The DTA-1 monoclonal antibody reacts with mouse GITR (glucocorticoid-induced TNFR-related gene), a 66-70 kDa co-stimulatory immune checkpoint molecule belonging to the Tumor Necrosis Factor superfamily (TNFRSF18). GITR is expressed at low levels on resting T lymphocytes and at high levels on regulatory T cells. GITR is upregulated on activated T cells where it provides co-stimulation. GITR ligand (GITRL) is found on B cells, macrophages, dendritic and endothelial cells, and is implicated in regulating both innate and adaptive immune responses. GITR is also thought to play a key role in dominant immunological self-tolerance maintained by regulatory T cells. Knockout studies in mice also suggest the role of this receptor is in the regulation of CD3-driven T cell activation and programmed cell death. The DTA-1 antibody is an agonistic antibody that is commonly used to induce GITR signaling in vivo.

INVIVOMAB ANTI-MOUSE GITR (CLONE: DTA-1)

Vashist, N., et al. (2018). “Influenza-Activated ILC1s Contribute to Antiviral Immunity Partially Influenced by Differential GITR Expression.” Front Immunol 9: 505. PubMed

Innate lymphoid cells (ILCs) represent diversified subsets of effector cells as well as immune regulators of mucosal immunity and are classified into group 1 ILCs, group 2 ILCs, and group 3 ILCs. Group 1 ILCs encompass natural killer (NK) cells and non-NK ILCs (ILC1s) and mediate their functionality via the rapid production of IFN-gamma and TNF-alpha. The current knowledge of ILC1s mainly associates them to inflammatory processes. Much less is known about their regulation during infection and their capacity to interact with cells of the adaptive immune system. The present study dissected the role of ILC1s during early influenza A virus infection, thereby revealing their impact on the antiviral response. Exploiting in vitro and in vivo H1N1 infection systems, a cross-talk of ILC1s with cells of the innate and the adaptive immunity was demonstrated, which contributes to anti-influenza immunity. A novel association of ILC1 functionality and the expression of the glucocorticoid-induced TNFR-related protein (GITR) was observed, which hints toward a so far undescribed role of GITR in regulating ILC1 responsiveness. Overexpression of GITR inhibits IFN-gamma production by ILC1s, whereas partial reduction of GITR expression can reverse this effect, thereby regulating ILC1 functionality. These new insights into ILC1 biology define potential intervention targets to modulate the functional properties of ILC1s, thus contributing toward the development of new immune interventions against influenza.

 

Bartkowiak, T., et al. (2015). “Unique potential of 4-1BB agonist antibody to promote durable regression of HPV+ tumors when combined with an E6/E7 peptide vaccine.” Proc Natl Acad Sci U S A 112(38): E5290-5299. PubMed

Antibody modulation of T-cell coinhibitory (e.g., CTLA-4) or costimulatory (e.g., 4-1BB) receptors promotes clinical responses to a variety of cancers. Therapeutic cancer vaccination, in contrast, has produced limited clinical benefit and no curative therapies. The E6 and E7 oncoproteins of human papilloma virus (HPV) drive the majority of genital cancers, and many oropharyngeal tumors. We discovered 15-19 amino acid peptides from HPV-16 E6/E7 for which induction of T-cell immunity correlates with disease-free survival in patients treated for high-grade cervical neoplasia. We report here that intranasal vaccination with these peptides and the adjuvant alpha-galactosylceramide elicits systemic and mucosal T-cell responses leading to reduced HPV(+) TC-1 tumor growth and prolonged survival in mice. We hypothesized that the inability of these T cells to fully reject established tumors resulted from suppression in the tumor microenvironment which could be ameliorated through checkpoint modulation. Combining this E6/E7 peptide vaccine with checkpoint blockade produced only modest benefit; however, coadministration with a 4-1BB agonist antibody promoted durable regression of established genital TC-1 tumors. Relative to other therapies tested, this combination of vaccine and alpha4-1BB promoted the highest CD8(+) versus regulatory FoxP3(+) T-cell ratios, elicited 2- to 5-fold higher infiltration by E7-specific CTL, and evoked higher densities of highly cytotoxic TcEO (T cytotoxic Eomesodermin) CD8 (>70-fold) and ThEO (T helper Eomesodermin) CD4 (>17-fold) T cells. These findings have immediate clinical relevance both in terms of the direct clinical utility of the vaccine studied and in illustrating the potential of 4-1BB antibody to convert therapeutic E6/E7 vaccines already in clinical trials into curative therapies.

 

Lu, L., et al. (2014). “Combined PD-1 blockade and GITR triggering induce a potent antitumor immunity in murine cancer models and synergizes with chemotherapeutic drugs.” J Transl Med 12: 36. PubMed

BACKGROUND: The coinhibitory receptor Programmed Death-1 (PD-1) inhibits effector functions of activated T cells and prevents autoimmunity, however, cancer hijack this pathway to escape from immune attack. The costimulatory receptor glucocorticoid-induced TNFR related protein (GITR) is up-regulated on activated T cells and increases their proliferation, activation and cytokine production. We hypothesize that concomitant PD-1 blockade and GITR triggering would synergistically improve the effector functions of tumor-infiltrating T cells and increase the antitumor immunity. In present study, we evaluated the antitumor effects and mechanisms of combined PD-1 blockade and GITR triggering in a clinically highly relevant murine ID8 ovarian cancer model. METHODS: Mice with 7 days-established peritoneal ID8 ovarian cancer were treated intraperitoneally (i.p.) with either control, anti-PD-1, anti-GITR or anti-PD-1/GITR monoclonal antibody (mAb) and their survival was evaluated; the phenotype and function of tumor-associated immune cells in peritoneal cavity of treated mice was analyzed by flow cytometry, and systemic antigen-specific immune response was evaluated by ELISA and cytotoxicity assay. RESULTS: Combined anti-PD-1/GITR mAb treatment remarkably inhibited peritoneal ID8 tumor growth with 20% of mice tumor free 90 days after tumor challenge while treatment with either anti-PD-1 or anti-GITR mAb alone exhibited little antitumor effect. The durable antitumor effect was associated with a memory immune response and conferred by CD4(+) cells and CD8(+) T cells. The treatment of anti-PD-1/GITR mAb increased the frequencies of interferon-gamma-producing effector T cells and decreased immunosuppressive regulatory T cells and myeloid-derived suppressor cells, shifting an immunosuppressive tumor milieu to an immunostimulatory state in peritoneal cavity. In addition, combined treatment of anti-PD-1/GITR mAb mounted an antigen-specific immune response as evidenced by antigen-specific IFN-gamma production and cytolytic activity of spleen cells from treated mice. More importantly, combined treatment of anti-PD-1/GITR mAb and chemotherapeutic drugs (cisplatin or paclitaxel) further increased the antitumor efficacy with 80% of mice obtaining tumor-free long-term survival in murine ID8 ovarian cancer and 4 T1 breast cancer models. CONCLUSIONS: Combined anti-PD-1/GITR mAb treatment induces a potent antitumor immunity, which can be further promoted by chemotherapeutic drugs. A combined strategy of anti-PD-1/GITR mAb plus cisplatin or paclitaxel should be considered translation into clinic.

 

Bulliard, Y., et al. (2013). “Activating Fc gamma receptors contribute to the antitumor activities of immunoregulatory receptor-targeting antibodies.” J Exp Med 210(9): 1685-1693. PubMed

Fc gamma receptor (FcgammaR) coengagement can facilitate antibody-mediated receptor activation in target cells. In particular, agonistic antibodies that target tumor necrosis factor receptor (TNFR) family members have shown dependence on expression of the inhibitory FcgammaR, FcgammaRIIB. It remains unclear if engagement of FcgammaRIIB also extends to the activities of antibodies targeting immunoregulatory TNFRs expressed by T cells. We have explored the requirement for activating and inhibitory FcgammaRs for the antitumor effects of antibodies targeting the TNFR glucocorticoid-induced TNFR-related protein (GITR; TNFRSF18; CD357) expressed on activated and regulatory T cells (T reg cells). We found that although FcgammaRIIB was dispensable for the in vivo efficacy of anti-GITR antibodies, in contrast, activating FcgammaRs were essential. Surprisingly, the dependence on activating FcgammaRs extended to an antibody targeting the non-TNFR receptor CTLA-4 (CD152) that acts as a negative regulator of T cell immunity. We define a common mechanism that correlated with tumor efficacy, whereby antibodies that coengaged activating FcgammaRs expressed by tumor-associated leukocytes facilitated the selective elimination of intratumoral T cell populations, particularly T reg cells. These findings may have broad implications for antibody engineering efforts aimed at enhancing the therapeutic activity of immunomodulatory antibodies.

 

Cote, A. L., et al. (2011). “Stimulation of the glucocorticoid-induced TNF receptor family-related receptor on CD8 T cells induces protective and high-avidity T cell responses to tumor-specific antigens.” J Immunol 186(1): 275-283. PubMed

Treatment of tumor-bearing mice with a stimulatory Ab to glucocorticoid-induced TNFR family-related receptor (GITR) has previously been shown to elicit protective T cell responses against poorly immunogenic tumors. However, the role of GITR stimulation on CD8 T cells and the nature of tumor rejection Ags have yet to be determined. In this study, we show that a stimulatory mAb to GITR (clone DTA-1) acts directly on CD8 T cells, but not on CD4(+)CD25(+) regulatory T (T(reg)) cells, in B16 tumor-bearing mice to induce concomitant immunity against secondary B16 tumors, as well as protective memory following surgical excision of the primary tumor. Melanoma growth itself induced GITR expression on tumor-specific CD8 T cells, providing a mechanism whereby these cells may respond to stimulatory anti-GITR. Unexpectedly, in contrast to T(reg) cell depletion therapy with anti-CD4, GITR stimulation induced very weak CD8 T cell responses to melanocyte differentiation Ags expressed by the tumor, and did not induce autoimmune vitiligo. Accordingly, GITR-stimulated hosts that were primed with B16 melanoma rejected B16, but not the unrelated JBRH melanoma, indicating that tumor rejection Ags are tumor-specific rather than shared. In support of this, we show that GITR stimulation induces CD8 T cell responses to a tumor-specific Ag, and that these responses are of higher functional avidity compared with those induced by T(reg) cell depletion. We conclude that stimulation of GITR on effector CD8 T cells results in high-avidity T cell responses to tumor-specific Ags, thereby inducing potent antitumor immunity in the absence of autoimmunity.

 

Johanns, T. M., et al. (2010). “Regulatory T cell suppressive potency dictates the balance between bacterial proliferation and clearance during persistent Salmonella infection.” PLoS Pathog 6(8): e1001043. PubMed

The pathogenesis of persistent infection is dictated by the balance between opposing immune activation and suppression signals. Herein, virulent Salmonella was used to explore the role and potential importance of Foxp3-expressing regulatory T cells in dictating the natural progression of persistent bacterial infection. Two distinct phases of persistent Salmonella infection are identified. In the first 3-4 weeks after infection, progressively increasing bacterial burden was associated with delayed effector T cell activation. Reciprocally, at later time points after infection, reductions in bacterial burden were associated with robust effector T cell activation. Using Foxp3(GFP) reporter mice for ex vivo isolation of regulatory T cells, we demonstrate that the dichotomy in infection tempo between early and late time points is directly paralleled by drastic changes in Foxp3(+) Treg suppressive potency. In complementary experiments using Foxp3(DTR) mice, the significance of these shifts in Treg suppressive potency on infection outcome was verified by enumerating the relative impacts of regulatory T cell ablation on bacterial burden and effector T cell activation at early and late time points during persistent Salmonella infection. Moreover, Treg expression of CTLA-4 directly paralleled changes in suppressive potency, and the relative effects of Treg ablation could be largely recapitulated by CTLA-4 in vivo blockade. Together, these results demonstrate that dynamic regulation of Treg suppressive potency dictates the course of persistent bacterial infection.