The immune suppressive molecule programmed death-1 (PD-1) is upregulated in activated T lymphocytes and inhibits T-cell function upon binding to its ligands B7-H1 (PD-L1, CD274) and B7-DC (PD-L2, CD273). Substantial experimental data from in vitro cell culture systems and animal models, and more recently from clinical trials, indicate that PD-1/PD-1-ligand interactions are a major mechanism of immune suppression within the tumor microenvironment. Initial clinical studies of antibodies directed against PD-1 and B7-H1 showed both an encouraging safety profile and remarkable antitumor activity in subsets of patients with metastatic disease, including malignancies—such as lung cancer—which were previously thought to be unresponsive to immunotherapy. Preliminary data have suggested a correlation between tumor membrane B7-H1 expression and clinical response to anti-PD-1 antibodies. Several key challenges remain to optimize development of PD-1/B7-H1 pathway blockade, including defining the biologic significance of all potential ligand–receptor interactions in the tumor microenvironment, developing more accurate predictive biomarkers of response, determining the breadth of activity in human malignancies, and developing rational combinations of therapy that address key mechanisms involved in positive and negative regulation of antitumor immune responses. Clin Cancer Res; 19(5); 1021–34. ©2013 AACR.

Combination checkpoint blockade (CCB) targeting inhibitory CTLA4 and PD1 receptors holds promise for cancer therapy. Immune-related adverse events (IRAEs) remain a major obstacle for the optimal application of CCB in cancer. Here, we analyzed B cell changes in patients with melanoma following treatment with either anti-CTLA4 or anti-PD1, or in combination. CCB therapy led to changes in circulating B cells that were detectable after the first cycle of therapy and characterized by a decline in circulating B cells and an increase in CD21^lo B cells and plasmablasts. PD1 expression was higher in the CD21^lo B cells, and B cell receptor sequencing of these cells demonstrated greater clonality and a higher frequency of clones compared with CD21^hi cells. CCB induced proliferation in the CD21^lo compartment, and single-cell RNA sequencing identified B cell activation in cells with genomic profiles of CD21^lo B cells in vivo. Increased clonality of circulating B cells following CCB occurred in some patients. Treatment-induced changes in B cells preceded and correlated with both the frequency and timing of IRAEs. Patients with early B cell changes experienced higher rates of grade 3 or higher IRAEs 6 months after CCB. Thus, early changes in B cells following CCB may identify patients who are at increased risk of IRAEs, and preemptive strategies targeting B cells may reduce toxicities in these patients.

Agents that modulate immune checkpoint proteins, such as cytotoxic T-lymphocyte antigen-4 (CTLA-4) and programmed death receptor-1 (PD-1), have become a mainstay in cancer treatment. The clinical benefit afforded by immune checkpoint inhibitors can be accompanied by immune-related adverse events (irAE) that affect the skin, gastrointestinal tract, liver, and endocrine system. The types of irAEs associated with immune checkpoint inhibitors are generally consistent across tumor types. Immune-related endocrine events can affect the pituitary, thyroid, and adrenal glands, as well as other downstream target organs. These events are unique when compared with other irAEs because the manifestations are often irreversible. Immune-related endocrine events are typically grade 1/2 in severity and often present with non-specific symptoms, making them difficult to diagnose. The mechanisms underlying immune-related target organ damage in select individuals remain mostly undefined. Management includes close patient monitoring, appropriate laboratory testing for endocrine function, replacement of hormones, and consultation with an endocrinologist when appropriate. An awareness of the symptoms and management of immune-related endocrine events may aid in the safe and appropriate use of immune checkpoint inhibitors in clinical practice.

Activating mutations in BRAF kinase are common in melanomas. Clinical trials with PLX4032, the mutant-BRAF inhibitor, show promising preliminary results in patients selected for the presence of V600E mutation. However, activating V600K mutation is the other most common mutation, yet patients with this variant are currently excluded from the PLX4032 trials. Here we present evidence that a patient bearing the BRAF V600K mutation responded remarkably to PLX4032, suggesting that clinical trials should include all patients with activating BRAF V600E/K mutations.

Heterogeneity of tumor cells and their microenvironment can affect outcome in cancer. Blockade of immune checkpoints (ICPs) expressed only on a subset of immune cells leads to durable responses in advanced melanoma. Tissue-resident memory T (T _RM ) cells have recently emerged as a distinct subset of memory T cells in nonlymphoid tissues. Here, we show that functional properties and expression of ICPs within tumor-infiltrating lymphocytes (TILs) differ from those of blood T cells. TILs secrete less IL-2, IFN-γ, and TNF-α compared with circulating counterparts, and expression of VEGF correlated with reduced TIL infiltration. Within tumors, ICPs are particularly enriched within T cells with phenotype and genomic features of T _RM cells and the CD16 ⁺ subset of myeloid cells. Concurrent T cell receptor (TCR) and tumor exome sequencing of individual metastases in the same patient revealed that interlesional diversity of TCRs exceeded differences in mutation/neoantigen load in tumor cells. These findings suggest that the T _RM subset of TILs may be the major target of ICP blockade and illustrate interlesional diversity of tissue-resident TCRs within individual metastases, which did not equilibrate between metastases and may differentially affect the outcome of immune therapy at each site.