Following immune attack, solid tumors upregulate coinhibitory ligands that bind to inhibitory receptors on T cells. This adaptive resistance compromises the efficacy of chimeric antigen receptor (CAR) T cell therapies, which redirect T cells to solid tumors. Here, we investigated whether programmed death-1-mediated (PD-1-mediated) T cell exhaustion affects mesothelin-targeted CAR T cells and explored cell-intrinsic strategies to overcome inhibition of CAR T cells. Using an orthotopic mouse model of pleural mesothelioma, we determined that relatively high doses of both CD28- and 4-1BB-based second-generation CAR T cells achieved tumor eradication. CAR-mediated CD28 and 4-1BB costimulation resulted in similar levels of T cell persistence in animals treated with low T cell doses; however, PD-1 upregulation within the tumor microenvironment inhibited T cell function. At lower doses, 4-1BB CAR T cells retained their cytotoxic and cytokine secretion functions longer than CD28 CAR T cells. The prolonged function of 4-1BB CAR T cells correlated with improved survival. PD-1/PD-1 ligand [PD-L1] pathway interference, through PD-1 antibody checkpoint blockade, cell-intrinsic PD-1 shRNA blockade, or a PD-1 dominant negative receptor, restored the effector function of CD28 CAR T cells. These findings provide mechanistic insights into human CAR T cell exhaustion in solid tumors and suggest that PD-1/PD-L1 blockade may be an effective strategy for improving the potency of CAR T cell therapies.

Translating the recent success of chimeric antigen receptor (CAR) T cell therapy for hematological malignancies to solid tumors will necessitate overcoming several obstacles, including inefficient T cell tumor infiltration and insufficient functional persistence. Taking advantage of an orthotopic model that faithfully mimics human pleural malignancy, we evaluated two routes of administration of mesothelin-targeted T cells using the M28z CAR. We found that intra-pleurally administered CAR T cells vastly out-performed systemically infused T cells, requiring 30-fold fewer M28z T cells to induce long-term complete remissions. Following intrapleural T cell administration, prompt in vivo antigen-induced T cell activation allowed robust CAR T cell expansion and effector differentiation, resulting in enhanced anti-tumor efficacy and functional T cell persistence for 200 days. Regional T cell administration also promoted efficient elimination of extrathoracic tumor sites. This therapeutic efficacy was dependent on early CD4+ T cell activation associated with a higher intra-tumoral CD4/CD8 cell ratios and CD28-dependent CD4+ T cell-mediated cytotoxicity. In contrast, intravenously delivered CAR T cells, even when accumulated at equivalent numbers in the pleural tumor, did not achieve comparable activation, tumor eradication or persistence. The remarkable ability of intrapleurally administered T cells to circulate and persist supports the concept of delivering optimal CAR T cell therapy through “regional distribution centers.” Based on these results, we are opening a phase I clinical trial to evaluate the safety of intrapleural administration of mesothelin-targeted CAR T cells in patients with primary or secondary pleural malignancies.

Contrary to the long held belief that chemotherapy is immunosuppressive, emerging evidence indicates that the anticancer activity of cisplatin is not limited to its ability to inhibit mitosis, but that cisplatin also has important immunomodulatory effects. We therefore methodically examined the relevant preclinical literature and identified four main mechanisms of cisplatin-induced antitumor immunomodulation: (1) MHC class I expression upregulation; (2) recruitment and proliferation of effector cells; (3) upregulation of the lytic activity of cytotoxic effectors; and (4) downregulation of the immunosuppressive microenvironment. Cisplatin-based combination chemotherapy’s antitumor immunomodulatory effects are also beginning to be harnessed in the clinic; we therefore additionally reviewed the applicable clinical literature and discussed how monitoring various components of the immune system (and their responses to cisplatin) can add new levels of sophistication to disease monitoring and prognostication. In summation, this growing body of literature on cisplatin-induced antitumor immunomodulation ultimately highlights the therapeutic potential of synergistic strategies that combine traditional chemotherapy with immunotherapy.

According to the IASLC/ATS/ERS classification, the lepidic predominant pattern consists of 3 subtypes: adenocarcinoma in situ (AIS), minimally invasive adenocarcinoma (MIA), and nonmucinous lepidic predominant invasive adenocarcinoma. We reviewed tumor slides from 1038 patients with stage I lung adenocarcinoma, recording the percentage of each histologic pattern and measuring invasive tumor size. Tumors were classified according to the IASLC/ATS/ERS classification: 2 were AIS, 34 MIA, and 103 lepidic predominant invasive. Cumulative incidence of recurrence (CIR) was used to estimate the probability of recurrence. Patients with AIS and MIA experienced no recurrences. Patients with lepidic predominant invasive tumors had a lower risk of recurrence (5-year CIR, 8%) than non-lepidic predominant tumors (n=899; 19%; P=0.003). Patients with >50% lepidic pattern tumors experienced no recurrences (n=84), those with >10%-

Purpose In an effort to identify molecular markers of tumor aggressiveness and therapeutic targets in lung adenocarcinoma (ADC), we investigated the expression of mesothelin (MSLN) in lung ADC, as well as its biological and clinical relevance. Experimental Design In a training and validation set of patients with early-stage (I–III) lung ADC (n=1209), a tissue microarray consisting of tumors and normal lung tissue was used to examine the association between MSLN expression and recurrence-free survival (RFS) and overall survival (OS). The influence of MSLN overexpression on lung ADC was investigated in vitro and in vivo by use of clinically relevant orthotopic and metastatic xenogeneic and syngeneic mouse models. Results MSLN was expressed in 69% of lung ADC tumors, with one in five patients strongly expressing MSLN and no expression in normal lung tissue. Increased MSLN expression was associated with reduced OS (HR, 1.78 [95% CI, 1.26–2.50]; P<0.01) and RFS (HR, 1.67 [95% CI, 1.21–2.27]; P<0.01) in multivariate analyses, even after adjustment for currently known markers of tumor aggressiveness in lung ADC: male sex, smoking history, increasing stage, morphologic pattern, visceral pleural invasion, lymphatic or vascular invasion, and mutation status. In vitro, lung ADC cells overexpressing MSLN demonstrated increased cell proliferation, migration, and invasion; in vivo, mice with MSLN(+) tumors demonstrated decreased survival (P=0.001). Conclusions MSLN expression in patients with early-stage lung ADC is associated with increased risk of recurrence and reduced OS, indicating that MSLN expression is a molecular marker of tumor aggressiveness and a potential target for therapy.