Graft-versus-host-related immunosuppression is induced in mixed chimeras by alloresponses against either host or donor lymphohematopoietic cells

Tolerance in intestinal transplantation

Intestinal transplantation (ITx) is highly immunogenic, resulting in the need for high levels of immunosuppression, with frequent complications along with high rejection rates. Tolerance induction would provide a solution to these limitations. Detailed studies of alloreactive T cell clones as well as multiparameter flow cytometry in the graft and peripheral tissues have provided evidence for several tolerance mechanisms that occur spontaneously following ITx, which might provide targets for further interventions. These include the frequent occurrence of macrochimerism and engraftment in the recipient bone marrow of donor hematopoietic stem and progenitor cells carried in the allograft. These phenomena are seen most frequently in recipients of multivisceral transplants and are associated with reduced rejection rates. They reflect powerful graft-vs-host responses that enter the peripheral lymphoid system and bone marrow after expanding within and emigrating from the allograft. Several mechanisms of tolerance that may result from this lymphohematopoietic graft-vs-host response are discussed. Transcriptional profiling in quiescent allografts reveals tolerization of pre-existing host-vs-graft-reactive T cells that enter the allograft mucosa and become tissue-resident memory cells. Dissection of the pathways driving and maintaining this tolerant tissue-resident state among donor-reactive T cells will allow controlled tolerance induction through specific therapeutic approaches.

Current Advances in Graft-versus-host Disease After Intestinal Transplantation

Graft-versus-host disease (GvHD) remains a potentially fatal complication following intestinal transplant (ITx). Over the past decade, advances in the understanding of the pathophysiology of this complex immunological phenomenon have led to the reassessment of the host systemic immune response and have created a gateway for novel preventive and therapeutic strategies. Although sufficient evidence dictates the use of corticosteroids as a first-line option, the treatment for refractory disease remains contentious and lacks a standardized therapeutic approach. Timely diagnosis remains crucial, and the advent of chimerism detection and immunological biomarkers have transformed the identification, prognostication, and potential for survival after GvHD in ITx. The objectives of the following review aim to discuss the clinical and diagnostic features, pathophysiology, advances in immune biomarkers, as well as therapeutic opportunities in the prevention and treatment of GvHD in ITx.

Leveraging the lymphohematopoietic graft-versus-host reaction (LGVHR) to achieve allograft tolerance and restore self tolerance with minimal toxicity

Mixed allogeneic chimerism has considerable potential to advance the achievement of immune tolerance to alloantigens for transplantation and the restoration of self-tolerance in patients with autoimmune disease. In this article, I review evidence that graft-versus-host (GVH) alloreactivity without graft-vs-host disease (GVHD), termed a lymphohematopoietic graft-vs-host reaction (LGVHR), can promote the induction of mixed chimerism with minimal toxicity. LGVHR was originally shown to occur in an animal model when non-tolerant donor lymphocytes were administered to mixed chimeras in the absence of inflammatory stimuli and was found to mediate powerful graft-vs-leukemia/lymphoma effects without GVHD. Recent large animal studies suggest a role for LGVHR in promoting durable mixed chimerism and the demonstration that LGVHR promotes chimerism in human intestinal allograft recipients has led to a pilot study aiming to achieve durable mixed chimerism.

Inverted direct allorecognition triggers early donor-specific antibody responses after transplantation

The generation of antibodies against donor-specific major histocompatibility complex (MHC) antigens, a type of donor-specific antibodies (DSAs), after transplantation requires that recipient's allospecific B cells receive help from T cells. The current dogma holds that this help is exclusively provided by the recipient's CD4+ T cells that recognize complexes of recipient's MHC II molecules and peptides derived from donor-specific MHC alloantigens, a process called indirect allorecognition. Here, we demonstrated that, after allogeneic heart transplantation, CD3ε knockout recipient mice lacking T cells generate a rapid, transient wave of switched alloantibodies, predominantly directed against MHC I molecules. This is due to the presence of donor CD4+ T cells within the graft that recognize intact recipient's MHC II molecules expressed by B cell receptor-activated allospecific B cells. Indirect evidence suggests that this inverted direct pathway is also operant in patients after transplantation. Resident memory donor CD4+ T cells were observed in perfusion liquids of human renal and lung grafts and acquired B cell helper functions upon in vitro stimulation. Furthermore, T follicular helper cells, specialized in helping B cells, were abundant in mucosa-associated lymphoid tissue of lung and intestinal grafts. In the latter, more graft-derived passenger T cells correlated with the detection of donor T cells in recipient's circulation; this, in turn, was associated with an early transient anti-MHC I DSA response and worse transplantation outcomes. We conclude that this inverted direct allorecognition is a possible explanation for the early transient anti-MHC DSA responses frequently observed after lung or intestinal transplantations.

High Throughput Human T Cell Receptor Sequencing: A New Window Into Repertoire Establishment and Alloreactivity

Recent advances in high throughput sequencing (HTS) of T cell receptors (TCRs) and in transcriptomic analysis, particularly at the single cell level, have opened the door to a new level of understanding of human immunology and immune-related diseases. In this article, we discuss the use of HTS of TCRs to discern the factors controlling human T cell repertoire development and how this approach can be used in combination with human immune system (HIS) mouse models to understand human repertoire selection in an unprecedented manner. An exceptionally high proportion of human T cells has alloreactive potential, which can best be understood as a consequence of the processes governing thymic selection. High throughput TCR sequencing has allowed assessment of the development, magnitude and nature of the human alloresponse at a new level and has provided a tool for tracking the fate of pre-transplant-defined donor- and host-reactive TCRs following transplantation. New insights into human allograft rejection and tolerance obtained with this method in combination with single cell transcriptional analyses are reviewed here.

Lymphohematopoietic graft-versus-host responses promote mixed chimerism in patients receiving intestinal transplantation

In humans receiving intestinal transplantation (ITx), long-term multilineage blood chimerism often develops. Donor T cell macrochimerism (≥4%) frequently occurs without graft-versus-host disease (GVHD) and is associated with reduced rejection. Here we demonstrate that patients with macrochimerism had high graft-versus-host (GvH) to host-versus-graft (HvG) T cell clonal ratios in their allografts. These GvH clones entered the circulation, where their peak levels were associated with declines in HvG clones early after transplant, suggesting that GvH reactions may contribute to chimerism and control HvG responses without causing GVHD. Consistently, donor-derived T cells, including GvH clones, and CD34+ hematopoietic stem and progenitor cells (HSPCs) were simultaneously detected in the recipients' BM more than 100 days after transplant. Individual GvH clones appeared in ileal mucosa or PBMCs before detection in recipient BM, consistent with an intestinal mucosal origin, where donor GvH-reactive T cells expanded early upon entry of recipient APCs into the graft. These results, combined with cytotoxic single-cell transcriptional profiles of donor T cells in recipient BM, suggest that tissue-resident GvH-reactive donor T cells migrated into the recipient circulation and BM, where they destroyed recipient hematopoietic cells through cytolytic effector functions and promoted engraftment of graft-derived HSPCs that maintain chimerism. These mechanisms suggest an approach to achieving intestinal allograft tolerance.

An Experience of Donor Lymphocyte Infusion after Reduced-Intensity Conditioning Allogeneic Hematopoietic Stem Cell Transplantation for Chronic Granulomatous Disease

Allogeneic hematopoietic stem-cell transplantation is a well-known curative treatment for patients with chronic granulomatous disease. We present our experiment regarding ten patients with chronic granulomatous disease who underwent a reduced intensity conditioning regimen consisting of melfalan, fludarabine, and antithymocyte globulin. Donor lymphocyte infusion was used in three representative patients who developed mixed donor chimerism. After at least 2 years of median follow-up, 8 of the 10 patients are alive and well.

Bone marrow aplasia following donor lymphocyte infusion in 4-year-old patient with chronic granulomatous disease after allogeneic stem cell transplantation: case report

Donor lymphocyte infusion (DLI) is typically used in 3 clinical situations: therapeutically for proven relapse of malignancy, prophylactically in patients with high-risk of relapse, and in case of mixed chimerism. Mixed chimerism, which occur after transplantation can be a sign of possible rejection. In case of increased mixed chimerism, immunotherapy with donor lymphocyte infusions could reverse this process. After DLI, both acute and chronic graft-versus-host disease and marrow aplasia are well-known toxicities. In this paper, we present a case report of young patient with chronic granulomatous disease (CGD) after allogeneic hematopoietic stem cell transplantation (allo-HSCT), with successful immunotherapy following mixed chimerism, which was complicated by bone marrow aplasia that required a second stem cell infusion. DLI seems to be an effective and highly promising treatment method of transplant rejection in patients with CGD but can induce bone marrow aplasia and may require a second stem cell infusion.

Transplantation tolerance in nonhuman primates and humans

This review focuses on our recent studies involving nonmyeloablative bone marrow transplantation as an approach to inducing organ allograft tolerance across MHC barriers in nonhuman primates and in patients. The clinical studies are focused on mechanisms of tolerance involved in a protocol carried out at Massachusetts General Hospital in HLA-mismatched haploidentical combinations for the induction of renal allograft tolerance. These studies, in which chimerism was only transient and GVHD did not occur, suggest an early role for donor-specific regulatory T cells in tolerance induction, followed by partial and gradual deletion of donor-reactive T cells. We utilized high-throughput sequencing methodologies in a novel way to identify and track large numbers of alloreactive T cell receptors (TCRs). This method has been shown to identify biologically significant alloreactive TCRs in transplant patients and pointed to clonal deletion as a major mechanism of long-term tolerance in these patients. More recently, we adapted this sequencing method to optimally identify the donor-specific regulatory T cell (Treg) repertoire. Interrogation of the early posttransplant repertoire demonstrated expansion of donor-specific Tregs in association with tolerance. Our studies suggest a role for the kidney graft in tolerance by these mechanisms in patients who had only transient chimerism. Nonhuman primate studies indicate that other organs, including the heart, the lungs and the liver, are less readily tolerated following a period of transient mixed chimerism. Our efforts to extend the reach of mixed chimerism for tolerance induction beyond the kidney are therefore focused on the addition of recipient Tregs to the protocol. This approach has the potential to enhance chimerism while further reducing the risk of GVHD.

Achievement of Tolerance Induction to Prevent Acute Graft-vs.-Host Disease

Acute graft-vs.-host disease (GVHD) limits the efficacy of allogeneic hematopoietic stem cell transplantation (allo-HSCT), a main therapy to treat various hematological disorders. Despite rapid progress in understanding GVHD pathogenesis, broad immunosuppressive agents are most often used to prevent and remain the first line of therapy to treat GVHD. Strategies enhancing immune tolerance in allo-HSCT would permit reductions in immunosuppressant use and their associated undesirable side effects. In this review, we discuss the mechanisms responsible for GVHD and advancement in strategies to achieve immune balance and tolerance thereby avoiding GVHD and its complications.

Human Intestinal Allografts Contain Functional Hematopoietic Stem and Progenitor Cells that Are Maintained by a Circulating Pool

Human intestinal transplantation often results in long-term mixed chimerism of donor and recipient blood in transplant patients. We followed the phenotypes of chimeric peripheral blood cells in 21 patients receiving intestinal allografts over 5 years. Donor lymphocyte phenotypes suggested a contribution of hematopoietic stem and progenitor cells (HSPCs) from the graft. Surprisingly, we detected donor-derived HSPCs in intestinal mucosa, Peyer's patches, mesenteric lymph nodes, and liver. Human gut HSPCs are phenotypically similar to bone marrow HSPCs and have multilineage differentiation potential in vitro and in vivo. Analysis of circulating post-transplant donor T cells suggests that they undergo selection in recipient lymphoid organs to acquire immune tolerance. Our longitudinal study of human HSPCs carried in intestinal allografts demonstrates their turnover kinetics and gradual replacement of donor-derived HSPCs from a circulating pool. Thus, we have demonstrated the existence of functioning HSPCs in human intestines with implications for promoting tolerance in transplant recipients.

Immunotherapy in myeloma: how far have we come?

The treatment of multiple myeloma (MM) has evolved substantially over the past decades, leading to a significantly improved outcome of MM patients. The introduction of high-dose therapy, especially, and autologous stem cell transplantation, as well as the development of new drugs, such as immunomodulatory drugs (IMiDs) and proteasome inhibitors have contributed to the improvement in survival. However, eventually most MM patients relapse, which indicates that there is a need for new agents and novel treatment strategies. Importantly, the long-term survival in a subset of MM patients after allogeneic stem cell transplantation illustrates the potential of immunotherapy in MM, but allogeneic stem cell transplantation is also associated with a high rate of treatment-related mortality. Recently, a better insight into several immune-evasion mechanisms, which contribute to tumor progression, has resulted in the development of active and well-tolerated novel forms of immunotherapy. These immunotherapeutic agents can be used as monotherapy, or, even more successfully, in combination with other established anti-MM agents to further improve depth and duration of response by preventing the outgrowth of resistant clones. This review will discuss the mechanisms used by MM cells to evade the immune system, and also provide an overview of currently approved immunotherapeutic drugs, such as IMiDs (e.g. lenalidomide and pomalidomide) and monoclonal antibodies that target cell surface antigens present on the MM cell (e.g. elotuzumab and daratumumab), as well as novel immunotherapies (e.g. chimeric antigen receptor T-cells, bispecific antibodies and checkpoint inhibitors) currently in clinical development in MM.

Immune monitoring of transplant patients in transient mixed chimerism tolerance trials

This review focuses on mechanistic studies performed in recipients of non-myeloablative bone marrow transplant regimens developed at Massachusetts General Hospital in HLA-identical and HLA-mismatched haploidentical combinations, initially as a platform for treatment of hematologic malignancies with immunotherapy in the form of donor leukocyte infusions, and later in combination with donor kidney transplantation for the induction of allograft tolerance. In patients with permanent mixed chimerism, central deletion may be a major mechanism of long-term tolerance. In patients in whom donor chimerism is only transient, the kidney itself plays a significant role in maintaining long-term tolerance. A high throughput sequencing approach to identifying and tracking a significant portion of the alloreactive T cell receptor repertoire has demonstrated biological significance in transplant patients and has been useful in pointing to clonal deletion as a long-term tolerance mechanism in recipients of HLA-mismatched combined kidney and bone marrow transplants with only transient chimerism.

Mechanisms of Mixed Chimerism-Based Transplant Tolerance

Immune responses to allografts represent a major barrier in organ transplantation. Immune tolerance to avoid chronic immunosuppression is a critical goal in the field, recently achieved in the clinic by combining bone marrow transplantation (BMT) with kidney transplantation following non-myeloablative conditioning. At high levels of chimerism such protocols can permit central deletional tolerance, but with a significant risk of graft-versus-host (GVH) disease (GVHD). By contrast, transient chimerism-based tolerance is devoid of GVHD risk and appears to initially depend on regulatory T cells (Tregs) followed by gradual, presumably peripheral, clonal deletion of donor-reactive T cells. Here we review recent mechanistic insights into tolerance and the development of more robust and safer protocols for tolerance induction that will be guided by innovative immune monitoring tools.

Efficacy of host-dendritic cell vaccinations with or without minor histocompatibility antigen loading, combined with donor lymphocyte infusion in multiple myeloma patients

Donor lymphocyte infusions (DLI) can induce durable remissions in multiple myeloma (MM) patients, but this occurs rather infrequently. As the graft-versus-tumor (GvT) effect of DLI depends on the presence of host-dendritic cells (DCs), we tested in a phase I/II trial whether the efficacy of DLI could be improved by simultaneous vaccination with host-DCs. We also analyzed the possibility of further improving the GvT effect by loading the DCs with peptides of mismatched hematopoietic cell-specific minor histocompatibility antigens (mHags). Fifteen MM patients not responding to a first DLI were included. Eleven patients could be treated with a second equivalent dose DLI combined with DC vaccinations, generated from host monocytes (moDC). For four patients, the DC products did not meet the quality criteria. In four of the treated patients the DCs were loaded with host mHag peptides. Toxicity was limited and no acute GvHD occurred. Most patients developed objective anti-host T-cell responses and in one patient a distinct mHag-specific T-cell response accompanied a temporary clinical response. These findings confirm that DLI combined with host-DC vaccination, either unloaded or loaded with mHag peptides, is feasible, safe and capable of inducing host-specific T-cell responses. The limited clinical effects may be improved by developing more immunogenic DC products or by combining this therapy with immune potentiating modalities like checkpoint inhibitors.

The Role of Animal Models in the Study of Hematopoietic Stem Cell Transplantation and GvHD: A Historical Overview

Bone marrow transplantation (BMT) is the only therapeutic option for many hematological malignancies, but its applicability is limited by life-threatening complications, such as graft-versus-host disease (GvHD). The last decades have seen great advances in the understanding of BMT and its related complications; in particular GvHD. Animal models are beneficial to study complex diseases, as they allow dissecting the contribution of single components in the development of the disease. Most of the current knowledge on the therapeutic mechanisms of BMT derives from studies in animal models. Parallel to BMT, the understanding of the pathophysiology of GvHD, as well as the development of new treatment regimens, has also been supported by studies in animal models. Pre-clinical experimentation is the basis for deep understanding and successful improvements of clinical applications. In this review, we retrace the history of BMT and GvHD by describing how the studies in animal models have paved the way to the many advances in the field. We also describe how animal models contributed to the understanding of GvHD pathophysiology and how they are fundamental for the discovery of new treatments.

Immune tolerance in recipients of combined haploidentical bone marrow and kidney transplantation

The success of allogeneic hematopoietic cell transplantation (HCT) has been limited by transplant-associated toxicities related to the conditioning regimens used and to graft-vs-host disease (GVHD). The frequency and severity of GVHD observed when extensive HLA barriers are transgressed has greatly impeded the routine use of extensively HLA-mismatched HCT. Allogeneic HCT also has potential as an approach to organ allograft tolerance induction, but this potential has not been previously realized because of the toxicity associated with traditional conditioning. This paper reviews an approach to HCT involving reduced intensity conditioning that demonstrated sufficient safety in patients with hematologic malignancies, even in the HLA-mismatched transplant setting, to be applied for the induction of kidney allograft tolerance in humans with no other indication for HCT. These studies provided the first successful example of intentional organ allograft tolerance induction across HLA barriers in humans. Current data and hypotheses on the mechanisms of tolerance in these patients are reviewed.

Minor histocompatibility Ags: identification strategies, clinical results and translational perspectives

Allogeneic stem cell transplantation (allo-SCT) and donor lymphocyte infusion are effective treatment modalities for various hematological malignancies. Their therapeutic effect, the graft-versus-tumor (GvT) effect, is based mainly on an alloimmune response of donor T cells directed at tumor cells, in which differences in the expression of minor histocompatibility Ags (mHags) on the cells of the patient and donor have a crucial role. However, these differences are also responsible for induction of sometimes detrimental GvHD. As relapse and development of GvHD pose major threats for a large proportion of allotransplanted patients, additional therapeutic strategies are required. To augment the GvT response without increasing the risk of GvHD, specific mHag-directed immunotherapeutic strategies have been developed. Over the past years, much effort has been put into the identification of therapeutically relevant mHags to enable these strategies for a substantial proportion of patients. Currently, the concept of mHag-directed immunotherapy is tested in clinical trials on feasibility, safety and efficacy. In this review, we will summarize the recent developments in mHag identification and the clinical data on mHag-specific immune responses and mHag-directed therapies in patients with hematological malignancies. Finally, we will outline the current challenges and future prospectives in the field.

Macrochimerism in Intestinal Transplantation: Association With Lower Rejection Rates and Multivisceral Transplants, Without GVHD

Blood chimerism has been reported sporadically among visceral transplant recipients, mostly in association with graft-vs-host disease (GVHD). We hypothesized that a higher degree of mixed chimerism would be observed in multivisceral (MVTx) than in isolated intestinal (iITx) and isolated liver transplant (iLTx) recipients, regardless of GVHD. We performed a longitudinal prospective study investigating multilineage blood chimerism with flow cytometry in 5 iITx and 4 MVTx recipients up to one year posttransplant. Although only one iITx patient experienced GVHD, T cell mixed chimerism was detected in 8 out of 9 iITx/MVTx recipients. Chimerism was significantly lower in the four subjects who displayed early moderate to severe rejection. Pre-formed high-titer donor-specific antibodies, bound in vivo to the circulating donor cells, were associated with an accelerated decline in chimerism. Blood chimerism was also studied in 10 iLTx controls. Among nonsensitized patients, MVTx recipients exhibited greater T and B cell chimerism than either iITx or iLTx recipients. Myeloid lineage chimerism was present exclusively among iLTx and MVTx (6/13) recipients, suggesting that its presence required the hepatic allograft. Our study demonstrates, for the first time, frequent T cell chimerism without GVHD following visceral transplantation and a possible relationship with reduced rejection rate in MVTx recipients.

Rapid Functional Decline of Activated and Memory Graft-versus-Host-Reactive T Cells Encountering Host Antigens in the Absence of Inflammation

Inflammation in the priming host environment has critical effects on the graft-versus-host (GVH) responses mediated by naive donor T cells. However, it is unclear how a quiescent or inflammatory environment impacts the activity of GVH-reactive primed T and memory cells. We show in this article that GVH-reactive primed donor T cells generated in irradiated recipients had diminished ability compared with naive T cells to increase donor chimerism when transferred to quiescent mixed allogeneic chimeras. GVH-reactive primed T cells showed marked loss of cytotoxic function and activation, and delayed but not decreased proliferation or accumulation in lymphoid tissues when transferred to quiescent mixed chimeras compared with freshly irradiated secondary recipients. Primed CD4 and CD8 T cells provided mutual help to sustain these functions in both subsets. CD8 help for CD4 cells was largely IFN-γ dependent. TLR stimulation after transfer of GVH-reactive primed T cells to mixed chimeras restored their cytotoxic effector function and permitted the generation of more effective T cell memory in association with reduced PD-1 expression on CD4 memory cells. Our data indicate that an inflammatory host environment is required for the maintenance of GVH-reactive primed T cell functions and the generation of memory T cells that can rapidly acquire effector functions. These findings have important implications for graft-versus-host disease and T cell-mediated immunotherapies.

Induction of tolerance through mixed chimerism

"Mixed chimerism" refers to a state in which the lymphohematopoietic system of the recipient of allogeneic hematopoietic stem cells comprises a mixture of host and donor cells. This state is usually attained through either bone marrow or mobilized peripheral blood stem cell transplantation. Although numerous treatment regimens have led to transplantation tolerance in mice, the induction of mixed chimerism is currently the only treatment modality that has been successfully extended to large animals and to the clinic. Here we describe and compare the use of mixed chimerism to establish transplantation tolerance in mice, pigs, monkeys, and in the clinic. We also attempt to correlate the mechanisms involved in achieving tolerance with the nature of the tolerance that has resulted in each case.

Nonalloreactive T cells prevent donor lymphocyte infusion-induced graft-versus-host disease by controlling microbial stimuli

In mice, graft-versus-host reactions, associated with powerful graft-versus-tumor effects, can be achieved without graft-versus-host disease (GVHD) by delayed administration of donor lymphocyte infusions (DLI) to established mixed chimeras. However, GVHD sometimes occurs after DLI in established mixed chimeric patients. In contrast to mice, in which T cell recovery from the thymus occurs prior to DLI administration, human T cell reconstitution following T cell-depleted hematopoietic cell transplantation is slow, resulting in lymphopenia at the time of DLI. We demonstrate in this study that T cell lymphopenia is an independent risk factor for GVHD following DLI in the absence of known inflammatory stimuli. DLI-induced GVHD was prevented in lymphopenic recipients by prior administration of a small number of nonalloreactive polyclonal T cells, insufficient to prevent lymphopenia-associated expansion of subsequently administered T cells, through a regulatory T cell-independent mechanism. GVHD was not inhibited by T cells with irrelevant specificity. Moreover, administration of antibiotics reduced the severity of GVHD in lymphopenic hosts. Accumulation of DLI-derived effector T cells and host hematopoietic cell elimination were markedly diminished by regulatory T cell-depleted, nonalloreactive T cells. Finally, thymectomized mixed chimeras showed increased GVHD following delayed DLI. Collectively, our data demonstrate that in the absence of known conditioning-induced inflammatory stimuli, T cell lymphopenia is a risk factor for GVHD in mixed chimeras receiving delayed DLI. Our data suggest that the predisposition to GVHD can at least in part be explained by the presence of occult inflammatory stimuli due to the absence of T cells to control microbial infections.

IFN-γ promotes graft-versus-leukemia effects without directly interacting with leukemia cells in mice after allogeneic hematopoietic cell transplantation

The ability of IFN-γ to enhance graft-versus-leukemia (GVL) activity without direct interaction with leukemia cells was examined by comparing GVL effects against IFN-γ receptor-deficient (GRKO) leukemia between wild-type (WT) and IFN-γ-deficient (GKO) allogeneic hematopoietic cell transplantation (allo-HCT). We established a primary IFN-γ-unresponsive T-cell leukemia model using virally-transduced GRKO B6 mouse bone marrow cells overexpressing Notch1. We first assessed GVL effects in lethally-irradiated B6 mice receiving CD4-depleted allo-HCT from WT or GKO BALB/c donors. Administration of CD4(+) cell-depleted allo-HCT from WT, but not GKO, BALB/c donors mediated significant GVL effects against GRKO leukemia. Similar results were obtained in pre-established allogeneic chimeras receiving delayed donor lymphocyte infusion (DLI). Although both WT and GKO DLI achieved significant anti-tumor responses, the former was markedly stronger than the latter. These data indicate that IFN-γ is capable of promoting GVL effects via mechanisms independent of its interaction with leukemia cells.

Translational studies in hematopoietic cell transplantation: treatment of hematologic malignancies as a stepping stone to tolerance induction

Allogeneic hematopoietic cell transplantation (HCT) has most commonly been used to treat hematologic malignancies, where it is often the only potentially curative option available. The success of HCT has been limited by transplant-associated toxicities related to the conditioning regimens used and to the common immunologic consequence of donor T cell recognition of recipient alloantigens, graft-vs-host disease (GVHD). The frequency and severity of GVHD observed when extensive HLA barriers are transgressed has essentially precluded the routine use of extensively HLA-mismatched HCT. Allogeneic HCT also has potential as an approach to organ allograft tolerance induction, but this potential has not been previously realized because of the toxicity associated with traditional conditioning. In this paper we review two approaches to HCT involving reduced intensity conditioning regimens that have been associated with improvements in safety in patients with hematologic malignancies, even in the HLA-mismatched transplant setting. These strategies have been applied in the first successful pilot studies for the induction of organ allograft tolerance in humans. Thus, we summarize an example of vertical translational research between animal models and humans and horizontal translation between two separate goals that culminated in the use of HCT to achieve allograft tolerance in humans.

Long-term follow-up of recipients of combined human leukocyte antigen-matched bone marrow and kidney transplantation for multiple myeloma with end-stage renal disease

BACKGROUND

Specific tolerance after combined kidney and bone marrow transplantation for multiple myeloma with end-stage renal disease through mixed lymphohematopoietic chimerism has been achieved, as evidenced by prolonged normal renal function without ongoing immunosuppression.

METHODS

To achieve potent antimyeloma responses and induce tolerance for the renal allograft, seven patients (median age: 48 years [range: 34-55 years]) with multiple myeloma and end-stage renal disease underwent a combined human leukocyte antigen-matched kidney and bone marrow transplant with lead follow-up time of more than 12 years. Preparative therapy for the transplant consisted of high-dose cyclophosphamide, equine antithymocyte globulin and pretransplant thymic irradiation. Cyclosporine as the sole posttransplant immunosuppressive therapy was tapered and discontinued as early as day 73 posttransplant.

RESULTS

All seven patients achieved mixed chimerism. One patient developed acute graft-versus-host disease and two chronic graft-versus-host disease. Five of seven patients are alive, four with no evidence of myeloma from 4 to 12.1 years posttransplant. Three patients have normal or near-normal renal function without needing systemic immunosuppression. Two patients with normal renal function off immunosuppression were returned to immunosuppressive therapy without evidence of rejection because of the occurrence of chronic graft-versus-host disease.

CONCLUSIONS

These long-term follow-up data show that sustained renal allograft tolerance and prolonged antimyeloma responses are achievable after human leukocyte antigen-matched kidney and bone marrow transplantation and the induction of mixed lymphohematopoietic chimerism.

Cell-based therapy in allergy

IgE-mediated allergy is an immunological disorder occurring in response to otherwise harmless environmental antigens (i.e., allergens). Development of effective therapeutic or preventive approaches inducing robust tolerance toward allergens remains an unmet goal. Several experimental tolerance approaches have been described. The therapeutic use of regulatory T cells (Tregs) and the establishment of molecular chimerism are two cell-based strategies that are of particular interest. Treg therapy is close to clinical application, but its efficacy remains to be fully defined. Recent proof-of-concept studies demonstrated that transplantation of syngeneic hematopoietic stem cells modified in vitro to express a major allergen leads to molecular chimerism and robust allergen-specific tolerance. Here we review cell-based tolerance strategies in allergy, discussing their potentials and limitations.

Pharmacologic modulation of niche accessibility via tyrosine kinase inhibition enhances marrow and thymic engraftment after hematopoietic stem cell transplantation

Essential survival signals within hematopoietic stem cell (HSC) and thymic niches are mediated by receptor tyrosine kinases, which can be reversibly inhibited using clinically available drugs. We studied whether sunitinib, a multityrosine kinase inhibitor that inhibits KIT, enhances engraftment after bone marrow transplantation (BMT) in mice. Sunitinib diminished hematopoietic progenitor cell numbers, and sunitinib enhanced marrow, peripheral myeloid, and lymphoid engraftment after BMT in Rag1(-/-) mice. Sunitinib augmented HSC engraftment because recipients displayed increased myeloid and lymphoid engraftment and because sunitinib-treated recipients of purified HSCs showed enhanced engraftment of secondary hosts. However, sunitinib preferentially augmented T-cell engraftment with lesser effects on myeloid and HSC engraftment. Consistent with this, sunitinib preferentially depleted the early thymic progenitor subset in the thymus. Sunitinib did not increase engraftment in mice with deficient KIT signaling, and the pattern of more potent effects on T cell compared with HSC engraftment observed in sunitinib-treated hosts was also observed after BMT into KIT(W/Wv) mice. These results implicate KIT as a critical modulator of thymic niches. We conclude that transient, pharmacologic inhibition of KIT enhances accessibility of marrow and thymic niches, and provides a novel, noncytotoxic approach to accomplish engraftment after stem cell transplantation.

Mechanisms of transplantation tolerance in animals and humans

Donor-specific immune tolerance would avoid the toxicities of chronic immunosuppressive therapies while preventing graft rejection. Hematopoietic cell transplantation has shown preliminary success for intentional tolerance induction in pilot clinical trials. The mechanisms of tolerance in these trials and the animal studies leading up to them are discussed.

Hematopoietic cell transplantation for tolerance induction: animal models to clinical trials

The induction of donor-specific immune tolerance is the "holy grail" of transplantation, as it would avoid the toxicities of chronic immunosuppressive therapies while preventing acute and chronic graft rejection. A large number of approaches to tolerance induction have been described in the experimental literature, but only hematopoietic cell transplantation has shown preliminary success for intentional tolerance induction in pilot clinical trials. This review summarizes the conditions that allow progress to be made in moving strategies for tolerance induction from the bench to the bedside and discuss the mechanisms by which tolerance may be achieved through hematopoietic cell transplantation.

Paradoxical effects of IFN-gamma in graft-versus-host disease reflect promotion of lymphohematopoietic graft-versus-host reactions and inhibition of epithelial tissue injury

Interferon-gamma (IFN-gamma) inhibits graft-versus-host disease (GVHD) in lethally irradiated mice receiving allogeneic hematopoietic cell transplantation (allo-HCT) but promotes lethality in unirradiated and sublethally irradiated recipients. We investigated the role of IFN-gamma in GVHD in sublethally irradiated B6D2F1 recipients of B6 allo-HCT. B6D2F1 mice receiving wild-type B6 splenocytes alone died rapidly, whereas those receiving wild-type B6 splenocytes plus marrow survived long-term. Mice in both groups showed rapid elimination of host hematopoietic cells but minimal parenchymal tissue injury. However, mice receiving allo-HCT from IFN-gamma-deficient donors died rapidly regardless of whether donor marrow was given, and they exhibited severe parenchymal injury but prolonged survival of host hematopoietic cells. IFN-gamma plays a similar role in another model involving delayed B6 donor leukocyte infusion (DLI) to established mixed allogeneic (B6-->BALB/c) chimeras. IFN-gamma promotes DLI-mediated conversion from mixed to full donor chimerism while attenuating GVHD. Importantly, IFN-gamma enhances graft-versus-leukemia (GVL) effects in both models. Our data indicate that previously reported IFN-gamma-induced early mortality in allo-HCT recipients is due to augmentation of lymphohematopoietic graft-versus-host reaction (LGVHR) and can be avoided by providing an adequate source of donor hematopoietic stem/progenitor cells. Furthermore, the magnitude of GVL is correlated with the strength of LGVHR, and IFN-gamma reduces the potential of this alloreactivity to cause epithelial tissue GVHD.

Donor T cells primed on leukemia lysate-pulsed recipient APCs mediate strong graft-versus-leukemia effects across MHC barriers in full chimeras

Antigen-presenting cells (APCs) of host origin drive graft-versus-leukemia (GVL) effects but can also trigger life-threatening graft-versus-host disease (GVHD) after hematopoietic cell transplantation (HCT) across major histocompatibility complex (MHC) barriers. We show that in vitro priming of donor lymphocytes can circumvent the need of recipient-derived APCs in vivo for mediating robust GVL effects and significantly diminishes the risk of severe GVHD. In vitro, generated and expanded T cells (ETCs) mediate anti-leukemia effects only when primed on recipient-derived APCs. Loading of APCs in vitro with leukemia cell lysate, chimerism status of the recipient, and timing of adoptive transfer after HCT are important factors determining the outcome. Delayed transfer of ETCs resulted in strong GVL effects in leukemia-bearing full chimera (FC) and mixed chimera (MC) recipients, which were comparable with the GVL/GVHD rates observed after the transfer of naive donor lymphocyte infusion (DLI). Upon early transfer, GVL effects were more pronounced with ETCs but at the expense of significant GVHD. The degree of GVHD was most severe in MCs after transfer of ETCs that had been in vitro primed either on nonpulsed recipient-derived APCs or with donor-derived APCs.

Clinical experience with mixed chimerism to induce transplantation tolerance

Lymphohematopoietic chimerism was first shown to be associated with donor-specific allograft tolerance more than 60 years ago. However, early clinical experience with bone marrow transplantation soon revealed that conventional, myeloablative approaches were far too toxic and the risk of graft-versus-host disease too great to justify using this technology for the purpose of organ allograft tolerance induction in the absence of malignant disease. In this review, we discuss a step-wise approach that has been applied by several centers to establish less toxic approaches to using hematopoietic cell transplantation (HCT) for tolerance induction. These steps include (i) feasibility and efficacy data for tolerance induction in large animal models; (ii) safety data in clinical trials for patients with hematologic malignancies; and (iii) pilot trials of combined HCT and kidney transplantation for tolerance induction. Thus far, only one published trial conducted at the Massachusetts General Hospital in Boston has achieved long-term acceptance of human leukocyte antigen-mismatched kidney allografts without chronic immunosuppressive therapy. Alternative protocols have been successful in large animals, but long-term organ allograft tolerance has not been reported in patients. Thus, proof-of-principle that nonmyeloablative induction of mixed chimerism can be used intentionally to induce organ allograft tolerance has now been achieved. Directions for further research to make this approach applicable for a broader patient population are discussed.

Graft-versus-host disease after donor leukocyte infusions: presentation and management

Donor leukocyte infusion (DLI) is used after both myeloablative and non-myeloablative stem-cell transplantation to treat and prevent relapse, to establish full donor chimerism, and to treat and prevent infections. The major treatment-related complication of DLI is graft-versus-host disease (GVHD). The presentation and treatment of GVHD after DLI is similar to its presentation and treatment after stem-cell transplantation, with some notable exceptions. While GVHD and graft-versus-tumor (GVT) effects are highly correlated after DLI, some patients experience remission without GVHD. Studies to define tumor-specific target antigens and GVT effector cells, as well as strategies of donor T-cell manipulation and optimization of DLI dose and schedule, may ultimately lead to the consistent ability to separate GVHD from GVT activity, improvement in the safety and specificity of DLI, and enhancement of the anti-tumor activity of donor T cells.

Clinical outcomes of late rather than early full-donor chimerism in patients with advanced lymphomas receiving nonmyeloablative allogeneic hematopoietic SCT

Allogeneic hematopoietic SCT (HSCT) can ideally provide long-term remission in advanced lymphoma patients by capturing a graft-vs-tumor (GVT) effect. On the basis of a murine model, we attempted to optimize a GVT effect through nonmyeloablative therapy and HLA-matched related donor HSCT with intentional induction of mixed chimerism followed by prophylactic donor lymphocyte infusion. A total of 26 advanced lymphoma patients were separated into an early and late full-donor chimerism (FDC) group using a median of 45 days post-HSCT as the defining point for FDC. Upon generating these groups, analysis by Student's t-test demonstrated that they were statistically distinct in time to develop FDC (P<0.01). There was a trend toward improved CR rates in the late group relative to the early group (62 vs 31%; P=0.12). A trend toward improved progression-free survival at 5 years was also observed in the late compared to the early group by Kaplan-Meier analysis (38 vs 8%; P=0.081). However, this did not correlate to a significant overall survival benefit. In conclusion, these data support the observation from our mouse models that the most potent GVT effect occurs in mixed chimeras with late chimerism conversion.

Manipulating the immune system for anti-tumor responses and transplant tolerance via mixed hematopoietic chimerism

SUMMARY

Stem cells (SCs) with varying potentiality have the capacity to repair injured tissues. While promising animal data have been obtained, allogeneic SCs and their progeny are subject to immune-mediated rejection. Here, we review the potential of hematopoietic stem cells (HSCs) to promote immune tolerance to allogeneic and xenogeneic organs and tissues, to reverse autoimmunity, and to be used optimally to cure hematologic malignancies. We also review the mechanisms by which hematopoietic cell transplantation (HCT) can promote anti-tumor responses and establish donor-specific transplantation tolerance. We discuss the barriers to clinical translation of animal studies and describe some recent studies indicating how they can be overcome. The recent achievements of durable mixed chimerism across human leukocyte antigen barriers without graft-versus-host disease and of organ allograft tolerance through combined kidney and bone marrow transplantation suggest that the potential of this approach for use in the treatment of many human diseases may ultimately be realized.

Co-infusion of donor bone marrow with host mesenchymal stem cells treats GVHD and promotes vascularized skin allograft survival in rats

We investigated the effect of autologous mesenchymal stem cells (MSC) on multiple unmodified donor bone marrow (BM) infusions and vascularized skin graft outcome. BM-derived rat MSC were examined for phenotype and function. MSC/MSC-conditioned-medium suppressed IFN-gamma production by T cells and modified DC function. Infusions of MSC with one-time BM improved vascularized skin graft survival, while with one-two-times BM reversed graft versus host disease (GVHD). Mixed chimerism was enhanced in recipients given two-four-times BM with MSC infusions. Interestingly, four-times BM infusions with MSC delayed GVHD onset, reduced host tissue damage and enhanced vascularized skin allograft survival compared to four-times BM alone. These data demonstrate that, the co-infusion of MSC with unmodified BM limit the toxicity of allogeneic BM transplantation, enhance mixed chimerism and improve vascularized skin graft survival. These findings provide insights for the development of autologous MSC-based BM transplantation and prevention of graft rejection or treatment of autoimmunity.

The anti-tumor effect of allogeneic bone marrow/stem cell transplant without graft vs. host disease toxicity and without a matched donor requirement?

The anti-tumor immune response that occurs in allogeneic bone marrow/stem cell transplant (BMT) settings is capable of eradicating tumors that are resistant to chemotherapy/radiation treatment. This anti-tumor immune response, known as the graft vs. tumor (GVT) effect, is the most effective immunotherapy treatment ever discovered. Unfortunately, the clinical application of GVT is severely limited due to the intimate association of GVT with the extremely toxic and often lethal side-effect known as graft vs. host disease (GVHD). It is a major research focus in the field of BMT to develop methods to separate the beneficial GVT effect from the detrimental GVHD toxicity. However, due to the intimate association of these effects, attempts to limit GVHD also have a tendency to limit the GVT effect. We propose a new concept for harnessing the power of the GVT effect without the toxicity of GVHD. Rather than trying to separate GVT from GVHD, we propose that these naturally coupled effects can 'mirrored' onto the host immune system and maintain their intimate association. The 'mirror' of GVHD is a host rejection of a graft (HVG). As rejection of an allograft would not be toxic, an HVG effect coupled to a host vs. tumor (HVT) effect, the 'mirror' of the GVT effect, would provide the anti-tumor effect of BMT without GVHD toxicity. In the 'mirror' setting, the HVT effect must occur against syngeneic tumors, while in the BMT setting the GVT effect occurs in the allogeneic setting. Previous attempts to elicit syngeneic anti-tumor immunity using therapeutic tumor vaccines have had disappointing results in the clinic due to the influence of tumor immunoavoidance mechanisms. We propose that the 'danger' signals that are released as a result of GVHD in the allogeneic BMT setting serve as an adjuvant to the GVT effect disabling tumor immunoavoidance. The chemotherapy/radiation conditioning prior to transplant is a required initiating event to the coupled GVT/GVHD effects. The conditioning releases 'danger' signals that mediate this adjuvant effect. To imitate this immunological event in immunocompetent, non-conditioned patients we propose that infusion of freshly activated, polyclonal CD4+ memory Th1 cells which express CD40L on the cell surface will stimulate a HVT/HVG 'mirror' effect, providing a non-toxic means to elicit the effective immune-mediated anti-tumor effect of BMT without the GVHD toxicity and without the requirement for a matched donor.

Establishment of transplantable porcine tumor cell lines derived from MHC-inbred miniature swine

The lack of transplantable tumors has limited assessment of graft-versus-tumor effects following hematopoietic cell transplantation in clinically relevant large-animal models. We describe the derivation and characterization of porcine tumor cell lines with initial efforts of tumor transplantation using immunocompromised mice and highly inbred sublines of Massachusetts General Hospital major histocompatibility complex (MHC)-inbred miniature swine. Autopsies were performed routinely on swine that died unexpectedly or had suspicion of malignancy based on clinical symptoms or peripheral blood analysis. Tissue samples were obtained for pathology, phenotyped by flow cytometry, and placed in culture. Based on growth, lines were selected for passage into nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice and miniature swine. Porcine tumor recipients were preconditioned with total body irradiation from 0 to 500 cGy or with a 30-day course of oral cyclosporine. We identified 19 cases of hematologic tumors. Nine distinct tumor cell lines were established from 8 of these cases, including 3 derived from highly inbred sublines. In vivo tumor growth and serial transfer were observed in immunocompromised mice for one tumor cell line and in miniature swine for 1 of 2 tumor cell lines expanded for this purpose. These results suggest the possibility of developing a transplantable tumor model in this large-animal system.

Thymus repopulation after allogeneic reconstitution in hematological malignancies

OBJECTIVE

Active vaccination in the allogeneically reconstituted tumor-bearing host essentially requires donor T-cell tolerance. To create a basis for vaccination in the allogeneically reconstituted, lymphoma-bearing host, we elaborate a reconstitution protocol that supports thymus repopulation and tolerance induction.

METHODS

Myeloreductively conditioned, lymphoma-bearing mice were vaccinated after reconstitution with hematopoietic progenitor cells. Readout systems included recovery of donor-derived T cells, graft vs host disease (GVHD), anti-host and anti-lymphoma cytotoxicity, as well as tumor growth rate and tumor rejection.

RESULTS

In tumor-free mice, myeloreductive conditioning, together with natural killer cell depletion of the host and transfer of T cell-depleted bone marrow cells, allows reconstitution without severe GVHD. However, in hematological malignancies, donor-derived T-progenitor cells hardly immigrated into the thymus. As a consequence, the frequency of severe GVHD was significantly increased, which prohibited active vaccination. Thymus repopulation became improved by strengthening myeloreductive conditioning; by supporting thymocyte expansion via interleukin-7; and, most strongly, by a small dose of donor-derived CD4(+)CD8(+) thymocytes, which preferentially homed into the thymus. Active vaccination, in combination with this reconstitution protocol, did not strengthen GVHD, but significantly improved survival time and survival rate of lymphoma-bearing mice.

CONCLUSION

The negative impact of hematological malignancies on thymus repopulation and central tolerance induction can, at least in part, be corrected by application of a small number of donor-derived T-progenitor cells.

Immune tolerance: mechanisms and application in clinical transplantation

The achievement of immune tolerance, a state of specific unresponsiveness to the donor graft, has the potential to overcome the current major limitations to progress in organ transplantation, namely late graft loss, organ shortage and the toxicities of chronic nonspecific immumnosuppressive therapy. Advances in our understanding of immunological processes, mechanisms of rejection and tolerance have led to encouraging developments in animal models, which are just beginning to be translated into clinical pilot studies. These advances are reviewed here and the appropriate timing for clinical trials is discussed.

Factors affecting human T cell engraftment, trafficking, and associated xenogeneic graft-vs-host disease in NOD/SCID beta2mnull mice

OBJECTIVE

Graft-vs-host disease (GVHD) is the major cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation. Models of immunodeficient mice that consistently and efficiently reconstitute with xenoreactive human T cells would be a valuable tool for the in vivo study of GVHD, as well as other human immune responses.

MATERIALS AND METHODS

We developed a consistent and sensitive model of human GVHD by retro-orbitally injecting purified human T cells into sublethally irradiated nonobese diabetic/severe combined immunodeficient (NOD/SCID)-beta2m(null) recipients. In addition, we characterized for the first time the trafficking patterns and expansion profiles of xenoreactive human T cells in NOD/SCID-beta2m(null) recipients using in vivo bioluminescence imaging.

RESULTS

All NOD/SCID-beta2m(null) mice conditioned with 300 cGy total body irradiation and injected with 1 x 10(7) human T cells exhibited human T-cell engraftment, activation, and expansion, with infiltration of multiple target tissues and a subsequent >20% loss of pretransplantation body weight. Importantly, histological examination of the GVHD target tissues revealed changes consistent with human GVHD. Furthermore, we also showed by in vivo bioluminescence imaging that development of lethal GVHD in the NOD/SCID-beta2m(null) recipients was dependent upon the initial retention and early expansion of human T cells in the retro-orbital sinus cavity.

CONCLUSION

Our NOD/SCID-beta2m(null) mouse model provides a system to study the pathophysiology of acute GVHD induced by human T cells and aids in development of more effective therapies for human GVHD.

Establishment of transplantable porcine tumor cell lines derived from MHC-inbred miniature swine

The lack of transplantable tumors has limited assessment of graft-versus-tumor effects following hematopoietic cell transplantation in clinically relevant large-animal models. We describe the derivation and characterization of porcine tumor cell lines with initial efforts of tumor transplantation using immunocompromised mice and highly inbred sublines of Massachusetts General Hospital major histocompatibility complex (MHC)-inbred miniature swine. Autopsies were performed routinely on swine that died unexpectedly or had suspicion of malignancy based on clinical symptoms or peripheral blood analysis. Tissue samples were obtained for pathology, phenotyped by flow cytometry, and placed in culture. Based on growth, lines were selected for passage into nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice and miniature swine. Porcine tumor recipients were preconditioned with total body irradiation from 0 to 500 cGy or with a 30-day course of oral cyclosporine. We identified 19 cases of hematologic tumors. Nine distinct tumor cell lines were established from 8 of these cases, including 3 derived from highly inbred sublines. In vivo tumor growth and serial transfer were observed in immunocompromised mice for one tumor cell line and in miniature swine for 1 of 2 tumor cell lines expanded for this purpose. These results suggest the possibility of developing a transplantable tumor model in this large-animal system.

Recent Progress in Tolerance Induction through Mixed Chimerism

Organ transplant recipients require life-long treatment with immunosuppressive drugs. Currently available immunosuppression is associated with substantial morbidity and mortality, and is ineffective in inhibiting chronic rejection and graft loss. Therefore, a permanent state of donor-specific tolerance remains a primary goal for transplantation research. The induction of mixed hematopoietic chimerism is an attractive concept in this regard. Hematopoietic chimerism modulates the immunologic repertoire by extending the mechanisms of self-tolerance to donor-specific allotolerance. Despite recent progress in developing nontoxic bone marrow transplantation protocols for rodents, translation to large animals has remained difficult. Here, we outline the concept of tolerance via mixed chimerism, and review recent progress and remaining challenges in bringing this approach to the clinical setting.

The Impact of Chimerism Patterns and Predonor Leukocyte Infusion Lymphopenia on Survival following T Cell-Depleted Reduced Intensity Conditioned Transplants

Donor leukocyte infusions (DLI) are frequently required following reduced intensity conditioned (RIC) allografts to convert mixed chimerism (MC) to full donor chimerism (FDC). The rationale is to break tolerance and maximize the graft-versus-leukemia responses. We analyzed the impact of chimerism in 125 recipients of RIC (Alemtuzumab containing) transplants. Four patterns of chimerism were seen: (1) always 100% donor chimerism (54%), (2) persisting MC (22%), (3) MC with subsequent development of FDC (18%), (4) lost donor chimerism (6%). Forty-five (36%) patients received DLI. Chimerism patterns and pre-DLI lymphocyte counts (pDLI[Ly]) were significantly associated with DLI responsiveness. Complete disease responses were seen in 6 of 17 (35%) group A patients, 9 of 10 (90%) group C patients, and 0 of 6 group B patients (P = .027), supporting reports that chimerism response is a surrogate marker for disease response. In those with MC, pDLI(Ly) were significantly lower in DLI responsive than nonresponsive patients (P = .044). At 2 years, group C patients had a significant survival advantage (P = .009) compared to all other groups. In conclusion, the chimerism pattern was the best indicator of improved survival in this cohort (ie, MC later converting to FDC). In those with MC, response to DLI therapy was associated with a low lymphocyte count pre-DLI.

Rapamycin Promotes Emergence of IL-10-Secreting Donor Lymphocyte Infusion-Derived T Cells Without Compromising Their Graft-Versus-Leukemia Reactivity

BACKGROUND

There are limited data examining the effects of pharmacological immunosuppression on the in vivo fate of donor lymphocyte infusions (DLI)-derived T cells, their function, and their antitumor efficacy.

METHODS

We addressed this question in a murine model in which DLI is given to stable mixed chimeras resulting in lymphohematopoietic graft-versus-host (LH-GVH) response. In this model, LH-GVH potency can be directly measured as the kinetics of conversion to full donor chimerism and can be correlated with associated graft-versus-leukemia (GVL) reactivity.

RESULTS

We found discordance in DLI-mediated LH-GVH reactivity depending on the timing of rapamycin (RAPA) administration. Delayed administration of RAPA in contrast to its early administration at the time of adoptive transfer did not interfere with conversion to full donor chimerism. Moreover, delayed administration of RAPA preserved the GVL reactivity of DLI. Analysis of the long-term chimeras showed that regardless of RAPA administration, adoptively transferred T cells mediating the LH-GVH response contribute minimally to the reconstitution of the peripheral T-cell compartment and exhibit profound hyporesponsiveness and decreased production of interleukin (IL)-2 on restimulation in vitro. However, we observed only in the RAPA-treated chimeras that the remaining hyporesponsive DLI-derived CD4+ T cells secrete large amounts of IL-10, a known immunoregulatory cytokine.

CONCLUSIONS

We conclude that delayed administration of RAPA after DLI does not interfere with their LH-GVH reactivity but promotes the emergence of IL-10-secreting DLI-derived CD4+ T cells that might contribute to the drug's known ability to promote bilateral donor host tolerance without interfering with GVL reactivity.

Factors governing the activation of adoptively transferred donor T cells infused after allogeneic bone marrow transplantation in the mouse

Murine models of bone marrow transplantation were used to study the mechanisms governing the activation of donor lymphocyte infusions (DLIs) manifesting as lymphohematopoietic graft-versus-host (LH-GVH) and graft-versus-leukemia (GVL) reactivities. We demonstrate here that established mixed chimerism influences the potency of DLI-mediated alloreactivity only in the MHC-mismatched but not MHC-matched setting. In the MHC-matched setting, high levels (>or= 40%) of residual host chimerism correlated negatively with DLI-mediated alloreactivity irrespective of the timing of their administration, the donor's previous sensitization to host antigens, or the level of residual host APCs. In vivo administration of Toll-like receptor (TLR) ligands was required to maximize DLI-mediated LH-GVH and GVL reactivities in chimeras with low levels (<or= 15%) of residual host chimerism. In contrast, coadministration of DLI with antigen-presenting cell (APC) activators was insufficient to augment their LH-GVH response in the presence of high levels of host chimerism unless the host's T cells were transiently depleted. Together, these results show the cardinal influence of donor-host incompatibility on DLI-mediated GVH responses and suggest that in MHC-matched chimeras, the induction of optimal alloreactivity requires not only donor T cells and host APCs but also TLR ligands and in the presence of high levels of host chimerism depletion of host T cells.

Myeloma responses and tolerance following combined kidney and nonmyeloablative marrow transplantation: in vivo and in vitro analyses

Six patients with renal failure due to multiple myeloma (MM) received simultaneous kidney and bone marrow transplantation (BMT) from HLA-identical sibling donors following nonmyeloablative conditioning, including cyclophosphamide (CP), peritransplant antithymocyte globulin and thymic irradiation. Cyclosporine (CyA) was given for approximately 2 months posttransplant, followed by donor leukocyte infusions. All six patients accepted their kidney grafts long-term. Three patients lost detectable chimerism but accepted their kidney grafts off immunosuppression for 1.3 to >7 years. One such patient had strong antidonor cytotoxic T lymphocyte (CTL) responses in association with marrow rejection. Two patients achieved full donor chimerism, but resumed immunosuppression to treat graft-versus-host disease. Only one patient experienced rejection following CyA withdrawal. He responded to immunosuppression, which was later successfully withdrawn. The rejection episode was associated with antidonor Th reactivity. Patients showed CTL unresponsiveness to cultured donor renal tubular epithelial cells. Initially recovering T cells were memory cells and were enriched for CD4+CD25+ cells. Three patients are in sustained complete remissions of MM, despite loss of chimerism in two. Combined kidney/BMT with nonmyeloablative conditioning can achieve renal allograft tolerance and excellent myeloma responses, even in the presence of donor marrow rejection and antidonor alloresponses in vitro.

Expression of chemokines in GVHD target organs is influenced by conditioning and genetic factors and amplified by GVHR

Graft-versus-host disease (GVHD) is the most significant clinical problem that arises after allogeneic hematopoietic cell transplantation. Because chemokines induced by proinflammatory conditioning treatment may promote T-cell migration into GVHD target tissues, we addressed the influence of conditioning on chemokine expression in GVHD target organs. Our results showed that (1) conditioning leads to rapid and transient chemokine upregulation in GVHD target tissues before the time of GVHD-associated T-cell infiltration; (2) conditioning intensity and mouse strain influence chemokine expression in GVHD target organs; and (3) compared with syngeneic bone marrow transplantation, allogeneic bone marrow transplantation led to marked amplification of chemokine expression in GVHD target organs after myeloablative conditioning. This is also reflected by chemokine protein expression that is measured in the serum and colon. Intestines showed the greatest sensitivity to conditioning intensity, and chemokines affecting T-helper type 1 cells (eg, interferon gamma-inducible protein 10 [CXCL10]) were most strongly expressed there after conditioning and during GVHD. However, severity of GVHD was not significantly different between recipients of CXCR3+/+ or CXCR3-/- splenocytes, indicating that this chemokine pathway does not play a critical role. In summary, our data show that conditioning and recipient strain influence chemokine expression in GVHD target organs and that GVH alloreactivity markedly amplifies this expression, thus contributing to the inflammatory cascade associated with tissue GVHD.

Reduction of graft-versus-host disease by histone deacetylase inhibitor suberonylanilide hydroxamic acid is associated with modulation of inflammatory cytokine milieu and involves inhibition of STAT1

Histone deacetylase (HDAC) inhibitors reduce development of graft-versus-host disease (GVHD) following allogeneic bone marrow transplantation (BMT). Administration of the HDAC inhibitor suberonylanilide hydroxamic acid (SAHA) resulted in a significantly reduced GVHD-dependent mortality following fully major histocompatibility complex-mismatched allogeneic BMT. However, SAHA treatment did not affect T-cell activation or T-cell expansion in vitro and in vivo. Therefore, we focused on the effects of SAHA treatment on cytokine production and intracellular signaling events in vitro and in vivo following GVHD induction. Cultivation in the presence of SAHA broadly inhibited lipopolysaccharide (LPS) and alloantigen-induced cytokine/chemokine production in vitro and led also to a significant decrease in interferon-gamma and tumor necrosis factor-alpha levels in vivo following induction of GVHD. Concomitantly, SAHA treatment inhibited phosphorylation of STAT1 and STAT3 in response to LPS and alloactivation in vitro. Induction of GVHD led to a rapid phosphorylation of STAT 1 in the liver and spleen, which was markedly reduced by SAHA treatment. In conclusion, GVHD is associated with a marked induction of phosphorylation of STAT1 in the liver and spleen, and SAHA-dependent reduction of GVHD is associated with systemic and local inhibition of phosphorylated STAT1 and blunting proinflammatory cytokine production during the initiation phase of GVHD.

Role of indirect allo- and autoreactivity in anti-tumor responses induced by recipient leukocyte infusions (RLI) in mixed chimeras prepared with nonmyeloablative conditioning

In mixed chimeras prepared with nonmyeloablative conditioning, we previously showed that recipient leukocyte infusions (RLI) induced loss of donor chimerism and anti-tumor responses against the A20 BALB/c B cell lymphoma. We also previously showed that RLI-mediated tumor rejection involved IFN-gamma-producing RLI-derived CD8+ cells and non-RLI, recipient-derived CD4 T cells, leading to the generation of anti-tumor cytotoxic cells. However, the mechanisms of such paradoxical anti-tumor responses remained to be clarified. In the present study, we further explored the cellular mechanisms of the anti-tumor effects of RLI in fully MHC-mismatched and haploidentical strain combinations. In both cases, we show that RLI breaks the tolerance of chimeric T cells toward donor antigens, in association with the in vivo expansion of recipient splenic T, B and CD4-CD8- cells and the production of IFN-gamma. RLI leads to the development of two types of tumor-specific responses. The first is mediated by indirect presentation of donor antigens and occurs independently of tumor injection. The second is observed only in recipients of RLI and tumor and may involve responses to self antigens. Anti-tumor cytotoxicity was mediated by CD8+ or CD4-CD8- effector cells. Thus, anti-tumor cytotoxic responses are generated following complex interactions between recipient APCs presenting donor and recipient antigens and host-type CD4+, CD8+ and CD4-CD8- cells.