OX40 Costimulation Synergizes with GM-CSF Whole-Cell Vaccination to Overcome Established CD8+ T Cell Tolerance to an Endogenous Tumor Antigen

Abstract

T cell costimulation via OX40 is known to increase CD4+ T cell expansion and effector function and enhances the development of T cell memory. OX40 costimulation can also prevent, and even reverse, CD4+ T cell anergy. However, the role of OX40 in CD8+ T cell function is less well defined, particularly in the setting of immune tolerance. To determine the effects of OX40 costimulation on the induction of the host CD8+ T cell repertoire to an endogenous tumor Ag, we examined the fate of CD8+ T cells specific for the immunodominant rat HER-2/neu epitope, RNEU420–429, in FVB MMTV-neu (neu-N) mice, which express rat HER-2/neu protein in a predominantly mammary-restricted fashion. We show that the RNEU420–429-specific T cell repertoire in neu-N mice expands transiently after vaccination with a neu-targeted GM-CSF-secreting whole-cell vaccine, but quickly declines to an undetectable level. However, OX40 costimulation, when combined with GM-CSF-secreting tumor-targeted vaccination, can break established CD8+ T cell tolerance in vivo by enhancing the expansion, and prolonging the survival and effector function of CD8+ T cells specific for RNEU420–429. Moreover, we demonstrate that OX40 expression is up-regulated on both CD4+ and CD8+ T cells shortly after administration of a GM-CSF expressing vaccine. These studies highlight the increased efficacy of OX40 costimulation when combined with a GM-CSF-secreting vaccine, and define a new role for OX40 costimulation of CD8+ T cells in overcoming tolerance and boosting antitumor immunity.

HER-2/neu-gene engineered dendritic cell vaccine stimulates stronger HER-2/neu-specific immune responses compared to DNA vaccination

“…This CTL activity is immunologically specific, in as much as none of these populations showed cytotoxic activities against the neu-negative CaD1 tumor cells. Similar degree of cytotoxicity was observed in the in vivo cytotoxicity assays, which is consistent with a report by Murata et al 45 that showed low to modest cytotoxicity activity in mice using this highly sensitive assay. More importantly, vaccination of DC neu cells stimulated significant anti-neu immunity in vivo, which protected all mice from challenge of Tg1-1 tumor cells expressing the rat neu Ag in wild-type FVB/N mice, whereas DNA vaccine only protected 50% of mice from Tg1-1 tumor cell challenge, indicating that DC neu vaccine induced much stronger neu-specific immunity than pcDNAneu DNA vaccine.…”

OX40 costimulation turns off Foxp3+ Tregs

“…17,[27][28][29][30][31][32] Conversely, amplified OX40 signaling can markedly enhance the protective immunity against infectious agents and tumors. 33 It is always believed that these findings are the sole costimulatory effects of OX40 to the T effector cells.…”

Pre-treatment with cyclophosphamide or OX40 (CD134) costimulation targeting regulatory T cell function enhances the anti-tumor immune effect of adoptively transferred CD8+ T cells from wild-type mice

“…The finding that OX40 signaling on Tregs leads to their functional inactivation without a reduction in their numbers suggests that OX40 could augment the antitumor immune effects of adoptive T cell therapy without inciting the replenishment of Tregs. OX40 costimulation enhances OX40-expressing CD8 + T cell function directly, as well as by means of CD4 + T cells (9). In the present experimental setting, in addition to the direct inhibition of Tregmediated suppression by OX40 costimulation, it is possible that OX40 signaling may have concomitantly increased a direct enhancement of adoptive CD8 + T cell function.…”

“…3T3 neu cells derived from NIH-3T3 cells overexpressing rat HER2/neu proto-oncogene were grown in 3T3 media with 0.3 μM methotrexate at 37˚C in 10% CO 2 . The 3T3 neu cells were genetically modified to express murine cytokine GM-CSF using retroviral vector MFG as previously described (9,16,17), resulting in a 3T3-neu/GM cell line.…”

“…OX40 costimulation enhances the effector function, memory development and survival of CD4 + or CD8 + T cells, resulting in the enhancement of anti-tumor immune effects in vivo (9)(10)(11)(12). OX40 signaling inhibits the Treg-mediated suppression of effector CD4 + T cells without reducing the number of Tregs (13,14), while the OX40-mediated abrogation of Treg function boosts adoptive immune response and increases tumor rejection (15).…”