Cancer vaccines: what's next?

The Tumor Immune Environment: Advances in the Cancer Immunotherapy Era

For over the last hundred years, the scientific community has demonstrated much interest in the roles of the immune system in regulating tumor progression. Extensive research that was performed in this context has revealed that mechanisms of acquired immunity can be highly potent in eradicating cancer cells, if given the right conditions to do so. Basic and clinical studies have paved the way toward the design of sophisticated modalities that improve the ability of T cells to efficiently recognize cancer antigens (when expressed by the tumor cells) and to expand thereafter; alongside developing procedures that prevent immune suppression caused by inhibitory immune checkpoints, these approaches offer cancer patients improved immunotherapies, which increase remission and prolong survival. The current chapter provides a summary of key aspects relevant to such immunotherapies, including the following: (1) cancer vaccines that enhance cancer antigen presentation; (2) adoptive cell transfer (ACT)-based therapies, like tumor-infiltrating lymphocytes (TILs) and chimeric antigen receptor expressing T cells (CAR-T cells); and (3) immune checkpoint blockades (ICBs) that downregulate the extent of immune suppression mediated by inhibitory immune checkpoint molecules, like cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), programmed cell death protein 1 (PD-1) and its ligands, primarily PD-L1 (and also PD-L2). These treatments have revolutionized the immunotherapy field, demonstrating the strong power of acquired immunity in preventing tumor growth and progression, giving much hope to cancer patients worldwide.

Tumour burden and antigen-specific T cell magnitude represent major parameters for clinical response to cancer vaccine and TCR-engineered T cell therapy

BACKGROUND

Cancer vaccines and T-cell receptor (TCR) engineered T cells (Tg-T cell) represent two different therapeutic strategies that can target the same tumour epitopes. The first approach requires the induction of a specific immune response in patients, while the second relies on the efficacy of adoptively transferred T cells. Because the ratio of antigen-specific T cells to tumour cells engaged by these strategies may influence the clinical outcome, we evaluated the efficacy of these two therapeutic approaches in solid tumours according to the tumour burden.

METHODS

We performed a meta-analysis restricted to the therapeutic vaccine and Tg-T cell trials, presenting annotated individual clinical data. We adapted a previously published mathematical model for tumour immune dynamics to estimate the clinical impact of the number of specific T cells in regard to the tumour burden.

RESULTS

A focused analysis of Tg-T cell studies revealed that clinical responses were mostly observed with the highest doses of infused T cells, suggesting that exceeding a threshold of effector T cells may be required for clinical efficacy. In silico modelling of cancer vaccine and Tg-T cell therapies starting at different tumour burdens showed that therapeutic vaccines control low or moderate tumour burdens, whereas increasing the amount of infused Tg-T cells succeeds in controlling high tumour masses.

CONCLUSION

We propose that therapeutic vaccines should be considered in the context of low or moderate tumour burden, whereas Tg-T cell strategies may be more adapted for the treatment of advanced metastatic diseases.

Targeted therapy and immunotherapy: Emerging biomarkers in metastatic melanoma

Targeted therapy directed against oncogenic BRAF mutations and immune checkpoint inhibitors have transformed melanoma therapy over the past decade and prominently improved patient outcomes. However, not all patients will respond to targeted therapy or immunotherapy and many relapse after initially responding to treatment. This unmet need presents two major challenges. First, can we elucidate novel oncogenic drivers to provide new therapeutic targets? Second, can we identify patients who are most likely to respond to current therapeutic strategies in order to both more accurately select populations and avoid undue drug exposure in patients unlikely to respond? In an effort to evaluate the current state of the field with respect to these questions, we provide an overview of some common oncogenic mutations in patients with metastatic melanoma and ongoing efforts to therapeutically target these populations, as well as a discussion of biomarkers for response to immune checkpoint inhibitors-including tumor programmed death ligand 1 expression and the future use of neoantigens as a means of truly personalized therapy. This information is becoming important in treatment decision making and provides the framework for a treatment algorithm based on the current landscape in metastatic melanoma.