4-1BB (CD137, TNFRSF9) is a costimulatory receptor expressed on several subsets of activated immune cells. Numerous studies of mouse and human T cells indicate that 4-1BB promotes cellular proliferation, survival, and cytokine production. 4-1BB agonist mAbs have demonstrated efficacy in prophylactic and therapeutic settings in both monotherapy and combination therapy tumor models and have established durable anti-tumor protective T-cell memory responses. PF-05082566 is a fully human IgG2 that binds to the extracellular domain of human 4-1BB with high affinity and specificity. In preclinical studies, this agonist antibody demonstrated its ability to activate NF-κB and induce downstream cytokine production, promote leukocyte proliferation, and inhibit tumor growth in a human PBMC xenograft tumor model. The mechanism of action and robust anti-tumor efficacy of PF-05082566 support its clinical development for the treatment of a broad spectrum of human malignancies.

Cardiac antigen-specific CD8(+) T cells are involved in the autoimmune component of human myocarditis. Here, we studied the differentiation and migration of pathogenic CD8(+) T cell effector cells in a new mouse model of autoimmune myocarditis. A transgenic mouse line was derived that expresses cardiac myocyte restricted membrane-bound ovalbumin (CMy-mOva). The endogenous adaptive immune system of CMy-mOva mice displays tolerance to ovalbumin. Adoptive transfer of naive CD8(+) T cells from the ovalbumin-specific T cell receptor-transgenic (TCR-transgenic) OT-I strain induces myocarditis in CMy-mOva mice only after subsequent inoculation with ovalbumin-expressing vesicular stomatitis virus (VSV-Ova). OT-I effector T cells derived in vitro in the presence or absence of IL-12 were adoptively transferred into CMy-mOva mice, and the consequences were compared. Although IL-12 was not required for the generation of cytolytic and IFN-gamma-producing effector T cells, only effectors primed in the presence of IL-12 infiltrated CMy-mOva hearts in significant numbers, causing lethal myocarditis. Furthermore, analysis of OT-I effectors collected from a mediastinal draining lymph node indicated that only effectors primed in vitro in the presence of IL-12 proliferated in vivo. These data demonstrate the importance of IL-12 in the differentiation of pathogenic CD8(+) T cells that can cause myocarditis.

Cardiac antigen-specific CD8 + T cells are involved in the autoimmune component of human myocarditis. Here, we studied the differentiation and migration of pathogenic CD8 + T cell effector cells in a new mouse model of autoimmune myocarditis. A transgenic mouse line was derived that expresses cardiac myocyte restricted membrane-bound ovalbumin (CMy-mOva). The endogenous adaptive immune system of CMy-mOva mice displays tolerance to ovalbumin. Adoptive transfer of naive CD8 + T cells from the ovalbumin-specific T cell receptor-transgenic (TCR-transgenic) OT-I strain induces myocarditis in CMy-mOva mice only after subsequent inoculation with ovalbuminexpressing vesicular stomatitis virus (VSV-Ova). OT-I effector T cells derived in vitro in the presence or absence of IL-12 were adoptively transferred into CMy-mOva mice, and the consequences were compared. Although IL-12 was not required for the generation of cytolytic and IFN-γ-producing effector T cells, only effectors primed in the presence of IL-12 infiltrated CMy-mOva hearts in significant numbers, causing lethal myocarditis. Furthermore, analysis of OT-I effectors collected from a mediastinal draining lymph node indicated that only effectors primed in vitro in the presence of IL-12 proliferated in vivo. These data demonstrate the importance of IL-12 in the differentiation of pathogenic CD8 + T cells that can cause myocarditis.

Abstract-CD8ϩ cytotoxic T lymphocytes contribute to viral and autoimmune myocarditis and cardiac allograft rejection. The role of cytotoxic T-lymphocyte-associated antigen (CTLA)-4 as a negative regulator of CD4 ϩ T cells is well defined, yet CTLA-4 regulation of CD8 ϩ T cells is less clear. We studied CTLA-4 regulation of cytotoxic T lymphocytes in a transgenic model of CD8 ϩ T-cell-mediated myocarditis. We generated CTLA-4 Ϫ/Ϫ Rag 2 Ϫ/Ϫ OT-1 mice, the CD8 ϩ T cells of which express an ovalbumin (OVA) peptide-specific, class I major histocompatibility complex-restricted T-cell receptor. CTLA-4Ϫ/ϪTc12 OT-1 effectors, differentiated with interleukin-12 present, are hyperproliferative in vitro, compared with CTLA-4 ϩ/ϩTc12 OT-1 controls. Transfer of low doses of CTLA-4 Ϫ/ϪTc12 OT-1 cells to cMy-mOVA mice, which express OVA on cardiac myocytes, causes severe myocarditis, with 99% mortality, compared with no mortality after transfer of low doses of CTLA-4 ϩ/ϩTc12 OT-1 cells. High doses of CTLA-4 ϩ/ϩTc12 cells cause lethal myocarditis in cMy-mOVA mice, but high doses of CTLA-4 ϩ/ϩTc0 CTL, generated without interleukin-12, are hypoproliferative within the cardiac-draining lymph node and do not significantly infiltrate the heart. In contrast, CTLA-4 Ϫ/ϪTc0 cytotoxic T lymphocytes do proliferate in the cardiac-draining lymph node and diffusely infiltrate the heart. Nonetheless, high doses of CTLA-4 Ϫ/ϪTc0 cells cause only limited tissue damage, and the disease is not lethal. These data show that CTLA-4 regulates myocarditic CD8 ϩ T cell responses and that CTLA-4 deficiency partly overcomes a differentiation block that exists when naïve CD8 ϩ T cells are stimulated without interleukin-12. Therefore, targeting CTLA-4 solely or in conjunction with interleukin-12 could influence effector CD8 ϩ T cell responses in therapeutically beneficial ways. ϩ T-cell activation and differentiation by members of the B7 and CD28 regulatory molecules remain incompletely understood. Cytotoxic T-lymphocyte antigen (CTLA)-4 is a CD28 family member that is expressed on the surface of lymphocytes after T-cell receptor (TCR) stimulation. 1 CTLA-4 and CD28 share specificity for the B7 molecules CD80 (B7-1) and CD86 (B7-2). It is well documented that CD80 and CD86 binding to CTLA-4 on CD4 ϩ T cells results in downregulation of cell-cycle progression and interleukin (IL)-2 production. 2,3 In contrast, there are conflicting studies regarding the effects of CTLA-4 ligation on CD8 ϩ T-cell regulation. 4,5 Several reports indicated that CTLA-4 blockade does not alter cytotoxic T lymphocyte (CTL) responses to lymphocytic choriomeningitis virus, mouse mammary tumor virus, or Leishmania major infection in mice. 4,6,7 Yet experiments with CTLA-4 -deficient class I major histocompatibility complex-restricted TCR transgenic mice indicate that CTLs are hyperresponsive to antigen on restimulation, suggesting a negative regulatory role in CTL activation. 4,5,8 Furthermore, blockade of CTLA-4 with neutralizing antibody augments CTL-mediated responses against tu...

No abstract