Role of T cell subsets in lethal graft-versus-host disease (GVHD) directed to class I versus class II H-2 differences. I. L3T4+ cells can either augment or retard GVHD elicited by Lyt-2+ cells in class I different hosts

Protocol for X-ray irradiation of C57BL/6J recipient mice followed by the transplantation of mTomato-expressing bone marrow cells

Bone marrow chimera is a useful tool to determine the pathophysiological contributions of hematopoietic versus stromal compartments. Here, we present a protocol for lethal irradiation of wild-type C57BL/6J recipient mice followed by the transplantation of bone marrow from mTomato-expressing donors. We then detail procedures for animal distress scoring and assessment of reconstitution efficiency. This protocol will minimize distress and ensure efficient hematopoietic reconstitution of donor cells in recipients.

Ruxolitinib as the first post-steroid treatment for acute and chronic graft-versus-host disease

INTRODUCTION

Acute and chronic graft-versus-host disease (GvHD) are potentially life-threatening complications occurring after allogeneic stem cell transplantation (allo-HSCT). Although steroids represent the first-line treatment for both conditions, in those patients who do not adequately benefit from steroid therapy, standardized treatment algorithms are lacking. In recent years, ruxolitinib has emerged as the most promising agent for the second-line therapy of steroid-refractory (SR)-GvHD.

AREAS COVERED

This review will summarize the biological properties and the mechanistic aspects that justify the therapeutic role of ruxolitinib in GvHD. In addition, current treatment options for SR-GvHD will be briefly discussed. Finally, results of the most relevant clinical trials on the use of ruxolitinib for SR-GvHD will be analyzed, with a particular focus on two phase-III randomized trials in which ruxolitinib demonstrated its superiority in comparison with the best available therapy.

EXPERT OPINION

Ruxolitinib has considerably improved the outcome of patients with SR-acute/chronic-GvHD and should be regarded as the standard-of-care option when corticosteroids fail or cannot be tapered. Nevertheless, a number of questions still remain unanswered and significant room for improvement exists. Additional observations derived from a longer follow-up will certainly increase our expertise in the management of this powerful therapy.

Insights into mechanisms of graft-versus-host disease through humanised mouse models

Graft-versus-host disease (GVHD) is a major complication that occurs following allogeneic haematopoietic stem cell transplantation (HSCT) for the treatment of haematological cancers and other blood-related disorders. GVHD is an inflammatory disorder, where the transplanted donor immune cells can mediate an immune response against the recipient and attack host tissues. Despite over 60 years of research, broad-range immune suppression is still used to prevent or treat GVHD, leading to an increased risk of cancer relapse and infection. Therefore, further insights into the disease mechanisms and development of predictive and prognostic biomarkers are key to improving outcomes and reducing GVHD development following allogeneic HSCT. An important preclinical tool to examine the pathophysiology of GVHD and to understand the key mechanisms that lead to GVHD development are preclinical humanised mouse models. Such models of GVHD are now well-established and can provide valuable insights into disease development. This review will focus on models where human peripheral blood mononuclear cells are injected into immune-deficient non-obese diabetic (NOD)-scid-interleukin-2(IL-2)Rγ mutant (NOD-scid-IL2Rγ^null) mice. Humanised mouse models of GVHD can mimic the clinical setting for GVHD development, with disease progression and tissues impacted like that observed in humans. This review will highlight key findings from preclinical humanised mouse models regarding the role of donor human immune cells, the function of cytokines and cell signalling molecules and their impact on specific target tissues and GVHD development. Further, specific therapeutic strategies tested in these preclinical models reveal key molecular pathways important in reducing the burden of GVHD following allogeneic HSCT.

Purinergic Signalling in Allogeneic Haematopoietic Stem Cell Transplantation and Graft-versus-Host Disease

Allogeneic haematopoietic stem cell transplantation (allo-HSCT) is a curative therapy for blood cancers and other haematological disorders. However, allo-HSCT leads to graft-versus-host disease (GVHD), a severe and often lethal immunological response, in the majority of transplant recipients. Current therapies for GVHD are limited and often reduce the effectiveness of allo-HSCT. Therefore, pro- and anti-inflammatory factors contributing to disease need to be explored in order to identify new treatment targets. Purinergic signalling plays important roles in haematopoiesis, inflammation and immunity, and recent evidence suggests that it can also affect haematopoietic stem cell transplantation and GVHD development. This review provides a detailed assessment of the emerging roles of purinergic receptors, most notably P2X7, P2Y2 and A2A receptors, and ectoenzymes, CD39 and CD73, in GVHD.

Mouse nidovirus LDV infection alleviates graft versus host disease and induces type I IFN-dependent inhibition of dendritic cells and allo-responsive T cells

Introduction

Viruses have developed multiple mechanisms to alter immune reactions. In 1969, it was reported that lactate dehydrogenase‐elevating virus (LDV), a single stranded positive sense mouse nidovirus, delays skin allograft rejection and inhibits spleen alterations in graft versus host disease (GVHD). As the underlying mechanisms have remained unresolved and given the need for new therapies of this disease, we reassessed the effects of the virus on GVHD and tried to uncover its mode of action.

Methods

GVHD was induced by transfer of parent (B6) spleen cells to non‐infected or LDV‐infected B6D2F1 recipients. In vitro mixed‐lymhocyte culture (MLC) reactions were used to test the effects of the virus on antigen‐presenting cells (APC) and responder T cells.

Results

LDV infection resulted in a threefold increase in survival rate with reduced weight loss and liver inflammation but with the establishment of permanent chimerism that correlated with decreased interleukine (IL)‐27 and interferon (IFN)γ plasma levels. Infected mice showed a transient elimination of splenic CD11b+ and CD8α+ conventional dendritic cells (cDCs) required for allogeneic CD4 and CD8 T cell responses in vitro. This drop of APC numbers was not observed with APCs derived from toll‐like receptor (TLR)7‐deficient mice. A second effect of the virus was a decreased T cell proliferation and IFNγ production during MLC without detectable changes in Foxp3+ regulatory T cell (Tregs) numbers. Both cDC and responder T cell inhibition were type I IFN dependent. Although the suppressive effects were very transient, the GVHD inhibition was long‐lasting.

Conclusion

A type I IFN‐dependent suppression of DC and T cells just after donor spleen cell transplantation induces permanent chimerism and donor cell implantation in a parent to F1 spleen cell transplantation model. If this procedure can be extended to full allogeneic bone marrow transplantation, it could open new therapeutic perspectives for hematopoietic stem cell transplantation (HSCT).

Bone Marrow Graft-Versus-Host Disease in Major Histocompatibility Complex-Matched Murine Reduced-Intensity Allogeneic Hemopoietic Cell Transplantation

BACKGROUND

Most clinical allogeneic hemopoietic cell transplants (alloHCT) are now performed using reduced-intensity conditioning (RIC) instead of myeloablative conditioning (MAC); however, the biology underlying this treatment remains incompletely understood.

METHODS

We investigated a murine model of major histocompatibility complex-matched multiple minor histocompatibility antigen-mismatched alloHCT using bone marrow (BM) cells and splenocytes from B6 (H-2) donor mice transplanted into BALB.B (H-2) recipients after RIC with fludarabine of 100 mg/kg per day for 5 days, cyclophosphamide of 60 mg/kg per day for 2 days, and total body irradiation (TBI).

RESULTS

The lowest TBI dose capable of achieving complete donor chimerism in this mouse strain combination was 325 cGy given as a single fraction. Mice that underwent RIC had a reduced incidence and delayed onset of graft-versus-host disease (GVHD) and significantly prolonged survival compared with MAC-transplanted recipients (TBI of 850 cGy plus cyclophosphamide of 60 mg/kg per day for 2 days). Compared with syngeneic controls, RIC mice with GVHD showed evidence of BM suppression, have anemia, reduced BM cellularity, and showed profound reduction in BM B cell lymphopoiesis associated with damage to the endosteal BM niche. This was associated with an increase in BM CD8 effector T cells in RIC mice and elevated blood and BM plasma levels of T helper1 cytokines. Increasing doses of splenocytes resulted in increased incidence of GVHD in RIC mice.

CONCLUSIONS

We demonstrate that the BM is a major target organ of GVHD in an informative clinically relevant RIC mouse major histocompatibility complex-matched alloHCT model by a process that seems to be driven by CD8 effector T cells.

Pathophysiology of GvHD and Other HSCT-Related Major Complications

For over 60 years, hematopoietic stem cell transplantation has been the major curative therapy for several hematological and genetic disorders, but its efficacy is limited by the secondary disease called graft versus host disease (GvHD). Huge advances have been made in successful transplantation in order to improve patient quality of life, and yet, complete success is hard to achieve. This review assimilates recent updates on pathophysiology of GvHD, prophylaxis and treatment of GvHD-related complications, and advances in the potential treatment of GvHD.

In vitro-generated MDSCs prevent murine GVHD by inducing type 2 T cells without disabling antitumor cytotoxicity

Myeloid-derived suppressor cells (MDSCs) inhibit T-cell expansion and functions by versatile mechanisms such as nutrient depletion, nitrosylation, or apoptosis. Since graft-versus-host disease (GVHD) is characterized by the expansion of donor-derived T cells destroying recipient tissue, we analyzed whether MDSCs can be used for GVHD prevention in murine allogeneic bone marrow transplantation models. Transplantation of MDSCs, generated from bone marrow cells by granulocyte-macrophage colony-stimulating factor (GM-CSF)/G-CSF in vitro, inhibited GVHD-induced death and attenuated histologic GVHD, whereas antitumor cytotoxicity of alloantigen-specific T cells was maintained. MDSCs expanded in vivo and invaded lymphatic and GVHD target organs. Major histocompatibility complex class I expression on MDSCs was dispensable for their suppressive capacity. Inhibition of GVHD required the presence of MDSCs during T-cell priming, whereas allogeneic T-cell numbers and homing in lymphoid and GVHD target organs were not considerably affected in MDSC-treated mice. However, MDSCs skewed allogeneic T cells toward type 2 T cells upregulating T helper 2 (Th2)-specific cytokines. Type 2 T-cell induction was indispensable for GVHD prevention since MDSC treatment failed to prevent GVHD when allogeneic STAT6-deficient T cells, which are unable to differentiate into Th2 cells, were transplanted. MDSC-induced Th2 induction might be applicable for GVHD treatment in clinical settings.

Glucocorticoids attenuate acute graft-versus-host disease by suppressing the cytotoxic capacity of CD8(+) T cells

Glucocorticoids (GCs) are released from the adrenal gland during inflammation and help to keep immune responses at bay. Owing to their potent anti-inflammatory activity, GCs also play a key role in controlling acute graft-versus-host disease (aGvHD). Here we demonstrate that mice lacking the glucocorticoid receptor (GR) in T cells develop fulminant disease after allogeneic bone marrow transplantation. In a fully MHC-mismatched model, transfer of GR-deficient T cells resulted in severe aGvHD symptoms and strongly decreased survival times. Histopathological features were aggravated and infiltration of CD8(+) T cells into the jejunum was increased when the GR was not expressed. Furthermore, serum levels of IL-2, IFNγ, and IL-17 were elevated and the cytotoxicity of CD8(+) T cells was enhanced after transfer of GR-deficient T cells. Short-term treatment with dexamethasone reduced cytokine secretion but neither impacted disease severity nor the CTLs' cytolytic capacity. Importantly, in an aGvHD model in which disease development exclusively depends on the presence of CD8(+) T cells in the transplant, transfer of GR-deficient T cells aggravated clinical symptoms and reduced survival times as well. Taken together, our findings highlight that suppression of CD8(+) T-cell function is a crucial mechanism in the control of aGvHD by endogenous GCs.

Utilizing glycogen synthase kinase-3β as a marker for the diagnosis of graft-versus-host disease

INTRODUCTION

Graft-versus-host disease (GVHD) is a deadly complication of allogeneic hematopoietic stem cell transplantation. Timely diagnosis is critical, because mortality rates for GVHD are high, increasing with disease severity. A diagnostic tool to predict GVHD before the onset of clinical symptoms could save many lives. On the cellular level, GVHD occurs when T cells from the transplant attack the tissues of the host, after perceiving them to be foreign. T-cell proliferation occurs even before clinical symptoms appear. Glycogen synthase kinase (GSK)-3β is a protein which regulates proliferation in many cell types including T-cells. GSK-3β has never been directly connected with GVHD and we applied GSK-3β as a novel marker for GVHD prediction, seeking herein to determine whether GSK-3β can be utilized as a marker for the early diagnosis of GVHD.

METHODS

For the mouse model of acute GVHD, irradiated mice underwent allogeneic splenocyte transplantation and GSK-3β expression levels and phosphorylation states were monitored in harvested spleens by western blot. FACS analysis was used to measure the number of T cells within the harvested spleens.

RESULTS

Mice developed observable GVHD symptoms by day 5 post-transplantation, with severe symptoms on day 6 requiring mice to be killed for humane reasons. A significantly increased number of T cells in the allogeneic mice correlated with GVHD development. GSK-3β protein expression levels and phosphorylation levels were significantly lower in allogeneic (GVHD) mice compared with negative (untreated) and positive (syngeneic transplant; non-GVHD) controls over time.

CONCLUSION

GSK-3β was directly connected with the onset and progression of GVHD. Therefore, it can be utilized as a marker for GVHD diagnosis in animals and potentially in humans.

Recombinant CD95-Fc (APG101) prevents graft-versus-host disease in mice without disabling antitumor cytotoxicity and T-cell functions

Graft-versus-host disease (GVHD) induced by transplant-derived T cells represents a major complication after allogeneic bone marrow transplantation (BMT). However, these T cells support engraftment, early T-cell immunity, and mediate the graft-versus-tumor (GVT) effect. Cytotoxic effector functions by transplanted T cells are predominantly mediated by the perforin/granzyme and the CD95/CD95L system. APG101, a novel recombinant human fusion protein consisting of the extracellular domain of CD95 and the Fc domain of an IgG1 antibody inhibited CD95L-induced apoptosis without interfering with T-cell function in vitro and was therefore tested for its ability to prevent GVHD in murine BMT models across minor or major histocompatibility barriers. Starting APG101 treatment either 1 day before or 6 days after transplantation effectively reduced clinical GVHD and rescued survival between 60% and 100% if GVHD was CD95L mediated. APG101 did not interfere with the GVT effect, because P815 mastocytoma and most importantly primary Bcr-Abl-transformed B-cell leukemias were completely eradicated by the alloantigen-specific T cells. Phenotype and homing of alloantigen-specific T cells or their perforin/granzyme-mediated cytotoxicity and proliferative capacity were not affected by APG101 treatment suggesting that APG101 therapy might be useful in GVHD prophylaxis without impairing T-cell function and most importantly preserving GVT activity.

Mouse models of graft-versus-host disease: advances and limitations

The limiting factor for successful hematopoietic stem cell transplantation (HSCT) is graft-versus-host disease (GvHD), a post-transplant disorder that results from immune-mediated attack of recipient tissue by donor T cells contained in the transplant. Mouse models of GvHD have provided important insights into the pathophysiology of this disease, which have helped to improve the success rate of HSCT in humans. The kinetics with which GvHD develops distinguishes acute from chronic GvHD, and it is clear from studies of mouse models of GvHD (and studies of human HSCT) that the pathophysiology of these two forms is also distinct. Mouse models also further the basic understanding of the immunological responses involved in GvHD pathology, such as antigen recognition and presentation, the involvement of the thymus and immune reconstitution after transplantation. In this Perspective, we provide an overview of currently available mouse models of acute and chronic GvHD, highlighting their benefits and limitations, and discuss research and clinical opportunities for the future.

In vitro-established alloantigen-specific CD8+ CTLs mediate graft-versus-tumor activity in the absence of graft-versus-host disease

Mature donor-derived T cells in allogeneic bone marrow (BM) transplants mediate the graft-versus-tumor (GVT) effect by recognizing alloantigens on leukemic cells. However, alloantigen reactivity towards non-malignant tissues also induces graft-versus-host disease (GVHD). Defining T-cell subpopulations that mediate the GVT effect in the absence of GVHD induction remains a major challenge in allogeneic BM transplantation. In this study, we show that in vitro-generated alloantigen-specific CD8(+) cytotoxic T cells (CTLs) established by weekly stimulation with alloantigen-expressing antigen-presenting cells did not induce GVHD in two major histocompatibility complex-mismatched BM transplantation models, where induction of lethal GVHD is dependent on the presence of either CD4(+) or CD8(+) T cells. Despite their strong alloantigen specificity, transplantation of CTLs did not induce the expression of GVHD-associated cytokines IFN-γ and TNF-α or clinical or histological signs of GVHD, and lead to a survival rate of above 90%. However, transplantation of unstimulated CD8(+) T cells, which were not primed by the alloantigen in vitro, induced GVHD in both the transplantation models. Although CTLs were impaired in GVHD induction, they efficiently eradicated Bcr-Abl-transformed B-cell leukemias or mastocytomas. Thus, in vitro-derived CTLs might be useful for optimizing anti-tumor therapy in the absence of GVHD induction.

Analysis of memory and effector CD8+ T cell subsets in chronic graft-versus-host disease

In humans, the selective depletion of CD8+ cells may prevent GVHD after allogeneic transplantation. These cells can infiltrate and damage target tissues. It is of interest to investigate the phenotypical characteristics and cytotoxic properties of the different CD8+ subsets in cGVHD patients. In a preliminary study we found that patients with cGVHD had a markedly elevated percentage of peripheral blood CCR7-/CD45RA+ cells compared to patients without cGVHD; conversely, the CCR7+/CD45RA+ subsets of CD8+ cells was significantly decreased. In this study, we report in depth on the phenotype of effector T cell subsets in cGVHD patients, as well as their proliferative capability, cytotoxic properties and cellular turnover. We confirm a predominance of effector T cell subsets in cGVHD patients and show that a large fraction of these cells down-regulate CCR7 and re-express CD45RA, thus approaching end-stage differentiation. Moreover CD8+ cells of cGVHD patients have low CD8 coreceptor expression, reduced proliferative potential and a high content of perforin and granzyme A. They also have a lower cell turnover and have more propensity to apoptosis, as demonstrated by BrdU incorporation. Taken together, our findings indicate a perturbation of the balance between naive/memory and effector/CD45RA+ CD8+ T cells, and suggest an involvement of the latter compartment characterized by a high content of cytotoxic equipment, in the pathogenesis of cGVHD.

Naive and memory T cells induce different types of graft-versus-host disease

The goal of this study was to compare the ability of donor naive and alloantigen-primed effector memory T cells to induce graft-vs-host disease after bone marrow transplantation in MHC-mismatched irradiated host mice. Purified CD4(+) naive (CD62L(high)CD44(low)) T cells and CD4(+) effector memory (CD62L(low)CD44(high)) T cells obtained from unprimed donors and donors primed to host alloantigens, respectively, were injected into host mice, and the rapidity, severity, and pattern of tissue injury of graft-vs-host disease was assessed. Unexpectedly, the naive T cells induced a more acute and severe colitis than the primed memory cells. Whereas the naive T cells expressing CD62L and CCR7 lymph node homing receptors vigorously expanded in mesenteric lymph nodes and colon by day 6 after transplantation, the primed memory T cells without these receptors had 20- to 100-fold lower accumulation at this early time point. These differences were reflected in the significantly more rapid decline in survival and weight loss induced by naive T cells. The primed memory T cells had a greater capacity to induce chronic colitis and liver injury and secrete IL-2 and IFN-gamma in response to alloantigenic stimulation compared with memory T cells from unprimed donors. Nevertheless, the expected increase in potency as compared with naive T cells was not observed due to differences in the pattern and kinetics of tissue injury.

Importance of interleukin-7 in the development of experimental graft-versus-host disease

Interleukin (IL)-7 promotes both thymopoiesis and mature T lymphocyte survival and proliferation in experimental murine models of hematopoietic stem cell (HSC) transplantation. Because HSC products for transplantation also may contain IL-7-responsive mature T lymphocytes, we examined whether IL-7 is necessary for the induction of GVHD after allogeneic bone marrow transplantation (BMT). Lethally irradiated C57BL6J (B6) and B6.IL-7(-/-) (both H2K(b)) recipient mice were co-transplanted with T cell-depleted (TCD) bone marrow cells and lymph nodes (LNs) from either congenic B6.SJL (CD45.1(+)) or allogeneic BALB/c (H2K(d)) donor mice. After transplantation, the recipient mice were subcutaneously injected with either human recombinant IL-7 or phosphate-buffered saline (PBS) for 60 days. No evidence of GVHD was detected in the congenic recipients or in the allogeneic B6/IL-7(-/-) recipients treated with PBS; in contrast, significantly increased rates of GVHD-related mortality and morbidity were found in the allogeneic B6.IL-7(-/-) recipients treated with IL-7. The proliferation and number of donor T cells were significantly lower at day 30 post-BMT in the PBS-treated B6.IL-7(-/-) recipients compared with the IL-7-treated B6.IL-7(-/-) mice. These experiments demonstrate that IL-7 is an important factor in the development of GVHD, presumably by supporting the survival, proliferation, and possibly activation of alloreactive donor-derived T cells in the recipients.

Radiation protocols determine acute graft-versus-host disease incidence after allogeneic bone marrow transplantation in murine models

PURPOSE

Effects of radiation sources used for total body irradiation (TBI) on Graft-versus-Host Disease (GvHD) induction were examined.

MATERIALS AND METHODS

In a T cell receptor (TCR) transgenic mouse model, single fraction TBI was performed with different radiation devices ((60)Cobalt; (137)Cesium; 6 MV linear accelerator), dose rates (0.85; 1.5; 2.9; 5 Gy/min) and total doses before allogeneic bone marrow transplantation (BMT). Recipients were observed for 120 days. Different tissues were examined histologically.

RESULTS

Acute GvHD was induced by a dose rate of 0.85 Gy/min ((60)Cobalt) and a total dose of 9 Gy and injection of 5 x 10(5) lymph node cells plus 5 x 10(6) bone marrow cells. Similar results were obtained using 6 MV linear accelerator- (linac-) photons with a dose rate of 1.5 Gy/min and 0.85 Gy/min, a total dose of 9.5 Gy and injection of same cell numbers. TBI with (137)Cesium (dose rate: 2.5 Gy/min) did not lead reproducibly to lethal acute GvHD.

CONCLUSIONS

Experimental TBI in murine models may induce different immunological responses, depending on total energy, total single dose and dose rate. GvHD might also be induced by TBI with low dose rates.

Prevention of graft-versus-host disease by anti IL-7Ralpha antibody

Graft-versus-host disease (GVHD) continues to be a serious complication that limits the success of allogeneic bone marrow transplantation (BMT). Using IL-7-deficient murine models, we have previously shown that IL-7 is necessary for the pathogenesis of GVHD. In the present study, we determined whether GVHD could be prevented by antibody-mediated blockade of IL-7 receptor alpha (IL-7Ralpha) signaling. C57/BL6 (H2K(b)) recipient mice were lethally irradiated and underwent cotransplantation with T-cell-depleted (TCD) BM and lymph node (LN) cells from allogeneic BALB/c (H2K(d)) donor mice. Following transplantation, the allogeneic BMT recipients were injected weekly with either anti-IL-7Ralpha antibody (100 mug per mouse per week) or PBS for 4 weeks. Anti-IL-7Ralpha antibody treatment significantly decreased GVHD-related morbidity and mortality compared with placebo (30% to 80%). IL-7Ralpha blockade resulted in the reduction of donor CD4(+) or CD8(+) T cells in the periphery by day 30 after transplantation. Paradoxically, the inhibition of GVHD by anti-IL-7Ralpha antibody treatment resulted in improved long-term thymic and immune function. Blockade of IL-7R by anti-IL-7Ralpha antibody resulted in elimination of alloreactive T cells, prevention of GVHD, and improvement of donor T-cell reconstitution.

Graft-versus-host disease

Allogeneic haematopoietic stem-cell transplantation (SCT) is a curative therapy for haematological malignancies and inherited disorders of blood cells, such as sickle-cell anaemia. Mature alphabeta T cells that are contained in the allografts reconstitute T-cell immunity and can eradicate malignant cells in the recipient. Unfortunately, these T cells recognize the recipient as 'non-self' and employ a wide range of immune mechanisms to attack recipient tissues in a process known as graft-versus-host disease (GVHD). The full therapeutic potential of allogeneic haematopoietic SCT will not be realized until approaches to minimize GVHD, while maintaining the positive contributions of donor T cells, are developed. This Review focuses on research in mouse models pursued to achieve this goal.

Advances in the understanding of acute graft-versus-host disease

Allogeneic stem cell transplantation (SCT) remains the definitive immunotherapy for malignancy. However, morbidity and mortality due to graft-vs.-host disease (GVHD) remains the major barrier to its advancement. Emerging experimental data highlights the immuno-modulatory roles of diverse cell populations in GVHD, including regulatory T cells, natural killer (NK) cells, NK T cells, gammadelta T cells, and antigen presenting cells (APC). Knowledge of the pathophysiology of GVHD has driven the investigation of new rational strategies to both prevent severe GVHD and treat steroid-refractory GVHD. Novel cytokine inhibitors, immune-suppressant agents known to preserve or even promote regulatory T-cell function and the depletion of specific alloreactive T-cell sub-populations all promise significant advances in the near future. As our knowledge and therapeutic options expand, the ability to limit GVHD whilst preserving anti-microbial and tumour responses becomes a realistic prospect.

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.

Revisiting the role of hematopoietic stem cell transplantation in chronic lymphocytic leukemia

Since the advent of hematopoietic stem cell transplantation more than 40 years ago, numerous methods of transplantation have been developed, modified and improved upon. Although hematopoietic stem cell transplantation has been used in a variety of malignant diseases since then, its use in the treatment of chronic lymphocytic leukemia has recently started to gain interest. Patients with chronic lymphocytic leukemia are generally elderly, and because of its relatively benign course, they were not considered suitable candidates for hematopoietic stem cell transplantation. Nonetheless, there have been marked improvements in transplantation techniques, including better conditioning regimens that have decreased treatment-related morbidity and mortality. In this article, the authors review the most recent data on hematopoietic stem cell transplantation in chronic lymphocytic leukemia as well as the change in risk stratification based on newer prognostic factors and its impact on treatment decisions in chronic lymphocytic leukemia.

A CD8 DE loop peptide analog prevents graft-versus-host disease in a multiple minor histocompatibility antigen-mismatched bone marrow transplantation model

Donor CD8(+) T cells can be potent mediators of graft-versus-host disease (GVHD) after allogeneic hematopoietic cell transplantation to either major histocompatibility complex (MHC) class I-or multiple minor histocompatibility antigen-mismatched recipients. To develop small molecular inhibitors of CD8(+) T-cell activity, theoretical structural analysis of the human CD8 alpha molecule was previously used to identify potential functional surface epitopes that interact with the MHC class I molecule. The DE loop (p71-78) was identified as such a target region, and a panel of synthetic cyclized peptide mimics of this region were tested for their inhibitory effects on cytotoxic T lymphocyte activity in human cell-mediated lympholysis assays. Peptide 1109 (CKRLGDTFVC) was most effective at inhibiting specific target cell lysis. Accordingly, studies were conducted to determine whether there was sufficient cross-species homology in the DE loop region and its nonpolymorphic interactive site on the beta(2)-microglobulin domain of the MHC class I molecule to allow similar inhibition of murine CD8(+) cytotoxic T lymphocyte activity. On the basis of strong in vitro inhibitory activity of 1109 in the murine system, the capacity of the peptide to inhibit in vivo CD8(+) T-cell effector functions in skin and hematopoietic stem cell transplantation models was examined. In the C57BL/6 anti-bm1 skin allograft rejection model, across an MHC class I barrier, a single injection of 1109 at the time of transplantation significantly prolonged graft survival. Moreover, 1109 administered at the time of transplantation in the multiple minor histocompatibility antigen-disparate B10.BR-->CBA GVHD model significantly prolonged the survival of lethally irradiated mice that underwent transplantation with donor bone marrow cells and CD8(+) T cells. Histopathologic analysis confirmed that mice treated with the synthetic peptide exhibited diminution of epithelial target cell injury. Specificity of the peptide effect was evidenced by draining lymph node cells from B10.BR mice that had been challenged with CBA lymphocytes and simultaneously treated with 1109. These cells could not generate secondary proliferative responses in vitro upon stimulation with CBA splenocytes but could respond to third-party C57BL/6 stimulation. Thus, the 1109 peptide has potential application in the prevention of CD8-mediated GVHD development.

Host dendritic cells alone are sufficient to initiate acute graft-versus-host disease

Alloantigen expression on host APCs is essential to initiate graft-vs-host disease (GVHD); however, critical APC subset remains to be elucidated. We compared the ability of dendritic cells (DCs) and B cells to initiate acute GVHD by an add-back study of MHC class II-expressing APCs (II(+/+)) into MHC class II-deficient (II(-/-)) mice that were resistant to CD4-dependent GVHD. Injection of host-derived, but not donor-derived, II(+/+) DCs or host-derived II(+/+) B cells, was sufficient to break GVHD resistance of II(-/-) mice and induced lethal acute GVHD. By contrast, host-derived II(+/+) B cells, both naive and LPS stimulated, failed to induce activation or tolerance of donor CD4(+) T cells. Similarly, in a model of CD8-dependent GVHD across MHC class I mismatch injection of allogeneic DCs, but not B cells, induced robust proliferation of donor CD8(+) T cells and broke GVHD resistance of chimeric recipients in which APCs were syngeneic to donors. These results demonstrate that host-derived DCs are critical in priming donor CD4(+) and CD8(+) T cells to cause GVHD, and selective targeting of host DCs may be a promising strategy to prevent GVHD.

CD4+ T Cells Regulate CD8+ T Cell-Mediated Cutaneous Immune Responses by Restricting Effector T Cell Development through a Fas Ligand-Dependent Mechanism

The magnitude and duration of CD8(+) T cell-mediated responses in the skin to hapten sensitization and challenge, contact hypersensitivity (CHS), is negatively regulated by CD4(+) T cells through an unknown mechanism. In this study we show that CD4(+) T cells restrict the development and expansion of hapten-specific CD8(+) T cells mediating CHS responses to 2,4-dinitrofluorobenzene. In the absence of CD4(+) T cells, high numbers of hapten-specific CD8(+) T cells producing IFN-gamma were detected in the skin-draining lymph nodes on day 5 postsensitization, and these numbers decreased slightly, but were maintained through day 9, correlating with the increased magnitude and duration of CHS responses observed in these mice. In the presence of CD4(+) T cells, the number of hapten-specific CD8(+) T cells producing IFN-gamma detected on day 5 postsensitization was lower and quickly fell to background levels by day 7. The limited development of effector CD8(+) T cells was associated with decreased numbers of hapten-presenting dendritic cells in the lymphoid priming site. This form of immunoregulation was absent after sensitization of Fas ligand-defective gld mice. Transfer of wild-type CD4(+) T cells to gld mice restored the negative regulation of CD8(+) T cell priming and the immune response to hapten challenge in gld-recipient mice. These results indicate that CD4(+) T cells restrict hapten-specific CD8(+) T cell priming for CHS responses through a Fas ligand-dependent mechanism.

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.

The balance between donor T cell anergy and suppression versus lethal graft-versus-host disease is determined by host conditioning

Graft-vs-host disease (GVHD) remains the most life-threatening complication following the transfer of allogeneic bone marrow into immunocompromised hosts. Transferred alloreactive T cells respond in a complex manner. While massive T cell expansion is observed upon entry into an allogeneic environment, anergy, apoptosis, and repertoire selection are also observed. The study presented here shows that alloreactive T cell expansion and differentiation vs anergy and suppression are dramatically influenced by host conditioning. Using alloreactive CD4(+) and CD8(+) TCR transgenic (Tg) T cells, a novel GVHD model is presented that allows for the visualization of how alloreactive T cells behave when host conditioning is manipulated. Following the transfer of alloreactive CD4(+) and CD8(+) TCR Tg T cells into sublethally irradiated hosts, both Tg T cells populations expand, develop effector function, and cause GVHD. In contrast, when Tg T cells are transferred in non-irradiated hosts, expansion is observed, but there is no development of effector function or disease. Assessment of CD4(+) Tg T cell function following transfer into non-irradiated hosts reveals that these CD4(+) Tg cells are profoundly anergic and have acquired a regulatory function, as manifested in their ability to suppress the expansion of naive TCR Tg T cells in vitro and in vivo as well as the development of GVHD. These findings underscore the decisive effect of the inflammatory environment created by irradiation in determining the ultimate fate and function of alloreactive T cells in vivo

Regulation of alloresponses after bone marrow transplantation using donor T cells expressing a thymidine kinase suicide gene

Donor T cells have a critical role in promoting engraftment after allogeneic bone marrow transplantation (BMT), but also cause graft versus host disease (GVHD). Ex vivo T cell depletion has been an effective strategy to reduce GVHD but has been associated with impaired alloengraftment and host immunity. Using an MHC-mismatched murine model, we have examined an alternative approach to GVHD prevention whereby donor T cells are selectively eliminated in vivo after BMT using transgenic T cells in which a thymidine kinase (TK) suicide gene is targeted to the T cell. Lethally irradiated AKR/J (H-2k) mice transplanted with TCD C57BL/6 (B6)(H-2b) bone marrow (BM) plus B6 TK+ T cells and then treated with GCV post-BMT had significantly less GVHD severity and improved immune reconstitution compared to untreated mice, providing proof of principle that this strategy could mitigate GVHD. To assess the impact of GCV administration on alloengraftment, sublethally irradiated AKR mice were transplanted with TCD B6 BM alone or admixed with limiting numbers (5 x 10(5)) of B6 TK+ T cells. When tested 3-4 weeks post-transplant, control TCD BM mice all rejected their grafts. Conversely, > 80% of GCV-treated mice had sustained donor T cell engraftment comparable to what was observed in untreated animals. Notably, GCV-treated mice were more likely to have mixed T cell chimerism early post-BMT than untreated animals, however, nearly all GCV-treated mice progressed to complete donor T cell engraftment by 2-3 months post-transplant. Preservation of engraftment was critically dependent upon the GCV administration schedule and required that GCV be delayed for at least one week post-transplant. These studies demonstrate that specific incorporation of a suicide gene into donor T cells is a viable strategy that can be employed to reduce GVHD without compromising alloengraftment.

Acute graft-versus-host disease does not require alloantigen expression on host epithelium

Alloantigen expression on host antigen-presenting cells (APCs) is essential to initiate graft-versus-host disease (GvHD); therefore, alloantigen expression on host target epithelium is also thought to be essential for tissue damage. We tested this hypothesis in mouse models of GvHD using bone-marrow chimeras in which either major histocompatibility complex class I or class II alloantigen was expressed only on APCs. We found that acute GvHD does not require alloantigen expression on host target epithelium and that neutralization of tumor necrosis factor-alpha and interleukin-1 prevents acute GvHD. These results pertain particularly to CD4-mediated GvHD but also apply, at least in part, to CD8-mediated GvHD. These results challenge current paradigms about the antigen specificity of GvHD effector mechanisms and confirm the central roles of both host APCs and inflammatory cytokines in acute GvHD.

Unique patterns of surface receptors, cytokine secretion, and immune functions distinguish T cells in the bone marrow from those in the periphery: impact on allogeneic bone marrow transplantation

The "conventional" NK1.1(-) T cells from mouse blood and marrow were compared with regard to surface receptors, cytokine secretion, and function. Most blood NK1.1(-) CD4(+) and CD8(+) T cells expressed the naive CD44(int/lo)CD62L(hi)CD45RB(hi) T-cell phenotype typical of those in the peripheral lymphoid tissues. In contrast, most marrow NK1.1(-) CD4(+) and CD8(+) T cells expressed an unusual CD44(hi)CD62L(hi)CD45RB(hi) phenotype. The blood NK1.1(-) CD4(+) T cells had a naive T-helper cytokine profile and a potent capacity to induce lethal graft versus host (GVH) disease in a C57BL/6 donor to a BALB/c host bone marrow transplantation model. In contrast, the marrow NK1.1(-) CD4(+) T cells had a Th0 cytokine profile and failed to induce lethal GVH disease, even at 20-fold higher numbers than those from the blood. NK1.1(-) CD8(+) T cells from the blood but not the marrow induced lethal GVH disease. Nevertheless, the marrow NK1.1(-) CD8(+) T cells induced potent antitumor activity that was augmented by marrow NK1.1(-) CD4(+) T cells and facilitated hematopoietic progenitor engraftment. The inability of marrow CD4(+) and CD8(+) T cells to induce GVH disease was associated with their inability to expand in the blood and gut of allogeneic recipients. Because neither the purified marrow CD4(+) or CD8(+) T cells induced GVH disease, their unique features are desirable for inclusion in allogeneic bone marrow or hematopoietic progenitor transplants.

Regulatory role of CD4+ T cells during the development of contact hypersensitivity responses

Contact hypersensitivity (CHS) is a T cell-mediated immune response to cutaneous sensitization and subsequent challenge with haptens such as dinitrofluorobenzene and oxazolone. Many aspects concerning the development and regulation of CHS remain unknown. Using CHS as a model of T cell-mediated immune responses to antigens deposited in the skin we have studied the development and function of effector and regulatory T cell components of this response. These studies have revealed the effector role of hapten-specific CD8+ T cells in this response. In contrast, hapten-specific CD4+ T cells negatively regulate the magnitude and duration of the response. In this article we propose a model in which the CD4+ T cell compartment regulates the development of effector CD8+ T cells during sensitization for CHS and discuss potential mechanisms that CD4+ T cells might utilize to mediate this regulation.

Injection of CD4+ and CD8+ cells with donor or host accessory cells induces acute graft-vs-host disease in human skin in immunodeficient mice

OBJECTIVE

We examined cell subsets with respect to cutaneous graft-vs-host disease by cell sorting selection of subsets of human mononuclear cells and injecting the subsets subcutaneously in a mouse model.

MATERIALS AND METHODS

Cell suspensions containing cultured human epidermal cells and dermal fibroblasts from a single donor mixed with lymphoid cell subsets positively selected using the FACSVantage cell sorting instrument and/or MACS cell isolation kits from unrelated individuals were injected into immunodeficient mice. This model is known to generate human skin with histologic findings similar to human graft-vs-host disease.

RESULTS

Donor T-cell subsets CD4(+) and CD8(+) plus either host or donor CD14(+) cells were necessary to cause acute cutaneous graft-vs-host disease. Although graft-vs-host disease can result from recognition of class I antigens expressed on human cutaneous cells by donor peripheral blood mononuclear cells, additional recognition of class II antigens expressed on host mononuclear cells resulted in more severe histologic manifestations. Dendritic cells that differentiated from donor and host monocytes also showed competent accessory cell function in this system.

CONCLUSIONS

Based on this model, human cutaneous graft-vs-host disease was caused by donor CD4(+) cells and CD8(+) cells activated through recognition of host antigens, including class I and class II antigens presented by either donor or host CD14(+) cells or dendritic cells.

Protection from lethal murine graft-versus-host disease without compromise of alloengraftment using transgenic donor T cells expressing a thymidine kinase suicide gene

Donor T cells play a pivotal role in facilitating alloengraftment but also cause graft-versus-host disease (GVHD). Ex vivo T-cell depletion (TCD) of donor marrow is the most effective strategy for reducing GVHD but can compromise engraftment. This study examined an approach whereby donor T cells are selectively eliminated in vivo after transplantation using transgenic mice in which a thymidine kinase (TK) suicide gene is targeted to the T cell using a CD3 promoter/enhancer construct. Lethally irradiated B10.BR mice transplanted with major histocompatibility complex (MHC)-incompatible TCD C57BL/6 (B6) bone marrow (BM) plus TK(+) T cells were protected from GVHD after treatment with ganciclovir (GCV) in a schedule-dependent fashion. To examine the effect of GCV treatment on alloengraftment, sublethally irradiated AKR mice underwent transplantation with TCD B6 BM plus limiting numbers (5 x 10(5)) of B6 TK(+) T cells. Animals treated with GCV had comparable donor engraftment but significantly reduced GVHD when compared with untreated mice. These mice also had a significantly increased number of donor splenic T cells when assessed 4 weeks after bone marrow transplantation. Thus, the administration of GCV did not render recipients T-cell deficient, but rather enhanced lymphocyte recovery. Adoptive transfer of spleen cells from GCV-treated chimeric mice into secondary AKR recipients failed to cause GVHD indicating that donor T cells were tolerant of recipient alloantigens. These studies demonstrate that administration of TK gene-modified donor T cells can be used as an approach to mitigate GVHD without compromising alloengraftment.

Decreased graft-versus-host disease after haplotype mismatched bone marrow allografts in miniature swine following interleukin-2 treatment

Graft-versus-host disease (GVHD) is an important complication of bone marrow transplantation after transplants between HLA-mismatched donor/recipient pairs. In mice, giving IL-2 post transplant decreases GVHD in this setting. We studied high-dose IL-2 therapy in pigs. Transplants were carried out after conditioning with fractionated total body radiation and cyclophosphamide. Fourteen pigs received a fully mismatched bone marrow transplant (six with IL-2; eight without IL-2), and six received a single haplotype class II mismatched transplant (three with IL-2; three without IL-2). GVHD was evaluated by skin histology. All fully mismatched recipients had severe GVHD (grade 2-3) and died within 13 to 51 days whether or not they received IL-2. Pigs receiving a one haplotype class II mismatched transplant without IL-2 developed severe skin GVHD lasting for 8-45 days; all died within 57 days. Similar pigs receiving IL-2 post transplant had no or only mild skin GVHD for less than 15 days; two are long-term survivors. Bone Marrow Transplantation (2000) 25, 47-52.

'Self' tolerance in a parent-->F1 radiation chimera

The extent to which T cell immune tolerance to self tissue antigens is acquired during intrathymic development, or also may occur elsewhere in the animal, remains unclear. Experiments have been designed to explore this using allogeneic hematopoietic radiation chimeras in which thymectomized CB6F1 (H-2(b/d)) host mice were engrafted with day 16 C57BL/6 (H-2b) fetal thymus tissues, irradiated with 950 rad 3 weeks later, and reconstituted with day 14 C57BL/6 fetal liver cells. Chimeras constructed in this manner had thymus grafts which developed with normal structure and cellularity as determined from histological sections, and had normal proportions of CD4+ 8- and CD4- 8+ peripheral T cells of donor H-2b origin. Mice showed no signs of acute or chronic GVHD when followed for six months and, although T cells from chimeras were non-reactive to donor (H-2b) or host (H-2d) MHC, they responded to third party (H-2k) alloantigens in primary mixed-lymphocyte reactions. To determine whether tolerance might have been induced by radioresistant host hematopoietic cells, mice were treated with anti-I-Ad monoclonal antibody after irradiation and fetal liver cell transfer. The pattern of alloreactivity of T cells from those animals closely resembled that of non-antibody treated mice, suggesting that tolerance to MHC expressed within the host probably was not due to radioresistant class-II-bearing cells in chimeras. These findings imply that immune tolerance to self antigens can be controlled at sites outside the thymus, and they provide further evidence that allogeneic chimeras can be constructed when elimination of mature T cells from the donor hematopoietic pool has been effectively achieved.

IL-11 separates graft-versus-leukemia effects from graft-versus-host disease after bone marrow transplantation

We recently showed that IL-11 prevents lethal graft-versus-host disease (GVHD) in a murine bone marrow transplantation (BMT) model of GVHD directed against MHC and minor antigens. In this study, we have investigated whether IL-11 can maintain a graft-versus-leukemia (GVL) effect. Lethally irradiated B6D2F1 mice were transplanted with either T cell-depleted (TCD) bone marrow (BM) alone or with BM and splenic T cells from allogeneic B6 donors. Animals also received host-type P815 mastocytoma cells at the time of BMT. Recipients were injected subcutaneously with recombinant human IL-11 or control diluent twice daily, from 2 days before BMT to 7 days after BMT. TCD recipients all died from leukemia by day 23. All control- and IL-11-treated allogeneic animals effectively rejected their leukemia, but IL-11 also reduced GVHD-related mortality. Examination of the cellular mechanisms of GVL and GVHD in this system showed that IL-11 selectively inhibited CD4-mediated GVHD, while retaining both CD4- and CD8-mediated GVL. In addition, IL-11 treatment did not affect cytolytic effector functions of T cells after BMT either in vivo or in vitro. Studies with perforin-deficient donor T cells demonstrated that the GVL effect was perforin dependent. These data demonstrated that IL-11 can significantly reduce CD4-dependent GVHD without impairing cytolytic function or subsequent GVL activity of CD8(+) T cells. Brief treatment with IL-11 shortly after BMT may therefore represent a novel strategy for separating GVHD and GVL.

The fate of donor T-cell receptor transgenic T cells with known host antigen specificity in a graft-versus-host disease model

BACKGROUND

The expansion of transgenic donor CD8+ T-cells with known allospecificity against a host MHC class I alloantigen was examined in a murine graft-versus-host disease (GVHD) model.

METHODS

Lethally irradiated, Ld+ BALB/c mice received bone marrow cells and spleen cells from anti-Ld 2C T-cell receptor (TCR)-transgenic B6 mice, alone or with normal B6 spleen cells. Transgenic TCR-bearing T-cell expansion, apoptosis, and function were monitored at various time points and were correlated with clinical outcome.

RESULTS

Fifteen-fold clonal expansion of 2C CD8 cells occurred by day 4 after bone marrow transplantation. Between days 4 and 7, increasing proportions of 2C CD8 cells underwent apoptotic cell death, coincident with a 7-15-fold decline in their numbers. CD8 and TCR expression were down-regulated on 2C CD8 cells by day +4 after bone marrow transplantation, and they were anergic to TCR-mediated stimulation. Clinically, the BALB/c recipients of 2C spleen cells exhibited only minimal chronic GVHD. In contrast, lethally irradiated BALB/c mice receiving similar numbers of non-transgenic B6 bone marrow cells and spleen cells exhibited severe GVHD (median survival time: 28 days). The addition of a small number of 2C spleen cells to the inoculum accelerated GVHD mortality, and 2C CD8 cells showed a similar time course of expansion and decline to that observed in recipients of larger numbers of 2C cells alone.

CONCLUSIONS

Initial clonal expansion, down-regulation of CD8 and TCR, anergy, and later deletion of graft-versus-host-reactive CD8 cells via apoptosis occurs in lethally irradiated recipients. Expansion of a single CD8 clone produces much less severe GVHD than that induced by a polyclonal, mixed CD4 plus CD8 response. These results have implications for GVHD pathogenesis and its sometimes self-limited nature.

Prevention of Graft-Versus-Host Disease by Induction of Immune Tolerance With Ultraviolet B-Irradiated Leukocytes in H-2 Disparate Bone Marrow Donor

Transfusions (Tx) of Ultraviolet B (UVB)-irradiated peripheral blood mononuclear leukocytes (MNL) have been shown to induce humoral immune tolerance to major histocompatability complex (MHC) antigens (Blood 88:4375, 1996). To determine whether cellular immune tolerance to MHC antigens can be induced by the same approach, transplantation of bone marrow and spleen cells from tolerant donors across the H-2 barrier was conducted to study its effect on prevention of graft-versus-host disease (GVHD). After immune tolerance induction by four weekly Tx of UVB-irradiated BALB/c (H-2d) peripheral blood MNL into CBA/HT6 (H-2k) mice, bone marrow cells (BMC) and spleen MNL from tolerant or naive CBA mice were transplanted into lethally irradiated BALB/c mice. The transplanted mice were followed by measuring body weight, peripheral leukocyte counts, GVHD, survival, and cytokine response. All BALB/c recipient mice were fully engrafted with H-2k CBA donor cells after transplantation. The severity of GVHD was significantly attenuated in BALB/c mice transplanted with BMC and spleen MNL from tolerant CBA donor mice. The recovery of peripheral leukocyte and lymphocyte counts were faster and more complete in mice transplanted with cells from the tolerant donors. The serum cytokine profile after transplantation with tolerant donor cells showed increased interleukin-4 and reduced gamma interferon that are consistent with a polarized Th2 response. The results pooled from three separate experiments showed that BALB/c mice transplanted with 5 × 106 BMC and 4 × 105spleen MNL from tolerant CBA donors had better overall survival than the control group (72% v 17%, P = .018). The findings show that transplantation with bone marrow and spleen cells from tolerant H-2 disparate donor mice is associated with significant attenuation of GVHD and better outcomes. The results also support that transfusions of UVB-irradiated leukocytes may induce cellular immune tolerance.

CD4 T cells can reject major histocompatibility complex class I-incompatible skin grafts

We have re-investigated the roles of CD4 and CD8 T cell subsets in skin graft rejection across a single class I MHC disparity. Recipient mice were transplanted with skin from donors transgenic for the class I MHC molecule Kb. As expected, CD8 T cells were sufficient for rapid injection; but surprisingly, CD4 T cells were also competent to do the same. Rejection was dependent on one or the other subset, since elimination of both resulted in indefinite graft survival. The possibility that alloantibody was the downstream effector of CD4 mediated rejection was excluded because CD8-depleted mice rendered B cell deficient still rejected rapidly, but T cell-depleted recipients with pre-existing high titers of alloantibody were unable to do so. In addition, if CD4 cells act to reject by recruiting and/or activating macrophages then this was not dependent on CR3, IFN-gamma or TNF-alpha. Transplantation of skin grafts where the MHC class I disparity was at the level of passenger leukocytes only, demonstrated that transient bystander damage could occur, but that this was insufficient to result in full rejection. We surmise that for CD4 T cells to reject an MHC class I-incompatible graft it is necessary that an appropriate allogeneic peptide is processed and presented in the context of recipient MHC class II. CD4 T cells from B6 mice may fail to reject skin from MHC class I mutants because of the lack of such MHC class II-restricted presentation.

Analysis of graft-versus-host disease (GVHD) and graft rejection using MHC class I-deficient mice

GVHD is a major complication in allogeneic bone marrow transplantation (BMT). MHC class I mismatching increases GVHD, but in MHC-matched BMT minor histocompatibility antigens (mH) presented by MHC class I result in significant GVHD. To examine the modification of GVHD in the absence of cell surface MHC class I molecules, beta2-microglobulin-deficient mice (beta2m(-/-)) were used as allogeneic BMT recipients in MHC- and mH-mismatched transplants. Beta2m(-/-) mice accepted MHC class I-expressing BM grafts and developed significant GVHD. MHC (H-2)-mismatched recipients developed acute lethal GVHD. In contrast, animals transplanted across mH barriers developed indolent chronic disease that was eventually fatal. Engrafted splenic T cells in all beta2m(-/-) recipients were predominantly CD3+alphabetaTCR+CD4+ cells (15-20% of all splenocytes). In contrast, CD8+ cells engrafted in very small numbers (1-5%) irrespective of the degree of MHC mismatching. T cells proliferated against recipient strain antigens and recognized recipient strain targets in cytolytic assays. Cytolysis was blocked by anti-MHC class II but not anti-CD8 or anti-MHC class I monoclonal antibodies (MoAbs). Cytolytic CD4+ T cells induced and maintained GVHD in mH-mismatched beta2m(-/-) mice, supporting endogenous mH presentation solely by MHC class II. Conversely, haematopoietic beta2m(-/-) cells were unable to engraft in normal MHC-matched recipients, presumably due to natural killer (NK)-mediated rejection of class I-negative cells. Donor-derived lymphokine-activated killer cells (LAK) were unable to overcome graft rejection (GR) and support engraftment.

A Common Immunoregulatory Locus Controls Susceptibility to Actively Induced Experimental Allergic Encephalomyelitis and Experimental Allergic Orchitis in BALB/c Mice

Previous studies have shown that differential susceptibility to actively induced experimental allergic encephalomyelitis (EAE) and experimental allergic orchitis (EAO) exists among various BALB/c substrains. Of eight substrains studied for EAE and 13 for EAO, BALB/cJ mice are phenotypically the most resistant to disease induction. Resistance to both diseases is controlled by single recessive mutations unlinked to any of the known alleles distinguishing BALB/cJ mice. In this study, segregation analysis employing a second generation backcross population shows that resistance to both EAE and EAO is due to a mutation in a common immunoregulatory gene. The role of immunoregulatory cells in controlling EAE resistance was examined using adoptive transfer protocols. BALB/cJ mice immunized with spinal cord homogenate plus adjuvants generate immunoregulatory spleen cells (SpC) that, when transferred to naive BALB/cByJ recipients, reduce the incidence and severity of EAE. Treatment of such cells with either cytotoxic monoclonal anti-Thy1.2 or anti-CD4 plus C′ before transfer abrogates the ability of BALB/cJ SpC to inhibit disease. In contrast, neither SpC from adjuvant-immunized BALB/cJ nor spinal cord homogenate- plus adjuvant-primed BALB/cByJ donors influences the incidence or severity of disease observed in recipients. In addition, the role of environment in influencing susceptibility to EAE and EAO in BALB/c mice is documented. Taken together, these results support the existence of a common disease susceptibility locus in the pathways leading to two autoantigenically distinct CD4+ T cell-mediated, organ-specific, autoimmune diseases.

Recent advances in graft-versus-host disease (GVHD) prevention

In the 1970s and 1980s, GVHD prevention approaches were limited in number. Recent advances in our understanding of the requirements for T-cell immune responses and for basic mechanism(s) involved in GVHD pathophysiology have led to exciting new strategies for GVHD prevention. This review focuses upon recent developments in GVHD prevention generated over the past 5 years. We have selected five different types of strategies to highlight including: 1) the in vivo targeting of GVHD-reactive T cells using either intact and F(ab')2 fragments of monoclonal antibodies directed against T-cell-surface determinants or immunotoxins which consist of antibodies linked to toxins, 2) a comparison of the in vivo immunosuppressive effects of FK506 and rapamycin on T-cell signaling, 3) the inhibition of T-cell activation through blockade of costimulatory or adhesogenic signals, 4) shifting the balance between acute GVHD-inducing T-helper-type 1 (Th1) T cells to anti-inflammatory T-helper-type 2 (Th2)-type T cells, and 5) the regulation of alloreactive T-cell activation by treatment with peptide analogs which affect either TCR/MHC, CD4/MHC class II, or CD8/MHC class I interactions. Collectively, these approaches are illustratrative of the progress made in extending our GVHD prevention armamentarium.

The role of T cells in infection-driven interstitial pneumonia after bone marrow transplantation in mice

Over the course of five weeks, there were no significant histopathological changes in the lungs of mice given either allogeneic or syngeneic bone marrow transplants (BMT) with whole body irradiation (WBI). However, all mice that received both WBI and Pneumocystis carinii inoculation developed a more protracted and severe interstitial pneumonia than that of normal mice given P carinii. This pneumonia was exacerbated by allogeneic BMT but was ameliorated by syngeneic BMT. The interstitial pneumonia caused by allogeneic BMT and P carinii infection was associated with the influx of large numbers of activated CD4+ cells of donor origin. Depletion of CD4+ T cells in vivo in these mice inhibited both the development of graft-versus-host disease (GVHD) and the interstitial pneumonia. In vitro depletion of T cells before allogeneic BMT and P carinii infection also inhibited GVHD-however, it did not stop the development of interstitial pneumonia caused by the infiltration of host-derived T cells. These results indicate that in this model infection is required for development of interstitial pneumonia after allogeneic BMT. This interstitial pneumonia can be caused by the accumulation of CD4+ cells of either donor or recipient origin but not by CD8+ cells. The accumulation of these cells in lungs of normal mice in response to P carinii does not cause interstitial pneumonia, but irradiation of the host before the cellular accumulation does. This interstitial pneumonia can occur in infected mice after either syngeneic or allogeneic BMT, but is exacerbated by GVHD.

Gamma delta T cells are secondary participants in acute graft-versus-host reactions initiated by CD4+ alpha beta T cells

To examine the role of T cell subpopulations in an acute graft-versus-host (GVH) reaction, gamma delta T cells and alpha beta T cells expressing one of the two prototypic V beta families were negatively isolated from adult blood samples and injected into allogeneic chick embryos. CD4+ alpha beta T cells expressing either V beta 1 or V beta 2 receptors were equally capable of inducing acute GVH reactions, consistent with the idea that alpha beta T cell alloreactivity is determined by CDR3 variability. By themselves, the gamma delta T cells were incapable of inducing GVH reactions. However, host gamma delta T cells were recruited into the donor alpha beta T cell-initiated lesions, where they were activated and induced to proliferate. The data suggest that gamma delta T cells may play a secondary role in GVH reactions.

The role of alloreactive cytotoxic and lymphokine-secreting T lymphocytes in the development of acute graft-versus-host disease

The development of acute graft-versus-host disease (GVHD) after allogeneic bone marrow transplantation is mediated by alloreactive donor T cells infused with the bone marrow inoculum. This review discusses the role and significance of host-specific cytotoxic and lymphokine-secreting donor T cells for the prediction and generation of acute GVHD.