Cellular therapy: exploiting NK cell alloreactivity in transplantation

Triplebody Mediates Increased Anti-Leukemic Reactivity of IL-2 Activated Donor Natural Killer (NK) Cells and Impairs Viability of Their CD33-Expressing NK Subset

Natural killer cells (NK) are essential for the elimination of resistant acute myeloid and acute lymphoblastic leukemia (AML and ALL) cells. NK cell-based immunotherapies have already successfully entered for clinical trials, but limitations due to immune escape mechanisms were identified. Therefore, we extended our established NK cell protocol by integration of the previously investigated powerful trispecific immunoligand ULBP2-aCD19-aCD33 [the so-called triplebodies (TBs)] to improve the anti-leukemic specificity of activated NK cells. IL-2-driven expansion led to strongly elevated natural killer group 2 member D (NKG2D) expressions on donor NK cells which promote the binding to ULBP2⁺ TBs. Similarly, CD33 expression on these NK cells could be detected. Dual-specific targeting and elimination were investigated against the B-cell precursor leukemia cell line BV-173 and patient blasts, which were positive for myeloid marker CD33 and B lymphoid marker CD19 exclusively presented on biphenotypic B/myeloid leukemia’s. Cytotoxicity assays demonstrated improved killing properties of NK cells pre-coated with TBs compared to untreated controls. Specific NKG2D blocking on those NK cells in response to TBs diminished this killing activity. On the contrary, the observed upregulation of surface CD33 on about 28.0% of the NK cells decreased their viability in response to TBs during cytotoxic interaction of effector and target cells. Similar side effects were also detected against CD33⁺ T- and CD19⁺ B-cells. Very preliminary proof of principle results showed promising effects using NK cells and TBs against primary leukemic cells. In summary, we demonstrated a promising strategy for redirecting primary human NK cells in response to TBs against leukemia, which may lead to a future progress in NK cell-based immunotherapies.

Dental and orofacial mesenchymal stem cells in craniofacial regeneration: The prosthodontist's point of view

Of the available regenerative treatment options, craniofacial tissue regeneration using mesenchymal stem cells (MSCs) shows promise. The ability of stem cells to produce multiple specialized cell types along with their extensive distribution in many adult tissues have made them an attractive target for applications in tissue engineering. MSCs reside in a wide spectrum of postnatal tissue types and have been successfully isolated from orofacial tissues. These dental- or orofacial-derived MSCs possess self-renewal and multilineage differentiation capacities. The craniofacial system is composed of complex hard and soft tissues derived from sophisticated processes starting with embryonic development. Because of the complexity of the craniofacial tissues, the application of stem cells presents challenges in terms of the size, shape, and form of the engineered structures, the specialized final developed cells, and the modulation of timely blood supply while limiting inflammatory and immunological responses. The cell delivery vehicle has an important role in the in vivo performance of stem cells and could dictate the success of the regenerative therapy. Among the available hydrogel biomaterials for cell encapsulation, alginate-based hydrogels have shown promising results in biomedical applications. Alginate scaffolds encapsulating MSCs can provide a suitable microenvironment for cell viability and differentiation for tissue regeneration applications. This review aims to summarize current applications of dental-derived stem cell therapy and highlight the use of alginate-based hydrogels for applications in craniofacial tissue engineering.

Killer-cell immunoglobulin-like receptor genes and ligands and their role in hematologic malignancies

Natural killer (NK) cells are considered crucial for the elimination of emerging tumor cells. Effector NK-cell functions are controlled by interactions of inhibitory and activating killer-cell immunoglobulin-like receptors (KIRs) on NK cells with human leukocyte antigen (HLA) class I ligands on target cells. KIR and HLA are highly polymorphic genetic systems segregating independently, creating a great diversity in KIR/HLA gene profiles in different individuals. There is an increasing evidence supporting the relevance of KIR and HLA ligand gene background for the occurrence and outcome of certain cancers. However, the data are still controversial and the mechanisms of receptor-ligand mediated NK-cell action remain unclear. Here, the main characteristics and functions of KIRs and their HLA class I ligands are reviewed. In addition, we review the HLA and KIR correlations with different hematological malignancies and discuss our current understanding of the biological significance and mechanisms underlying these associations.

Allogeneic cardiosphere-derived cells for myocardial regeneration: current progress and recent results

Early-phase clinical testing of autologous cardiosphere-derived cells (CDCs) has yielded intriguing results, consistent with therapeutic myocardial regeneration. However, autologous therapy is associated with significant technical, timing, economic and logistic constraints, prompting researchers to explore the potential of allogeneic CDC therapy. CDCs exhibit a favorable immunologic antigenic profile and are hypoimmunogenic in vitro. Preclinical studies in immunologically mismatched animals demonstrate that allogeneic CDC transplantation without immunosuppression is safe and produces sustained functional and structural benefits through stimulation of endogenous regenerative pathways. Currently, allogeneic human CDCs are being tested clinically in the ALLSTAR and DYNAMIC trials. Potential establishment of clinical safety and efficacy of allogeneic CDCs combined with generation of highly standardized, ‘off-the-shelf’ allogeneic cellular products would facilitate broad clinical adoption of cell therapy.

Immunogenicity and escape mechanisms of allogeneic tendon-derived stem cells

The immunogenicity of tendon-derived stem cells (TDSCs) has implications for their clinical use for the promotion of tendon repair. The immunogenicity and escape mechanisms of rat patellar TDSCs were examined after allogeneic transplantation. Our results showed that TDSCs exhibited low immunogenicity as evidenced by the following: (i) the incubation of target TDSCs with immunized serum did not show antibody recognition and did not induce the complement-dependent cytotoxicity; (ii) target TDSCs elicited a very low level of lymphocyte proliferation and did not exhibit host lymphocyte-mediated cytotoxicity; and (iii) target TDSCs dose dependently suppressed the phorbol 12-myristate 13-acetate (PMA)- and ionomycin-induced host lymphocyte proliferation. For the mechanistic studies, TDSCs expressed major histocompatibility complex (MHC)-I but a very low level of MHC-II, CD86 and CD80 for the induction of T-cell response. Also, TDSCs were found to express intracellular Fas and FasL. γ-IFN pretreatment did not increase the level of MHC-II and CD86 for the upregulation of immune response. Moreover, the immunosuppressive mediators indoleamine 2,3-dioxygenase (IDO) and transforming growth factor-beta 1 (TGF-β1) were found not to be involved in the escape mechanism of target TDSCs from host lymphocyte attack. In conclusion, allogeneic TDSCs exhibited low immunogenicity. Allogeneic TDSCs might be used for transplantation.

Haploidentical stem cell transplantation

The feasibility of stem cell transplantation across the major histocompatibility barrier-as in haploidentical stem cell transplantation-has been proved for some time in several studies. The main limitations include a higher graft failure rate, delayed immune reconstitution after transplantation with high rates of life-threatening infections, a higher incidence of post-transplant lymphoproliferative disease, and severe acute and chronic graft-versus-host disease. In an attempt to reduce the transplant-related morbidity/mortality, several techniques had been evaluated involving conditioning regimen intensity, graft engineering, post-transplant cellular therapy and immunosuppression. This review will describe the current situation. It will also discuss initiatives and strategies to overcome the limitations associated with transplant across the MHC barrier.

Safety and efficacy of allogeneic cell therapy in infarcted rats transplanted with mismatched cardiosphere-derived cells

BACKGROUND

Cardiosphere-derived cells (CDCs) are an attractive cell type for tissue regeneration, and autologous CDCs are being tested clinically. However, autologous therapy necessitates patient-specific tissue harvesting and cell processing, with delays to therapy and possible variations in cell potency. The use of allogeneic CDCs, if safe and effective, would obviate such limitations. We compared syngeneic and allogeneic CDC transplantation in rats from immunologically-mismatched inbred strains.

METHODS AND RESULTS

In vitro, CDCs expressed major histocompatibility complex class I but not class II antigens or B7 costimulatory molecules. In mixed-lymphocyte cocultures, allogeneic CDCs elicited negligible lymphocyte proliferation and inflammatory cytokine secretion. In vivo, syngeneic and allogeneic CDCs survived at similar levels in the infarcted rat heart 1 week after delivery, but few syngeneic (and even fewer allogeneic) CDCs remained at 3 weeks. Allogeneic CDCs induced a transient, mild, local immune reaction in the heart, without histologically evident rejection or systemic immunogenicity. Improvements in cardiac structure and function, sustained for 6 months, were comparable with syngeneic and allogeneic CDCs. Allogeneic CDCs stimulated endogenous regenerative mechanisms (cardiomyocyte cycling, recruitment of c-kit(+) cells, angiogenesis) and increased myocardial vascular endothelial growth factor, insulin-like growth factor-1, and hepatocyte growth factor equally with syngeneic CDCs.

CONCLUSIONS

Allogeneic CDC transplantation without immunosuppression is safe, promotes cardiac regeneration, and improves heart function in a rat myocardial infarction model, mainly through stimulation of endogenous repair mechanisms. The indirect mechanism of action rationalizes the persistence of benefit despite the evanescence of transplanted cell survival. This work motivates the testing of allogeneic human CDCs as a potential off-the-shelf product for cellular cardiomyoplasty.

Interleukin-15 supports generation of highly potent clinical-grade natural killer cells in long-term cultures for targeting hematological malignancies

OBJECTIVE

Interleukin (IL)-15 is a promising novel cytokine for natural killer (NK) cell activation and survival. We studied the effects of IL-15 compared to IL-2 on NK cells in long-term cultures for clinical translation.

MATERIALS AND METHODS

CD56(+)CD3(-) NK cells were expanded with IL-2 or IL-15 for 2 to 4 weeks within lymphokine-activated killer (LAK) cell cultures (LAK-NK) in serum-enriched AIM V or CellGro Stem Cell Growth Medium (SCGM). Cell growth, viability, and NK cell content were monitored and cytotoxicity assessed in a flow cytometric cytotoxicity assay.

RESULTS

IL-15 (100-1000 U/mL) could replace IL-2 (1000 U/mL) in AIM V cultures to achieve efficient LAK cell expansion. However, IL-15-stimulated LAK cells exceeded cytotoxicity of IL-2-stimulated LAK cells against K562, notably at later culture points. In the powerful CellGro SCGM, LAK cells expanded over 28 days an average of 905-fold ± 320-fold standard error of the mean (SEM) for IL-2 (500 U/mL) and 484-fold ± 98-fold SEM for IL-15 (500 U/mL), and NK cells within such LAK cultures expanded an average of 2320-fold ± 975-fold SEM for IL-2 and 1084-fold ± 309-fold SEM for IL-15. Importantly, such IL-15-activated LAK-NK cells retained enhanced cytotoxicity at later culture points against K562 as well. IL-15-stimulated effectors were also highly cytotoxic against hematological targets MOLT-4 and KU812 and nontoxic against autologous nonmalignant cells. Interestingly, IL-15-LAK-NK cells showed overall significant upregulation of the main activating and inhibitory NK cell receptors after long-term cytokine stimulation.

CONCLUSIONS

Our results demonstrate the potential for IL-15 to support large-scale expansion of clinical-grade LAK-NK effectors, which could retain enhanced longer-term potency and preserve activation receptors in therapy of hematological malignancies. Protocols are readily clinically translatable.

From bone marrow transplantation to complex biological therapy

The major complications after bone marrow transplant are related to opportunistic infections or to graft-versus-host disease. Today, there is a wealth of information associated with bone marrow transplantation and new treatment approaches have been proposed to overcome these complications. Behind these new therapies, such as adoptive transfer of T cells or mesenchymal stem cell infusions, there is significant basic research to support these clinical advances. Most of this knowledge has derived from the development of animal models and intense laboratory work to test and confirm hypotheses. There is no doubt that basic research is still necessary to better understand the basis for clinical outcome improvements.

Allogeneic immunotherapy to optimize the graft-versus-tumor effect: concepts and controversies

This article focuses on the recent evolution of novel conditioning regimens in combination with adoptive cellular therapy in the allogeneic transplant setting for hematologic malignancies. Building on data from animal models, the field of allogeneic transplantation is undergoing a paradigm shift toward immunosuppressive regimens with less toxicity that allow donor hematopoietic engraftment in order to provide a graft-versus-tumor effect as the primary goal of transplantation, rather than chemoablation. In addition, the strategies described in this article, including the use of T-cell subsets as adoptive therapy, will apply to a much broader pool of patients than traditional transplant approaches, thereby allowing more patients with life-limiting illnesses, previously deemed ineligible, to pursue therapy with curative intent.

Cancer immunotherapy

Recent scientific advances have expanded our understanding of the immune system and its response to malignant cells. The clinical goal of tumour immunotherapy is to provide either passive or active immunity against malignancies by harnessing the immune system to target tumours. Monoclonal antibodies, cytokines, cellular immunotherapy, and vaccines have increasingly become successful therapeutic agents for the treatment of solid and haematological cancers in preclinical models, clinical trials, and practice. In this article, we review recent advances in the immunotherapy of cancer, focusing on new strategies and future perspectives as well as on clinical trials attempting to enhance the efficacy of immunotherapeutic modalities and translate this knowledge into effective cancer therapies.

Cellular immune reconstitution and its impact on clinical outcome in children with beta thalassemia major undergoing a matched related myeloablative allogeneic bone marrow transplant

We have prospectively analyzed cellular immune reconstitution (IR) in 63 consecutive pediatric patients with beta thalassemia major who underwent an HLA matched related allogeneic bone marrow transplant (BMT). Samples from bone marrow graft and posttransplant peripheral blood samples from recipients at specified time points were assessed for IR of cellular subsets. The median age of the cohort was 7 years, and there were 37 (59%) males. A CD34 cell dose above the median value of 7.3 x 10(6)/kg had a lower incidence of bacterial (P = .003) and fungal (P = .003) infections in the posttransplant period, and was not associated with an increased risk of graft-versus-host disease (GVHD). Among cases that did develop grade II-IV GVHD the absolute CD8 (116 versus 52 cells/microL, P = .012), CD8 naïve (74 versus 9 cells/microL, P = .005), and CD8 memory counts (44 versus 21 cells/microL, P = .010) were significantly higher on day 15. Fifteen patients (24%) rejected their graft (7 primary and 8 secondary). The day 28 natural killer (NK) cell count was significantly associated with secondary graft rejection, event-free survival (EFS), and overall survival (OS) (P = .044, .013, and .034, respectively). On a multivariate analysis, patients with a day 28 NK cell count below the median value of 142/microL had a significantly higher rejection rate (hazard ratio [HR] = 11.1, P = .038) and a lower EFS (HR = 16.3, P = .034).

Biologic characteristics of mesenchymal stromal cells and their clinical applications in pediatric patients

In the past few years, intensive research in the understanding of the biologic characteristics of the mesenchymal stromal cells has already led to some early clinical applications. The aim of this review is to summarize the latest information from basic science advances and the outcome of their use in clinical practice with a particular focus in pediatric patients. The minimum criteria required to identify mesenchymal stromal cells, their immunosuppressive-nonimmunogenic properties and their attribution in the treatment of graft-versus-host disease, in the acceleration of hematopoietic recovery, in tissue repair/tissue engineering and in the treatment of selected inherited disorders are discussed. Appropriate preclinical models, completion of ongoing and development of new clinical trials will establish the role of these cells in the treatment of both adult and pediatric patients.

Rapid and effective CD3 T-cell depletion with a magnetic cell sorting program to produce peripheral blood progenitor cell products for haploidentical transplantation in children and adults

BACKGROUND

Effective T-cell depletion is a prerequisite for haploidentical peripheral blood progenitor cell (PBPC) transplantation. This study was performed to investigate the performance of magnetic cell sorting-based direct large-scale T-cell depletion, which is an attractive alternative to standard PBPC enrichment procedures.

STUDY DESIGN AND METHODS

PBPCs were harvested from 11 human leukocyte antigen (HLA)-haploidentical donors. T cells labeled with anti-CD3-coated beads were depleted with a commercially available magnetic separation unit (CliniMACS, Miltenyi Biotec) with either the Depletion 2.1 (D2.1, n=11) or the novel Depletion 3.1 (D3.1, n=12) program. If indicated, additional CD34+ selections were performed (n=6). Eleven patients received T-cell-depleted grafts after reduced-intensity conditioning.

RESULTS

The median log T-cell depletion was better with the D2.1 compared to the D3.1 (log 3.6 vs. log 2.3, p<0.05) and was further improved by introducing an immunoglobulin G (IgG)-blocking step (log 4.5 and log 3.4, respectively). The D3.1 was superior to the D2.1 (p<0.05) in median recovery of CD34+ cells (90% vs. 78%) and in median recovery of CD3- cells (87% vs. 76%). The median processing times per 10(10) total cells were 0.90 hours (D2.1) and 0.35 hours (D3.1). The transplanted grafts (directly T-cell-depleted products with or without positively selected CD34+ cells) contained a median of 10.5 x 10(6) per kg CD34+, 0.93x10(5) per kg CD3+, and 11.6x10(6) per kg CD56+. Rapid engraftment was achieved in 10 patients. The incidences of acute graft-versus-host disease were less than 10 percent (Grade I/II) and 0 percent (Grade III/IV).

CONCLUSION

The novel D3.1 program with IgG blocking enables highly effective, time-saving large-scale T-cell depletion. Combining direct depletion techniques with standard CD34+ selection enables the composition of grafts optimized to the specific requirements of the patients.

Immune response to stem cells and strategies to induce tolerance

Although recent progress in cardiovascular tissue engineering has generated great expectations for the exploitation of stem cells to restore cardiac form and function, the prospects of a common mass-produced cell resource for clinically viable engineered tissues and organs remain problematic. The refinement of stem cell culture protocols to increase induction of the cardiomyocyte phenotype and the assembly of transplantable vascularized tissue are areas of intense current research, but the problem of immune rejection of heterologous cell type poses perhaps the most significant hurdle to overcome. This article focuses on the potential advantages and problems encountered with various stem cell sources for reconstruction of the damaged or failing myocardium or heart valves and also discusses the need for integrating advances in developmental and stem cell biology, immunology and tissue engineering to achieve the full potential of cardiac tissue engineering. The ultimate goal is to produce 'off-the-shelf' cells and tissues capable of inducing specific immune tolerance.

Mesenchymal stem cells: Immunobiology and therapeutic potential in kidney disease (Review Article)

Mesenchymal stem cells (MSC) are non-haematopoietic cells that are prevalent in the adult bone marrow but can also be isolated from a variety of other postnatal tissues. MSC are non-immunogenic and are immunosuppressive, with the ability to inhibit maturation of dendritic cells and suppress the function of naïve and memory T cells, B cells and NK cells. In addition to their immunomodulatory properties, MSC are capable of differentiating into various tissues of mesenchymal and non-mesenchymal origin and migrating to sites of tissue injury and inflammation to participate in tissue repair. A number of studies in animal models of cardiac injury, stroke and ischaemic renal injury have demonstrated the clinical potential of MSC in tissue regeneration and repair. MSC are currently being evaluated in various preclinical and clinical studies in humans and offer significant potential as a novel cellular therapy for tissue regeneration and immunological conditions. The present review focuses on the unique immunomodulatory and regenerative properties of MSC and their potential role in the treatment of kidney disease.

Natural-killer-cell-based treatment in haematopoietic stem-cell transplantation

Adoptive immunotherapy using natural killer (NK) cells is currently under investigation, especially in situations where anti-neoplastic effect is needed but infusion of T cells is considered hazardous, such as in recipients of haematopoietic stem-cell transplantation (HSCT) from haploidentical donors. NK-cell therapy is mainly but not exclusively investigated in the setting of allogeneic stem-cell transplantation. NK cells may induce potent anti-leukaemic and possibly anti-rejection activity, and may even mitigate graft-versus-host disease (GvHD). It remains to be determined whether such effects are clinically important and whether or not they are mediated mainly or exclusively by KIR-HLA class I interactions. Recent advances in graft engineering has provided methods for isolating large numbers of purified NK cells. Several groups have shown that clinical-grade NK cells at doses up to 10(7)/kg may be collected and purified for the purpose of infusion to patients. Early results in a limited number of patients show that these cell doses may be administered without adverse events and possibly without inducing GvHD. Further study is required to determine whether such infusions will be useful in preventing graft rejection, exerting graft-versus-leukaemia effects, and/or hastening immune recovery.

Phenotypic and cytolytic activity of Macaca nemestrina natural killer cells isolated from blood and expanded in vitro

Natural killer (NK) cells from nonhuman primates have not been completely characterized, and methods for expanding nonhuman primates NK cells in vitro have been described only in rhesus species. The purpose of this report was to characterize NK cells in pigtail macaques (Macaca nemestrina), a species that is frequently used in studies of transplantation biology/immunology, virology, vaccine development, and reproductive biology. NK cells from Macaca nemestrina peripheral blood were best defined by the expression of CD16 and CD8alpha, and the absence of CD3. Subsets of these cells express CD56, NKp30, and NKp46. An enhanced ability to kill K562 cells was not present in fluorescence activated cell sorted (FACS)-purified CD16-/CD3+ and CD16-/CD56+ cells isolated from fresh peripheral blood. However, FACS-purified CD16+/CD3- and CD16+/CD56- cells were highly efficient killers of K562 cells. Macaca nemestrina NK cells can be expanded by in vitro culturing of FACS-purified CD16+/CD2-/CD3-/CD56- cells, or from peripheral blood cells depleted of cells expressing CD3, CD4, and HLA-DR. Cells in these cultures expand 70-fold after 21 days of culturing. After culturing, these cells express high levels of natural cytotoxicity receptors (NCRs) NKp30 and NKp46. NK cell populations obtained from FACS-purified CD16+/CD3-, CD16+/CD56- cells and CD3/CD4/HLA-DR-depleted cells were highly efficient killers of K562 cells. These data suggest that a population of highly enriched cytolytic NK cells can be obtained from purified CD16+/CD3- and CD16+/CD56- cells obtained from peripheral blood, as well as from cells that have been cultured and expanded from peripheral blood that is depleted of CD3/CD4/HLA-DR-expressing cells.

NK cell-based immunotherapies against tumors

Natural killer (NK) cells provide the first line of defence against pathogens and tumors. Their activation status is regulated by pro-inflammatory cytokines and by ligands that either target inhibitory or activating cell surface receptors belonging to the immunoglobulin-like, C-type lectin or natural cytotoxicity receptor families. Apart from non-classical HLA-E, membrane-bound heat shock protein 70 (Hsp70) has been identified as a tumor-specific recognition structure for NK cells expressing high amounts of the C-type lectin receptor CD94, acting as one component of an activating heterodimeric receptor complex. Full-length Hsp70 protein (Hsp70) or the 14-mer Hsp70 peptide T-K-D-N-N-L-L-G-R-F-E-L-S-G (TKD) in combination with pro-inflammatory cytokines enhances the cytolytic activity of NK cells towards Hsp70 membrane-positive tumors. Based on these findings cytokine/TKD-activated NK cells were adoptively transferred in tumor patients. These findings were compared to results of clinical trials using cytokine-activated NK cells.

Novel approaches using natural killer cells in cancer therapy

Strategies are emerging to apply natural killer (NK) cells as therapeutic agents against a broad range of malignancies. Novel clinical approaches aim to overcome limitations of original therapies, which have utilized lymphokine activated killer cells or systemic cytokine treatments. Remarkable results, including survival improvements and amelioration of graft versus host disease, were obtained with alloreactive NK cells in some cases. Other approaches in clinical evaluation include targeting heat-shock protein (Hsp) 70 expressing tumors with pre-stimulated autologous NK cells or the application of an NK cell line, NK-92, with enhanced cytolytic activity. Further mechanistic insights into NK cell cytotoxicity are a prelude to improved clinical cancer therapies.

Prophylaxis and treatment of acute graft-versus-host disease

Acute graft-versus-host disease (GVHD) remains a major obstacle to successful allogeneic hematopoietic stem cell transplantation (HSCT). The ability to prevent GVHD--the application of successful prophylaxis--is crucial as treatment when prophylaxis fails or remains suboptimal. A calcineurin inhibitor in combination with methotrexate is still the mainstream regimen for prophylaxis of GVHD. Despite a steady increase in the repertoire of available drugs, corticosteroids remain the first-line therapy for patients who fail prevention and develop GVHD. Pan T-cell depletion studies suggest that success in prophylaxis and treatment of GVHD will depend on whether GVHD can be prevented without losing anti-malignancy and anti-infectious effects. Better understanding of the allogeneic response that is responsible for GVHD will facilitate the development of such an approach.

Pathophysiology of graft-versus-host disease

Complications of allogeneic hematopoietic stem cell transplantation (HSCT) remain barriers to its wider application for a variety of diseases. Graft-versus-host disease (GVHD) is the major cause of morbidity and mortality following allogeneic HSCT. GVHD can be considered an exaggerated, undesirable manifestation of a normal inflammatory mechanism, in which donor lymphocytes encounter foreign antigens in a milieu that fosters inflammation. Recent advances in the study of cytokine networks, chemokine gradients, and the direct mediators of cellular cytotoxicity have led to improved understanding of this complex syndrome. The pathophysiology of acute GVHD can be considered as a three-step process in which the innate and adaptive immune systems interact: (1) tissue damage to the recipient by the radiation/chemotherapy pretransplant conditioning regimen; (2) donor T-cell activation and clonal expansion; and (3) cellular and inflammatory factors. Here we review the immunologic interactions that cause clinical GVHD and discuss the risk factors and prophylactic strategies for acute GVHD according to this model.

Immunogenicity of adult mesenchymal stem cells: lessons from the fetal allograft

Herein we review recent data that support host tolerance of allogeneic adult mesenchymal stem cells (MSC). Evidence is emerging that donor MSC deploy a very powerful array of mechanisms that allow escape from host allogeneic responses. These mechanisms include limited expression of alloantigen by the stem cell and cell contact-dependent and -independent mechanisms. MSC modulate host dendritic cell and T cell function, promoting induction of suppressor or regulatory T cells. These effects are complemented by the induction of divisional arrest anergy in T cells and by stem cell production of soluble immunomodulatory factors, including interleukin-10, transforming growth factor-beta, prostaglandin E2, and hepatocyte growth factor. In addition, MSC express the enzyme indoleamine 2,3-dioxygenase, which creates a tryptophan-depleted milieu that promotes immunosuppression. We propose that these observations show striking similarity to emerging data on the maternal acceptance of the fetal allograft. This comparison suggests new approaches to determine the contribution of different mechanisms to the successful use of MSC in regenerative medicine.

The use of CD 34(+) mobilized peripheral blood as a donor cell source does not improve chimerism after in utero hematopoietic stem cell transplantation in non-human primates

In utero hematopoietic stem cell transplantation is a therapeutic procedure that could potentially cure many developmental diseases affecting the immune and hematopoietic systems. In most clinical and experimental settings of fetal hematopoietic transplantation the level of donor cell engraftment has been low, suggesting that even in the fetus there are significant barriers to donor cell engraftment. In postnatal hematopoietic transplantation donor cells obtained from mobilized peripheral blood engraft more rapidly than cells derived from marrow. We tested the hypothesis that use of donor hematopoietic/stem cells obtained from mobilized peripheral blood would improve engraftment and the level of chimerism after in utero transplantation in non-human primates. Despite the potential competitive advantage from the use of CD 34(+) from mobilized peripheral blood, the level of chimerism was not appreciably different from a group of animals receiving marrow-derived CD 34(+) donor cells. Based on these results, it is unlikely that this single change in cell source will influence the clinical outcome of fetal hematopoietic transplantation.

Mesenchymal stem cells avoid allogeneic rejection

Adult bone marrow derived mesenchymal stem cells offer the potential to open a new frontier in medicine. Regenerative medicine aims to replace effete cells in a broad range of conditions associated with damaged cartilage, bone, muscle, tendon and ligament. However the normal process of immune rejection of mismatched allogeneic tissue would appear to prevent the realisation of such ambitions. In fact mesenchymal stem cells avoid allogeneic rejection in humans and in animal models. These finding are supported by in vitro co-culture studies. Three broad mechanisms contribute to this effect. Firstly, mesenchymal stem cells are hypoimmunogenic, often lacking MHC-II and costimulatory molecule expression. Secondly, these stem cells prevent T cell responses indirectly through modulation of dendritic cells and directly by disrupting NK as well as CD8+ and CD4+ T cell function. Thirdly, mesenchymal stem cells induce a suppressive local microenvironment through the production of prostaglandins and interleukin-10 as well as by the expression of indoleamine 2,3,-dioxygenase, which depletes the local milieu of tryptophan. Comparison is made to maternal tolerance of the fetal allograft, and contrasted with the immune evasion mechanisms of tumor cells. Mesenchymal stem cells are a highly regulated self-renewing population of cells with potent mechanisms to avoid allogeneic rejection.

The Pathophysiology of Acute Graft-Versus-Host Disease

Despite improvements in allogeneic stem cell transplantation, acute graft-versus-host disease (GVHD) remains a significant problem after transplantation, and it is still a major cause of post-transplant mortality. Disease progression is characterized by the differentiation of alloreactive T cells to effector cells leading to tissue damage, recruitment of additional inflammatory cell populations and further cytokine dysregulation. To make the complex process of acute GVHD more explicit, the pathophysiology of acute GVHD is often divided into three different phases. This review summarizes the mechanisms involved in the three phases of acute GVHD.

Specific targeting of CD33(+) leukemia cells by a natural killer cell line modified with a chimeric receptor

We directed the human natural killer (NK) cell line YT by gene transfer of a humanized chimeric immunoglobulin T cell receptor to CD33, a marker on myeloid leukemias. The chimeric receptor was generated using a CD33 specific single-chain Fv (scFv) fragment based on the humanized antibody HuM195, the human IgG1 Fc domains and the human CD3 zeta signal chain. YT cells transfected by electroporation with the chimeric receptor gene specifically lysed the acute myeloid leukemia (AML) cell line KG1. This gene-modified NK cell line available in unlimited source could be an attractive tool in immunotherapy.

Application of natural killer T-cells to posttransplantation immunotherapy

Graft-versus-host disease (GVHD) and graft-versus leukemia (GVL) effects are closely related to each other after allogeneic stem cell transplantation. This association exists because of the extensive and complicated interaction between cellular donor components and recipient components concomitant with cytokine storms. It has been demonstrated that part of this interaction may be related to the induction of a variety of regulatory cells, such as regulatory T-cells and natural killer T (NKT) cells. A lower number of NKT cells may be found in patients with autoimmune diseases, cancer, viral infection, and severe GVHD. When activated, NKT cells rapidly release suppressive cytokines, such as interleukin 4 (IL-4), IL-10, and IL-13, as well as inflammatory cytokines, such as interferon gamma and tumor necrosis factor alpha. NKT cells therefore act as a double-edged sword in their progressive or suppressive effects on diseases. Such contradictory phenomena may be related to the function or types of antigen-presenting cells (APCs) in response to their ligand. A single-dose injection of a ligand for NKT cells, alpha-galactosylceramide (alpha-GalCer), can induce immunity through fully mature dendritic cells in an antigen-specific manner. By contrast, multiple injections of alpha-GalCer would induce tolerance, which may be caused by immature APCs. This response suggests that the function of NKT cells can be determined by alpha-GalCer for controlling the immune response. Furthermore, activation of NKT cells followed by activation of APCs and IL-12 production may lead to activation of NK cells and suppress GVHD in mismatched major histocompatibility complex combinations or may induce GVL effects. Control and modification of NKT cell function may play an important role in regulating GVHD/GVL effects.

Difference in target cell recognition of naive and activated human natural killer cells: Role of Haymaker (p38.5) in tumoricidal activity

The human Haymaker gene, at 19q13.2 in the Leukocyte Receptor-Receptor-Related Complexes, encodes a 38.5-kDa non-MHC protein found on the plasma membrane of tumor cell lines that are highly susceptible to lysis by naive (unstimulated) natural killer (nNK) cells. We hypothesized that Haymaker might act as a ligand in the tumoricidal activity of nNK cells because this molecule was absent from the surface of malignant cell lines that were resistant to their cytolytic activity. We examined the capacity of this protein to act as a ligand in the tumoricidal activity of freshly isolated nNK cells and IL-2 activated natural killer (NK) cells (aNK cells) by performing blocking studies with recombinant Haymaker (r-Haymaker) and peptide-specific anti-Haymaker antibodies. These competition studies demonstrated that both r-Haymaker and anti-Haymaker antibodies inhibited the tumoricidal function of nNK but not aNK cells. We conclude that Haymaker likely plays an essential role as an activating ligand in nNK-cell-mediated cytotoxicity, whereas the tumoricidal activity of aNK cells is, for the most part, induced by other molecules.

Allogeneic peripheral blood stem cell graft composition affects early T-cell chimaerism and later clinical outcomes after non-myeloablative conditioning

We have studied the influence of cell subsets [CD34, CD3, CD4, CD8, CD14, CD20, natural killer (NK; CD3(-)/CD56(+)), NKT (CD3(+)/CD56(+)), DC1, and DC2 cells] of granulocyte colony-stimulating factor mobilized peripheral blood stem cells (PBSC) on early T-cell chimaerism and later clinical outcomes in 125 patients with haematological malignancies who received human leucocyte antigen (HLA)-matched related grafts after non-myeloablative conditioning. Conditioning consisted of 2 Gy total body irradiation (TBI) alone (n = 28), or 2 Gy TBI preceded by either 90 mg/m(2) fludarabine (n = 62) or planned autologous haematopoietic cell transplantation (HCT) (n = 35). Post-transplant immunosuppression included mycophenolate mofetil and ciclosporin. Multivariate analysis showed that higher numbers of grafted NK cells predicted higher early T-cell chimaerism (P = 0.03), while higher numbers of B cells were associated with better clinical outcomes and a higher risk for chronic graft-versus-host disease (P = 0.05). Higher numbers of CD14(+) cells were associated with worse overall survival (P = 0.03), while higher numbers of CD34(+) cells showed better survival (P = 0.03). The addition of fludarabine or autologous HCT predicted higher early T-cell chimaerism (P = 0.001), while advanced donor age predicted lower chimaerism (P < or = 0.02). Patients with aggressive diseases were at higher risk for relapse/disease progression, and shorter progression-free and overall survival (P < 0.01). These results suggest that the dosing of certain cellular subsets of PBSC products can influence important outcomes post-HCT after non-myeloablative conditioning.

Use of natural killer cells in hematopoetic stem cell transplantation

Adoptive immunotherapy using natural killer (NK) cells may prove useful, especially in situations where infusion of T cells is impractical such as in recipients of haploidentical stem cell transplantation (HSCT) from haploidentical donors. NK cells may induce potent antileukemic and possibly antirejection activity and may even mitigate graft versus host disease (GvHD). Whether such effects are clinically important and whether they are mediated mainly or exclusively by KIR-HLA class I interactions remains to be determined. Recent advances in graft engineering provide for methods to isolate large numbers of purified NK cells. Several groups have shown that clinical grade NK cells up to a dose of 10(7)/kg may be collected and purified for the purpose of infusion to patients. Early results, in a limited number of patients, show that these cell doses may be administered without adverse events and without inducing GvHD. Whether such infusions will be useful in preventing graft rejection, or exerting graft versus leukemia effects and hastening immune recovery requires further study.

IL-2-activated cord blood mononuclear cells

BACKGROUND

[corrected] Recent findings in cord blood (CB) research indicate the potential clinical usefulness of IL-2-activated CB in eradication of minimal malignant residual disease after hematopoietic stem cell transplantation. This feasible approach to immunotherapy merits further pre-clinical investigations using human tumor models of hematologic malignancy.

METHODS

The aim of our study was to compare the anti-tumor potential of CB mononuclear cells (MNC), matured in the presence of IL-2, to BM, and to determine phenotype and cytokine secretion in IL-2 CB MNC culture during the peak of their anti-leukemia cytotoxic activity. Phenotype change was analysed with flow cytometry, cytokine secretion with ELISA tests and cytotoxic activity with cytotoxicity assays.

RESULTS

Following IL-2 maturation, the phenotype of CB MNC was remarkably changed. Lengthening IL-2 culture to 8 days significantly increased CD8+, CD16+ CD56+, CD56+ and CD56+ CD8+ populations. Interestingly, FACS analyzes revealed the occurrence of CD8+ CD56+ cells that were not present in non-stimulated CB. Cultures progressively produced higher levels of INF-gamma, TNF-alpha and GM-SCF. The IL-2-activated cells manifested potent lytic capabilities against both NK- and LAK-sensitive tumor cell targets.

DISCUSSION

At the peak of cytotoxic activity during 8-day IL-2 CB MNC culture, we found increased numbers of various cytotoxic cells and increased secretion of cytokines that may contribute further to their potential therapeutic effect. The duration of CB IL-2 cultures may be crucial for successful application of CB in transplant situations to boost the CB GvL.

A one-step large-scale method for T- and B-cell depletion of mobilized PBSC for allogeneic transplantation

BACKGROUND

The presence of T and B cells in allogeneic grafts contributes to GvHD and to EBV-associated lymphoproliferative disease (LPD). Depletion of T and B cells from the graft decreases the risk of these complications.

METHODS

T and B cells were depleted from mobilized peripheral stem cells from volunteer donors (n=5) using anti-CD3 and anti-CD19 Abs conjugated to magnetic microbeads, and the CliniMACS device. The function of the stem cells after depletion was evaluated using colony assays and non-obese diabetic (NOD)/SCID repopulating experiments.

RESULTS

The mean mononuclear cell (MNC) count prior to T- and B-cell depletion was 2.19x10(10) (range 1.48-3.53). After depletion, the mean percentage of contaminating T cells was 0.02% (range 0.01-0.04%) with a mean log(10) depletion of 3.4 (range 3-3.8). The mean percentage of contaminating B cells was 0.1% (range 0.01-0.4%) with a mean log(10) depletion of 2.2 (range 1.4-3). The mean recovery of CD3- and CD19-negative MNCs after depletion was 70% (range 54-88%) and the mean recovery of CD34(+) stem cells was 69% (range 52-98%). The mean number of natural killer (NK) cells after T- and B-cell depletion was 5.2x10(8) (range 2-10x10(8)). In vitro colony assays and in vivo NOD/SCID repopulation assays showed no negative impact of this method on the function of the hematopoietic stem cells.

DISCUSSION

Our results show that the CliniMACS system can be used to efficiently deplete PBSC of T and B cells simultaneously, without adverse effect on the graft.

Fetal Immune Suppression as Adjunctive Therapy for In Utero Hematopoietic Stem Cell Transplantation in Nonhuman Primates

In utero hematopoietic stem cell transplantation could potentially be used to treat many genetic diseases but rarely has been successful except in severe immunodeficiency syndromes. We explored two ways to potentially increase chimerism in a nonhuman primate model: (a) fetal immune suppression at the time of transplantation and (b) postnatal donor stem cell infusion. Fetal Macaca nemestrina treated with a combination of the corticosteroid betamethasone (0.9 mg/kg) and rabbit thymoglobulin (ATG; 50 mg/kg) were given haploidentical, marrow-derived, CD34+ -enriched donor cells. Animals treated postnatally received either donor-derived T cell-depleted or CD34+ -enriched marrow cells. Chimerism was determined by traditional and real-time polymerase chain reaction from marrow, marrow progenitors, peripheral blood, and mature peripheral blood progeny. After birth, the level of chimerism in the progenitor population was higher in the immune-suppressed animals relative to controls (11.3% +/- 2.7% and 5.1% +/- 1.5%, respectively; p = .057). Chimerism remained significantly elevated in both marrow (p = .02) and fluorescence-activated cell sorted and purified CD34+ cells (p = .01) relative to control animals at > or = 14 months of age. Peripheral blood chimerism, both at birth and long term, was similar in immune-suppressed and control animals. In the animals receiving postnatal donor cell infusions, there was an initial increase in progenitor chimerism; however, at 6-month follow-up, the level of chimerism was unchanged from the preinfusion values. Although fetal immune suppression was associated with an increase in the level of progenitor and marrow chimerism, the total contribution to marrow and the levels of mature donor progeny in the peripheral blood remained low. The level of long-term chimerism also was not improved with postnatal donor cell infusion.

NK cells: innate immunity against hematological malignancies?

Recent advances in the treatment of malignant haemopathies enable increased remission and cure rates, however, many patients relapse and finally die. Although specific immunity mediated by cytolytic T-lymphocytes might have an anti-cancer role, tumours escape from T-cell-based immune surveillance using various mechanisms, such as downregulation, mutation or loss of HLA class I molecules. As a consequence, these transformed cells could become targets for natural killer (NK) cells, whose cytotoxic capabilities are not blocked by HLA class I molecule engagement by specific inhibitory receptors. Novel developments in NK-cell research, particularly the identification of the role of non-HLA-restricted activating receptors (and in some cases of their ligands), have recently enabled us to reconsider NK-cell interactions with haematological malignant cells.

Differential expansion of umbilical cord blood mononuclear cell–derived natural killer cells dependent on the dose of interleukin-15 with Flt3L

OBJECTIVE

We investigated the effect of interleukin-15 (IL-15) with Flt3 ligand (Flt3L) on the expansion and activation of NK cells derived from umbilical cord blood mononuclear cells (UCB-MNCs).

MATERIALS AND METHODS

UCB-MNCs were cultured at 1 to 100 ng/mL of IL-15 + Flt3L (10 ng/mL) compared with 1 to 500 ng/mL of IL-2 + Flt3L (10 ng/mL). Cultured cells were assessed for surface marker and we calculated absolute number of NK cells and T cells. The cytotoxic activity was analyzed with purified NK cells.

RESULTS

After 2 weeks culture with 5 ng/mL of IL-15 + Flt3L, the fold inductions of absolute number of NK cells significantly increased to 20.9-fold +/- 9.3-fold of the number of NK cells on day 0 (p < 0.05), with 24.4-fold +/- 16.1-fold of T cells. But with 50 ng/mL of IL-15 + Flt3L, fold induction of NK cells decreased to 5.1-fold +/- 3.9-fold, while T cells showed 34.8-fold +/- 18.7-fold (n = 8). The proportion of NK vs T cells showed to be significantly higher (1.61 +/- 0.91) with 5 ng/mL of IL-15 than with 50 ng/mL of IL-15 (0.12 +/- 0.03). Such proportional change of NK/T cells could not be observed with IL-2. Immunophenotypes of CD56, CD16, LFA1, CD94, CD8, and perforin of cultured NK cells with 10 ng/mL of IL-15 + Flt3L showed the same pattern of those with 50 ng/mL of IL-2 + Flt3L. Cytotoxic activity against K562 of cultured NK cells resulted in the same level as adult peripheral blood (PB)-derived NK cells.

CONCLUSIONS

Higher induction of NK cells derived from UCB-MNCs was achieved by low dose (5 to 10 ng/mL) rather than high dose (> 50 ng/mL) of IL-15.

Allogeneic versus syngeneic killer splenocytes as effector cells for the induction of graft-versus-tumor effect

The effect of allogeneic versus syngeneic killer cells derived from normal or severe combined immunodeficiency disease (SCID) mice was evaluated for induction of antitumor reaction in a murine model of mammary carcinoma. Tumor cells of H-2d origin were injected intravenously into H-2(d/b) mice 24 hours after total body irradiation (4 Gy). On the following day, lymphokine-activated killer (LAK) splenocytes, derived from either minor (H-2d) or major (H-2b) histocompatibility complex (MHC)-mismatched parental normal mice or MHC (H-2b)-mismatched SCID mice, were given intravenously. LAK cells of H-2d normal or SCID mice, syngeneic to the tumor, were inoculated in parallel. The results show that LAK cells derived from minor histocompatibility complex-mismatched or MHC-mismatched parental normal mice improved the probability of tumor-free survival as compared with LAK cells syngeneic to the tumor cells, but they aggravated the severity of graft-versus-host disease. SCID splenocytes serving as a source of natural killer (NK) cells were expanded and activated in vitro by rIL-2 to obtain a sufficient number of DX5+ CD3- CD8- NK cells (SCID-LAK). H-2b SCID-LAK cells did not cause graft-versus-host disease and significantly delayed tumor growth compared with syngeneic H-2d SCID-LAK cells, as indicated by tumor colony assays in vitro and adoptive transfer experiments. However, the graft-versus-tumor effect was not long lasting, and treated mice finally died of tumor. Our results show an advantage of allogeneic over syngeneic cell therapy for achieving a graft-versus-tumor effect by rIL-2-activated T cells and NK cells. Periodic repetition of NK treatments may be required to achieve more durable antitumor effects.

Mesenchymal stem cells inhibit the formation of cytotoxic T lymphocytes, but not activated cytotoxic T lymphocytes or natural killer cells

BACKGROUND

Mesenchymal stem cells (MSCs) can reduce the incidence of graft-versus-host disease because of their ability to inhibit T-lymphocyte proliferation. There are no publications on the effect that MSCs have on cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells, effector cells vital for the graft-versus-leukemia effect.

METHODS

Cytotoxic T cells were primed in mixed lymphocyte culture (MLC) against irradiated stimulator lymphocytes, and irradiated third-party MSCs were added at different time points. The CTLs were collected, and their cytotoxic potential was analyzed in a chromium-release assay against the same stimulator cells as in the MLC. Purified NK cells were mixed with irradiated MSCs, and the lysis was measured in chromium-release assay against K562 target cells.

RESULTS

We found that MSCs inhibited CTL-mediated lysis by 70% if added at the beginning of the 6-day MLC. The lysis was not affected on day 3 or in the cytotoxic phase. Furthermore, MSCs inhibited the formation of cytotoxic lymphocytes when the cells were separated in a transwell system, which indicates that the effect is mediated by a soluble factor. NK cell-mediated lysis of K562 cells was not inhibited by MSCs. MSCs did not induce proliferation of allogeneic lymphocytes, and they were not lysed by allogeneic CTLs or NK cells.

CONCLUSION

Our findings indicate that MSCs escape recognition by CTLs and alloreactive NK cells, and inhibit the formation of cytotoxic T cells by secreting a soluble factor, but that they do not interfere with CTLs and NK cell lysis.

Phenotypic analysis of human BM T-cell depleted by soybean lectin agglutination and E rosetting with sheep RBC: relative enrichment of NK cells and a CD3(+),CD2(-dim) population

BACKGROUND

T-cell depletion (TCD) of BM allows transplantation across HLA barriers. Although different methods are used throughout the world, the optimal application of TCD still remains unclear, partly due to the lack of thorough analyses of the cellular fractions eliminated or retained in each method, and their possible implications regarding GvHD, GvL, or engraftment. We have analyzed the phenotype of the successive fractions of 19 BM samples depleted by soybean lectin agglutination and sheep erythrocyte rosetting (elimination of T cells that form rosettes through CD2), focusing on the final fraction infused to patients.

METHODS

Analysis was performed using three-color flow cytometry and strategies for optimal staining and individualism of the subsets of interest.

RESULTS

The relative composition of the lymphoid population varied significantly along the successive steps in TCD: at the agglutination step, B cells and CD4 T cells are greatly reduced, while natural killer cells (NK) and TCRgammadelta+ T are augmented. The rosetting steps imply the relative enrichment of CD2-dim T cells, together with a further rise in the proportion of NK and double-negative T cells frequently TCRgammadelta+.

DISCUSSION

The presence of minor subsets of CD2- TCRgammadelta+ and CD2- TCRalphabeta T cells has already been described in the peripheral blood of normal individuals. We report that, by using this method of TCD, CD2-dim T cells, frequently TCRgammadelta+, are retained in the grafts and infused in patients, together with NK cells as the main lymphoid population. We discuss the possible implications of these populations in the biology of the graft, regarding GvHD, GvL and engraftment.

The Pathophysiology of Acute Graft-versus-Host Disease

The pathophysiology of acute graft-versus-host disease (GVHD) is a complex process that can be conceptualized in three phases. In the first phase, high-dose chemoradiotherapy causes damage to host tissues, including a self-limited burst of inflammatory cytokines such as tumor necrosis factor (TNF)-alpha and interleukin 1. These cytokines activate host antigen-presenting cells (APCs). In the second phase, donor T-cells recognize alloantigens on host APCs. These activated T-cells then proliferate, differentiate into effector cells, and secrete cytokines, particularly interferon (IFN)-gamma. In the third phase, target cells undergo apoptosis mediated by cellular effectors (eg, donor cytotoxic T-lymphocytes) and inflammatory cytokines such as TNF-alpha. TNF-alpha secretion is amplified by stimuli such as endotoxin that leaks across damaged gastrointestinal mucosa injured by the chemoradiotherapy in the first phase. TNF-alpha and IFN-gamma cause further injury to gastrointestinal epithelium, causing more endotoxin leakage and establishing a positive inflammatory feedback loop. These events are examined in detail in the following review.

Rapid improvement of disseminated intravascular coagulation by donor leukocyte infusions in a patient with promyelocytic crisis of chronic myelogenous leukemia after reduced-intensity stem cell transplantation from an HLA 2-antigen-mismatched mother

Donor leukocyte infusion (DLI) is recognized as effective therapy for relapse after stem cell transplantation in patients with chronic myelogenous leukemia (CML). However, the clinical efficacy of DLI in the advanced phase of CML or other types of leukemia has not been clearly defined because of its varying degree of success. We describe a 22-year-old male patient with promyelocytic crisis of CML who had a relapse after peripheral blood stem cell transplantation, under reduced-intensity conditioning, from his HLA 2-antigen-mismatched mother. Complete hematologic remission was obtained after transplantation. However, a relapse that occurred on day 66 posttransplantion was characterized by an increase in number of leukemic promyelocytes with simultaneous exacerbation of disseminated intravascular coagulation (DIC). The patient received DLI containing 1 x 10(7)/kg CD3+ cells on day 73. Because rapid improvement of DIC paralleled the decrease in leukemic cells and because it was observed soon after DLI and before the development of acute graft-versus-host disease (GVHD), we hypothesized that leukemia-specific cells other than natural killer cells or cytotoxic T-cells unrelated to GVHD played a role in the graft-versus-leukemia effect observed in our patient. In addition, this may be the first report of effective correction of DIC by DLI after stem cell transplantation.

Alloreactive killer cells: hindrance and help for haematopoietic transplants

Haematopoietic-cell transplantation is a treatment for leukaemia and lymphoma. To reduce the incidence of graft-versus-host disease (GVHD) caused by transplanted T cells, donors and recipients are HLA matched. For patients for whom a matched donor is not available, one option is transplantation from an HLA-mismatched relative who shares one HLA haplotype. This procedure is distinguished by the use of a stronger conditioning regimen for the patient and of a T-cell-depleted graft containing numerous stem cells. After transplantation, natural killer cells are prevalent, and they can include alloreactive cells that kill tumour cells and prevent GVHD. The alloreactions seem to be determined by the mismatched HLA class I ligands and their killer-cell immunoglobulin-like receptors.

New strategies for prevention and treatment of graft-versus-host disease and for induction of graft-versus-leukemia effects

Graft-versus-host disease (GVHD) continues to be a problem in allogeneic hemopoietic stem cell transplantation; however, our understanding of the basic pathophysiology of GVHD has improved. Although not all data obtained from murine or other animal models can be extrapolated to the clinic, there are leads that deserve to be pursued. The skin, intestinal tract, and liver are the 3 major target organs of GVHD and share the feature of presenting a barrier to the "environment" of the host. There is evidence that the damage inflicted to these organs, the epithelial and endothelial cells in particular, by the conditioning regimen causes a release of various cytokines and a penetration of endotoxin into the systemic circulation. According to these observations, the nonimmunologic aspects of GVHD have been likened to an inflammatory process. If this characterization is valid, blocking these nonspecific inflammatory changes would ameliorate GVHD without interfering with the graft-versus-leukemia (GVL) reaction. In fact, one study has shown a substantial amelioration of GVHD with a molecule that directly blocks endotoxin. Clinical data also suggest that patients with organ dysfunction early after transplantation that is presumed to be treatment related may benefit from preemptive interventions aimed at controlling GVHD. Furthermore, there is growing evidence that the mechanisms involved in GVHD may differ from organ to organ (for example, Fas/Fas-ligand interactions in the liver versus tumor necrosis factor alpha/receptor interactions in the intestinal tract), and from a therapeutic point of view, the time of onset of clinical GVHD may be important in choosing the appropriate therapy. Thus, combinations of interventions chosen and timed appropriately may be more effective in preventing and managing GVHD than are the standard across-the-board approaches that have been used so far. Such a strategy may also be successful in maintaining a GVL effect and possibly in incorporating direct antileukemic therapy, such as the use of cytotoxic T-cells directed at minor histocompatibility antigens, without increasing the risk of GVHD. The development of nonmyeloablative conditioning regimens and the observations on GVHD kinetics and the progression or eradication of leukemia with that strategy are likely to add new insights into how one can optimally combine various modalities to achieve engraftment, prevent GVHD, and at the same time maintain a GVL effect.

New Developments in Allotransplant Immunology

After allogeneic stem cell transplantation, the establishment of the donor’s immune system in an antigenically distinct recipient confers a therapeutic graft-versus-malignancy effect, but also causes graft-versus-host disease (GVHD) and protracted immune dysfunction. In the last decade, a molecular-level description of alloimmune interactions and the process of immune recovery leading to tolerance has emerged. Here, new developments in understanding alloresponses, genetic factors that modify them, and strategies to control immune reconstitution are described.

In Section I, Dr. John Barrett and colleagues describe the cellular and molecular basis of the alloresponse and the mechanisms underlying the three major outcomes of engraftment, GVHD and the graft-versus-leukemia (GVL) effect. Increasing knowledge of leukemia-restricted antigens suggests ways to separate GVHD and GVL. Recent findings highlight a central role of hematopoietic-derived antigen-presenting cells in the initiation of GVHD and distinct properties of natural killer (NK) cell alloreactivity in engraftment and GVL that are of therapeutic importance. Finally, a detailed map of cellular immune recovery post-transplant is emerging which highlights the importance of post-thymic lymphocytes in determining outcome in the critical first few months following stem cell transplantation. Factors that modify immune reconstitution include immunosuppression, GVHD, the cytokine milieu and poorly-defined homeostatic mechanisms which encourage irregular T cell expansions driven by immunodominant T cell–antigen interactions.

In Section II, Prof. Anne Dickinson and colleagues describe genetic polymorphisms outside the human leukocyte antigen (HLA) system that determine the nature of immune reconstitution after allogeneic stem cell transplantation (SCT) and thereby affect transplant outcomethrough GVHD, GVL, and transplant-related mortality. Polymorphisms in cytokine gene promotors and other less characterized genes affect the cytokine milieu of the recipient and the immune reactivity of the donor. Some cytokine gene polymorphisms are significantly associated with transplant outcome. Other non-HLA genes strongly affecting alloresponses code for minor histocompatibility antigens (mHA). Differences between donor and recipient mHA cause GVHD or GVL reactions or graft rejection. Both cytokine gene polymorphisms (CGP) and mHA differences resulting on donor-recipient incompatibilities can be jointly assessed in the skin explant assay as a functional way to select the most suitable donor or the best transplant approach for the recipient.

In Section III, Dr. Nelson Chao describes non-pharmaceutical techniques to control immune reconstitution post-transplant. T cells stimulated by host alloantigens can be distinguished from resting T cells by the expression of a variety of activation markers (IL-2 receptor, FAS, CD69, CD71) and by an increased photosensitivity to rhodamine dyes. These differences form the basis for eliminating GVHD-reactive T cells in vitro while conserving GVL and anti-viral immunity. Other attempts to control immune reactions post-transplant include the insertion of suicide genes into the transplanted T cells for effective termination of GVHD reactions, the removal of CD62 ligand expressing cells, and the modulation of T cell reactivity by favoring Th2, Tc2 lymphocyte subset expansion. These technologies could eliminate GVHD while preserving T cell responses to leukemia and reactivating viruses.