Reconstitution of the immune system after hematopoietic stem cell transplantation in humans. Semin Immunopathol. 2008;30:425-437. [PMID: 18949477 DOI: 10.1007/s00281-008-0132-5]

Child with Wiskott–Aldrich syndrome underwent atypical immune reconstruction after umbilical cord blood transplantation: A case report

BACKGROUND

Timely reconstitution of a donor-derived immune system is important for recovery and long-term survival of patients after allogeneic hematopoietic stem cell transplantation (HSCT). We describe a case of Wiskott–Aldrich syndrome (WAS) treated by umbilical cord blood transplantation (UCBT) with atypical immune reconstruction.

CASE SUMMARY

A 1-year-old Chinese male infant was diagnosed with WAS. WAS gene sequencing identified the mutation c.777 + 1G>A (IVS8). On August 8, 2017, he was admitted to our hospital for HSCT. We selected an unrelated Human leukocyte antigen 6/10-matched donor for UCBT. After HSCT, the immune reconstitution process was atypical, the lymphocytes reached 0.5 × 10⁹/L on day 23, and the neutrophils reached 0.5 × 10⁹/L on day 34. The patient’s recovery throughout the year was good.

CONCLUSION

An increase in lymphocytes (especially T cells) earlier than granulocytes may be a marker of a good prognosis in UCBT.

Quantitative Analysis of Thymus-Independent Donor-Derived T Cell Expansion in Transplant Patients

Although thymus-independent donor-derived T cell expansion may determine the occurrence of graft-versus-host disease (GVHD) and relapse after transplantation, the characteristics and dynamics of the expansion process remain unclear. To address this issue, we monitored T cell receptor β repertoire at day 0, day 28, and day 61 after transplantation in 30 patients with hematologic malignancies by next-generation sequencing. The clonality index showed an increasing clonality over time (P = .001). The top 200 clonotypes accounted for more than half of the total clonotypes (median frequency, 63.55%) at day 61, and there was a remarkable overlapping between the top 200 clonotypes of each repertoire and its former repertoire (>50%). A normalized index, called the T Cell Response Index (TCRI), was designed on the basis of rank-shift analysis to quantify antigen-driven expansion. The TCRI during the first month was not related to relapse or GVHD (P> .05), whereas the TCRI during the second month was related to relapse (P = .006). Recipients with a TCRI below 1.0 during the second month had a higher cumulative relapse rate (31.25% versus 0%, P = .0323) and had a lower 1-year survival rate (56.25% versus 78.57%, P = .281). The clonotypes with strong competitiveness in the second month in the nonrelapse group preferentially used TRBV2, TRBV12-3, TRBJ1-1 and TRBJ1-5 segments (P< .01). In conclusion, homeostatic expansion predominates in the first month due to nonspecific T cell proliferation, whereas antigen-driven expansion predominates in the second month and results in a graft-versus-tumor (GvT) effect. Moreover, TCRI could serve as a quantitative indicator of GvT against relapse within the first year. The difference in V and J segment usage reveals that T cells responsible for potent GvT effect are similar among patients.

Long-Term Follow-Up of Antibody Titers Against Measles, Mumps, and Rubella in Recipients of Allogenic Hematopoietic Cell Transplantation

Outbreaks of viral infections, such as measles, are regularly observed and pose a serious threat to recipients of allogeneic hematopoietic cell transplantation (HCT). The questions of how long cellular and humoral protective host immunity persists, and whether donor immunity can be transferred has not been clarified. Here we present a retrospective analysis of humoral immunity-serial antibody titers against measles, mumps, and rubella-in 331 patients who underwent allogeneic HCT at our single center between 2002 and 2015. Associations between the loss of protective antibody levels and clinical patient characteristics and transplantation parameters were examined. In general, antibody protection against measles persisted longer, with 72% of patients maintaining sufficient titers at 5 years post-HCT even without revaccination, while at that time only 65% and 50% of patients had protective immunity against rubella and mumps, respectively. The great majority of donors were seropositive for all 3 viruses; however, it appeared that donor humoral immunity could not be transferred and had no impact on post-HCT serostatus. Rather, the most relevant factor for persistent protective antibody titers against measles and rubella was whether patients were born before the introduction of the respective vaccine and thus were immunized by the wild-type disease-inducing virus instead of the vaccine. Moreover, the presence of moderate and severe chronic graft-versus-host disease (GVHD) was associated with more rapid loss of immune protection. In contrast, underlying disease, intensity of the conditioning regimen, use of antithymocyte globulin, age, and graft source had no influence on antibody titers. Overall, our findings suggest that the majority of antibodies against measles, mumps, and rubella originate from residual host cells, whereas donor immune status appears to have no influence on antibody protection post-HCT.

A New Conditioning Regimen Can Significantly Promote Post-Transplant Immune Reconstitution and Improve the Outcome of Umbilical Cord Blood Transplantation for Patients

This study included data from 81 consecutively enrolled patients with hematological diseases who had been treated with unrelated umbilical cord blood transplantation (UCBT) between September 2014 and April 2019. All patients received intense conditioning regimens with combined fludarabine and high-dose cyclophosphamide (FC) before undergoing UCBT. Sixty-seven patients received a single UCBT, and 14 patients received a double UCBT. Fifty patients were pretreated with the fludarabine, busulfan, and cyclophosphamide (FBC) protocol, while 31 patients were treated with FC before transplantation. Graft-versus-host disease (GVHD) was prevented with cyclosporine A and mycophenolate mofetil administration. According to low-resolution, human leukocyte antigen (HLA) donor-recipient matching at six sites, 53 patients had 5-6 matches, while 28 patients had 4 matches. Seventy-eight patients (96.3%) achieved complete engraftment in this study. Thirty-six patients developed acute GVHD (aGVHD). The cumulative incidence of grade I-II aGVHD at day 100 posthematopoietic stem cell transplantation was 29.6%, and the cumulative incidence of grade III-IV aGVHD was 14.8%. At the end of the follow-up, 12 patients died due to treatment-related complications, and 4 died of disease relapse after transplantation. The transplant-related deaths were due to transplant-related infection (8 of 81), GVHD (2 of 81), and organ toxicity (2 of 81). The probability of overall survival (OS) was 80.2%. A higher dose of cyclophosphamide combined with fludarabine conditioning in UCBT was an effective curative method for treatment of hematologic disorders and could enhance the engraftment of umbilical cord blood stem cells, promote post-transplant immune reconstitution, and improve OS.

Stem cell transplantation impairs dendritic cell trafficking and herpesvirus immunity

Long-term survivors after hematopoietic stem cell transplantation are at high risk of infection, which accounts for one-third of all deaths related to stem cell transplantation. Little is known about the cause of inferior host defense after immune cell reconstitution. Here, we exploited a murine syngeneic BM transplantation (BMT) model of late infection with murine gammaherpesvirus 68 (MHV-68) to determine the role of conventional DC (cDC) trafficking in adaptive immunity in BMT mice. After infection, the expression of chemokine Ccl21 in the lung is reduced and the migration of cDCs into lung draining lymph nodes (dLNs) is impaired in BMT mice, limiting the opportunity for cDCs to prime Th cells in the dLNs. While cDC subsets are redundant in priming Th1 cells, Notch2 functions in cDC2s are required for priming increased Th17 responses in BMT mice, and cDC1s can lessen this activity. Importantly, Th17 cells can be primed both in the lungs and dLNs, allowing for increased Th17 responses without optimum cDC trafficking in BMT mice. Taken together, impaired cDC trafficking in BMT mice reduces protective Th1 responses and allows increased pathogenic Th17 responses. Thus, we have revealed a previously unknown mechanism for BMT procedures to cause long-term inferior immune responses to herpes viral infection.

SR-BI (Scavenger Receptor Class B Type 1) Is Critical in Maintaining Normal T-Cell Development and Enhancing Thymic Regeneration

Objective- Continuous T-cell production from thymus is essential in replenishing naïve T-cell pool and maintaining optimal T-cell functions. However, the underlying mechanisms regulating the T-cell development in thymus remains largely unknown. Approach and Results- We identified SR-BI (scavenger receptor class B type 1), an HDL (high-density lipoprotein) receptor, as a novel modulator in T-cell development. We found that SR-BI deficiency in mice led to reduced thymus size and decreased T-cell production, which was accompanied by narrowed peripheral naïve T-cell pool. Further investigation revealed that SR-BI deficiency impaired progenitor thymic homing, causing a dramatic reduction in the percentage of earliest thymic progenitors, but did not affect other downstream T-cell developmental steps inside the thymus. As a result of the impaired progenitor thymic homing, SR-BI-deficient mice displayed delayed thymic regeneration postirradiation. Using a variety of experimental approaches, we revealed that the impaired T-cell development in SR-BI-deficient mice was not caused by hematopoietic SR-BI deficiency or SR-BI deficiency-induced hypercholesterolemia, but mainly attributed to the SR-BI deficiency in adrenal glands, as adrenal-specific SR-BI-deficient mice exhibited similar defects in T-cell development and thymic regeneration with SR-BI-deficient mice. Conclusions- This study demonstrates that SR-BI deficiency impaired T-cell development and delayed thymic regeneration by affecting progenitor thymic homing in mice, elucidating a previously unrecognized link between SR-BI and adaptive immunity.

The CD14+HLA-DRlo/neg Monocyte: An Immunosuppressive Phenotype That Restrains Responses to Cancer Immunotherapy

Recent successes in cancer immunotherapy have been tempered by sub-optimal clinical responses in the majority of patients. The impaired anti-tumor immune responses observed in these patients are likely a consequence of immune system dysfunction contributed to by a variety of factors that include, but are not limited to, diminished antigen presentation/detection, leukopenia, a coordinated network of immunosuppressive cell surface proteins, cytokines and cellular mediators. Monocytes that have diminished or no HLA-DR expression, called CD14⁺HLA-DR^lo/neg monocytes, have emerged as important mediators of tumor-induced immunosuppression. These cells have been grouped into a larger class of suppressive cells called myeloid derived suppressor cells (MDSCs) and are commonly referred to as monocytic myeloid derived suppressor cells. CD14⁺HLA-DR^lo/neg monocytes were first characterized in patients with sepsis and were shown to regulate the transition from the inflammatory state to immune suppression, ultimately leading to immune paralysis. These immunosuppressive monocytes have also recently been shown to negatively affect responses to PD-1 and CTLA-4 checkpoint inhibition, CAR-T cell therapy, cancer vaccines, and hematopoietic stem cell transplantation. Ultimately, the goal is to understand the role of these cells in the context of immunosuppression not only to facilitate the development of targeted therapies to circumvent their effects, but also to potentially use them as a biomarker for understanding disparate responses to immunotherapeutic regimens. Practical aspects to be explored for development of CD14⁺HLA-DR^lo/neg monocyte detection in patients are the standardization of flow cytometric gating methods to assess HLA-DR expression, an appropriate quantitation method, test sample type, and processing guidances. Once detection methods are established that yield consistently reproducible results, then further progress can be made toward understanding the role of CD14⁺HLA-DR^lo/neg monocytes in the immunosuppressive state.

Concise Review: Boosting T-Cell Reconstitution Following Allogeneic Transplantation-Current Concepts and Future Perspectives

Allogeneic hematopoietic stem cell transplantation (HSCT) is the treatment of choice for a large number of malignant and nonmalignant (inherited) diseases of the hematopoietic system. Nevertheless, non‐HLA identical transplantations are complicated by a severe T‐cell immunodeficiency associated with a high rate of infection, relapse and graft‐versus‐host disease. Initial recovery of T‐cell immunity following HSCT relies on peripheral expansion of memory T cells mostly driven by cytokines. The reconstitution of a diverse, self‐tolerant, and naive T‐cell repertoire, however, may take up to 2 years and crucially relies on the interaction of T‐cell progenitors with the host thymic epithelium, which may be altered by GvHD, age or transplant‐related toxicities. In this review, we summarize current concepts to stimulate reconstitution of a peripheral and polyclonal T‐cell compartment following allogeneic transplantation such as graft manipulation (i.e., T‐cell depletion), transfusion of ex vivo manipulated donor T cells or the exogenous administration of cytokines and growth factors to stimulate host‐thymopoiesis with emphasis on approaches which have led to clinical trials. Particular attention will be given to the development of cellular therapies such as the ex vivo generation of T‐cell precursors to fasten generation of a polyclonal and functional host‐derived T‐cell repertoire. Having been tested so far only in preclinical mouse models, clinical studies are now on the way to validate the efficacy of such T‐cell progenitors in enhancing immune reconstitution following HSCT in various clinical settings. stem cells translational medicine2019;00:1–8

Pathology of Gastrointestinal and Liver Complications of Hematopoietic Stem Cell Transplantation

CONTEXT.—

Despite advances in therapeutic and preventive measures, hematopoietic stem cell transplant recipients remain at risk for a variety of gastrointestinal and liver complications.

OBJECTIVE.—

To detail the pathologic features of the various gastrointestinal and liver complications occurring after hematopoietic stem cell transplantation in relation to their clinical context. The specific complications covered include graft-versus-host disease, mycophenolate mofetil-induced injury, timeline of infections, neutropenic enterocolitis, gastrointestinal thrombotic microangiopathy, sinusoidal obstruction syndrome, hepatic iron overload, and the controversy around cord colitis syndrome.

DATA SOURCES.—

The content of this article is based on pertinent peer-reviewed articles in PubMed, relevant textbooks, and on the authors' personal experiences.

CONCLUSIONS.—

The final histopathologic diagnosis requires the integration of clinical and histologic findings and the exclusion of other competing causes of injury. Review of the clinical data, including the original disease pretransplant, the type of transplant, the timing of the gastrointestinal and/or liver manifestations, the timing of the biopsy after transplant, the presence of graft-versus-host disease in other organs and sites, the list of drug regimens, and the clinical and laboratory evidence of infection, is the key to reaching the proper histologic diagnosis.

Differences of Immune Reconstitution of Dendritic Cells in Pediatric GvHD Patients After Allogenic Stem Cell Transplantation

BACKGROUND

Hematopoietic stem cell transplantation (HSCT) is a life-saving procedure for children with a variety of (non) malignant conditions. GvHD is a severe complication with high morbidity and mortality. The pathogenesis remains unclear. We studied dendritic cell (DC) reconstitution to detect potential differences, which may improve our knowledge in the development of chronic GvHD (cGvHD).

PROCEDURE

We examined immune reconstitution (T, B, and NK cells and dendritic cells) at defined time points in a pediatric cohort who underwent 61 allogeneic HSCTs.

RESULTS

Regarding DC reconstitution we found a fast reconstitution of the DC compartment negatively correlated with age. After HSCT, both myeloid DC (mDC) and plasmacytoid DC (pDC) counts recover to pre-HSCT levels within 2 months. Higher CCR7 positive cell counts were found in patients receiving TBI during engraftment and during the whole posttransplant period we found a correlation with an improved outcome. In cGVHD patients decreased total DC counts and increased pDCs were found after day+100. No relevant correlation was achieved regarding to HLA-matching, stem cell manipulation of the graft as well as HSCT-indication compared with different DC counts.

DISCUSSION

Pathogenesis of cGvHD remains complex. Our data suggest an influence of dendritic cells, which may contribute to the clinical picture and should be further investigated in future studies.

IL-7 Is the Limiting Homeostatic Factor that Constrains Homeostatic Proliferation of CD8+ T Cells after Allogeneic Stem Cell Transplantation and Graft-versus-Host Disease

Immune reconstitution after allogeneic hematopoietic stem cell transplantation relies primarily on homeostatic proliferation (HP) of mature T lymphocytes, but this process is typically impaired during graft-versus-host disease (GVHD). We previously showed that low IL-7 levels combined with lack of dendritic cell (DC) regeneration constrain CD4⁺ T cell HP during GVHD. However, it is not clear whether these alterations to the peripheral CD4⁺ T cell niche also contribute to impair CD8⁺ T cell regeneration during GVHD. We found that IL-7 therapy was sufficient for restoring CD8⁺ T cell HP in GVHD hosts while forcing DC regeneration with Flt3-L had only a modest effect on CD8⁺ T cell HP in IL-7 treated mice. Using bone marrow chimeras, we showed that HP of naïve CD8⁺ T cells is primarily regulated by MHC class I on radio-resistant stromal cells, yet optimal recovery of CD8⁺ T cell counts still requires expression of MHC class I on both radio-resistant and radio-sensitive hematopoietic cells. Thus, IL-7 level is the primary limiting factor that constrains naïve CD8⁺ T cell HP during GVHD, and accessibility of MHC class I on stromal cells explains how IL-7 therapy, as a single agent, can induce robust CD8 ⁺ T cell HP in the absence of DCs.

Autologous Hematopoietic Stem Cell Transplantation for Autoimmune Diseases: From Mechanistic Insights to Biomarkers

Phase I/II clinical trials of autologous hematopoietic stem cell transplantation (AHSCT) have led to increased safety and efficacy of this therapy for severe and refractory autoimmune diseases (AD). Recent phase III randomized studies have demonstrated that AHSCT induces long-term disease remission in most patients without any further immunosuppression, with superior efficacy when compared to conventional treatments. Immune monitoring studies have revealed the regeneration of a self-tolerant T and B cell repertoire, enhancement of immune regulatory mechanisms, and changes toward an anti-inflammatory milieu in patients that are responsive to AHSCT. However, some patients reactivate the disease after transplantation due to reasons not yet completely understood. This scenario emphasizes that additional specific immunological interventions are still required to improve or sustain therapeutic efficacy of AHSCT in patients with AD. Here, we critically review the current knowledge about the operating immune mechanisms or established mechanistic biomarkers of AHSCT for AD. In addition, we suggest recommendations for future immune monitoring studies and biobanking to allow discovery and development of biomarkers. In our view, AHSCT for AD has entered a new era and researchers of this field should work to identify robust predictive, prognostic, treatment-response biomarkers and to establish new guidelines for immune monitoring studies and combined therapeutic interventions to further improve the AHSCT protocols and their therapeutic efficacy.

Dendritic Cells Are Critical for the Activation and Expansion of Vδ2+ T Cells After Allogeneic Hematopoietic Transplantation

γδ T cells perform antitumor and antiviral effector functions and are involved in both innate and adaptive immunity. Vδ2⁺ T cells represent the predominant γδ T subset in the peripheral blood of healthy subjects. Vδ2⁺ T cells can be selectively activated and expanded by phosphoantigens (pAgs). Dendritic cells (DCs), as potent antigen-presenting cells, are capable of mediating pAgs–triggered Vδ2⁺ T cells expansion. However, the association between DCs and Vδ2⁺ T cell recovery in the context of hematopoietic stem cell transplantation (HSCT) remains unclear. We previously demonstrated that the recovery of Vδ2⁺ T cells was hampered and inversely correlated with Epstein-Barr virus (EBV) reactivation in patients undergoing haploidentical HSCT (haploHSCT). Whether Vδ2⁺ T cells from haploHSCT recipients can be expanded by stimulation with aminobisphosphonates or pAg–presenting DCs is of particular interest. Herein, we showed that Vδ2⁺ T cells recovered after haploHSCT failed to expand after ex-vivo stimulation with pamidronate. In addition, we found that the recovery of DC subsets was significantly decreased, and the concentration of myeloid DCs (mDCs) correlated significantly with Vδ2⁺ T cell recovery in the setting of allogeneic HSCT. Furthermore, coculture of peripheral lymphocytes from recipients with monocyte-derived and pamidronate-pretreated autologous or allogeneic DCs induced the successful expansion of Vδ2⁺ T cells. Of note, allogeneic DCs from third-party donors stimulated a significantly higher efficiency of Vδ2⁺ T cell expansion than autologous DCs. More importantly, the memory features were well-retained and the cytotoxic cytokines-production capacity was significantly enhanced in the expanded Vδ2⁺ T cells. Taken together, these results suggest that the frequency and function of DCs are critical for the recovery of Vδ2⁺ T cells after allogeneic HSCT. The fact that vigorous expansions of Vδ2⁺ T cells were induced by phosphoantigen-pretreated DCs, especially by allogeneic third-party DCs, provides additional options for the development of individualized immunotherapy strategies that utilize the anti-viral and anti-leukemic effects of γδ T cells in the context of hematopoietic transplantation.

Continuous Immune Cell Differentiation Inferred From Single-Cell Measurements Following Allogeneic Stem Cell Transplantation

The process of immune system regeneration after allogeneic stem cell transplantation is slow, complex, and insufficiently understood. An entire immune system with all of its cell populations must regenerate from infused donor hematopoietic stem cells over the course of weeks and months post-transplantation. Both innate and adaptive arms of the immune system differ in their capacity and speed to reconstitiute in the recipient, which contributes to inadequacy in global immunity during the delayed reconstitution period. Systems-level analyses of immune systems in human patients have been made possible by high-throughput and high-dimensional, state-of-the-art, single-cell methodologies such as mass cytometry. Mass cytometry has revolutionized our ability to comprehensively profile all immune cell populations simultaneously in blood or tissue samples, providing signatures of differentially regulated cells in a range of clinical conditions. Such kind of systems immunology analyses promise not only for more accurate descriptions of variation between patients but also within individual patients over time, inter-dependencies between cell populations and the inference of developmental trajectories for specific cell populations. Here, we took advantage of a recently performed longitudinal mass cytometry analysis in 26 patients with hematological malignancies followed during the first 12 months following allogeneic stem cell transplantation. We present a proof-of-principle analysis to understand the evolution of individual immune cell populations. By applying non-linear dimensionality reduction and feauture extraction algorithms, we infer trajectories for individual immune cell populations, and map continuous marker expression changes occuring during immune cell regeneration that add novel information about this developmental process.

Comparison of target volume and clinical effects of four radiotherapy plans for acute lymphoblastic leukemia prior to hematopoietic stem cell transplantation

The present study aimed to investigate the variations in target volume, clinical reaction and transplantation effects of helical tomotherapy (HT)-total body irradiation (TBI), HT-total marrow and lymphatic irradiation (TMLI), intensity modulated radiotherapy (IMRT)-TBI and IMRT-TMLI within patients with acute lymphoblastic leukemia (ALL). A total of 18 patients with ALL were treated with the four aforementioned radiotherapy plans prior to hematopoietic stem cell transplantation. A planned prescribed dose of 12 Gy/6 Frequency was administered to determine planning target volume (PTV). Dosimetry evaluation indexes in PTV and organs at risk were analyzed. Comparison of clinical untoward effects and the results of transplantation among the four plans were performed. The conformity index of HT plans was significantly increased compared with those in IMRT plans. The mean dose (D) to the lung and volume ratio of target volume occupied by 5 Gy (V₅) in TMLI plans were lower compared with TBI plans. Doses to organs were controlled within the normal range. D_max, D_mean and V₅ of bilateral lungs and D_max and D_mean of bilateral crystalline lens in IMRT plans were significantly higher compared with HT plans. There were no significant differences in untoward effects among the four plans. Subsequent to symptomatic treatments with antiemetic, antidiarrheal and fluid infusion, untoward effects improved, and all patients demonstrated tolerance to these therapies. A total of six patients treated with HT-TBI revealed complete and successful transplantation; however, one patient following transplantation suffered from severe rejection and had succumbed to mortality due to severe infection. Patients treated with HT-TMLI, IMRT-TBI and IMRT-TMLI completed successful transplantation and no rejection responses were observed. Conformity of HT plans are higher than that of IMRT plans. The four radiotherapy plans exhibit similar clinical untoward effects and the same transplantation success rate. HT-TMLI is more feasible in dosimetry compared with HT-TBI, IMRT-TBI and IMRT-TMLI, which require further long-term observation.

Restoring T Cell Homeostasis After Allogeneic Stem Cell Transplantation; Principal Limitations and Future Challenges

For several leukemia patients, allogeneic stem cell transplantation (allogeneic-SCT) is the unique therapeutic modality that could potentially cure their disease. Despite significant progress made in clinical management of allogeneic-SCT, acute graft-versus-host disease (aGVHD) and infectious complications remain the second and third cause of death after disease recurrence. Clinical options to restore immunocompetence after allogeneic-SCT are very limited as studies have raised awareness about the safety with regards to graft-versus-host disease (GVHD). Preclinical works are now focusing on strategies to improve thymic functions and to restore the peripheral niche that have been damaged by alloreactive T cells. In this mini review, we will provide a brief overview about the adverse effects of GVHD on the thymus and the peripheral niche and the resulting negative outcome on peripheral T cell homeostasis. Finally, we will discuss the potential relevance of coordinating our studies on thymic rejuvenation and improvement of the peripheral lymphoid niche to achieve optimal T cell regeneration in GVHD patients.

Severe hematuria in a hematopoietic cell transplant recipient caused by Ureaplasma urealyticum not by BK virus or adenovirus infection

A 17-year-old male with acute lymphoblastic leukemia developed severe hematuria and scrotal swelling after haploidentical hematopoietic cell transplantation (HCT). Urine culture was negative. BK virus and adenovirus were negative. However, Ureaplasma urealyticum was detected. He showed dramatic improvement after doxycycline treatment. This is the first report in the literature of hemorrhagic cystitis caused by U. urealyticum in a HCT recipient. In HCT recipients with hemorrhagic cystitis, U. urealyticum should be considered as a potential cause.

Mass Cytometry and Topological Data Analysis Reveal Immune Parameters Associated with Complications after Allogeneic Stem Cell Transplantation

Human immune systems are variable, and immune responses are often unpredictable. Systems-level analyses offer increased power to sort patients on the basis of coordinated changes across immune cells and proteins. Allogeneic stem cell transplantation is a well-established form of immunotherapy whereby a donor immune system induces a graft-versus-leukemia response. This fails when the donor immune system regenerates improperly, leaving the patient susceptible to infections and leukemia relapse. We present a systems-level analysis by mass cytometry and serum profiling in 26 patients sampled 1, 2, 3, 6, and 12 months after transplantation. Using a combination of machine learning and topological data analyses, we show that global immune signatures associated with clinical outcome can be revealed, even when patients are few and heterogeneous. This high-resolution systems immune monitoring approach holds the potential for improving the development and evaluation of immunotherapies in the future.

Long-Term Engraftment of Primary Bone Marrow Stromal Cells Repairs Niche Damage and Improves Hematopoietic Stem Cell Transplantation

Hematopoietic stem cell (HSC) transplantation represents a curative treatment for various hematological disorders. However, delayed reconstitution of innate and adaptive immunity often causes fatal complications. HSC maintenance and lineage differentiation are supported by stromal niches, and we now find that bone marrow stroma cells (BMSCs) are severely and permanently damaged by the pre-conditioning irradiation required for efficient HSC transplantation. Using mouse models, we show that stromal insufficiency limits the number of donor-derived HSCs and B lymphopoiesis. Intra-bone transplantation of primary, but not cultured, BMSCs quantitatively reconstitutes stroma function in vivo, which is mediated by a multipotent NT5E⁺ (CD73)⁺ ENG^- (CD105)^- LY6A⁺ (SCA1)⁺ BMSC subpopulation. BMSC co-transplantation doubles the number of functional, donor-derived HSCs and significantly reduces clinically relevant side effects associated with HSC transplantation including neutropenia and humoral immunodeficiency. These data demonstrate the potential of stroma recovery to improve HSC transplantation.

A novel approach to improve immune effector responses post transplant by restoration of CCL21 expression

Chemotherapy or chemoradiotherapy conditioning regimens required for bone marrow transplantation (BMT) cause significant morbidity and mortality as a result of insufficient immune surveillance mechanisms leading to increased risks of infection and tumor recurrence. Such conditioning causes host stromal cell injury, impairing restoration of the central (thymus) and peripheral (spleen and lymph node) T cell compartments and slow immune reconstitution. The chemokine, CCL21, produced by host stromal cells, recruits T- and B-cells that provide lymphotoxin mediated instructive signals to stromal cells for lymphoid organogenesis. Moreover, T- and B-cell recruitment into these sites is required for optimal adaptive immune responses to pathogens and tumor antigens. Previously, we reported that CCL21 was markedly reduced in secondary lymphoid organs of transplanted animals. Here, we utilized adenoviral CCL21 gene transduced dendritic cells (DC/CCL21) given by footpad injections as a novel approach to restore CCL21 expression in secondary lymphoid organs post-transplant. CCL21 expression in secondary lymphoid organs reached levels of naïve controls and resulted in increased T cell trafficking to draining lymph nodes (LNs). An increase in both lymphoid tissue inducer cells and the B cell chemokine CXCL13 known to be important in LN formation was observed. Strikingly, only mice vaccinated with DC/CCL21 loaded with bacterial, viral or tumor antigens and not recipients of DC/control adenovirus loaded cells or no DCs had a marked increase in the systemic clearance of pathogens (bacteria; virus) and leukemia cells. Because DC/CCL21 vaccines have been tested in clinical trials for patients with lung cancer and melanoma, our studies provide the foundation for future trials of DC/CCL21 vaccination in patients receiving pre-transplant conditioning regimens.

Paradoxical immune reconstitution inflammatory syndrome associated with disseminated tuberculosis infection in an unrelated donor cord blood transplant recipient

Tuberculosis (TB) is an infrequent infection after hematopoietic cell transplant (HCT), with associated mortality up to 30%. The utility of universal screening for latent TB in HCT candidates is controversial due to the lack of sensitive screening tests. We describe a case of disseminated TB infection complicated by immune reconstitution inflammatory syndrome in an adult double unit umbilical cord blood transplant recipient who originated from the United Arab Emirates.

Immunological effects of nilotinib prophylaxis after allogeneic stem cell transplantation in patients with advanced chronic myeloid leukemia or philadelphia chromosome-positive acute lymphoblastic leukemia

Allogeneic stem cell transplantation remains the standard treatment for resistant advanced chronic myeloid leukemia and Philadelphia chromosome–positive acute lymphoblastic leukemia. Relapse is the major cause of treatment failure in both diseases. Post-allo-SCT administration of TKIs could potentially reduce relapse rates, but concerns regarding their effect on immune reconstitution have been raised. We aimed to assess immune functions of 12 advanced CML and Ph+ ALL patients who received post-allo-SCT nilotinib. Lymphocyte subpopulations and their functional activities including T-cell response to mitogens, NK cytotoxic activity and thymic function, determined by quantification of the T cell receptor (TCR) excision circles (TREC) and TCR repertoire, were evaluated at several time points, including pre-nilotib-post-allo-SCT, and up to 365 days on nilotinib treatment. NK cells were the first to recover post allo-SCT. Concomitant to nilotinib administration, total lymphocyte counts and subpopulations gradually increased. CD8 T cells were rapidly reconstituted and continued to increase until day 180 post SCT, while CD4 T cells counts were low until 180−270 days post nilotinib treatment. T-cell response to mitogenic stimulation was not inhibited by nilotinib administration. Thymic activity, measured by TREC copies and surface membrane expression of 24 different TCR Vβ families, was evident in all patients at the end of follow-up after allo-SCT and nilotinib treatment. Finally, nilotinib did not inhibit NK cytotoxic activity. In conclusion, administration of nilotinib post allo-SCT, in attempt to reduce relapse rates or progression of Ph+ ALL and CML, did not jeopardize immune reconstitution or function following transplantation.

Thymopoiesis following HSCT; a retrospective review comparing interventions for aGVHD in a pediatric cohort

Acute graft-versus-host disease (aGVHD) complicates allogeneic hematopoietic stem cell transplantation (HSCT), and is treated with topical and/or systemic corticosteroids. Systemic corticosteroids and aGVHD damage thymic tissue. We compared thymopoietic effect of topical steroid therapy, corticosteroids and extracorporeal photopheresis (ECP) in 102 pediatric allogeneic HSCT patients. We categorized patients into 4 groups: - no aGVHD, aGVHD treated with topical or systemic steroid, or ECP. Naïve CD4⁺CD45RA⁺CD27⁺ T-lymphocyte values at 3, 6, 9, 12months post-HSCT were recorded: for ECP patients, values were recorded at 3, 6, 9, 12months during ECP. Differences were compared using the Kruskal-Wallis test. 41 patients had no aGVHD, 23 had aGVHD treated topically or systemically (25), 13 received ECP. Rate of thymopoiesis was significantly different between all groups at all time-points post-transplant (p=0.002, p<0.001, p<0.001, p=0.001 respectively). Even mild aGVHD impairs thymopoiesis. Worst recovery was in ECP patients. Earlier institution of ECP may speed thymic recovery.

Mucosal-Associated Invariant T Cells Display a Poor Reconstitution and Altered Phenotype after Allogeneic Hematopoietic Stem Cell Transplantation

Mucosal-associated invariant T (MAIT) cells are innate-like T cells which are important in the defense against certain bacteria and yeast. The reconstitution of MAIT cells after allogeneic hematopoietic stem cell transplantation (HSCT) is not known. We investigated MAIT cell phenotype and function in 17 patients devoid of relapse and severe graft-versus-host disease (GvHD) in paired samples collected 1-2, 3-6, 12, and 24 months after transplantation. Data were compared to 17 healthy controls (HC), as well as 22 patients with acute GvHD grade 2-3. The frequency of MAIT cells within CD3⁺ cells was approximately 10-fold lower than in HC and did not increase over the 2 years following HSCT. MAIT cells in HSCT patients displayed an elevated expression of CD69 and intracellular granzyme B and were predominantly composed of CD4/CD8 double-negative cells. The expression of PD-1 on MAIT cells was low and did not change during the observational time, whereas the CD3⁺CD161^dim/negTCRVα7.2^dim/neg cells (non-MAIT T cells) displayed a high expression early after HSCT that decreased to normal levels at 24 months. MAIT cells collected 2-6 months post-HSCT showed an impaired IFN-γ and perforin response after bacterial stimulation, but the response was restored at 24 months. Patients with acute GvHD had similar proportions of MAIT cells as patients with grade 0-1, but consisted mainly of CD8⁺ cells. Finally, MAIT cells were more sensitive to cyclosporine A and sirolimus than non-MAIT T cells. To conclude, MAIT cell reconstitution following HSCT is deficient compared to non-MAIT T cells and GvHD grade ≥2 is not correlated with MAIT cell frequency. MAIT cell functionality was impaired early after HSCT, but restored at 24 months post-HSCT. MAIT cells have an increased sensibility to common immunosuppressive drugs, which maybe could explain their hampered reconstitution after HSCT.

GMP-production of purified human B lymphocytes for the adoptive transfer in patients after allogeneic hematopoietic stem cell transplantation

Background

We have recently shown that memory B cells from murine CMV immune donor animals adoptively transferred into immunodeficient mice were highly effective in protecting from a viral infection indicating a therapeutic potential of virus specific memory B cells. These preclinical data provided evidence that a cell-based strategy supporting the humoral immune response might be effective in a clinical setting of immunodeficiency after allogeneic hematopoietic stem cell transplantation. As adoptive transfer of B cells has not been used before in a clinical setting it was necessary to establish a technology for the generation of good manufacturing practice (GMP)-grade B cell products.

Methods

Starting from the leukapheresis product of healthy blood donors, B cells were purified by two different separation strategies using GMP-grade microbeads and the CliniMACS system. A one-step protocol was used for positive enrichment of B lymphocytes with anti-CD19 microbeads. In a two-step enrichment protocol, first T lymphocytes were depleted by anti-CD3 microbeads and the remaining fraction was positively selected by anti-CD19 microbeads.

Results

The purity and recovery after enrichment of B lymphocytes from the leukapheresis material in both separations strategies was not statistically different. However, contamination of the B-cell product with T cells was significantly lower after the two-step protocol (0.16%, range 0.01–0.43% after two-step separation and 0.55%, range 0.28–0.85% after one-step separation, p < 0.05). Therefore, a combined CD3 depletion and CD19 enrichment was used for the production of GMP-conform B-cell products from the leukapheresis material of 17 healthy stem cell donors. The absolute B-cell numbers obtained in the final product was 4.70 ± 3.64 × 10⁸ with a purity of 95.98 ± 3.31% B lymphocytes and a recovery of 18.9 ± 10.6%. Importantly, the contamination with CD3⁺ T cells was extremely low in the final B- cell products (0.10 ± 0.20%). Purified B cells exhibited normal antibody production after in vitro stimulation and showed excellent viability after cryopreservation.

Conclusions

A GMP-grade B-cell product can be obtained with high purity and very low T-cell contamination using the two-step enrichment protocol based on CliniMACS® technology.

CD28 Blockade Ex Vivo Induces Alloantigen-Specific Immune Tolerance but Preserves T-Cell Pathogen Reactivity

Donor T-cells contribute to reconstitution of protective immunity after allogeneic hematopoietic stem cell transplantation (HSCT) but must acquire specific tolerance against recipient alloantigens to avoid life-threatening graft-versus-host disease (GvHD). Systemic immunosuppressive drugs may abrogate severe GvHD, but this also impedes memory responses to invading pathogens. Here, we tested whether ex vivo blockade of CD28 co-stimulation can enable selective T-cell tolerization to alloantigens by facilitating CD80/86-cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) signaling. Treatment of human allogeneic dendritic cell/T-cell co-cultures with a human CD28 blocking antibody fragment (α-huCD28) significantly abrogated subsequent allospecific immune responses, seen by decreased T-cell proliferation and of type 1 cytokine (IFN-γ and IL-2) expression. Allo-tolerization persisted after discontinuation of CD28 blockade and secondary alloantigen stimulation, as confirmed by enhanced CTLA-4 and PD-1 immune checkpoint signaling. However, T-cells retained reactivity to pathogens, supported by clonotyping of neo-primed and cross-reactive T-cells specific for Candida albicans or third-party antigens using deep sequencing analysis. In an MHC-mismatched murine model, we tolerized C57BL/6 T-cells by ex vivo exposure to a murine single chain Fv specific for CD28 (α-muCD28). Infusion of these cells, after α-muCD28 washout, into bone marrow-transplanted BALB/c mice caused allo-tolerance and did not induce GvHD-associated hepatic pathology. We conclude that selective CD28 blockade ex vivo can allow the generation of stably allo-tolerized T-cells that in turn do not induce graft-versus-host reactions while maintaining pathogen reactivity. Hence, CD28 co-stimulation blockade of donor T-cells may be a useful therapeutic approach to support the immune system after HSCT.

Comparison of reference values for immune recovery between event-free patients receiving haploidentical allografts and those receiving human leukocyte antigen-matched sibling donor allografts

To establish optimal reference values for recovered immune cell subsets, we prospectively investigated post-transplant immune reconstitution (IR) in 144 patients who received allogeneic stem cell transplantation (allo- SCT) and without showing any of the following events: poor graft function, grades II‒IV acute graft-versus-host disease (GVHD), serious chronic GVHD, serious bacterial infection, invasive fungal infection, or relapse or death in the first year after transplantation. IR was rapid in monocytes, intermediate in lymphocytes, CD3⁺ Tcells, CD8⁺ T cells, and CD19⁺ B cells, and very slow in CD4⁺ T cells in the entire patient cohort. Immune recovery was generally faster under HLA-matched sibling donor transplantation than under haploidentical transplantation. Results suggest that patients with an IR comparable to the reference values display superior survival, and the levels of recovery in immune cells need not reach those in healthy donor in the first year after transplantation.We suggest that data from this recipient cohort should be used as reference values for post-transplant immune cell counts in patients receiving HSCT.

miR-625-3p is upregulated in CD8+ T cells during early immune reconstitution after allogeneic stem cell transplantation

Alloreactive CD8+ T-cells mediate the curative graft-versus-leukaemia effect, the anti-viral immunity and graft-versus-host-disease (GvHD) after allogeneic stem cell transplantation (SCT). Thus, immune reconstitution with CD8+ T-cells is critical for the outcome of patients after allogeneic SCT. Certain miRNAs such as miR-146a or miR-155 play an important role in the regulation of post-transplant immunity in mice. While some miRNAs e.g. miR-423 or miR-155 are regulated in plasma or full blood during acute GvHD also in man, the relevance and expression profile of miRNAs in T-cells after allogeneic SCT is unknown. miR-625-3p has recently been described to be overexpressed in colorectal malignancies where it promotes migration, invasion and apoptosis resistance. Since similar regulative functions in cancer and T-cells have been described for an increasing number of miRNAs, we assumed a role for the cancer-related miR-625-3p also in T-cells. Here, we studied miR-625-3p expression selectively in CD8+ T-cells both in vitro and during immune reconstitution after allogeneic SCT in man. T-cell receptor stimulation lead to miR-625-3p upregulation in human CD8+ T-cells in vitro. Maintenance of elevated miR-625-3p expression levels was dependent on ongoing T-cell proliferation and was abrogated by withdrawal of interleukin 2 or the mTOR inhibitor rapamycin. Finally, miR-625-3p expression was analyzed in human CD8+ T-cells purified from 137 peripheral blood samples longitudinally collected from 74 patients after allogeneic SCT. miR-625-3p expression was upregulated on day 25 and on day 45, i.e. during the early phase of CD8+ T-cell reconstitution after allogeneic SCT and subsequently declined with completion of CD8+ T-cell reconstitution until day 150. In conclusion, this study has shown for the first time that miR-625-3p is regulated in CD8+ T-cells during proliferation in vitro and during early immune reconstitution after allogeneic SCT in vivo. These results warrant further studies to identify the targets and function of miR-625-3p in CD8+ T-cells and to analyze its predictive value for an effective immune reconstitution.

Lymphocyte recovery is an independent predictor of relapse in allogeneic hematopoietic cell transplantation recipients for acute leukemia

AIM

To examine the optimal absolute lymphocyte count (ALC) cut-off utilizing receiver operator characteristics (ROC) in addition to graft characteristics associated with early ALC recovery.

METHODS

Patients who received T-cell replete peripheral hematopoietic cell transplantation (HCT) for acute leukemia were identified. ALC cut-off was established using ROC analysis and subsequently the cohort was stratified. Time to endpoint analysis and cox regression modelling was computed to analyze outcomes.

RESULTS

A total of 72 patients met the inclusion criteria and were analyzed. Optimal ALC cut-off was established to be on day 14 (D14) with ALC > 0.3 × 10⁹/L. At 2 years, cumulative incidence of relapse was 16.9% vs 46.9% (P = 0.025) for early and delayed lymphocyte recovery cohorts, respectively. Chronic graft vs host disease was more prevalent in the early lymphocyte recovery (ELR) group at 70% vs 27%, respectively (P = 0.0006). On multivariable analysis for relapse, ELR retained its prognostic significance with HR = 0.27 (0.05-0.94, P = 0.038).

CONCLUSION

ELR is an independent predictor for relapse in patients receiving allogeneic HCT for acute leukemia. ELR was influenced by graft characteristics particularly CD34 count.

Immune Reconstitution after Allogeneic Hematopoietic Stem Cell Transplantation: Time To T Up the Thymus

The success of allogeneic hematopoietic stem cell transplantation, a key treatment for many disorders, is intertwined with T cell immune reconstitution. The thymus plays a key role post allogeneic hematopoietic stem cell transplantation in the generation of a broad but self-tolerant T cell repertoire, but it is exquisitely sensitive to a range of insults during the transplant period, including conditioning regimens, corticosteroids, infections, and graft-versus-host disease. Although endogenous thymic repair is possible it is often suboptimal, and there is a need to develop exogenous strategies to help regenerate the thymus. Therapies currently in clinical trials in the transplant setting include keratinocyte growth factor, cytokines (IL-7 and IL-22), and hormonal modulation including sex steroid inhibition and growth hormone administration. Such regenerative strategies may ultimately enable the thymus to play as prominent a role after transplant as it once did in early childhood, allowing a more complete restoration of the T cell compartment.

Dynamics of Torque Teno virus plasma DNAemia in allogeneic stem cell transplant recipients

BACKGROUND

Torque Teno virus (TTV) plasma DNA load directly correlate with the level of immunosuppresion in different clinical settings. It is uncertain whether this may be the case in allogeneic hematopoietic stem cell transplant recipients (allo-HSCT).

OBJECTIVES

We characterized the dynamics of TTV DNAemia in patients undergoing T-cell replete allo-SCT.

STUDY DESIGN

Retrospective single-center observational study including 72 allo-HSCT patients. Plasma TTV DNA loads were quantified before initiating the conditioning regimen and at different time-points after transplant by real-time PCR. White blood cells (WBC) and absolute lymphocyte counts (ALC) were measured by flow cytometry.

RESULTS

A dramatic drop in plasma TTV DNA load was observed shortly after conditioning. The TTV DNA load increased steadily after engraftment reaching its peak at day +90 after transplant. The increase in TTV DNA load paralleled that of ALC, and was of greater magnitude in patients who developed severe (grades II-IV) acute graft vs. host disease.

CONCLUSION

Repopulation of lymphocytes early after allo-HSCT correlates with an increase of plasma TTV DNA load. Prospective studies are nevertheless needed to determine whether the kinetics of TTV DNAemia may allow inference of the degree of overall immunocompetence in these patients.

Hematopoietic stem cell transplantation in autoimmune disorders: From immune-regulatory processes to clinical implications

Autoimmune diseases are characterized by the development of autoreactive T- and B-cells targeting self-antigens, which eventually can result in chronic and persistent organ damage. The autologous hematopoietic stem cell transplantation (AHSCT) opened new avenues in the treatment of patients with severe, treatment-resistant autoimmune diseases. This paper reviews the immune-regulatory mechanisms behind AHSCT, and also summarizes the experiences of clinical practice related to the therapy in organ-specific and systemic autoimmune diseases. It seems that the intricate interplay of various immune competent cells with regulatory capacity control in a synergistic manner the repopulated immune system after AHSCT, which potentially leads to a significant clinical improvement in certain autoimmune diseases. However, the widespread use of AHSCT was intrinsically limited, due to the serious side-effects of conditioning treatment and relatively high treatment-related mortality; moreover, the development of new effective and safe therapeutic approaches and the dawn of biological agents further limited its indications in the last decade. Nevertheless, with an appropriate patient selection and increased experience of transplant centres, the risks can be minimized, and AHSCT remained still a reasonable choice in multiple sclerosis and systemic sclerosis when the conventional therapy failed and further progression of disease is inevitable.

Severe Acute Hepatitis B in HBV-Vaccinated Partner of a Patient with Multiple Myeloma Treated with Cyclophosphamide, Bortezomib, and Dexamethasone and Autologous Stem Cell Transplant

Hepatitis B reactivation can occur with various forms of immunosuppression. Cyclophosphamide, Bortezomib, and Dexamethasone (CYBOR-D) chemotherapy is commonly used for the treatment of multiple myeloma and has not been noted in guidelines to be causative in HBV reactivation. Indeed, current guidelines do not recommend providing antiviral prophylaxis to patients with prior HBV infection. We present a case of HBV reactivation as a result of CYBOR-D and autologous stem cell transplant which is complicated by the patient's partner who developed acute hepatitis B. Our case highlights the need to review the role of antiviral prophylaxis for patients undergoing treatment of multiple myeloma and also the role of ensuring immunity for close contacts of these patients who may also be at risk.

Treatment of Pediatric Acute Graft-versus-Host Disease-Lessons from Primary Immunodeficiency?

Allogeneic hematopoietic stem cell transplant (HSCT) is used to treat increasing numbers of malignant and non-malignant disorders. Despite significant advances in improved human leukocyte antigens-typing techniques, less toxic conditioning regimens and better supportive care, resulting in improved clinical outcomes, acute graft-versus-host disease (aGvHD) continues to be a major obstacle and, although it principally involves the skin, gastrointestinal tract, and liver, the thymus is also a primary target. An important aim following HSCT is to achieve complete and durable immunoreconstitution with a diverse T-cell receptor (TCR) repertoire to recognize a broad range of pathogens providing adequate long-term adaptive T-lymphocyte immunity, essential to reduce the risk of infection, disease relapse, and secondary malignancies. Reconstitution of adaptive T-lymphocyte immunity is a lengthy and complex process which requires a functioning and structurally intact thymus responsible for the production of new naïve T-lymphocytes with a broad TCR repertoire. Damage to the thymic microenvironment, secondary to aGvHD and the effect of corticosteroid treatment, disturbs normal signaling required for thymocyte development, resulting in impaired T-lymphopoiesis and reduced thymic export. Primary immunodeficiencies, in which failure of central or peripheral tolerance is a major feature, because of intrinsic defects in hematopoietic stem cells leading to abnormal T-lymphocyte development, or defects in thymic stroma, can give insights into critical processes important for recovery from aGvHD. Extracorporeal photopheresis is a potential alternative therapy for aGvHD, which acts in an immunomodulatory fashion, through the generation of regulatory T-lymphocytes (Tregs), alteration of cytokine patterns and modulation of dendritic cells. Promoting normal central and peripheral immune tolerance, with selective downregulation of immune stimulation, could reduce aGvHD, and enable a reduction in other immunosuppression, facilitating thymic recovery, restoration of normal T-lymphocyte ontogeny, and complete immunoreconstitution with improved clinical outcome as the ability to fight infections improves and risk of secondary malignancy or relapse diminishes.

Stem cell transplantation during cancer

Hematological malignancies account for approximately 9.5% of new cancers diagnosed annually. Lymphoma is the most frequent of all known categories of hematological malignancies. Worldwide, extensive research has focused on this type of cancer. However, new treatments are investigated in various clinical as well as pre-clinical studies. Hematopoietic stem cell transplantation (HSCT) is a recent and upcoming treatment strategy for patients with hematopoietic malignancies and inborn errors of metabolism or immune deficiencies. Recent studies have revealed that successful clinical outcome of this treatment strategy depends on multiple factors including the protocol applied, disease under treatment, health of the patient, source of the grafts, severity of complications such as graft versus host disease during grafting and associated infections. The scope of this review is to achieve greater understanding of various clinical effects of the disease and related mechanisms. The electronic database Pubmed was searched for pre-clinical as well as clinical controlled trials reporting efficacy of the HSCT against hematological malignancies.

Increased Foxp3+Helios+ Regulatory T Cells and Decreased Acute Graft-versus-Host Disease after Allogeneic Bone Marrow Transplantation in Patients Receiving Sirolimus and RGI-2001, an Activator of Invariant Natural Killer T Cells

Regulatory T (Treg) cells play a central role in immune tolerance and prevention of aberrant immune responses. Several studies have suggested that the risk of graft-versus-host disease (GVHD) after allogeneic hematopoietic cell transplantation (HCT) can be ameliorated by increasing Tregs. We have developed an approach of in vivo expansion of Tregs with RGI-2001, a novel liposomal formulation of a synthetic derivative of alpha-galactosylceramide, a naturally occurring ligand that binds to CD1 and activates and expands invariant natural killer cells. In preclinical studies, a single intravenous infusion of RGI-2001 expanded Treg and could ameliorate GVHD in a mouse model of allogeneic HCT. To explore the role of RGI-2001 in clinical HCT, we initiated a phase 2A clinical trial (n = 29), testing 2 different doses of RGI-2001 administered as a single infusion on day 0 of allogeneic HCT. RGI-2001 was well tolerated and without infusion reactions or cytokine release syndrome. A subset of patients (8 of 29, 28%) responded to RGI-2001 by inducing a markedly increased number of cells with a Treg phenotype. The Treg had a high Ki-67 index and were almost exclusively Helios⁺ and Foxp3⁺, indicating that their accumulation was due to expansion of natural Treg. Notably, the incidence of grade 2 to 4 GVHD in the 8 patients who responded to RGI-2001 was 12.5%, compared with 52.4% in the 21 patients who did not respond. No grade 3 or 4 GVHD was observed in the responder group, compared with a 9.5% incidence among nonresponders. Immunosuppression with sirolimus was also associated with a low incidence of GVHD, suggesting that RGI-2001 may have synergized with sirolimus to promote Treg expansion.

Altered immune reconstitution of B and T cells precedes the onset of clinical symptoms of chronic graft-versus-host disease and is influenced by the type of onset

We analyzed lymphocyte subpopulations and cytokines 3 months after allogeneic hematopoietic stem cell transplantation aiming to identify predictive cellular and serum markers for chronic graft-versus-host disease (cGVHD). Samples of 49 patients (pts) (no cGVHD (n = 14), subsequent quiescent onset (n = 16), de novo onset of cGVHD (n = 19)) were analyzed in the absence of active GVHD by flow cytometry and enzyme-linked immunosorbent assay. All mean absolute cell counts are presented as cells per microliter; relative cell counts are presented as percentage of lymphocytes. Pts with subsequent de novo cGVHD had significantly higher relative and absolute counts of CD4+ T cells including higher absolute counts of CD4+ memory T cells (22.36%; 206.55/μl; 136/μl, respectively) compared to pts with subsequent quiescent onset of cGVHD (12.41%; 83.42/μl; 54.3/μl) and pts without cGVHD (10.55%) with regard to relative counts of CD4+ T cells. Similarly, significantly more relative and absolute regulatory T cell numbers (CD4+FOXP3+) were detected in pts with de novo onset of cGVHD (3.08% and 24.63/μl) compared to those in pts without (1.25% and 9.06/μl) or with quiescent onset of cGVHD (1.15% and 6.91/μl). Finally, relative B cell counts, including naïve and memory B cells, were also significantly decreased in pts developing quiescent cGVHD (0.85, 0.73, 0.12% resp.) when compared to pts with de novo onset (5.61, 5.24, 0.38%). The results demonstrate that alterations in immune reconstitution are already present before onset of clinical symptoms and differ between de novo and quiescent onset of disease.

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.

T Cell Genesis: In Vitro Veritas Est?

T cells, as orchestrators of the adaptive immune response, serve important physiological and potentially therapeutic roles, for example in cancer immunotherapy. T cells are readily isolated from patients; however, the yield of antigen-specific T cells is limited, thus making their clinical use challenging. Therefore, the generation of T lymphocytes from hematopoietic stem/progenitor cells (HSPCs) and human pluripotent stem cells (PSCs) in vitro provides an attractive method for the large-scale production and genetic manipulation of T cells. In this review, we discuss recent strategies for the generation of T cells from human HSPCs and PSCs in vitro. Continued advancement in the generation of human T cells in vitro will expand their benefits and therapeutic potential in the clinic.

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.

Extracoporeal photopheresis treatment of acute graft-versus-host disease following allogeneic haematopoietic stem cell transplantation

Acute graft-versus-host disease (aGvHD) continues to be a major obstacle to allogeneic haematopoietic stem cell transplantation. Thymic damage secondary to aGvHD along with corticosteroids and other non-selective T lymphocyte-suppressive agents used in the treatment of aGvHD concurrently impair thymopoiesis and negatively impact on immunoreconstitution of the adaptive immune compartment and ultimately adversely affect clinical outcome. Extracorporeal photopheresis (ECP) is an alternative therapeutic strategy that appears to act in an immunomodulatory fashion, potentially involving regulatory T lymphocytes and dendritic cells. By promoting immune tolerance and simultaneously avoiding systemic immunosuppression, ECP could reduce aGvHD and enable a reduction in other immunosuppression, allowing thymic recovery, restoration of normal T lymphopoiesis, and complete immunoreconstitution with improved clinical outcome. Although the safety and efficacy of ECP has been demonstrated, further randomised controlled studies are needed as well as elucidation of the underlying mechanisms responsible and the effect of ECP on thymic recovery.

Evaluation of engraftment syndrome in children following full-matched related donor hematopoietic stem cell transplantations

The term "ES" has been widely used for describing a clinical condition consisting of skin rash, fever, and weight gain that occur during neutrophil recovery period following HSCT. In this study, the incidence, clinical features, risk factors, and outcomes of ES were evaluated in 169 children following allogeneic HSCT from full-matched related donor according to the Spitzer criteria. Seventeen patients (10.1%) presented with clinical conditions suggesting ES. In both univariate and multivariate analysis underlying malignant disease and early release of monocytes to the PB, and in univariate analysis using only CsA for GVHD prophylaxis were found to be the significant risk factors for the development of ES. Patients with ES experienced significantly higher incidence of acute and chronic GVHD and propensity toward a higher rate of TRM. OS did not differ between the patient groups. Thirteen of 17 patients received steroid therapy, and all but one patient responded to therapy. Monitoring for early detection of ES and early intervention with steroid therapy is the key for recovery. The most crucial approach for this purpose mainly is to find out and use the most useful and feasible diagnostic criteria for routine medical practice.

Alterations of the bone marrow stromal microenvironment in adult patients with acute myeloid and lymphoblastic leukemias before and after allogeneic hematopoietic stem cell transplantation

Bone marrow (BM) derived adult multipotent mesenchymal stromal cells (MMSCs) and fibroblast colony-forming units (CFU-Fs) of 20 patients with acute myeloid leukemia (AML) and 15 patients with acute lymphoblastic leukemia (ALL) before and during 1 year after receiving allogeneic hematopoietic stem cell transplantation (allo-HSCT) were studied. The growth characteristics of MMSCs of all patients before allo-HSCT were not altered; however, relative expression level (REL) of some genes in MMSCs, but not in CFU-Fs, from AML and ALL patients significantly changed. After allo-HSCT, CFU-F concentration and MMSC production were significantly decreased for 1 year; REL of several genes in MMSCs and CFU-F-derived colonies were also significantly downregulated. Thus, chemotherapy that was used for induction of remission did not impair the function of stromal precursors, but gene expression levels were altered. Allo-HSCT conditioning regimens significantly damaged MMSCs and CFU-Fs, and the effect lasted for at least 1 year.

Memory B-cell reconstitution following allogeneic hematopoietic stem cell transplantation is an EBV-associated transformation event

Allogeneic stem cell transplantation (allo-HSCT) provides a unique opportunity to track Epstein-Barr virus (EBV) infection in the context of the reconstituting B-cell system. Although many allo-HSCT recipients maintain low or undetectable levels of EBV DNA posttransplant, a significant proportion exhibit elevated and rapidly increasing EBV loads which, if left untreated, may lead to potentially fatal EBV-associated posttransplant lymphoproliferative disease. Intriguingly, this high-level EBV reactivation typically arises in the first 3 months posttransplant, at a time when the peripheral blood contains low numbers of CD27+ memory cells which are the site of EBV persistence in healthy immunocompetent donors. To investigate this apparent paradox, we prospectively monitored EBV levels and B-cell reconstitution in a cohort of allo-HSCT patients for up to 12 months posttransplant. In patients with low or undetectable levels of EBV, the circulating B-cell pool consisted predominantly of transitional and naive cells, with a marked deficiency of CD27+ memory cells which lasted >12 months. However, among patients with high EBV loads, there was a significant increase in both the proportion and number of CD27+ memory B cells. Analysis of sorted CD27+ memory B cells from these patients revealed that this population was preferentially infected with EBV, expressed EBV latent transcripts associated with B-cell growth transformation, had a plasmablastic phenotype, and frequently expressed the proliferation marker Ki-67. These findings suggest that high-level EBV reactivation following allo-HSCT may drive the expansion of latently infected CD27+ B lymphoblasts in the peripheral blood.