Citations

11534 Background: To date, there are no validated blood-based biomarkers of predicting response to PD-1 blockade. We previously reported that Bim is a downstream signaling molecule of the PD-1 pathway, and that measurement of Bim levels in circulating T-cells may predict and monitor responses to anti–PD-1 therapy in melanoma. We have identified the existence of sPD-L1 in cancer patients and showed that the sPD-L1 is biologically active and capable of triggering apoptosis in activated T-cells. Here we evaluated T cell Bim and sPD-L1 in the peripheral blood (PB) as biomarkers of response in a cohort of patients with metastatic melanoma and lung cancer undergoing anti-PD1 therapy. Methods: 60 pts treated with anti-PD-1 had PB collected at baseline and at radiographic tumor evaluation. Frequencies of Bim+ T cells and Bim median fluorescence intensity (MFI) were measured by flow cytometry in gated tumor-reactive CD11ahighPD1+ CD8+ T cells. We also measured levels of sPD-L1 at baseline and serially during treatment with sPD-L1 ELISA. Baseline Bim and sPD-L1 levels and percent change in Bim levels in patients (pts) who had a radiographic response (CR/PR) were compared to those who had progressive disease (PD) at 12 wks. Results: Similarly to previously reported preliminary data, pts with objective response (CR/PR, 15/60) after 4 cycles of anti-PD1 therapy had higher frequency of Bim T cells at baseline compared to pts with PD (16/60) (mean 43% vs. 30%, P = 0.0484). The frequencies of Bim+ T cells decreased significantly after the first 3 months of treatment in responders compared with progressors (mean -16% vs. + 40% P = 0.0111). High baseline sPD-L1 were associated with progression on anti-PD1 therapy (mean 2.8 ng/mL vs. 0.7 ng/mL, p = 0.07, n = 13) and the levels increased by the first tumor assessment in patients resistant to anti-PD-1. Conclusions: Measurements of Bim and sPD-L1 levels may help to select patients who are likely to benefit from anti-PD1 monotherapy versus combinatorial strategies, and provide a new non-invasive way to monitor response to anti-PD-1 blockade. A larger validation study is underway.

Although immune checkpoint inhibitors have resulted in durable clinical benefits in a subset of patients with advanced cancer, some patients who did not respond to initial anti–PD-1 therapy have been found to benefit from the addition of salvage chemotherapy. However, the mechanism responsible for the successful chemoimmunotherapy is not completely understood. Here we show that a subset of circulating CD8 + T cells expressing the chemokine receptor CX3CR1 are able to withstand the toxicity of chemotherapy and are increased in patients with metastatic melanoma who responded to chemoimmunotherapy (paclitaxel and carboplatin plus PD-1 blockade). These CX3CR1 + CD8 + T cells have effector memory phenotypes and the ability to efflux chemotherapy drugs via the ABCB1 transporter. In line with clinical observation, our preclinical models identified an optimal sequencing of chemoimmunotherapy that resulted in an increase of CX3CR1 + CD8 + T cells. Taken together, we found a subset of PD-1 therapy–responsive CD8 + T cells that were capable of withstanding chemotherapy and executing tumor rejection with their unique abilities of drug efflux (ABCB1), cytolytic activity (granzyme B and perforin), and migration to and retention (CX3CR1 and CD11a) at tumor sites. Future strategies to monitor and increase the frequency of CX3CR1 + CD8 + T cells may help to design effective chemoimmunotherapy to overcome cancer resistance to immune checkpoint blockade therapy.

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.

Abstract We investigated the influence of PD-1 expression on the systemic antitumor response (abscopal effect) induced by stereotactic ablative radiotherapy (SABR) in preclinical melanoma and renal cell carcinoma models. We compared the SABR-induced antitumor response in PD-1–expressing wild-type (WT) and PD-1–deficient knockout (KO) mice and found that PD-1 expression compromises the survival of tumor-bearing mice treated with SABR. None of the PD-1 WT mice survived beyond 25 days, whereas 20% of the PD-1 KO mice survived beyond 40 days. Similarly, PD-1–blocking antibody in WT mice was able to recapitulate SABR-induced antitumor responses observed in PD-1 KO mice and led to increased survival. The combination of SABR plus PD-1 blockade induced near complete regression of the irradiated primary tumor (synergistic effect), as opposed to SABR alone or SABR plus control antibody. The combination of SABR plus PD-1 blockade therapy elicited a 66% reduction in size of nonirradiated, secondary tumors outside the SABR radiation field (abscopal effect). The observed abscopal effect was tumor specific and was not dependent on tumor histology or host genetic background. The CD11ahigh CD8+ T-cell phenotype identifies a tumor-reactive population, which was associated in frequency and function with a SABR-induced antitumor immune response in PD-1 KO mice. We conclude that SABR induces an abscopal tumor-specific immune response in both the irradiated and nonirradiated tumors, which is potentiated by PD-1 blockade. The combination of SABR and PD-1 blockade has the potential to translate into a potent immunotherapy strategy in the management of patients with metastatic cancer. Cancer Immunol Res; 3(6); 610–9. ©2015 AACR.

Abstract An immunoinhibitory role of B7 homologue 1 (B7-H1) expressed by non-T cells has been established; however, the function of B7-H1 expressed by T cells is not clear. Peak expression of B7-H1 on Ag-primed CD8 T cells was observed during the contraction phase of an immune response. Unexpectedly, B7-H1 blockade at this stage reduced the numbers of effector CD8 T cells, suggesting B7-H1 blocking Ab may disturb an unknown function of B7-H1 expressed by CD8 T cells. To exclusively examine the role of B7-H1 expressed by T cells, we introduced B7-H1 deficiency into TCR transgenic (OT-1) mice. Naive B7-H1–deficient CD8 T cells proliferated normally following Ag stimulation; however, once activated, they underwent more robust contraction in vivo and more apoptosis in vitro. In addition, B7-H1–deficient CD8 T cells were more sensitive to Ca-dependent and Fas ligand-dependent killing by cytotoxic T lymphocytes. Activation-induced Bcl-xL expression was lower in activated B7-H1–deficient CD8 T cells, whereas Bcl-2 and Bim expression were comparable to the wild type. Transfer of effector B7-H1–deficient CD8 T cells failed to suppress tumor growth in vivo. Thus, upregulation of B7-H1 on primed T cells helps effector T cells survive the contraction phase and consequently generate optimal protective immunity.