OMIP‐060: 30‐Parameter Flow Cytometry Panel to Assess T Cell Effector Functions and Regulatory T Cells

2019 ◽  
Vol 95 (11) ◽  
pp. 1129-1134 ◽  
Author(s):  
Thomas Liechti ◽  
Mario Roederer
Keyword(s):  
Flow Cytometry ◽  
T Cells ◽  
T Cell ◽  
Regulatory T Cells ◽  
Effector Functions ◽  
Cell Effector

scholarly journals Type 1 diabetes progression is associated with loss of CD3+CD56+ regulatory T cells that control CD8+ T-cell effector functions

2020 ◽  
Vol 2 (2) ◽  
pp. 142-152 ◽  
Author(s):  
Giuseppe Terrazzano ◽  
Sara Bruzzaniti ◽  
Valentina Rubino ◽  
Marianna Santopaolo ◽  
Anna Teresa Palatucci ◽  
...  
Keyword(s):  
T Cells ◽  
Type 1 Diabetes ◽  
T Cell ◽  
Regulatory T Cells ◽  
Cd8 T Cell ◽  
Effector Functions ◽  
Diabetes Progression ◽  
Cell Effector

scholarly journals P08.05 Combined pharmacological targeting of adenosine 2a- and 2b-receptor enhances CAR T cell function

2021 ◽  
Vol 9 (Suppl 1) ◽  
pp. A26.2-A27
Author(s):  
M Seifert ◽  
M Benmebarek ◽  
B Cadilha ◽  
J Jobst ◽  
J Dörr ◽  
...  
Keyword(s):  
Flow Cytometry ◽  
T Cells ◽  
T Cell ◽  
Combination Therapy ◽  
Cell Function ◽  
Cytokine Secretion ◽  
Car T Cells ◽  
Car T Cell ◽  
Car T ◽  
Cell Effector

BackgroundDespite remarkable response rates mediated by anti-CD19 chimeric antigen receptor (CAR) T cells in selected B cell malignancies, CAR T cell therapy still lacks efficacy in the vast majority of tumors. A substantial limiting factor of CAR T cell function is the immunosuppressive tumor microenvironment. Among other mechanisms, the accumulation of adenosine within the tumor can contribute to disease progression by suppressing anti-tumor immune responses. Adenosine 2a- and 2b-receptor (A2A and A2B)-mediated cAMP build-up suppresses T cell effector functions. In the present study we hypothesize, that combination therapy with the selective A2A/A2B dual antagonist AB928 (etrumadenant) enhances CAR T cell efficacy.Materials and MethodsSecond generation murine (anti-EPCAM) and human (anti-MSLN) CAR constructs, containing intracellular CD28 and CD3ζ domains, were fused via overlap extension PCR cloning. Murine or human T cells were retrovirally transduced to stably express the CAR constructs. A2A/A2B signaling in CAR T cells was analyzed by phospho-specific flow cytometry of CREB (pS133)/ATF-1 (pS63). CAR T cell activation was quantified by flow cytometry and enzyme-linked immunosorbent assay (ELISA) of IFN-γ, IL-2 and TNF-α. CAR T cell proliferation was assessed by flow cytometry. CAR T cell cytotoxicity was assessed by impedance based real-time cell analysis.ResultsAB928 protected murine CAR T cells from cAMP response element-binding protein (CREB) phosphorylation in the presence of stable adenosine analogue 5′-N-ethylcarboxamidoadenosine (NECA). NECA inhibited antigen-dependent CAR T cell cytokine secretion in response to four murine tumor cell lines. CAR T cell-mediated tumor cell lysis as well as proliferation were decreased in the presence of NECA or adenosine. Importantly, AB928 fully restored CAR T cell cytotoxicity, proliferation, and cytokine secretion in a dose dependent manner. Further, AB928 also restored antigen dependent cytokine secretion of human CAR T cells in the presence of NECA.ConclusionsHere we used the A2A/A2B dual antagonist AB928 to overcome adenosine-mediated suppression of CAR T cells. We found that AB928 enhanced important CAR T cell effector functions in the presence of the adenosine analogue, suggesting that combination therapy with AB928 may improve CAR T cell efficacy. This study was limited to in vitro experiments. To confirm the relevance of our findings, this combination therapy must be further investigated in an in vivo setting.Disclosure InformationM. Seifert: None. M. Benmebarek : None. B. Cadilha : None. J. Jobst: None. J. Dörr: None. T. Lorenzini: None. D. Dhoqina: None. J. Zhang: None. J. Zhang: None. U. Schindler: E. Ownership Interest (stock, stock options, patent or other intellectual property); Modest; Amgen Inc., Arcus Biosciences. Other; Significant; Arcus Biosciences. S. Endres: None. S. Kobold: B. Research Grant (principal investigator, collaborator or consultant and pending grants as well as grants already received); Significant; Arcus Biosciences.

scholarly journals Increased frequencies of CD4+CD25high regulatory T cells in acute dengue infection

2007 ◽  
Vol 204 (5) ◽  
pp. 979-985 ◽  
Author(s):  
Kerstin Lühn ◽  
Cameron P. Simmons ◽  
Edward Moran ◽  
Nguyen Thi Phuong Dung ◽  
Tran Nguyen Bich Chau ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Regulatory T Cells ◽  
Severe Disease ◽  
Acute Infection ◽  
Dengue Infection ◽  
Hemorrhagic Fever ◽  
Severe Dengue ◽  
Effector T Cell ◽  
Cell Effector

Dengue virus infection is an increasingly important tropical disease, causing 100 million cases each year. Symptoms range from mild febrile illness to severe hemorrhagic fever. The pathogenesis is incompletely understood, but immunopathology is thought to play a part, with antibody-dependent enhancement and massive immune activation of T cells and monocytes/macrophages leading to a disproportionate production of proinflammatory cytokines. We sought to investigate whether a defective population of regulatory T cells (T reg cells) could be contributing to immunopathology in severe dengue disease. CD4+CD25highFoxP3+ T reg cells of patients with acute dengue infection of different severities showed a conventional phenotype. Unexpectedly, their capacity to suppress T cell proliferation and to secrete interleukin-10 was not altered. Moreover, T reg cells suppressed the production of vasoactive cytokines after dengue-specific stimulation. Furthermore, T reg cell frequencies and also T reg cell/effector T cell ratios were increased in patients with acute infection. A strong indication that a relative rise of T reg cell/effector T cell ratios is beneficial for disease outcome comes from patients with mild disease in which this ratio is significantly increased (P < 0.0001) in contrast to severe cases (P = 0.2145). We conclude that although T reg cells expand and function normally in acute dengue infection, their relative frequencies are insufficient to control the immunopathology of severe disease.

scholarly journals Galectin-9 expression defines exhausted T cells and impaired cytotoxic NK cells in patients with virus-associated solid tumors

2020 ◽  
Vol 8 (2) ◽  
pp. e001849
Author(s):  
Isobel Okoye ◽  
Lai Xu ◽  
Melika Motamedi ◽  
Pallavi Parashar ◽  
John W Walker ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Nk Cells ◽  
Solid Tumors ◽  
Mononuclear Cells ◽  
Cell Phenotype ◽  
Peripheral Blood Mononuclear ◽  
Effector Functions ◽  
Cell Functions ◽  
Cell Effector

BackgroundWe have previously reported that the upregulation of galectin-9 (Gal-9) on CD4+ and CD8+ T cells in HIV patients was associated with impaired T cell effector functions. Gal-9 is a ligand for T cell immunoglobulin and mucin domain-3, and its expression on T cells in cancer has not been investigated. Therefore, we aimed to investigate the expression level and effects of Gal-9 on T cell functions in patients with virus-associated solid tumors (VASTs).Methods40 patients with VASTs through a non-randomized and biomarker-driven phase II LATENT trial were investigated. Peripheral blood mononuclear cells and tumor biopsies were obtained and subjected to immunophenotyping. In this trial, the effects of oral valproate and avelumab (anti-PD-L1) was investigated in regards to the expression of Gal-9 on T cells.ResultsWe report the upregulation of Gal-9 expression by peripheral and tumor-infiltrating CD4+ and CD8+ T lymphocytes in patients with VASTs. Our results indicate that Gal-9 expression is associated with dysfunctional T cell effector functions in the periphery and tumor microenvironment (TME). Coexpression of Gal-9 with PD-1 or T cell immunoglobulin and ITIM domain (TIGIT) exhibited a synergistic inhibitory effect and enhanced an exhausted T cell phenotype. Besides, responding patients to treatment had lower Gal-9 mRNA expression in the TME. Translocation of Gal-9 from the cytosol to the cell membrane of T cells following stimulation suggests persistent T cell receptor (TCR) stimulation as a potential contributing factor in Gal-9 upregulation in patients with VASTs. Moreover, partial colocalization of Gal-9 with CD3 on T cells likely impacts the initiation of signal transduction via TCR as shown by the upregulation of ZAP70 in Gal-9+ T cells. Also, we found an expansion of Gal-9+ but not TIGIT+ NK cells in patients with VASTs; however, dichotomous to TIGIT+ NK cells, Gal-9+ NK cells exhibited impaired cytotoxic molecules but higher Interferon gamma (IFN-γ) expression.ConclusionOur data indicate that higher Gal-9-expressing CD8+ T cells were associated with poor prognosis following immunotherapy with anti-Programmed death-ligand 1 (PD-L1) (avelumab) in our patients’ cohort. Therefore, for the very first time to our knowledge, we report Gal-9 as a novel marker of T cell exhaustion and the potential target of immunotherapy in patients with VASTs.

Double Negative T Cells Influence TCR VB Variablity to Induce Allotolerance.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 759-759
Author(s):  
Zachariah A. McIver ◽  
Marcin Wlodarski ◽  
Jennifer Powers ◽  
Christine O’Keefe ◽  
Tao Jin ◽  
...  
Keyword(s):  
Flow Cytometry ◽  
T Cells ◽  
T Cell ◽  
Regulatory T Cells ◽  
Peripheral Tolerance ◽  
Double Negative ◽  
Clonal Deletion ◽  
Tcr Repertoire ◽  
Double Negative T Cells

Abstract Immune alloresponsiveness following allogeneic HSCT is influenced by the dynamics of immune reconstitution and development of allotolerance. In general, tolerance is induced by thymic clonal deletion (central) and apoptosis or suppression of alloresponsive lymphocytes by regulatory T cells in the periphery. We have recently demonstrated that the size of the TCR repertoire within the CD4 and CD8 compartments can be assessed using VB spectrum by flow cytometry, and expansions/losses of individual TCR VB families can be used as a surrogate marker of TCR variability. (Exp. Hem.32: 1010–1022; Br. J. Haematol.129:411–419). Additionally, regulatory T cells can also impact the clonal contractions and expansions within the TCR VB repertoire. Various types of regulatory T cells have been described including CD4+CD25+, CD8+, NK T−cells, and CD3+CD4/CD8− double negative T cells (DN Tregs). In our current study we investigated the role of DN Tregs on the restoration of immune repertoire diversity. We hypothesized that alloresponsiveness clinically detected as a manifestation of GvHD may be associated with oligoclonal T−cell expansions, and in this context decreased numbers of regulatory T cells suggest deficient tolerizing function by regulatory T cells including DN Tregs. Here we studied a cohort of 60 HSCT recipients (AML, CML, CLL, NHL, AA, and PV), of which 25 patients received matched unrelated donor grafts and 35 received matched sibling donor grafts. Blood was sampled between 2003–2006 at monthly intervals after HSCT, and flow cytometry for TCR repertoire in CD4 and CD8 cells as well as the numbers of DN cells were recorded. Additionally, separate samples were collected for measurement of chimerism and were included in analysis when donor lymphoid chimerism was > 60%. A subset analysis was performed based on the presence/absence of GvHD. For the 27/60 (45%) patients with episodes of GvHD, results were obtained at the time of diagnosis of GvHD (grade > 2), while for patients in whom notable GvHD was not captured, the steady−state values at corresponding times were used for analysis. For all patients serial evaluations were available. For the purpose of this study, significant VB expansions/contractions were defined as +/− 2 standard deviation over the average VB family size. Using Cox proportional hazards analysis to identify univariate risk factors for GVHD, CD8 VB TCR contractions > 14 VB families (58.3% contraction of entire CD4 VB repertoire) constituted a strong indicator for increased risk (HR=7.61, p=0.011). This observation is consistent with the fact that oligoclonality of alloreactive T cell clones is frequently accompanied by a significant contraction/loss of remaining VB families and may herald heightened alloresponsiveness as a manifestation of GvHD. Estimation for correlation by Pearson’s correlation coefficient also demonstrated that percentage of DN cells strongly correlated with a normalization of CD4 VB TCR repertoire (lower number of expansions; N=57, R= −0.51, p=0.027), supporting our hypothesis that DN cells participate in peripheral tolerance and suppress proliferative, alloresponsive CD4 clones. In summary, our results further characterize TCR variability post HSCT and define the role of DN cells in the induction of allotolerance.

Multiple Inhibitory Receptors Are Expressed on Central Memory and Memory Stem T Cells Infiltrating the Bone Marrow of AML Patients Relapsing after Allo-HSCT

Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 4564-4564 ◽  
Author(s):  
Maddalena Noviello ◽  
Francesco Manfredi ◽  
Tommaso Perini ◽  
Giacomo Oliveira ◽  
Filippo Cortesi ◽  
...  
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
T Cell ◽  
Research Funding ◽  
Central Memory ◽  
Cd8 Cells ◽  
Effector Functions ◽  
Cell Dysfunction ◽  
T Cell Dysfunction ◽  
Cell Effector

Abstract Background:Allogeneic Hematopoietic Stem Cell Transplantation (HSCT) is the only cure for high-risk acute myeloid leukemia (AML). Unfortunately, relapse still remains the major cause of death after HSCT. We investigated if T-cell dysfunction is associated to post-transplant relapse. Patients and Methods: To this,we longitudinally analyzed the T-cell dynamics in bone marrow (BM) and peripheral blood (PB) of 32 AML patients receiving HSCT from HLA identical (HLAid, 20 pts) or HLA haploidentical (haplo, 12 pts) donors. Samples were analysed by multi-parametric flow cytometry to investigate the expression of inhibitory receptors (IRs) on CD4 and CD8 T-cell subsets defined by CD45RA, CD62L and CD95 expression, and to assess the proportion of regulatory T cells (Tregs; CD4+CD25+FoxP3+). Results were also analyzed with the BH-SNE algorithm, an unbiased computational method for the analysis of FACS data. To evaluate T-cell effector functions, the CD107a degranulation assay was performed and the production of cytokines (IL-2, IFNg and TNFa) was measured by intracellular staining. BM and PB were collected 60 days after HSCT and at relapse (median 237 days; 16 pts) or, when complete remission was maintained (CR; 16 pts), at 1 year. Samples from 8 healthy donors (HD) were used as controls. Results:After transplant, BM and PB T cells showed a lower CD4/CD8 ratio (p<0.01) and a preferential late differentiation profile (p<0.05) when compared to HD. A higher proportion of BM Tregs was documented at relapse (p<0.01), independently from the donor source. We next investigated the expression of several IRs as T-cell exhaustion markers. After haplo-HSCT, PD-1, CTLA-4, 2B4 and Tim-3 were significantly upregulated in BM and PB T cells at all time-points, compared to HD and independently from the clinical outcome. Conversely, after HLAid-HSCT, at the late time-point, patients who relapsed, displayed a higher frequency of BM infiltrating T cells expressing PD-1, CTLA-4 and Tim-3 than CR pts (p<0.05) and HD (p<0.01). We then investigated the profile of each T-cell subset in our cohort. In the BM of HD the IR expression was confined to effector memory and effectors. While a similar IR distribution was observed in CR, at relapse, PD-1, 2B4 and Tim-3 were also upregulated in BM infiltrating central memory (p<0.01) and memory stem T cells (p<0.05). Interestingly, at relapse, leukemia expressed PD-L1 (9/9 cases) and Galectin-9 (6/9). The levels of Tim-3 on BM CD8 cells associates with that of Galectin-9 on autologous blasts (p<0.05), suggesting a preferential role for this immunomodulatory axis after HSCT. Based on phenotype similarities, the BH-SNE algorithm positioned HD samples separately from transplanted pts in bi-dimensional maps. 93 significant clusters were identified. Clusters associated with relapse after HLA-id (5) and after haplo (15) were composed of T cells expressing multiple IRs, while CR-specific clusters were diminished in IR fluorescence. To verify whether the T-cell exhaustion phenotypic profile at relapse associates with functional impairment, we evaluated T-cell effector functions upon polyclonal stimulation. Strikingly, we observed a lower degranulation ability of CD8 cells at relapse when compared to CR (p<0.05). In two patients, selected based on samples availability, we isolated and expanded by rapid expansion protocol (REP) T cells expressing one or more IRs (IR+) or no IR (IR-). Expansion rates were high and similar in IR+ and IR- T cells (mean fold increase 624 and 781, respectively at day 21). The degranulation ability measured ex-vivo in those patients (mean 4.4% on CD8 cells) was dramatically increased upon REP expansion (95% and 88.9% for IR+ and IR-, respectively). Similarly, the frequency of IFN-g producing CD8 cells increased in IR+ and IR- cells upon REP, indicating that the T-cell dysfunction observed at relapse can be efficiently reversed. We next challenged IR+ and IR- T cells against autologous blasts. Preliminary results suggest that IR+ T cells are enriched in leukemia specificity (elimination index of 66% and 44% in IR+ and IR- cells respectively at an E/T ratio of 100:1). Conclusions: After HSCT, the molecular signature of exhausted CD8 cells in relapsing pts includes PD-1, CTLA-4, 2B4 and Tim-3. The expression of IRs on early differentiated central memory and memory stem T cells at relapse suggests a wide, though reversible, immunological dysfunction mediated by AML relapsing blasts. Disclosures Bondanza: TxCell: Research Funding; MolMed SpA: Research Funding; Formula Pharmaceuticals: Honoraria. Ciceri:MolMed SpA: Consultancy. Bonini:TxCell: Membership on an entity's Board of Directors or advisory committees; Molmed SpA: Consultancy.

Obesity results in higher PD-1-mediated T-cell suppression but greater T-cell effector functions following blockade.

2018 ◽  
Vol 36 (5_suppl) ◽  
pp. 65-65 ◽  
Author(s):  
Robert J. Canter ◽  
Ethan Aguilar ◽  
Ziming Wang ◽  
Catherine Le ◽  
Lam Khuat ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
T Cell Responses ◽  
Murine Cytomegalovirus ◽  
Obese Mice ◽  
Effector Functions ◽  
Cell Responses ◽  
The Central Nervous System ◽  
The Impact ◽  
Cell Effector

65 Background: Obesity is increasingly prevalent and viewed as a critical co-factor in many pathologic conditions due to metabolic, inflammatory and immune perturbations. We performed a multi-species evaluation of the impact of obesity T cell effector functions and markers of immune exhaustion. Methods: We examined the impact of obesity on PD-1 and T cell-mediated responses across different pre-clinical models (tumor, infection, and autoimmune encephalomyelitis [EAE]) and species (mouse, dog, non-human primate, and human). Results: CD4 and CD8 T cells from obese mice, dogs, non-human primates and humans displayed increases in memory T cells and PD-1 expression, as well as impaired proliferative responses compared to lean controls, indicating a greater degree of T cell exhaustion at baseline. Following immunization with myelin oligodendrocyte glycoprotein, obese mice were resistant to induction of EAE, correlating with reduced antigen-specific CD4 T cells in the central nervous system. Administration of anti-PD-1 resulted in restoration of EAE and increased antigen-specific T cell numbers in obese mice. Tumors in obese mice exhibited accelerated growth compared to lean mice, and T cells displayed higher PD-1 expression correlating with RNAseq/molecular signatures of exhaustion compared to tumor-bearing lean mice. PD-1 blockade resulted in marked anti-tumor effects only in obese mice, and not lean. Impaired viral resistance to murine cytomegalovirus (MCMV) resulted was seen in obese mice, associated with increased PD-1/PD-L1 expression, which was reversible by PD-1/PD-L1 blockade. Conclusions: Obesity results in an increase in PD-1/PD-L1 expression and inhibition of T cell responses across species, and blockade not only reverses this inhibition but also leads to markedly augmented T cell effector responses compared to lean counterparts where no effects were observed. These results highlight how the immune system has evolved to control T cell responses using checkpoints contingent on dynamic host conditions and have translational relevance for predicting both efficacy and toxicity in clinical immuno-oncology.

Regulatory T cells mediate resistance to radiotherapy in head and neck squamous cell carcinoma.

2019 ◽  
Vol 37 (8_suppl) ◽  
pp. 70-70 ◽  
Author(s):  
Ayman Oweida ◽  
Laurel Darragh ◽  
Shilpa Bhatia ◽  
David Raben ◽  
Lynn Heasley ◽  
...  
Keyword(s):  
Flow Cytometry ◽  
T Cells ◽  
T Cell ◽  
Regulatory T Cells ◽  
Tumor Growth ◽  
Head And Neck ◽  
Critical Role ◽  
Growth Delay ◽  
Functional Changes ◽  
Treg Depletion

70 Background: Head and neck tumors are highly enriched in regulatory T cells which dampen the response to radiotherapy by creating an immune-inhibitory microenvironment. We explored mechanisms of Treg infiltration and assessed their modulation by RT in murine models of HNSCC. Methods: Mechanisms of Treg infiltration were investigated in murine HNSCC tumors using whole genome sequencing and flow cytometry. Mice were treated with anti-CTLA-4, anti-CD-25 and/or anti-PD-L1 alone and in combination with RT. Tumor growth and survival were assessed. Flow cytometry was used to assess phenotypic and functional changes in intratumoral T cell populations. Multiplex ELISA was performed for assessment of cytokines. RNA Sequencing was performed to interrogate mechanisms of response and resistance to treatment. Results: Treatment with anti-CD-25 concurrently with RT led to significant tumor growth delay, enhanced T cell cytotoxicity, decreased Tregs and improved survival. In contrast CTLA-4 blockade did not affect tumor growth or survival. Treg depletion induced an influx of CD8 and CD4 T cells when combined with RT. In addition, Treg depletion in combination with RT transformed myeloid populations decreasing M2 macrophages and MDSCs and increasing M1 macrophages. Mechanistically, tumors secrete CCL20, a potent Treg chemoattractant responsible for creating a highly immunuosuppressive tumor microenvironment and potentially responsible for treatment resistance. Conclusions: These data reveal a critical role for regulatory T cells in mediating resistance to RT. Targeted depletion of Tregs represents an important mechanism of sensitizing tumors to RT. Our data support the design of clinical trials integrating targeted Treg inhibitors in the standard of care for cancer patients receiving RT.

Combining Established and Novel Immunomodulators: Synergistic Inhibition of Major T Cell Effector Functions by Dexamethasone and Dasatinib

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 2564-2564
Author(s):  
Ruth Seggewiss ◽  
Carolin Dix ◽  
Hermann Einsele
Keyword(s):  
T Cells ◽  
T Cell ◽  
Cd8 T Cells ◽  
Synergistic Effects ◽  
Complete Inhibition ◽  
Inhibitory Effects ◽  
Effector Functions ◽  
The Impact ◽  
Dose Dependent ◽  
Cell Effector

Abstract Introduction. An increasing body of evidence suggests that in addition to their molecular targeted antitumor activity tyrosine kinase inhibitors (TKIs) exert immunomodulatory effects on T cells. Others (Blake et al 2008; Schade et al 2008) and we (Weichsel et al 2008) have recently shown that dasatinib (a multitargeting TKI) may lead to a complete inhibition of TCR dependent T cell effector functions via the SRC kinases LCK and FYN. Because TKIs act as competitive enzyme inhibitors with short half life, they permit better side effect control in the clinic. We investigated the impact of combining clinically relevant doses of dasatinib (1–100nM) with the established immunosuppressant dexamethasone (1–1000nM) on T cells. Materials and Methods. Purified human CD3+ T cells from healthy blood donors were studied directly ex vivo. Functional outcomes assessed included cytokine production (IL-2), activation (CD69 upregulation), proliferation (CFSE dilution) and apoptosis/necrosis induction. EBV or CMV specific proliferation of antigen specific CD8+ T cells were evaluated applying tetramer technology. To distinguish between rapid non-genomic and genomic effects all assessments compared the impact of pre-treating T-cells with dexamethasone for 1 vs. 24h. Results and Discussion. Complete inhibition of proliferation and activation occurred with dasatinib alone at levels of 50nM and above, whereas application of dexamethasone did not lead to a complete inhibition even at doses up to 1000nM. Dose-dependent inhibition of with the monoclonal CD3 antibody OKT3 induced T cell activation and proliferation was observed with the combination of dasatinib and dexamethasone. Strongest synergistic inhibitory effects of the drug combination were observed for OKT3 induced cytotoxic CD8+ T cell proliferation (mean±SEM given: OKT3 induced 63±5% proliferating T cells after 4 days incubation, OKT3 + 10nM dexamethasone 44±5%, OKT3 + 10nM dasatinib 39±10%, OKT3 + combination 16±4%; n=5; p&lt;0.05). A significant inhibition of OKT3 induced up-regulation of the activation marker CD69 was demonstrated with the combination but not for dexamethasone alone (n=5). Our previously published data on dasatinib alone also showed inhibition of OKT3 induced up-regulation of CD69 expression, and this was potentiated in combination with dexamethasone. The pre-treatment time did not influence the dexamethasone effect except for increased reduction of IL-2 production after 24h vs. 1h pre-incubation. Overall, helper CD4+ T cells were more sensitive to the inhibitory effects of the drug combination regarding activation and proliferation than cytotoxic CD8+ T cells. Of note, synergistic effects occurred primarily in the different memory CD4 and CD8 T cell subsets but not in the naïve CD4 and CD8 T cells (e.g. for CD8+CD45RO+CD27+ memory T cells mean±SEM given for percentage of proliferating cells after 4 days: OKT3 92±1%, OKT3 + 100nM dexamethasone 77±2%, OKT3 + 10nM dasatinib 69±15%, and OKT3 + combination 27±11%; n=5; p&lt;0.05). IL-2 production in purified T cells was significantly reduced (p&lt;0.05) in a dose dependent nature for both dasatinib and dexamethasone compared to the OKT3 stimulated condition, either alone or in combination (n=5). Similarly, activation induced cell death (AICD) was significant reduced when the two drugs were combined, whereas no synergistic effects were observed regarding necrosis inhibition (n=5; p&lt;0.05). In contrast, initial results suggested that dexamethasone did not inhibit clinically relevant EBV or CMV antigen specific CD8+ memory T cell proliferation when used alone and did not show synergistic effects with dasatinib (n=3). This may be due to a reduced sensitivity of the specific viral memory subsets towards dexamethasone. Outlook and Conclusion. As viral reactivation especially with CMV is a major cause for morbidity after allogeneic stem cell transplantation, our results warrant further studies in vitro and in vivo. With an indication that each drug, when combined could be used at reduced dose, this research may then pave the way for synergistic uses of TKIs and glucocorticosteroids in treatment of graft versus host disease or autoimmune diseases potentially without increased risk of infections.

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