scholarly journals CD8β Depletion Does Not Prevent Control of Viral Replication or Protection from Challenge in Macaques Chronically Infected with a Live Attenuated Simian Immunodeficiency Virus

2019 ◽  
Vol 93 (15) ◽  
Author(s):  
Matthew S. Sutton ◽  
Amy Ellis-Connell ◽  
Alexis J. Balgeman ◽  
Gabrielle Barry ◽  
Andrea M. Weiler ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Nk Cells ◽  
Chronic Infection ◽  
Γδ T Cells ◽  
Cell Populations ◽  
Plasma Viremia ◽  
Immunodeficiency Virus ◽  
Cynomolgus Macaques ◽  
The Impact

ABSTRACTWe evaluated the contribution of CD8αβ+T cells to control of live-attenuated simian immunodeficiency virus (LASIV) replication during chronic infection and subsequent protection from pathogenic SIV challenge. Unlike previous reports with a CD8α-specific depleting monoclonal antibody (mAb), the CD8β-specific mAb CD8β255R1 selectively depleted CD8αβ+T cells without also depleting non-CD8+T cell populations that express CD8α, such as natural killer (NK) cells and γδ T cells. Following infusion with CD8β255R1, plasma viremia transiently increased coincident with declining peripheral CD8αβ+T cells. Interestingly, plasma viremia returned to predepletion levels even when peripheral CD8αβ+T cells did not. Although depletion of CD8αβ+T cells in the lymph node (LN) was incomplete, frequencies of these cells were 3-fold lower (P = 0.006) in animals that received CD8β255R1 than in those that received control IgG. It is possible that these residual SIV-specific CD8αβ+T cells may have contributed to suppression of viremia during chronic infection. We also determined whether infusion of CD8β255R1 in the LASIV-vaccinated animals increased their susceptibility to infection following intravenous challenge with pathogenic SIVmac239. We found that 7/8 animals infused with CD8β255R1, and 3/4 animals infused with the control IgG, were resistant to SIVmac239 infection. These results suggest that infusion with CD8β255R1 did not eliminate the protection afforded to LASIV vaccination. This provides a comprehensive description of the impact of CD8β255R1 infusion on the immunological composition in cynomolgus macaques, compared to an isotype-matched control IgG, while showing that the control of LASIV viremia and protection from challenge can occur even after CD8β255R1 administration.IMPORTANCEStudies of SIV-infected macaques that deplete CD8+T cellsin vivowith monoclonal antibodies have provided compelling evidence for their direct antiviral role. These studies utilized CD8α-specific mAbs that target both the major (CD8αβ+) and minor (CD8αα+) populations of CD8+T cells but additionally deplete non-CD8+T cell populations that express CD8α, such as NK cells and γδ T cells. In the current study, we administered the CD8β-specific depleting mAb CD8β255R1 to cynomolgus macaques chronically infected with a LASIV to selectively deplete CD8αβ+T cells without removing CD8αα+lymphocytes. We evaluated the impact on control of virus replication and protection from pathogenic SIVmac239 challenge. These results underscore the utility of CD8β255R1 for studying the direct contribution of CD8αβ+T cells in various disease states.

scholarly journals Extensive CD8β depletion does not prevent control of viral replication or protection from challenge in macaques chronically infected with a live attenuated simian immunodeficiency virus

2019 ◽  
Author(s):  
Matthew S. Sutton ◽  
Amy Ellis-Connell ◽  
Alexis J. Balgeman ◽  
Gabrielle Barry ◽  
Andrea M. Weiler ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Cd8 T Cells ◽  
Chronic Infection ◽  
Γδ T Cells ◽  
Cd8 T Cell ◽  
Cell Populations ◽  
Plasma Viremia ◽  
Immunodeficiency Virus ◽  
The Impact

AbstractWe evaluated the contribution of CD8αβ+ T cells on control of live-attenuated simian immunodeficiency virus (LASIV) replication during chronic infection and subsequent protection from pathogenic SIV challenge. Unlike previous reports with a CD8α-specific depleting monoclonal antibody (mAb), the CD8β-specific mAb CD8β255R1 selectively depleted CD8αβ+ T cells without also depleting non-CD8+ T cell populations that express CD8α, such as natural killer (NK) cells and γδ T cells. Following infusion with CD8β255R1, plasma viremia transiently increased coincident with declining peripheral CD8αβ+ T cells. Interestingly, plasma viremia returned to pre-depletion levels even when peripheral CD8αβ+ T cells did not. Although depletion of CD8αβ+ T cells in the lymph node (LN) was incomplete, frequencies of these cells were three-fold lower (p=0.006) in animals that received CD8β255R1 compared to control IgG. It is possible that these residual SIV-specific CD8αβ+ T cells may have contributed to suppression of viremia during chronic infection. We also determined whether infusion of CD8β255R1 in the LASIV-vaccinated animals increased their susceptibility to infection following intravenous challenge with pathogenic SIVmac239. We found that 7/8 animals infused with CD8β255R1, and 3/4 animals infused with the control IgG, were resistant to SIVmac239 infection. These results suggest that infusion with CD8β255R1 did not eliminate the protection afforded to LASIV vaccination. This provides a comprehensive description of the impact of CD8β255R1 infusion on the immunological composition of the host, when compared to an isotype matched control IgG, while showing that the control of LASIV viremia and protection from challenge can occur even after CD8β255R1 administration.ImportanceStudies of SIV-infected macaques that deplete CD8+ T cellsin vivowith monoclonal antibodies have provided compelling evidence for their direct antiviral role. These studies utilized CD8α-specific mAbs that target both the major (CD8αβ+) and minor (CD8αα+) populations of CD8+ T cells, but additionally deplete non-CD8+ T cell populations that express CD8α, such as NK cells and γδ T cells. In the current study, we administered the CD8β-specific depleting mAb CD8β255R1 to cynomolgus macaques chronically infected with a LASIV to selectively deplete CD8αβ+ T cells without removing CD8αα+ lymphocytes. We evaluated the impact on control of virus replication and protection from pathogenic SIVmac239 challenge. These results underscore the utility of CD8β255R1 for studying the direct contribution of CD8αβ+ T cells in various disease states.

scholarly journals FoxP3+ CD25+ CD8+ T-Cell Induction during Primary Simian Immunodeficiency Virus Infection in Cynomolgus Macaques Correlates with Low CD4+ T-Cell Activation and High Viral Load

2007 ◽  
Vol 81 (24) ◽  
pp. 13444-13455 ◽  
Author(s):  
Ingrid Karlsson ◽  
Benoît Malleret ◽  
Patricia Brochard ◽  
Benoît Delache ◽  
Julien Calvo ◽  
...  
Keyword(s):  
T Cells ◽  
Viral Load ◽  
T Cell ◽  
T Cell Activation ◽  
Chronic Infection ◽  
Primary Infection ◽  
Plasma Viral Load ◽  
Cell Activation ◽  
Immunodeficiency Virus ◽  
Cynomolgus Macaques

ABSTRACT The early immune response fails to prevent the establishment of chronic human immunodeficiency virus (HIV) infection but may influence viremia during primary infection, thereby possibly affecting long-term disease progression. CD25+ FoxP3+ regulatory T cells may contribute to HIV/simian immunodeficiency virus (SIV) pathogenesis by suppressing efficient antiviral responses during primary infection, favoring high levels of viral replication and the establishment of chronic infection. In contrast, they may decrease immune activation during chronic infection. CD4+ regulatory T cells have been studied in the most detail, but CD8+ CD25+ FoxP3+ T cells also have regulatory properties. We monitored the dynamics of CD25+ FoxP3+ T cells during primary and chronic SIVmac251 infection in cynomolgus macaques. The number of peripheral CD4+ CD25+ FoxP3+ T cells paralleled that of memory CD4+ T cells, with a rapid decline during primary infection followed by a rebound to levels just below baseline and gradual depletion during the course of infection. No change in the proportion of CD25+ FoxP3+ T cells was observed in peripheral lymph nodes. A small number of CD4+ CD25+ FoxP3+ T cells at set point was associated with a high plasma viral load. In contrast, peripheral CD8+ CD25+ FoxP3+ T cells were induced a few days after peak plasma viral load during primary infection. The number of these cells was positively correlated with viral load and negatively correlated with CD4+ T-cell activation, SIV antigen-specific proliferative responses during primary infection, and plasma viral load at set point, with large numbers of CD8+ CD25+ FoxP3+ T cells being indicative of a poor prognosis.

scholarly journals ALT-803 Transiently Reduces Simian Immunodeficiency Virus Replication in the Absence of Antiretroviral Treatment

2017 ◽  
Vol 92 (3) ◽  
Author(s):  
Amy L. Ellis-Connell ◽  
Alexis J. Balgeman ◽  
Katie R. Zarbock ◽  
Gabrielle Barry ◽  
Andrea Weiler ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Nk Cells ◽  
Simian Immunodeficiency Virus ◽  
Nk Cell ◽  
Cell Populations ◽  
Viral Loads ◽  
The Third ◽  
Immunodeficiency Virus

ABSTRACTDeveloping biological interventions to control human immunodeficiency virus (HIV) replication in the absence of antiretroviral therapy (ART) could contribute to the development of a functional cure. As a potential alternative to ART, the interleukin-15 (IL-15) superagonist ALT-803 has been shown to boost the number and function of HIV-specific CD8+T and NK cell populationsin vitro. Four simian immunodeficiency virus (SIV)-positive rhesus macaques, three of whom possessed major histocompatibility complex alleles associated with control of SIV and all of whom had received SIV vaccine vectors that had the potential to elicit CD8+T cell responses, were given ALT-803 in three treatment cycles. The first and second cycles of treatment were separated by 2 weeks, while the third cycle was administered after a 29-week break. ALT-803 transiently elevated the total CD8+effector and central memory T cell and NK cell populations in peripheral blood, while viral loads transiently decreased by ∼2 logs in all animals. Virus suppression was not sustained as T cells became less responsive to ALT-803 and waned in numbers. No effect on viral loads was observed in the second cycle of ALT-803, concurrent with downregulation of the IL-2/15 common γC and β chain receptors on both CD8+T cells and NK cells. Furthermore, populations of immunosuppressive T cells increased during the second cycle of ALT-803 treatment. During the third treatment cycle, responsiveness to ALT-803 was restored. CD8+T cells and NK cells increased again 3- to 5-fold, and viral loads transiently decreased again by 1 to 2 logs.IMPORTANCEOverall, our data show that ALT-803 has the potential to be used as an immunomodulatory agent to elicit effective immune control of HIV/SIV replication. We identify mechanisms to explain why virus control is transient, so that this model can be used to define a clinically appropriate treatment regimen.

scholarly journals Distinct contributions of CD4+ T cell subsets in hepatic ischemia/reperfusion injury

2009 ◽  
Vol 296 (5) ◽  
pp. G1054-G1059 ◽  
Author(s):  
Satoshi Kuboki ◽  
Nozomu Sakai ◽  
Johannes Tschöp ◽  
Michael J. Edwards ◽  
Alex B. Lentsch ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Nk Cells ◽  
Ischemia Reperfusion ◽  
Γδ T Cells ◽  
Nkt Cells ◽  
T Cell Subsets ◽  
Wild Type ◽  
Hepatic Ischemia ◽  
Hepatic Ischemia Reperfusion

Helper T cells are known to mediate hepatic ischemia/reperfusion (I/R) injury. However, the precise mechanisms and subsets of CD4+ T cells that contribute to this injury are still controversial. Therefore, we sought to determine the contributions of different CD4+ T cell subsets during hepatic I/R injury. Wild-type, OT-II, or T cell receptor (TCR)-δ-deficient mice were subjected to 90 min of partial hepatic ischemia followed by 8 h of reperfusion. Additionally, wild-type mice were pretreated with anti-CD1d, -NK1.1, or -IL-2R-α antibodies before I/R injury. OT-II mice had diminished liver injury compared with wild-type mice, implicating that antigen-dependent activation of CD4+ T cells through TCRs is involved in hepatic I/R injury. TCR-δ knockout mice had decreased hepatic neutrophil accumulation, suggesting that γδ T cells regulate neutrophil recruitment. We found that natural killer T (NKT) cells, but not NK cells, contribute to hepatic I/R injury via CD1d-dependent activation of their TCRs, as depletion of NKT cells by anti-CD1d antibody or depletion of both NKT cells and NK cells by anti-NK1.1 attenuated liver injury. Although regulatory T cells (Treg) are known to suppress T cell-dependent inflammation, depletion of Treg cells had little effect on hepatic I/R injury. The data suggest that antigen-dependent activation of CD4+ T cells contributes to hepatic I/R injury. Among the subsets of CD4+ T cells, it appears that γδ T cells contribute to neutrophil recruitment and that NKT cells directly injure the liver. In contrast, NK cells and Treg have little effects on hepatic I/R injury.

scholarly journals B cell, CD8+ T cell and gamma delta T cell infiltration alters alveolar immune cell homeostasis in HIV-infected Malawian adults

2018 ◽  
Vol 2 ◽  
pp. 105 ◽  
Author(s):  
Andrew Mwale ◽  
Annemarie Hummel ◽  
Leonard Mvaya ◽  
Raphael Kamng'ona ◽  
Elizabeth Chimbayo ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Hiv Infection ◽  
Immune Cell ◽  
Cell Populations ◽  
Monocyte Subset ◽  
Gamma Delta ◽  
Cell Homeostasis ◽  
Tract Infections ◽  
The Impact

Background: HIV infection is associated with increased risk to lower respiratory tract infections (LRTI). However, the impact of HIV infection on immune cell populations in the lung is not well defined. We sought to comprehensively characterise the impact of HIV infection on immune cell populations in the lung. Methods: Twenty HIV-uninfected controls and 17 HIV-1 infected ART-naïve adults were recruited from Queen Elizabeth Central Hospital, Malawi. Immunophenotyping of lymphocyte and myeloid cell populations was done on bronchoalveolar lavage fluid and peripheral blood cells. Results: We found that the numbers of CD8 + T cells, B cells and gamma delta T cells were higher in BAL fluid of HIV-infected adults compared to HIV-uninfected controls (all p<0.05). In contrast, there was no difference in the numbers of alveolar CD4 + T cells in HIV-infected adults compared to HIV-uninfected controls (p=0.7065). Intermediate monocytes were the predominant monocyte subset in BAL fluid (HIV-, 63%; HIV+ 81%), while the numbers of classical monocytes was lower in HIV-infected individuals compared to HIV-uninfected adults (1 × 10 5 vs. 2.8 × 10 5 cells/100ml of BAL fluid, p=0.0001). The proportions of alveolar macrophages and myeloid dendritic cells was lower in HIV-infected adults compared to HIV-uninfected controls (all p<0.05). Conclusions: Chronic HIV infection is associated with broad alteration of immune cell populations in the lung, but does not lead to massive depletion of alveolar CD4 + T cells. Disruption of alveolar immune cell homeostasis likely explains in part the susceptibility for LRTIs in HIV-infected adults.

scholarly journals Vγ9Vδ2 T Cells: Can We Re-Purpose a Potent Anti-Infection Mechanism for Cancer Therapy?

Cells ◽  
2020 ◽  
Vol 9 (4) ◽  
pp. 829 ◽  
Author(s):  
Klaus-Peter Künkele ◽  
Daniela Wesch ◽  
Hans-Heinrich Oberg ◽  
Martin Aichinger ◽  
Verena Supper ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Tumor Therapy ◽  
Γδ T Cells ◽  
Host Cells ◽  
Advantages And Disadvantages ◽  
Therapeutic Concepts ◽  
Vγ9vδ2 T Cells ◽  
The Impact

Cancer therapies based on in vivo stimulation, or on adoptive T cell transfer of Vγ9Vδ2 T cells, have been tested in the past decades but have failed to provide consistent clinical efficacy. New, promising concepts such as γδ Chimeric Antigen Receptor (CAR) -T cells and γδ T-cell engagers are currently under preclinical evaluation. Since the impact of factors, such as the relatively low abundance of γδ T cells within tumor tissue is still under investigation, it remains to be shown whether these effector T cells can provide significant efficacy against solid tumors. Here, we highlight key learnings from the natural role of Vγ9Vδ2 T cells in the elimination of host cells bearing intracellular bacterial agents and we translate these into the setting of tumor therapy. We discuss the availability and relevance of preclinical models as well as currently available tools and knowledge from a drug development perspective. Finally, we compare advantages and disadvantages of existing therapeutic concepts and propose a role for Vγ9Vδ2 T cells in immune-oncology next to Cluster of Differentiation (CD) 3 activating therapies.

scholarly journals Expansion of Simian Immunodeficiency Virus (SIV)-Specific CD8 T Cell Lines from SIV-Naive Mauritian Cynomolgus Macaques for Adoptive Transfer

2015 ◽  
Vol 89 (19) ◽  
pp. 9748-9757 ◽  
Author(s):  
Mariel S. Mohns ◽  
Justin M. Greene ◽  
Brian T. Cain ◽  
Ngoc H. Pham ◽  
Emma Gostick ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Simian Immunodeficiency Virus ◽  
Cell Lines ◽  
Cd8 T Cells ◽  
Adoptive Transfer ◽  
Cd8 T Cell ◽  
Immunodeficiency Virus ◽  
Cynomolgus Macaques ◽  
Transfer Strategies

ABSTRACTCD8 T cells play a crucial role in the control of human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV). However, the specific qualities and characteristics of an effective CD8 T cell response remain unclear. Although targeting breadth, cross-reactivity, polyfunctionality, avidity, and specificity are correlated with HIV control, further investigation is needed to determine the precise contributions of these various attributes to CD8 T cell efficacy. We developed protocols for isolating and expanding SIV-specific CD8 T cells from SIV-naive Mauritian cynomolgus macaques (MCM). These cells exhibited an effector memory phenotype, produced cytokines in response to cognate antigen, and suppressed viral replicationin vitro. We further cultured cell lines specific for four SIV-derived epitopes, Nef103–111RM9, Gag389–394GW9, Env338–346RF9, and Nef254–262LT9. These cell lines were up to 94.4% pure, as determined by major histocompatibility complex (MHC) tetramer analysis. After autologous transfer into two MCM recipients, expanded CD8 T cells persisted in peripheral blood and lung tissue for at least 24 weeks and trafficked to multiple extralymphoid tissues. However, these cells did not impact the acute-phase SIV load after challenge compared to historic controls. The expansion and autologous transfer of SIV-specific T cells into naive animals provide a unique model for exploring cellular immunity and the control of SIV infection and facilitate a systematic evaluation of therapeutic adoptive transfer strategies for eradication of the latent reservoir.IMPORTANCECD8 T cells play a crucial role in the control of human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV). Autologous adoptive transfer studies followed by SIV challenge may help define the critical elements of an effective T cell response to HIV and SIV infection. We developed protocols for isolating and expanding SIV-specific CD8 T cells from SIV-naive Mauritian cynomolgus macaques. This is an important first step toward the development of autologous transfer strategies to explore cellular immunity and potential therapeutic applications in the SIV model.

719 CD122-directed interleukin-2 complexes and αPD-L1 differentially require innate and adaptive immunity to treat local and metastatic bladder cancer

2020 ◽  
Vol 8 (Suppl 3) ◽  
pp. A761-A761
Author(s):  
Ryan Reyes ◽  
Yilun Deng ◽  
Deyi Zhang ◽  
Niannian Ji ◽  
Neelam Mukherjee ◽  
...  
Keyword(s):  
Bladder Cancer ◽  
T Cells ◽  
T Cell ◽  
Nk Cells ◽  
San Antonio ◽  
Interleukin 2 ◽  
Γδ T Cells ◽  
List Type ◽  
Γδ T Cell

BackgroundαPD-L1 bladder cancer (BC) immunotherapy is effective in <30% of cases.1 To address the large αPD-L1-unresponsive subset of patients, we tested αIL-2/IL-2 complexes (IL-2c) that block IL-2 from binding high-affinity IL-2Rα (CD25) for preferential IL-2Rβ (CD122) binding.2 Immunosuppressive regulatory T cells capture IL-2 by CD25 whereas antitumor CD8+ T, γδ T, and NK cells use CD122. We hypothesized that the tumor microenvironment, including local immune cells in primary versus metastatic BC, differentially affects immunotherapy responses and that IL-2c effects could differ from, and thus complement αPD-L1.MethodsWe used PD-L1+ mouse BC cell lines MB49 and MBT-2, for orthotopic, intravesical (i.e., in bladder) and intravenous challenge studies of local versus lung metastatic BC.ResultsαPD-L1 or IL-2c alone reduced tumor burden and extended survival in local MB49 and MBT-2. Using in vivo cell depletions, we found that γδ T cells and NK cells, but strikingly not CD8+ T cells, were necessary for IL-2c efficacy in bladder. We confirmed γδ T cell requirements for IL-2c, but not αPD-L1 efficacy in γδ T cell-null TCRδKO mice. TCRβKO conventional T cell-null mice exhibited IL-2c, but not αPD-L1 responsiveness for orthotopic BC treatment. Neither agent alone treated lung metastatic MB49 or MBT-2 but the drug combination improved survival in both tumor models. Combination treatment effects in lungs were distinct from bladder, requiring CD8+ T and NK cells, but not γδ T cells.ConclusionsBC immunotherapy effects differ by anatomic compartment and use distinct mechanisms to treat primary and metastatic BC. CD122-directed IL-2 is a promising BC immunotherapy strategy, and IL-2c is a candidate mediator through innate immune effects. αPD-L1 could improve IL-2c efficacy by engagement of adaptive immune responses including to improve metastatic disease treatment efficacy.Ethics ApprovalAll procedures involving animals in this study were approved by the UT Health San Antonio Institutional Animal Care and Use Committee (IACUC) and conducted in accordance with UT Health San Antonio Department of Laboratory Animal Resources standards.ReferencesShah AY, Gao J, Siefker-Radtke AO. Five new therapies or just one new treatment? A critical look at immune checkpoint inhibition in urothelial cancer: Future Medicine, 2017.Arenas-Ramirez N, Zou C, Popp S, et al. Improved cancer immunotherapy by a CD25-mimobody conferring selectivity to human interleukin-2. Science translational medicine 2016;8(367):367ra166-367ra166.

NK Cells Suppress Gvhd by Directly Inhibiting Activated Alloreactive T Cells through An NKG2D-Mediated Mechanism

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 61-61 ◽  
Author(s):  
Janelle A Olson ◽  
Dennis B Leveson-Gower ◽  
Jeanette Baker ◽  
Andreas Beilhack ◽  
Robert Negrin
Keyword(s):  
T Cells ◽  
T Cell ◽  
Lymph Nodes ◽  
Nk Cells ◽  
Nk Cell ◽  
Cell Transplant ◽  
Donor Strain ◽  
Specific Lysis ◽  
Donor T Cells ◽  
The Impact

Abstract Natural Killer (NK) cells have the ability to suppress graft-versus-host disease (GVHD) while inducing a graft-versus-tumor response (GVT) following murine allogeneic bone marrow transplantation (BMT). Prior studies have shown that NK cells suppress GVHD by eliminating recipient dendritic cells. To assess additional potential mechanisms of GVHD suppression we evaluated the impact of donor NK cells on GVHD-inducing donor T cells. Interleukin-2 activated allogeneic NK cells isolated from C57Bl6 (H-2b) or FVB (H-2q) animals were transplanted along with T cell-depleted bone marrow (TCD-BM) into lethally irradiated BALB/c (H-2d) mice, followed 2 days later by luciferase-expressing CD4+ and CD8+ conventional T cells (Tcon) from the same donor strain (Tcon+NK group). Control mice received TCD-BM on day 0, and luciferase-expressing T cells on day 2 after transplant (Tcon group). Bioluminescence imaging of Tcon+NK mice revealed a significantly lower T cell bioluminescent signal compared to Tcon mice (p=0.01 on day 5 post T cell transplant). We assessed the impact of NK cells on donor T cell activation and proliferation. CFSE proliferation analysis of alloreactive CD4 and CD8 T cells reisolated on day 4 post transplant showed a decreased percentage of dividing donor T cells in the Tcon+NK group. A reduced percentage of T cells in the Tcon+NK group as compared to the Tcon group expressed the T cell activation marker CD25 (11% and 49%, respectively, among donor CD4) and a reduced percentage of T cells from the Tcon+NK group down-regulated CD62L. Reisolated donor T cell numbers were reduced in the Tcon+NK mice compared to Tcon control mice. The impact of donor NK cells on donor Tcon function was addressed by intracellular cytokine staining. Fewer donor T cells reisolated from the spleen and lymph nodes of Tcon+NK mice produced the proinflammatory cytokines IFN-γ and IL-2 on day 3 after transplant. These observations can be explained by an NK cell-mediated induction of apoptosis in the donor Tcon. T cells reisolated from the peripheral lymph nodes of Tcon+NK animals at day 4 post transplant stained higher for the TUNEL apoptosis marker than those from Tcon mice (p&lt;0.0001 for CD4 and CD8). To determine if this increase in apoptosis was due to a direct interaction between the donor T cells and NK cells, donor Tcon were reisolated from transplanted mice and used as targets in a killing assay. We demonstrated direct, specific lysis of these reisolated T cells by activated NK cells, both of which are from the donor strain and thus syngeneic to each other. Donor T cells reisolated from the lymph nodes of transplanted mice upregulated the NKG2D ligand Rae1γ as compared to naïve T cells, as shown by FACS. Further, use of an NKG2D-blocking antibody decreased the specific lysis of donor Tcon reisolated from the lymph nodes by activated NK cells in the in vitro killing assay, compared to an isotype control antibody (p=0.004). These data indicate that NK cells are causing direct, NKG2D-dependent lysis of alloreactive donor T cells in vivo during GVHD induction. Recent data from our laboratory has shown a lack of NKG2D ligand expression on GVHD target tissues in irradiated recipient mice. The tissue-specific expression of NKG2D ligands may explain why allogeneic NK cells do not cause GVHD but do impact donor T cells. We further investigated the ability of T cells in this model to elicit a GVT effect in the presence or absence of NK cells. Using a luciferase-expressing A20 lymphoma cell line, we demonstrated tumor clearance in groups receiving A20+Tcon and A20+Tcon+NK, as measured by A20 bioluminescence signal. Animals in the A20+Tcon+NK group had a lower peak bioluminescent signal than animals in the A20+Tcon group (p=0.03 on day 4 post T cell transplant), indicating an additive GVT effect of the T cells and NK cells. Thus, the T cells in this model are capable of mounting an effective GVT response. In addition to the established mechanism of NK cell-mediated elimination of recipient dendritic cells, we have demonstrated a novel mechanism of NK cell action in murine models of GVHD, whereby the donor NK cells inhibit T cell proliferation and activation and cause direct, NKG2D-mediated lysis of alloreactive donor T cells.

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