Two Photon Intravital Microscopy Reveals CD4+ T Cells Making Cognate Interactions With Tissue Dendritic Cells In Skin Graft-Versus-Host-Disease

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 2004-2004
Author(s):  
Sarah Morin-Zorman ◽  
Christian Wysocki ◽  
Edwina Kisanga ◽  
David Gonzalez ◽  
David Rothstein ◽  
...  
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
Dendritic Cells ◽  
T Cell ◽  
Cd4 T Cells ◽  
Cd4 T Cell ◽  
Cd4 Cells ◽  
Cd8 Cells ◽  
Graft Versus Host ◽  
Two Photon

Abstract Graft-versus-host disease (GVHD) limits the broader application of allogeneic hematopoietic stem cell transplantation. In prior studies we defined roles for both host and donor-derived antigen presenting cells (APCs) in the activation of alloreactive donor T cells and promotion of GVHD. While initial T cell activation in GVHD occurs predominantly in secondary lymphoid organs (SLO), we have consistently observed MHCII+ donor-derived tissue APCs (t-APCs), including tissue dendritic cells (t-DCs) in histopathologic GVHD lesions, frequently adjacent to infiltrating T cells. We hypothesize that productive interactions occur between donor APCs and T cells in situ in GVHD target tissues, which propagate disease locally. We could not use knockout or APC depletion approaches to study T cell: t-APCs interactions as they impact APCs systemically and might therefore affect T cell stimulation in SLO. We therefore utilized two-photon intravital microscopy to analyze interactions between fluorescent donor CD4+ T cells and t-DCs in skin. 129 (H-2b) hosts were irradiated and reconstituted with B6 (H-2b) CD11c-YFP transgenic (Tg) Bone Marrow (BM) with B6 RFP Tg CD4 cells and nonfluorescent B6 CD8 cells. We imaged ear skin in GVHD mice 4 weeks later. In general CD4 cells co-localized with DCs. We observed CD4+ T cells that were highly motile and only in transient contact with DCs and others that made stable contact with DCs. To determine how much TCR: MHCII interactions drive sustained CD4+ T cell: DC interactions and arrest CD4+ T cell motility, mice were imaged and then injected with an MHCII blocking antibody (Ab; Y3P) with continued imaging of the same regions. After injection, T cell mean speed significantly increased and the proportion of T cells in stable contact with DCs decreased, indicating that transient disruption of TCR: MHCII is sufficient to restore motility to some T cells. In a second approach to assess the specificity of CD4+ T cell: t-DC interactions we transplanted 129 mice with B6 RFP+ CD4 cells, nonfluorescent CD8 cells and a mix of CD11c-YFP MHCII-/- and RFP wt BM or a mix of CD11c-YFP wt and RFP Tg MHCII-/- BM. We are currently comparing the motility of CD4 cells that make contact with MHCII+ as compared to MHCII- DCs, with the prediction that contact times will be shorter with the latter. Our data suggest that CD4+ T cells make cognate interactions with t-DCs in skin and we hypothesize that these interactions promote GVHD locally. Because the graft-versus-leukemia effect occurs primarily in bone marrow and secondary lymphoid tissues, targeting of tissue-infiltrating APCs could represent a unique strategy to ameliorate GVHD while preserving GVL. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Response of naive antigen-specific CD4+ T cells in vitro: characteristics and antigen-presenting cell requirements.

1992 ◽  
Vol 176 (5) ◽  
pp. 1431-1437 ◽  
Author(s):  
M Croft ◽  
D D Duncan ◽  
S L Swain
Keyword(s):  
T Cells ◽  
Dendritic Cells ◽  
T Cell ◽  
Cd4 T Cells ◽  
Cd4 Cells ◽  
Peptide Antigen ◽  
Naive T Cells ◽  
Naïve T Cells ◽  
Antigen Presenting

Because of the low frequency of T cells for any particular soluble protein antigen in unprimed animals, the requirements for naive T cell responses in specific antigens have not been clearly delineated and they have been difficult to study in vitro. We have taken advantage of mice transgenic for the V beta 3/V alpha 11 T cell receptor (TCR), which can recognize a peptide of cytochrome c presented by IEk. 85-90% of CD4+ T cells in these mice express the transgenic TCR, and we show that almost all such V beta 3/V alpha 11 receptor-positive cells have a phenotype characteristic of naive T cells, including expression of high levels of CD45RB, high levels of L-selectin (Mel-14), low levels of CD44 (Pgp-1), and secretion of interleukin 2 (IL-2) as the major cytokine. Naive T cells, separated on the basis of CD45RB high expression, gave vigorous responses (proliferation and IL-2 secretion) to peptide antigen presented in vitro by a mixed antigen-presenting cell population. At least 50% of the T cell population appeared to respond, as assessed by blast transformation, entry into G1, and expression of increased levels of CD44 by 24 h. Significant contributions to the response by contaminating memory CD4+ cells were ruled out by demonstrating that the majority of the CD45RB low, L-selectin low, CD44 high cells did not express the V beta 3/V alpha 11 TCR and responded poorly to antigen. We find that proliferation and IL-2 secretion of the naive CD4 cells is minimal when resting B cells present peptide antigen, and that both splenic and bone marrow-derived macrophages are weak stimulators. Naive T cells did respond well to high numbers of activated B cells. However, dendritic cells were the most potent stimulators of proliferation and IL-2 secretion at low cell numbers, and were far superior inducers of IL-2 at higher numbers. These studies establish that naive CD4 T cells can respond vigorously to soluble antigen and indicate that maximal stimulation can be achieved by presentation of antigen on dendritic cells. This model should prove very useful in further investigations of activation requirements and functional characteristics of naive helper T cells.

scholarly journals Contact-dependent delivery of IL-2 by dendritic cells to CD4 T cells in the contraction phase promotes their long-term survival

2019 ◽  
Vol 11 (2) ◽  
pp. 108-123
Author(s):  
Dan Tong ◽  
Li Zhang ◽  
Fei Ning ◽  
Ying Xu ◽  
Xiaoyu Hu ◽  
...  
Keyword(s):  
T Cells ◽  
Dendritic Cells ◽  
T Cell ◽  
T Cell Activation ◽  
Cd4 T Cells ◽  
Cell Activation ◽  
Cd4 T Cell ◽  
Immune Memory ◽  
Term Survival

Abstract Common γ chain cytokines are important for immune memory formation. Among them, the role of IL-2 remains to be fully explored. It has been suggested that this cytokine is critically needed in the late phase of primary CD4 T cell activation. Lack of IL-2 at this stage sets for a diminished recall response in subsequent challenges. However, as IL-2 peak production is over at this point, the source and the exact mechanism that promotes its production remain elusive. We report here that resting, previously antigen-stimulated CD4 T cells maintain a minimalist response to dendritic cells after their peak activation in vitro. This subtle activation event may be induced by DCs without overt presence of antigen and appears to be stronger if IL-2 comes from the same dendritic cells. This encounter reactivates a miniature IL-2 production and leads a gene expression profile change in these previously activated CD4 T cells. The CD4 T cells so experienced show enhanced reactivation intensity upon secondary challenges later on. Although mostly relying on in vitro evidence, our work may implicate a subtle programing for CD4 T cell survival after primary activation in vivo.

scholarly journals T-cell ontogeny after autologous bone marrow transplantation: failure to synthesize interleukin-2 (IL-2) and lack of CD2- and CD3-mediated proliferation by both CD4- and CD8+ cells even in the presence of exogeneous IL-2

Blood ◽  
1989 ◽  
Vol 74 (6) ◽  
pp. 2270-2277 ◽  
Author(s):  
S Cayeux ◽  
S Meuer ◽  
A Pezzutto ◽  
M Korbling ◽  
R Haas ◽  
...  
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
T Cell ◽  
Autologous Bone Marrow Transplantation ◽  
Interleukin 2 ◽  
Autologous Bone Marrow ◽  
Cd4 Cells ◽  
Cd8 Cells ◽  
Autologous Bone ◽  
Cell Ontogeny

Abstract T cells generated during a second round of ontogeny after autologous bone marrow transplantation (ABMT) represent a unique model of early T- cell ontogeny in an autologous situation. Since grafted bone marrows were pretreated in vitro with the cyclophosphamide derivative ASTA Z 7557, circulating T cells had to be regenerated from reinfused hematopoietic progenitor cells. The T-cell population derived from 25 patients post-ABMT was phenotypically characterized: an increase in CD8+ cells, a low percentage of CD4+ cells, and a median of 12% CD56+ (NKH1+) cells were found. When the T cells were stimulated with phytohemagglutinin (PHA) and phorbol myristate acetate (PMA), defective interleukin-2 (IL-2) secretion was observed. In addition, proliferative responses of the T cells after activation through the antigen-receptor- dependent CD3 pathway, through the CD2 dependent alternative T-cell pathway, and by the lectin PHA were investigated. Despite the presence of CD2, CD3, alpha/beta chains of the T-cell receptor, and CD25+ IL-2 surface receptors, abnormal proliferative responses were obtained even in the presence of exogeneous IL-2. In experiments where the T-cell population was separated into CD4+ cells and CD8+ cells, both the CD4- and CD8+ subsets were unable to respond to activating and proliferating signals. Thus, T cells at early stages of ontogeny not only possess an intrinsic defect in IL-2 synthesis but, in addition, were unable to express functional IL-2 receptors in response to mitogenic stimuli.

scholarly journals CD4+ T-cell killing of multiple myeloma cells is mediated by resident bone marrow macrophages

2020 ◽  
Vol 4 (12) ◽  
pp. 2595-2605 ◽  
Author(s):  
Ole Audun W. Haabeth ◽  
Kjartan Hennig ◽  
Marte Fauskanger ◽  
Geir Åge Løset ◽  
Bjarne Bogen ◽  
...  
Keyword(s):  
Multiple Myeloma ◽  
Bone Marrow ◽  
T Cells ◽  
T Cell ◽  
Cd4 T Cells ◽  
Antigen Presenting Cells ◽  
Bone Marrow Microenvironment ◽  
Cd4 T Cell ◽  
Myeloma Cells ◽  
Antigen Presenting

Abstract CD4+ T cells may induce potent antitumor immune responses through interaction with antigen-presenting cells within the tumor microenvironment. Using a murine model of multiple myeloma, we demonstrated that adoptive transfer of idiotype-specific CD4+ T cells may elicit curative responses against established multifocal myeloma in bone marrow. This finding indicates that the myeloma bone marrow niche contains antigen-presenting cells that may be rendered tumoricidal. Given the complexity of the bone marrow microenvironment, the mechanistic basis of such immunotherapeutic responses is not known. Through a functional characterization of antitumor CD4+ T-cell responses within the bone marrow microenvironment, we found that killing of myeloma cells is orchestrated by a population of bone marrow–resident CD11b+F4/80+MHC-IIHigh macrophages that have taken up and present secreted myeloma protein. The present results demonstrate the potential of resident macrophages as powerful mediators of tumor killing within the bone marrow and provide a basis for novel therapeutic strategies against multiple myeloma and other malignancies that affect the bone marrow.

Promoting Regulation Via the Inhibition of DNAM-1 After Transplantation

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 338-338
Author(s):  
Motoko Koyama ◽  
Rachel D Kuns ◽  
Stuart D Olver ◽  
Katie E Lineburg ◽  
Mary Lor ◽  
...  
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
Steady State ◽  
T Cell ◽  
Median Survival ◽  
Cd4 T Cells ◽  
Cell Expansion ◽  
Acute Gvhd ◽  
Cd4 T Cell

Abstract Abstract 338 Graft-versus-host disease (GVHD) is the major limitation of allogeneic hematopoietic bone marrow transplantation (BMT). Donor T cells play pivotal roles in GVHD and graft-versus-leukemia (GVL) effects and following BMT all T cell fractions, including regulatory T cells (Treg) express the DNAX accessory molecule-1 (DNAM-1, CD226) and T cell Immunoglobulin and ITIM domain (TIGIT) molecule. DNAM-1 is a co-stimulatory and adhesion molecule, expressed mainly by NK cells and CD8+ T cells at steady state to promote adhesion to ligand (CD155, CD112)–expressing targets and enhance cytolysis. TIGIT is a regulatory ligand expressed predominantly by Treg as steady state which competes for CD155 binding, We have analyzed the role of this pathway in GVHD and GVL. Lethally irradiated C3H/Hej (H-2k) mice were injected with bone marrow cells and T cells from MHC disparate wild-type (wt) or DNAM-1–/– C57Bl6 (H-2b) mice. Recipients of DNAM-1–/– grafts were protected from GVHD (survival 67% vs. 7%, P < .0001). We also confirmed the role of DNAM-1 in GVHD in a MHC-matched BMT model (B6 → BALB/B (H-2b)) where GVHD is directed to multiple minor histocompatibility antigens. Next we examined the donor populations expressing DNAM-1 which mediate this effect. DNAM-1 had little impact on acute GVHD severity in the B6 → bm1 BMT model where GVHD is directed against an isolated MHC class I mismatch and is CD8-dependent. In contrast, recipients of wt bone marrow and DNAM-1–/– CD4 T cells survived long-term (compared to recipients of wt CD4 T cells, survival 81% vs. 25%, P = .003) in the B6 → B6C3F1 BMT model, confirming the protection from GVHD is CD4-dependent. Donor CD4 T cell expansion and effector function (Th1 and Th17), and CD8 T cell expansion and cytotoxic function were equivalent in recipients of wt and DNAM-1–/– grafts. However the percentage and number of Treg were significantly increased in recipients of DNAM-1–/– grafts compared to those of wt grafts. The depletion of Treg from donor grafts eliminated the protection from GVHD seen in the absence of DNAM-1 signalling (median survival 16 days vs. 15.5 days, P = 0.53). Adoptive transfer experiments using FACS-sorted Treg were undertaken to compare the relative ability of B6.WT and B6.DNAM-1–/– Treg to suppress GVHD. The majority of recipients of DNAM-1–/– Treg survived beyond day 50 (median survival; day 56), demonstrating a superior ability to suppress acute GVHD relative to wt Treg where the median survival was day 36 (survival 47% vs. 0%, P = .001). These data demonstrate that donor DNAM-1 expression promotes GVHD in a CD4+ T cell-dependent manner via the inhibition of donor Foxp3+ Treg. Finally, the absence of donor DNAM-1 did not influence leukemia-specific mortality in multiple GVL models, regardless of whether the tumor expressed CD155 or not. Thus we demonstrate that the DNAM-1 pathway promotes GVHD, putatively due to competition with TIGIT on Treg, thereby inhibiting regulatory function. This provides support for therapeutic DNAM-1 inhibition to promote tolerance not only after transplant but also in relevant inflammatory based diseases characterized by T cell activation. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Direct Expansion of Functional CD25+ CD4+ Regulatory T Cells by Antigen-processing Dendritic Cells

2003 ◽  
Vol 198 (2) ◽  
pp. 235-247 ◽  
Author(s):  
Sayuri Yamazaki ◽  
Tomonori Iyoda ◽  
Kristin Tarbell ◽  
Kara Olson ◽  
Klara Velinzon ◽  
...  
Keyword(s):  
T Cells ◽  
Dendritic Cells ◽  
T Cell ◽  
T Cell Receptor ◽  
Cd4 T Cells ◽  
Antigen Processing ◽  
Specific Antigen ◽  
Cell Receptor ◽  
Cd4 T Cell

An important pathway for immune tolerance is provided by thymic-derived CD25+ CD4+ T cells that suppress other CD25− autoimmune disease–inducing T cells. The antigen-presenting cell (APC) requirements for the control of CD25+ CD4+ suppressor T cells remain to be identified, hampering their study in experimental and clinical situations. CD25+ CD4+ T cells are classically anergic, unable to proliferate in response to mitogenic antibodies to the T cell receptor complex. We now find that CD25+ CD4+ T cells can proliferate in the absence of added cytokines in culture and in vivo when stimulated by antigen-loaded dendritic cells (DCs), especially mature DCs. With high doses of DCs in culture, CD25+ CD4+ and CD25− CD4+ populations initially proliferate to a comparable extent. With current methods, one third of the antigen-reactive T cell receptor transgenic T cells enter into cycle for an average of three divisions in 3 d. The expansion of CD25+ CD4+ T cells stops by day 5, in the absence or presence of exogenous interleukin (IL)-2, whereas CD25− CD4+ T cells continue to grow. CD25+ CD4+ T cell growth requires DC–T cell contact and is partially dependent upon the production of small amounts of IL-2 by the T cells and B7 costimulation by the DCs. After antigen-specific expansion, the CD25+ CD4+ T cells retain their known surface features and actively suppress CD25− CD4+ T cell proliferation to splenic APCs. DCs also can expand CD25+ CD4+ T cells in the absence of specific antigen but in the presence of exogenous IL-2. In vivo, both steady state and mature antigen-processing DCs induce proliferation of adoptively transferred CD25+ CD4+ T cells. The capacity to expand CD25+ CD4+ T cells provides DCs with an additional mechanism to regulate autoimmunity and other immune responses.

Requirements for the promotion of allogeneic engraftment by anti-CD154 (anti-CD40L) monoclonal antibody under nonmyeloablative conditions

Blood ◽  
2001 ◽  
Vol 98 (2) ◽  
pp. 467-474 ◽  
Author(s):  
Patricia A. Taylor ◽  
Christopher J. Lees ◽  
Herman Waldmann ◽  
Randolph J. Noelle ◽  
Bruce R. Blazar
Keyword(s):  
Monoclonal Antibody ◽  
Bone Marrow ◽  
T Cells ◽  
T Cell ◽  
Cd8 T Cells ◽  
Immune Suppression ◽  
Regulatory T Cell ◽  
Cd4 Cells ◽  
Major Goal ◽  
Cd8 Cells

The promotion of alloengraftment in the absence of global immune suppression and multiorgan toxicity is a major goal of transplantation. It is demonstrated that the infusion of a single modest bone marrow dosage in 200 cGy-irradiated recipients treated with anti-CD154 (anti-CD40L) monoclonal antibody (mAb) resulted in chimerism levels of 48%. Reducing irradiation to 100 or 50 cGy permitted 24% and 10% chimerism, respectively. In contrast, pan–T-cell depletion resulted in only transient engraftment in 200 cGy-irradiated recipients. Host CD4+ cells were essential for alloengraftment as depletion of CD4+ cells abrogated engraftment in anti-CD154–treated recipients. Strikingly, the depletion of CD8+ cells did not further enhance engraftment in anti-CD154 mAb–treated recipients in a model in which rejection is mediated by both CD4+ and CD8+ T cells. However, anti-CD154 mAb did facilitate engraftment in a model in which only CD8+ T cells mediate rejection. Furthermore, CD154 deletional mice irradiated with 200 cGy irradiation were not tolerant of grafts, suggesting that engraftment promotion by anti-CD154 mAb may not simply be the result of CD154:CD40 blockade. Together, these data suggest that a CD4+regulatory T cell may be induced by anti-CD154 mAb. In contrast to anti-CD154 mAb, anti-B7 mAb did not promote donor engraftment. Additionally, the administration of either anti-CD28 mAb or anti-CD152 (anti–CTLA-4) mAb or the use of CD28 deletional recipients abrogated engraftment in anti-CD154 mAb–treated mice, suggesting that balanced CD28/CD152:B7 interactions are required for the engraftment-promoting capacity of anti-CD154 mAb. These data have important ramifications for the design of clinical nonmyeloablative regimens based on anti-CD154 mAb administration.

scholarly journals Plasmacytoid dendritic cells have divergent effects on HIV infection of initial target cells and induce a pro-retention phenotype

2021 ◽  
Vol 17 (4) ◽  
pp. e1009522
Author(s):  
Orion Tong ◽  
Gabriel Duette ◽  
Thomas Ray O’Neil ◽  
Caroline M. Royle ◽  
Hafsa Rana ◽  
...  
Keyword(s):  
T Cells ◽  
Dendritic Cells ◽  
T Cell ◽  
Hiv Infection ◽  
Reverse Transcriptase ◽  
Cd4 T Cells ◽  
Cd4 T Cell ◽  
Target Cells ◽  
Ccr5 Expression ◽  
Memory Cd4 T Cells

Although HIV infection inhibits interferon responses in its target cells in vitro, interferon signatures can be detected in vivo soon after sexual transmission, mainly attributed to plasmacytoid dendritic cells (pDCs). In this study, we examined the physiological contributions of pDCs to early HIV acquisition using coculture models of pDCs with myeloid DCs, macrophages and the resting central, transitional and effector memory CD4 T cell subsets. pDCs impacted infection in a cell-specific manner. In myeloid cells, HIV infection was decreased via antiviral effects, cell maturation and downregulation of CCR5 expression. In contrast, in resting memory CD4 T cells, pDCs induced a subset-specific increase in intracellular HIV p24 protein expression without any activation or increase in CCR5 expression, as measured by flow cytometry. This increase was due to reactivation rather than enhanced viral spread, as blocking HIV entry via CCR5 did not alter the increased intracellular p24 expression. Furthermore, the load and proportion of cells expressing HIV DNA were restricted in the presence of pDCs while reverse transcriptase and p24 ELISA assays showed no increase in particle associated reverse transcriptase or extracellular p24 production. In addition, PDCs also markedly induced the expression of CD69 on infected CD4 T cells and other markers of CD4 T cell tissue retention. These phenotypic changes showed marked parallels with resident memory CD4 T cells isolated from anogenital tissue using enzymatic digestion. Production of IFNα by pDCs was the main driving factor for all these results. Thus, pDCs may reduce HIV spread during initial mucosal acquisition by inhibiting replication in myeloid cells while reactivating latent virus in resting memory CD4 T cells and retaining them for immune clearance.

scholarly journals In vivo dynamics of T cells and their interactions with dendritic cells in mouse cutaneous graft-versus-host disease

2019 ◽  
Vol 3 (14) ◽  
pp. 2082-2092
Author(s):  
Sarah Morin-Zorman ◽  
Christian Wysocki ◽  
Jieqing Zhu ◽  
Hongmei Li ◽  
Sylvain Zorman ◽  
...  
Keyword(s):  
T Cells ◽  
Dendritic Cells ◽  
Graft Versus Host Disease ◽  
Cd4 Cells ◽  
Tcr Signaling ◽  
Hematopoietic Stem ◽  
Host Disease ◽  
Cd8 Cells ◽  
Graft Versus Host

Abstract Graft-versus-host disease (GVHD) is a major cause of morbidity and mortality in allogeneic hematopoietic stem cell transplantation (alloSCT). By static microscopy, cutaneous GVHD lesions contain a mix of T cells and myeloid cells. We used 2-photon intravital microscopy to investigate the dynamics of CD4+ and CD8+ T cells and donor dendritic cells (DCs) in cutaneous GVHD lesions in an MHC-matched, multiple minor histocompatibility antigen-mismatched (miHA) model. The majority of CD4 and CD8 cells were stationary, and few cells entered and stopped or were stopped and left the imaged volumes. CD8 cells made TCR:MHCI-dependent interactions with CD11c+ cells, as measured by the durations that CD8 cells contacted MHCI+ vs MHCI− DCs. The acute deletion of Langerin+CD103+ DCs, which were relatively rare, did not affect CD8 cell motility and DC contact times, indicating that Langerin−CD103− DCs provide stop signals to CD8 cells. CD4 cells, in contrast, had similar contact durations with MHCII+ and MHCII− DCs. However, CD4 motility rapidly increased after the infusion of an MHCII-blocking antibody, indicating that TCR signaling actively suppressed CD4 movements. Many CD4 cells still were stationary after anti-MHCII antibody infusion, suggesting CD4 cell heterogeneity within the lesion. These data support a model of local GVHD maintenance within target tissues.

T Cells Motility in the Colonic Gvhd Is Influenced By Both Cognate Interaction and Microenvironment

Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 3346-3346
Author(s):  
Jieqing Zhu ◽  
Cassandra Secunda ◽  
Michael Parrish ◽  
David Gonzalez ◽  
Ann Haberman ◽  
...  
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
T Cell ◽  
Cell Motility ◽  
Conflicts Of Interest ◽  
Allogeneic Bone Marrow Transplantation ◽  
Allogeneic Bone ◽  
Cd4 Cells ◽  
Cd8 Cells ◽  
Cell Stability

Abstract Graft-versus-host disease (GVHD) accounts for substantial morbidity and mortality after allogeneic bone marrow transplantation. Allograft T cells are stimulated by both host and donor-derived antigen presenting cells (APCs). After differentiating into T effector cells, donor T cells migrate to GVHD target organs where they mediate damage directly and indirectly. However, very little is known about the dynamics of T cells in GVHD target tissues and how their behaviors are affected by the local environments, including by tissue-resident APCs. We utilized two-photon intravital microscopy (2PIM) to analyze T cell locations, motility and interactions with APCs. 129S1/SVLmJ (129) (H-2b) hosts were irradiated and reconstituted with C57Bl/6 (B6) (H-2b) CD11-YFP transgenic mice bone marrow together with B6 dsRed (RFP) CD8 cells and cyan fluorescent protein (CFP) CD4 cells. Mice were imaged from days 25-42 post-transplant. We focused on the colon which is strongly targeted in this model and in humans and which previously has been difficult to image by 2PIM. In syngeneic B6 into B6 recipients, donor CD11c+, CD8+ and CD4+ cells populate the colonic mucosa. However, a greater number of cells accumulated in the allogenic as compared to syngeneic recipients. Based on the analysis of 7-8 mice per group, T cells in allogenic mice were less motile. The mean CD8 speeds in syngeneic and allogeneic mice were 3.38 ± 0.07 µm/min and 2.21 ± 0.03 µm/min, respectively. Mean CD4 speeds in syngeneic and allogeneic mice were 3.11 ± 0.08 µm/min and 2.38 ± 0.04 µm/min, respectively. The majority of T cells were stationary, with few entering or leaving the imaged volume. Perfusion was confirmed by i.v. rhodamine-dextran; therefore, stationary behaviors was not due to tissue viability. Using optical clearing we imaged whole-mount colonic tissue from mucosa to serosa. T cells were aggregated in the sub-mucosa and infiltrated crypts and surprisingly also the muscular layer. Ki67+ T cells were found throughout, especially in the submucosa. Given the 2PIM data which show few new T cells entering the imaged volumes, these cells were likely stimulated to divide locally. Preliminary data with EdU pulsing suggest this to be the case. To determine whether T cell stability is microenvironment- or antigen-driven, we injected OT-1 TCR transgenic effectors which do not recognize any antigen in the recipient and imaged the next day. Most colonic OT-1 cells showed the same stationary behavior as nearby donor-derived CD4 and CD8 cells, suggesting that factors in the GVHD colon microenvironment drive T cell stability. Nonetheless there was also an antigen-driven component as injection of an anti-MHCII antibody (but not isotype control Ab) increased CD4+ T cell motility presumably by disrupting TCR:MHCII interaction. These results show the motility of T cells in the GVHD colon is influence by both TCR:MHC cognate interactions and by the microenvironment. That T cells are dividing and may be activated in situ, suggesting GVHD may be maintained locally. Current studies are focusing on what antigen-independent factors affect T cell motility and on defining the roles played by tissue APCs. Disclosures No relevant conflicts of interest to declare.

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