Pratima Bansal-Pakala

Signaling through OX40 (CD134) breaks peripheral T-cell tolerance

Peripheral T-cell tolerance is a mechanism to limit autoimmunity, but represents a major obstacle in diseases such as cancer. Tolerance is due to limited accumulation of antigen-specific T cells accompanied by functional hypo-responsiveness, and is induced by antigen encounter in a non-inflammatory environment. In contrast to advances in preventing induction of T-cell tolerance, there has been little progress in defining targets to reverse established tolerance. Here we show that signals from a single dose of an agonistic antibody against OX40 (CD134, a member of the tumor necrosis-factor family of receptors) can break an existing state of tolerance in the CD4+ T-cell compartment. OX40 signals promote T-cell expansion after the hypo-responsive phenotype is induced and restore normal functionality. These data highlight the potent costimulatory capacity of OX40, and indicate OX40 as a target for therapeutic intervention in a variety of related diseases.

Costimulation of CD8 T Cell Responses by OX40

The persistence of functional CD8 T cell responses is dependent on checkpoints established during priming. Although naive CD8 cells can proliferate with a short period of stimulation, CD4 help, inflammation, and/or high peptide affinity are necessary for the survival of CTL and for effective priming. Using OX40-deficient CD8 cells specific for a defined Ag, and agonist and antagonist OX40 reagents, we show that OX40/OX40 ligand interactions can determine the extent of expansion of CD8 T cells during responses to conventional protein Ag and can provide sufficient signals to confer CTL-mediated protection against tumor growth. OX40 signaling primarily functions to maintain CTL survival during the initial rounds of cell division after Ag encounter. Thus, OX40 is one of the costimulatory molecules that can contribute signals to regulate the accumulation of Ag-reactive CD8 cells during immune responses.

4–1BB (CD137) controls the clonal expansion and survival of CD8 T cells in vivo but does not contribute to the development of cytotoxicity

4–1BB is expressed on activated T cells. We analyzed the role of 4–1BB during the CD8 T cell response of OT‐I TCR‐transgenic T cells to ovalbumin. In vitro, blocking 4–1BB during peptide presentation reduced proliferation of naive CD8 T cells, but did not affect the generation of CTL. Using an in vivo adoptive transfer model, clonal expansion of CD8 T cells to whole protein in adjuvant was significantly reduced when 4–1BB was blocked, with 50–70% fewer CD8 T cells accumulating. This was due to a reduction in T cell division and to enhanced apoptosis of CD8 T cellsthat had undergone many divisions. T cells generated in the absence of 4–1BB were impaired in their ability to secrete IFN‐γ whereas CTL activity of the T cells that survived was unaffected. These findings demonstrate that 4–1BB contributes to clonal expansion, survival, and development of Tc1 cells when protein antigen is encountered by primary CD8 T cells in an inflammatory environment in vivo.

Prevention of diabetes in NOD mice at a late stage by targeting OX40/OX40 ligand interactions.

Autoreactive T cells play a major role in the development of insulin‐dependent diabetes mellitus, suggesting that costimulatory molecules that regulate T cell responses might be essential for disease progression. In NOD mice, CD28/B7 and CD40/CD40 ligand (L) interactions control the onset of diabetes from 2 to 4 weeks of age, but blocking these molecules has little effect after this time. Hence, it is possible that other ligand/receptor pairs control a later phase of disease. We now show that OX40 is expressed on CD4 and CD8 T cells several weeks prior to islet destruction, which is initiated around weeks 12–14, and that OX40L is present on dendritic cells in both secondary lymphoid organs and the pancreas from 11 to 13 weeks of age. Blocking OX40L at 6, 9, or 15 weeks after birth had little effect on disease; however, inhibiting OX40/OX40L interactions at week 12, or continuous treatment from week 12 onwards, significantly reduced the incidence of diabetes. Histological examination showed that islet destruction was prevented and insulitis reduced by targeting OX40L. These studies show that OX40/OX40L interactions form a late checkpoint in diabetes development and suggest that these molecules are realistic targets for therapeutic intervention.

Breaking Immunological Tolerance through OX40 (CD134)

Immunological tolerance represents a mechanism by which cells of the host remain protected from the immune system. Breaking of immunological tolerance can result in a variety of autoimmune diseases such as rheumatoid arthritis, diabetes, and multiple sclerosis. The reasons for tolerance breaking down and autoimmune processes arising are largely unknown but of obvious interest for therapeutic intervention of these diseases. Although reversal of the tolerant state is generally unwanted, there are instances where this may be of benefit to the host. In particular, one way a cancerous cell escapes being targeted by the immune system is through tolerance mechanisms that in effect turn off the reactivity of T lymphocytes that can respond to tumor-associated peptides. Thus tolerance represents a major obstacle in developing effective immunotherapy against tumors. The molecules that are involved in regulating immunological tolerance are then of interest as they may be great targets for positively or negatively manipulating the tolerance process.