Variable capacity of L3T4+ T cells to cause lethal graft-versus-host disease across minor histocompatibility barriers in mice

Outcomes of human leukocyte antigen matched sibling transplant from consanguineous versus non-consanguineous parents, a single center experience

Matching HLA between donor and recipient pairs significantly improves engraftment and decreases GvHD. However, even in HLA matched siblings, the risk of graft failure and GvHD still exist and is partially attributed to the bidirectional alloreactivity generated from minor histocompatibility antigens (miHA) mismatching between donors and recipients. Consanguineous marriage increases the chance of miHA matching. This fact may be an advantage or disadvantage in consanguineous MSD transplants. We retrospectively reviewed our institutional transplant registry and selected AML and ALL patients who received a MSD allo-HCT between January 2006 and December 2020. The objective was to compare the outcomes of transplant among consanguineous vs non-consanguineous pairs. Analysis was conducted using RStudio. Version 1.4.1106 © 2009-2021 RStudio, PBC. 271 patients met the eligibility criteria were included in this study. Sixty-three were consanguineous and 208 were not. The median follow-up time was 72.6 months. The five years OS and DFS were not statistically different between consanguineous and non-consanguineous group. A trend toward a higher relapse rate in the consanguineous group was observed. The five years NRM for the whole group was 10.5% with no statistically significant difference between groups. The grade II-IV aGvHD incidence was 25.8% for the whole group with no statistically significant difference between groups. The all grade cGvHD incidence was 52.8% with no statistically significant difference between groups. Populations with high levels of consanguinity, complex consanguinity loops often arise from cousin marriages across multiple generations. This means that even individuals who consider themselves non-consanguineous may still share genetic traits associated with consanguinity. Therefore, high level of homozygosity probably exist in the non-consanguineous cohort and explain these results.

Graft-Versus-Host Disease Mouse Models: A Clinical-Translational Perspective

A variety of graft-versus-host disease (GVHD) models have been developed in mice for the purpose of allowing laboratory investigation of the pathobiology, prevention, and treatment of GVHD in humans. While such models are crucial in advancing our knowledge in this field, there are some key limitations that need to be considered when translating laboratory discoveries into the clinical context. This chapter will discuss current clinical practices in transplantation and GVHD and the relative strengths and weaknesses of mouse models that attempt to replicate these states.

Murine models of graft versus host disease (GVHD): Focus on ocular GVHD

Graft versus host disease (GVHD) remains a major and serious complication of allogeneic hematopoietic stem cell transplantation. Based on the time of onset, clinical phenotypes, progression kinetics, and pathophysiology, GVHD is stratified into acute, chronic, and overlapping types. The eyes are among the most commonly affected organs in GVHD. Mouse models have played an important role in understanding the several key elements of GVHD pathobiology. The current review discusses the immunology, pathology, and key phenotypic features of mouse models of systemic GVHD. Furthermore, a critical appraisal of mouse models of ocular GVHD (oGVHD) is provided. The disease mechanisms underlying the ocular surface, meibomian gland, and lacrimal gland injury in these models are reviewed, and the relevance of oGVHD murine models to clinical oGVHD is also included.

Immunopathogenic mechanisms and modulatory approaches to graft-versus-host disease prevention in acute myeloid leukaemia

Allogeneic haematopoietic stem cell transplantation (HSCT) remains the only potential cure for intermediate to high-risk acute myeloid leukaemia (AML). The therapeutic effect of HSCT is largely dependent on the powerful donor-derived immune response against recipient leukaemia cells, known as graft-versus-leukaemia effect (GvL). However, the donor-derived immune system can also cause acute or chronic damage to normal recipient organs and tissues, in a process known as graft-versus-host disease (GvHD). GvHD is a leading cause of non-relapse mortality in HSCT recipients. There are many similarities and cross talk between the immune pathways of GvL and GvHD. Studies have demonstrated that both processes require the presence of mismatched alloantigens between the donor and recipient, and activation of immune responses centered around donor T-cells, which can be further modulated by various recipient or donor factors. Dissecting GvL from GvHD to achieve more effective GvHD prevention and enhanced GvL has been the holy grail of HSCT research. In this review, we focused on the key factors that contribute to the immune responses of GvL and GvHD, the effect on GvL with different GvHD prophylactic strategies, and the potential impact of various AML relapse prevention therapy or treatments on GvHD.

mTOR Signaling Regulates the Development and Therapeutic Efficacy of PMN-MDSCs in Acute GVHD

Myeloid-derived suppressor cells (MDSCs) represent a population of heterogeneous myeloid cells, which are characterized by their remarkable ability to suppress T cells and natural killer cells. MDSCs have been proven to play a positive role in protecting acute graft-versus-host disease (aGVHD). Here, we aimed to describe the mechanism behind how mTOR signaling regulates MDSCs' generation and explore its prophylactic and therapeutic potential in aGVHD. Reducing mTOR expression retains myeloid cells with immature characteristics and promotes polymorphonuclear MDSC (PMN-MDSC) immunosuppressive function through STAT3-C/EBPβ pathway. Prophylactic transfusion of mTORKO PMN-MDSCs could alleviate aGVHD while maintaining the graft-versus-leukemia (GVL) effect, which could downregulate the Th1/Th2 ratio, decrease serum proinflammatory cytokines, and increase the proportion of regulatory T cells (Tregs) in aGVHD models at the early stage after transplantation. Moreover, transfusion therapy could promote the reconstruction and function of donor-derived PMN-MDSCs. Not only the percentage and the absolute number of donor-derived PMN-MDSCs significantly increased but also the immunosuppressive ability was much more robust compared to other groups. Altogether, these findings indicated that mTOR is an intrinsic regulator for PMN-MDSCs' differentiation and immunosuppressive function. Together, mTORKO PMN-MDSC transfusion can play a protective role in alleviating cytokine storm at the initial stage and promoting the quantitative and functional recoveries of donor-derived PMN-MDSCs in aGVHD.

Murine Models Provide New Insights Into Pathogenesis of Chronic Graft-Versus-Host Disease in Humans

Allogeneic hematopoietic cell transplantation (allo-HCT) is a curative therapy for hematologic malignancies, but its success is complicated by graft-versus-host disease (GVHD). GVHD can be divided into acute and chronic types. Acute GVHD represents an acute alloimmune inflammatory response initiated by donor T cells that recognize recipient alloantigens. Chronic GVHD has a more complex pathophysiology involving donor-derived T cells that recognize recipient-specific antigens, donor-specific antigens, and antigens shared by the recipient and donor. Antibodies produced by donor B cells contribute to the pathogenesis of chronic GVHD but not acute GVHD. Acute GVHD can often be effectively controlled by treatment with corticosteroids or other immunosuppressant for a period of weeks, but successful control of chronic GVHD requires much longer treatment. Therefore, chronic GVHD remains the major cause of long-term morbidity and mortality after allo-HCT. Murine models of allo-HCT have made great contributions to our understanding pathogenesis of acute and chronic GVHD. In this review, we summarize new mechanistic findings from murine models of chronic GVHD, and we discuss the relevance of these insights to chronic GVHD pathogenesis in humans and their potential impact on clinical prevention and treatment.

Obesity induces gut microbiota alterations and augments acute graft-versus-host disease after allogeneic stem cell transplantation

The efficacy of allogeneic hematopoietic stem cell transplantation (allo-HSCT) is limited by acute and chronic graft-versus-host disease (GVHD). The impact of obesity on allo-HSCT outcomes is poorly understood. Here, we report that obesity had a negative and selective impact on acute gut GVHD after allo-HSCT in mice with diet-induced obesity (DIO). These animals exhibited increased gut permeability, endotoxin translocation across the gut, and radiation-induced gastrointestinal damage after allo-HSCT. After allo-HSCT, both male and female DIO mouse recipients showed increased proinflammatory cytokine production and expression of the GVHD marker ST2 (IL-33R) and MHC class II molecules; they also exhibited decreased survival associated with acute severe gut GVHD. This rapid-onset, obesity-associated gut GVHD depended on donor CD4⁺ T cells and occurred even with a minor MHC mismatch between donor and recipient animals. Retrospective analysis of clinical cohorts receiving allo-HSCT transplants from unrelated donors revealed that recipients with a high body mass index (BMI, >30) had reduced survival and higher serum ST2 concentrations compared with nonobese transplant recipients. Assessment of both DIO mice and allo-HSCT recipients with a high BMI revealed reduced gut microbiota diversity and decreased Clostridiaceae abundance. Prophylactic antibiotic treatment protected DIO mouse recipients from endotoxin translocation across the gut and increased inflammatory cytokine production, as well as gut pathology and mortality, but did not protect against later development of chronic skin GVHD. These results suggest that obesity-induced alterations of the gut microbiota may affect GVHD after allo-HSCT in DIO mice, which could be ameliorated by prophylactic antibiotic treatment.

CD4+CD8+ T-Lymphocytes in Xenogeneic and Human Graft-versus-Host Disease

Mechanisms driving acute graft-versus-host disease (aGVHD) onset in patients undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT) are still poorly understood. To provide a detailed characterization of tissue-infiltrating T lymphocytes (TL) and search for eventual site-specific specificities, we developed a xenogeneic model of aGVHD in immunodeficient mice. Phenotypic characterization of xenoreactive T lymphocytes (TL) in diseased mice disclosed a massive infiltration of GVHD target organs by an original CD4⁺CD8⁺ TL subset. Immunophenotypic and transcriptional profiling shows that CD4⁺CD8⁺ TL comprise a major PD1⁺CD62L^−/+ transitional memory subset (>60%) characterized by low level expression of cytotoxicity-related transcripts. CD4⁺CD8⁺ TL produce high IL-10 and IL-13 levels, and low IL-2 and IFN-γ, suggestive of regulatory function. In vivo tracking of genetically labeled CD4⁺ or CD8⁺ TL subsequently found that CD4⁺CD8⁺ TL mainly originate from chronically activated cytotoxic TL (CTL). On the other hand, phenotypic profiling of CD3⁺ TL from blood, duodenum or rectal mucosa in a cohort of allo-HSCT patients failed to disclose abnormal expansion of CD4⁺CD8⁺ TL independent of aGVHD development. Collectively, our results show that acquisition of surface CD4 by xenoreactive CD8⁺ CTL is associated with functional diversion toward a regulatory phenotype, but rule out a central role of this subset in the pathogenesis of aGVHD in allo-HSCT patients.

A mathematical model for dynamics of soluble form of DNAM-1 as a biomarker for graft-versus-host disease

DNAM-1 (CD226) is an activating immunoreceptor expressed on T cells and NK cells and involved in the pathogenesis of acute graft-versus-host disease (aGVHD) after allogeneic hematopoietic stem cell transplantation (allo-HSCT). We previously reported that a soluble form of DNAM-1 (sDNAM-1) is generated by shedding from activated T cells. Moreover, higher serum levels of sDNAM-1 in patients before allo-HSCT is a predictive biomarker for the development of aGVHD based on the retrospective univariate and multivariate analyses in allo-HSCT patients. However, it remains unclear how the serum levels of sDNAM-1 are regulated after allo-HSCT and whether they are associated with the development of aGVHD. Here, we constructed a mathematical model to assess the dynamics of sDNAM-1 after allo-HSCT by assuming that there are three types of sDNAM-1 (the first and the second were from alloreactive and non-alloreactive donor lymphocytes, respectively, and the third from recipient lymphocytes). Our mathematical model fitted well to the data set of sDNAM-1 in patients (n = 67) who had undergone allo-HSCT and suggest that the high proportion of the first type of sDNAM-1 to the total of the first and second types is associated with high risk of the development of severe aGVHD. Thus, sDNAM-1 after allo-HSCT can be a biomarker for the development of aGVHD.

Treg-mediated prolonged survival of skin allografts without immunosuppression

Injection of Interleukin-2 (IL-2) complexed with a particular anti-IL-2 monoclonal antibody (mab) JES6-1 has been shown to selectively expand CD4⁺Foxp3⁺ T regulatory T cells (Tregs) in vivo. Although the potency of this approach with regard to transplantation has already been proven in an islet transplantation model, skin graft survival could not be prolonged. Since the latter is relevant to human allograft survival, we sought to improve the efficiency of IL-2 complex (cplx) treatment for skin allograft survival in a stringent murine skin graft model. Here, we show that combining low doses of IL-2 cplxs with rapamycin and blockade of the inflammatory cytokine IL-6 leads to long-term (>75 d) survival of major histocompatibility complex-different skin allografts without the need for immunosuppression. Allograft survival was critically dependent on CD25⁺FoxP3⁺ Tregs and was not accompanied by impaired responsiveness toward donor alloantigens in vitro after IL-2 cplx treatment was stopped. Furthermore, second donor-type skin grafts were rejected and provoked rejection of the primary graft, suggesting that operational tolerance is not systemic but restricted to the graft. These findings plus the lack of donor-specific antibody formation imply that prolonged graft survival was largely a reflection of immunological ignorance. The results may represent a potentially clinically translatable strategy for the development of protocols for tolerance induction.

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.

The mechanistic study behind suppression of GVHD while retaining GVL activities by myeloid-derived suppressor cells

Graft-versus-host disease (GVHD) is a major barrier to the widespread use of allogeneic hematopoietic stem cell transplantation (allo-HSCT) for treating hematologic malignancies. Myeloid-derived suppressor cells (MDSCs) have been recognized as crucial immunosuppressive cells in various pathologic settings. Here, we investigated whether the unique functional properties of MDSCs could be harnessed to control allo-HSCT-associated GVHD. Using multiple murine GVHD/GVL models including both MHC-mismatched and miHA-mismatched, we demonstrated that treatment with CD115+ MDSCs efficiently suppressed GVHD but did not significantly impair graft-versus-leukemia (GVL) activity, leading to 80% and 67% protection in treated mice in GVHD and GVL models, respectively. The mechanism for this dissociation of GVHD from GVL, specifically the emergence of donor-derived NKG2D⁺ CD8 T cells with a memory phenotype in MDSC-treated recipient mice, was identified. NKG2D expression on donor T cells was required for eradication of allogeneic lymphoma cells. Furthermore, long-term surviving MDSC recipients that exhibited cytolytic activities against allogeneic leukemia cells had a significantly increased percentage of T regulatory cells and, more importantly, NKG2D⁺ CD8 T cells. These findings indicate that MDSCs can be used as a novel cell-based therapy to suppress GVHD while maintaining GVL activities through selective induction of NKG2D⁺ CD8 memory T cells.

Myeloablative hematopoietic stem cell transplantation improves survival but is not curative in a pre-clinical model of myelodysplastic syndrome

Allogeneic hematopoietic stem cell transplantation (A-HSCT) remains the only curative option for patients with myelodysplastic syndrome (MDS). We used the NUP98-HOXD13 (NHD13) murine model for MDS to study HSCT in a pre-clinical setting. NHD13 recipients transplanted with syngeneic bone marrow (S-HSCT) following myeloablative irradiation showed disease remission, with normalization of peripheral blood parameters and marked decrease in circulating leukocytes derived from the MDS clone. Despite the disease remission and improved survival compared to non-transplanted NHD13 controls, all mice eventually relapsed, indicating persistence of a long-lived radio-resistant MDS clone. In an effort to induce a graft versus leukemia (GVL) effect, A-HSCT with donor bone marrow that was mismatched at minor histocompatibility loci was compared to S-HSCT. Although recipients in the A-HSCT showed a lower early relapse rate than in S-HSCT, all mice in both groups eventually relapsed and died by 54 weeks post-transplant. To obtain a more significant GVL effect, donor splenocytes containing reactive T-cells were transplanted with allogeneic bone marrow. Although the relapse rate was only 20% at post-transplantation week 38, suggesting a GVL effect, this was accompanied by a severe graft versus host disease (GVHD) Taken together, these findings indicate that a myeloablative dose of ionizing radiation is insufficient to eradicate the MDS initiating cell, and that transplantation of donor splenocytes leads to decreased relapse rates, at the cost of severe GVHD. We suggest that NHD13 mice represent a feasible pre-clinical model for the study of HSCT for MDS.

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.

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.

A preclinical acute GVHD mouse model based on chemotherapy conditioning and MHC-matched transplantation

Animal disease models have been criticized for lack of resemblance to human illnesses, hampering transfer of knowledge from preclinical research to clinical medicine. In the field of allogeneic hematopoietic stem cell transplantation (allo-HSCT), it is standard practice to study GVHD in lethal TBI-based murine models. Frequently, MHC-mismatched donors are used in GVHD models. In contrast, in clinical allo-HSCT conditioning with chemotherapy (+/-TBI) is common and donors are often MHC-matched. Aiming at a more clinically oriented situation, we established and characterized a murine MHC-matched, minor histocompatibility antigen mismatched GVHD model (LP/J [H2k(b)]-->C57BL/6 [H2k(b)]) using busulfan and cyclophosphamide conditioning. We found typical clinical and histological features of acute GVHD. T-cell infiltration, GVHD-specific damage and systemic inflammation were similar to observations made in patients after allo-HSCT. In survivors of acute GVHD, we found expansion of CD4+ T cells and the development of scleroderma-like chronic GVHD. The use of chemotherapy-based, minor histocompatibility antigen (miHA)-mismatched GVHD animal models may be a good option when studying clinically relevant questions in the field of allo-HSCT.

Recruitment of Donor T Cells to the Eyes During Ocular GVHD in Recipients of MHC-Matched Allogeneic Hematopoietic Stem Cell Transplants

PURPOSE

The primary objective of the present study was to identify the kinetics and origin of ocular infiltrating T cells in a preclinical model of graft-versus-host disease (GVHD) that induces eye tissue damage.

METHODS

Graft-versus-host disease was induced using an major histocompatibility complex (MHC)-matched, minor histocompatibility-mismatched hematopoietic stem cell transplant (HSCT) model. This approach, which utilized congenic and EGFP-labeled donor populations, mimics a matched, clinically unrelated donor (MUD) cell transplant. Systemic and ocular GVHD were assessed at varying time points using clinical examination, intravital microscopy, immune phenotype via flow cytometric analyses, and immunohistochemical staining.

RESULTS

Following transplant, we observed characteristic changes in GVHD-associated immune phenotype as well as clinical signs present in recipients post transplant. Notably, the kinetics of the systemic changes and the ocular damage paralleled what is observed clinically, including damage to the cornea as well as the conjunctiva and lacrimal gland. Importantly, the infiltrate contained predominantly donor CD4 as well as CD8 T cells with an activated phenotype and macrophages together with effector cytokines consistent with the presence of a TH1 alloreactive population.

CONCLUSIONS

Overall, the findings here unequivocally demonstrated that donor T cells compose part of the corneal and ocular adnexa infiltrate in animals undergoing ocular GVHD. In total, the results describe a novel and promising preclinical model characterized by both systemic and ocular changes as detected in significant numbers of patients undergoing GVHD following allo-HSCT, which can help facilitate dissecting the underlying immune mechanisms leading to damage associated with ocular GVHD.

Basophils inhibit proliferation of CD4⁺ T cells in autologous and allogeneic mixed lymphocyte reactions and limit disease activity in a murine model of graft versus host disease

Basophils are known to modulate the phenotype of CD4(+) T cells and to enhance T helper type 2 responses in vitro and in vivo. In this study, we demonstrate that murine basophils inhibit proliferation of CD4(+) T cells in autologous and allogeneic mixed lymphocyte reactions. The inhibition is independent of Fas and MHC class II, but dependent on activation of basophils with subsequent release of interleukin-4 (IL-4) and IL-6. The inhibitory effect of basophils on T-cell proliferation can be blocked with antibodies against IL-4 and IL-6 and is absent in IL-4/IL-6 double-deficient mice. In addition, we show that basophils and IL-4 have beneficial effects on disease activity in a murine model of acute graft-versus-host disease (GvHD). When basophils were depleted with the antibody MAR-1 before induction of GvHD, weight loss, GvHD score, mortality and plasma tumour necrosis factor levels were increased while injection of IL-4 improved GvHD. Basophil-depleted mice with GvHD also have increased numbers of CD4(+) T cells in the mesenteric lymph nodes. Our data show for the first time that basophils suppress autologous and allogeneic CD4(+) T-cell proliferation in an IL-4-dependent manner.

Inhibition of the Immunoproteasome Subunit LMP7 with ONX 0914 Ameliorates Graft-versus-Host Disease in an MHC-Matched Minor Histocompatibility Antigen-Disparate Murine Model

In the current study we evaluated the effects of immunoproteasome inhibition using ONX 0914 (formerly PR-957) to ameliorate graft-versus-host disease (GVHD). ONX 0914, an LMP7-selective epoxyketone inhibitor of the immunoproteasome, has been shown to reduce cytokine production in activated monocytes and T cells and attenuate disease progression in mouse models of rheumatoid arthritis, colitis, systemic lupus erythematosus, and, more recently, encephalomyelitis. Inhibition of LMP7 with ONX 0914 in the B10.BR→CBA MHC-matched/minor histocompatibility antigen (miHA)-disparate murine blood and marrow transplant (BMT) model caused a modest but significant improvement in the survival of mice experiencing GVHD. Concomitant with these results, in vitro mixed lymphocyte cultures revealed that stimulator splenocytes, but not responder T cells, treated with ONX 0914 resulted in decreased IFN-γ production by allogeneic T cells in both MHC-disparate (B10.BR anti-B6) and miHA-mismatched (B10.BR anti-CBA) settings. In addition, a reduction in the expression of the MHC class I-restricted SIINFEKL peptide was observed in splenocytes from transgenic C57BL/6-Tg(CAG-OVA)916Jen/J mice exposed to ONX 0914. Taken together, these data support that LMP7 inhibition in the context of BMT modulates allogeneic responses by decreasing endogenous miHA presentation and that the consequential reduction in allogeneic stimulation and cytokine production reduces GVHD development.

Establishment of a murine graft-versus-myeloma model using allogeneic stem cell transplantation

Background

Multiple myeloma (MM) is a malignant plasma cell disorder with poor long-term survival and high recurrence rates. Despite evidence of graft-versus-myeloma (GvM) effects, the use of allogeneic hematopoietic stem cell transplantation (allo-SCT) remains controversial in MM. In the current study, we investigated the anti-myeloma effects of allo-SCT from B10.D2 mice into MHC-matched myeloma-bearing Balb/cJ mice, with concomitant development of chronic graft-versus-host disease (GvHD).

Methods and results

Balb/cJ mice were injected intravenously with luciferase-transfected MOPC315.BM cells, and received an allogeneic (B10.D2 donor) or autologous (Balb/cJ donor) transplant 30 days later. We observed a GvM effect in 94% of the allogeneic transplanted mice, as the luciferase signal completely disappeared after transplantation, whereas all the autologous transplanted mice showed myeloma progression. Lower serum paraprotein levels and lower myeloma infiltration in bone marrow and spleen in the allogeneic setting confirmed the observed GvM effect. In addition, the treated mice also displayed chronic GvHD symptoms. In vivo and in vitro data suggested the involvement of effector memory CD4 and CD8 T cells associated with the GvM response. The essential role of CD8 T cells was demonstrated in vivo where CD8 T-cell depletion of the graft resulted in reduced GvM effects. Finally, TCR Vβ spectratyping analysis identified Vβ families within CD4 and CD8 T cells, which were associated with both GvM effects and GvHD, whereas other Vβ families within CD4 T cells were associated exclusively with either GvM or GvHD responses.

Conclusions

We successfully established an immunocompetent murine model of graft-versus-myeloma. This is the first murine GvM model using immunocompetent mice that develop MM which closely resembles human MM disease and that are treated after disease establishment with an allo-SCT. Importantly, using TCR Vβ spectratyping, we also demonstrated the presence of GvM unique responses potentially associated with the curative capacity of this immunotherapeutic approach.

Treatment of graft-versus-host disease with naturally occurring T regulatory cells

A significant body of evidence suggests that treatment with naturally occurring CD4⁺CD25⁺ T regulatory cells (Tregs) is an appropriate therapy for graft-versus-host disease (GvHD). GvHD is a major complication of bone marrow transplantation in which the transplanted immune system recognizes recipient tissues as a non-self and destroys them. In many cases, this condition significantly deteriorates the quality of life of the affected patients. It is also one of the most important causes of death after bone marrow transplantation. Tregs constitute a population responsible for dominant tolerance to self-tissues in the immune system. These cells prevent autoimmune and allergic reactions and decrease the risk of rejection of allotransplants. For these reasons, Tregs are considered as a cellular drug in GvHD. The results of the first clinical trials with these cells are already available. In this review we present important experimental facts which led to the clinical use of Tregs. We then critically evaluate specific requirements for Treg therapy in GvHD and therapies with Tregs currently under clinical investigation, including our experience and future perspectives on this kind of cellular treatment.

Acute lymphoid leukemia cells with greater stem cell antigen-1 (Ly6a/Sca-1) expression exhibit higher levels of metalloproteinase activity and are more aggressive in vivo

Stem cell antigen-1 (Ly6a/Sca-1) is a gene that is expressed in activated lymphocytes, hematopoietic stem cells and stem cells of a variety of tissues in mice. Despite decades of study its functions remain poorly defined. These studies explored the impact of expression of this stem cell associated gene in acute lymphoid leukemia. Higher levels of Ly6a/Sca-1 expression led to more aggressive leukemia growth in vivo and earlier death of hosts. Leukemias expressing higher levels of Ly6a/Sca-1 exhibited higher levels of matrix metalloproteinases. The results suggest the hypothesis that the more aggressive behavior of Ly6a/Sca-1 expressing leukemias is due at least in part to greater capacity to degrade microenvironmental stroma and invade tissues.

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.

Immune reconstitution and graft-versus-host reactions in rat models of allogeneic hematopoietic cell transplantation

Allogeneic hematopoietic cell transplantation (alloHCT) extends the lives of thousands of patients who would otherwise succumb to hematopoietic malignancies such as leukemias and lymphomas, aplastic anemia, and disorders of the immune system. In alloHCT, different immune cell types mediate beneficial graft-versus-tumor (GvT) effects, regulate detrimental graft-versus-host disease (GvHD), and are required for protection against infections. Today, the “good” (GvT effector cells and memory cells conferring protection) cannot be easily separated from the “bad” (GvHD-causing cells), and alloHCT remains a hazardous medical modality. The transplantation of hematopoietic stem cells into an immunosuppressed patient creates a delicate environment for the reconstitution of donor blood and immune cells in co-existence with host cells. Immunological reconstitution determines to a large extent the immune status of the allo-transplanted host against infections and the recurrence of cancer, and is critical for long-term protection and survival after clinical alloHCT. Animal models continue to be extremely valuable experimental tools that widen our understanding of, for example, the dynamics of post-transplant hematopoiesis and the complexity of immune reconstitution with multiple ways of interaction between host and donor cells. In this review, we discuss the rat as an experimental model of HCT between allogeneic individuals. We summarize our findings on lymphocyte reconstitution in transplanted rats and illustrate the disease pathology of this particular model. We also introduce the rat skin explant assay, a feasible alternative to in vivo transplantation studies. The skin explant assay can be used to elucidate the biology of graft-versus-host reactions, which are known to have a major impact on immune reconstitution, and to perform genome-wide gene expression studies using controlled combinations of minor and major histocompatibility between the donor and the recipient.

Unraveling graft-versus-host disease and graft-versus-leukemia responses using TCR Vβ spectratype analysis in a murine bone marrow transplantation model

The optimum use of allogeneic blood and marrow transplantation (BMT) as a curative therapy for hematological malignancies lies in the successful separation of mature donor T cells that are host reactive and induce graft-versus-host disease (GVHD) from those that are tumor reactive and mediate graft-versus-leukemia (GVL) effects. To study whether this separation was possible in an MHC-matched murine BMT model (B10.BR→CBA) with a CBA-derived myeloid leukemia line, MMC6, we used TCR Vβ CDR3-size spectratype analysis to first show that the Vβ13 family was highly skewed in the B10.BR anti-MMC6 CD8(+) T cell response but not in the alloresponse against recipient cells alone. Transplantation of CD8(+)Vβ13(+) T cells at the dose equivalent of their constituency in 1 × 10(7) CD8(+) T cells, a dose that had been shown to mediate lethal GVHD in recipient mice, induced a slight GVL response with no concomitant GVHD. Increasing doses of CD8(+)Vβ13(+) T cells led to more significant GVL responses but also increased GVHD symptoms and associated mortality. Subsequent spectratype analysis of GVHD target tissues revealed involvement of gut-infiltrating CD8(+)Vβ13(+) T cells accounting for the observed in vivo effects. When BMT recipients were given MMC6-presensitized CD8(+)Vβ13(+) T cells, they displayed a significant GVL response with minimal GVHD. Spectratype analysis of tumor-presensitized, gut-infiltrating CD8(+)Vβ13(+) T cells showed preferential usage of tumor-reactive CDR3-size lengths, and these cells expressed increased effector memory phenotype (CD44(+)CD62L(-/lo)). Thus, Vβ spectratyping can identify T cells involved in antihost and antitumor reactivity and tumor presensitization can aid in the separation of GVHD and GVL responses.

Graft-versus-host disease-related cytokine-driven apoptosis depends on p73 in cytokeratin 15-positive target cells

Acute graft-versus-host disease (GVHD), a major complication of allogeneic stem cell transplantation, involves cytotoxic soluble and cellular effectors that selectively induce apoptosis in normally apoptosis-resistant, cytokeratin 15 (K15)-expressing epithelial stem cells residing at the tips of rete ridges of human epidermis and in analogous rete-like prominences (RLPs) of murine dorsal lingual epithelium. The mechanisms whereby epithelial stem cells are rendered vulnerable to apoptosis during allostimulation are unknown. We hypothesized that GVHD-induced target cell injury may be related to pathways involving the p53 family that are constitutively expressed by epithelial stem cells and designed to trigger physiological apoptosis as a result of environmental danger signals. Among the p53 family members, we found that p73 protein and mRNA were preferentially expressed in K15(+) RLPs of murine lingual squamous epithelium. On in vitro exposure to recombinant TNF-α and IL-1 in an organ culture model previously shown to replicate early GVHD-like target cell injury, apoptosis was selectively induced in K15(+) stem cell regions and was associated with induction of phosphorylated p73, a marker for p73 activation, and apoptosis was abrogated in target tissue obtained from p73-deficient (p73(-/-)) mice. Evaluation of early in vivo lesions in experimental murine GVHD disclosed identical patterns of phosphorylated p73 expression that coincided with the onset of effector T cell infiltration and target cell apoptosis within K15(+) RLPs. This study is the first to suggest that paradoxical apoptosis in GVHD of physiologically protected K15(+) epithelial stem cells is explainable, at least in part, by cytokine-induced activation of suicide pathways designed to eliminate stem cells after exposure to deleterious factors perceived to be harmful to the host.

Inhibition of cathepsin S reduces allogeneic T cell priming but not graft-versus-host disease against minor histocompatibility antigens

Cathepsin (Cathepsin) S, L, and B proteases mediate antigen presentation on major histocompatibility complex (MHC) class II by degrading the invariant chain Ii, which blocks peptide loading. The ability of the Cathepsin S inhibitor LHVS (morpholinurea-leucine-homophenylalanine-vinylsulfone phenyl) to impede antigen presentation has led its development as a therapy for autoimmune diseases. There is substantial evidence that donor T cell recognition of host minor histocompatibility antigens (miHA) and subsequent destruction of host tissue mediates graft-versus-host disease (GVHD). We hypothesized that enzymes involved in antigen presentation may play a role in the development of GVHD. Using the C57BL/6 → BALB.B minor mismatch acute GVHD (aGVHD) model, we found that the cathepsin S activity of spleens from allogenetically transplanted mice were significantly increased 1 week after transplantation compared with syngeneic mice. Although LHVS decreased T cell priming responses against both single OVA antigen and miHA in vitro, LHVS did not reduce the severity of aGVHD. In fact, LHVS exacerbated a CD4(+)-T cell-dependent model of GVHD similar to chronic GVHD. This suggests that cytokines rather than T cells may mediate much of the damage in the aGVHD model and that therapeutics based on inhibition of antigen presentation for GVHD must be approached with caution.

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.

Extracorporeal photopheresis attenuates murine graft-versus-host disease via bone marrow-derived interleukin-10 and preserves responses to dendritic cell vaccination

Extracorporeal photopheresis (ECP) is emerging as a therapy for graft-versus-host-disease (GVHD), but the full mechanism of action and the impact on immunity have not been fully established. After murine minor histocompatibility antigen-mismatched bone marrow (BM) transplantation (allo-BMT), coinfusion of ECP-treated splenocytes with T cell-replete BM attenuated GVHD irrespective of the donor strain of the ECP-treated splenocytes, and was associated with increased numbers of regulatory T cells. Coculture of myeloid dendritic cells (DCs) with ECP-treated splenocytes resulted in increased interleukin (IL)-10 production after submaximal stimulation with lipopolysaccharide. Furthermore, male myeloid DCs exposed to ECP-treated splenocytes were less potent at inducing CD8(+) HY responses when used as a vaccine in vivo. The efficacy of ECP-treated splenocytes was enhanced when administered just before delayed donor lymphocyte infusion following T cell-depleted allo-BMT, allowing for the administration of sufficient numbers of T cells to respond to myeloid DC vaccination in the absence of a thymus. Finally, the therapeutic effect of ECP-treated splenocytes was lost in recipients of IL-10-deficient BM. We demonstrate that ECP-treated splenocytes attenuate GVHD irrespective of the source of ECP-treated cells via a mechanism that likely involves modulation of DCs and requires IL-10 produced by BM-derived cells. Importantly, the attenuation of GVHD by ECP-treated splenocytes permits donor lymphocyte infusion-dependent responses to DC vaccines after allo-BMT.

The immunological impact of genetic drift in the B10.BR congenic inbred mouse strain

The MHC-matched, minor histocompatibility Ag (miHA)-mismatched B10.BR-->CBA strain combination has been used to elucidate the immunobiology of graft-vs-host disease (GVHD) following allogeneic bone marrow transplantation. Studies conducted in the 1980s had established that B10.BR CD8+ T cells were capable of mediating GVHD in the absence of CD4+ T cells, and that CD4+ T cells were unable to induce lethal disease. In more recent studies with this GVHD model, we detected etiological discrepancies with the previously published results, which suggested that genetic drift might have occurred within the B10.BR strain. In particular, there was increased allorecognition of CBA miHA by B10.BR CD4+ T cells, as determined by both TCR Vbeta spectratype analysis and the induction of lethal GVHD in CBA recipients. Additionally, alloreactivity was observed between the genetically drifted mice (B10.BR/Jdrif) and mice rederived from frozen embryos of the original strain (B10.BR/Jrep) using Vbeta spectratype analysis and IFN-gamma ELISPOT assays, suggesting that new miHA differences had arisen between the mice. Furthermore, T cell-depleted B10.BR/Jdrif bone marrow cells were unable to provide long-term survival following either allogeneic or syngeneic bone marrow transplantation. Gene expression analysis revealed several genes involved in hematopoiesis that were overexpressed in the lineage-negative fraction of B10.BR/Jdrif bone marrow, as compared with B10.BR/Jrep mice. Taken together, these results suggest that genetic drift in the B10.BR strain has significantly impacted the immune alloreactive response in the GVHD model by causing altered expression of miHA and diminished capacity for survival following transplantation into lethally irradiated recipients.

Cellular tumor vaccines administered after T cell-depleted allogeneic bone marrow transplantation induce effective anti-tumor immune responses

In allogeneic hematopoietic stem cell (HSC) transplantation, graft vs. tumor (GVT) activity contributes to the cancer cure. It is closely associated with graft vs. host disease (GVHD), an immune response initiated by transplanted donor T-cell responses against host minor histocompatibility antigens (mHAgs). GVHD is prevented by T-cell depletion of the donor graft, but T-cell depletion also abrogates curative GVT. We wished to test the hypothesis that cellular tumor vaccines administered after T cell-depleted HSC transplant can induce significant GVT effects, despite the absence of transplanted mature donor T cells. In this investigation, a murine model of major histocompatibility complex (MHC)-matched, mHAg-mismatched allogeneic HSC transplant was studied. T cell-depleted or normal T cell-containing grafts were given to myeloablated recipients. Following reconstitution the recipients were vaccinated with tumor vaccines. GVT responses were measured in vitro by T-cell function assays and flow cytometry, and in vivo by tumor burden or survival. Post-transplant tumor vaccines induced effective anti-tumor responses in recipients of T cell-depleted transplants, producing cytolytic and cytokine responses, reduced tumor burden and prolonged survival. Recipients of T cell-depleted transplants that still have significant thymic function may be suitable subjects for post-transplant vaccine therapy.

Mouse models of bone marrow transplantation

Over the last 50 years, mouse models of bone marrow transplantation have provided the critical links between graft-versus-host disease (GVHD) and graft-versus-leukemia (GVL) pathophysiology and clinical practice. The initial insight from mouse models that GVHD and GVL were T cell dependent has long been confirmed clinically. More recent translations from mouse models have included the important role of inflammatory cytokines in GVHD. Newly developed concepts relating to the ability of antigen presenting cell (APC) and T cell subsets to mediate GVHD now promise significant clinical advances. The ability to use knockout and transgenic approaches to dissect mechanisms of GVHD and GVL mean that mouse systems will continue as the predominant preclinical platform. The basic transplant approach in these models, coupled with modern "real-time" immunologic imaging of GVHD and GVL is discussed.

Bone marrow deficient in IFN-{gamma} signaling selectively reverses GVHD-associated immunosuppression and enhances a tumor-specific GVT effect

Vaccine-based expansion of T cells is one approach to enhance the graft-versus-tumor effect of allogeneic bone marrow transplantation (BMT), but the complex immunobiology of the allogeneic environment on responses to tumor vaccines has not been well characterized. We hypothesized that subclinical graft-versus-host disease (GVHD) impairs immunity, but modulation of gamma interferon (IFN-gamma) signaling could reverse this effect. Dendritic cell vaccines and donor lymphocyte infusions (DLIs) were incorporated into a minor histocompatibility antigen-mismatched, T cell-depleted, allogeneic BMT mouse model. Animals were then challenged with H-Y expressing tumors. CD4(+) and CD8(+) responses to H-Y were diminished in vaccinated allogeneic versus syngeneic BMT recipients with DLI doses below the threshold for clinical GVHD, especially in thymectomized hosts. IFN-gamma receptor 1-deficient (IFN-gammaR1(-/-)) T cells cannot cause GVHD but also have diminished vaccine responses. Remarkably, IFN-gammaR1(-/-) bone marrow abrogates GVHD, allowing higher DLI doses to be tolerated, but improves vaccine responses and tumor protection. We conclude that tumor vaccines administered after allogeneic BMT can augment graft-versus-tumor if GVHD is avoided and that prevention of IFN-gamma signaling on donor bone marrow is an effective approach to preventing GVHD while preserving immunocompetence.

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.

Graft-versus-host disease causes failure of donor hematopoiesis and lymphopoiesis in interferon-gamma receptor-deficient hosts

The immunopathologic condition known as graft-versus-host disease (GVHD) results from a type I T-cell process. However, a prototypical type I cytokine, interferon-gamma (IFN-gamma), can protect against several manifestations of GVHD in recipients of major histocompatibility complex (MHC)-mismatched hematopoietic cells. We transplanted hematopoietic cells from C3H.SW donors in wild-type (wt) and IFN-gamma-receptor-deficient (IFN-gammaRKO) MHC-matched C57BL/6 recipients. In IFN-gammaRKO recipients, host cells were unresponsive to IFN-gamma, whereas wt donor cells were exposed to exceptionally high levels of IFN-gamma. From an IFN-gamma perspective, we could therefore evaluate the impact of a loss-of-function on host cells and gain-of-function on donor cells. We found that lack of IFN-gammaR prevented up-regulation of MHC proteins on host cells but did not mitigate damage to most target organs. Two salient phenotypes in IFN-gammaRKO recipients involved donor cells: lymphoid hypoplasia and hematopoietic failure. Lymphopenia was due to FasL-induced apoptosis and decreased cell proliferation. Bone marrow aplasia resulted from a decreased proliferation of hematopoietic stem/progenitor cells that was associated with down-regulation of 2 genes negatively regulated by IFN-gamma: Ccnd1 and Myc. We conclude that IFN-gamma produced by alloreactive T cells may entail a severe graft-versus-graft reaction and could be responsible for cytopenias that are frequently observed in subjects with GVHD.

Murine models of chronic graft-versus-host disease: insights and unresolved issues

Chronic graft-versus-host-disease (cGVHD) is a major barrier to successful allogeneic hematopoietic stem cell transplantation (allo-HSCT), with highly variable clinical presentations. The pathophysiology of cGVHD remains relatively poorly understood. The utilization of murine models to study cGVHD encompasses experimental challenges distinct from those that have been successfully used to study acute GVHD (aGVHD). Nevertheless, despite these challenges, murine models of cGVHD have contributed to the understanding of cGVHD, and highlight its mechanistic complexity. In this article, insights into the pathophysiology of cGVHD obtained from murine studies are summarized in the context of their relevancy to clinical cGVHD. Despite experimental limitations, current and future models of murine cGVHD will continue to provide insights into the understanding of clinical cGVHD and provide information for new therapeutic interventions.

Target cells in graft-versus-host disease: implications for cancer therapy

Acute graft-versus-host disease (GVHD) conceptually may be divided into three evolutionary stages: allostimulation, effector cell homing to specific tissues, and cellular targeting and injury. Surprisingly, little is known regarding the targeting stage of GVHD. Recently, we have learned that epithelial target cell injury is mediated by specific subpopulations of effector T cells that may be identified based on Vbeta family expansion during allostimulation. Antibody probes specific for these Vbeta families have permitted precise identification of effector cell homing patterns. In squamous epithelium, allospecific T cells selectively home to basal cell layer subpopulations that express cytokeratin 15 (CK15) and that undergo target cell injury via apoptosis. Interestingly, these target cells coincide with basal layer subpopulations that have properties of epithelial stem cells and that normally express an apoptosis-resistant genomic profile. Accordingly, epithelial cell injury in GVHD appears to involve selective targeting of stem-cell subpopulations via conversion from an anti-apoptotic to a pro-apoptotic phenotype. Understanding of the mechanism(s) of this conversion could facilitate development of translationally relevant approaches to shielding target cells from injury in GVHD. Moreover, determination of how putative apoptosis-resistant stem cells may be rendered vulnerable to immune-mediated targeting has implications potentially relevant to more directed immunotherapeutic approaches focused at elimination of neoplastic (cancer) stem cells.

PD-1-PD-L1 pathway is involved in suppressing alloreactivity of heart infiltrating t cells during murine gvhd across minor histocompatibility antigen barriers

BACKGROUND

Graft-versus-host disease (GVHD) is still a major cause of morbidity and mortality after allogeneic stem cell transplantation. GVHD mainly affects skin, liver, and intestine, whereas other organs usually are spared. In the present study, we wanted to investigate whether local regulatory T cells (Treg) or differential expression of immunomodulatory molecules contribute to organ specificity of GVHD.

METHODS

In a murine B10.D2->BALB/c (both H-2) model, GVHD was induced by transplantation of 1x10 bone marrow and 1x10 spleen cells. We compared expression of T-cell and dendritic cell markers, CD40-CD40L, various B7 family members, FoxP3, and Th1/Th2 cytokines between ileum (GVHD-target organ) and heart (nontarget organ).

RESULTS

GVHD was documented by an increase of CD4 T cells with accompanying tissue destruction in ileum but not in heart. We found a significantly increased expression of PD-L1 in heart on day 14 and 21 as well as of CTLA-4 on day 21 after transplantation, whereas all other molecules were not different between heart and ileum. In heart, PD-L1 was expressed on lymphoid cells, endothelial cells, CD8alpha+CD11c+DCs, and up-regulated during GVHD. In contrast, in the ileum only endothelial cells stained weekly positive for PD-L1. Furthermore, we could not find any evidence for the presence of Tregs in the heart.

CONCLUSIONS

Our data indicate that immunomodulatory molecules such as PD-L1 rather than Tregs play pivotal roles in the tissue-specific regulation of alloresponses. Further studies are needed to refine the significance of the PD-L1 pathway in GVHD and its versatility for therapeutic intervention.

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.

T-cell receptor V(alpha) usage by effector CD4+Vbeta11+ T cells mediating graft-versus-host disease directed to minor histocompatibility antigens

T-cell receptor (TCR) Valpha (TRAV) and Vbeta (TRBV) chains provide the T-cell specificity for recognition of major histocompatibility complex (MHC)-bound antigens. However, there is limited information on the diversity of TRAV use within an antigen response. Previous investigation of CD4(+) T-cell-mediated graft-versus-host disease (GVHD) in the minor histocompatibility antigen-mismatched C57BL/6 (B6)-->BALB.B irradiated murine model determined that Vbeta11(+) T cells were associated with disease severity. Polymerase chain reaction (PCR)-based complementarity-determining region 3 (CDR3)-sized spectratype analysis of B6 Vbeta11(+) T cells from the spleens of recipient BALB.B mice undergoing GVHD indicated biased use within the V(alpha)6, 9, 13, 14, 18, and 22 families. To probe deeper into this limited V(alpha) response, the current study was undertaken to further define TRAV-Jalpha (TRAJ) nucleotide sequences found in host-presensitized B6 Vbeta11(+) T cells proliferating in response to in vitro stimulation with BALB.B splenocytes. Using the nonpalindromic adaptor PCR method, we found dominant use of the TRAV13-TRAJ16 transcript combination. Then, using laser capture microdissection, we found use of the identical TRAV-TRAJ nucleotide sequence in areas dominated by infiltrating Vbeta11(+) CD4(+) T cells during the development of GVHD in both the rete-like prominences of the dorsal lingual epithelium and the ileal crypts of the small intestine.

Crossing barriers in transplantation

In 1978, Jonathan Sprent and Robert Korngold proved that graft-versus-host disease (GVHD) is caused by donor T cells that attack the host's non-MHC antigens. T cell depletion of donor grafts has since become a staple of transplantation strategies to combat leukemia and other inherited blood disorders.

Hematopoietic stem cell recipients do not develop post-transplantation immune tolerance to antigens present on minimal residual disease

The immune environment present after allogeneic hematopoietic stem cell transplantation (HSCT) contributes to the control of leukemia. Our laboratory has demonstrated in a murine model that vaccination of recipients after transplantation with recipient tumor vaccines does not exacerbate graft-versus-host disease but does induce meaningful graft-versus-tumor effects. We previously demonstrated that part of the reason for the lack of graft-versus-host disease from post-transplantation vaccination is due to gradual acquisition of tolerance or unresponsiveness to recipient immunodominant minor histocompatibility antigens that are ubiquitously expressed in the recipient. However, our prior studies have not critically addressed the question of whether a similar process of acquisition of unresponsiveness to or tolerance of antigens present on minimal residual disease also occurs. The present study tested the hypothesis that unresponsiveness to antigens present on minimal residual disease present at the time of HSCT would also occur. The answer to this question would have a significant effect on the potential efficacy of post-transplantation tumor vaccines. In a murine model of major histocompatibility complex matched, minor histocompatibility antigen mismatched HSCT (C3.SW female donors and C57BL/6 female recipients), we tested whether transplant recipients would acquire unresponsiveness to antigens present on small numbers of residual leukemia/lymphoma cells. We employed a male C57BL/6 lymphoid malignancy with an immunoglobulin/c-myc oncogene in these studies using as a model of tumor-restricted antigen the well-characterized male (HY) antigen system present only on the tumor but not present as ubiquitous minor antigens in the recipient. After HSCT, recipients did not mount immune responses to the ubiquitously distributed immunodominant recipient strain H7 minor histocompatibility antigen, but did retain the capacity to mount significant T cell responses to HY antigens present on small numbers of HY+ tumor cells present at transplantation. Additional studies using small numbers of nonmalignant recipient male B cells or dendritic cells as models of minimal residual disease also demonstrated that the transplant recipients retained their capacity to mount anti-HY T cell responses. After HSCT, recipients may retain the capacity to mount effective T cell responses to antigens present on minimal residual disease and still acquire relative tolerance to ubiquitously distributed immunodominant minor antigens that are related to graft-versus-host disease.

Host-derived Langerhans cells persist after MHC-matched allografting independent of donor T cells and critically influence the alloresponses mediated by donor lymphocyte infusions

Mouse models of minor histocompatibility Ag-mismatched bone marrow transplantation were used to study donor dendritic cell (DC) reconstitution after conditioning, variables influencing the persistence of residual host DCs in different compartments, their phenotype, and their role in governing donor lymphocyte infusion (DLI)-mediated alloresponses. Reconstitution of all splenic DC subsets occurred rapidly after bone marrow transplantation and before T cell reconstitution. However, in contrast to MHC-mismatched chimeras, residual host-derived DCs persisted in the cutaneous lymph nodes (CLNs) of MHC-matched chimeras despite the presence or addition of donor T cells to the graft. The phenotype of these residual host-derived DCs in CLNs was consistent with Langerhans' cells (LCs). We confirmed their skin origin and found near-complete preservation of host-derived LCs in the skin. Host-derived LCs retained their ability to continuously traffic to the CLNs, expressed homogeneously increased levels of costimulatory molecules, and could capture and carry epicutaneously applied Ags. To determine the role of residual host LCs in governing DLI-mediated alloresponses, we administered DLI alone or after topical application of the TLR7 ligand imiquimod, which is known to enhance the LC emigration from the skin. DLI administration resulted in a decrease in host-derived DCs in the CLNs and increased recruitment of donor-derived DCs to the skin, whereas imiquimod augmented their alloreactivity. These results suggest uniqueness of the MHC-matched setting in relation to the persistence of host-derived DCs in the skin and points to a previously unrecognized role of host-derived LCs in the induction of DLI-mediated graft-vs-host alloresponses.

Sequential expression of adhesion and costimulatory molecules in graft-versus-host disease target organs after murine bone marrow transplantation across minor histocompatibility antigen barriers

Graft-versus-host disease (GVHD) is a potentially fatal complication after allogeneic bone marrow transplantation. However, few data exist thus far on the molecular signals governing leukocyte trafficking during the disease. We therefore investigated the sequential pattern of distinct adhesion, costimulatory, and apoptosis-related molecules in GVHD organs (ileum, colon, skin, and liver) after transplantation across minor histocompatibility barriers (B10.D2 --> BALB/c, both H-2d). To distinguish changes induced by the conditioning regimen from effects achieved by allogeneic cell transfer, syngeneic transplant recipients (BALB/c --> BALB/c) and irradiated nontransplanted mice were added as controls. Irradiation upregulated the expression of vascular cell adhesion molecule (VCAM)-1, intercellular adhesion molecule (ICAM)-l, and B7-2 in ileum, as well as VCAM-1 and B7-2 in colon, on day 3 in all animals. Whereas in syngeneic mice these effects were reversed from day 9 on, allogeneic recipients showed further upregulation of VCAM-1, ICAM-1, B7-1, and B7-2 in these organs on day 22, when GVHD became clinically evident. Infiltration of CD4+ and CD8+ donor T cells was noted on day 9 in skin and liver and on day 22 in ileum and colon. Surprisingly, the expression of several other adhesion molecules, such as ICAM-2, platelet-endothelial cell adhesion molecule 1, E-selectin, and mucosal addressin cell adhesion molecule 1, did not change. Proapoptotic and antiapoptotic markers were balanced in GVHD organs with the exception of spleen, in which a preferential expression of the proapoptotic Bax could be noted. Our results indicate that irradiation-induced upregulation of VCAM-1, ICAM-1, and B7-2 provides early costimulatory signals to incoming donor T cells in the intestine, followed by a cascade of proinflammatory signals in other organs once the alloresponse is established.