Enhanced Tumor Eradication by Combining CTLA-4 or PD-1 Blockade With CpG Therapy

Abstract

Tumor immunotherapy aims to break effector T-cell anergy and to block suppressive cell types and ligands allowing effector cells to exert tumor eradication. Previous reports demonstrate that cytotoxic T lymphocyte antigen-4 (CTLA-4)-blocking antibodies promote T-cell activation and render T effector cells resistant to T regulatory cells (Tregs) whereas programmed death receptor-1 (PD-1)/PD-L1 blockade results in loss of peripheral tolerance. Herein, we explored single or combined antibody blockade of CTLA-4 and PD-1 alone or combined with the toll-like receptor agonists CpG or bacillus Calmette-Guérin for treatment of murine experimental bladder cancer. In therapeutic studies, tumors were rejected by anti-CTLA-4 (aCTLA-4) while anti-PD-1 (aPD-1) suppressed tumor growth. The combination had no additive effect compared with aCTLA-4 alone. However, elevated levels of circulating CD107a expressing CD8 T cells were found in the aCTLA-4 plus aPD-1 group. In addition, levels of antinuclear antibodies correlated inversely with tumor size. Next, we combined CpG or bacillus Calmette-Guérin with aCTLA-4, aPD-1, or aPD-L1 and found that CpG in combination with aCTLA-4 or aPD-1 increased the survival of mice, with aPD-1 plus CpG being superior to either agent alone. CpG plus aCTLA-4 or aPD-1 increased the numbers of circulating tumor-specific CD107a expressing CD8 T cells as well as activated (CD25FoxP3-) CD4 splenocytes. Further, we investigated the numbers of Tregs in the tumor area of treated animals and detected decreased levels after aCTLA-4 or aPD-1 plus CpG therapy. Thus, the combination of CpG with CTLA-4 or PD-1 blockade improved long-term survival and led to increased levels of tumor-reactive T cells and reduced numbers of Tregs at the tumor site.

Locally Delivered CD40 Agonist Antibody Accumulates in Secondary Lymphoid Organs and Eradicates Experimental Disseminated Bladder Cancer

“…Radical cystectomy for patients with muscle-invasive bladder cancer results in initial tumor control, but provides a 5-year survival rate of only 40% to 60% due to the presence of micrometastatic disease (2). We have previously shown that local adenoviral CD40L (AdCD40L) as well as CpG therapy can induce systemic antitumor responses in experimental bladder cancer (5,6). AdCD40L therapy has proven efficient and safe in both humans (7) and dogs (8).…”

Signaling Mechanisms that Balance Anti-viral, Auto-reactive, and Antitumor Potential of Low Affinity T Cells

“…However, other reports show that the therapeutic improvements are modest [80] and in some cases restricted to antigen presentation in the context of minor histocompatibility complexes [63]. In most of the experimental systems and clinical trials, PD-L1/PD-1 blockade works best in combination with other immune-stimulatory approaches, or even chemotherapy [62,64,81,82]. Even though PD-L1/PD-1 blockade may in fact lead to inflammatory responses (Table 1), we propose that reinforcing T cell differentiation by providing strong signals three will certainly improve PD-L1/PD-1 blocking as an effective therapeutic strategy.…”

“…Thus, its blockade augments anti-cancer immune responses and improves immunotherapy [59,60]. However, in many instances PD-L1/PD-1 blockade or silencing using siRNA results in limited therapeutic activities, unless given in combination with other treatments such as co-administration with anti-CTLA4 antibodies [61,62], PD-L2-blocking antibodies [63], TLR ligands [62], chemotherapy [64], cytokine treatments [65] or modulators of intracellular signalling pathways in DCs [39]. It is yet unclear why PD-L1/PD-1 blockade on its own does not achieve optimal therapeutic effects in these experimental models.…”

Animal Models for Basic and Preclinical Research in Bladder Cancer

“…Antibodies able to block PD-L1 and CTLA-4 administered intratumorally improves long-term survival and leads to increased levels of tumor-reactive T cells and decreased numbers of Tregs at the tumor site. Therefore, this experimental model has allowed an approach to the understanding of immune suppression during immune therapy with BCG and represents a new therapeutic option in the treatment of bladder cancer (Mangsbo et al, 2010).…”