICANCE

We describe the current state of knowledge of how the Notch receptor is controlled through its interaction with ligands and how this is regulated by associated factors. The functional consequences of Notch receptor activation on cell fate decisions are discussed. We illustrate the importance of Notch's role in cell fate decisions in adult stem cells using examples from the intestine, skin, lung, blood, and muscle. This article is part of a Special Issue entitled Biochemistry of Stem Cells.

Hematopoietic stem cell transplantation for primary immunodeficiency diseases

Hematopoietic stem cell transplantation (HSCT) is now highly successfully curing a widening range of primary immunodeficiencies (PIDs). Better tissue typing, matching of donors, less toxic chemotherapy, better virus detection and treatment, improved supportive care, and graft-versus-host disease prophylaxis mean up to a 90% cure for severe combined immunodeficiency patients and a 70-80% cure for other PIDs given a matched unrelated donor, and rising to 95% for young patients with specific PIDs, such as Wiskott-Aldrich syndrome. Precise molecular diagnosis, detailed data on prognosis, and careful pre-HSCT assessment of infective lung and liver damage will ensure an informed benefit analysis of HSCT and the best outcome. It is now recognized that the best treatment option for chronic granulomatous disease is HSCT, which can also be curative for CD40 ligand deficiency and complex immune dysregulation disorders.

Keratinocyte growth factor enhanced immune reconstitution in murine allogeneic umbilical cord blood cell transplant

Umbilical cord blood (UCB) is used increasingly as a source of hematopoietic cells because of a lower risk of graft-versus-host disease (GVHD). Myeloablative conditioning before allogeneic umbilical cord blood transplant (allo-UCBT) results in thymic epithelial cell injury and T-cell immune deficiency. Full-term fetal blood cells were used as hematopoietic cells in a previous murine allo-UCBT model with a limited number of mice surviving the myeloablative conditioning. We designed a viable murine allo-UCBT protocol with platelet concentrate support. Keratinocyte growth factor (KGF) is a mitogen of thymic epithelial cells that promotes recovery of thymic epithelium when given before total body irradiation (TBI)-containing conditioning in experimental murine models. We hypothesized that KGF pre-administration would improve post-allo-UCBT thymopoiesis. To test this hypothesis, allo-UCBT recipient mice were given KGF or control saline prior to UCBT. Platelet concentrate support significantly improved the survival rate of murine allo-UCBT recipients. KGF administration significantly increased donor-derived T and natural killer T (NKT) cells at day +35 in spleens of allo-UCBT recipients. KGF administration also improved thymic function after allo-UCBT, resulting in higher copies of signal joint T-cell receptor rearrangement excision circles (sjTRECs) in splenocytes. Finally, we found that KGF pre-administration could enhance the graft-versus-leukemia effect. In conclusion, KGF can be administered safely to recipients of allo-UCBT to enhance T-cell immune reconstitution.

Key players for T-cell regeneration

PURPOSE OF REVIEW

The thymus provides a unique and essential microenvironment for T-cell precursors to develop into mature functionally competent T lymphocytes. Ageing causes architectural changes in the thymus resulting in a loss of thymic epithelial space required for thymopoiesis - a process known as thymic involution. Additionally, cytoablative regimens used to treat malignancies also destroy thymic architecture. The net result of both processes is diminished thymic output and function that may lead to impaired immunity. Thus, immunocompromised individuals would benefit from strategies aimed at enhancing T-cell reconstitution.

RECENT FINDINGS

Here we discuss strategies such as the use of sex steroid ablation, keratinocyte growth factor, interleukin-7, and in-vitro-generated progenitor T cells as candidates for restoring T-cell immunity. Using various animal models of ageing or hematopoietic stem cell transplantation, these strategies have been shown to restore thymic architecture and cellularity, resulting in increased output and T-cell function in the periphery.

SUMMARY

These candidate approaches are currently being tested in clinical trials, with preliminary evidence showing encouraging effects on T-cell reconstitution. Nevertheless, although these strategies show clear promise in animal models, and in early human trials, further data are needed to determine their efficacy in patients.

Therapeutic cell engineering with surface-conjugated synthetic nanoparticles

A major limitation of cell therapies is the rapid decline in viability and function of the transplanted cells. Here we describe a strategy to enhance cell therapy via the conjugation of adjuvant drug-loaded nanoparticles to the surfaces of therapeutic cells. With this method of providing sustained pseudoautocrine stimulation to donor cells, we elicited marked enhancements in tumor elimination in a model of adoptive T cell therapy for cancer. We also increased the in vivo repopulation rate of hematopoietic stem cell grafts with very low doses of adjuvant drugs that were ineffective when given systemically. This approach is a simple and generalizable strategy to augment cytoreagents while minimizing the systemic side effects of adjuvant drugs. In addition, these results suggest therapeutic cells are promising vectors for actively targeted drug delivery.

Notch signaling in the immune system

The Notch signaling pathway regulates many aspects of embryonic development, as well as differentiation processes and tissue homeostasis in multiple adult organ systems. Disregulation of Notch signaling is associated with several human disorders, including cancer. In the last decade, it became evident that Notch signaling plays important roles within the hematopoietic and immune systems. Notch plays an essential role in the development of embryonic hematopoietic stem cells and influences multiple lineage decisions of developing lymphoid and myeloid cells. Moreover, recent evidence suggests that Notch is an important modulator of T cell-mediated immune responses. In this review, we discuss Notch signaling in hematopoiesis, lymphocyte development, and function as well as in T cell acute lymphoblastic leukemia.

Notch signaling in the hematopoietic system

Because of its multiple effects in tissue homeostasis and cancer, Notch signaling is gaining increasing attention as a potential therapeutic target. Notch proteins belong to a family of highly conserved cell surface receptors. Ligand binding leads to proteolytic cleavage of Notch receptors by the gamma-secretase complex, followed by translocation of the active intracellular Notch domain into the nucleus and transcriptional activation. Multiple genetic and pharmacological methods are available to inhibit or activate the Notch pathway, some of which are entering human clinical trials. In this review, we discuss our current understanding of Notch signaling in the hematopoietic system. Canonical Notch signaling is essential for the generation of definitive embryonic hematopoietic stem cells, but dispensable for their maintenance during adult life. Notch controls several early steps of T cell development, as well as specific cell fate and differentiation decisions in other hematopoietic lineages. In addition, emerging evidence indicates that Notch is a potent, context-specific regulator of T cell immune responses, including in several disease models relevant to patients. This knowledge will constitute a framework to explore Notch modulation as a therapeutic strategy and to understand potential hematopoietic side effects of systemic Notch inhibition.

Induction of notch signaling by immobilization of jagged-1 on self-assembled monolayers

Notch signaling is a key mechanism during mammal development and stem cell regulation. This study aims to target and control Notch signaling by ligands immobilization using self-assembled monolayers (SAMs) as model surfaces. Non-fouling substrates were prepared by immersion of gold substrates in (1-Mercapto-11-undecyl)tetra(ethylene glycol) thiol solutions. These surfaces were activated with N,N'-carbonyldiimidazole (CDI) at different concentrations (0, 0.03, 0.3, 3 and 30 mg/ml) and an anti-human IgG, Fc specific fragment antibody (Ab) was covalently bound to EG4-SAMs to guarantee the correct exposure of the Notch ligand Jagged-1/Fc chimera (Jag-1). The presence of Ab and Jag-1 was confirmed by radiolabeling, X-ray photoelectron spectroscopy (XPS), ellipsometry and ELISA. The biological activity of Jag-1-Ab-SAMs was assessed by real-time PCR for Hes-1 family gene expression, a Notch pathway target gene, in HL-60 cell line. Results have shown an increase of the amount of immobilized Ab with increasing surface activator concentrations. Jag-1 concentration also increases with Ab concentration. Interestingly, a higher Jagged-1 exposure and fold increase in Hes-1 expression were obtained for surfaces activated with the lowest concentration of CDI (0.03 mg/ml). These results illustrate the great importance of ligands orientation and exposure, when compared with density. This investigation brings new insights into Notch signaling mechanisms. In particular, Jag-1-Ab-SAMs have shown to be adequate model surfaces to study Notch pathway activation and may provide a basis to develop new interfaces in biomaterials to control Notch mechanism in different cell systems.