Immunopharmacodynamic response to blinatumomab in patients with relapsed/refractory B-precursor acute lymphoblastic leukemia (ALL).

2013 ◽  
Vol 31 (15_suppl) ◽  
pp. 7020-7020 ◽  
Author(s):  
Andrea Schub ◽  
Virginie Nägele ◽  
Gerhard Zugmaier ◽  
Christian Brandl ◽  
Youssef Hijazi ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
B Cell ◽  
T Cell Activation ◽  
Cell Activation ◽  
Lymphoblastic Leukemia ◽  
Granzyme B ◽  
Significant Proportion ◽  
Target Cells ◽  
Cell Counts

7020 Background: Blinatumomab is an anti-CD19/anti-CD3 bispecific T cell engager (BiTE) that induces target cell-dependent, polyclonal T cell activation and proliferation, resulting in redirected lysis of CD19+ target cells. Methods: In a phase 2 study, adult patients (N=36) with relapsed/refractory B-precursor ALL received continuous blinatumomab IV infusion for 28 days in ≤5 treatment/consolidation cycles. Whole blood and serum samples were collected throughout treatment and analyzed for lymphocyte subpopulations, cytokines, granzyme B, and blinatumomab serum concentrations. Results: Lymphocytes in all patients responded in a similar fashion. After infusion start, peripheral B cell counts dropped to ≤1 B cell/μL in <1 week and remained undetectable throughout treatment. Peripheral T cells showed a redistribution characterized by swift disappearance within the first 2-6 hrs and subsequent recovery to baseline within several days. Otherwise, T cell counts remained at least stable in most patients. In some patients even an expansion of the T cell compartments was observed, most likely due to specific proliferation of activated T cells but could not be defined as prerequisite for treatment efficacy. During the first infusion days, a significant proportion of T cells newly expressed the activation marker CD69, and the T cell effector molecule granzyme B was detectable in serum. Additionally, a transient cytokine release dominated by IL-10, IL-6 and IFN-γ was observed in most patients shortly after first infusion start, which was alleviated or absent in subsequent cycles. Blinatumomab serum steady state concentrations (mean±SD) were 198±61 pg/mL and 694±236 pg/mL at doses of 5 and 15 μg/m²/d, respectively, which is comparable to those from previous studies. Conclusions: Immunopharmacodynamic response to blinatumomab was characterized by B cell depletion, T cell activation and redistribution, and release of granzyme B and cytokines, suggesting T cell engagement according to the expected BiTE mode of action. The tested pharmacodynamic markers did not allow for predictive differentiation between patients achieving a hematologic response and those who did not. Clinical trial information: NCT01209286.

A T Cell-Engaging CD3 Recruit-Tandab Potently Kills CD19+ Tumor B Cells

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 3721-3721
Author(s):  
Eugene Zhukovsky ◽  
Uwe Reusch ◽  
Carmen Burkhardt ◽  
Stefan Knackmuss ◽  
Ivica Fucek ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Tumor Growth ◽  
B Cell ◽  
T Cell Activation ◽  
Cell Activation ◽  
Target Cells ◽  
Cytotoxicity Assays

Abstract Abstract 3721 Background: CD19 is expressed from early B cell development through differentiation into plasma cells, and is an attractive alternative to CD20 as a target for the development of therapeutic antibodies to treat B cell malignancies. T cells are potent tumor-killing effector cells that cannot be recruited by native antibodies. The CD3 RECRUIT-TandAb AFM11, a humanized bispecific tetravalent antibody with two binding sites for both CD3 and CD19, is a novel therapeutic for the treatment of NHL that harnesses the cytotoxic nature of T cells. Methods: We engineered a bispecific anti-CD19/anti-CD3e tetravalent TandAb with humanized and affinity-matured variable domains. The TandAb's binding properties, T cell-mediated cytotoxic activity, and target-mediated T cell activation were characterized in a panel of in vitro assays. In vivo efficacy was evaluated in a murine NOD/scid xenograft model reconstituted with human PBMC. Results: AFM11 mediates highly potent CD19+ tumor cell lysis in cytotoxicity assays performed on a panel of cell lines (JOK-1, Raji, Nalm-6, MEC-1, VAL, Daudi) and primary B-CLL tumors: EC50 values are in the low- to sub-picomolar range and do not correlate with the expression density of CD19 on the target cell lines. The cytotoxic activity of tetravalent AFM11 is superior to that of alternative bivalent antibody formats possessing only a single binding site for both CD19 and CD3. High affinity binding of AFM11 to CD19 and to CD3 is essential for efficacious T cell recruitment. Both CD8+ and CD4+ T cells mediate cytotoxicity however the former exhibit much faster killing. We observe that AFM11 displays similar cytotoxic efficacy at different effector to target ratios (from 5:1 to 1:5) in cytotoxicity assays; this suggests that T cells are engaged in the serial killing of CD19+ target cells. In the absence of CD19+ target cells in vitro, AFM11 does not elicit T cell activation as manifested by cytokine release (from a panel of ten cytokines associated with T cell activation), their proliferation, or their expression of activation markers. AFM11 activates T cells exclusively in the presence of its targets and mediates lysis of CD19+ cells while sparing antigen-negative bystanders. In the absence of CD19+ target cells, AFM11 concentrations in excess of 500-fold over EC50 induce down-modulation of the CD3/TCR complex. Yet, AFM11-treated T cells can be re-engaged for target cell lysis. All of these features of AFM11-induced T cell activation may contribute additional safety without compromising its efficacy. In vivo AFM11 demonstrates a robust dose-dependent inhibition of subcutaneous Raji tumors in mice. At 5 mg/kg AFM11 demonstrates a complete suppression of tumor growth, and even at 5 ug/kg tumor growth is reduced by 60%. Moreover, we observe that a single administration of AFM11 produces inhibition of tumor growth similar to that of 5 consecutive administrations. Conclusions: In summary, our in vitro and in vivo experiments with AFM11 demonstrate the high potency and efficacy of its anti-tumor cytotoxicity. Thus, AFM11 is a novel highly efficacious drug candidate for the treatment of B cell malignancies with an advantageous safety profile. Disclosures: Zhukovsky: Affimed Therapeutics AG: Employment, Equity Ownership. Reusch:Affimed Therapeutics AG: Employment. Burkhardt:Affimed Therapeutics AG: Employment. Knackmuss:Affimed Therapeutics AG: Employment. Fucek:Affimed Therapeutics AG: Employment. Eser:Affimed Therapeutics AG: Employment. McAleese:Affimed Therapeutics AG: Employment. Ellwanger:Affimed Therapeutics AG: Employment.

High affinity CD3 RECRUIT TandAb for T cell-mediated lysis of CD19+ tumor B cells.

2012 ◽  
Vol 30 (15_suppl) ◽  
pp. 8059-8059 ◽  
Author(s):  
Eugene Zhukovsky ◽  
Uwe Reusch ◽  
Carmen Burkhardt ◽  
Stefan Knackmuss ◽  
Ivica Fucek ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
B Cell ◽  
T Cell Activation ◽  
Cell Activation ◽  
In Vitro Assays ◽  
Target Cells ◽  
B Cell Malignancies ◽  
High Affinity

8059 Background: CD19 is expressed from early B cell development to the differentiation into plasma cells and is an attractive target for B cell malignancies either lacking CD20 expression or refractory to anti-CD20 antibody therapies. T cells are potent tumor killing effector cells that are not recruited by native antibodies. The CD3 RECRUIT-TandAb AFM11, a human bispecific tetravalent antibody with two binding sites for both CD3 and CD19, is a novel therapeutic for the treatment of NHL that harnesses the cytotoxic nature of T cells. Methods: A bispecific anti-CD19/anti-CD3 tetravalent TandAb with humanized and affinity matured variable domains was constructed. The TandAb’s binding, T-cell mediated cytotoxic activity, and cytokine release were characterized in a panel of in vitro assays. In vivo efficacy was evaluated in a murine NOD/scid xenograft model reconstituted with human PBMC. Results: AFM11 mediates highly potent target tumor cell lysis in cytotoxicity assays: EC50 values are low to sub-picomolar range in a panel of CD19+ cell lines and primary B-CLL tumor cells. The cytotoxic activity of tetravalent AFM11 is superior to that of alternative bivalent antibody formats possessing only a single binding site for both CD19 and CD3. High affinity binding of AFM11 to CD19, and more so to CD3 (low to sub-nanomolar Kd), is essential for efficacious T cell recruitment. The high affinity bivalent binding of AFM11 to CD3 does not trigger T cell activation in the absence of CD19+ target cells in functional in vitro assays. AFM11 activates T cells only in the presence of its targets and mediates lysis while sparing antigen-negative bystanders. AFM11 induces down-modulation of the CD3/TCR complex in the absence of target cells and at high concentrations. Also, AFM11-treated T cells can be re-engaged for target cell lysis. These features of AFM11-induced T cell activation may contribute additional safety with no compromise of efficacy. Finally, AFM11 demonstrates a robust dose-dependent inhibition of subcutaneous Raji tumors in mice. Conclusions: AFM11 is a novel highly efficacious drug candidate for the treatment of B cell malignancies with an advantageous safety profile.

scholarly journals Targeting CD20+ Relapsed Refractory B Cell Lymphoma with ACTR087, Antibody-Coupled T-Cell Receptor (ACTR) Engineered Autologous T Cells, in Combination with Rituximab

Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 3512-3512 ◽  
Author(s):  
Heather A Huet ◽  
Casey Judge ◽  
R. Anthony Barnitz ◽  
Ryan Boomer ◽  
Kathleen McGinness ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
B Cell ◽  
T Cell Activation ◽  
Cell Activation ◽  
Cell Lymphoma ◽  
Phase 1 ◽  
B Cell Lymphoma ◽  
T Cell Response ◽  
Target Cells

Abstract The Antibody-Coupled T-cell Receptor (ACTR) platform is a universal engineered T cell therapy developed to mediate anti-tumor activity in combination with tumor-targeting antibodies. The ACTR construct is composed of the extracellular domain of CD16 (FCGR3A; high-affinity V158 variant) linked to CD3ζ signaling and 41BB co-stimulatory domains. ACTR-expressing T cells recognize antibodies bound to antigen on the surface of target cells, and this receptor engagement results in T cell activation, proliferation, and cytotoxic attack of target cells. Previous preclinical research has demonstrated that ACTR T cells elicit tumor cell cytotoxicity in combination with rituximab, trastuzumab, and hu14.18K322A against CD20, HER2, and GD2 expressing tumor cell lines, respectively (Kudo et al., Cancer Res 2014; 74:93-103). The safety of ACTR T cells in combination with rituximab for subjects with B-cell malignancies is currently being explored in a pilot phase 1 clinical study (ATTCK-20) sponsored by National University Hospital, Singapore. Electroporation of mRNA is being used to deliver the ACTR transgene to study subjects' T-cells, creating a transiently active form of the therapy. In this study, we present non-clinical data supporting the first-in-human clinical trial of ACTR087, the ACTR transgene (CD16V-41BB-CD3ζ) delivered by γ-retrovirus to human T cells, in combination with rituximab in relapsed refractory B cell lymphoma (NCT02776813). In vitro data demonstrate that in the absence of rituximab or in the presence of non-targeting antibodies, no increase in cytotoxicity is observed, demonstrating that ACTR signaling is target- and antibody-specific. ACTR T cells proliferate in response to rituximab-bound lymphoma cells, but this proliferation is antibody-dependent and self-limiting in the absence of antibody. In vivo efficacy and pharmacokinetic studies further support the dependence on adequate rituximab exposure for ACTR T cell response, suggesting that ACTR T cell activity can be modulated by antibody dose and schedule, which is a potential advantage over other chimeric antigen receptor (CAR) T cell therapies. Additional in vitro studies were conducted to explore the effects of potential interventional antibody therapies used to mitigate adverse events reported for CAR-T therapies in similar patient populations. These include tocilizumab, used to treat cytokine release syndrome (CRS), and intravenous immunoglobulin (IVIG), used to treat hypogammaglobulinemia complicated by recurrent sinopulmonary infections. At therapeutically relevant doses, rituximab was able to compete with substantial excess IVIG to induce a CD20-specific ACTR T cell response. Importantly, IVIG did not induce greater cytokine release from ACTR T cells. Likewise, tocilizumab did not mediate ACTR T cell activation or cytotoxicity of IL-6R+ target cells, consistent with reports that tocilizumab is ADCC-deficient. These data illustrate an important principal of Fc receptor biology: not all IgG1 antibodies mediate ADCC despite binding to CD16, and support the considered use in the presence of ACTR T cells under certain circumstances. Taken together, these non-clinical data demonstrate the specificity and versatility of the ACTR T cell therapeutic approach to target diverse cancer antigens. The Phase 1 study (ATTCK20-2, ClinicalTrial.gov No. NCT02776813) of ACTR087 plus rituximab in subjects with relapsed or refractory CD20-positive B cell lymphoma is a multi-center, single-arm, open-label study evaluating the safety and efficacy of an autologous T-cells, culture expanded and transduced ex vivo with a γ-retrovirus containing an ACTR expression construct (CD16V-41BB-CD3ζ). Subjects who meet eligibility requirements with histologically-confirmed relapsed or refractory CD20+ B-cell lymphoma of one of the following types are eligible for the study: DLBCL, MCL, PMBCL, Gr3b-FL, TH-FL. Following a conditioning regimen with fludarabine and cyclophosphamide, and prior to ACTR087 infusion, subjects will receive rituximab at the standard IV clinical dose, 375 mg/m2. Subjects may receive up to 7 additional cycles of rituximab 375 mg/m2 at 3-week intervals and continuing as long as they show evidence of response. Disclosures Huet: Unum Therapeutics: Employment. Judge:Unum Therapeutics: Employment. Barnitz:Unum Therapeutics: Employment. Boomer:Unum Therapeutics: Employment. McGinness:Unum Therapeutics: Employment. Shin:Unum Therapeutics: Employment. Cheema:Unum Therapeutics: Employment. Whiteman:Unum Therapeutics: Employment. Schultes:Unum Therapeutics: Employment. Ranger:Unum Therapeutics: Employment. Cao:Unum Therapeutics: Employment. Hodge:Unum Therapeutics: Employment. Vasconcelles:Unum Therapeutics: Employment. Ettenberg:Unum Therapeutics: Employment.

scholarly journals Costimulation by B7 Modulates Specificity of Cytotoxic T Lymphocytes: A Missing Link That Explains Some Bystander T Cell Activation

1997 ◽  
Vol 186 (10) ◽  
pp. 1787-1791 ◽  
Author(s):  
Pan Zheng ◽  
Yang Liu
Keyword(s):  
Cell Proliferation ◽  
T Cells ◽  
Influenza Virus ◽  
T Cell ◽  
T Cell Activation ◽  
Cell Activation ◽  
T Cell Proliferation ◽  
Target Cells ◽  
Cell Proliferation And Differentiation ◽  
Proliferation And Differentiation

It has been proposed that some bystander T cell activation may in fact be due to T cell antigen receptor (TCR) cross-reactivity that is too low to be detected by the effector cytotoxic T lymphocyte (CTL). However, this hypothesis is not supported by direct evidence since no TCR ligand is known to induce T cell proliferation and differentiation without being recognized by the effector CTL. Here we report that transgenic T cells expressing a T cell receptor to influenza virus A/NT/68 nucleoprotein (NP) 366-374:Db complexes clonally expand and become effector CTLs in response to homologous peptides from either A/PR8/34 (H1N1), A/AA/60 (H2N2), or A/NT/68 (H3N2). However, the effector T cells induced by each of the three peptides kill target cells pulsed with NP peptides from the H3N2 and H2N2 viruses, but not from the H1N1 virus. Thus, NP366–374 from influenza virus H1N1 is the first TCR ligand that can induce T cell proliferation and differentiation without being recognized by CTLs. Since induction of T cell proliferation was mediated by antigen-presenting cells that express costimulatory molecules such as B7, we investigated if cytolysis of H1N1 NP peptide–pulsed targets can be restored by expressing B7-1 on the target cells. Our results revealed that this is the case. These data demonstrated that costimulatory molecule B7 modulates antigen specificity of CTLs, and provides a missing link that explains some of the bystander T cell activation.

107 Effects of IL-2 and IL-15 on the proliferative and antitumor capacities of allogeneic CD20 CAR-engineered γδ T cells in a 3D B cell lymphoma spheroid assay

2020 ◽  
Vol 8 (Suppl 3) ◽  
pp. A119-A119
Author(s):  
Lu Bai ◽  
Kevin Nishimoto ◽  
Mustafa Turkoz ◽  
Marissa Herrman ◽  
Jason Romero ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
B Cell ◽  
T Cell Activation ◽  
Cell Activation ◽  
Cytokine Production ◽  
Γδ T Cells ◽  
Γδ T Cell ◽  
Car T

BackgroundAutologous chimeric antigen receptor (CAR) T cells have been shown to be efficacious for the treatment of B cell malignancies; however, widespread adoption and application of CAR T cell products still face a number of challenges. To overcome these challenges, Adicet Bio is developing an allogeneic γδ T cell-based CAR T cell platform, which capitalizes on the intrinsic abilities of Vδ1 γδ T cells to recognize and kill transformed cells in an MHC-unrestricted manner, to migrate to epithelial tissues, and to function in hypoxic conditions. To gain a better understanding of the requirements for optimal intratumoral CAR Vδ1 γδ T cell activation, proliferation, and differentiation, we developed a three-dimensional (3D) tumor spheroid assay, in which tumor cells acquire the structural organization of a solid tumor and establish a microenvironment that has oxygen and nutrient gradients. Moreover, through the addition of cytokines and/or tumor stromal cell types, the spheroid microenvironment can be modified to reflect hot or cold tumors. Here, we report on the use of a 3D CD20+ Raji lymphoma spheroid assay to evaluate the effects of IL-2 and IL-15, positive regulators of T cell homeostasis and differentiation, on the proliferative and antitumor capacities of CD20 CAR Vδ1 γδ T cells.MethodsMolecular, phenotypic, and functional profiling were performed to characterize the in vitro dynamics of the intraspheroid CD20 CAR Vδ1 γδ T cell response to target antigen in the presence of IL-2, IL-15, or no added cytokine.ResultsWhen compared to no added cytokine, the addition of IL-2 or IL-15 enhanced CD20 CAR Vδ1 γδ T cell activation, proliferation, survival, and cytokine production in a dose-dependent manner but were only able to alter the kinetics of Raji cell killing at low effector to target ratios. Notably, differential gene expression analysis using NanoString nCounter® Technology confirmed the positive effects of IL-2 or IL-15 on CAR-activated Vδ1 γδ T cells as evidenced by the upregulation of genes involved in activation, cell cycle, mitochondrial biogenesis, cytotoxicity, and cytokine production.ConclusionsTogether, these results not only show that the addition of IL-2 or IL-15 can potentiate CD20 CAR Vδ1 γδ T cell activation, proliferation, survival, and differentiation into antitumor effectors but also highlight the utility of the 3D spheroid assay as a high throughput in vitro method for assessing and predicting CAR Vδ1 γδ T cell activation, proliferation, survival, and differentiation in hot and cold tumors.

scholarly journals Brucella Peptide Cross-Reactive MHC I Presentation Activates SIINFEKL-Specific TCR Expressing T Cells

2018 ◽  
Author(s):  
Jerome S. Harms ◽  
Mike Khan ◽  
Cherisse Hall ◽  
Gary A. Splitter ◽  
E. Jane Homan ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
T Cell Activation ◽  
Pathogenic Bacteria ◽  
Cell Activation ◽  
Immune Surveillance ◽  
Cross Reactivity ◽  
Near Neighbor ◽  
Target Cells ◽  
Mhc I

ABSTRACTBrucella spp are intracellular pathogenic bacteria remarkable in their ability to escape immune surveillance and therefore inflict a state of chronic disease within the host. To enable further immune response studies, Brucella were engineered to express the well characterized chicken ovalbumin (OVA). Surprisingly, we found that CD8 T cells bearing T cell receptors (TCR) nominally specific for the OVA peptide SIINFEKL (OT-1) reacted to parental Brucella-infected targets as well as OVA-expressing Brucella variants in cytotoxicity assays. Furthermore, splenocytes from Brucella immunized mice produced IFN-γ and exhibited cytotoxicity in response to SIINFEKL-pulsed target cells. To determine if the SIINFEKL-reactive OT-1 TCR could be cross-reacting to Brucella peptides, we searched the Brucella proteome using an algorithm to generate a list of near-neighbor nonamer peptides that would bind to H2Kb. Selecting five Brucella peptide candidates, along with controls, we verified that several of these peptides mimicked SIINFEKL resulting in T cell activation through the “SIINFEKL-specific” TCR. Activation was dependent on peptide concentration as well as sequence. Our results underscore the complexity and ubiquity of cross-reactivity in T cell recognition. This cross-reactivity may enable microbes such as Brucella to escape immune surveillance by presenting peptides similar to the host, and may also lead to the activation of autoreactive T cells.

scholarly journals Vector Order Determines Protection against Pathogenic Simian Immunodeficiency Virus Infection in a Triple-Component Vaccine by Balancing CD4+ and CD8+ T-Cell Responses

2017 ◽  
Vol 91 (23) ◽  
Author(s):  
Ulrike Sauermann ◽  
Antonia Radaelli ◽  
Nicole Stolte-Leeb ◽  
Katharina Raue ◽  
Massimiliano Bissa ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Immune Responses ◽  
T Cell Activation ◽  
Cell Activation ◽  
T Cell Responses ◽  
Target Cells ◽  
Aids Vaccine ◽  
Cell Responses ◽  
Antibody Titers

ABSTRACT An effective AIDS vaccine should elicit strong humoral and cellular immune responses while maintaining low levels of CD4+ T-cell activation to avoid the generation of target cells for viral infection. The present study investigated two prime-boost regimens, both starting vaccination with single-cycle immunodeficiency virus, followed by two mucosal boosts with either recombinant adenovirus (rAd) or fowlpox virus (rFWPV) expressing SIVmac239 or SIVmac251 gag/pol and env genes, respectively. Finally, vectors were switched and systemically administered to the reciprocal group of animals. Only mucosal rFWPV immunizations followed by systemic rAd boost significantly protected animals against a repeated low-dose intrarectal challenge with pathogenic SIVmac251, resulting in a vaccine efficacy (i.e., risk reduction per exposure) of 68%. Delayed viral acquisition was associated with higher levels of activated CD8+ T cells and Gag-specific gamma interferon (IFN-γ)-secreting CD8+ cells, low virus-specific CD4+ T-cell responses, and low Env antibody titers. In contrast, the systemic rFWPV boost induced strong virus-specific CD4+ T-cell activity. rAd and rFWPV also induced differential patterns of the innate immune responses, thereby possibly shaping the specific immunity. Plasma CXCL10 levels after final immunization correlated directly with virus-specific CD4+ T-cell responses and inversely with the number of exposures to infection. Also, the percentage of activated CD69+ CD8+ T cells correlated with the number of exposures to infection. Differential stimulation of the immune response likely provided the basis for the diverging levels of protection afforded by the vaccine regimen. IMPORTANCE A failed phase II AIDS vaccine trial led to the hypothesis that CD4+ T-cell activation can abrogate any potentially protective effects delivered by vaccination or promote acquisition of the virus because CD4+ T helper cells, required for an effective immune response, also represent the target cells for viral infection. We compared two vaccination protocols that elicited similar levels of Gag-specific immune responses in rhesus macaques. Only the animal group that had a low level of virus-specific CD4+ T cells in combination with high levels of activated CD8+ T cells was significantly protected from infection. Notably, protection was achieved despite the lack of appreciable Env antibody titers. Moreover, we show that both the vector and the route of immunization affected the level of CD4+ T-cell responses. Thus, mucosal immunization with FWPV-based vaccines should be considered a potent prime in prime-boost vaccination protocols.

scholarly journals Immunologic ignorance of vascular endothelial cells expressing minor histocompatibility antigen

Blood ◽  
2008 ◽  
Vol 111 (9) ◽  
pp. 4588-4595 ◽  
Author(s):  
Beatrice Bolinger ◽  
Philippe Krebs ◽  
Yinghua Tian ◽  
Daniel Engeler ◽  
Elke Scandella ◽  
...  
Keyword(s):  
T Cells ◽  
Endothelial Cells ◽  
T Cell ◽  
T Cell Activation ◽  
Cd8 T Cells ◽  
Cell Activation ◽  
Histocompatibility Antigen ◽  
Target Cells ◽  
Minor Histocompatibility Antigen

Abstract Endothelial cells (ECs) presenting minor histocompatibility antigen (mhAg) are major target cells for alloreactive effector CD8+ T cells during chronic transplant rejection and graft-versus-host disease (GVHD). The contribution of ECs to T-cell activation, however, is still a controversial issue. In this study, we have assessed the antigen-presenting capacity of ECs in vivo using a transgenic mouse model with beta-galactosidase (β-gal) expression confined to the vascular endothelium (Tie2-LacZ mice). In a GVHD-like setting with adoptive transfer of β-gal–specific T-cell receptor–transgenic T cells, β-gal expression by ECs was not sufficient to either activate or tolerize CD8+ T cells. Likewise, transplantation of fully vascularized heart or liver grafts from Tie2-LacZ mice into nontransgenic recipients did not suffice to activate β-gal–specific CD8+ T cells, indicating that CD8+ T-cell responses against mhAg cannot be initiated by ECs. Moreover, we could show that spontaneous activation of β-gal–specific CD8+ T cells in Tie2-LacZ mice was exclusively dependent on CD11c+ dendritic cells (DCs), demonstrating that mhAgs presented by ECs remain immunologically ignored unless presentation by DCs is granted.

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