ARHGAP45 controls naïve T- and B-cell entry into lymph nodes and T-cell progenitor thymus seeding.

T and B cells continually recirculate between blood and secondary lymphoid organs. To promote their trans-endothelial migration (TEM), chemokine receptors control the activity of RHO family small GTPases in part via GTPase-activating proteins (GAPs). T and B cells express several RHO-GAPs, the function of most of which remains unknown. The ARHGAP45 GAP is predominantly expressed in hematopoietic cells. To define its in vivo function, we describe two mouse models where ARHGAP45 is ablated systemically or selectively in T cells. We combine their analysis with affinity purification coupled to mass spectrometry to determine the ARHGAP45 interactome in T cells and with time-lapse and reflection interference contrast microscopy to assess the role of ARGHAP45 in T-cell polarization and motility. We demonstrate that ARHGAP45 regulates naïve T-cell deformability and motility. Under physiological conditions, ARHGAP45 controls the entry of naïve T and B cells into lymph nodes whereas under competitive repopulation it further regulates hematopoietic progenitor cell engraftment in the bone marrow, and T-cell progenitor thymus seeding. Therefore, the ARGHAP45 GAP controls multiple key steps in the life of T and B cells.

Absence of MHC class II on cDC1 dendritic cells triggers fatal autoimmunity to a cross-presented self-antigen.

Conventional dendritic cells expressing the XCR1 chemokine receptor (cDC1s) excel at cross-presentation. Here, we developed and used a mouse model in which a Cre recombinase is expressed under the control of the Xcr1 gene while preserving XCR1 expression. We used it to generate mice with conditional deletion of MHC class II (MHCII) molecules on cDC1s. By preventing cDC1s to receive suppressive regulatory T cell inputs via MHCII-restricted interactions, the objective of the present study was to gauge whether MHCII-deficient cDC1s lose their capacity of tolerizing autoreactive CD8+ T cells. Whereas MHCII+ cDC1 readily cross-tolerized strongly autoreactive CD8+ T cells specific for a keratinocyte-derived self-antigen, MHCII-deficient cDC1s converted them into potent effectors capable of triggering a fast-onset lethal autoimmunity associated with severe skin histopathological manifestations. Preventing egress of such pathogenic self-reactive CD8+ T cell effectors from the cutaneous draining lymph nodes abrogated the autoimmune condition. Therefore, our results revealed that the cross-tolerizing capacity of cDC1s is not a property fully acquired at the time they undergo homeostatic maturation but needs to be enforced via MHCII-restricted, suppressive interactions with regulatory T cells.

Alloantigen gene transfer to hepatocytes promotes tolerance to pancreatic islet graft by inducing CD8+ regulatory T cells.

BACKGROUND & AIMS: Induction of donor-specific immune tolerance is a good alternative to chronic life-long immunosuppression for transplant patients. Donor major histocompatibility complex (MHC) molecules represent the main targets of the allogeneic immune response of transplant recipients. Liver targeted gene transfer with viral vectors induces tolerance toward the encoded antigen. The aim of this work was to determine whether alloantigen gene transfer to hepatocytes induces tolerance and promotes graft acceptance. METHODS: C57BL/6 (H-2b) mice were treated with adeno-associated viral (AAV) vector targeting the expression of the MHC class I molecule H-2Kd to hepatocytes, before transplantation with fully allogeneic pancreatic islet from BALB/c mice (H-2d). RESULTS: AAV H-2Kd treated mice were tolerant to the alloantigen, as demonstrated by its long-term expression by the hepatocytes, even after a highly immunogenic challenge with an adenoviral vector. After chemical induction of diabetes, the AAV treated mice had significantly delayed rejection of fully allogeneic pancreatic islet grafts, with more than 40% of recipients tolerant (>100days). AAV-mediated expression of H-2Kd in the liver induced the local expansion of CD8+ T lymphocytes with allo-specific suppressive properties. The adoptive transfer of these liver-generated CD8+ Tregs into naive diabetic mice promoted the long-term survival of allogeneic pancreatic islet grafts. CONCLUSION: AAV-mediated long-term expression of a single MHC class I molecule in the liver induces the generation of a subset of allo-specific CD8+ Treg cells, which promote tolerance toward fully allogeneic graft. Liver gene transfer represents a promising strategy for in vivo induction of donor-specific tolerance. LAY SUMMARY: The liver has a special immune system, biased toward tolerance. In this study, we investigated the possibility of harnessing this property of the liver to induce tolerance to an allogeneic transplantation. We demonstrate for the first time that the in vivo gene transfer of an allogeneic antigen with an adeno-associated viral vector to mouse hepatocytes induces the expansion of a population of CD8+ regulatory T lymphocytes. These Tregs are then instrumental in preventing the rejection of allogeneic pancreatic islets transplanted in these animals. Allogeneic transplantation is the main treatment for the end-stage diseases of a number of organs. Life-long immunosuppressive treatments are still required to limit graft rejection, and these treatments exhibit serious side effects. Our present findings open a new avenue for promoting allo-specific tolerance via in vivo induction of CD8+ Treg expansion.

Agonistic anti-CD137 antibody treatment leads to antitumor response in mice with liver cancer.

Immunotherapy is a promising strategy against hepatocellular carcinoma (HCC). We assessed the therapeutic effects of stimulating CD137, a member of the TNF receptor family, with agonistic monoclonal antibodies (mAb). Agonistic anti-CD137 mAb treatment was tested on two in situ models of HCC in immunocompetent mice. We also studied the mediators involved at different time points. In an orthotopic HCC the treatment consistently leads to complete tumor regression in 40-60% of animals. The protection is long lasting in the animals responding to the treatment, which can reject a second tumor challenge more than 3 months after treatment and eradication of the first malignancy. The main mediators of the effect are T lymphocytes and NK cells, demonstrated through depletion experiments. In addition, adoptive transfer of splenocytes prepared from anti-CD137 mAb-treated and -cured mice to naive mice allowed them to, in turn, reject the tumor. The efficacy of anti-CD137 mAb treatment is associated with early, sustained recruitment of iNOS-positive macrophages within tumor nodules. Moreover, in the absence of treatment, tumor development is accompanied by infiltration by myeloid derived suppressor cells (MDSC) and regulatory T lymphocytes. In mice responding to the anti-CD137 mAb treatment, this infiltration is very limited, and a combination treatment with a depletion of MDSC leads to the recovery of 80% of the mice. These results demonstrate that agonistic anti-CD137 mAb is a promising therapeutic strategy for anti-tumor immunity stimulation against HCC.