InVivoMAb anti-mouse/human/rat/monkey ICOS (CD278)

InVivoMAb anti-mouse/human/rat/monkey ICOS (CD278) (CLONE: C398.4A)

Stone, E. L., et al (2015). "ICOS coreceptor signaling inactivates the transcription factor FOXO1 to promote Tfh cell differentiation" Immunity 42(2): 239-251. PubMed

T follicular helper (Tfh) cells are essential in the induction of high-affinity, class-switched antibodies. The differentiation of Tfh cells is a multi-step process that depends upon the co-receptor ICOS and the activation of phosphoinositide-3 kinase leading to the expression of key Tfh cell genes. We report that ICOS signaling inactivates the transcription factor FOXO1, and a Foxo1 genetic deletion allowed for generation of Tfh cells with reduced dependence on ICOS ligand. Conversely, enforced nuclear localization of FOXO1 inhibited Tfh cell development even though ICOS was overexpressed. FOXO1 regulated Tfh cell differentiation through a broad program of gene expression exemplified by its negative regulation of Bcl6. Final differentiation to germinal center Tfh cells (GC-Tfh) was instead FOXO1 dependent as the Foxo1(-/-) GC-Tfh cell population was substantially reduced. We propose that ICOS signaling transiently inactivates FOXO1 to initiate a Tfh cell contingency that is completed in a FOXO1-dependent manner.

Hasegawa, M., et al (2013). "Augmented ICOS expression in patients with early diffuse cutaneous systemic sclerosis" Rheumatology (Oxford) 52(2): 242-251. PubMed

OBJECTIVE: Inducible costimulator (ICOS), expressed on activated T cells, and its ligand, ICOS ligand (ICOSL), expressed on antigen-presenting cells, have been considered a single receptor-ligand pair. Here we investigated the expression of ICOS and ICOSL in patients with SSc. METHODS: ICOS expression on peripheral blood T cells, and ICOSL expression on B cells and macrophages was determined by flow cytometry. Expression of ICOS and ICOSL was assessed by immunohistological staining and real-time PCR of lesional skin. RESULTS: ICOS expression levels were specifically increased on both peripheral blood memory T cells and Tregs from early dcSSc patients compared with those from healthy controls. Mean ICOSL expression on B cells or macrophages was comparable between SSc patients and healthy controls. ICOS-expressing T cells, ICOSL-expressing macrophages and mRNA levels of ICOS and ICOSL were increased in the lesional skin of patients with early dcSSc. In vitro ICOS costimulation enhanced production of IFN-γ, IL-4 and IL-17A from T cells in SSc patients vs normal controls. Soluble ICOS levels were significantly increased in SSc patients and were negatively associated with the presence of ACAs and positively associated with CRP values. Serum levels of soluble ICOS were more closely associated with clinical features compared with levels of soluble IL-2 receptor. CONCLUSION: Augmented ICOS signalling may contribute to the pathogenesis of SSc during early progressive disease. Soluble ICOS levels may be used as a serum marker for the activity and severity of SSc.

Fu, T., et al (2011). "The ICOS/ICOSL pathway is required for optimal antitumor responses mediated by anti-CTLA-4 therapy" Cancer Res 71(16): 5445-5454. PubMed

The anti-CTL-associated antigen 4 (anti-CTLA-4) antibody ipilimumab is the first agent to show improved survival in a randomized phase III trial that enrolled patients with metastatic melanoma. Studies are ongoing to identify mechanisms that elicit clinical benefit in the setting of anti-CTLA-4 therapy. We previously reported that treated patients had an increase in the frequency of T cells expressing the inducible costimulator (ICOS) molecule, a T-cell-specific molecule that belongs to the CD28/CTLA-4/B7 immunoglobulin superfamily. ICOS and its ligand (ICOSL) have been shown to play diverse roles in T-cell responses such as mediating autoimmunity as well as enhancing the development/activity of regulatory T cells. These seemingly opposing roles have made it difficult to determine whether the ICOS/ICOSL pathway is necessary for antitumor responses. To determine whether the ICOS/ICOSL pathway might play a causal role in the antitumor effects mediated by anti-CTLA-4, we conducted studies in ICOS-sufficient and ICOS-deficient mice bearing B16/BL6 melanoma. We show that ICOS(+) T cells comprised a population of Th1 cytokine producing and tumor antigen-specific effector cells. Furthermore, in the absence of ICOS, antitumor T-cell responses elicited by anti-CTLA-4 are significantly diminished, thereby impairing tumor rejection. Our findings establish that the ICOS/ICOSL pathway is necessary for the optimal therapeutic effect of anti-CTLA-4, thus implicating this pathway as a target for future combinatorial strategies to improve the efficacy of anti-CTLA-4 therapy.

Redoglia, V., et al (1996). "Characterization of H4: a mouse T lymphocyte activation molecule functionally associated with the CD3/T cell receptor" Eur J Immunol 26(11): 2781-2789. PubMed

The monoclonal antibody C398.4A was produced by immunizing Armenian hamsters with the mouse T cell clone D10.G4.1. It recognizes a molecule selectively expressed by activated mouse T cells and was named H4. H4 is expressed on the T cell surface about 24 h after activation and peaks at day 7. By contrast, it is not expressed by resting or activated B cells, macrophages, or fibroblasts. It is also expressed by CD4 or CD8 single-positive mature thymocytes. Immunoprecipitation showed that H4 is a disulfide-linked dimer, precipitating as a broad band at about 50-65 kDa under nonreducing conditions and at 25 and 29 kDa under reducing conditions. Deglycosylation of the reduced H4 by N-glycanase gave rise to a single band of about 21 kDa, suggesting that the two chains may be differentially glycosylated forms of the same protein. The H4 expression pattern and biochemical features, together with cross-blocking, co-capping, co-modulation, and immunoprecipitation preclearing experiments showed that H4 is different from other known co-stimulatory molecules such as CD69, CD2, Ly-6, CD25, OX-40, Mac-1 and LFA-1. By in vitro kinase assay, H4 was found to co-precipitate a tyrosine kinase activity that phosphorylated substrates of about 29 and 25 kDa. Co-modulation and co-capping experiments showed that H4 is physically associated with the CD3/T cell receptor. These data suggest that H4 may function as a T cell-specific co-stimulatory molecule and play a role in the T cell response when the activation stimulus is limited either because the antigen is only available in low concentration or has a low agonistic activity.