Frank J. Ward

The soluble isoform of CTLA-4 as a regulator of T-cell responses

CTLA‐4 is a crucial immune regulator that mediates both negative costimulation signals to T cells, and regulatory T (Treg)‐cell extrinsic control of effector responses. Here we present evidence supporting a novel mechanism for this extrinsic suppression, executed by the alternatively spliced soluble CTLA‐4 isoform (sCTLA‐4). Analyses of human T cells in vitro show that sCTLA‐4 secretion can be increased during responses, and has potent inhibitory properties, since isoform‐specific blockade of its activity significantly increased Ag‐driven proliferation and cytokine (IFN‐γ, IL‐17) secretion. Treg cells were demonstrated to be a prominent source of sCTLA‐4, which contributed to suppression in vitro when their numbers were limiting. The soluble isoform was also produced by, and inhibited, murine T cells responding to Ag in vitro, and blockade of its activity in vivo protected against metastatic spread of melanoma in mice. We conclude that sCTLA‐4 is an important immune regulator, responsible for at least some of the inhibitory effects previously ascribed to the membrane‐bound isoform. These results suggest that the immune system exploits the different CTLA‐4 isoforms for either intrinsic or extrinsic regulation of T‐cell activity.

Targeting the alternatively spliced soluble isoform of CTLA-4: prospects for immunotherapy?

CTLA-4 is an inhibitory protein that contributes to immune homeostasis and tolerance, a role that has led to its exploitation as a therapeutic in several clinical settings including cancer and autoimmune disease. Development of CTLA-4 therapies focused largely on the full-length receptor isoform but other CTLA-4 isoforms are also expressed, including a secretable form of CTLA-4 (soluble CTLA-4 [sCTLA-4]). The contribution of sCTLA-4 to immune regulation has been less well studied, primarily because it was identified some years after the original description of CTLA-4. Here, we examine how sCTLA-4 might contribute to immune regulation and ask whether it might be a biomarker to inform current CTLA-4 therapies or represent a novel CTLA-4 target for future therapeutics.

Indoleamine 2,3 dioxygenase contributes to transferable tolerance in rat red blood cell inducible model of experimental autoimmune haemolytic anaemia

Autoimmune haemolytic anaemia (AIHA) is caused by autoantibodies against red blood cell (RBC) surface antigens that render RBC susceptible to Fc‐mediated phagocytosis and complement‐mediated lysis. Experimental AIHA can be induced by injection of rat RBC to naive mice, but a lymphocyte‐mediated regulatory mechanism eventually suppresses the production of autoantibodies specific for mouse RBC. Critically, this tolerogenic response can be transferred to naive mice by splenocytes from the rat RBC‐immunized mouse. Here we investigate whether indoleamine 2,3 dioxygenase (IDO) or the initiators of IDO cascade, including the cytotoxic T lymphocyte antigen (CTLA)‐4 receptor and its soluble isoform, contribute to this tolerogenic mechanism. Splenocytes from experimental AIHA mice were transferred adoptively to naive mice under the cover of anti‐CTLA‐4, anti‐soluble CTLA‐4 antibodies or IDO inhibitor 1‐methyl tryptophan (1‐MT). Recipient mice were immunized with rat RBC and levels of antibody against self‐RBC and rat‐RBC were monitored. Our results indicate that transfer of tolerance to naive recipients is dependent upon IDO‐mediated immunosuppression, as mice receiving previously tolerized splenocytes under the cover of 1‐MT were refractory to tolerance and developed haemolytic disease upon further challenge with rat RBC. Initiators of IDO activity, CTLA‐4 or soluble CTLA‐4 did not mediate this tolerogenic process but, on their blockade, boosted antigen‐specific effector immune responses.

Immunoregulatory soluble CTLA-4 modifies effector T-cell responses in systemic lupus erythematosus.

BackgroundThe inhibitory CTLA-4 molecule is a crucial regulator of immune responses and a target for therapeutic intervention in both autoimmunity and cancer. In particular, CTLA-4 is important in controlling antigen-specific immunity, including responses to autoantigens associated with autoimmune disease. Here, we investigate cytokine responses to a range of lupus-associated autoantigens and assess whether the alternatively spliced isoform of CTLA-4, soluble CTLA-4 (sCTLA-4), contributes to immune regulation of autoantigen-specific immunity in systemic lupus erythematosus (SLE).MethodsThe cell culture supernatant production of sCTLA-4 as well as the cytokines IL-10, IFN-γ, and IL-17 from peripheral blood mononuclear cells (PBMC) from lupus patients and age- and sex-matched healthy volunteer donors were measured in response to previously identified histone and small nuclear ribonucleoprotein (snRNP) autoantigen-derived peptides (H391-105, H471-93, and U170K131-151) by ELISA. We also examined the functional contribution of sCTLA-4 to immune regulation in the context of these autoantigenic peptides following blockade of sCTLA-4 with a selective anti-sCTLA-4 monoclonal antibody, JMW-3B3.ResultsWe identified responses to autoantigenic peptides, which revealed qualitative differences in cytokine (IL-10, IL-17, and IFN-γ) profiles between SLE patients and healthy donors. PBMC from healthy donors responded to each of the lupus peptides by secreting IFN-γ and IL-17, but PBMC from SLE patients produced IL-10. Although we did not observe differences in the levels of serum or PBMC culture supernatant sCTLA-4 in either cohort, blockade of sCTLA-4 in PBMC cultures responding to antigen enhanced the cytokine profiles associated with each group.ConclusionThe results show that lupus autoantigen-derived peptides display varied immunogenicity in lupus versus healthy volunteer donors, while sCTLA-4 acts to regulate the T-cell activity independently of response profile.

Hiding in Plain Sight: Soluble Immunomodulatory Receptors

Alternatively spliced natural soluble isoforms of immunomodulatory receptors [cytotoxic T lymphocyte antigen-4 (CTLA-4), 4-1BB, and programmed death-1 (PD-1)/PD-L1] have been overlooked in favor of their cell-surface-bound counterparts that have generated blockbuster antibodies for the treatment of cancer. We propose that the soluble variants of these receptors contribute to immune regulation and offer potential as targets for immunotherapy.

On the Road to Immunotherapy—Prospects for Treating Head and Neck Cancers With Checkpoint Inhibitor Antibodies

Head and neck cancers (HNC) represent a heterogeneous cluster of aggressive malignancies that account for 3% of all cancer cases in the UK. HNC is increasing in frequency particularly in the developing world, which is related to changes in risk factors. Unfortunately, the mortality rate is high, which is chiefly attributed to late diagnosis at stages where traditional treatments fail. Cancer immunotherapy has achieved great successes in anti-tumor therapy. Checkpoint inhibitor (CI) antibodies enhance anti-tumor activity by blocking inhibitory receptors to drive tumor-specific T and NK cell effector responses. Since their introduction in 2011, CI antibodies have been approved for many cancer types including HNC. Here, we examine the development of CI therapies and look forward to future developments for treatment of HNC with CI therapies.

Isolation, Polarization, and Expansion of CD4 + Helper T Cell Lines and Clones Using Magnetic Beads

Autoreactive CD4⁺ helper T cells specific for a range of nucleoprotein-derived autoantigens are an important feature of systemic lupus erythematosus, driving B cell differentiation and autoantibody production and contributing to the inflammatory lesions caused by immune complex deposition. Several peptide epitopes from nucleoprotein antigens have been identified and offer a means selectively to manipulate T cell responses by skewing toward a profile of cytokines that is less pro-inflammatory. Antigen-specific T cell lines and clones can be useful in the study of helper T cell subsets because their life span is prolonged and many individual cells can be generated, allowing particular phenotypes to be studied in detail. Magnetic beads offer a robust and convenient method for the isolation, polarization, and expansion of T cells, which can be adapted for a broad range of applications.