N-terminal trimer extension of nominal CD8 T cell epitopes is sufficient to promote cross-presentation to cognate CD8 T cells in vivo

Brachyury-targeted immunotherapy combined with gemcitabine against head and neck cancer

Brachyury is a transcription factor belonging to the T-box gene family and is involved in the posterior formation of the mesoderm and differentiation of chordates. As the overexpression of Brachyury is a poor prognostic factor in a variety of cancers, the establishment of Brachyury-targeted therapy would be beneficial for the treatment of aggressive tumors. Because transcription factors are difficult to treat with a therapeutic antibody, peptide vaccines are a feasible approach for targeting Brachyury. In this study, we identified Brachyury-derived epitopes that elicit antigen-specific and tumor-reactive CD4⁺ T cells that directly kill tumors. T cells recognizing Brachyury epitopes were present in patients with head and neck squamous cell carcinoma. Next, we focused on gemcitabine (GEM) as an immunoadjuvant to augment the efficacy of antitumor responses by T cells. Interestingly, GEM upregulated HLA class I and HLA-DR expression in tumor, followed by the upregulation of anti-tumor T cell responses. As tumoral PD-L1 expression was also augmented by GEM, PD-1/PD-L1 blockade and GEM synergistically enhanced the tumor-reactivity of Brachyury-reactive T cells. The synergy between the PD-1/PD-L1 blockade and GEM was also confirmed in a mouse model of head and neck squamous cell carcinoma. These results suggest that the combined treatment of Brachyury peptide with GEM and immune checkpoint blockade could be a promising immunotherapy against head and neck cancer.

Antitumor Peptide-Based Vaccine in the Limelight

The success of the immune checkpoint blockade has provided a proof of concept that immune cells are capable of attacking tumors in the clinic. However, clinical benefit is only observed in less than 20% of the patients due to the non-specific activation of immune cells by the immune checkpoint blockade. Developing tumor-specific immune responses is a challenging task that can be achieved by targeting tumor antigens to generate tumor-specific T-cell responses. The recent advancements in peptide-based immunotherapy have encouraged clinicians and patients who are struggling with cancer that is otherwise non-treatable with current therapeutics. By selecting appropriate epitopes from tumor antigens with suitable adjuvants, peptides can elicit robust antitumor responses in both mice and humans. Although recent experimental data and clinical trials suggest the potency of tumor reduction by peptide-based vaccines, earlier clinical trials based on the inadequate hypothesis have misled that peptide vaccines are not efficient in eliminating tumor cells. In this review, we highlighted the recent evidence that supports the rationale of peptide-based antitumor vaccines. We also discussed the strategies to select the optimal epitope for vaccines and the mechanism of how adjuvants increase the efficacy of this promising approach to treat cancer.

Peripheral Deletion of CD8 T Cells Requires p38 MAPK in Cross-Presenting Dendritic Cells

Peripheral tolerance mechanisms exist to prevent autoimmune destruction by self-reactive T cells that escape thymic deletion. Dominant tolerance imposed by CD4⁺Foxp3⁺ T regulatory cells can actively control autoaggressive T cell responses. Tolerance mechanisms that act endogenous to the T cell also exist. These mechanisms include T cell inactivation (anergy) and deletion. A major difference between anergic T cells and T cells undergoing peripheral deletion is the capacity of the latter to still signal through MAPKs upon TCR stimulation, suggesting these signals may be required for T deletion. In this study, we used several different models of CD8 T cell deletion to investigate the contribution of MAPK activation. Using chemical inhibitors, we established that inhibition of p38, but not ERK or JNK, rescue T cells from undergoing peripheral deletion both in vitro and in vivo. Using T cell-specific murine lines genetically altered in expression of p38α, and mice in which p38α was deleted only in CD11c-expressing cells, we surprisingly found that CD8 T cell-intrinsic p38α activation was not responsible for increased survival, but rather that inhibition of p38α in the Ag-presenting dendritic cells prevented CD8 T cell deletion.

Peptide vaccines in cancer-old concept revisited

Synthetic peptide vaccines aim to elicit and expand tumor-specific T cells capable of controlling or eradicating the tumor. Despite the high expectations based on preclinical studies, the results of clinical trials using peptide vaccines have been disappointing. Thus, many researchers in the field have considered peptide vaccines as outdated and no longer viable for cancer therapy. However, recent progress in understanding the critical roles of immune adjuvants, modes of vaccine administration and T cell dynamics has lead to a rebirth of this approach and reconsidering the use of peptide vaccines for treating malignant disorders.

Contribution of TCR signaling strength to CD8+ T cell peripheral tolerance mechanisms

Peripheral tolerance mechanisms are in place to prevent T cells from mediating aberrant immune responses directed against self and environmental Ags. Mechanisms involved in the induction of peripheral tolerance include T cell-intrinsic pathways, such as anergy or deletion, or exogenous tolerance mediated by regulatory T cells. We have previously shown that the density of peptide-MHC class I recognized by the TCR determines whether CD8(+) T cells undergo anergy or deletion. Specifically, using a TCR-transgenic CD8(+) T cell model, we demonstrated that persistent peripheral exposure to low- or high-dose peptides in the absence of inflammatory signals resulted in clonal deletion or anergy of the T cell, respectively. In this study, by altering the affinity of the peptide-MHC tolerogen for TCR, we have confirmed that this mechanism is dependent on the level of TCR signaling that the CD8(+) T cell receives. Using altered peptide ligands (APLs) displaying high TCR affinities, we show that increasing the TCR signaling favors anergy induction. Conversely, using APLs displaying a decreased TCR affinity tilted our system in the direction of deletional tolerance. We demonstrate how differential peripheral CD8(+) T cell tolerance mechanisms are controlled by both the potency and density of MHC class I-peptide tolerogen.

Mechanisms of peptide vaccination in mouse models: tolerance, immunity, and hyperreactivity

The development of synthetic peptide vaccines capable of inducing strong and protective T-cell immunity has taken more than 20 years. Peptide vaccines come in many flavors and although their design is simple, their use is more complicated as the success of a particular peptide vaccine is influenced by many parameters. In fact, peptide vaccination may lead to tolerance, immunity or even hyper-reactivity causing death of the animals. Here we systematically dissect the parameters that influence the final outcome of peptide vaccines as examined in mouse models and this will guide the rational design of new vaccines in the future.

Designing CD8+ T cell vaccines: it's not rocket science (yet)

CD8+ T cells play important roles in clearing viral infections and eradicating tumors. Designing vaccines that elicit effective CD8+ T cell responses requires a thorough knowledge of the pathways of antigen presentation in vivo. Here, I review recent progress in understanding the activation of naïve CD8+ T cells in vivo, with particular emphasis on cross-priming, the presentation of protein antigens acquired by dendritic cells from their environment. With the rapid advances in this area of research, the dawn of rational vaccine design is at hand.