CD4+CD25+ Regulatory T Cells in Hematopoietic Stem Cell Transplantation

The Therapeutic Strategies of Regulatory T Cells in Malignancies and Stem Cell Transplantations

Regulatory T cells (Treg cells) are considered one of the main dynamic cell types within the immune system. Because Treg cells suppress immune responses, they have potential roles in immunological self-tolerance and may help to maintain immune homeostasis. Promoting Treg cell function and increasing their numbers might be useful in treating autoimmune disorders, as well as preventing allograft rejection. However, studies of mice and humans demonstrate that Treg cells promote cancer progression and suppress antitumor immunity. Therefore, suppressing Treg cell function or reducing their numbers could support the immune system's response to pathogenic microorganisms and tumors. As a result, there is great interest in investigating the Treg cells role in the treatment of hematological and nonhematological malignancies. Consequently, Treg cells could be a fundamentally important target for pathologies of the immune system. Targeting effector Treg cells could help to distinguish and selectively decrease these cells while preserving other Treg cells needed to suppress autoimmunity. Currently, a promising way to treat malignancies and other autoimmune disorders is stem cell transplantation. Stem cell transplants (SCT) can help to manage the production of Treg cells and also may produce more efficient Treg cells, thereby suppressing clinical disease progression. Specifically, mature T cells within the engrafted stem cells mediate this SCT beneficial effect. During SCT, the recipient's immune system is replaced with a donor, which allows for improved immune system function. In addition, SCT can protect from disease relapse, as graft-versus-host disease (GvHD) in transplant patients can be protective against cancer recurrence. The current review will define the role of regulatory T cells in treatment of malignancy. Additionally, it will summarize current promising research regarding the utility of regulatory T cells in stem cell transplantation.

Distribution and clonality of the vα and vβ T-cell receptor repertoire of regulatory T cells in leukemia patients with and without graft versus host disease

Graft versus host disease (GVHD) is the main complication following allogeneic hematopoietic stem cell transplantation (allo-HSCT). Recent data indicated that regulatory T (Treg) cells might relate to GVHD, and such functions might be mediated by certain T-cell receptor (TCR) subfamily of Treg cells. Thus, we analyzed the distribution and clonality of the TCR Vα and Vβ repertoire of Treg cells from leukemia patients with and without GVHD after allo-HSCT. Numerous TCR Vα subfamilies, including Vα1, Vα9, Vα13, Vα16-19, and Vα24-29, were absent in Treg cells after allo-HSCT. The usage numbers for the TCR Vα and Vβ subfamilies in Treg cells from patients without GVHD appeared more widely. The expression frequencies of Vα10 or Vα20 between both groups were significantly different. Moreover, the expression frequency of TCR Vβ2 subfamily in patients without GVHD was significantly higher than that in patients with GVHD. Oligoclonally expanded TCR Vα and Vβ Treg cells were identified in a few samples in both groups. Restricted utilization of the Vα and Vβ subfamilies and the absence of some important TCR rearrangements in Treg cells may be related to GVHD due to a lower regulating function of Treg subfamilies.

CD4+CD25highCD127low regulatory T cells in peripheral blood are not an independent factor for chronic graft-versus-host disease after allogeneic stem cell transplantation

Background. The therapeutic efficacy of allogeneic hemopoietic stem cell transplantation (HSCT) largely relies on the graft-versus-leukemia (GVL) effect. Uncontrolled graft-versus-host disease (GVHD) is a feared complication of HSCT. Regulatory T cells (Treg) are a subset of CD4+ T-helper cells believed to maintain tolerance after HSCT. It remains unclear whether low peripheral blood Treg have an impact on the risk for acute (aGVHD) and chronic GVHD (cGVHD). Methods. In this paper we enumerated the CD4+CD25highCD127low Treg in the peripheral blood of 84 patients after at least 150 days from HSCT and in 20 healthy age-matched controls. Results. Although similar mean lymphocyte counts were found in patients and controls, CD3+CD4+ T-cell counts were significantly lower in patients. Patients also had significantly lower Treg percentages among lymphocytes as compared to controls. Patients with cGVHD had even higher percentages of Treg if compared to patients without cGVHD. In multivariate analysis, Treg percentages were not an independent factor for cGVHD. Conclusions. This paper did not show a relation between deficient peripheral blood Treg and cGVHD, therefore cGVHD does not seem to occur as a result of peripheral Treg paucity.

PI16 is expressed by a subset of human memory Treg with enhanced migration to CCL17 and CCL20

The peptidase inhibitor PI16 was shown previously by microarray analysis to be over-expressed by CD4-positive/CD25-positive Treg compared with CD4-positive/CD25-negative Th cells. Using a monoclonal antibody to the human PI16 protein, we found that PI16-positive Treg have a memory (CD45RO-positive) phenotype and express higher levels of FOXP3 than PI16-negative Treg. PI16-positive Treg are functional in suppressor assays in vitro with potency similar to PI16-negative Treg. Further phenotyping of the PI16-positive Treg revealed that the chemokine receptors CCR4 and CCR6 are expressed by more of the PI16-positive/CD45RO-positive Treg compared with PI16-negative/CD45RO-positive Treg or Th cells. PI16-positive Treg showed enhanced in vitro migration towards the inflammatory chemokines CCL17 and CCL20, suggesting they can migrate to sites of inflammation. We conclude that PI16 identifies a novel distinct subset of functional memory Treg which can migrate to sites of inflammation and regulate the pro-inflammatory response at those sites.

Identification of a unique double-negative regulatory T-cell population

Regulatory T (Treg) cells represent one of the main mechanisms of regulating self-reactive immune cells. Treg cells are thought to play a role in down-regulating immune responses to self or allogeneic antigens in the periphery. Although the function of Treg cells has been demonstrated in many experimental settings, the precise mechanisms and antigen specificity often remain unclear. In a hepatitis B e antigen-T-cell receptor (HBeAg-TCR) double transgenic mouse model, we observed a phenotypically unique (TCR+)  CD4- /CD8-  CD25(+/-)  GITR(high)  PD-1(high)  FoxP3-) HBeAg-specific population that demonstrates immune regulatory function. This HBeAg-specific double-negative regulatory cell population proliferates vigorously in vitro, in contrast to any other known regulatory population, in an interleukin-2-independent manner.

Abrogation of Treg function deteriorates rheumatoid arthritis

An early prognostic indicator which warns of progressive joint destruction of rheumatoid arthritis (RA) was explored using a novel suspension-array technique in moderate (Steinbrocker stage I and II) and severe (Steinbrocker stage IV) RA patients. DNA microarray analysis of peripheral blood lymphocytes showed significant increase of interleukin (IL)-2 receptor α-chain (CD25) gene expression, a regulatory T cell (Treg) surface marker in severe RA patients. In contrast, suspension array, a comprehensive bead-based enzyme-linked immunosorbent assay (ELISA), revealed decreased production of IL-10 and increased production of interferon (IFN)-γ in sera in the incipient stage of the aggressive disease process. Both in moderate and in severe RA patients, the IFN-γ/IL-10 ratio indicated deterioration of the disease with universal validity. Fluorescence-activated cell sorting (FACS) and reverse-transcription polymerase chain reaction (RT-PCR) analysis showed extant CD4+CD25+ regulatory T cells in severe RA patients, however Foxp3, a regulatory T cell-specific transcription factor, gene expression was absent, while glucocorticoid-induced tumor necrosis factor (TNF) receptor family-related protein (GITR), which transmits a signal that abrogates regulatory T cell functions, was elevated. In the current study, we showed the validity of suspension-array analysis for enabling more complete understanding of RA, and showed that IFN-γ/IL-10 ratio can be a prognostic tool for early lesion and more aggressive RA.

T(reg) cells: collection, processing, storage and clinical use

T regulatory cells are fundamental in the maintenance of immune homeostasis and self-tolerance. Experimental models suggest the existence of two functional types of T(reg) cells designated naturally occurring and induced. Interest in T(reg) cells increased with evidence from experimental mouse and human models demonstrating that the immunosuppressive potential of these cells can be utilized in the treatment of various pathological conditions. The existence of a subpopulation of suppressive T cells was the subject of significant controversy among immunologists for many years. T regulatory cells limit immune activation through a variety of direct and indirect interactions, many of which are yet to be determined. Fully understanding T(reg) cells biology will lead us to harnessing the capacity of these cells in order to develop strategies to prevent autoimmune disorders and tolerance to transplantation. Efficient isolation, expansion and cryopreservation strategies that comply with Good Manufacturing Practice (GMP) guidelines are prerequisites for the clinical application of human CD4+ CD25+ CD127(low) FOXP3+ regulatory T cells.

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.

T cells for suicide gene therapy: activation, functionality and clinical relevance

In order to control graft-versus-host disease after donor lymphocyte infusion, T cells can be retrovirally transduced with a suicide gene. However, the immune competence of activated T cells appears compromised, responsible for reduced alloreactivity. The present study compared different activation protocols using soluble or bead-coupled antibodies regarding T-cell subtype expansion capacity and functionality. T cells were purified on a laboratory and clinical scale using both CD3 and CD4/CD8 antibodies for selection, leading to a mean purity of 96%. Transductions were performed with a GMP-grade CD34/HSV-TK vector. Activation with soluble CD3/CD28-antibodies +1000 U/ml IL-2 induced a 50-fold expansion of T cells over 14 days, whereas T cells activated with bead-coupled antibodies only expanded 2-4-fold restricted to the first week. Apart from using soluble antibodies, proliferation was highly IL-2 dependent. Expansion of CMV-specific T cells coincided with the expansion of whole CD3(+) cells. Soluble antibodies and higher IL-2 concentrations preferentially stimulated CD8(+) T cells, while bead-coupled antibodies +20 U/ml IL-2 preserved the CD4/CD8 ratio. Irrespective of the activation protocol, there was a shift from a naive to memory phenotype. When activated with soluble antibodies, mainly CD8(+) T cells were transduced. Furthermore, Th1/Th2 cytokine secretion was reduced. In contrast, CD4(+)/CD8(+) T cells activated with bead-coupled antibodies were rather homogenously transduced and cytokine secretion did not appear to be affected.

Regulatory T cells in cancer

Increasing evidence supports the existence of elevated numbers of regulatory T cells (T(reg) cells) in solid tumors and hematologic malignancies. Whereas the biology of CD4(+)CD25(+)FOXP3(+) T(reg) cells in murine models seems to be rather straightforward, studies in human diseases are more difficult to interpret due to expression of CD25 on activated effector T cells as well as T(reg) cells. More importantly, early studies in human tumors were mainly focused on CD4(+)CD25(+) T(reg) cells lacking interrogation of more specific markers such as FOXP3 expression. Although the increase of T(reg) cells seems to be a characteristic feature in most tumors, little is known about the molecular and cellular mechanisms responsible for the increase and maintenance of elevated levels of T(reg) cells in cancer. We will discuss earlier data in the context of recent findings in T(reg)-cell biology with a particular emphasis on CD4(+)CD25(high)FOXP3(+) T(reg) cells in human malignancies.

Interleukin-10-secreting type 1 regulatory T cells in rodents and humans

Interleukin-10 (IL-10)-secreting T regulatory type 1 (Tr1) cells are defined by their specific cytokine production profile, which includes the secretion of high levels of IL-10 and transforming growth factor-beta(TGF-beta), and by their ability to suppress antigen-specific effector T-cell responses via a cytokine-dependent mechanism. In contrast to the naturally occurring CD4+ CD25+ T regulatory cells (Tregs) that emerge directly from the thymus, Tr1 cells are induced by antigen stimulation via an IL-10-dependent process in vitro and in vivo. Specialized IL-10-producing dendritic cells, such as those in an immature state or those modulated by tolerogenic stimuli, play a key role in this process. We propose to use the term Tr1 cells for all IL-10-producing T-cell populations that are induced by IL-10 and have regulatory activity. The full biological characterization of Tr1 cells has been hampered by the difficulty in generating these cells in vitro and by the lack of specific marker molecules. However, it is clear that Tr1 cells play a key role in regulating adaptive immune responses both in mice and in humans. Further work to delineate the specific molecular signature of Tr1 cells, to determine their relationship with CD4+ CD25+ Tregs, and to elucidate their respective role in maintaining peripheral tolerance is crucial to advance our knowledge on this Treg subset. Furthermore, results from clinical protocols using Tr1 cells to modulate immune responses in vivo in autoimmunity, transplantation, and chronic inflammatory diseases will undoubtedly prove the biological relevance of these cells in immunotolerance.

Stem cell mobilization with G-CSF analogs: a rational approach to separate GVHD and GVL?

The separation of graft-versus-host disease (GVHD) and graft-versus-leukemia (GVL) remains the "holy grail" of allogeneic stem cell transplantation, and improvements are urgently needed to allow more effective therapy of malignant disease. The use of G-CSF-mobilized peripheral blood as a clinical stem cell source is associated with enhanced GVL effects without amplification of significant acute GVHD. Preclinical studies have demonstrated that G-CSF modulates donor T cell function before transplantation, promoting T(H)2 differentiation and regulatory T cell function. In addition, the expansion of immature antigen-presenting cells (APCs) and plasmacytoid dendritic cells (DCs) favors the maintenance of this pattern of T cell differentiation after transplantation. Although these patterns of T cell differentiation attenuate acute GVHD, they do not have an impact on the cytolytic pathways of the CD8(+) T cells that are critical for effective GVL. Recently, it has been demonstrated that modification of G-CSF, either by pegylation of the native cytokine or conjugation to Flt-3L, results in the expansion and activation of donor iNKT cells, which significantly augment CD8(+) T cell-mediated cytotoxicity and GVL effects after transplantation. Given that these cytokines also enhance the expansion of regulatory T cells and APCs, they further separate GVHD and GVL, offering potential clinical advantages for the transplant recipient.