The future of targeting cytotoxic T-lymphocyte-associated protein-4: Is there a role?

Impact of tumor localization on antitumor immunity with conditionally activated CTLA-4 blockade

BACKGROUND

Immune checkpoint blockade (ICB) can induce antitumor efficacy but also induces immune-related adverse events. Systemically administered ICB can activate immune cells throughout the host. Conditionally active ICB with proteolytically cleaved masking domains can potentially reduce the adverse events seen with anti-cytotoxic T-lymphocyte associated protein 4 (CTLA-4) antibody.

METHODS

We examined how different formats of a conditionally activated dual variable domain IgG (DVD) that binds CTLA-4 and the tumor-associated antigen prostate stem cell antigen (PSCA) can lead to efficacy in syngeneic subcutaneous and metastatic murine tumor models. We also defined the capacity of these DVDs to modulate immune responses by multiparameter flow cytometry.

RESULTS

Conditionally active DVDs can uncouple antitumor efficacy from toxicity. A fully cleavable construct (symmetric DVD, sDVD), which can be released from the target tumor cells, showed superior antitumor efficacy compared with asymmetric DVD, which retains its tumor antigen binding. The sDVD elicited the highest tumor-antigen-specific T-cell responses detected in tumors and tumor-draining lymph nodes, as well as presenting the highest rate of intratumoral and splenic "non-exhausted" antigen-specific CD8 T cells. SDVD also induced the highest degrees of T-cell memory and self-renewal potential. These effects were dependent on PSCA expression by the tumors.

CONCLUSIONS

These findings support the notion that ICB modulation of antitumor immunity away from the tumor cells is critically important for optimal antitumor immunity. The bispecific sDVD antibody design may enable improved systemic antitumor responses than traditional ICB in both primary tumors and metastases.

Non-Genetic Biomarkers in Merkel Cell Carcinoma: Prognostic Implications and Predictive Utility for Response to Anti-PD-(L)1 Immune Checkpoint Inhibitors

Merkel cell carcinoma (MCC) is a skin cancer that arises due to either Merkel cell polyomavirus infection (MCPyV) or ultraviolet (UV) radiation exposure, presenting primarily in the head and neck region of fair-skinned males. The recent success of PD-(L)1 immune checkpoint inhibitors (ICIs) in locally advanced/metastatic MCC, with an objective response rate (ORR) around 50% and improved survival, as a first-line treatment has moved ICIs to the forefront of therapy for MCC and generated interest in identifying biomarkers to predict clinical response. The MCC tumour microenvironment (TME) contains various components of the adaptive and innate immune system. These components can contribute to tumour immune escape through immunosuppression by preventing entrance of other immune cells or by aiding in the cytotoxic clearance of tumour cells. We aim to combine information from studies of baseline and on-treatment monitoring of the TME to help predict the success of ICIs in MCC. This review enhances the understanding of how CD8 T cells, γδ T cells and macrophages may impact predictions of response rates to ICIs in MCC patients. These immune cells are non-genetic biomarkers that can also be used to determine prognosis in MCC treatment.

Targeting PD-1/PD-L1 in tumor immunotherapy: Mechanisms and interactions with host growth regulatory pathways

Tumor immunotherapy has garnered considerable attention, emerging as a new standard of care in cancer treatment. The conventional targets, such as VEGF and EGFR, have been extended to others including BRAF and PD-1/PD-L1, which have shown significant potential in recent cancer treatments. This review aims to succinctly overview the impact and mechanisms of therapies that modulate PD-1/PD-L1 expression by targeting VEGF, EGFR, LAG-3, CTLA-4 and BRAF. We investigated how modulation of PD-1/PD-L1 expression impacts growth factor signaling, shedding light on the interplay between immunomodulatory pathways and growth factor networks within the tumor microenvironment. By elucidating these interactions, we aim to provide insights into novel potential synergistic therapeutic strategies for cancer immunotherapy.

Combination immune checkpoint and targeted protein kinase inhibitors for the treatment of renal cell carcinomas

Kidney cancers comprise about 3% of all new malignancies in the United States. Renal cell carcinomas (RCCs) are the most common type of renal malignancy making up about 85% of kidney cancer cases. Signs and symptoms of renal cell carcinomas can result from local tumor growth, paraneoplastic syndromes, or distant metastases. The classic triad of presentation with flank pain, hematuria, and a palpable abdominal mass occurs in fewer than 10% of patients. Most diagnoses result from incidental imaging findings (ultrasonography or abdominal CT imaging) performed for another reason. Localized disease is treated by partial nephrectomy, total nephrectomy, or ablation (tumor destruction with heat or cold). When the tumors have metastasized, systemic therapy with protein-tyrosine kinase antagonists including sorafenib, sunitinib, pazopanib, and tivozanib that target vascular endothelial, platelet-derived, fibroblast, hepatocyte, and stem cell factor growth factor receptors (VEGFR, PDGFR, FGFR, MET, and Kit) were prescribed after 2005. The monoclonal antibody immune checkpoint inhibitor nivolumab (targeting programed cell death protein 1, PD1) was approved for the treatment of RCCs in 2015. It is usually used now in combination with ipilimumab (targeting CTLA-4) or cabozantinib (a multikinase blocker). Other combination therapies include pembrolizumab (targeting PD1) and axitinib (a VEGFR and PDGFR blocker) or lenvatinib (a multikinase inhibitor). Since the KEYNOTE-426 clinical trial, the use of immune checkpoint inhibitors in combination with protein-tyrosine kinase inhibitors is now the standard of care for most patients with metastatic renal cell carcinomas and monotherapies are used only in those individuals who cannot receive or tolerate immune checkpoint inhibitors.

Targeting T regulatory (Treg) cells in immunotherapy-resistant cancers

Primary or secondary (i.e., acquired) resistance is a common occurrence in cancer patients and is often associated with high numbers of T regulatory (Treg) cells (CD4+CD25+FOXP3+). The approval of ipilimumab and the development of similar pharmacological agents targeting cell surface proteins on Treg cells demonstrates that such intervention may overcome resistance in cancer patients. Hence, the clinical development and subsequent approval of Cytotoxic T Lymphocyte Antigen-4 (CTLA-4) targeting agents can serve as a prototype for similar agents. Such new agents aspire to be highly specific and have a reduced toxicity profile while increasing effector T cell function or effector T/T regulatory (Teff/Treg) ratio. While clinical development with large molecules has shown the greatest advancement, small molecule inhibitors that target immunomodulation are increasingly entering early clinical investigation. These new small molecule inhibitors often target specific intracellular signaling pathways [e.g., phosphoinositide-3-kinase delta (PI3K-δ)] that play an important role in regulating the function of Treg cells. This review will summarize the lessons currently applied to develop novel clinical agents that target Treg cells.