Activation-associated phenotype of CD3 T cells in acute graft-versus-host disease

Immunological dynamic characteristics in acute myeloid leukemia predict the long-term outcomes and graft-versus host-disease occurrences post-transplantation

To investigate the relationship between immune dynamic and graft-versus-host-disease (GVHD) risk, 111 initial diagnostic acute myeloid leukemia patients were reviewed. The flow cytometry data of 12 major lymphocyte subsets in bone marrow (BM) from 60 transplant patients at four different time points were analyzed. Additionally, 90 immune subsets in peripheral blood (PB) of 11 post-transplantation on day 100 were reviewed. Our results demonstrated that transplant patients had longer OS compared to non-transplant patients (P < 0.001). Among transplant patients, those who developed GVHD showed longer OS than those without GVHD (P < 0.05). URD donors and CMV-negative status donors were associated with improved OS in transplant patients (P < 0.05). Importantly, we observed a decreased Th/Tc ratio in BM at initial diagnostic in patients with GVHD compared to those without GVHD (P = 0.034). Receiver operating characteristic analysis indicated that a low Th/Tc ratio predicted an increased risk of GVHD with a sensitivity of 44.44% and specificity of 87.50%. Moreover, an increased T/NK ratio in BM of post-induction chemotherapy was found to be associated with GVHD, with a sensitivity of 75.76% and specificity of 65.22%. Additionally, we observed a decreased percentage of NK1 (CD56-CD16+NK) in PB on day 100 post-transplantation in the GVHD group (P < 0.05). These three indicators exhibit promising potential as specific and useful biomarkers for predicting GVHD. These findings provide valuable insights for the early identification and management of GVHD risk, thereby facilitating the possibility of improving patient outcomes.

Engineering T cells to suppress acute GVHD and leukemia relapse after allogeneic hematopoietic stem cell transplantation

Acute graft-versus-host disease (aGVHD) limits the therapeutic benefit of allogeneic hematopoietic stem cell transplantation (allo-HSCT) and requires immunosuppressive prophylaxis that compromises antitumor and antipathogen immunity. OX40 is a costimulatory receptor upregulated on circulating T cells in aGVHD and plays a central role in driving the expansion of alloreactive T cells. Here, we show that OX40 is also upregulated on T cells infiltrating GVHD target organs in a rhesus macaque model, supporting the hypothesis that targeted ablation of OX40+ T cells will mitigate GVHD pathogenesis. We thus created an OX40-specific cytotoxic receptor that, when expressed on human T cells, enables selective elimination of OX40+ T cells. Because OX40 is primarily upregulated on CD4+ T cells upon activation, engineered OX40-specific T cells mediated potent cytotoxicity against activated CD4+ T cells and suppressed alloreactive T-cell expansion in a mixed lymphocyte reaction model. OX40 targeting did not inhibit antiviral activity of memory T cells specific to Epstein-Barr virus, cytomegalovirus, and adenoviral antigens. Systemic administration of OX40-targeting T cells fully protected mice from fatal xenogeneic GVHD mediated by human peripheral blood mononuclear cells. Furthermore, combining OX40 targeting with a leukemia-specific chimeric antigen receptor in a single T cell product provides simultaneous protection against leukemia and aGVHD in a mouse xenograft model of residual disease posttransplant. These results underscore the central role of OX40+ T cells in mediating aGVHD pathogenesis and support the feasibility of a bifunctional engineered T-cell product derived from the stem cell donor to suppress both disease relapse and aGVHD following allo-HSCT.

LPSlow-Macrophages Alleviate the Outcome of Graft-Versus-Host Disease Without Aggravating Lymphoma Growth in Mice

Despite significant therapeutic advances, graft-versus-host disease (GvHD) remains the main life-threatening complication following allogeneic hematopoietic stem cell transplantation. The pathogenesis of GvHD is dominated by a dysregulated allogeneic immune response that drives fibrosis and autoimmunity in chronic forms. A multitude of cell therapy approaches, including infusion of myeloid cells, has been proposed to prevent GvHD through tolerance induction but yielded variable results. Myeloid cells like macrophages can be reprogrammed to develop adaptive-like features following antigenic challenge to reinforce or inhibit a subsequent immune response; a phenomenon termed ‘trained immunity’. Here we report that, whereas LPS^low-trained macrophages elicit a suppressor effect on allogeneic T cell proliferation and function in vitro in an IL-10-dependent manner, Bacille Calmette et Guérin (BCG)-trained macrophages exert an opposite effect. In a murine model of sclerodermatous chronic GvHD, LPS^low-trained macrophages attenuate clinical signs of GvHD with significant effects on T cell phenotype and function, autoantibodies production, and tissue fibrosis. Furthermore, infusion of LPS^low-macrophages significantly improves survival in mice with acute GvHD. Importantly, we also provide evidence that LPS^low-macrophages do not accelerate A20-lymphoma tumor growth, which is significantly reduced upon transfer of BCG-macrophages. Collectively, these data indicate that macrophages can be trained to significantly inhibit in vitro and in vivo allo-reactive T cell proliferation without exhibiting pro-tumoral effect, thereby opening the way to promising clinical applications.

GVHD Pathogenesis, Prevention and Treatment: Lessons From Humanized Mouse Transplant Models

Graft-vs-host disease (GVHD) is the most common cause of non-relapse mortality following allogeneic hematopoietic stem cell transplantation (HSCT) despite advances in conditioning regimens, HLA genotyping and immune suppression. While murine studies have yielded important insights into the cellular responses of GVHD, differences between murine and human biology has hindered the translation of novel therapies into the clinic. Recently, the field has expanded the ability to investigate primary human T cell responses through the transplantation of human T cells into immunodeficient mice. These xenogeneic HSCT models benefit from the human T cell receptors, CD4 and CD8 proteins having cross-reactivity to murine MHC in addition to several cytokines and co-stimulatory proteins. This has allowed for the direct assessment of key factors in GVHD pathogenesis to be investigated prior to entering clinical trials. In this review, we will summarize the current state of clinical GVHD research and discuss how xenogeneic HSCT models will aid in advancing the current pipeline of novel GVHD prophylaxis therapies into the clinic.

Vulnerability to reservoir reseeding due to high immune activation after allogeneic hematopoietic stem cell transplantation in individuals with HIV-1

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the only medical intervention that has led to an HIV cure. Whereas the HIV reservoir sharply decreases after allo-HSCT, the dynamics of the T cell reconstitution has not been comprehensively described. We analyzed the activation and differentiation of CD4⁺ and CD8⁺ T cells, and the breadth and quality of HIV- and CMV-specific CD8⁺ T cell responses in 16 patients with HIV who underwent allo-HSCT (including five individuals who received cells from CCR5Δ32/Δ32 donors) to treat their underlying hematological malignancy and who remained on antiretroviral therapy (ART). We found that reconstitution of the T cell compartment after allo-HSCT was slow and heterogeneous with an initial expansion of activated CD4⁺ T cells that preceded the expansion of CD8⁺ T cells. Although HIV-specific CD8⁺ T cells disappeared immediately after allo-HSCT, weak HIV-specific CD8⁺ T cell responses were detectable several weeks after transplant and could still be detected at the time of full T cell chimerism, indicating that de novo priming, and hence antigen exposure, occurred during the time of T cell expansion. These HIV-specific T cells had limited functionality compared with CMV-specific CD8⁺ T cells and persisted years after allo-HSCT. In conclusion, immune reconstitution was slow, heterogeneous, and incomplete and coincided with de novo detection of weak HIV-specific T cell responses. The initial short phase of high T cell activation, in which HIV antigens were present, may constitute a window of vulnerability for the reseeding of viral reservoirs, emphasizing the importance of maintaining ART directly after allo-HSCT.

Advances in the treatment of graft-versus-host disease with immunomodulatory cells

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) has been widely used to treat hematological malignancies and genetic diseases. Graft-versus-host disease (GVHD) induced by donor immune system is the most common complication, contributing to severe morbidity and mortality after allo-HSCT. Currently, in terms of the prevention and treatment of GVHD, the major first-line therapeutic drugs are corticosteroids. However, most patients with systemic corticosteroid treatment are prone to steroid-refractory and poor prognosis. The use of several immune cells including Tregs, Bregs and mesenchymal stromal cells (MSCs) as an alternative on prevention or therapy of GVHD has been demonstrated to be beneficial. However, there are still many defects to a certain degree. Based on immune cells, it is promising to develop new and better approaches to improve GVHD. In this article, we will review the current advance of immune cells (Tregs, Bregs, MSCs) with negative regulation in the treatment of GVHD and present emerging strategies for the prevention and treatment of GVHD by other immune regulatory cells and chimeric antigen receptor (CAR) Tregs. In addition, these new therapeutic options need to be further evaluated in well-designed prospective multicenter trials to determine the optimal treatment for GVHD patients and improve their prognosis.

Visualization of Activated T Cells by OX40-ImmunoPET as a Strategy for Diagnosis of Acute Graft-versus-Host Disease

Graft-versus-host disease (GvHD) is a major complication of allogeneic hematopoietic cell transplantation (HCT), mediated primarily by donor T cells that become activated and attack host tissues. Noninvasive strategies detecting T-cell activation would allow for early diagnosis and possibly more effective management of HCT recipients. PET imaging is a sensitive and clinically relevant modality ideal for GvHD diagnosis, and there is a strong rationale for the use of PET tracers that can monitor T-cell activation and expansion with high specificity. The TNF receptor superfamily member OX40 (CD134) is a cell surface marker that is highly specific for activated T cells, is upregulated during GvHD, and mediates disease pathogenesis. We recently reported the development of an antibody-based activated T-cell imaging agent targeting OX40. In the present study, we visualize the dynamics of OX40 expression in an MHC-mismatch mouse model of acute GvHD using OX40-immunoPET. This approach enabled visualization of T-cell activation at early stages of disease, prior to overt clinical symptoms with high sensitivity and specificity. This study highlights the potential utility of the OX40 PET imaging as a new strategy for GvHD diagnosis and therapy monitoring. SIGNIFICANCE: OX40-immunoPET imaging is a promising noninvasive strategy for early detection of GvHD, capable of detecting signs of GvHD pathology even prior to the development of overt clinical symptoms.

CD38brightCD8+ T Cells Associated with the Development of Acute GVHD Are Activated, Proliferating, and Cytotoxic Trafficking Cells

We have previously reported that a peripheral blood absolute CD38^brightCD8⁺ effector memory T cell (TEM) population expansion of >35 cells/µL predicts the development of acute graft-versus-host disease (GVHD). We hypothesized that these T cells are activated, proliferating, and cytotoxic trafficking cells that are not a response to viral reactivation and may be involved in acute GVHD. We characterized peripheral blood T cell populations at the time of maximum CD38^brightCD8⁺ TEM expansion in patients from our originally reported pediatric allogeneic hematopoietic cell transplantation recipient cohort. Samples were incubated with fluorochrome-conjugated antibodies directed against CD3, CD8, CD38, HLA-DR (T cell activation), Ki-67 (T cell proliferation), granzyme B (marker of cytotoxic T cells), CLA (skin trafficking), CCR5 (visceral trafficking), and CXCR6 (liver trafficking). We also incubated samples with Epstein-Barr virus (EBV) and cytomegalovirus (CMV) peptide pools and measured IFN-γ production by flow cytometry and performed EBV and CMV tetramer staining. Higher median proportions of cell expression of HLA-DR, Ki-67, granzyme B, CLA, CCR5, and CXCR6 were observed for CD38^brightCD8⁺ T cells compared with CD38^nonbrightCD8⁺ T cells in patients with acute GVHD (P < .05) but not in patients without acute GVHD (P not significant). No IFN-γ production was observed after incubation with CMV and EBV peptide pools. EBV-specific tetramer populations of 6.85% and 3.17% were detected in 2 patients with acute GVHD, whereas a CMV-specific tetramer population of 3.77% was detected in 1 patient with acute GVHD. No EBV- or CMV-specific tetramer populations were detected in any patient without acute GVHD. We conclude that CD38^brightCD8⁺ T cells associated with the development of acute GVHD are activated, proliferating, and cytotoxic trafficking cells that do not appear to respond to CMV or EBV reactivation. Further studies are needed to determine whether these cells are directly involved in acute GVHD pathogenesis.

The Role of Co-stimulatory/Co-inhibitory Signals in Graft-vs.-Host Disease

Allogeneic hematopoietic cell transplantation (allo-HCT) is an effective immunotherapeutic approach for various hematologic and immunologic ailments. Despite the beneficial impact of allo-HCT, its adverse effects cause severe health concerns. After transplantation, recognition of host cells as foreign entities by donor T cells induces graft-vs.-host disease (GVHD). Activation, proliferation and trafficking of donor T cells to target organs and tissues are critical steps in the pathogenesis of GVHD. T cell activation is a synergistic process of T cell receptor (TCR) recognition of major histocompatibility complex (MHC)-anchored antigen and co-stimulatory/co-inhibitory signaling in the presence of cytokines. Most of the currently used therapeutic regimens for GVHD are based on inhibiting the allogeneic T cell response or T-cell depletion (TCD). However, the immunosuppressive drugs and TCD hamper the therapeutic potential of allo-HCT, resulting in attenuated graft-vs.-leukemia (GVL) effect as well as increased vulnerability to infection. In view of the drawback of overbroad immunosuppression, co-stimulatory, and co-inhibitory molecules are plausible targets for selective modulation of T cell activation and function that can improve the effectiveness of allo-HCT. Therefore, this review collates existing knowledge of T cell co-stimulation and co-inhibition with current research that may have the potential to provide novel approaches to cure GVHD without sacrificing the beneficial effects of allo-HCT.

HHV-6B infection, T-cell reconstitution, and graft-vs-host disease after hematopoietic stem cell transplantation

Successful and sustained CD4⁺ T-cell reconstitution is associated with increased survival after hematopoietic cell transplantation (HCT), but opportunistic infections may adversely affect the time and extent of immune reconstitution. Human herpesvirus 6B (HHV-6B) efficiently infects CD4⁺ T cells and utilizes as a receptor CD134 (OX40), a member of the TNF superfamily that antagonizes regulatory T-cell (T_reg) activity. Reactivation of HHV-6B has been associated with aberrant immune reconstitution and acute graft-versus-host disease (aGVHD) after HCT. Given that T_reg counts are negatively correlated with aGVHD severity, we postulate that one mechanism for the poor CD4⁺ T-cell reconstitution observed shortly after transplant may be HHV-6B infection and depletion of peripheral (extra-thymic) CD4⁺ T cells, including a subpopulation of T_reg cells. In turn, this may trigger a series of adverse events resulting in poor clinical outcomes such as severe aGVHD. In addition, recent evidence has linked HHV-6B reactivation with aberrant CD4⁺ T-cell reconstitution late after transplantation, which may be mediated by a different mechanism, possibly related to central (thymic) suppression of T-cell reconstitution. These observations suggest that aggressive management of HHV-6B reactivation in transplant patients may facilitate CD4⁺ T-cell reconstitution and improve the quality of life and survival of HCT patients.

Imaging activated T cells predicts response to cancer vaccines

In situ cancer vaccines are under active clinical investigation, given their reported ability to eradicate both local and disseminated malignancies. Intratumoral vaccine administration is thought to activate a T cell-mediated immune response, which begins in the treated tumor and cascades systemically. In this study, we describe a PET tracer (64Cu-DOTA-AbOX40) that enabled noninvasive and longitudinal imaging of OX40, a cell-surface marker of T cell activation. We report the spatiotemporal dynamics of T cell activation following in situ vaccination with CpG oligodeoxynucleotide in a dual tumor-bearing mouse model. We demonstrate that OX40 imaging was able to predict tumor responses on day 9 after treatment on the basis of tumor tracer uptake on day 2, with greater accuracy than both anatomical and blood-based measurements. These studies provide key insights into global T cell activation following local CpG treatment and indicate that 64Cu-DOTA-AbOX40 is a promising candidate for monitoring clinical cancer immunotherapy strategies.

Human Herpesvirus-6B Reactivation Is a Risk Factor for Grades II to IV Acute Graft-versus-Host Disease after Hematopoietic Stem Cell Transplantation: A Systematic Review and Meta-Analysis

Graft-versus-host disease (GVHD) is an important cause of morbidity and mortality after allogeneic hematopoietic cell transplantation (HCT). Many studies have suggested that human herpesvirus-6B (HHV-6B) plays a role in acute GVHD (aGVHD) after HCT. Our objective was to systematically summarize and analyze evidence regarding HHV-6B reactivation and development of aGVHD. PubMed and EMBASE databases were searched using terms for HHV-6, HCT, and aGVHD, yielding 865 unique results. Case reports, reviews, articles focusing on inherited chromosomally integrated HHV-6, poster presentations, and articles not published in English were excluded. The remaining 467 articles were reviewed for the following requirements: a statistical analysis of HHV-6B reactivation and a GVHD was described, HHV-6B reactivation was defined by PCR, and blood (plasma, serum, or peripheral blood mononuclear cells) was used for HHV-6B PCR. Data were abstracted from publications that met these criteria (n = 33). Publications were assigned to 1 of 3 groups: (1) HHV-6B reactivation was analyzed as a time-dependent risk factor for subsequent aGVHD (n = 14), (2) aGVHD was analyzed as a time-dependent risk factor for subsequent HHV-6B reactivation (n = 1), and (3) analysis without temporal specification (n = 18). A statistically significant association (P < .05) between HHV-6B reactivation and aGVHD was observed in 10 of 14 studies (71%) in group 1, 0 of 1 study (0%) in Group 2, and 8 of 18 studies (44.4%) in Group 3. Of the 14 studies that analyzed HHV-6B as a risk factor for subsequent aGVHD, 11 performed a multivariate analysis and reported a hazard ratio, which reached statistical significance in 9 of these s tudies. Meta-analysis of these 11 studies demonstrated a statistically significant association between HHV-6B and subsequent grades II to IV aGVHD (hazard ratio, 2.65; 95% confidence interval, 1.89 to 3.72; P < .001).HHV-6B reactivation is associated with aGVHD, and when studies have a temporal component to their design, HHV-6B reactivation is associated with subsequent aGVHD. Further research is needed to investigate whether antiviral prophylaxis reduces incidence or severity of aGVHD.

Human CD134 (OX40) expressed on T cells plays a key role for human herpesvirus 6B replication after allogeneic hematopoietic stem cell transplantation

BACKGROUND

CD134 (OX40), which is a cellular receptor for human herpesvirus-6B (HHV-6B) and expresses on activated T cells, may play a key role for HHV-6B replication after allogeneic hematopoietic stem cell transplantation (allo-HSCT).

OBJECTIVES

Therefore, we examined the CD134 expression on T cells and HHV-6B replication after allo-HSCT, and analyzed the correlation between them.

STUDY DESIGN

Twenty-three patients after allo-HSCT were enrolled. The percentages of CD134-positive cells within the CD4⁺ and CD8⁺ cell populations were measured by flow cytometry, and the viral copy number of HHV-6B was simultaneously quantified by real-time PCR. The correlation between CD134 and HHV-6B viral load was then statistically analyzed.

RESULTS

HHV-6B reactivation occurred in 11 of 23 patients (47.8%). CD134 expression was seen on T cells and was coincident with the time of peak viral load. The percentage of CD134-positive cells decreased significantly when HHV-6B DNA disappeared (p = .005 in CD4⁺ T cells, p = .02 in CD8⁺ T cells). In the 4 patients who underwent umbilical cord blood transplantation (UCBT), the viral load varied with the percentage of CD134-positive cells. In the comparison between the HHV-6B reactivation group and non-reactivation group, maximum percentages of CD134-positive cells among CD4⁺ T cells in reactivation group were significantly higher than those in non-reactivation group (p = .04).

CONCLUSIONS

This is the first study to show that a correlation of CD134 expression on T cells with HHV-6B replication after allo-HSCT, especially in UCBT. The results possibly indicate that CD134 on T cells plays a key role for HHV-6B replication after allo-HSCT.

Of the multiple mechanisms leading to type 1 diabetes, T cell receptor revision may play a prominent role (is type 1 diabetes more than a single disease?)

A single determinant factor for autoimmunity does not exist; disease development probably involves contributions from genetics, the environment and immune dysfunction. Type 1 diabetes is no exception. Genomewide-associated studies (GWAS) analysis in T1D has proved disappointing in revealing contributors to disease prediction; the only reliable marker has been human leucocyte antigen (HLA). Specific HLAs include DR3/DR4/DQ2/DQ8, for example. Because HLA molecules present antigen to T cells, it is reasonable that certain HLA molecules have a higher affinity to present self-antigen. Recent studies have shown that additional polymorphisms in HLA that are restricted to autoimmune conditions are further contributory. A caveat is that not all individuals with the appropriate 'pro-autoimmune' HLA develop an autoimmune disease. Another crucial component is autoaggressive T cells. Finding a biomarker to discriminate autoaggressive T cells has been elusive. However, a subset of CD4 helper cells that express the CD40 receptor have been described as becoming pathogenic. An interesting function of CD40 on T cells is to induce the recombination-activating gene (RAG)1/RAG2 T cell receptor recombination machinery. This observation is contrary to immunology paradigms that changes in TCR molecules cannot take place outside the thymic microenvironment. Alteration in TCR, called TCR revision, not only occurs, but may help to account for the development of autoaggressive T cells. Another interesting facet is that type 1 diabetes (T1D) may be more than a single disease; that is, multiple cellular components contribute uniquely, but result ultimately in the same clinical outcome, T1D. This review considers the process of T cell maturation and how that could favor auto-aggressive T cell development in T1D. The potential contribution of TCR revision to autoimmunity is also considered.

Programmed death-1 controls T cell survival by regulating oxidative metabolism

The coinhibitory receptor programmed death-1 (PD-1) maintains immune homeostasis by negatively regulating T cell function and survival. Blockade of PD-1 increases the severity of graft-versus-host disease (GVHD), but the interplay between PD-1 inhibition and T cell metabolism is not well studied. We found that both murine and human alloreactive T cells concomitantly upregulated PD-1 expression and increased levels of reactive oxygen species (ROS) following allogeneic bone marrow transplantation. This PD-1(Hi)ROS(Hi) phenotype was specific to alloreactive T cells and was not observed in syngeneic T cells during homeostatic proliferation. Blockade of PD-1 signaling decreased both mitochondrial H2O2 and total cellular ROS levels, and PD-1-driven increases in ROS were dependent upon the oxidation of fatty acids, because treatment with etomoxir nullified changes in ROS levels following PD-1 blockade. Downstream of PD-1, elevated ROS levels impaired T cell survival in a process reversed by antioxidants. Furthermore, PD-1-driven changes in ROS were fundamental to establishing a cell's susceptibility to subsequent metabolic inhibition, because blockade of PD-1 decreased the efficacy of later F1F0-ATP synthase modulation. These data indicate that PD-1 facilitates apoptosis in alloreactive T cells by increasing ROS in a process dependent upon the oxidation of fat. In addition, blockade of PD-1 undermines the potential for subsequent metabolic inhibition, an important consideration given the increasing use of anti-PD-1 therapies in the clinic.

Peripheral Blood CD38 Bright CD8+ Effector Memory T Cells Predict Acute Graft-versus-Host Disease

Acute graft-versus-host disease (aGVHD) is mediated by allogeneic T cell responses. We hypothesized that increases of peripheral blood-activated CD8+ effector memory T (TEM) cells would be observed after hematopoietic stem cell transplantation (HSCT) before onset of aGVHD symptoms. Blood was collected twice weekly after HSCT for 7 weeks in 49 consecutive pediatric and adult HSCT recipients. Samples were incubated with fluorochrome-conjugated antibodies against CD45, CD3, CD8, CD38, CD45RA, and CCR7 and analyzed using flow cytometry. TEM cells were defined as CD3+ CD8+ CCR7- CD45RA(-) lymphocytes. CD38 expression was used as a marker of T cell activation. Patients were followed for 100 days for development of aGVHD. Twenty-three patients developed grade 1 to 4 aGVHD at a median of 37 days (range, 15 to 79 days) after HCST. Absolute CD38 bright CD8+ TEM of > 35 cells/μL predicted aGVHD at a median of 8 days (range, 1 to 34) before aGVHD onset with a sensitivity of 82.6% and specificity of 91.6%. The cumulative incidence of aGVHD was 90% in patients with absolute CD38 bright CD8+ TEM >35 cells/μL and 15% in patients without (P < .0001). Quantification of CD38 bright CD8+ TEM cells may predict aGVHD in children and young adult HSCT recipients.

Anti-CMV-IgG positivity of donors is beneficial for alloHSCT recipients with respect to the better short-term immunological recovery and high level of CD4+CD25high lymphocytes

Hematopoietic stem cell transplantation from anti-cytomegalovirus immunoglobulin G (anti-CMV-IgG) positive donors facilitated immunological recovery post-transplant, which may indicate that chronic CMV infection has an effect on the immune system. This can be seen in the recipients after reconstitution with donor lymphocytes. We evaluated the composition of lymphocytes at hematologic recovery in 99 patients with hematologic malignancies post hematopoietic stem cell transplantation (HSCT). Anti-CMV-IgG seropositivity of the donor was associated with higher proportions of CD4+ (227.963 ± 304.858 × 106 vs. 102.050 ± 17.247 × 106 cells/L, p = 0.009) and CD4+CD25high (3.456 ± 0.436 × 106 vs. 1.589 ± 0.218 × 106 cells/L, p = 0.003) lymphocytes in the blood at hematologic recovery. The latter parameter exerted a diverse influence on the risk of acute graft-versus-host disease (GvHD) if low (1.483 ± 0.360 × 106 vs. 3.778 ± 0.484 × 106 cells/L, p < 0.001) and de novo chronic GvHD (cGvHD) if high (3.778 ± 0.780 × 106 vs. 2.042 ± 0.261 × 106 cells/L, p = 0.041). Higher values of CD4+ lymphocytes in patients who received transplants from anti-CMV-IgG-positive donors translated into a reduced demand for IgG support (23/63 vs. 19/33, p = 0.048), and these patients also exhibited reduced susceptibility to cytomegalovirus (CMV), Epstein-Barr virus (EBV) and/or human herpes 6 virus (HHV6) infection/reactivation (12/50 vs. 21/47, p = 0.032). Finally, high levels (³0.4%) of CD4+CD25high lymphocytes were significantly associated with better post-transplant survival (56% vs. 38%, four-year survival, p = 0.040). Donors who experience CMV infection/reactivation provide the recipients with lymphocytes, which readily reinforce the recovery of the transplanted patients' immune system.

Achievement of early complete donor chimerism in CD25+-activated leukocytes is a strong predictor of the development of graft-versus-host-disease after stem cell transplantation

Chimerism dynamics in bone marrow, peripheral blood (PB), and T lymphocytes (TL) has been associated with the development of various complications after allogeneic stem-cell transplantation (allo-SCT). In the present study, the usefulness of chimerism monitoring in CD25(+)-activated leukocytes (AL), together with that in bone marrow, PB, and TL, for the anticipation of complications after allo-SCT, has been analyzed in 68 patients. In AL, we observed a slower dynamics toward complete chimerism (CC) than in PB (p = 0.042), while no significant differences were found between TL and PB (p = 0.12). Complete chimerism achievement in AL at day +30 has shown to be an independent risk factor for the development of grade II-IV acute graft-versus-host disease (aGvHD; hazard ratio [95% confidence interval]: 11.9 [1.5-91.7]; p = 0.017). Moreover, among patients achieving CC in TL and AL at different time-points after SCT (n = 17/68), the incidence of grade II-IV aGvHD was significantly higher in patients who achieved CC earlier in AL (5/5) than in those who achieved CC earlier in TL (1/11; p = 0.001). Therefore, achievement of early complete donor chimerism in CD25(+) AL is a strong predictor for the development of aGvHD. Prospective analysis of chimerism in AL could improve the post-SCT management of immunosuppressive therapy in transplanted patients.

In vivo expansion of co-transplanted T cells impacts on tumor re-initiating activity of human acute myeloid leukemia in NSG mice

Human cells from acute myeloid leukemia (AML) patients are frequently transplanted into immune-compromised mouse strains to provide an in vivo environment for studies on the biology of the disease. Since frequencies of leukemia re-initiating cells are low and a unique cell surface phenotype that includes all tumor re-initiating activity remains unknown, the underlying mechanisms leading to limitations in the xenotransplantation assay need to be understood and overcome to obtain robust engraftment of AML-containing samples. We report here that in the NSG xenotransplantation assay, the large majority of mononucleated cells from patients with AML fail to establish a reproducible myeloid engraftment despite high donor chimerism. Instead, donor-derived cells mainly consist of polyclonal disease-unrelated expanded co-transplanted human T lymphocytes that induce xenogeneic graft versus host disease and mask the engraftment of human AML in mice. Engraftment of mainly myeloid cell types can be enforced by the prevention of T cell expansion through the depletion of lymphocytes from the graft prior transplantation.

Low levels of NF-κB/p65 mark anergic CD4+ T cells and correlate with disease severity in sarcoidosis

T lymphocytes from patients with sarcoidosis respond weakly when stimulated with mitogen or antigen. However, the mechanisms responsible for this anergy are not fully understood. Here, we investigated the protein levels of nuclear transcription factor NF-κB (p50, p65, and p105), IκBα (inhibitor of NF-κB), T-cell receptor (TCR) CD3ζ-chain, tyrosine kinase p56(LCK), and nuclear factor of activated T cells c2 (NF-ATc2) in peripheral blood CD4(+) T cells from patients with sarcoidosis. Baseline expression of p65 in these lymphocytes was reduced in 50% of patients. The reduced levels of p65 in sarcoid CD4(+) T cells concurred with decreased levels of p50, p105, CD3ζ, p56(LCK), IκBα, and NF-ATc2. Polyclonal stimulation of NF-κB-deficient sarcoid T cells resulted in reduced expression of CD69 and CD154, decreased proliferation, and cytokine (i.e., interleukin 2 [IL-2] and gamma interferon [IFN-γ]) production. The clinical significance of these findings is suggested by the association between low p65 levels and the development of more severe and active sarcoidosis. Although correlative, our results support a model in which multiple intrinsic signaling defects contribute to peripheral T-cell anergy and the persistence of chronic inflammation in sarcoidosis.

T-cell costimulatory molecules in acute-graft-versus host disease: therapeutic implications

Acute Graft-versus-host disease (GVHD) is a major complication after allogeneic hematopoietic stem cell transplantation. Although this process is thought to consist of several phases, T-cell activation plays a critical role in the pathogenesis of acute GVHD. To become efficient effectors, T-cells require additional costimulation after T-cell receptor signaling. A number of molecules are involved in costimulation of T-cells such as CD28, CD40L, CD30, OX40, 4-1BB, ICOS, and LIGHT. The system is regulated by inhibitory molecules, CTLA-4, and PD-1. There is experimental evidence that those molecules are implicated in the pathogenesis of GHVD. We describe how these molecules are involved in acute GVHD and how the blockade of costimulatory molecules may have potential implications for the treatment of patients with acute GVHD.

CD134-allodepletion allows selective elimination of alloreactive human T cells without loss of virus-specific and leukemia-specific effectors

Graft-versus-host disease (GVHD) remains a frequent and severe complication of allogeneic stem cell transplantation (SCT). One approach to reducing alloreactivity is to deplete the graft of alloreactive T cells. Global T cell depletion results in poor immune reconstitution with high mortality from viral infections and disease relapse. Therefore, an approach to selectively deplete alloreactive T cells without compromising other responses would be highly beneficial. We undertook studies to identify an inducible activation marker expressed on alloreactive effector T cells following culture with HLA-mismatched allostimulators. Compared to other markers, CD134 was superior because of its negative baseline expression and rapid upregulation after activation. Depletion of CD134(+) cells from responder populations dramatically reduced specific alloreactivity as determined by reduction of helper T cell precursor frequencies below the threshold predicting development of clinical GVHD while retaining responses to third-party alloantigens. CD134-allodepleted populations retained effectors specific for the Wilms' tumor (WT1) leukemia antigen as determined by WT1 specific pentamers, and CMV-specific effectors as determined by CMV-specific pentamers and CMV-specific ELISpot. Thus, use of CD134-allodepleted grafts may improve allogeneic SCT by reducing GVHD without loss of pathogen-specific and leukemia-specific immunity.