Dong, Haidong

ProblemPregnancy requires balance between tolerance to the haploidentical fetus and the mother's ability to mount immune responses. There are parallels to this phenomenon that occur in metastatic cancer. We assessed soluble program death ligand‐1 soluble PD‐L1 (sPD‐L1) and galectin‐9 in the blood of pregnant women during gestation as these molecules are highly involved in immune suppression during cancer.Method of studyMaternal blood was collected from 30 primigravida women at monthly intervals during pregnancy, delivery and 6‐week post‐partum. Blood was analyzed for sPD‐L1 and galectin‐9 concentrations by ELISA. Term placentas were collected in formalin and IHC was completed for PD‐L1 and galectin‐9 expression.ResultsMaternal blood levels of sPD‐L1 (0.438 ng/mL) and galectin‐9 (1976 pg/mL) were elevated early in normal pregnancies compared to non‐pregnant controls (0.242 ng/mL and 773 pg/mL, respectively). sPD‐L1 increased throughout gestation, whereas galectin‐9 remained elevated until parturition; both proteins returned to control levels post‐partum. Women carrying male fetuses had significantly higher galectin‐9 levels, but not sPD‐L1, than those carrying females (2263 pg/mL vs 1874 pg/mL; P = .0005). Trophoblast cells of the term placenta coexpress galectin‐9 and PD‐L1.ConclusionImmune‐regulatory molecules galectin‐9 and sPD‐L1 increased during pregnancy and may play a role in immune tolerance that is critical for the fetus.

Key Points Pembrolizumab was first shown to be clinically active in CLL patients with RT. PD-1 and PD-L1 expression in tumor microenvironment are promising biomarkers to select RT patients for PD-1 blockade.

Abstract B7-H1 (aka PD-L1) blocking antibodies have been tested in the treatment of human cancers through blocking B7-H1 expressed by tumor cells; however, its impact on B7-H1 expressed by tumor-reactive CD8+ T cells is still unknown. Here, we report that tumor-reactive CD8+ T cells expressing B7-H1 were functional effector cells. An agonist antibody to PD-L1 deleted B7-H1+ PD-1+ tumor-reactive CD8+ T cells via activation of p38 MAPK, and failed to suppress tumor growth. As activation of p38 MAPK leads to CD8+ T cell apoptosis upon T cell activation, a PD-L1 antibody that activated p38 MAPK enhanced apoptosis of activated CD8+ T cells. An intracellular molecule, DNA-PKcs, was identified in association with B7-H1 and a DNA-PKcs inhibitor increased p38 MAPK activation in wild type but not in B7-H1 deficient CD8+ T cells. Our results suggest B7-H1 suppresses p38 MAPK activation via DNA-PKcs to prevent CD8+ T cell death. To maximize antitumor function, PD-L1 antibodies should be selected to avoid their collateral activation of p38 MAPK in tumor-reactive CD8+ T cells. Citation Format: Siyu Cao, Xin Liu, Xiaosheng Wu, Aaron Mansfield, Haidong Dong. B7-H1 identifies tumor-reactive effector CD8 T cells susceptible of deletion by agonist PD-L1 antibodies [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A131.

Immune checkpoint therapy with PD-1 blockade has emerged as an effective therapy for many advanced cancers; however, only a small fraction of patients achieve durable responses. To date, there is no validated blood-based means of predicting the response to PD-1 blockade. We report that Bim is a downstream signaling molecule of the PD-1 pathway, and its detection in T cells is significantly associated with expression of PD-1 and effector T cell markers. High levels of Bim in circulating tumor-reactive (PD-1 + CD11a hi CD8 + ) T cells were prognostic of poor survival in patients with metastatic melanoma who did not receive anti–PD-1 therapy and were also predictive of clinical benefit in patients with metastatic melanoma who were treated with anti–PD-1 therapy. Moreover, this circulating tumor-reactive T cell population significantly decreased after successful anti–PD-1 therapy. Our study supports a crucial role of Bim in both T cell activation and apoptosis as regulated by PD-1 and PD-L1 interactions in effector CD8 + T cells. Measurement of Bim levels in circulating T cells of patients with cancer may provide a less invasive strategy to predict and monitor responses to anti–PD-1 therapy, although future prospective analyses are needed to validate its utility.

The use of programmed cell death 1 ligand 1 (PD‐L1) as a predictive biomarker to select patients to receive programmed cell death 1 (PD‐1) or PD‐L1 inhibitors in non‐small cell lung cancer (NSCLC) is limited by the definitions of positivity, interassay agreement, and intra‐ and intertumoral heterogeneity of expression. Although PD‐L1 expression enriches for responses, the lack of expression does not exclude clinical benefit.