However, biomarkers and assays development to guide cancer immunotherapy is highly challenging for several reasons: (i) multiplicity of immunotherapy agents with different mechanisms of action including immunotherapies that target activating and inhibitory T cell receptors (e.g., CTLA-4, PD-1, etc.); adoptive T cell therapies that include tissue infiltrating lymphocytes (TILs), chimeric antigen receptors (CARs), and T cell receptor (TCR) modified T cells; (ii) tumor heterogeneity including changes in antigenic profiles over time and location in individual patient; and (iii) a variety of immune-suppressive mechanisms in the tumor microenvironment (TME) including T regulatory cells (Treg), myeloid derived suppressor cells (MDSC) and immunosuppressive cytokines.
Since the CD8<sup>+</sup> T cells derived from tongue tumors also showed high levels of the immune checkpoint inhibitory receptor CTLA-4, we tested combination immunotherapy targeting both CTLA-4 and PD-1 together and observed 93.3% survival of mice bearing tumors in the tongue for the duration of our 100-day study.
Immunohistochemistry analysis of CTLA-4 and p-Akt in pretreatment tumor samples provides useful biomarkers that may enable improved patient selection for ipilimumab therapy.
The recent clinical success of immune checkpoint blockade (antagonists of CTLA-4, PD-1 and PD-L1) highlights both the universal power of treating the immune system across tumour types and the unique features of cancer immunotherapy.
Blocking antibodies, designed to interfere with checkpoint molecules CTLA-4 and PD-1/PD-L1 and counteract these immune suppressive mechanisms, have shown significant success in promoting immune responses against cancer and can result in tumor regression in many patients.
In cancer, therapeutic approaches targeting CTLA-4 by humanized blocking antibodies has been demonstrated to be an effective immunotherapy by reversing T-cell tolerance against tumors.
Therapeutic targeting of the immune checkpoints cytotoxic T-lymphocyte-associated molecule-4 (CTLA-4) and PD-1/PD-L1 has demonstrated tumor regression in clinical trials, and phase 2 trials are ongoing in glioblastoma (GBM).
Antitumor activity with or without anti-CTLA4 monoclonal antibody (mAb) therapy has been observed in patients with melanoma, and major tumor regressions have been observed in patients with pancreatic cancer, mesothelioma, and other tumors in combination with chemotherapy.
The impact of CTLA-4 blockade and interferon-α on clonality of T-cell repertoire in the tumor microenvironment and peripheral blood of metastatic melanoma patients.
Whereas single-agent blockade led to tumor outgrowth in all animals, dual antibody blockade against PD-1/CTLA-4 or triple blockade against PD-1/LAG-3/CTLA-4 resulted in tumor-free survival in 20% of treated mice.
<i>Methods:</i> Tumor weight, area, T cells and tumor growth (immunohistochemistry), oxidative stress, apoptosis, autophagy, and signaling (NF-κB and sirtuin-1) markers were analyzed (immunoblotting) in subcutaneous tumor of BALB/c mice injected with LP07 adenocarcinoma cells treated with monoclonal antibodies (CD-137, CTLA-4, PD-1, and CD-19, <i>N</i> = 9/group) and non-treated control animals.
Accordingly, the recent development of antibodies which target tumor cell evasion of immune checkpoints such as the cytotoxic T lymphocyte associated antigen-4 (CTLA-4) as well as the programmed cell death protein (PD-1) and the PD-1 ligand (PD-L1) has been a major and apparently highly effective approach in the treatment and/or eradication of a variety of highly malignant forms of cancers.
Compared to single treatments, a combination of intradermal DNA vaccination (ovalbumin or gp100 plasmid adjuvanted with IL12 plasmid) and immune checkpoint CTLA-4/PD-1 blockade resulted in a significant delay in tumor growth and prolonged survival of treated mice.
Additionally, manipulation of tumor immune surveillance by inhibitors of the immune suppressive programmed cell death 1 receptor (PD-1) and cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) pathways have recently demonstrated durable responses in various cancers by promoting an anti-tumor immune response.
After tumor establishment, mice were administered recombinant mouse IL-21 (mIL-21) alone or in combination with blocking monoclonal antibodies against mouse PD-1 or CTLA-4.
Treatment with anti-CTLA-4 antibody and cryoablation delayed the growth of the distant tumor by 14.8 days (p = 0.0006) and decreased the mortality rate by factor of 4 (p = 0.0003) when compared to cryoablation alone.
In a spontaneous model of breast cancer, subtle reductions in CTLA4 expression impeded tumor onset and progression, providing the first direct evidence that CTLA4 inhibits spontaneous tumor development.
While mAbs to CTLA4 plus PD-1 were therapeutically ineffective, combining the 2 of them with intraperitoneal cisplatin, 10 mg/kg, induced long-term complete tumor regression in most mice with small TC1 tumors and the therapeutic efficacy against larger tumors improved by administrating cisplatin together with the 3 or 4 mAb combination.
CTLA-4 blockade synergized more than Treg depletion with TERT DNA vaccine, suggesting that the effect of CTLA-4 blockade is more likely due to the expansion of effector T cells in the tumor rather than a reduction in the frequency of Tregs.
Combination of the mGITRL-FP with antibodies targeting PD-L1, PD-1, or CTLA-4 was analyzed in mice bearing CT26 tumors.<b>Results:</b> The mGITRL-FP had an almost 50-fold higher EC<sub>50</sub> value compared with an anti-murine GITR antibody.