Allogeneic Stimulator Cells Research Articles

The TreaT-Assay: A Novel Urine-Derived Donor Kidney Cell-Based Assay for Prediction of Kidney Transplantation Outcome

Donor-reactive immunity plays a major role in rejection after kidney transplantation, but analysis of donor-reactive T-cells is not applied routinely. However, it has been shown that this could help to identify patients at risk of acute rejection. A major obstacle is the limited quantity or quality of the required allogenic stimulator cells, including a limited availability of donor-splenocytes or an insufficient HLA-matching with HLA-bank cells. To overcome these limitations, we developed a novel assay, termed the TreaT (Transplant reactive T-cells)-assay. We cultivated renal tubular epithelial cells from the urine of kidney transplant patients and used them as stimulators for donor-reactive T-cells, which we analyzed by flow cytometry. We could demonstrate that using the TreaT-assay the quantification and characterization of alloreactive T-cells is superior to other stimulators. In a pilot study, the number of pre-transplant alloreactive T-cells negatively correlated with the post-transplant eGFR. Frequencies of pre-transplant CD161+ alloreactive CD4+ T-cells and granzyme B producing alloreactive CD8+ T-cells were substantially higher in patients with early acute rejection compared to patients without complications. In conclusion, we established a novel assay for the assessment of donor-reactive memory T-cells based on kidney cells with the potential to predict early acute rejection and post-transplant eGFR.

Alloactivation of Naïve CD4+CD8-CD25+T Regulatory Cells: Expression of CD8α Identifies Potent Suppressor Cells That Can Promote Transplant Tolerance Induction.

Therapy with alloantigen-specific CD4+CD25+ T regulatory cells (Treg) for induction of transplant tolerance is desirable, as naïve thymic Treg (tTreg) are not alloantigen-specific and are weak suppressor cells. Naïve tTreg from DA rats cultured with fully allogeneic PVG stimulator cells in the presence of rIL-2 express IFN-gamma receptor (IFNGR) and IL-12 receptor beta2 (IL-12Rβ2) and are more potent alloantigen-specific regulators that we call Ts1 cells. This study examined additional markers that could identify the activated alloantigen-specific Treg as a subpopulation within the CD4+CD25+Foxp3+Treg. After culture of naïve DA CD4+CD8−CD25+T cells with rIL-2 and PVG alloantigen, or rIL-2 without alloantigen, CD8α was expressed on 10–20% and CD8β on <5% of these cells. These cells expressed ifngr and Il12rb2. CD8α+ cells had increased Ifngr that characterizes Ts1 cells as well was Irf4, a transcription factor induced by TCR activation. Proliferation induced by re-culture with rIL-12 and alloantigen was greater with CD4+CD8α+CD25+Treg consistent with the CD8α+ cells expressing IL-12R. In MLC, the CD8α+ fraction suppressed responses against allogeneic stimulators more than the mixed Ts1 population, whereas the CD4+CD8−CD25+T cells were less potent. In an adoptive transfer assay, rIL-2 and alloantigen activated Treg suppress rejection at a ratio of 1:10 with naïve effector cells, whereas alloantigen and rIL-2 activated tTreg depleted of the CD8α+ cells were much less effective. This study demonstrated that expression of CD8α by rIL-2 and alloantigen activation of CD4+CD8−CD25+Foxp3+T cells was a marker of activated and potent Treg that included alloantigen-specific Treg.

Harnessing alloreactive responses by patient lymphocytes to achieve anti-cancer responses

Abstract Potent immune responses are induced by encounter with cells from a different (allogeneic) individual. The increased number of responding alloreactive T cells can be explained by the cross-reactivity exhibited by T cell receptors (TCR). This cross-reactivity also allows these TCR to bind to syngeneic major histocompatibility complex molecules expressing peptides derived from pathogens or cancer cells. Initial studies showed that CD3+ lymphocytes isolated from newly diagnosed leukemic patients were able to lyse syngeneic leukemic cells after stimulation with allogeneic cells in about half of the patients. These findings raise the possibility that manipulating the alloreactive responses by patient lymphocytes could result in enhanced anti-cancer responses. Further studies utilized a mouse acute myeloid leukemic cell line, C1498, derived from a C57BL/6 mouse. C57BL/6 splenocytes stimulated with allogeneic stimulator cells were shown to be able to lyse allogeneic target cells as well as the syngeneic C1498 leukemic cells. The level of lysis of the syngeneic leukemic cells was dependent on the strain from which the allogeneic stimulator cells were obtained. Immunization of C57BL/6 mice with C1498 cells or subcellular antigen enhanced the anti-C1498 response when stimulated with allogeneic cells. Ongoing experiments are defining whether naïve or memory effector cells are responsible for the lysis of the syngeneic leukemic cells as well as the nature of the peptide antigens that allow the syngeneic cancer cells to be recognized. The results of these studies will facilitate the use of protocols which harness alloreactive responses by patient lymphocytes to generate anti-cancer responses.

Recently alloactivated CD4+CD8−CD25+T regulatory cells express CD8alpha and are potent suppressor cells

Abstract Therapy with antigen-specific CD4+CD25+ T regulatory cells (Treg) for induction of transplant tolerance is desirable, as naïve thymic Treg (tTreg) are non-antigen specific and weak suppressor cells. Naïve tTreg from DA rats cultured with fully allogeneic PVG stimulator cells and IL-2 express IFN-gamma receptor (IFNGR) and IL-12 receptor beta2 (IL-12Rb2) and are more potent alloantigen-specific regulators that we call Ts1 cells. This study examined other markers that could identify the activated alloantigen-specific Treg as a subpopulation within the CD4+CD25+Foxp3+Treg. After culture of naïve DA CD4+CD8−CD25+T cells with rIL-2 and PVG alloantigen, CD8a was expressed on 10–20% and CD8b on &amp;lt;5% of these cells. RT-PCR showed the CD8+ cells had increased Ifngr that characterizes Ts1 cells as well was Irf4, a transcription factor induced by TCR activation. Proliferation induced by re-culture with rIL-12 and alloantigen was greater with CD4+CD8+CD25+Treg consistent with the CD8a+ cells expressing IL-12R. In MLC, the CD8+ fraction had greater suppression than the mixed Ts1 population, whereas the CD4+CD8−CD25+T cells had less suppression. In an adoptive transfer assay, rIL-2 and alloantigen activated Treg suppress rejection at a ratio of 1:10 with naïve effector cells, whereas alloantigen and rIL-2 activated tTreg depleted of the CD8a cells did not prevent rejection. This study showed the expression of CD8alpha by rIL-2 and alloantigen activation of CD4+CD8−CD25+Foxp3+T cells was a marker of alloantigen-specific Treg and may be of use to enrich alloantigen-specific Treg.

Induction of anti-leukemic responses by stimulation of leukemic CD3+ cells with allogeneic stimulator cells

BackgroundImmunotherapeutic protocols have focused on identification of stimuli that induce effective anti-leukemic immune responses. One potent immune stimulus is the encounter with allogeneic cells. Our group previously showed that the infusion of haploidentical donor white blood cells (1–2 × 108 CD3+ cells/kg) into patients with refractory hematological malignancies induced responses of varying magnitude in over half of the patients. Because donor cells were eliminated within 2 weeks in these patients, it is presumed that the responses of recipient lymphocytes were critically important in achieving prolonged anti-leukemic responses.MethodsThe role of patient CD3+ cells in anti-leukemic responses was examined by isolating peripheral blood mononuclear cells from newly diagnosed leukemic patients. Immunophenotyping was performed on these peripheral blood mononuclear cells. CD3+ cells were isolated from the peripheral blood mononuclear cells and tested for their ability to proliferate and lyse autologous leukemic cells when stimulated with unrelated allogeneic cells.ResultsAllostimulated CD3+ cells effectively generated cytolytic responses to autologous CD3-cells in 11/21 patients. Increased numbers of CD4+ cells expressing high levels of granzyme A, B and perforin and CD8+CD39+ cells were found in nonresponsive CD3+ cells.ConclusionsThese results indicate that CD3+ cells from leukemic patients are capable of generating anti-leukemic responses when stimulated with unrelated allogeneic cells. This model can be used to identify approaches using alloreactive responses by patient lymphocytes to enhance in vivo anti-leukemic responses.

The Suppressive Function of the Human Regulatory Macrophages In-Vitro have more Potency but not In-Vivo

Centre for Transplant & Renal Research. Introduction Human regulatory macrophages (Mregs) have been shown to suppress mitogen-driven T cell proliferation in vitro and are under evaluation as a cellular therapy in renal transplantation in THE ONE STUDY clinical trial. In this study, we investigated whether human Mregs were capable of suppressing the allogeneic response in vitro and protecting islet xeno-grafts in humanizing mice in vivo. Methods Human CD14+ cells were isolated from healthy donor peripheral blood monocytes (PBMCs) using CD14 magnetic beads. Mregs induction was performed by culturing CD14+ cells with M-CSF for 6 days and be stimulated with IFN-γ for a further 24 hr. The phenotype of Mregs was characterized by flow cytometry, and their suppressive activity was tested by mixed-lymphocyte reaction (MLR) using human PBMCs as responder cells, autologous Mregs as suppressor cells and irradiated allogeneic PBMCs as stimulator cells. In a separate transwell MLR setting, responder and allogeneic stimulator cells were cultured in the upper chamber and autologous Mregs were seeded in the lower chamber. Supernatants collected from MLR cultures were used for cytokine detection. Isolated the neonatal porcine islet cell clusters (NICCs) and cultured for 6 days. In vivo, every 5,000 IEQ NICCs were transplanted into NOD-SCID IL2R gamma -/- mice under the two sides of renal capsules. Adoptive transfer of human PBMCs and Mregs were suspended in PBS and injected into mice at doses of 10×106 and 2×106 by tail vein within 7 days after transplant. Graft rejection was defined as little or no intact graft with a heavy lymphocytic infiltrate on histological examination, survival was analyzed by H&E staining and endocrine secreting cells was analyzed by insulin staining. Results The resulting induced human Mregs demonstrated a typical Mregs phenotype, CD14lowCD80lowCD86+HLA-DR+CD83-/lowCD16-, and as a result, potent suppression of proliferating alloreactive PBMC even at Mregs: responder cells ratios >1:16. Separation of Mregs from responder and allogeneic stimulators in a transwell MLR system had the mild impact on their suppressive potency in the allogeneic response at all ratios of Mregs: responder cells tested. Upregulated levels of Mregs function related molecules TGF-b and IDO were detected in the supernatants collected from both non-transwell and transwell MLR cultures containing Mregs. In treated mice, the human PBMC were identified in the porcine-NICC-xenografts, as well as systemically in the spleens, blood, and kidneys. However, injected Mregs cannot be detected by flow cytometry, and there were no intact xenografts were found with mid-term. Conclusions In vitro induced human Mregs showed the capacity to suppress the allogeneic response in vitro and that was not cell-cell contact dependent. The porcine-NICC-xenografts cannot be protected by Human-Mregs in vivo as Mregs cannot proliferation. The suppressive function of the Mregs have more potency in vitro, but not in vivo.

Human CD4+CD25+CD127loFOXP3+Treg Activation by IL-4 and Alloantigen Induces Activated Treg that do not Express CD45RA and Express the IL-5 Receptor Alpha (CD125)

Aim: Transplant tolerance induction requires CD4+CD25+FOXP3+Treg (tTreg). tTreg are not antigen-specific and for therapy large numbers are required. Antigen-specific CD4+CD25+FOXP3+Treg that are present when a host develops transplant tolerance are more potent and alloantigen-specific. In rats, culture of naïve tTreg with rIL-4 and alloantigen induces IL-5Rα expressing antigen-specific Treg. These activated Treg are further expanded by IL-5. Here, we aim to examine if similar activation pathways occur in human CD4+CD25+CD127loFOXP3+ Treg. Methods: Treg were isolated from healthy human blood using a Human CD4+CD127loCD25+ Regulatory T cell isolation Kit and their purity assayed by multicolour flow cytometry. These enriched tTreg were cultured with human rIL-4 (200Units/ml) and allogeneic stimulator cells to examine proliferation, changes in surface molecules by FACS and expression of cytokine and cytokine receptors by RT-PCR. Results: tTreg had significant proliferation at 3-7d with rIL-4 and antigen with a peak at 4d. The level of proliferation was less than with rIL-2, however. FACS showed a reduction in CD45RAhi, an increase in CD45RAintermediate population and a marked increase in CD45RA− population (43% vs 11%). CD45RO+ and CD45RB+ population also increased. In the CD45RA-/lo population, the expression of CD25 and FOXP3 increased. Nearly all cells continued to express CD62L. RT-PCR showed induction of IL-5Rα (CDw125) but not IFNGR. Conclusions: Human CD4+CD25+CD127loFOXP3+Treg can be activated by alloantigen and rIL-4 to express the IL-5 receptor, similar to our observation in rats. This suggests IL-5 may promote the activation of antigen-specific Treg. The rIL-4 has two effects; 1. It induces polyclonal activation of tTreg that continue to express CD45RA. 2. The increased CD45RA−/CD45RO+ population was consistent with activation of antigen-specific Treg. The activated cells had increased CD25 and FOXP3 expression, markers that distinguish them from naïve tTreg, which are CD45RA+ and have less CD25 and FOXP3 expression. Thus, alternate tTreg activation pathway may produce potent antigen-specific Treg for therapy circumventing requirement for high tTreg numbers needed to induce transplant tolerance.

Repeated Injections of IL-2 Break Renal Allograft Tolerance Induced via Mixed Hematopoietic Chimerism in Monkeys.

Tolerance of allografts achieved in mice via stable mixed hematopoietic chimerism relies essentially on continuous elimination of developing alloreactive T cells in the thymus (central deletion). Conversely, while only transient mixed chimerism is observed in nonhuman primates and patients, it is sufficient to ensure tolerance of kidney allografts. In this setting, it is likely that tolerance depends on peripheral regulatory mechanisms rather than thymic deletion. This implies that, in primates, upsetting the balance between inflammatory and regulatory alloimmunity could abolish tolerance and trigger the rejection of previously accepted renal allografts. In this study, six monkeys that were treated with a mixed chimerism protocol and had accepted a kidney allograft for periods of 1-10 years after withdrawal of immunosuppression received subcutaneous injections of IL-2 cytokine (0.6-3 × 10(6) IU/m(2) ). This resulted in rapid rejection of previously tolerated renal transplants and was associated with an expansion and reactivation of alloreactive pro-inflammatory memory T cells in the host's lymphoid organs and in the graft. This phenomenon was prevented by anti-CD8 antibody treatment. Finally, this process was reversible in that cessation of IL-2 administration aborted the rejection process and restored normal kidney graft function.

Revisiting the first long-term culture of antigen-specific cytotoxic T cells.

Revisiting the first long-term culture of antigen-specific cytotoxic T cells.

The immunomodulating effect of semen on maternal T cells

Introduction: Semen contains a variety of immunoregulatory factors that may play an important role in the creation of a tolerogenec environment at the implantation site leading to normal pregnancy. The aim of this studywas to investigate the influence of seminal plasma onmaternal peripheral blood mononuclear cells (mPBMCs). Method: First, the direct effect of semen on mPBMCs was measured by incubating these with semen of different sperm quality. Second, to simulate implantation where the immune system of the mother meets her semiallogeneic fetus, mPBMCs were stimulated with paternal PBMCswith one HLA-DRmismatch in amixed lymphocyte culture in theabsenceandpresenceof semen. Furthermore, supernatants were harvested at day 5 and cytokine concentrations were determined using the Luminex method. In addition, mRNA analysis was performed to measure the immediate effect of semen on mPBMCs. Results: Maternal cells showed a significant proliferation and cytokine production when semen was added. In particular, IL-10, IL-17, IL-2, TNF-a, and Il-1b were produced in large amounts bymaternal cells in the presence of semen. Additional mRNA analysis showed a quick and significant upregulation of CD25 and IL-10 in T-cells under the influence of semen. Semen had a differential effect on the immune responseofmaternal cells to allogeneic stimulator cells. Both an increased and decreased MLC response was observed. So far no factors could be identified, explaining this different effect of semen on the alloimmune response. Conclusion: Semen has a direct effect on maternal T cells as reflected by a proliferative response and the secretion of cytokines. Upregulation of both CD25 and IL-10 mRNA by the addition of semen suggests the induction of amore regulatory phenotype of the immune response. The absence of immunoregulatory function and/or less exposure to semen may be the underlying cause in abnormal implantation and lead to complicated pregnancies.

Anti-tumor responses driven by alloreactivity (P2058)

Abstract Previous work by our group found that infusion of G-CSF mobilized haploidentical donor white blood cells at a dose of 1 - 2 x 108 CD3+ cells/kg into refractory cancer patients who had received 100 cGy total body irradiation resulted in responses in a majority (14/27, 9 major) of patients with hematological malignancies despite elimination of the donor cells. The effector mechanism(s) responsible for these anti-cancer responses were not determined although it was noted that there was a cytokine storm that appeared within a day following the infusion of cells. One possible mechanism is that the alloreactive response overrides inhibitory mechanisms already in place in the cancer bearing patient allowing cancer reactive effector cells that are already present to become activated and lyse cancer cells. To test if this is the case, T cells were isolated from peripheral blood mononuclear cells obtained from newly diagnosed leukemic patients, mixed with fully allogeneic stimulator cells (from 1 or 2 different donors) and then tested for their ability to proliferate in response to the allogeneic stimulator cells on day five and for their ability to lyse autologous leukemia cells after stimulation for seven days. Anti-leukemic effector cells could be generated in eight out of the sixteen patients enrolled to date. The characteristics of the effector cells and the explanations for the lack of responses in some patients are the subject of current ongoing studies.

Stimulation of Human EBV- and CMV-Specific Cytolytic Effector Function Using Allogeneic HLA Molecules

Viral infection is a major cause of morbidity and mortality, and there are few therapeutic options available to augment a virus-specific T cell response. Although allo-HLA cross-reactivity from virus-specific memory T cells is common, it is unclear whether priming with specific allogeneic cells could conversely elicit a viral peptide/self-HLA restricted cytotoxic T cell response in humans. First, we used the previously described allo-HLA-B*44:02 cross-reactivity of EBV peptide/HLA-B8 restricted T cells, to determine whether allogeneic HLA stimulation can elicit a cytolytic immune response against EBV. HLA-B8(+) HLA-B44(-) EBV-seropositive PBMCs were stimulated with either HLA-B*44:02(+) or HLA-B*44:03(+) mismatched irradiated PBMCs in a 7-10 d MLR. The allo-HLA stimulated responder cells were then evaluated for cytotoxicity using EBV peptide loaded autologous target cells and unloaded HLA-B8(+) EBV LCL target cells. PBMCs from EBV-seropositive donors gained EBV-specific cytolytic effector function following specific allo-HLA stimulation. Finally, we also elicited cytolytic CMV-specific responses using specific allogeneic cell stimulation, to confirm that this technique can be used to elicit viral peptide/self-HLA restricted responses even from nonpublic TCR responses. Allogeneic cell stimulation used as a cell therapy may be a potential tool to augment an antiviral T cell response in patients with EBV or CMV infection.

Alloreactivity Across HLA Barriers Is Mediated by Both Naïve and Antigen-Experienced T Cells

T cell responses to allogeneic targets arise predominantly from the naïve pool. However, in humans, the risk of graft-versus-host disease is increased if the donor has circulating T cells recognizing multiple persistent DNA viruses, suggesting that memory T cells also contribute to the alloresponse. To examine HLA alloreactivity, we used flow cytometry-based proliferation and cytokine production assays. We identified the clonal identity of virus-specific T cells cross-reacting with HLA-disparate targets by sequencing the T cell receptor β chains in virus-specific T cell lines restimulated with cognate and HLA-disparate targets and sorting these chains according to cytokine response. We confirmed that naïve T cells from cord blood and adult individuals responded to HLA-mismatched target cells. In addition, in adults, we identified memory T cells responding by cytokine release to HLA-mismatched targets both in direct assays and after 8 days of culture with allogeneic stimulator cells. Epstein-Barr virus-specific and cytomegalovirus-specific T cells, tested against a panel of 30 T cell antigen-presenting cells with a broad coverage of the most prominent HLA types, displayed specificity for certain mismatched HLA alleles. Sequencing of the T cell receptor β chain demonstrated a clonotypic identity of cells that responded to both viral and allogeneic stimulation. These findings show conclusively that alloresponses in humans are not confined to the naïve T cell subset, and that memory viral antigen-specific T cells can cross-react with specific mismatched HLA-peptide complexes not presenting with cytomegalovirus or Epstein-Barr virus peptides.

CD4+CD25+TREGS ACTIVATED IN VITRO WITH IL-2 AND IL-12P70 SUPPRESS REJECTION OF FULLY ALLOGENEIC GRAFTS IN ANIMALS WITH NO OTHER IMMUNOSUPPRESSION.

Hall, B. M.1; Verma, N. D.1; Boyd, R.1; Robinson, C. M.1; Tran, G. T.1; Wang, C.2; Bishop, G. A.3; Hodgkinson, S. J.1 Author Information

The Triterpenoid CDDO-Me Delays Murine Acute Graft-versus-Host Disease with the Preservation of Graft-versus-Tumor Effects after Allogeneic Bone Marrow Transplantation

The occurrence of acute graft-versus-host disease (aGVHD) and tumor relapse represent the two major obstacles impeding the efficacy of allogeneic bone marrow transplantation (BMT) in cancer. We have previously shown that the synthetic triterpenoid 2-cyano-3, 12-dioxooleana-1, 9-dien-28-oic acid (CDDO) can inhibit murine early aGVHD, but antitumor effects were not assessed. In the current study, we found that a new derivative of CDDO, CDDO-Me, had an increased ability to inhibit allogeneic T cell responses and induce cell death of alloreactive T cells in vitro. Administration of CDDO-Me to mice following allogeneic BMT resulted in significant and increased protection from lethal aGVHD compared to CDDO. This correlated with reduced TNF-alpha production, reduced donor T cell proliferation, and decreased adhesion molecule (alpha(4)beta(7) integrin) expression on the donor T cells. CDDO-Me was also superior to CDDO in inhibiting leukemia growth in vitro. When CDDO-Me was administered following an allogeneic BMT to leukemia-bearing mice, significant increases in survival were observed. These findings suggest that CDDO-Me is superior to CDDO in delaying aGVHD, while preserving or possibly even augmenting GVT effects.

Inactivation of Human Leukocytes in Platelet Products After Pathogen Reduction Technology Treatment in the Presence of Platelet Additive Solution.

Abstract 2116Poster Board II-93During the transfusion of blood or blood products, a recipient can receive a large number of allogeneic leukocytes. This can lead to leukocyte-mediated adverse reactions in the recipient and include donor anti-recipient responses such as the life-threatening transfusion-associated graft versus host disease (TA-GVHD) and cytokine production; or recipient anti-donor responses that are induced by direct presentation of foreign antigen by donor leukocytes or indirectly after processing of the donor cells by recipient antigen-presenting cells. To avoid or minimize leukocyte mediated reactions, the leukocytes present in blood products are inactivated or depleted prior to administration. Nucleic acid targeted pathogen reduction processes (PRT) are well suited for leukocyte inactivation. The Mirasol® PRT System uses riboflavin (Vitamin B2) and ultraviolet (UV) light to reduce the active pathogen load and inactivate residual leukocytes in blood products used for transfusion. To make the PRT System more widely applicable, the effect of treating leukocytes in the presence of platelet additive solution (PAS) was tested. Human peripheral blood mononuclear cells (PBMNC) were purified by Ficoll-Hypaque discontinuous centrifugation and placed in 350 ml of storage solution consisting of 65% PAS (SSP+) and 35% plasma. An untreated control sample was removed before addition of 35 ml of riboflavin (500 μM) and exposure to UV light (9.1 J/ml). PBMNC were recovered after treatment and tested for their ability to proliferate in response to polyclonal stimulators such as phytohemagglutinin, and anti-CD3/CD28 or to allogeneic stimulator cells in a mixed lymphocyte culture (MLC). Treatment was found to inhibit proliferation as well as T cell activation as measured by the upregulation of CD69 expression when incubated with phorbol 12-myristate 13-acetate. Treated PBMNC were unable to produce inflammatory or TH1/TH2 cytokines when stimulated with lipopolysaccharide for 24 hours or anti-CD3/CD28 for 72 hours. Levels of cytokines that are released in the absence of activation, such as IL-6, IL-8 and IL1β, were reduced below levels of detection of the assay after PRT-treatment. Quantitation of the degree of inactivation using limiting dilution assays showed that 5.2 log inactivation could be achieved at the specified energy doses. These treatment conditions resulted in acceptable platelet cell quality over 8 days in storage. In summary, PRT treatment was able to functionally inactivate leukocytes in the presence of PAS to the levels seen with gamma-irradiation without adversely affecting the quality of the platelets. Disclosures:Fast:CaridianBCT Biotechnologies: Research Funding. Marschner:CaridianBCT Biotechnologies: Employment. Goodrich:CaridianBCT Biotechnologies: Employment.

Treatment with Tyrosine Kinase Inhibitors May Impair the Potential Curative Effect of Allogeneic Stem Cell Transplantation.

Abstract 857▪▪This icon denotes an abstract that is clinically relevant.Tyrosine kinase inhibitors (TKI) like imatinib and dasatinib are the current treatment of choice for patients with chronic myeloid leukemia (CML). Although most patients enter a complete remission during treatment, cure of the disease is usually not achieved since recurrence of the disease is seen in the majority of patients upon discontinuation of the treatment, indicating that the leukemic stem cell is not efficiently targeted. Furthermore, in accelerated phase and blast crisis of CML TKI treatment only results in temporary control of the disease. In these situations allogeneic stem cell transplantation (allo-SCT) and application of donor T cells may be the only curative treatment. Besides the direct anti-leukemic effect of allo-SCT, alloreactive T cells recognizing CML (progenitor) cells, and the formation of immunological memory may lead to effective lifelong immune surveillance. Therefore, we investigated whether the leukemic cells persisting during TKI treatment are susceptible targets for the anti-leukemic effect mediated by donor T cells after allo-SCT and whether continuous TKI treatment may have an additive effect during the immunological intervention. To investigate the anti-leukemic effect of the two strategies, CD34+ positive CML cells were isolated from bone marrow, and labeled with the fluorescent dyes CFSE or PKH to allow monitoring of single cell proliferation. CML cells were exposed to imatinib (1-100μM) or dasatinib (0.01-50nM), and/or to CD8+ alloreactive cytotoxic T lymphocyte (CTL) clones in the presence of proliferation-inducing cytokines. The number, phenotype, and proliferative status of the CML cells persisting after single and combined interventions were measured by quantitative flowcytometric analysis. In the absence of therapeutic interventions the majority of CD34+ CML cells entered proliferation. However, a small population of CD34+ CML stem cells residing in the non-dividing peak could be identified despite the addition of cytokines. Addition of imatinib or dasatinib resulted in efficient dose-dependent induction of cell death of the leukemic cells (99% lysis by 25μM imatinib or 10nM dasatinib). However, the population of quiescent CD34+ CML stem cells was not affected. Moreover, the number of cells present in the non-dividing population increased 2-fold compared to the non-treated controls at the highest TKI concentrations, indicating additional growth arrest of a population of proliferating CML precursor cells. We next tested the capacity of different HLA-A2-restricted CD8+ CTL clones to kill non-treated or imatinib or dasatinib treated CML cells. Whereas the proliferating CD34+ CML precursors were efficiently lysed, the population of quiescent stem cells was capable of withstanding CTL exposure. Detailed phenotypic analysis revealed significant downregulation of HLA-A2 and the adhesion molecules CD49d and CD58 on these quiescent cells, probably resulting in the impaired ability of these target cells to form a high avidity interaction with the T cells. The increased population of non-dividing cells as a result of the TKI pretreatment showed similar resistance to T cell induced cell death, indicating that TKI treatment may even diminish the anti-leukemic effect of allo-SCT. In the absence of therapeutic control, as mimicked by the removal of T cells and TKI from the cultures, outgrowth of the leukemic cells re-occurred, illustrating their capacity to give rise to a relapse of the disease. Next, we analyzed the effect of TKI treatment on T cell survival and functionality. Whereas resting primary T cells were insensitive to TKI treatment, T cells activated by either polyclonal stimulation with anti-CD3/CD28 beads or stimulation with allogeneic stimulator cells died after TKI exposure at similar concentrations as the leukemic cells. In conclusion, TKI treatment results in selection of a population of quiescent leukemic stem cells showing cross-resistance to CTL-induced cell death, most likely due to their inability to form a high avidity interaction. Moreover, T cells actively participating in the anti-leukemic immune response after allo-SCT are suppressed by TKI. These data indicate that continuous TKI treatment may potentially hamper the curative effect of allo-SCT. Disclosures:No relevant conflicts of interest to declare.

Transfusion‐associated graft‐versus‐host disease

Transfusion‐associated graft‐versus‐host disease

The role of adherent cells in the immunosuppressed state of mouse progeny transplacentally exposed to benzo(α)pyrene

In recent studies, we showed that murine fetal liver cells from progeny exposed to benzo(alpha)pyrene in utero by intraperitoneal injection of the dam at midpregnancy (12 d) suppressed cell proliferation in an allogeneic mixed lymphocyte response. On the other hand, fetal liver cells from the corn oil (vehicle for the carcinogen)-exposed progeny (control) appeared to enhance proliferation. Suppression or enhancement appeared to be mediated by fetal liver bearing CD8+ and Lyt 1+ (CD5+) cells. Despite these manifestations, the role of third-party cells needs to be considered. As a first premise, adherent cells were targeted as possible third-party cells. To test the role of the adherent cells, liver cells from benzo(alpha)pyrene-exposed fetuses were treated with ficoll-hypaque, and the interface cells were fractionated through glass wool or nylon wool. It is known that adhering cells, macrophages and B cells, readily attach to glass or nylon wool. The effluent cells and the adherent cells were cultured with syngeneic responder cells and allogeneic stimulator cells in a mixed lymphocyte response. The results showed that benzo(alpha)pyrene-effluent cells led to the enhancement of proliferation in the mixed lymphocyte response, while benzo(alpha)pyrene-adherent cells led to suppression. The effluent and adherent cells of corn oil controls did not modify cell proliferation in the mixed lymphocyte response. These data suggest that a third-party cell, reasonably the macrophage or possibly B cells or both, since these are adherent cells, play a decided role in mediating suppression in the benzo(alpha)pyrene-exposed progeny.

Ex Vivo Generation of Human Alloantigen-Specific Regulatory T Cells from CD4posCD25high T Cells for Immunotherapy

BackgroundRegulatory T cell (Treg) based immunotherapy is a potential treatment for several immune disorders. By now, this approach proved successful in preclinical animal transplantation and auto-immunity models. In these models the success of Treg based immunotherapy crucially depends on the antigen-specificity of the infused Treg population. For the human setting, information is lacking on how to generate Treg with direct antigen-specificity ex vivo to be used for immunotherapy.Methodology/Principal FindingsHere, we demonstrate that in as little as two stimulation cycles with HLA mismatched allogeneic stimulator cells and T cell growth factors a very high degree of alloantigen-specificity was reached in magnetic bead isolated human CD4posCD25high Treg. Efficient increases in cell numbers were obtained. Primary allogeneic stimulation appeared a prerequisite in the generation of alloantigen-specific Treg, while secondary allogeneic or polyclonal stimulation with anti-CD3 plus anti-CD28 monoclonal antibodies enriched alloantigen-specificity and cell yield to a similar extent.Conclusions/SignificanceThe ex vivo expansion protocol that we describe will very likely increase the success of clinical Treg-based immunotherapy, and will help to induce tolerance to selected antigens, while minimizing general immune suppression. This approach is of particular interest for recipients of HLA mismatched transplants.