The impact of T-cell depletion techniques on the outcome after haploidentical hematopoietic SCT

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.

Cell-free DNA levels are increased in acute graft-versus-host disease

BACKGROUND

Cell-free DNA (cfDNA) and nucleosomes, consisting of cfDNA and histones, are markers of cell activation and damage. In systemic inflammation these markers predict severity and fatality. However, the role of cfDNA in acute Graft-versus-Host Disease (aGvHD), a major complication of allogeneic hematopoietic stem cell transplantation (HSCT), is unknown.

OBJECTIVE

The aim of this study is to investigate the role of cfDNA as a marker of aGvHD.

METHODS

We followed nucleosome levels in 37 allogeneic HSCT patients and an established xenotransplantation mouse model. We determined the origin of cfDNA with a species-specific polymerase chain reaction.

RESULTS

In the plasma of aGvHD patients, nucleosome levels significantly increased around the time of aGvHD diagnosis compared to pretransplant, concurrently with a significant increase of known aGvHD markers ST2 and REG3α. In mice, we confirmed that nucleosomes were elevated during clinically detectable aGvHD. We found cfDNA to be mainly of human origin and to a lesser extent of mouse origin, indicating that cfDNA is released by (proliferating) human xeno-reactive PBMC and damaged mouse cells.

CONCLUSION

We show increased cfDNA both in an aGvHD mouse model and in aGvHD patients. We also demonstrate that donor hematopoietic cells and to a lesser degree (damaged) host cells are the cellular source of cfDNA in aGvHD. We propose that nucleosomes and cfDNA might be an additive marker for aGvHD.

Incidence and impact of community respiratory viral infections in post-transplant cyclophosphamide-based graft-versus-host disease prophylaxis and haploidentical stem cell transplantation

Community respiratory viral infections (CRVIs) are associated with pulmonary function impairment, alloimmune lung syndromes and inferior survival in human leucocyte antigen (HLA)-matched allogeneic haematopoietic stem cell transplant (HCT) recipients. Although the incidence of viral infections in HLA-haploidentical HCT recipients who receive post-transplant cyclophosphamide (PTCy)-based graft-versus-host disease (GVHD) prophylaxis is reportedly increased, there are insufficient data describing the incidence of CRVIs and the impact of donor source and PTCy on transplant outcomes. Analysing patients receiving their first HCT between 2012 and 2017 for acute myeloid leukaemia, acute lymphoblastic leukaemia and myelodysplastic syndromes, we describe comparative outcomes between matched sibling transplants receiving either calcineurin-based GVHD prophylaxis (SibCNI, N = 1605) or PTCy (SibCy, N = 403), and related haploidentical transplants receiving PTCy (HaploCy, N = 757). The incidence of CRVIs was higher for patients receiving PTCy, regardless of donor type. Patients in the HaploCy cohort who developed a CRVI by day +180 had both a higher risk of treatment-related mortality [hazard ratio (HR) 2⋅14, 99% confidence interval (CI) 1⋅13-4⋅07; P = 0⋅002] and inferior 2-year overall survival (HR 1⋅65, 99% CI 1⋅11-2⋅43; P = 0⋅001) compared to SibCNI with no CRVI. This finding justifies further research into long-term antiviral immune recovery, as well as development of preventive and treatment strategies to improve long-term outcomes in such patients.

Inferior outcomes with reduced intensity conditioning followed by allogeneic hematopoietic cell transplantation in fit individuals with acute lymphoblastic leukemia: a Canadian single-center study and a comparison to registry data

Allogeneic hematopoietic cell transplantation (HCT) can offer cure to some patients with acute lymphoblastic leukemia (ALL). It remains unclear how conditioning intensity affects transplant outcomes in ALL. In this retrospective study, we compared outcomes between 27 patients <60 who received reduced intensity conditioning (RIC) at Princess Margaret Hospital Cancer Center (PMCC) and 226 Cell Therapy Transplant Canada (CTTC) age-matched controls who received myeloablative conditioning (MAC) between 2007 and 2018. Compared to CTTC patients, PMCC patients had an inferior 2-y OS: 0.29 (95% CI: 0.11-0.49) vs 0.63 (0.56-0.70), HR = 2.10 (1.23-3.55), p = 0.006, higher TRM: 0.41 (0.22-0.60) vs 0.24 (0.18-0.30), HR = 2.00 (1.05-3.81), p = 0.04 and a trend toward increased risk of relapse: 0.36 (0.17-0.56) versus 0.17 (0.12-0.22), HR = 1.72 (0.82-3.62), p = 0.15. In multivariate analysis, RIC and the use of T-cell depletion (TCD) were associated with inferior OS. In ALL patients <60, the use of RIC with TCD is associated with inferior allogeneic HCT outcomes.

American Society of Transplantation and Cellular Therapy Series, 2: Management and Prevention of Aspergillosis in Hematopoietic Cell Transplantation Recipients

The Practice Guidelines Committee of the American Society of Transplantation and Cellular Therapy partnered with its Transplant Infectious Disease Special Interest Group to update its 2009 compendium-style infectious disease guidelines for hematopoietic cell transplantation (HCT). A completely fresh approach was taken with the goal of better serving clinical providers by publishing each standalone topic in the infectious disease series as a concise format of frequently asked questions (FAQs), tables, and figures. Adult and pediatric infectious disease and HCT content experts developed, then answered FAQs, and finalized topics with harmonized recommendations that were made by assigning an A through E strength of recommendation paired with a level of supporting evidence graded I through III. This second guideline in the series focuses on invasive aspergillosis, a potentially life-threatening infection in the peri-HCT period. The relevant risk factors, diagnostic considerations, and prophylaxis and treatment approaches are reviewed.

Recent Approaches and Strategies in the Generation of Anti-human Cytomegalovirus Vaccines

Human cytomegalovirus is the largest human herpesvirus and shares many core features of other herpesviruses such as tightly regulated gene expression during genome replication and latency as well as the establishment of lifelong persistence following infection. In contrast to stereotypic clinical syndromes associated with alpha-herpesvirus infections, almost all primary HCMV infections are asymptomatic and acquired early in life in most populations in the world. Although asymptomatic in most individuals, HCMV is a major cause of disease in hosts with deficits in adaptive and innate immunity such as infants who are infected in utero and allograft recipients following transplantation. Congenital HCMV is a commonly acquired infection in the developing fetus that can result in a number of neurodevelopmental abnormalities. Similarly, HCMV is a major cause of disease in allograft recipients in the immediate and late posttransplant period and is thought to be a major contributor to chronic allograft rejection. Even though HCMV induces robust innate and adaptive immune responses, it also encodes a vast array of immune evasion functions that are thought aid in its persistence. Immune correlates of protective immunity that prevent or modify intrauterine HCMV infection remain incompletely defined but are thought to consist primarily of adaptive responses in the pregnant mother, thus making congenital HCMV a potentially vaccine modifiable disease. Similarly, HCMV infection in allograft recipients is often more severe in recipients without preexisting adaptive immunity to HCMV. Thus, there has been a considerable effort to modify HCMV specific immunity in transplant recipient either through active immunization or passive transfer of adaptive effector functions. Although efforts to develop an efficacious vaccine and/or passive immunotherapy to limit HCMV disease have been underway for nearly six decades, most have met with limited success at best. In contrast to previous efforts, current HCMV vaccine development has relied on observations of unique properties of HCMV in hopes of reproducing immune responses that at a minimum will be similar to that following natural infection. However, more recent findings have suggested that immunity following naturally acquired HCMV infection may have limited protective activity and almost certainly, is not sterilizing. Such observations suggest that either the induction of natural immunity must be specifically tailored to generate protective activity or alternatively, that providing targeted passive immunity to susceptible populations could be prove to be more efficacious.

Flow cytometric measurement of STAT5 phosphorylation in cytomegalovirus-stimulated T cells

Cytomegalovirus (CMV)-specific T cells expand with CMV reactivation and are probably prerequisite for control and protection. Given the critical role STAT5A phosphorylation (pSTAT5A) in T cell proliferation, this study presents a simple and sensitive flow cytometric-based pSTAT5A assay to quickly identify CMV-specific T cell proliferation. We determined pSTAT5A in T cells treated with CMV-specific peptide mix (pp65 + IE1 peptides) from 20 healthy adult subjects and three immunodeficient patients with CARMIL-2 mutation. After stimulation, the percentage of pSTAT5A⁺ T cells in CMV-seropositive (CMV⁺ ) subjects significantly increased from 3.0% ± 1.9% (unstimulated) to 11.4% ± 5.9% (stimulated) for 24 h. After 7 days of stimulation, the percentage of expanded T cells amounted to 26% ± 17.2%. Conversely, the percentage of pSTAT5A⁺ T cells and T cell proliferation from CMV-seronegative (CMV^- ) subjects hardly changed (from 3.0% ± 1.3% to 3.7% ± 1.8% and from 4.3% ± 2.1% to 5.7% ± 1.7%, respectively). We analyzed the correlation between the percentage of pSTAT5A⁺ T cells versus (1) CMV-IgG concentrations versus (2) the percentage of expanded T cells and versus (3) the percentage of initial CMV-specific T cells. In immunodeficient patients with CARMIL-2 mutation, CMV-specific pSTAT5A and T cell proliferation were completely deficient. In conclusion, flow cytometric-based pSTAT5A assay represents an appropriate tool to quickly identify CMV-specific T cell proliferation and helps to understand dysfunctions in controlling other pathogens. Flow cytometric-based pSTAT5A assay may be a useful test in clinical practice and merits further validation in large studies.

Pharmacokinetics of alemtuzumab in pediatric patients undergoing ex vivo T-cell-depleted haploidentical hematopoietic cell transplantation

PURPOSE

Alemtuzumab is a humanized monoclonal antibody against CD52 which is predominantly present on T and B lymphocytes. Alemtuzumab has been used as part of conditioning regimens for prophylaxis against rejection and GVHD. While the mechanism of action is well understood, the pharmacokinetics of this drug in children needed to be studied in more detail especially in the setting of ex vivo T-cell-depleted hematopoietic cell transplantation (HCT).

METHODS

Serum alemtuzumab levels were measured at various time points in 13 patients who underwent haploidentical HCT utilizing ex vivo donor T-cell depletion. Alemtuzumab was administered subcutaneously at a cumulative dose of 45 mg/m² from days - 13 to - 11. A one-compartmental model was used to fit the data using non-linear mixed effects modeling.

RESULTS

We determined the median half-life to be 11 days. Alemtuzumab clearance increased with increasing baseline lymphocyte count (p = 0.008). Additionally, clearance increased with weight and age (p ≤ 0.035). AUC of alemtuzumab did not have any significant relationship with type of leukemia, overall survival, engraftment, immune reconstitution, mixed chimerism or GVHD, although the number of subjects in this pilot study was limited.

CONCLUSION

Absolute lymphocyte count and body weight affect alemtuzumab clearance. We also demonstrate feasibility of body-surface area-based dosing of alemtuzumab in pediatric HCT patients. Further studies are needed to evaluate the role of monitoring alemtuzumab serum concentrations to balance the prevention of graft rejection and GVHD with the promotion of rapid donor immune reconstitution.

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.

NK Cell Reconstitution in Paediatric Leukemic Patients after T-Cell-Depleted HLA-Haploidentical Haematopoietic Stem Cell Transplantation Followed by the Reinfusion of iCasp9-Modified Donor T Cells

T-cell-depleted (TCD) human leukocyte antigen (HLA) haploidentical (haplo) hematopoietic stem cell transplantation (HSCT) (TCD-haplo-HSCT) has had a huge impact on the treatment of many haematological diseases. The adoptive transfer of a titrated number of T cells genetically modified with a gene suicide can improve immune reconstitution and represents an interesting strategy to enhance the success of haplo-HSCT. Natural killer (NK) cells are the first donor-derived lymphocyte population to reconstitute following transplantation, and play a pivotal role in mediating graft-versus-leukaemia (GvL). We recently described a CD56^lowCD16^low NK cell subset that mediates both cytotoxic activity and cytokine production. Given the multifunctional properties of this subset, we studied its functional recovery in a cohort of children given α/βT-cell-depleted haplo-HSCT followed by the infusion of a titrated number of iCasp-9-modified T cells (iCasp-9 HSCT). The data obtained indicate that multifunctional CD56^lowCD16^low NK cell frequency is similar to that of healthy donors (HD) at all time points analysed, showing enrichment in the bone marrow (BM). Interestingly, with regard to functional acquisition, we identified two groups of patients, namely those whose NK cells did (responder) or did not (non responder) degranulate or produce cytokines. Moreover, in patients analysed for both functions, we observed that the acquisition of degranulation capacity was not associated with the ability to produce interferon-gamma (IFN-γ Intriguingly, we found a higher BM and peripheral blood (PB) frequency of iCas9 donor T cells only in patients characterized by the ability of CD56^lowCD16^low NK cells to degranulate. Collectively, these findings suggest that donor iCasp9-T lymphocytes do not have a significant influence on NK cell reconstitution, even if they may positively affect the acquisition of target-induced degranulation of CD56^lowCD16^low NK cells in the T-cell-depleted haplo-HSC transplanted patients.

TCR α+ β+ /CD19+ cell-depleted hematopoietic stem cell transplantation for pediatric patients

TCR α⁺ β⁺ /CD19⁺ cell depletion is an emerging technique for ex vivo graft manipulation in HSCT. We report 20 pediatric patients who underwent TCR α⁺ β⁺ /CD19⁺ cell-depleted HSCT in four Australian centers. Conditioning regimen was dependent on HSCT indication, which included immunodeficiency (n = 14), Fanconi anemia (n = 3), and acute leukemia (n = 3). Donor sources were haploidentical parent (n = 17), haploidentical sibling (n = 2), or matched unrelated donor (n = 1). Mean cell dose was 8.2 × 10⁸ /kg TNC, 12.1 × 10⁶ /kg CD34⁺ cells, and 0.4 × 10⁵ /kg TCR α⁺ β⁺ cells. All patients achieved primary neutrophil and platelet engraftment, with average time to neutrophil engraftment 11 days (range 8-22) and platelet engraftment 24 days (range 12-69). TRM at 1 year was 15%. Rate of grade II-IV aGVHD at 1 year was 20% with no grade III-IV aGVHD seen. CMV reactivation occurred in 81% of CMV-positive recipients, with one patient developing CMV disease. Average time to CD4 recovery (>400 × 10⁶ /L) was 258 days. Overall survival for the cohort at 5 years was 80%. This report highlights the initial experience of TCR α⁺ β⁺ /CD19⁺ cell-depleted HSCT in Australian centers, with high rates of engraftment, low rates of aGVHD, and acceptable TRM.

Cytomegalovirus retinitis in children and adolescents with acute leukemia following allogeneic hematopoietic stem cell transplantation

Cytomegalovirus retinitis (CMVR) may occur after allogeneic hematopoietic stem cell transplantation (HSCT). However, little is known about its incidence, strategies for ophthalmic surveillance, and timely implementation of adequate antiviral treatment in pediatric allogeneic HSCT recipients. We provide a retrospective analysis of the epidemiology and clinical features of CMVR in pediatric allogeneic HSCT patients transplanted at our center over a 16-year period. Two patients of this cohort with leukemia are presented. Our analysis is supplemented by a systematic review on pediatric patients with leukemia and CMVR in the setting of allogeneic HSCT. The overall incidence of CMVR in our cohort was 1% (4/338) and 14.2% (3/21) in leukemic patients. In published cases, CMVR occurred at a median of 143 days after transplantation, and, in the majority of patients, was preceded by CMV detection in blood by a median of 93 days. Continued immune suppression following engraftment likely triggers CMVR. Preemptive treatment with ganciclovir as standard is usually successful. Foscarnet is used in case of resistance to ganciclovir or drug-induced granulocytopenia. Overall, CMVR after HSCT in pediatric leukemic patients is rare, but a potentially higher vulnerability of this population for involvement of the eye warrants a standardized ophthalmological examination plan.

New therapies for human cytomegalovirus infections

The recent approval of letermovir marks a new era of therapy for human cytomegalovirus (HCMV) infections, particularly for the prevention of HCMV disease in hematopoietic stem cell transplant recipients. For almost 30 years ganciclovir has been the therapy of choice for these infections and by today's standards this drug exhibits only modest antiviral activity that is often insufficient to completely suppress viral replication, and drives the selection of drug-resistant variants that continue to replicate and contribute to disease. While ganciclovir remains the therapy of choice, additional drugs that inhibit novel molecular targets, such as letermovir, will be required as highly effective combination therapies are developed not only for the treatment of immunocompromised hosts, but also for congenitally infected infants. Sustained efforts, largely in the biotech industry and academia, have identified additional highly active lead compounds that have progressed into clinical studies with varying levels of success and at least two have the potential to be approved in the near future. Some of the new drugs in the pipeline inhibit new molecular targets, remain effective against isolates that have developed resistance to existing therapies, and promise to augment existing therapeutic regimens. Here, we will describe some of the unique features of HCMV biology and discuss their effect on therapeutic needs. Existing drugs will also be discussed and some of the more promising candidates will be reviewed with an emphasis on those progressing through clinical studies. The in vitro and in vivo antiviral activity, spectrum of antiviral activity, and mechanism of action of new compounds will be reviewed to provide an update on potential new therapies for HCMV infections that have progressed significantly in recent years.

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.

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.

Functionality testing of stem cell grafts to predict infectious complications after allogeneic hematopoietic stem cell transplantation

BACKGROUND AND OBJECTIVES

Allogeneic hematopoietic stem cell transplantation (HSCT) is a routine clinical procedure performed to treat patients with haematological malignancies, primary immune deficiencies or metabolic disorders. Infections during lymphopenia after allogeneic HSCT are associated with high mortality and morbidity. Typical infectious agents are Epstein-Barr virus, cytomegalovirus, herpes simplex virus, varicella-zoster virus and fungi. The study aim was to evaluate whether measurement of the responses of antigen-specific T-cells, recognizing infectious pathogens would correlate to protective functions in the stem cell recipient post-transplant.

MATERIALS AND METHODS

Twenty-one grafts were analysed by flow cytometry and cells were stimulated in vitro with relevant infectious antigens, followed by evaluation of T-cell proliferation and cytokine production. Results were compared to the recipients' clinical records 1-year post-transplantation.

RESULTS

We show that an extensive repertoire of transferred antigen-specific T-cells from allogeneic donor grafts against infectious agents, involved in post-transplant infections, are linked to an absence of infectious complications for the recipient up-to 1-year post-transplant. The protective effect was associated with antigen-specific T-cell proliferation and IL-1β secretion.

CONCLUSION

Our results suggest that assaying T-cell function before HSCT could determine individual risks for infectious complications and thus aid in clinical decision-making regarding prophylactic and pre-emptive anti-infective therapy.

Intravenous mesenchymal stromal cell therapy for inflammatory bowel disease: Lessons from the acute graft versus host disease experience

Bone marrow-derived mesenchymal stromal cells (BMSCs) are primitive, supportive cells of the bone marrow with tri-lineage potential to differentiate into bone, cartilage, fat and muscle. These cells possess both in vitro and in vivo immunomodulatory and wound-healing properties. Several studies have demonstrated efficacy of intravenously administered BMSCs in treating acute graft-versus-host disease (GvHD). Use of intravenous (IV) BMSCs in inflammatory bowel diseases (IBD) in humans has been limited to small studies in adults, but results have been promising. There remain many unanswered questions regarding safety, tolerability, effectiveness and optimal use of BMSCs to treat IBD, particularly in immunocompromised patients. This article reviews the evidence for using BMSCs to treat acute GvHD and how this experience may inform the potential use of BMSCs as a treatment for IBD.

Immune Reconstitution after Allogeneic Hematopoietic Stem Cell Transplantation

The timely reconstitution and regain of function of a donor-derived immune system is of utmost importance for the recovery and long-term survival of patients after allogeneic hematopoietic stem cell transplantation (HSCT). Of note, new developments such as umbilical cord blood or haploidentical grafts were associated with prolonged immunodeficiency due to delayed immune reconstitution, raising the need for better understanding and enhancing the process of immune reconstitution and finding strategies to further optimize these transplant procedures. Immune reconstitution post-HSCT occurs in several phases, innate immunity being the first to regain function. The slow T cell reconstitution is regarded as primarily responsible for deleterious infections with latent viruses or fungi, occurrence of graft-versus-host disease, and relapse. Here we aim to summarize the major steps of the adaptive immune reconstitution and will discuss the importance of immune balance in patients after HSCT.

Recent Developments in Cellular Immunotherapy for HSCT-Associated Complications

Allogeneic hematopoietic stem cell transplantation is associated with serious complications, and improvement of the overall clinical outcome of patients with hematological malignancies is necessary. During the last decades, posttransplant donor-derived adoptive cellular immunotherapeutic strategies have been progressively developed for the treatment of graft-versus-host disease (GvHD), infectious complications, and tumor relapses. To date, the common challenge of all these cell-based approaches is their implementation for clinical application. Establishing an appropriate manufacturing process, to guarantee safe and effective therapeutics with simultaneous consideration of economic requirements is one of the most critical hurdles. In this review, we will discuss the recent scientific findings, clinical experiences, and technological advances for cell processing toward the application of mesenchymal stromal cells as a therapy for treatment of severe GvHD, virus-specific T cells for targeting life-threating infections, and of chimeric antigen receptors-engineered T cells to treat relapsed leukemia.

Immunity to Infections after Haploidentical Hematopoietic Stem Cell Transplantation

The advantage of using a Human Leukocyte Antigen (HLA)-mismatched related donor is that almost every patient who does not have an HLA-identical donor or who urgently needs hematopoietic stem cell transplantation (HSCT) has at least one family member with whom shares one haplotype (haploidentical) and who is promptly available as a donor. The major challenge of haplo-HSCT is intense bi-directional alloreactivity leading to high incidences of graft rejection and graft-versus-host disease (GVHD). Advances in graft processing and pharmacologic prophylaxis of GVHD have reduced these risks and have made haplo-HSCT a viable alternative for patients lacking a matched donor. Indeed, the haplo-HSCT has spread to centers worldwide even though some centers have preferred an approach based on T cell depletion of G-CSF-mobilized peripheral blood progenitor cells (PBPCs), others have focused on new strategies for GvHD prevention, such as G-CSF priming of bone marrow and robust post-transplant immune suppression or post-transplant cyclophosphamide (PTCY). Today, the graft can be a megadose of T-cell depleted PBPCs or a standard dose of unmanipulated bone marrow and/or PBPCs. Although haplo-HSCT modalities are based mainly on high intensity conditioning regimens, recently introduced reduced intensity regimens (RIC) showed promise in decreasing early transplant-related mortality (TRM), and extending the opportunity of HSCT to an elderly population with more comorbidities. Infections are still mostly responsible for toxicity and non-relapse mortality due to prolonged immunosuppression related, or not, to GVHD. Future challenges lie in determining the safest preparative conditioning regimen, minimizing GvHD and promoting rapid and more robust immune reconstitution.

Does ex vivo CD34+ positive selection influence outcome after autologous hematopoietic stem cell transplantation in systemic sclerosis patients?

This EBMT Autoimmune Disease Working Party study aimed to evaluate the influence of CD34+ positive graft selection (CD34+) on the outcome of systemic sclerosis (SSc) patients after autologous hematopoietic stem cell transplantation (AHSCT). Clinical and laboratory data from 138 SSc patients at diagnosis, before and after AHSCT were retrospectively analyzed. CD34+ selection was performed in 47.1% (n=65) patients. By multivariate analysis adjusting for all factors differing between the two groups (without or with CD34+), there was no statistically significant difference in terms of overall survival (hazard ratio (HR): 0.98, 95% confidence interval (CI) 0.40-2.39, P=0.96), PFS (HR: 1.55, 95% CI 0.83-2.88, P=0.17) and incidence of relapse or progression (HR: 1.70, 95% CI 0.85-3.38, P=0.13). We demonstrate that CD34+ does not add benefit to the outcome of SSc patient treated with AHSCT. These findings should be further confirmed by prospective randomized trials.

The immune response to cytomegalovirus in allogeneic hematopoietic stem cell transplant recipients

Approximately, up to 70 % of the human population is infected with cytomegalovirus (CMV) that persists for life in a latent state. In healthy people, CMV reactivation induces the expansion of CMV-specific T cells up to 10 % of the entire T cell repertoire. On the contrary, CMV infection is a major opportunistic viral pathogen that remains a leading cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation. Due to the delayed CMV-specific immune recovery, the incidence of CMV reactivation during post-transplant period is very high. Several methods are currently available for the monitoring of CMV-specific responses that help in clinical monitoring. In this review, essential aspects in the immune recovery against CMV are discussed to improve the better understanding of the immune system relying on CMV infection and, thereby, helping the avoidance of CMV disease or reactivation following hematopoietic stem cell transplantation with severe consequences for the transplanted patients.

Diagnosis and treatment of cytomegalovirus 2013

PURPOSE OF REVIEW

Despite significant improvements in the management of patients undergoing allogeneic stem cell transplantation, including anticytomegalovirus (CMV) prophylaxis and treatment, clinical handling of CMV infection remains challenging in the light of high morbidity and mortality rates. Thus, novel strategies and agents to control CMV infection and disease will be discussed.

RECENT FINDINGS

Novel assays to quantify viral load and detect antiviral resistance mechanisms on the basis of next-generation sequencing have been described and will help to earlier and more effectively control CMV infection. In addition, safer and more effective antiviral agents are now available and strategies to boost the CMV-directed immune responses are being explored in the clinic.

SUMMARY

Novel diagnostic tests, novel agents and the increased understanding of the immune response to CMV have and will have a major impact on improving the management of CMV infection in hematological patients.

T-cell depleted allogeneic hematopoietic cell transplants as a platform for adoptive therapy with leukemia selective or virus-specific T-cells

Allogeneic hematopoietic cell transplants adequately depleted of T-cells can reduce or prevent acute and chronic GVHD in both HLA-matched and haplotype-disparate hosts, without post-transplant prophylaxis with immunosuppressive drugs. Recent trials indicate that high doses of CD34+ progenitors from G-CSF mobilized peripheral blood leukocytes isolated and T-cell depleted by immunoadsorption to paramagnetic beads, when administered after myeloablative conditioning with TBI and chemotherapy or chemotherapy alone can secure consistent engraftment and abrogate GVHD in patients with acute leukemia without incurring an increased risk of a recurrent leukemia. Early clinical trials also indicate that high doses of in vitro generated leukemia-reactive donor T-cells can be adoptively transferred and can induce remissions of leukemia relapse without GVHD. Similarly, virus-specific T-cells generated from the transplant donor or an HLA partially matched third party, have induced remissions of Rituxan-refractory EBV lymphomas and can clear CMV disease or viremia persisting despite antiviral therapy in a high proportion of cases. Analyses of treatment responses and failures illustrate both the advantages and limitations of donor or banked, third party-derived T-cells, but underscore the potential of adoptive T-cell therapy in the absence of ongoing immunosuppression.

Stem cell comparison: what can we learn clinically from unrelated cord blood transplantation as an alternative stem cell source?

Allogeneic hematopoietic cell transplantation (HCT) is an important therapeutic option for a variety of malignant and non-malignant disorders (NMD). The use of umbilical cord blood transplantation (UCBT) has made HCT available to many more patients. The increased level of human leukocyte antigen disparity that can be tolerated makes UCBT a very attractive alternative source of hematopoietic stem cells; however, the increased risk of early death observed after UCBT remains an obstacle. Novel strategies such as ex vivo stem cell expansion are now becoming part of the standard clinical approach, and preliminary results are extremely encouraging with suggestion of reduction of early transplant-related mortality. Although there are no randomized studies that compare the risks and benefits of UCBT relative to those observed with related and unrelated donors both for malignant and NMD, several retrospective studies have compared outcomes between UCBT and other stem cell sources. In this review, we aim to describe and summarize the findings of the principal studies in this field. We hope that what we can learn from these studies and how we can use this information will improve the outcomes of HCT for patients with malignant and NMD.

A GVHD kill switch helps immune reconstitution

In this issue of Blood, Zhou et al report long-term follow-up and detailed analysis of immune reconstitution associated with a different suicide gene strategy to abrogate graft-versus-host disease (GVHD).

EBMT risk score can predict the outcome of leukaemia after unmanipulated haploidentical blood and marrow transplantation

Systematic, standardised pretransplant risk assessment is an important tool for predicting patient outcomes following allogeneic haematopoietic SCT (HSCT). To assess the European Group for Blood and Marrow Transplantation (EBMT) risk score capacities for predicting patient outcomes following unmanipulated haploidentical blood and marrow transplantation (HBMT), we analysed 502 leukaemia patients who received transplants at our centre between 2008 and 2010. The cohort OS and leukaemia-free survival (LFS) were 72.1% and 68.1%, whereas the cumulative non-relapse mortality (NRM) and relapse incidences were 16.5% and 16.1%. According to univariate analysis, the values for OS, LFS and NRM were worse for an EBMT risk score of 6 (40.0, 40.0, 50.0%) than a score of 1 (83.1, 78.3, 8.4%). Hazard ratios steadily increased for each additional score point. Likewise, a higher EBMT risk score was associated with an increased relapse incidence. Importantly, the EBMT risk score prognostic value regarding OS, LFS, NRM and relapse was maintained in the multivariate analysis. Moreover, we also made a haploidentical EBMT (haplo-EBMT) risk score, which used number of HLA disparity instead of donor type, and the haplo-EBMT risk scores can also be used to predict patient outcomes following unmanipulated HBMT.

Long-term outcome after haploidentical stem cell transplant and infusion of T cells expressing the inducible caspase 9 safety transgene

Adoptive transfer of donor-derived T lymphocytes expressing a safety switch may promote immune reconstitution in patients undergoing haploidentical hematopoietic stem cell transplant (haplo-HSCT) without the risk for uncontrolled graft versus host disease (GvHD). Thus, patients who develop GvHD after infusion of allodepleted donor-derived T cells expressing an inducible human caspase 9 (iC9) had their disease effectively controlled by a single administration of a small-molecule drug (AP1903) that dimerizes and activates the iC9 transgene. We now report the long-term follow-up of 10 patients infused with such safety switch-modified T cells. We find long-term persistence of iC9-modified (iC9-T) T cells in vivo in the absence of emerging oligoclonality and a robust immunologic benefit, mediated initially by the infused cells themselves and subsequently by an apparently accelerated reconstitution of endogenous naive T lymphocytes. As a consequence, these patients have immediate and sustained protection from major pathogens, including cytomegalovirus, adenovirus, BK virus, and Epstein-Barr virus in the absence of acute or chronic GvHD, supporting the beneficial effects of this approach to immune reconstitution after haplo-HSCT. This study was registered at www.clinicaltrials.gov as #NCT00710892.