In vitro and in vivo analysis of bone marrow-derived CD3+, CD4-, CD8-, NK1.1+ cell lines

Antitumor Immunity Exerted by Natural Killer and Natural Killer T Cells in the Liver

The liver plays crucial roles in systemic immunity and greatly contributes to the systemic defense mechanism. Antitumor immunity in the liver is especially critical for the defense against systemic tumor cell dissemination. To achieve effective defense against metastatic tumor cells, liver immune cells with powerful cytotoxic activities construct a potent defense mechanism. In the liver, as compared with other organs, there is a significantly more intense percentage of innate immune lymphocytes, such as natural killer (NK) and NKT cells. These characteristic lymphocytes survey the portal blood transferred to the liver from the alimentary tract and eliminate malignant cells with their robust cytotoxic ability. Additionally, with their active cytokine-producing capacity, these innate lymphocytes initiate immunological sequences by adaptive immune cells. Therefore, they are crucial contributors to systemic antitumor immunity. These attractive immune cells help conduct a fundamental investigation of tumor immunity and act as a target of clinical measures for cancer therapies. This review discusses the mechanisms of these innate lymphocytes regarding recognition and cytotoxicity against tumor cells and the possibility of clinical applications for therapeutic measures.

Double Negative T Regulatory Cells: An Emerging Paradigm Shift in Reproductive Immune Tolerance?

Immune regulation of female reproductive function plays a crucial role in fertility, as alterations in the relationship between immune and reproductive processes result in autoimmune subfertility or infertility. The breakdown of immune tolerance leads to ovulation dysfunction, implantation failure, and pregnancy loss. In this regard, immune cells with regulatory activities are essential to restore self-tolerance. Apart from regulatory T cells, double negative T regulatory cells (DNTregs) characterized by TCRαβ+/γδ+CD3+CD4–CD8– (and negative for natural killer cell markers) are emerging as effector cells capable of mediating immune tolerance in the female reproductive system. DNTregs are present in the female reproductive tract of humans and murine models. However, their full potential as immune regulators is evolving, and studies so far indicate that DNTregs exhibit features that can also maintain tolerance in the female reproductive microenvironment. This review describes recent progress on the presence, role and mechanisms of DNTregs in the female reproductive system immune regulation and tolerance. In addition, we address how DNTregs can potentially provide a paradigm shift from the known roles of conventional regulatory T cells and immune tolerance by maintaining and restoring balance in the reproductive microenvironment of female fertility.

Insights into the role of the JAK/STAT signaling pathway in graft-versus-host disease

Allogeneic hematopoietic transplantation (allo-HCT) is a curative therapy for a variety of hematologic malignancies, primarily through immune-mediated clearance of malignant cells. This graft-versus-leukemia (GvL) effect is mediated by alloreactive donor T-cells against recipient malignant cells. Unfortunately, graft versus host disease is a potentially lethal complication of this procedure, also mediated by alloreactive donor T-cells against recipient normal tissues. Graft-versus-host disease (GVHD) remains a key contributor to nonrelapse mortality and long-term morbidity in patients undergoing allo-HCT. Reducing GVHD without interfering with - or ideally while enhancing - GvL, would improve outcomes and increase patient eligibility for allo-HCT. The JAK/STAT signaling pathway acts downstream of over 50 cytokines and is central to a wide variety of inflammatory pathways. These pathways play a role in the development and maintenance of GVHD throughout the disease process and within T-cells, B-cells, macrophages, neutrophils, and natural killer cells. Agents targeting JAK/STAT signaling pathways have shown clinical efficacy and gained US Food and Drug Administration approval for numerous diseases. Here, we review the preclinical and clinical evidence for the role of JAK/STAT signaling in the development and maintenance of GVHD and the utility of blocking agents at preventing and treating GVHD.

Developing understanding of the roles of CD1d-restricted T cell subsets in cancer: reversing tumor-induced defects

Invariant natural killer T-cells ('iNKT') are the best-known CD1d-restricted T-cells, with recently-defined roles in controlling adaptive immunity. CD1d-restricted T-cells can rapidly produce large amounts of Th1 and/or Th2//Treg/Th17-type cytokines, thereby regulating immunity. iNKT can stimulate potent anti-tumor immune responses via production of Th1 cytokines, direct cytotoxicity, and activation of effectors. However, Th2//Treg-type iNKT can inhibit anti-tumor activity. Furthermore, iNKT are decreased and/or reversibly functionally impaired in many advanced cancers. In some cases, CD1d-restricted T-cell cancer defects can be traced to CD1d(+) tumor interactions, since hematopoietic, prostate, and some other tumors can express CD1d. Ligand and IL-12 can reverse iNKT defects and therapeutic opportunities exist in correcting such defects alone and in combination. Early stage clinical trials have shown potential for reconstitution of iNKT IFN-gamma responses and evidence of activity in a subset of patients, with rational new approaches to capitalize on this progress ongoing, as will be discussed here.

NKT cells, Treg, and their interactions in bone marrow transplantation

Bone marrow transplantation (BMT) is a potentially curative treatment for patients with leukemia and lymphoma. Tumor eradication is promoted by the anti-tumor activity of donor T cells contained in the transplant; however, donor T cells also mediate the serious side effect of graft-versus-host disease (GVHD). Separation of GVHD from graft anti-tumor activity is an important goal of research in improving transplant outcome. One approach is to take advantage of the immunomodulatory activity of regulatory NKT cells and CD4(+)CD25(+) Treg of host and/or donor origin. Both host and donor NKT cells and donor Treg are able to prevent GVHD in murine models. In this review, we summarize the mechanisms of NKT cell- and Treg-mediated protection against GVHD in mice while maintaining graft anti-tumor activity. In addition, we also examine the interactions between NKT cells and Treg in the context of BMT, and integrate the data from murine experimental models with the observations made in humans.

Regulatory T cells in transplantation: does extracellular adenosine triphosphate metabolism through CD39 play a crucial role?

Despite tremendous improvements in short-term renal allograft survival, many patients still have chronic rejection or side effects of nonspecific immunosuppression. The discovery of Foxp3(+) regulatory T cells (Tregs) has revolutionized the concepts in immunoregulation and offers perspectives for overcoming rejection. Recently, a subset of Foxp3(+)CD39(+) effector/memory-like Tregs (T(REM)) was identified. The role of CD39(+) Tregs in immunoregulation is supported by the occurrence of alopecia areata and experimental autoimmune encephalomyelitis in CD39-deficient mice and by the failure of CD39(-) Tregs to suppress contact hypersensitivity. In humans, CD39 polymorphisms have been associated with diabetes and nephropathy, and multiple sclerosis patients have reduced numbers of blood CD39(+) Tregs. Preliminary experiments in a murine transplantation model showed that CD39(+) Tregs can determine allograft outcome. CD39 degrades the extracellular adenosine triphosphate (ATP) released during tissue injury, which otherwise would trigger inflammation. Currently, our groups are assessing the role of CD39(+) Tregs and extracellular ATP metabolism in clinical transplantation and whether tolerogenic Treg profiles possess immunopredictive value, envisioning the development of clinical trials using CD39(+) Treg-based vaccination for autoimmunity or transplantation. This is a comprehensive review on the fundamentals of Treg biology, the potential role of ATP metabolism in immunoregulation, and the potential use of Treg-based immunotherapy in transplantation.

Host and donor immune responses contribute to antiviral effects of amotosalen-treated donor lymphocytes following early posttransplant cytomegalovirus infection

We have previously shown that amotosalen-treated splenocytes rescued allorecipients from a lethal dose of mouse CMV (MCMV) administered on day 0 in experimental parent C57BL/6-->CB6F1 allogeneic bone marrow transplant. In this study, we investigated the mechanism of antiviral activity of amotosalen-treated donor splenocytes when sublethal MCMV infections were administered 7 days posttransplant. Recipients of 3 x 10(6) untreated splenocytes were used as control. Following MCMV infection, recipients of untreated splenocytes had 40% early mortality due to acute graft-vs-host disease compared with no deaths among recipients of 10 x 10(6) treated splenocytes. However, recipients of both types of donor splenocytes effectively cleared MCMV from their liver. Like the untreated CD8(+) T cells, amotosalen-treated CD8(+) T cells equally retained their in vivo CTL activity against MCMV early peptide-pulsed targets and expressed similar levels of granzyme B within 11 days of infection. In contrast to full donor chimerism in recipients of untreated splenocytes, recipients of amotosalen-treated splenocytes showed mixed chimerism with both donor spleen- and host-derived anti-MCMV CD8(+) T cells in their blood and lymphoid organs, with significantly higher numbers of host-derived CD4(-)CD8(-) (double negative) T cells in the spleens of recipients of treated splenocytes compared with the recipients of untreated splenocytes. Additionally, recipients of amotosalen-treated splenocytes had lower levels of serum IFN-gamma and TNF-alpha in response to MCMV infection compared with untreated recipients. Thus, adoptive immunotherapy with treated T cells is a novel therapeutic approach that facilitates hematopoietic engraftment and permits antiviral immunity of both donor and host T cells without graft-vs-host disease.

Peripheral blood progenitor cell product contains Th1-biased noninvariant CD1d-reactive natural killer T cells: implications for posttransplant survival

OBJECTIVE

Bone marrow (BM) Th1 populations can contribute to graft-vs-leukemia responses. Granulocyte/granulocyte macrophage colony-stimulating factor (CSF)-mobilized peripheral blood progenitor cells (PBPC) have become widely accepted alternatives to BM transplantation. T cells coexpressing natural killer cell proteins (NKT) include a CD1d-reactive subset that influences immunity by rapidly producing large amounts of Th1 and/or Th2 cytokines dependent upon microenvironment and disease. There are two types of CD1d-reactive NKT. iNKT express a semi-invariant T-cell receptor-alpha. Other noninvariant CD1d-reactive NKT from BM and liver produce large amounts of interleukin-4 or interferon-gamma, respectively, and within the intestine can be biased in either direction. Recent data suggests that NKT might contribute to clinical benefits of PBPC.

MATERIALS AND METHODS

To address these issues, we phenotypically and functionally studied PBPC NKT.

RESULTS

Similarly to BM, NKT-like cells were common in allogeneic and autologous PBPC, there were relatively few classical iNKT, but high CD1d-reactivity concentrated in NKT fractions. Significantly, PBPC CD1d-reactive cells were relatively Th1-biased and their presence was associated with better prognosis. Granulocyte CSF treatment of BM to yield PBPC in vivo as well as in vitro Th2-polarizes conventional T cells and iNKT. However, granulocyte CSF treatment of BM in vitro produced Th1-biased NKT, providing a mechanism for opposite polarization of NKT from BM vs PBPC.

CONCLUSIONS

These results suggest distinct Th1 CD1d-reactive NKT cells could stimulate anti-tumor responses from those previously described, which can suppress graft-vs-host disease.

Immune tolerance: mechanisms and application in clinical transplantation

The achievement of immune tolerance, a state of specific unresponsiveness to the donor graft, has the potential to overcome the current major limitations to progress in organ transplantation, namely late graft loss, organ shortage and the toxicities of chronic nonspecific immumnosuppressive therapy. Advances in our understanding of immunological processes, mechanisms of rejection and tolerance have led to encouraging developments in animal models, which are just beginning to be translated into clinical pilot studies. These advances are reviewed here and the appropriate timing for clinical trials is discussed.

New differentiation pathway for double-negative regulatory T cells that regulates the magnitude of immune responses

Recent studies have demonstrated that in peripheral lymphoid tissues of normal mice and healthy humans, 1% to 5% of alphabeta T-cell receptor-positive (TCR(+)) T cells are CD4(-)CD8(-) (double-negative [DN]) T cells, capable of down-regulating immune responses. However, the origin and developmental pathway of DN T cells is still not clear. In this study, by monitoring CD4 expression during T-cell proliferation and differentiation, we identified a new differentiation pathway for the conversion of CD4(+) T cells to DN regulatory T cells. We showed that the converted DN T cells retained a stable phenotype after restimulation and that furthermore, the disappearance of cell-surface CD4 molecules on converted DN T cells was a result of CD4 gene silencing. The converted DN T cells were resistant to activation-induced cell death (AICD) and expressed a unique set of cell-surface markers and gene profiles. These cells were highly potent in suppressing alloimmune responses both in vitro and in vivo in an antigen-specific manner. Perforin was highly expressed by the converted DN regulatory T cells and played a role in DN T-cell-mediated suppression. Our findings thus identify a new differentiation pathway for DN regulatory T cells and uncover a new intrinsic homeostatic mechanism that regulates the magnitude of immune responses. This pathway provides a novel, cell-based, therapeutic approach for preventing allograft rejection.

Influence of transplanted dose of CD56+ cells on development of graft-versus-host disease in patients receiving G-CSF-mobilized peripheral blood progenitor cells from HLA-identical sibling donors

We investigated effects of variations in the cellular composition of G-CSF-mobilized peripheral blood progenitor cell (G-PBPC) allografts on clinical outcomes of allogeneic PBPC transplantation. We retrospectively analyzed transplanted doses of various immunocompetent cells from 27 HLA-identical sibling donors in relation to engraftment, incidence of graft-versus-host disease (GVHD), and survival. Significant variability was documented in both absolute numbers and relative proportions of CD34+, CD2+, CD3+, CD4(high)+, CD4+25+, CD8(high)+, CD19+, CD56+, and CD56+16+ cells contained in these allografts. Stepwise Cox regression analysis revealed that the CD56+ cell dose was significantly inversely correlated with the incidence of GVHD. Thus, there was a significantly higher incidence of grade II acute GVHD in patients receiving a lower CD56+16+ cell dose (hazard ratio (HR) 0.0090; 95% confidence interval (CI), <0.00001-3.38; P=0.031), a higher incidence of chronic GVHD in those receiving allografts with a lower CD56+16+ to CD34+ ratio (HR <0.00001; 95% CI <0.00001-0.0007; P=0.0035), and a higher incidence of extensive chronic GVHD in those receiving allografts with a lower CD56+ to CD34+ ratio (HR <0.00001; 95% CI <0.00001-0.053; P=0.0083). These results suggest that CD56+ cells in G-PBPC allografts from HLA-identical sibling donors may play an important role in preventing the development of GVHD.

A novel micro-cell-mediated lympholytic assay for the evaluation of regulatory cells in human alloreactive CTL responses

Since cell-mediated lympholysis (CML), the most commonly used in vitro experimental cytotoxic method for the evaluation of regulatory cells, requires large numbers of cells that are often the limiting factor, we have developed a new micro-cell-mediated lympholytic (m-CML) assay. Various numbers of responding cells were stimulated with equivalent numbers of allogeneic irradiated stimulator cells in the presence of (fivefold) serial dilutions of regulatory cells. On the 8th day, 4-h 51Cr-release assays were performed by adding 5000 labeled target cells from the corresponding stimulators to the cultures. Even though results that were comparable to the macro- (bulk) CML and MLR modulation experiments were obtained with all the cell combinations tested in the m-CML, the combinations with 50,000 responder cells and stimulating cells and dilutions of 25,000 to 40 modulator (regulatory) cells were found to be the most reproducible for assaying regulatory cell potency in vitro. Similarly, expression of the results as percentage inhibition using percent specific lysis values was the simplest method of calculation. This assay was standardized for the evaluation of the inhibitory activity of a variety of regulatory cells, including long-term cultures of cadaver-donor vertebral body bone marrow cells (vDBMC-L), in vitro generated CD8 positive and CD28 negative suppressor T cells and donor chimeric cells isolated from renal transplant recipients who had been perioperatively infused with donor bone marrow cells (DBMC). The results indicate that the m-CML assay is a sensitive and reliable micromethod with at least 10-fold fewer responders, stimulator and modulator cell numbers needed than macro-CML assays for the evaluation of regulatory cells obtained from a variety of immune systems in vitro.

NKT cell defects in NOD mice suggest therapeutic opportunities

Recent studies have reported that immunoregulatory NKT cells are defective in NOD mice and that treatment of mice with alpha-galactosylceramide that selectively stimulate NKT cells, is anti-diabetogenic. The objective of this study was to document the natural history of changes in NKT cells in various organs in NOD mice in the period up to the time of diabetes onset so that novel intervention therapies could be devised. We found that NKT cell-specific receptor (NKT-TCR) Valpha14Jalpha281 expressions by quantitative (RealTime) RT-PCR in thymus, spleen and liver of NOD male and female mice were low at 1-3 months of life compared to BALB/c and C57BL/6 mice, albeit a transient spike in levels occurred in female NOD livers at 2 months. Female pancreases showed low levels of these transcripts despite their active and destructive insulitis. In contrast, NOD males exhibited high expression of this invariant TCR in pancreas, where their insulitis was less destructive. A survey of NKT-TCR expressions in a battery of congenic, non-diabetes prone NOD strains indicated that this NKT phenotype was quite variable but higher than diabetes prone NOD. Bone marrow transplantation of NOD females from B6.NOD-H2(g7) donors raised their NKT-TCR expressions. Tuberculin administrations in the forms of BCG and CFA in a manner known to protect NOD mice from diabetes both raised NKT-TCR levels, as did the anti-inflammatory PPAR-gamma agonist rosiglitazone. These findings provide exciting therapeutic avenues to be explored in the treatment of human immune mediated type-1 diabetes where there are similar immunoregulatory lesions.

CD8(+), alphabeta-TCR(+), and gammadelta-TCR(+) cells in the recipient hematopoietic environment mediate resistance to engraftment of allogeneic donor bone marrow

Historically, conditioning for engraftment of hematopoietic stem cells has been nonspecific. In the present study, we characterized which cells in the recipient hematopoietic microenvironment prevent allogeneic marrow engraftment. Mice defective in production of alphabeta-TCR(+), gammadelta-TCR(+), alphabeta- plus gammadelta-TCR(+), CD8(+), or CD4(+) cells were transplanted with MHC-disparate allogeneic bone marrow. Conditioning with 500 cGy total body irradiation (TBI) plus a single dose of cyclophosphamide (CyP) on day +2 establishes chimerism in normal recipients. When mice were conditioned with 300 cGy TBI plus a single dose of CyP on day +2, all engrafted, except wild-type controls and those defective in production of CD4(+) T cells. Mice lacking both alphabeta- and gammadelta-TCR(+) cells engrafted without conditioning, suggesting that both alphabeta- and gammadelta-TCR T cells in the host play critical and nonredundant roles in preventing engraftment of allogeneic bone marrow. CD8 knockout (KO) mice engrafted without TBI, but only if they received CyP on day +2 relative to the marrow infusion, showing that a CD8(-) cell was targeted by the CyP conditioning. The CD8(+) cell effector function is mechanistically different from that for conventional T cells, and independent of CD4(+) T helper cells because CD4 KO mice require substantially higher levels of conditioning than the other KO phenotypes. These results suggest that a number of cell populations with different mechanisms of action mediate resistance to engraftment of allogeneic marrow. Targeting of specific recipient cellular populations may permit conditioning approaches to allow mixed chimerism with minimal morbidity and could potentially avoid the requirement for myelotoxic agents altogether.

Tolerance, mixed chimerism and protection against graft-versus-host disease after total lymphoid irradiation

Total lymphoid irradiation (TLI), originally developed as a non-myeloablative treatment for Hodgkin's disease, has been adapted for the induction of immune tolerance to organ allografts in rodents, dogs and non-human primates. Moreover, pretransplantation TLI has been used in prospective studies to demonstrate the feasibility of the induction of tolerance to cadaveric kidney allografts in humans. Two types of tolerance, chimeric and non-chimeric, develop after TLI treatment of hosts depending on whether donor bone marrow cells are transplanted along with the organ allograft. An advantageous feature of TLI for combined marrow and organ transplantation is the protection against graft-versus-host disease (GVHD) and facilitation of chimerism afforded by the predominance of CD4+ NK1.1(+) -like T cells in the irradiated host lymphoid tissues. Recently, a completely post-transplantation TLI regimen has been developed resulting in stable mixed chimerism and tolerance that is enhanced by a brief course of cyclosporine. The post-transplantation protocol is suitable for clinical cadaveric kidney transplantation. This review summarizes the evolution of TLI protocols for eventual application to human clinical transplantation and discusses the mechanisms involved in the induction of mixed chimerism and protection from GVHD.

Predominance of NK1.1+TCR alpha beta+ or DX5+TCR alpha beta+ T cells in mice conditioned with fractionated lymphoid irradiation protects against graft-versus-host disease: "natural suppressor" cells

We developed a nonmyeloablative host conditioning regimen in a mouse model of MHC-mismatched bone marrow transplantation that not only reduces radiation toxicity, but also protects against graft-vs-host disease. The regimen of fractionated irradiation directed to the lymphoid tissues and depletive anti-T cell Abs results in a marked change in the residual host T cells, such that NK1.1+ or DX5+asialo-GM1+ T cells become the predominant T cell subset in the lymphoid tissues of C57BL/6 and BALB/c mice, respectively. The latter "natural suppressor" T cells protect hosts from graft-vs-host disease after the infusion of allogeneic bone marrow and peripheral blood cells that ordinarily kill hosts conditioned with sublethal or lethal total body irradiation. Protected hosts become stable mixed chimeras, but fail to show the early expansion and infiltration of donor T cells in the gut, liver, and blood associated with host tissue injury. Cytokine secretion and adoptive transfer studies using wild-type and IL-4(-/-) mice showed that protection afforded by NK1.1+ and DX5+asialo-GM1+ T cells derived from either donors or hosts conditioned with lymphoid irradiation is dependent on their secretion of high levels of IL-4.

Donor bone marrow-derived chimeric cells present in renal transplant recipients infused with donor marrow. I. Potent regulators of recipient antidonor immune responses

BACKGROUND

Even though a number of transplant centers have adopted donor-specific bone marrow cell (DBMC) infusions to enhance donor cell chimerism, to date there has been no direct evidence linking chimerism with tolerance induction in human organ transplant recipients.

METHODS

Cells of donor phenotype were isolated 1 year postoperatively from the peripheral blood lymphocytes and iliac crest bone marrow of 11 living-related-donor (LRD) renal transplant recipients, who had received perioperative donor bone marrow cell infusions. These recipient-derived donor (RdD) cells were characterized phenotypically by flow cytometric analysis and functionally as modulators in mixed lymphocyte reaction (MLR) and cell-mediated lympholysis (CML) assays.

RESULTS

The yield of RdD cells ranged from 0.1 to O.9% of the starting material with the majority being TcRalphabeta, CD3 positive T cells, a substantial percentage of which coexpressed CD28. At 1 year posttransplant almost 50% of the LRD-kidney/DBMC recipients tested so far exhibited donor-specific unresponsiveness in MLR (7/17) and CML (6/13) reactions and this trend was further enhanced at 23 years. In the recipients with residual positive antidonor immune responses, the RdD cells inhibited recipient antidonor MLR and CML responses significantly more strongly than freshly isolated and similarly treated iliac crest bone marrow cells from the donor. RdD cells also inhibited the MLR of the recipient to third party allogeneic stimulator cells; however, this nonspecific effect was significantly weaker than specific inhibition. We also established long-term bone marrow cultures stimulated every 2 weeks with irradiated alogeneic feeder cells, that had similar functional properties thus possibly providing us with an in vitro correlate the RdD cells.

CONCLUSIONS

These results clearly support the notion that the infused donor cells play a positive role in the induction and/or maintenance of transplant tolerance.

Involvement of multiple subpopulations of human bone marrow cells in the regulation of allogeneic cellular immune responses

BACKGROUND

The identity of the cells in the human bone marrow that function as effective regulators of in vitro and possibly in vivo cellular immune responses is not well established.

METHODS

Cell subpopulations were isolated from cadaver donor vertebral-body bone marrow cells (DBMC) by using immuno-magnetic microbeads and were tested as inhibitors (modulators) in cell-mediated lympholysis (CML) and mixed lymphocyte reaction (MLR) responses of normal peripheral blood lymphocytes stimulated with irradiated cadaver donor spleen cells.

RESULTS

Compared with spleen cells as controls, un-irradiated T-cell depleted DBMC inhibited both the MLR and CML responses of allogeneic responder cells in a dose dependent manner (as in our previous reports). The inhibition was also mediated by a number of purified subpopulations including pluripotent CD34+ stem cells, and their CD34 negative early progeny of both lymphoid and myeloid lineages. These included DBMC enriched for non-T-cell lymphoid precursors (NT-LP/DBMC; i.e., DBMC depleted of CD3, CD15, and glycophorin-A positive cells) and DBMC positively selected for CD38+, CD2+, CD5+, and CD1+ lymphoid cells (all were depleted of CD3+ cells) as well as CD33+ (but CD15 negative) myeloid precursors. However, positively selected CD19+ B-cells and CD15+ myeloid cells did not inhibit the MLR and CML responses. The NT-LP/DBMC that had been repeatedly stimulated with irradiated allogeneic peripheral blood lymphocytes caused the strongest inhibition of the MLR and CML responses of the same allogeneic cells with 200 times fewer modulator cells needed than uncultured DBMC (P<0.001). Flow cytometric analysis revealed that majority of cells in these cell lines had become CD3+ TcR-alphabeta+ CD4+ and CD28+ cells.

CONCLUSION

A variety of less differentiated cells of various lineages residing in the human bone marrow are immunoregulatory in vitro. Among them, there is at least one subset that can undergo differentiation in vitro into regulatory T cells that can be maintained in long-term cultures.

Identification of a previously unknown antigen-specific regulatory T cell and its mechanism of suppression

Despite increasing evidence for the existence of antigen-specific regulatory T cells, the mechanisms underlying suppression remain unclear. In this study we have identified and cloned a novel subset of antigen-specific regulatory T cells and demonstrated that these T cells possess a unique combination of cell surface markers and array of cytokines. The regulatory T cells are able to inhibit the function of T cells carrying the same T-cell receptor specificity and prevent skin allograft rejection in an antigen-specific, dose-dependent manner. The regulatory T cells are able to acquire alloantigen from antigen-presenting cells, present the alloantigen to activated syngeneic CD8+ T cells and then send death signals to CD8+ T cells. These findings provide a novel mechanism of regulatory T-cell-mediated, antigen-specific suppression.

Natural killer 1.1(+) T cells and "natural suppressor" T cells in the bone marrow

Unusual cells in the bone marrow of mice and/or humans suppress immune responses and inhibit the mixed leukocyte reaction, graft-versus-host disease, and systemic autoimmunity. Previous studies showed that these "natural suppressor" T cells expressed the CD4(-)CD8(-) T-cell receptor-alphabeta(+) phenotype. More recent studies demonstrate that the latter cells express the natural killer 1.1 (NK1.1) marker and are members of the NK1.1(+) T-cell family that secrete high levels of IFN-gamma and IL-4 after initial activation. The suppressive activity of the bone marrow NK1.1(+) T cells is dependent on their rapid secretion of high levels of IL-4. This unique cytokine secretion is not observed in conventional NK1. 1(-) T cells and can downregulate the function of the latter cells.

Role of Immunoregulatory Donor T Cells in Suppression of Graft-Versus-Host Disease Following Donor Leukocyte Infusion Therapy

In murine models of allogeneic bone marrow transplantation (BMT), MHC-mismatched recipients given a delayed infusion of donor leukocytes (DLI) at 21 days posttransplant develop significant GVHD whereas MHC-matched recipients do not. The current study was initially designed to test the hypothesis that small numbers of T cells in the MHC-mismatched donor bone marrow (BM) graft exacerbated graft-vs-host disease (GVHD) when DLI was administered at 21 days after BMT. Ex vivo depletion of Thy1+ cells from the donor BM had no impact on the severity of GVHD after DLI. However, depletion of donor T cells in vivo with a Thy1 allele-specific mAb given after BMT resulted in significantly more severe GVHD after DLI. Similar results were obtained in a MHC-matched model of allogeneic BMT, indicating that this was a general phenomenon and not model dependent. These results indicated that a population of donor-derived Thy1+ cells suppressed graft-vs-host reactivity after DLI. Results of experiments with thymectomized recipients demonstrated that an intact thymus was required for generation of the immunoregulatory donor cells. Experiments using TCR β-chain knockout mice as BM donors indicated that the immunosuppressive Thy1+ cells coexpressed αβTCR heterodimers. Similar experiments with CD4 and CD8 knockout donor BM suggested that the immunoregulatory Thy1+αβTCR+ cells consisted of two subpopulations: a CD4+CD8− subpopulation and a CD4−CD8− subpopulation. Together, these results show that thymus-derived, Thy1+αβTCR+ donor cells generated early after allogeneic BMT suppress the graft-vs-host reactivity of T cells given as DLI. These cells may mediate dominant peripheral tolerance after allogeneic BMT.

Bone marrow NK1.1(-) and NK1.1(+) T cells reciprocally regulate acute graft versus host disease

Sorted CD4(+) and CD8(+) T cells from the peripheral blood or bone marrow of donor C57BL/6 (H-2(b)) mice were tested for their capacity to induce graft-versus-host disease (GVHD) by injecting the cells, along with stringently T cell-depleted donor marrow cells, into lethally irradiated BALB/c (H-2(d)) host mice. The peripheral blood T cells were at least 30 times more potent than the marrow T cells in inducing lethal GVHD. As NK1.1(+) T cells represented <1% of all T cells in the blood and approximately 30% of T cells in the marrow, the capacity of sorted marrow NK1.1(-) CD4(+) and CD8(+) T cells to induce GVHD was tested. The latter cells had markedly increased potency, and adding back marrow NK1.1(+) T cells suppressed GVHD. The marrow NK1.1(+) T cells secreted high levels of both interferon gamma (IFN-gamma) and interleukin 4 (IL-4), and the NK1.1(-) T cells secreted high levels of IFN-gamma with little IL-4. Marrow NK1.1(+) T cells obtained from IL-4(-/-) rather than wild-type C57BL/6 donors not only failed to prevent GVHD but actually increased its severity. Together, these results demonstrate that GVHD is reciprocally regulated by the NK1.1(-) and NK1.1(+) T cell subsets via their differential production of cytokines.

Sca1(+)/Mac1(+) nitric oxide-producing cells in the spleens of recipients early following bone marrow transplant suppress T cell responses in vitro

Spleen cells collected from allogeneic chimeras early after bone marrow transplantation (BMT) consistently showed suppressed proliferative responses to interleukin-2 in vitro and failed to proliferate in mixed lymphocyte reaction (MLR) assays. However, isolation of Thy 1.2(+) T cells from the heterogeneous spleen cell suspension prior to culture resulted in heightened proliferation, suggesting the presence of cells capable of suppressing T cell responses in vitro. When separated into subpopulations by negative and positive selection with specific monoclonal antibodies, a non-T, non-B population with immunosuppressive properties was identified. The suppressive cells were found in the spleens of both allogeneic and syngeneic chimeras, but not normal donor mice. Suppressor activity was transient and typically declined by 3 weeks post-BMT. The cells suppressed the response of alloactivated T cells isolated from BMT chimeras as well as naive donor T cells in MLR assays in a dose-dependent manner. To explore the mechanism(s) involved in the suppression, the effects of interferon-gamma (IFN-gamma)-specific mAb and the nitric oxide (NO) synthase inhibitor NG-methyl-l-arginine were examined. The results support a role for both IFN-gamma and NO in the suppressive activity. Separation of cells based on Mac-1 expression indicated that there were both Mac-1-enriched and Mac-1-depleted cells capable of producing NO, but that the Mac-1-depleted cells were the most potent suppressors in MLR assays. The Mac-1-depleted cells still contained a residual population of Mac-1(dim) cells which showed increased levels of Mac-1 expression after overnight culture. Intracellular staining with an inducible nitric oxide synthase (iNOS)-specific mAb indicated that the NO-producing cells expressed the cell surface markers Mac-1 and Sca-1. When iNOS knockout transgenic mice were used as transplant donors, in vitro suppression of T cell responses was reduced but not eliminated, suggesting that other mechanism(s) could contribute to the suppression. Collectively, these results demonstrate that Sca-1(+)/Mac-1(+) cells capable of producing NO are present in the spleens of recipients early after BMT and suggest that these cells may have immunoregulatory roles in vivo.

Granulocyte Colony-Stimulating Factor Reduces the Capacity of Blood Mononuclear Cells to Induce Graft-Versus-Host Disease: Impact on Blood Progenitor Cell Transplantation

The feasibility of transplanting peripheral blood mononuclear cells (PBMC) from granulocyte colony-stimulating factor (G-CSF)–treated normal human donors to myeloablated allogeneic hosts has been demonstrated recently. The current work examined the ability of recombinant G-CSF to alter peripheral blood T-cell function and graft-versus-host disease (GVHD) in a murine model of allogeneic G-CSF–mobilized PBMC transplantation. Administration of recombinant G-CSF to C57BL/Ka mice markedly increased the capacity of PBMC to reconstitute lethally irradiated syngeneic hosts. T- and B-lineage lymphocytes were depleted about 10-fold in the bone marrow of the treated mice, and the T-cell yield in the blood was increased about fourfold. The ability of PBMC or purified CD4+ and CD8+ T cells to induce acute lethal GVHD in irradiated BALB/c mice was reduced after the administration of G-CSF. This was associated with decreased secretion of interferonγ and interleukin-2 (IL-2) and an increased secretion of IL-4. The donor cell inoculum, which was most successful in the rescue of irradiated allogeneic hosts, was the low-density fraction of PBMC from G-CSF–treated mice. These low-density cells were enriched for CD4−CD8−NK1.1+ T cells and secreted about 10-fold more IL-4 than the unfractionated cells from the G-CSF–treated donors.

Granulocyte Colony-Stimulating Factor Reduces the Capacity of Blood Mononuclear Cells to Induce Graft-Versus-Host Disease: Impact on Blood Progenitor Cell Transplantation

The feasibility of transplanting peripheral blood mononuclear cells (PBMC) from granulocyte colony-stimulating factor (G-CSF)–treated normal human donors to myeloablated allogeneic hosts has been demonstrated recently. The current work examined the ability of recombinant G-CSF to alter peripheral blood T-cell function and graft-versus-host disease (GVHD) in a murine model of allogeneic G-CSF–mobilized PBMC transplantation. Administration of recombinant G-CSF to C57BL/Ka mice markedly increased the capacity of PBMC to reconstitute lethally irradiated syngeneic hosts. T- and B-lineage lymphocytes were depleted about 10-fold in the bone marrow of the treated mice, and the T-cell yield in the blood was increased about fourfold. The ability of PBMC or purified CD4+ and CD8+ T cells to induce acute lethal GVHD in irradiated BALB/c mice was reduced after the administration of G-CSF. This was associated with decreased secretion of interferonγ and interleukin-2 (IL-2) and an increased secretion of IL-4. The donor cell inoculum, which was most successful in the rescue of irradiated allogeneic hosts, was the low-density fraction of PBMC from G-CSF–treated mice. These low-density cells were enriched for CD4−CD8−NK1.1+ T cells and secreted about 10-fold more IL-4 than the unfractionated cells from the G-CSF–treated donors.

Natural killer cells weakly resist engraftment of allogeneic, long-term, multilineage-repopulating hematopoietic stem cells

Natural killer (NK) cells effect hybrid resistance, in which parental hematopoietic cell grafts are rejected by F1 recipients. NK cells can also resist engraftment of fully MHC-mismatched allogeneic marrow. However, studies of NK cell-mediated alloresistance have relied on short-term proliferation, colony, or survival assays; therefore, their results may not reflect effects of NK cells on the engraftment of allogeneic pluripotent hematopoietic stem cells (PHSC). We have now addressed the role of NK cells in resisting engraftment of these most primitive hematopoietic cells, which provide long-term repopulation of multiple hematopoietic lineages. We took advantage of a nonmyeloablative conditioning regimen that permits allogeneic marrow engraftment and induction of mixed chimerism in mice to evaluate the effect of host NK cell depletion with mAb PK136 on long-term competitive repopulating ability of allogeneic marrow. Mice were pretreated with depleting anti-CD4 and anti-CD8 mAbs, then received 3 Gy of whole body irradiation and 7 Gy of thymic irradiation prior to allogeneic bone marrow transplantation. Depending on the strain combination used, statistically significant increases in long-term allogeneic repopulation of both myeloid and lymphoid cell lineages were observed in recipients depleted of NK cells before bone marrow transplantation compared with controls. Depletion of host NK cells alone was sufficient to enhance donor PHSC engraftment. However, a statistically significant increase in allogeneic reconstitution in NK cell-depleted chimeras compared with control chimeras was not observed in every experiment, and differences were most readily apparent in a strain combination in which recipient NK cells have been shown to have high resistance to engraftment of donor short-term repopulating cells. Chronic (16 weeks) anti-NK1.1 treatment resulted in higher levels of donor-type repopulation than that in animals receiving only pretransplant NK cell depletion. Our studies demonstrate for the first time that host NK cells resist engraftment of allogeneic long-term repopulating PHSC, and provide a model for studying the elements that determine what is regarded as "self" and "non-self" by newly developing NK cells.

Similar rates of production of T and B lymphocytes in the bone marrow

The rate of renewal of T lymphocytes in the bone marrow of euthymic C57BL/Ka and athymic nu/nu BALB/c mice was estimated by in vivo labeling with bromodeoxyuridine. T lymphocytes accounted for 16-18% of marrow cells in euthymic mice as judged by immunofluorescent staining with monoclonal antibodies for Thy-1, CD3, and alpha/beta T cell antigen receptor markers. About 70% of marrow cells expressed receptors (Mac-1, Gr-1, B220) for myeloid, macrophage, and B lineage cells. Approximately 13% of cells in the athymic bone marrow expressed alpha/beta T cell receptors. Sorted marrow T cells proliferated in response to stimulation with anti-alpha/beta antibodies in vitro and showed functional rearrangements of V beta and J beta genes. Sorted non-T cells did not respond to stimulation in vitro, and all V beta and J beta gene rearrangements identified were nonfunctional. In vivo labeling studies indicated that approximately 17 x 10(6) bone marrow T cells are renewed daily in euthymic mice and approximately 14 x 10(6) are renewed in athymic mice. Approximately 11 x 10(6) mature B cells (immunoglobulin M+) are renewed daily in the bone marrow of the latter mice. To determine whether marrow precursors can give rise to T cells directly, marrow cells from euthymic and athymic mice were depleted of T cells by cell sorting and incubated in vitro for 48 h in the absence of exogenous growth factors or thymic stromal cells. Examination of the cells after culture showed that 10-12% stained brightly for alpha/beta T cell receptors. Although functional rearrangements of V beta and J beta genes were not detected before culture, the majority of rearrangements were functional after culture. The emergence of the bright alpha/beta T cells in culture was dependent on depletion T cells from the marrow cells before culture. The results suggest that most marrow T cells are generated in the marrow itself.

Mac1 discriminates unusual CD4-CD8- double-negative T cells bearing alpha beta antigen receptor from conventional ones with either CD4 or CD8 in murine lung

Pulmonary intraparenchymal leukocytes were purified from normal mice. By flow cytometry, 20-30% of the lymphocytes were positive for the expression of Mac1, a cell-surface antigen largely restricted to macrophages, neutrophils and natural killer (NK) cells. Sorted Mac1+ lung lymphocytes were large and had abundant cytoplasm with few azurophilic granules. Because Mac1+ lymphocytes did not contain any asiallo GM1+ cells, they are not likely to be NK cells. By a two-color flow cytometric analysis, Mac1+ lymphocytes were demonstrated to be TCR-alpha beta intermediate+, TCR-gamma delta-, CD3intermediate+, CD4-, CD8-, Thy1-, CD5-, and B220-. These Mac1+ alpha beta T cells were not found in other organs such as spleen, thymus, liver, bone marrow and intestine of mice uninfected and infected with Mycobacterium bovis BCG. There was a considerable population of this unusual subset of alpha beta T cells in the lungs of congenitally athymic nude mice. In the Mac1+ alpha beta T-cell population, the proportions of V beta 8+ T cells and of forbidden T-cell clones expressing V beta 6 TCR were not much different from that in the conventional T-cell population. These results indicated that extrathymically developed alpha beta T cells reside in considerable proportions in the lung and that Mac1 clearly discriminates these cells from conventional ones. Interestingly, the proportion of these cells increased in the lungs of mice infected with M. bovis BCG, which raises a possibility that these cells may play some role in the host defense against mycobacterial infection.

Novel approaches to the control of graft versus host disease

Graft versus host disease (GVHD) remains the major obstacle to the application of bone marrow transplantation across HLA barriers. Recent advances in our understanding of GVHD pathophysiology have resulted in the evaluation in animal models and in clinical trials of some novel approaches to avoiding and treating GVHD. Continued advances in our knowledge are likely to result in the clinical application of biological therapies to maximize graft versus leukemia effects and alloengraftment, while avoiding GVHD.

Effect of the YCD3-1 anti-mouse monoclonal on murine GvHD

The potential for applying the YCD3-1 rat-anti-mouse IgG2b anti-CD3-epsilon monoclonal antibody (MAB) to the study of graft-versus-host disease (GvHD) in mouse models has been examined. This MAB, unlike the previously developed hamster-anti-mouse-CD3 MABs, had been reported to exhibit strong cytolytic properties when applied in vitro in the presence of complement. Therefore, it was of interest to determine whether it could be effectively used for T-cell depletion in mice to suppress GvHD in the same manner as the anti-human-CD3 MABs have been applied in clinical transplantation. Evaluation of the effectiveness of this antibody was carried out both under fully allogeneic MHC-mismatched and under unrelated-donor MHC-matched marrow transplant conditions. For both types of transplantation, depletion of the donor cells with YCD3-1 plus complement prior to their injection into lethally irradiated recipients significantly suppressed GvHD, resulting in survivals of 75-79%, as compared to 8-13% in the controls that received undepleted cells from the same donors (p < 0.0001). These results suggest that the YCD3-1 MAB may have a potential for use as a negative selection agent in the further definition of the roles of the various T-cell subtypes, as well as the possible roles of natural-killer cells, in future studies into the mechanisms of GvHD, and of the graft-versus-leukemia effect.