Lymphopenia-induced proliferation of donor T cells reduces their capacity for causing acute graft-versus-host disease

Rearrangement of T Cell genome architecture regulates GVHD

WAPL, cohesin's DNA release factor, regulates three-dimensional (3D) chromatin architecture. The 3D chromatin structure and its relevance to mature T cell functions is not well understood. We show that in vivo lymphopenic expansion, and alloantigen-driven proliferation, alters the 3D structure and function of the genome in mature T cells. Conditional deletion of WAPL, cohesin's DNA release factor, in T cells reduced long-range genomic interactions and altered chromatin A/B compartments and interactions within topologically associating domains (TADs) of the chromatin in T cells at baseline. WAPL deficiency in T cells reduced loop extensions, changed expression of cell cycling genes and reduced proliferation following in vitro and in vivo stimulation, and reduced severity of graft-versus-host disease (GVHD) following experimental allogeneic hematopoietic stem cell transplantation. These data collectively characterize 3D genomic architecture of T cells in vivo and demonstrate biological and clinical implications for its disruption by cohesin release factor WAPL.

Histological features of the nasal mucosa in hematopoietic stem cell transplantation

BACKGROUND

Immunosuppression is the leading cause of recurrent sinus infections after hematopoietic stem cell transplant (HSCT), with increased incidence of sinusitis in patients with chronic graft versus host disease (GVHD). Histological descriptions of the oral mucosa, lung ciliary epithelium, and intestinal mucosa related to HSCT have been described. However, few have described the nasal mucosa. We, therefore, sought to elucidate the histological and ultrastructural features of the nasal mucosa in patients after HSCT to better understand the pathophysiology of the immune response.

METHODS

Uncinate processes from 24 HSCT patients and 12 immunocompetent patients were subjected to histological analyses via light and transmission electron microscopy (TEM).

RESULTS

TEM revealed aberrant cilia structure, altered mitochondria quantity, microvilli, and cytoplasm vacuolization. All HSCT patients with rhinosinusitis had significant loss or absence of cilia (p = 0.018). Apoptotic bodies were increased and Goblet cells decreased in nasal epithelium from patients with chronic GVHD (p = 0.04).

CONCLUSION

This tissue destruction likely enhances pathogen penetration resulting in recurrent infection.

Blockade of IL-6-signaling inhibits the pathogenesis of CD4+ T cell-mediated lethal graft-versus-host reaction against minor histocompatibility antigen

Graft-versus-host reaction (GVHR) is considered as a problem in hematopoietic cell transplantation. We found that CD45RB(high) CD62L(+) naïve CD4(+) T cells from wild-type B10D2 (H-2d MMTV6(-)) mice immediately differentiated into effector T cells producing high-levels of various cytokines after the transfer into BALB/c RAG2(-/-) (H-2d MMTV6(+)) mice. The expanded CD4(+) T cells, which have almost TCR Vβ3 chain, recognized the minor antigen of recipient mice and brought typical severe GVHR symptoms such as eyelid irritation, diarrhea, and liver failure. Eventually, all of the recipient mice transferred CD4(+) T cells was dead within 10 days. We demonstrated here that blockade of IL-6 signaling by administration of anti-IL-6 receptor (IL-6R) monoclonal antibody (mAb) remarkably inhibited the CD4(+) T cell-mediated lethal GVHR. In addition, we confirmed that the in vivo injection of anti-IL-6R mAb prevented the generation of effector CD4(+) T cells which produce the inflammatory cytokines such as IFN-γ, TNF-α, and IL-17. These findings indicated that IL-6 was a critical factor in the CD4(+) T cell-dependent acute GVHR induced by a minor-antigen, suggesting that IL-6-mediated signaling pathway would be a strong therapeutic target in T cell-mediated GVHR as well as other diseases including autoimmune and inflammation.

Negative regulators in homeostasis of naïve peripheral T cells

It is now apparent that naïve peripheral T cells are a dynamic population where active processes prevent inappropriate activation while supporting survival. The process of thymic education makes naïve peripheral T cells dependent on interactions with self-MHC for survival. However, as these signals can potentially result in inappropriate activation, various non-redundant, intrinsic negative regulatory molecules including Tob, Nfatc2, and Smad3 actively enforce T cell quiescence. Interactions among these pathways are only now coming to light and may include positive or negative crosstalk. In the case of positive crosstalk, self-MHC initiated signals and intrinsic negative regulatory factors may cooperate to dampen T cell activation and sustain peripheral tolerance in a binary fashion (on-off). In the case of negative crosstalk, self-MHC signals may promote survival through partial activation while intrinsic negative regulatory factors act as rheostats to restrain cell cycle entry and prevent T cells from crossing a threshold that would break tolerance.

Histone deacetylase inhibition modulates indoleamine 2,3-dioxygenase-dependent DC functions and regulates experimental graft-versus-host disease in mice

Histone deacetylase (HDAC) inhibitors are antitumor agents that also have antiinflammatory properties. However, the mechanisms of their immunomodulatory functions are not known. We investigated the mechanisms of action of 2 HDAC inhibitors, suberoylanilide hydroxamic acid (SAHA) and ITF 2357, on mouse DC responses. Pretreatment of DCs with HDAC inhibitors significantly reduced TLR-induced secretion of proinflammatory cytokines, suppressed the expression of CD40 and CD80, and reduced the in vitro and in vivo allostimulatory responses induced by the DCs. In addition, injection of DCs treated ex vivo with HDAC inhibitors reduced experimental graft-versus-host disease (GVHD) in a murine allogeneic BM transplantation model. Exposure of DCs to HDAC inhibitors increased expression of indoleamine 2,3-dioxygenase (IDO), a suppressor of DC function. Blockade of IDO in WT DCs with siRNA and with DCs from IDO-deficient animals caused substantial reversal of HDAC inhibition-induced in vitro suppression of DC-stimulated responses. Direct injection of HDAC inhibitors early after allogeneic BM transplantation to chimeric animals whose BM-derived cells lacked IDO failed to protect from GVHD, demonstrating an in vivo functional role for IDO. Together, these data show that HDAC inhibitors regulate multiple DC functions through the induction of IDO and suggest that they may represent a novel class of agents to treat immune-mediated diseases.

The influence of CD4 T-cell subsets on control of CD4 T-cell-mediated graft-versus-host disease

In this study, we tested the effect of different T-cell subpopulations on antigen driven effector cell expansion in lymphopenic hosts, making use of an experimental model of graft-versus-host disease (GVHD). Fluorescence-activated cell sorted (FACS) naïve CD4 T cells from C57BL/6 mice, transferred into lymphopenic F1 (C57BL/6 x BALB/c) Rag-deficient hosts, proliferated extensively and migrated systemically causing acute GVHD within 4 weeks after transfer. Adoptive hosts of CD4 memory T cells on the other hand developed milder symptoms of GVHD with later onset. T-cell expansion and migration to peripheral sites as well as development of GVHD were prevented when naïve T cells were transferred together with CD4(+) CD25(+) T cells, but co-transfer of memory T cells with naïve T cells could not prevent GVHD, although its onset was delayed. OX40, a costimulatory marker that is upregulated at an early time point after T-cell activation and enhances T-cell proliferation, cytokine secretion and survival, was strongly upregulated during GVH responses. Naïve T cells deficient in OX40 expression caused markedly reduced GVH in onset and severity despite some level of expansion in the adoptive host, suggesting an important role of this molecule in the immune pathology of GVHD.

Bone marrow-derived CD8alpha+TCR- cells that facilitate allogeneic bone marrow transplantation are a mixed population of lymphoid and myeloid progenitors

OBJECTIVE

We have characterized a hematopoietic cell population isolated from murine bone marrow that can facilitate purified hematopoietic stem cell engraftment across fully allogeneic major histocompatibility complex barriers. These facilitating cells (FCs) are classically identified as CD8alpha(+)TCR(-) by flow cytometry. Prior work has demonstrated that FCs are comprised of a heterogeneous cell population with both lymphoid and myeloid phenotypes. The present investigation was designed to more precisely characterize these subsets in terms of both phenotype and developmental potential.

METHODS

Using fluorescence-activated cell sorting analysis, freshly isolated FCs were characterized for phenotypic expression of various lymphocyte progenitor markers. The lymphopoietic potential of FCs was evaluated by culturing freshly isolated FCs on bone marrow stroma cells overexpressing notch ligand 1 (OP9-DL1). Transcripts specific to pTalpha and TCRalpha were quantitated by employing real-time reverse transcription polymerase chain reaction. Maturation of the T-cell receptor (TCR) on FCs was biochemically analyzed by immunoprecipitation.

RESULT

Freshly isolated FCs had significant expression of CD44(+)CD25(-) and CD44(+)CD25(+) phenotypes. A discrete subset of CD8(+)CD4(+) cells are also identified in the FC population, similar to the double-positive phase of thymocyte development. Of particular interest, FCs express pre-TCRalpha (pTalpha) mRNA and protein as demonstrated by reverse transcription polymerase chain reaction, intracellular staining and immunoprecipitation. FCs grown on OP9-DL1 with interleukin-7 and FMS-like tyrosine kinase 3 ligand can mature into CD44(-)CD25(+), CD8(+)CD4(+) and CD8(+) T cells. During this developmental process, expression of the 33-kDa pTalpha chain was replaced by a mature 40-kDa TCRalpha chain.

CONCLUSION

Taken together, these data demonstrate for the first time that the marrow-derived FC contains a T-cell progenitor population that closely resembles developing thymocytes.

Pathophysiology of acute graft-versus-host disease: recent advances

Allogeneic hematopoietic stem cell transplantation (HSCT) is a potentially curative therapy for many malignant and nonmalignant hematologic diseases. Donor T cells from the allografts are critical for the success of this effective therapy. Unfortunately these T cells not only recognize and attack the disease cells/tissues but also the other normal tissues of the recipient as "foreign" or "nonself" and cause severe, immune-mediated toxicity, graft-versus-host disease (GVHD). Several insights into the complex pathophysiology of GVHD have been gained from recent experimental observations, which show that acute GVHD is a consequence of interactions between both the donor and the host innate and adaptive immune systems. These insights have identified a role for a variety of cytokines, chemokines, novel T-cell subsets (naĩve, memory, regulatory, and NKT cells) and for non-T cells of both the donor and the host (antigen presenting cells, delta T cells, B cells, and NK cells) in modulating the induction, severity, and maintenance of acute GVHD. This review will focus on the immunobiology of experimental acute GVHD with an emphasis on the recent observations.