The potential role of NK cells in the separation of graft-versus-tumor effects from graft-versus-host disease after allogeneic bone marrow transplantation

The potential of cytotherapeutics in hematologic reconstitution and in the treatment and prophylaxis of graft-versus-host disease. Chapter II: emerging transformational cytotherapies

Hematopoietic stem cell transplantation (HSCT) is a life-saving treatment for inherited anemias, immunodeficiencies or hematologic malignancies. A major complication of allo-HSCT associated with high transplant-related mortality rates is graft-versus-host disease (GvHD). Current and future clinical benefits in HSCT enabled by advances in hematopoietic stem cells, mesenchymal stem cells, Tregs and natural killer cells technologies are reviewed here and discussed. Among these evolutions, based on the need for mesenchymal stem cells to be recruited by an inflammatory environment, the development and use of novel GvHD biomarkers could be explored further to deliver the right pharmaceutical to the right patient at the right time. The successful commercialization of cytotherapeutics to efficiently manage GvHD will create a virtuous ‘halo’ effect for regenerative medicine.

Double negative Treg cells promote nonmyeloablative bone marrow chimerism by inducing T-cell clonal deletion and suppressing NK cell function

The establishment of immune tolerance and prevention of chronic rejection remain major goals in clinical transplantation. In bone marrow (BM) transplantation, T cells and NK cells play important roles for graft rejection. In addition, graft-versus-host-disease (GVHD) remains a major obstacle for BM transplantation. In this study, we aimed to establish mixed chimerism in an irradiation-free condition. Our data indicate that adoptive transfer of donor-derived T-cell receptor (TCR) αβ(+) CD3(+) CD4(-) CD8(-) NK1.1(-) (double negative, DN) Treg cells prior to C57BL/6 to BALB/c BM transplantation, in combination with cyclophosphamide, induced a stable-mixed chimerism and acceptance of C57BL/6 skin allografts but rejection of third-party C3H (H-2k) skin grafts. Adoptive transfer of CD4(+) and CD8(+) T cells, but not DN Treg cells, induced GVHD in this regimen. The recipient T-cell alloreactive responsiveness was reduced in the DN Treg cell-treated group and clonal deletions of TCRVβ2, 7, 8.1/2, and 8.3 were observed in both CD4(+) and CD8(+) T cells. Furthermore, DN Treg-cell treatment suppressed NK cell-mediated BM rejection in a perforin-dependent manner. Taken together, our results suggest that adoptive transfer of DN Treg cells can control both adoptive and innate immunities and promote stable-mixed chimerism and donor-specific tolerance in the irradiation-free regimen.

The kinetics of mRNA transforming growth factor beta1 expression and its serum concentration in graft-versus-host disease after allogeneic hemopoietic stem cell transplantation for myeloid leukemias

Background

Graft-versus-host disease (GVHD) is still a major complication following allogeneic hematopoietic stem cell transplantation (alloHSCT). Recent data indicates that transforming growth factor beta1 (TGF-β1) may play a role in development of GVH reaction.

Material/Methods

Forty patients with acute myeloid leukemia (AML) and chronic myeloid leukemia (CML) were included. Quantitative real time polymerase chain reaction (RT-qPCR) was performed to assess the expression of mRNA TGF-β1. TGF-β1 serum concentration was assessed using a commercial ELISA.

Results

In all patients, a prompt decrease in TGF-β1 mRNA expression and its serum concentration was demonstrated after conditioning. In patients with acute GVHD, TGF-β1 mRNA expression and its serum concentration remained low until day +30 after transplant as compared to the day of transplant (p<0.03 and p<0.006, respectively). TGF-β1 mRNA expression and its serum concentration significantly increased on day +100 in patients who developed chronic GVHD as compared to the day of transplant (p<0.0009 and p<0.02, respectively).

Conclusions

TGF-β1 seems to be an additional regulator of donor engraftment; its low levels probably being one of the factors contributing to the development of acute GVHD. On the other hand, chronic GVHD symptoms seem to correlate with high TGF-β1 mRNA expression and its serum concentration in patients who underwent bone marrow transplantation for myeloid leukemias. Nevertheless, further studies with greater numbers of patients are needed to establish the role of TGF-β1 in graft-versus-host disease pathophysiology.

Phase I study of recombinant human interleukin-7 administration in subjects with refractory malignancy

PURPOSE

Interleukin-7 (IL-7) has critical and nonredundant roles in T-cell development, hematopoiesis, and postdevelopmental immune functions as a prototypic homeostatic cytokine. Based on a large body of preclinical evidence, it may have multiple therapeutic applications in immunodeficiency states, either physiologic (immunosenescence), pathologic (HIV), or iatrogenic (postchemotherapy and posthematopoietic stem cell transplant), and may have roles in immune reconstitution or enhancement of immunotherapy. We report here on the toxicity and biological activity of recombinant human IL-7 (rhIL-7) in humans.

DESIGN

Subjects with incurable malignancy received rhIL-7 subcutaneously every other day for 2 weeks in a phase I interpatient dose escalation study (3, 10, 30, and 60 microg/kg/dose). The objectives were safety and dose-limiting toxicity determination, identification of a range of biologically active doses, and characterization of biological and, possibly, antitumor effects.

RESULTS

Mild to moderate constitutional symptoms, reversible spleen and lymph node enlargement, and marked increase in peripheral CD3(+), CD4(+), and CD8(+) lymphocytes were seen in a dose-dependent and age-independent manner in all subjects receiving >or=10 microg/kg/dose, resulting in a rejuvenated circulating T-cell profile, resembling that seen earlier in life. In some subjects, rhIL-7 induced in the bone marrow a marked, transient polyclonal proliferation of pre-B cells showing a spectrum of maturation as well as an increase in circulating transitional B cells.

CONCLUSION

This study shows the potent biological activity of rhIL-7 in humans over a well-tolerated dose range and allows further exploration of its possible therapeutic applications.

Effects of activating NK cell receptor expression and NK cell reconstitution on the outcomes of unrelated donor hematopoietic cell transplantation for hematologic malignancies

Inhibitory NK cell receptors are recognized as important determinants of NK cell activity in hematopoietic cell transplantation (HCT). The role of activating receptors and their acquisition after HCT is less certain. Therefore, we comprehensively evaluated both inhibitory and activating receptors in 59 patients receiving unrelated donor HCT. NK cell numbers normalized quickly relative to B and T cells; however, the expression of both inhibitory and activating isoforms of killer immunoglobulin-like receptors (KIRs) was delayed. Most NK cells expressed an immature phenotype during the first 6 months post-HCT; however, we found high expression of activating NKp46 and NKp44 natural cytotoxicity receptors (NCRs), and cytotoxicity was preserved. Early reconstituting NK cells from unmanipulated grafts showed lower cytotoxicity than those from T-cell-depleted grafts. Differences in NK cell reconstitution had significant effects on clinical outcomes. Patients whose NK cells reconstituted earlier had better survival and lower relapse rates. The best survival group was recipients who possessed HLA-C2 but their donor lacked the cognate-activating KIR2DS1. Collectively, our data underscore the clinical relevance of reconstituting NK cells and their activating KIRs and NCRs. In addition to NK cell quantification and genotyping, comprehensive assessment of NK cell functions and phenotypes, including activating receptors, is essential.

Immunotherapy of AML

The applications of chemotherapy for the treatment of AML have been unchanged over the past three decades, with only 30% of patients demonstrating disease-free survival (DFS) [118]. Despite achieving CR following induction chemotherapy, the majority of patients relapse and succumb to their disease [6]. In view of the limitations encountered by cytarabine/anthracycline based regimes, attention has shifted to immunotherapy as a means to treat AML and provide significant long-term DFS. This chapter will discuss the role of the immune system and recent advances in immunotherapy for the treatment of AML, focusing on cellular and non-cellular approaches.

Interleukin-7 Immunotherapy

IL-7 is a member of the common gamma-chain family of cytokines sharing a common gamma-chain in their receptor. Beyond its long-established pivotal role in immune development, it has been more recently recognized as a critically important regulator of peripheral naïve and memory T cell homeostasis while its role in postdevelopment thymic function remains at best, poorly defined, and controversial. Its multiple immune-enhancing properties, most notably in the maintenance of T cell homeostasis, make it a very attractive candidate for immunotherapy in a wide variety of clinical situations. Following many years of rich preclinical data in murine and simian models, IL-7 is now emerging in human phase I trials as a very promising immunotherapeutic agent. Human in vivo data discussed here are derived from the phase I study initiated at the National Cancer Institute in collaboration with Cytheris, Inc., in a cohort of subjects with incurable malignancy.

Impact of early NK cell recovery on development of GvHD and CMV reactivation in dose-reduced regimen prior to allogeneic PBSCT

Dose-reduced allogeneic peripheral blood stem cell transplantation (PBSCT) is a therapeutic approach for patients with haematological malignancies who are not eligible for conventional allogeneic PBSCT. We analysed early development of lymphocyte subpopulations and the occurrence of cytomegalovirus (CMV) reactivation and acute graft-versus-host reaction (GvHD) in patients undergoing the protocol according to Slavin vs conventionally treated patients. Lymphocyte status prior to conditioning and at day +30 after allogeneic PBSCT was determined in 24 out of 51 patients who received conventional allogeneic PBSCT (eg cyclophosphamide plus total body irradiation) and compared with 27 patients being treated according to the Slavin protocol (fludarabine, busulphan and ATG). There is a significant delay in CD4 (T helper) cell development and consecutive lower CD4/CD8 ratios and a better reconstitution of CD8 (T cytotoxic) and NK (natural killer) cells after the Slavin protocol. Patients undergoing this protocol and no, or only grade I, acute GvHD show an even better NK cell reconstitution compared to patients with grade II-IV GvHD. A low CD4/CD8 ratio represents a CMV risk factor only in conventionally treated patients with grade 0-I GvHD, while after preparative regimen according to the Slavin protocol, the NK/CD8 ratio might be a marker for the prediction of CMV reactivation in addition to CMV risk status.

Adoptive transfer of small numbers of DX5+ cells alleviates graft-versus-host disease in a murine model of semiallogeneic bone marrow transplantation: a potential role for NKT lymphocytes

Natural killer T (NKT) lymphocyte cells are a subset of regulatory lymphocytes with important immunemodulatory effects. Our aim was to evaluate the effect of transplantation of NKT lymphocytes on graft versus host disease (GVHD) in a murine model of semiallogeneic BMT. GVHD was generated by infusion of 2 x 107 splenocytes from C57BL/6 donor mice into irradiated (C57BL/6 x Balb/c)F1 recipient mice. Adoptive transfer of increasing numbers of DX5+ cells was performed. Recipient mice were followed for histological parameters of GVHD-associated liver, bowel, and cutaneous injury. Intrahepatic and intrasplenic lymphocytes were isolated and analyzed by FACS for CD4+ and CD8+ subpopulations. It was seen that adoptive transfer of 4.5 x 106 DX5+ cells significantly alleviated GVHD-related hepatic, bowel, and cutaneous injury, and improved survival (85% survival on day 28). In contrast, depletion of DX5+ cells led to severe GVHD-associated multiorgan injury and 100% mortality. A direct correlation with the number of transplanted DX5+ cells was noted (maximal effect with transplantation of 4.5 x 106 DX5+ cells). Tolerance induction was associated with an increased peripheral CD4/CD8 ratio, intrahepatic trapping of CD8 lymphocytes and a shift towards a Th2-type cytokine profile, manifested by decreased IL-12/IL10, IL-12/IL-4, IFNgamma/IL-10, and IFNgamma/IL-4 ratios. Transplantation of DX5+ cells holds promise as a novel therapeutic measure for GVHD.

NK-KIR Transcript Kinetics Correlate With Acute Graft-Versus-Host Disease Occurrence After Allogeneic Bone Marrow Transplantation

Natural killer (NK) cell alloreactivity observed during stem cell transplantation (SCT) can be either beneficial (graft-versus-leukemia effect) or detrimental to the host (graft-versus-host disease). Killer immunoglobulin-like receptors (KIRs), expressed on NK and CD8 memory T cells, are regulated at a posttranscriptional level and, because there are currently no KIR-specific antibodies available, the analysis of these receptors remains elusive. To better define the role of cells expressing KIR after SCT, we studied KIR transcript repertoires in 29 grafted patients who received myeloablative or nonmyeloablative regimens. We restricted our analysis to 3DL1, 3DL2, 2DL4, 2DS3, and 2DS4 KIR transcripts 6 months after SCT. Absolute counts of NK and CD8 T cells were determined by flow cytometry, and KIR transcripts were quantified by real-time reverse transcription polymerase chain reaction at days 14, 28, 60, 100, and 180 after transplantation. Three groups of patients were identified. Groups I and III were characterized by the absence or a delayed appearance of KIR transcripts, which correlated with the highest risk of acute graft-versus-host disease (aGvHD). In contrast, in group II, a significant transcript peak was observed early, and only one patient suffered from aGvHD (p = 0.025). Thus determining the kinetics of KIR transcription should make it possible to identify transplanted patients at a high risk of developing aGvHD.

Natural killer cells: can they be useful as adoptive immunotherapy for cancer?

As part of the innate immune system, natural killer (NK) cells form the first line of defence against pathogens or transformed/cancerous host cells. Recent experimental and clinical data show the possibility of exploiting NK activity as a cell-based immunotherapy to treat cancer. This review discusses the recent knowledge on NK cell biology that has impacted on its development as a treatment for cancer.

The safety of interferon-?-1b therapy for invasive fungal infections after hematopoietic stem cell transplantation

BACKGROUND

The restoration of normal immune responses, especially of the T-helper type 1 immune response, is an important predictor of fungal infection outcome in patients with malignant disease who undergo hematopoietic stem cell transplantation (HSCT). The authors sought to evaluate the safety of adjuvant recombinant interferon-gamma-1b as an immune-modulatory therapy HSCT recipients.

METHODS

Thirty-two patients received interferon-gamma-1b after undergoing HSCT at the author's institution between 1998 and 2003. A retrospective analysis was undertaken after obtaining permission from the Institutional Review Board.

RESULTS

Twenty-six of 32 patients (81%) received allogeneic stem cell grafts. All but 1 patient received interferon-gamma-1b and antifungals to treat infections; the other patients received interferon-gamma-1b to promote autologous graft-versus-tumor effect. Interferon-gamma-1b usually was administered at a dose of 50 mug subcutaneously every other day. The median duration (+/- standard deviation) of interferon-gamma-1b therapy was 6+/-6.5 doses (range, 1-29 doses), and the median cumulative dose was 487+/-453 mug (range, 35-2175 microg). During therapy with interferon-gamma-1b, fever was common (n=9 patients; 28%). In 1 patient (3%), new-onset lymphocytopenia occurred but resolved after cytokine therapy was discontinued; there were no interferon- gamma-1b-related episodes of neutropenia, thrombocytopenia, anemia, or liver dysfunction. Interferon-gamma-1b therapy did not precipitate or exacerbate acute or chronic graft-versus-host disease (GVHD). In fact, in 2 of 7 patients (29%) with acute GVHD and in 3 of 10 patients (30%) with chronic GVHD, significant improvements in GVHD were noted during therapy with interferon-gamma-1b. Among the 26 patients with aspergillosis, 14 patients (54%) died. However, 5 of 10 patients (50%) with presumed pulmonary aspergillosis, 3 of 9 patients (33%) with probable pulmonary aspergillosis, 1 of 2 patients (50%) with definite pulmonary aspergillosis, and 3 of 5 patients (60%) with disseminated aspergillosis responded to antifungals and adjuvant interferon-gamma-1b.

CONCLUSIONS

Recombinant interferon-gamma-1b was tolerated without serious adverse reactions in HSCT recipients. A large, prospective, randomized study will be needed to evaluate the efficacy of this cytokine in high-risk HSCT recipients who have invasive mycoses.

The beneficial role of inhibitory KIR genes of HLA class I NK epitopes in haploidentically mismatched stem cell allografts may be masked by residual donor-alloreactive T cells causing GVHD

HLA allele mismatches will provoke T-cell alloreactivity after allogeneic stem cell transplantation. As donors and recipients are usually HLA matched, the public HLA epitopes that are recognized by natural killer (NK) cells (NK epitopes) are rarely mismatched, and therefore there is rarely potential for NK alloreactivity arising from the absence of ligands for inhibitory killer immunoglobulin-like receptors (KIR). Transplants using related donors sharing only one haplotype (haploidentical donors) represent a setting in which NK epitopes are often mismatched, thus resulting in the potential for NK alloreactivity. We have analyzed engraftment, acute graft vs host disease (GVHD), leukemia relapse, and survival in 62 haploidentical transplants in relationship with potential NK alloreactivity, inhibitory, and activating KIR genes of class I HLA NK epitopes. Potential NK alloreactivity in the rejection direction was not associated with any outcome variable. Potential NK alloreactivity in the GVHD direction was associated with an increased incidence of severe GVHD and poorer patient survival but not with non-engraftment nor leukemia relapse. A higher number of activating KIR receptors in the genome of the donor was associated with a higher prevalence of GVHD. These results suggest that lack of extensive T-cell depletion in haploidentical transplantation is associated with high GVHD rates and diminishes the benefits of NK-cell alloreactivity.

Differential expansion of umbilical cord blood mononuclear cell–derived natural killer cells dependent on the dose of interleukin-15 with Flt3L

OBJECTIVE

We investigated the effect of interleukin-15 (IL-15) with Flt3 ligand (Flt3L) on the expansion and activation of NK cells derived from umbilical cord blood mononuclear cells (UCB-MNCs).

MATERIALS AND METHODS

UCB-MNCs were cultured at 1 to 100 ng/mL of IL-15 + Flt3L (10 ng/mL) compared with 1 to 500 ng/mL of IL-2 + Flt3L (10 ng/mL). Cultured cells were assessed for surface marker and we calculated absolute number of NK cells and T cells. The cytotoxic activity was analyzed with purified NK cells.

RESULTS

After 2 weeks culture with 5 ng/mL of IL-15 + Flt3L, the fold inductions of absolute number of NK cells significantly increased to 20.9-fold +/- 9.3-fold of the number of NK cells on day 0 (p < 0.05), with 24.4-fold +/- 16.1-fold of T cells. But with 50 ng/mL of IL-15 + Flt3L, fold induction of NK cells decreased to 5.1-fold +/- 3.9-fold, while T cells showed 34.8-fold +/- 18.7-fold (n = 8). The proportion of NK vs T cells showed to be significantly higher (1.61 +/- 0.91) with 5 ng/mL of IL-15 than with 50 ng/mL of IL-15 (0.12 +/- 0.03). Such proportional change of NK/T cells could not be observed with IL-2. Immunophenotypes of CD56, CD16, LFA1, CD94, CD8, and perforin of cultured NK cells with 10 ng/mL of IL-15 + Flt3L showed the same pattern of those with 50 ng/mL of IL-2 + Flt3L. Cytotoxic activity against K562 of cultured NK cells resulted in the same level as adult peripheral blood (PB)-derived NK cells.

CONCLUSIONS

Higher induction of NK cells derived from UCB-MNCs was achieved by low dose (5 to 10 ng/mL) rather than high dose (> 50 ng/mL) of IL-15.

Allogeneic versus syngeneic killer splenocytes as effector cells for the induction of graft-versus-tumor effect

The effect of allogeneic versus syngeneic killer cells derived from normal or severe combined immunodeficiency disease (SCID) mice was evaluated for induction of antitumor reaction in a murine model of mammary carcinoma. Tumor cells of H-2d origin were injected intravenously into H-2(d/b) mice 24 hours after total body irradiation (4 Gy). On the following day, lymphokine-activated killer (LAK) splenocytes, derived from either minor (H-2d) or major (H-2b) histocompatibility complex (MHC)-mismatched parental normal mice or MHC (H-2b)-mismatched SCID mice, were given intravenously. LAK cells of H-2d normal or SCID mice, syngeneic to the tumor, were inoculated in parallel. The results show that LAK cells derived from minor histocompatibility complex-mismatched or MHC-mismatched parental normal mice improved the probability of tumor-free survival as compared with LAK cells syngeneic to the tumor cells, but they aggravated the severity of graft-versus-host disease. SCID splenocytes serving as a source of natural killer (NK) cells were expanded and activated in vitro by rIL-2 to obtain a sufficient number of DX5+ CD3- CD8- NK cells (SCID-LAK). H-2b SCID-LAK cells did not cause graft-versus-host disease and significantly delayed tumor growth compared with syngeneic H-2d SCID-LAK cells, as indicated by tumor colony assays in vitro and adoptive transfer experiments. However, the graft-versus-tumor effect was not long lasting, and treated mice finally died of tumor. Our results show an advantage of allogeneic over syngeneic cell therapy for achieving a graft-versus-tumor effect by rIL-2-activated T cells and NK cells. Periodic repetition of NK treatments may be required to achieve more durable antitumor effects.

Mesenchymal stem cells inhibit the formation of cytotoxic T lymphocytes, but not activated cytotoxic T lymphocytes or natural killer cells

BACKGROUND

Mesenchymal stem cells (MSCs) can reduce the incidence of graft-versus-host disease because of their ability to inhibit T-lymphocyte proliferation. There are no publications on the effect that MSCs have on cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells, effector cells vital for the graft-versus-leukemia effect.

METHODS

Cytotoxic T cells were primed in mixed lymphocyte culture (MLC) against irradiated stimulator lymphocytes, and irradiated third-party MSCs were added at different time points. The CTLs were collected, and their cytotoxic potential was analyzed in a chromium-release assay against the same stimulator cells as in the MLC. Purified NK cells were mixed with irradiated MSCs, and the lysis was measured in chromium-release assay against K562 target cells.

RESULTS

We found that MSCs inhibited CTL-mediated lysis by 70% if added at the beginning of the 6-day MLC. The lysis was not affected on day 3 or in the cytotoxic phase. Furthermore, MSCs inhibited the formation of cytotoxic lymphocytes when the cells were separated in a transwell system, which indicates that the effect is mediated by a soluble factor. NK cell-mediated lysis of K562 cells was not inhibited by MSCs. MSCs did not induce proliferation of allogeneic lymphocytes, and they were not lysed by allogeneic CTLs or NK cells.

CONCLUSION

Our findings indicate that MSCs escape recognition by CTLs and alloreactive NK cells, and inhibit the formation of cytotoxic T cells by secreting a soluble factor, but that they do not interfere with CTLs and NK cell lysis.

Tumor Vaccination after Allogeneic Bone Marrow Cell Reconstitution of the Nonmyeloablatively Conditioned Tumor-Bearing Murine Host

Allogeneic bone marrow cell reconstitution of the nonmyeloablatively conditioned host is supposed to provide an optimized platform for tumor vaccination. We recently showed that an allogeneic T cell-depleted graft was well accepted if the tumor-bearing host was NK depleted. Based on this finding, a vaccination protocol in tumor-bearing, nonmyeloablatively conditioned, allogeneically reconstituted mice was elaborated. Allogeneically reconstituted mice, bearing a renal cell carcinoma, received tumor-primed donor lymph node cells (LNC), which had or had not matured in the allogeneic host. Primed LNC were supported by tumor lysate-pulsed dendritic cells, which were donor or host derived. Optimal responses against the tumor were observed with host-tolerant, tumor-primed LNC in combination with host-derived dendritic cells. High frequencies of tumor-specific proliferating and CTLs were recorded; the survival time of tumor-bearing mice was significantly prolonged, and in >50% of mice the tumor was completely rejected. Notably, severe graft-vs-host disease was observed in reconstituted mice that received tumor-primed LNC, which had not matured in the allogeneic host. However, graft-vs-host was not aggravated after vaccination with tumor-primed, host-tolerant LNC. Thus, the LNC were tolerant toward the host, but not toward the tumor. The finding convincingly demonstrates the feasibility and efficacy of tumor vaccination after allogeneic reconstitution of the nonmyeloablatively conditioned host.

The immunobiology of natural killer cells and bone marrow allograft rejection

Natural killer (NK) cells mediate the acute rejection of bone marrow cell (BMC) allografts, but not solid tissue grafts, in lethally irradiated mice. However, the mechanisms underlying this capability for rejecting BMC remain unclear. NK cells express (1) inhibitory receptors specific for major histocompatibility complex (MHC) class I molecules and (2) activating receptors with diverse specificities. Inhibitory NK receptors confer to NK cells the ability to discriminate between MHC class I-positive and -negative target cells and are therefore involved in the control of NK cell tolerance to self, as well as in the elimination of cells that have downregulation of MHC class I molecules. Preclinical studies in mice have provided good evidence that subsets of NK cells that bear different combinations of both inhibitory and activating Ly49 receptors can interact with each other and target specific BMC rejection, as well as NK cell responses toward tumor cells. Recent clinical studies have also shown that the use of killer cell immunoglobulin-like receptor ligand incompatibility in patients with leukemia who received hematopoietic stem cell transplants correlated not only with the elimination of graft rejection, but also with eradication of tumor and prevention of graft-versus-host disease; this offers a significant advantage for survival. In this review, we attempt to bring together literature regarding the biology of NK cells and discuss the current issues in bone marrow transplantation and the potential clinical role of NK cell alloreactivity in the efficacy of this procedure for immunotherapy of cancer and infectious states.

Functional expression and release of ligands for the activating immunoreceptor NKG2D in leukemia

NKG2D ligands (NKG2DLs) mark malignant cells for recognition by natural killer (NK) cells and cytotoxic T lymphocytes via the activating immunoreceptor NKG2D. This led to the hypothesis that NKG2DLs play a critical role in tumor immune surveillance. The human NKG2DLs MICA and MICB are expressed on tumors of epithelial origin in vivo. For the other recently described set of human NKG2DLs, the UL16-binding proteins (ULBPs), expression in vivo is as yet undefined. In this study we investigated expression and function of NKG2DLs in leukemia using a panel of newly generated NKG2DL-specific monoclonal antibodies. We report that leukemia cells from patients variously express MIC and ULBP molecules on the cell surface with MICA most frequently detected. Patient leukemia cells expressing MICA were lysed by NK cells in an NKG2D-dependent fashion. Sera of patients, but not of healthy donors, contained elevated levels of soluble MICA (sMICA). We also detected increased sMICB levels in patient sera using a newly established MICB-specific enzyme-linked immunosorbent assay. Reduction of leukemia MIC surface expression by shedding may impair NKG2D-mediated immune surveillance of leukemias. In addition, determination of sMICA and sMICB levels may be implemented as a prognostic parameter in patients with hematopoietic malignancies.

Immunotherapy of cancer by active vaccination: does allogeneic bone marrow transplantation after non-myeloablative conditioning provide a new option?

The critical role of antigen-specific T cells in cancer immunotherapy has been amply demonstrated in many model systems. Though success of clinical trials still remains far behind expectation, the continuous improvement in our understanding of the biology of the immune response will provide the basis of optimized cancer vaccines and allow for new modalities of cancer treatment. This review focuses on the current status of active therapeutic vaccination and future prospects. The latter will mainly be concerned with allogeneic bone marrow cell transplantation after non-myeloablative conditioning, because it is my belief that this approach could provide a major breakthrough in cancer immunotherapy. Concerning active vaccination protocols the following aspects will be addressed: i) the targets of immunotherapeutic approaches; ii) the response elements needed for raising a therapeutically successful immune reaction; iii) ways to achieve an optimal confrontation of the immune system with the tumor and iv) supportive regimen of immunomodulation. Hazards which one is most frequently confronted with in trials to attack tumors with the inherent weapon of immune defense will only be briefly mentioned. Many question remain to be answered in the field of allogeneic bone marrow transplantation after non-myeloablative conditioning to optimize the therapeutic setting for this likely very powerful tool of cancer therapy. Current considerations to improve engraftment and to reduce graft versus host disease while strengthening graft versus tumor reactivity will be briefly reviewed. Finally, I will discuss whether tumor-reactive T cells can be "naturally" maintained during the process of T cell maturation in the allogeneic host. Provided this hypothesis can be substantiated, a T cell vaccine will meet a pool of virgin T cells in the allogeneically reconstituted host, which are tolerant towards the host, but not anergised towards tumor antigens presented by MHC molecules of the host.

IL-2 does not enhance the conversion to complete donor chimerism following nonmyeloablative hematopoietic cell transplantation in dogs

A dog model of stable mixed hematopoietic chimerism was established in which leukocyte-antigen-identical littermates receive nonmyeloablative total body irradiation before hematopoietic cell transplantation and postgrafting immunosuppression with mycophenolate mofetil and cyclosporine. Unmodified donor lymphocyte infusion (DLI) into stable mixed chimeras failed to increase donor chimerism, while DLI from donors sensitized to recipient minor-histocompatibility antigens promptly converted all recipients to complete donor chimerism. This established a model for studying approaches to enhance the graft-versus-host (GVH)-effect, a potential surrogate for graft-versus-leukemia activity. We asked if interleukin-2 (IL-2) given after unmodified DLI could result in reliable conversion to complete donor chimerism. IL-2, 4 x 10(5) IU/kg/day, was administered to six mixed chimeric dogs for 14 days. Four dogs received unmodified DLI with IL-2. At 20-40 weeks after DLI, all dogs remained mixed chimeras. For the two recipients of IL-2 only, mixed chimerism also remained unchanged. These results show that IL-2 given with DLI after nonmyeloablative transplantation in dogs is not effective in reliably converting mixed to complete donor chimerism.

Analysis of donor NK and T cells infused in patients undergoing MHC-matched allogeneic hematopoietic transplantation

We retrospectively analyzed the percentages and absolute numbers of T cells, natural killer (NK) cells and NK cell subsets in cryopreserved samples of either bone marrow or blood non-T cell-depleted allogeneic MHC-matched hematopoietic grafts. Using flow cytometry, we found higher numbers of NK cells in aphereses than in bone marrow collections. We further investigated the distribution of NK cell subsets, defined by the cell surface expression of MHC class I-specific receptors, in these allogeneic grafts. The distribution of NK cell subsets from the two different origins were similar, with the exception of the CD158a/h(+) NK cell subset, whose size appeared to be smaller in bone marrow. The search for relations between the numbers of infused cells and post-transplantation events demonstrated that increasing numbers of infused T cells but not NK cells are related with decreased overall survival. Our study highlights the toxicity of infused T cells but not NK cells in allogeneic MHC-matched hematopoietic grafts. These data pave the way for further trials to investigate the effect of NK cell infusion in MHC-matched allogeneic transplantation, and in particular whether ex vivo NK cell expansion and activation may enhance the anti-tumoral effect of the procedure and decrease its morbidity.

Defective expression and function of natural killer cell-triggering receptors in patients with acute myeloid leukemia

The cytolytic function of natural killer (NK) cells is induced by the engagement of a series of activating receptors and coreceptors some of which have recently been identified and collectively termed natural cytotoxicity receptors (NCRs). Here, we analyzed the cytolytic function of NK cells obtained from patients with acute myeloid leukemia (AML). In sharp contrast with healthy donors, in most (16 of 18) patients with AML the majority of NK cells displayed low NCR surface density (NCR(dull)). This phenotype correlated with a weak cytolytic activity against autologous leukemic cells that could not be reversed by the monoclonal antibody-mediated disruption of HLA class I/killer immunoglobulinlike receptor interaction. The remaining 2 patients were characterized by NK cells having an NCR(bright) phenotype. Surprisingly, although displaying NCR-mediated cytolytic activity, these NCR(bright) NK cells were unable to kill autologous leukemic blasts. Importantly, the leukemic blasts from these 2 patients were also resistant to lysis mediated by normal NCR(bright) allogeneic NK cells. Our study suggests that in most instances the inability of NK cells to kill autologous leukemic blasts is consequent to low NCR surface expression. In few cases, however, this failure appears to involve a mechanism of tumor escape based on down-regulation of ligands relevant for NCR-mediated target cell recognition.

The biology of natural killer cells in cancer, infection, and pregnancy

OBJECTIVE

NK cells are important cells of the immune system. They are ultimately derived from pluripotent hematopoietic stem cells. NK cell cytotoxicity and other functions are tightly regulated by numerous activating and inhibitory receptors including newly discovered receptors that selectively recognize major histocompatibility complex class I alleles. Based on their defining function of spontaneous cytotoxicity without prior immunization, NK cells have been thought to play a critical role in immune surveillance and cancer therapy. However, new insights into NK cell biology have suggested major roles for NK cells in infection control and uterine function. The purpose of this review is to provide an update on NK cell function, ontogeny, and biology in order to better understand the role of NK cells in health and disease.

DATA SOURCES

In the Medline database, the major subject heading "Natural Killer Cells" was introduced in 1983, identifying 16,848 citations as of December 31, 2000. Since 1986, there have been approximately 1000 citations per year under this subject heading. In this database, 68% of manuscripts are limited to human NK cells; 40% of citations cross with the major sub-heading of cytotoxicity, 40% with cytokines, 36% with neoplasm, 5% with antibody-dependent cellular cytotoxicity, 2.8% with pregnancy, and 1.3% with infection. Of references from the year 2000-2001, 46 were selected to combine with contributions from earlier literature.

CONCLUSIONS

NK cells should no longer be thought of as direct cytotoxic killers alone as they clearly serve a critical role in cytokine production which may be important to control cancer, infection, and fetal implantation. Understanding mechanisms of NK cell functions may lead to novel therapeutic strategies for the treatment of human disease.

HLA-C mismatches induce strong cytotoxic T-cell reactivity in the presence of an additional DRB/DQB mismatch and affect NK cell-mediated alloreactivity

BACKGROUND

The functional relevance of HLA-C mismatches in an alloresponse is still much debated, putting into doubt the relevance of matching for this antigen in selection of an allogeneic bone marrow donor. In addition to presenting peptides to T cells, HLA-C also functions as a ligand for killing inhibitory receptors (KIRs) on natural killer (NK) cells. In the current study we provide an in vitro basis to address the question of whether mismatches for this antigen are a risk factor for acute graft-versus-host disease (GVHD).

METHODS AND RESULTS

By analysis of cytotoxic and helper T-lymphocyte precursor frequency (CTLp-f and HTLp-f) in 153 pairs, we are able to show that isolated HLA-C mismatches appear less immunogenic than do isolated HLA-A mismatches. Strikingly, the presence of an HLA-C mismatch next to a HLA-DRB or HLA-DQB mismatch leads to a synergistic increase in CTLp-f outcome. Moreover, we are the first to show that absence of a single inhibitory epitope as a result of an HLA-C mismatch can be sufficient to induce NK mediated alloreactivity, that is, kill and proliferate.

CONCLUSIONS

We conclude that, in most cases, isolated HLA-C mismatches may be acceptable with respect to T-cell-mediated alloreactivity; however, the presence of a strong helper epitope (DR/DQ mismatch) appears sufficient to overcome the low immunogenicity of HLA-C. HLA-C mismatches that affect KIR epitopes, can induce NK mediated alloreactivity. This suggests that, in HLA-A-, -B-, -DR-, and -DQ-matched patients, NK cells may play a role in the induction and development of acute GVHD.

Immune reconstitution following allogeneic stem cell transplantation in recipients conditioned by low intensity vs myeloablative regimen

We have investigated the immune status of patients with hematologic malignancies treated with a low intensity conditioning in preparation for allogeneic stem cell transplantation. Conditioning consisted of fludarabine, anti-T lymphocyte globulin and low-dose busulfan, followed by infusion of allogeneic blood stem cells. This protocol resulted in rapid engraftment and complete replacement of host with donor hematopoietic cells. Immunological parameters of these patients were compared to those patients who were conditioned by an aggressive myeloablative regimen. Distribution of cell surface markers of lymphocyte subsets from both groups of patients was similar, but different from that of normal control cells. Reduced intensity or non-myeloablative conditioning prior to allogeneic stem cell transplantation (NST), hardly lowered the normal T cell-dependent mitogenic response even during the early period following transplant, while the myeloablative treatments resulted in a suppressed mitogenic reaction and in slow immune recovery. Reactivity of non-MHC restricted cytotoxic T cells was also at a normal level in patients who were treated with NST. We conclude that stem cell engraftment following reduced conditioning may result in early reconstitution of immune responses assessed in vitro. We hypothesize that clinical application of NST may lead to faster development of effective immune responses against residual host-type malignant and abnormal non-malignant hematopoietic cells, although the role of fludarabine on post-transplant infections remains to be investigated in a larger cohort of patients.

The biology of natural killer cells and implications for therapy of human disease

Natural killer (NK) cells are unique lymphocytes capable of lysing target cells without prior immunization. NK cells activated with cytokines, like interleukin-2 (IL-2), have been used since the 1980s as adoptive immunotherapy against metastatic solid tumors, but their effectiveness has been limited. The mechanisms by which NK cells recognize their targets are complex, including newly identified receptors that recognize class I MHC molecules. Understanding these mechanisms may support the use of NK cells as clinical therapy against infectious diseases and cancer. We have been interested in the use of NK cells clinically for their potential to eradicate minimal residual disease and prevent relapses after autologous stem cell transplantation. Several strategies are discussed to increase the specificity and efficacy of NK cell therapy. One method is to increase the targeting of NK cells by the use of monoclonal antibodies. Another approach uses allogeneic NK cells to overcome the inhibitory receptor mechanisms that may block target cell lysis by recognition of class I molecules. These and other novel strategies may prove to be attractive and effective immunotherapeutic tools to manipulate NK cells to fight human disease.

Human leukocyte antigens (HLA)-Cw as prognostic indicators in autologous transplantation for lymphoma

The human leukocyte antigens (HLA) function as transplantation antigens and as markers in disease association. Disparity at the HLA A, B, Cw, and DR loci in allogeneic stem cell transplants results in an increased incidence of graft-versus-host disease, graft rejection, and decreased survival. HLA class I loci A, B, and Cw also function as ligands for natural killer (NK) cell receptors in an interaction that predominantly inhibits cytolysis of target antigens. This HLA-NK cell inhibitory function is required for protection against auto-aggression, and is of unclear significance in other clinical settings. Furthermore, the prevention of auto-aggression is HLA molecule specific as demonstrated by the association of specific HLA types with autoimmune diseases. It is not known whether the HLA molecules might serve as markers for outcome in autologous transplants. We investigated an association of HLA class I molecules and early transplant outcome in a cohort of patients who underwent autologous transplantation for the treatment of lymphoma. In this retrospective study, HLA class I molecules were analyzed to determine whether they affect transplant outcome. HLA typing was performed by microlymphocytotoxicity assays. Factors such as age, sex, disease type, lactate dehydrogenase (LDH), cell dose, type of graft, and transfusion events were reviewed. Outcome was defined as death (or survival) at 6 months from the date of transplant. HLA-Cw8 was significantly associated with poor outcome (odds ratio = 18 and 9.3, p = 0.01 and 0.02 in homozygous and all patients, respectively). The HLA-A and B locus molecules were not associated with outcome. Age, sex, elevated LDH, and cell dose were not associated with outcome. A blood progenitor cell dose of greater than 6 x 10(8) nucleated cells/kg was favorably associated with outcome (p = 0.08). The number of transfusions received was not associated with outcome. In the multivariate analysis of HLAs and factors associated with outcome, HLA-Cw8 emerged as an independent risk factor for poor outcome (p = 0.03) following autologous transplantation in lymphoma patients. The association of HLA-Cw molecules with outcome in this study group indicates a need for further investigation of the HLA-mediated interactions that affect antitumor cytotoxicity, cytokine release, and regimen related toxicity.

Nutrient support in hematopoietic cell transplantation

High-dose cytoreduction and hematopoietic stem cell infusion form the basis for treatment of hematologic cancers, defects or failure of hematopoiesis, and some solid tumors. As an antitumor therapy, allogeneic hematopoietic cell transplantation (HCT) is superior to autologous HCT by induction of a graft-vs-tumor effect. However, recipients of allografts suffer higher transplant-related mortality owing to graft-vs-host disease (GVHD). Nutrition support research must recognize that HCT is a heterogeneous modality whose short and long-term outcomes are affected by transplant type, preparative regimens, diagnosis, disease stage, age, and nutritional status. The field of HCT will diversify further as lower dose cytoreduction and mixed chimerism grafts allow expansion of the technique to older patients and to other diseases.

Long-term donor chimerism after MHC (RT1) mismatched bone marrow transplantation in the rat: the role of host alloreactive NK cells

We have investigated the role of major histocompatibility complex (MHC) (RT1) disparities in the engraftment of bone marrow (BM) cells after whole body irradiation of rats. Mononuclear BM cells from PVG.RT7.2 (RT1c) rats were injected i.v. into sublethally (10Gy) whole body irradiated PVG (RT1c) rats and RT1 congenic and recombinant PVG rats. Repopulation of the BM, spleen, and blood with donor cells was assessed by FACS analysis of cells labelled with the fluorescein isothiocyanate (FITC)-labelled HIS41 monoclonal antibody (MoAb) against the RT7.2 marker. In RT1 matched (PVG.RT7.2 --> PVG) and RT1-mismatched combinations (PVG.RT7.2 --> PVG.1AV1), where radioresistant host natural killer (NK) cells could not recognize the BM inoculum as foreign, a donor chimerism close to 100% was observed after 6-8 weeks. However, in rat strain combinations where host NK cells could recognize an RT1 mismatch, almost no donor cells survived, and the rats were repopulated with leukocytes of host origin. In intra-MHC recombinant rat strains the element determining rejection or acceptance of the allograft mapped to the RT1-B/D-C/E/M region in PVG.R8 and PVG.R23 rats, in accordance with the patterns of NK alloreactivity in these strain combinations. NK cells may therefore be a primary obstacle to successful allogeneic BM engraftment in this model.

Altered expression of receptors for thyroid hormone and insulin-like growth factor-I during reconstitution after allogeneic hematopoietic stem cell transplantation

Treatment with neuroendocrine hormones has been suggested to promote reconstitution of the immune system after hematopoietic stem cell transplantation (HSCT). We investigated the expression of genes encoding receptors for growth hormone (GH), insulin-like growth factor-I (IGF-I) and triiodothyronine (T3), at various time points after HSCT in 16 patients and 15 healthy controls. Peripheral blood mononuclear cells were isolated and RNA for GH receptor (GHR), IGF-I receptor (IGF-IR) and thyroid hormone receptor (TRalpha1) was amplified by RT-PCR. The expression of the genes was compared with the expression of beta-actin. We demonstrate increased expression of TRalpha1 RNA in patients at 1.5 months post HSCT, compared to a group of healthy controls, and decreased expression of IGF-IR RNA at 2 and 3 months post HSCT, compared to the controls. Serum from three of the patients was also analyzed for levels of T3, T4, TSH and IGF-I at several time points after HSCT. Serum levels for T3, thyroxine (T4), thyroid stimulating hormone (TSH) and IGF-I were within the normal range in all samples. Our results on the molecular level indicate a role for thyroid hormones and IGF-I in immune reconstitution after HSCT, even though the serum levels of T3, T4, TSH and IGF-I are normal.

Transforming growth factor-beta inhibits lymphokine activated killer cytotoxicity of bone marrow cells: implications for the graft-versus-leukemia effect in irradiation allogeneic bone marrow chimeras

BACKGROUND

We have previously shown that allogeneic bone marrow (BM) chimeras preconditioned with total lymphoid irradiation and low-dose total body irradiation (TLI/TBI) develop a stronger graft-versus-leukemia (GVL) effect than chimeras preconditioned with high-dose total body irradiation only (TBI). Here, we report on the possible role of cytokines in the mechanism underlying this GVL effect.

METHODS

Splenic mRNA levels of the cytokines interleukin (IL)-1, IL-2, IL-4, IL-6, IL-7, IL-10, IL-12, IL-15, interferon-gamma, tumor necrosis factor-alpha, and transforming growth factor-beta (TGF-beta), and of inducible nitric oxide synthetase were determined by reverse transcription-polymerase chain reaction in TLI/TBI- or TBI-conditioned C3H/AKR BM chimeras challenged with AKR-type BW5147.3 leukemia cells. Ex vivo TGF-beta protein production by splenocytes was determined using ELISA. The possibility that cytokines influence the GVL effect by modulating the activity of IL-2-activated lymphocytes (LAK cells) was investigated by in vitro assays on donor-type BM cells.

RESULTS

Of all cytokine mRNA levels studied, those of TGF-beta and IL-7 were different between groups; both were significantly more elevated in TBI- than in TLI/ TBI-conditioned or normal mice. Differences were apparent after conditioning and were not influenced by additionally injected BM or leukemia cells. Cultured splenocytes of TBI-conditioned animals produced significantly more TGF-beta protein than those of TLI/TBI-conditioned ones or normal controls. r-TGF-beta but not r-IL-7 suppressed in vitro LAK activity of donor-type BM cells against BW5147.3 cells in a dose-dependent way.

CONCLUSIONS

High-dose TBI-induced, host-derived splenic TGF-beta may inhibit generation of LAK cells from subsequently transplanted donor BM cells, suppressing their capacity to generate cytotoxicity upon injection of leukemia cells. The cytokine profile, induced by irradiation in host hematopoietic organs, can significantly modify posttransplant immunological processes such as the GVL effect and graft-versus-host disease (GVHD).

Peptide specificity of RT1-A1(c), an inhibitory rat major histocompatibility complex class I natural killer cell ligand

The rat major histocompatibility complex class Ia allelomorph RT1-A1(c) is a potent ligand for the recently identified inhibitory rLy-49 receptor, STOK-2. With the ultimate objective of studying the interactions of these molecules using structural and functional methods, we undertook a detailed study of its peptide specificity. The study revealed that designing an "ideal peptide" by choosing the most abundant residues in the "binding motif" obtained by pool sequencing does not necessarily yield an optimal binding peptide. For RT1-A1(c), as many as four positions, P2, P4, P5, and P9, were detected as putative anchors. Since this molecule displays a preference for highly hydrophobic peptides, we tested binding of peptides derived from the known leader peptide sequences of other rat histocompatibility complex class I molecules. One such peptide, found to bind well, requiring 1.6 microm peptide to achieve 50% stabilization, was searched for in vivo. Natural RT1-A1(c) binding peptides were purified from rat splenocytes and characterized by mass spectrometry using a combined matrix-assisted laser desorption ionization/time-of-flight and quadrupole time-of-flight approach. Results showed that the signal sequence-derived peptide was not detectable in the purified peptide pool, which was composed of a complex spectrum of peptides. Seven of these self-peptides were successfully sequenced.

Graft-versus-leukemia effect in minor antigen mismatched chimeras given delayed donor leucocyte infusion: immunoregulatory aspects and role of donor T and ASGM1-positive cells

BACKGROUND

Previous studies have demonstrated that delayed donor leukocyte infusion (DLI) can increase graft-versus-leukemia (GVL) without increasing graft-versus-host-disease (GVHD) in MHC mismatched bone marrow (BM) chimeras. In our report, the immune status of minor antigen mismatched BM chimeras given DLI was studied. Particularly the role of donor ASGM1 positive or T cells in the graft-versus-leukemia effect (GVL) was investigated.

METHODS

AKR mice (H2k, Mls1a, Thy1.1) received TBI (9,5 Gy) and T cell-depleted (TCD) C3H (H2k, Mls2a, Thy1.2) BM alone (BM chimeras), or TCD BM together with immunocompetent C3H spleen cells at the time of BM transplantation (BM+SP chimeras), or TCD BM and 3 weeks later C3H spleen cells (DLI chimeras). Chimerism and T lymphocyte subsets were scored using FACS and anti-Thy, anti-Vbeta6, anti-IL2-beta receptor, anti-CD4, anti-CD3, and anti-CD8 mAbs. Leukemia challenge consisted of 5 x 10(6) AKR T cell lymphoma (BW4157) cells injected i.v. ASGM1 positive (ASGM1+) cells and T cells were depleted using anti-ASGM1 or anti-Thy1.2 antibodies, respectively. Immune tolerance was studied using MLR and CML tests.

RESULTS

BM + SP chimeras developed acute and lethal GVHD, whereas DLI chimeras were totally free from GVHD. In DLI chimeras, host-reactive cytotoxic T cells (CTL) could not be induced and host-reactive CD8Vbeta6 cells were deleted whereas CD4Vbeta6 cells and MLR reactivity persisted temporarily. In contrast, in BM+SP chimeras, anti-host CTL were easily generated and an expansion of both host-reactive CD8Vbeta6 and CD4Vbeta6 T cells was found as well as high anti-host MLR reactivity. Depletion of either ASGM1 + cells or T cells from the DLI inoculum resulted in an abrogation of GVL reactivity, suggesting that both cell populations were involved in the protection against BW4157 leukemia. Three weeks after DLI, the GVL effect waned which correlated with the disappearance of host-reactive CD4 cells and MLR reactivity.

CONCLUSION

In minor antigen mismatched BM chimeras, anti-host reactivity after DLI is characterized by (1) an absence of clinical GVHD, (2) clonal deletion of host-reactive CD8 cells, (3) an absence of anti-host CTL induction, and ( 4) a temporary persistence of host-reactive CD4 T cells and of MLR reactivity. In addition, either donor ASGM1+ cells or an interaction between these cells and T cells contribute to the GVL effect.

Graft-Versus-Leukemia Effect and Graft-Versus-Host Disease Can Be Differentiated by Cytotoxic Mechanisms in a Murine Model of Allogeneic Bone Marrow Transplantation

Allogeneic bone marrow transplantation (allo-BMT) is associated with both graft-versus-host disease (GVHD) and graft-versus-leukemia (GVL) effect. In the present study, we examined the contribution of cytotoxic effector mechanisms, which are mediated by tumor necrosis factor- (TNF-), Fas ligand (FasL), or perforin, to GVHD and GVL effect in a murine BMT model. Bone marrow cells plus spleen cells (BMS) from wild-type, FasL-defective, or perforin-deficient donors were transferred into lethally irradiated recipients in the parent (C57BL/6) to F1 (C57BL/6 × DBA/2) BMT model with or without prior inoculation of DBA/2 leukemia L1210 or P815 mast cytoma cells. The effect of anti–TNF- antibody administration was also examined. Whereas the defect or blockade of each cytotoxic pathway could ameliorate lethal acute GVHD, the GVL effect was differentially affected. The wild-type BMS recipients died of acute GVHD within 50 days without residual leukemia cells. The FasL-defective BMS recipients showed 60%< survival over 80 days without acute GVHD or residual leukemia cells. Administration of anti–TNF- antibody resulted in early leukemia relapse and the recipients died within 25 days with massive leukemia infiltration in the liver. The perforin-deficient BMS recipients died within 60 days with residual leukemia cells. These results suggest that blockade of the Fas/FasL pathway could be used for ameliorating GVHD without impairing GVL effect in allo-BMT.

Graft-Versus-Leukemia Effect and Graft-Versus-Host Disease Can Be Differentiated by Cytotoxic Mechanisms in a Murine Model of Allogeneic Bone Marrow Transplantation

Allogeneic bone marrow transplantation (allo-BMT) is associated with both graft-versus-host disease (GVHD) and graft-versus-leukemia (GVL) effect. In the present study, we examined the contribution of cytotoxic effector mechanisms, which are mediated by tumor necrosis factor- (TNF-), Fas ligand (FasL), or perforin, to GVHD and GVL effect in a murine BMT model. Bone marrow cells plus spleen cells (BMS) from wild-type, FasL-defective, or perforin-deficient donors were transferred into lethally irradiated recipients in the parent (C57BL/6) to F1 (C57BL/6 × DBA/2) BMT model with or without prior inoculation of DBA/2 leukemia L1210 or P815 mast cytoma cells. The effect of anti–TNF- antibody administration was also examined. Whereas the defect or blockade of each cytotoxic pathway could ameliorate lethal acute GVHD, the GVL effect was differentially affected. The wild-type BMS recipients died of acute GVHD within 50 days without residual leukemia cells. The FasL-defective BMS recipients showed 60%&lt; survival over 80 days without acute GVHD or residual leukemia cells. Administration of anti–TNF- antibody resulted in early leukemia relapse and the recipients died within 25 days with massive leukemia infiltration in the liver. The perforin-deficient BMS recipients died within 60 days with residual leukemia cells. These results suggest that blockade of the Fas/FasL pathway could be used for ameliorating GVHD without impairing GVL effect in allo-BMT.

Differential effects of the absence of interferon-gamma and IL-4 in acute graft-versus-host disease after allogeneic bone marrow transplantation in mice

Graft-versus-host disease (GVHD), in which immunocompetent donor cells attack the host, remains a major cause of morbidity after allogeneic bone marrow transplantation (BMT). To understand the role of cytokines in the pathobiology of GVHD, we used cytokine knockout (KO) mice as a source of donor T cells. Two different MHC-disparate strain combinations were examined: BALB/c (H2(d)) donors into lethally irradiated C57BL/6 (H2(b)) recipients or C57BL/6 (H2(b)) donors into B10.BR (H2(k)) recipients. Donor cells were from mice in which either the interferon-gamma (IFN-gamma) or the IL-4 gene was selectively disrupted to understand the role of these cytokines in acute GVHD. In both strain combinations the same pattern was noted with regard to GVHD onset and morbidity. All mice exhibited the classic signs of acute GVHD: weight loss with skin, gut, and liver pathology resulting in morbidity and mortality. Surprisingly, donor cells obtained from mice lacking IFN-gamma gave rise to accelerated morbidity from GVHD when compared with cells from wild-type control donors. Similar results were obtained using normal donors when neutralizing antibodies to IFN-gamma were administered immediately after the BMT. These results suggest that IFN-gamma plays a role in protection from acute GVHD. In marked contrast, cells obtained from IL-4 KO mice resulted in protection from GVHD compared with control donors. Splenocytes from IFN KO mice stimulated with a mitogen proliferated to a significantly greater extent and produced more IL-2 compared with splenocytes obtained from IL-4 KO or control mice. Additionally, there was increased IL-2 production in the spleens of mice undergoing GVHD using IFN-gamma KO donors. These results therefore indicate, with regard to the TH1/ TH2 cytokine paradigm, the absence of a TH1-type cytokine can be deleterious in acute GVHD, whereas absence of a TH2 cytokine can be protective.