The coinhibitory receptor, PD-1, is of major importance for the suppression of T cell activation in various types of immune responses. A high-resolution imaging study showed that PD-1 forms a coinhibitory signalosome, “PD-1 microcluster”, with the phosphatase, SHP2, to dephosphorylate the TCR/CD3 complex and its downstream signaling molecules. Such a consecutive reaction entirely depended on PD-1–PD-L1/2 binding. PD-L2 is expressed on professional antigen-presenting cells and also on some tumor cells, which possibly explains the discrepant efficacy of immune checkpoint therapy for PD-L1-negative tumors. Here, we performed precise imaging analysis of PD-L2 forming PD-1–PD-L2 clusters associating with SHP2. PD-L2 could compete with PD-L1 for binding to PD-1, occupying the same space at TCR microclusters. The PD-1 microcluster formation was inhibited by certain mAbs with functional consequences. Thus, PD-1 microcluster formation provides a visible index for the effectiveness of anti-PD-1- or anti-PD-L1/2-mediated T cell suppression. PD-L2 may exert immune suppressive responses cooperatively with PD-L1 on the microcluster scale.
Tumours show an increased interstitial fluid pressure, which correlates with various pathophysiological features. Moreover, interstitial fluid pressure is a prognostic factor for cervical and lung cancer. However, there have been no reports on the usefulness of measuring interstitial fluid pressure in thymic epithelial tumours. Therefore, this study aimed to examine the relationship between interstitial fluid pressure and the clinicopathological characteristics of thymic epithelial tumours. Interstitial fluid pressure was prospectively measured at the centre of the tumour using a 1-Fr Mikro-Tip sensor catheter in 44 patients with thymic epithelial tumours, 40 with thymomas and 4 with thymic carcinomas. Data from these 44 patients were analysed for correlations between interstitial fluid pressure and clinicopathological and demographic factors including sex, age, tumour size, World Health Organization histological subtypes, myasthenia gravis, capsular invasion, mediastinal pleura invasion, lung invasion, pericardium invasion, dissemination, Masaoka-Koga stage, maximal standardized uptake value and recurrence-free survival (RFS). The mean interstitial fluid pressure was 11.3 mmHg; interstitial fluid pressure was significantly correlated with maximal standardized uptake value, lung invasion, dissemination and Masaoka-Koga stage. Low interstitial fluid pressure (≤14 mmHg) showed a tendency for better RFS compared with high interstitial pressure (P = 0.053). Lung invasion, dissemination and Masaoka-Koga stage were correlated with RFS in univariable analysis; lung invasion was selected as an independent prognostic factor in multivariable analysis. On the basis of these results, interstitial fluid pressure of thymic epithelial tumours has been shown to correlate with their clinicopathological features.
With recent advances in immune checkpoint inhibitors (ICIs), cancer immunotherapy has become the standard treatment for various malignant tumors. Their indications and dosages have been determined on the basis of several clinical trials conducted separately. In this study, we have established an advanced imaging system to visualize “human PD-1 microclusters,” in which PD-1 actually dephosphorylates both the TCR/CD3 complex and its downstream signaling molecules via the recruitment of a phosphatase, SHP2. Furthermore, each antibody required its own concentration and gained much greater effects in combination with other antibodies against different targets. We propose that our imaging system could digitally evaluate the PD-1-mediated T cell suppression and practical effects of each ICI. Currently, numerous new ICIs are tested, and more suitable combinations of them with other ICIs or conventional cancer treatments are being explored. Our study will have a wide range of applications to clinical practice in the future.
With recent advances in immune checkpoint inhibitors (ICIs), immunotherapy has become the standard treatment for various malignant tumors. Their indications and dosages have been determined empirically, taking individually conducted clinical trials into consideration, but without a standard method to evaluate them. Here we establish an advanced imaging system to visualize human PD-1 microclusters, in which a minimal T cell receptor (TCR) signaling unit co-localizes with the inhibitory co-receptor PD-1 in vitro. In these microclusters PD-1 dephosphorylates both the TCR/CD3 complex and its downstream signaling molecules via the recruitment of a phosphatase, SHP2, upon stimulation with the ligand hPD-L1. In this system, blocking antibodies for hPD-1-hPD-L1 binding inhibits hPD-1 microcluster formation, and each therapeutic antibody (pembrolizumab, nivolumab, durvalumab and atezolizumab) is characterized by a proprietary optimal concentration and combinatorial efficiency enhancement. We propose that our imaging system could digitally evaluate PD-1-mediated T cell suppression to evaluate their clinical usefulness and to develop the most suitable combinations among ICIs or between ICIs and conventional cancer treatments.
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