Clinically relevant orthotopic pancreatic cancer models for adoptive T cell transfer therapy

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive tumor. Prognosis is poor and survival is low in patients diagnosed with this disease, with a survival rate of ~12% at 5 years. Immunotherapy, including adoptive T cell transfer therapy, has not impacted the outcomes in patients with PDAC, due in part to the hostile tumor microenvironment (TME) which limits T cell trafficking and persistence. We posit that murine models serve as useful tools to study the fate of T cell therapy. Currently, genetically engineered mouse models (GEMMs) for PDAC are considered a "gold-standard" as they recapitulate many aspects of human disease. However, these models have limitations, including marked tumor variability across individual mice and the cost of colony maintenance.

METHODS

Using flow cytometry and immunohistochemistry, we characterized the immunological features and trafficking patterns of adoptively transferred T cells in orthotopic PDAC (C57BL/6) models using two mouse cell lines, KPC-Luc and MT-5, isolated from C57BL/6 KPC-GEMM (KrasLSL-G12D/+p53-/- and KrasLSL-G12D/+p53LSL-R172H/+, respectively).

RESULTS

The MT-5 orthotopic model best recapitulates the cellular and stromal features of the TME in the PDAC GEMM. In contrast, far more host immune cells infiltrate the KPC-Luc tumors, which have less stroma, although CD4+ and CD8+ T cells were similarly detected in the MT-5 tumors compared with KPC-GEMM in mice. Interestingly, we found that chimeric antigen receptor (CAR) T cells redirected to recognize mesothelin on these tumors that signal via CD3ζ and 41BB (Meso-41BBζ-CAR T cells) infiltrated the tumors of mice bearing stroma-devoid KPC-Luc orthotopic tumors, but not MT-5 tumors.

CONCLUSIONS

Our data establish for the first time a reproducible and realistic clinical system useful for modeling stroma-rich and stroma-devoid PDAC tumors. These models shall serve an indepth study of how to overcome barriers that limit antitumor activity of adoptively transferred T cells.

Galectin-9 expression and decreased survival in advanced biliary tract cancers

465

Background: Biliary tract cancers (BTCs) are a group of rare and aggressive malignancies often refractory to chemotherapeutic or targeted therapies, carrying an overall poor prognosis and high mortality. Identifying prognostic biomarkers and effective therapeutic targets for this disease therefore remains a high priority. T-cell immunoglobulin mucin domain-containing protein 3 (TIM-3), a negative regulatory immune checkpoint receptor, is known to induce immune tolerance and inhibit T-cell antitumor immunity. Its ligand, galectin-9 (Gal-9), has been shown to play a paradoxical role in tumorigenesis in a number of disease states. However, the role of Gal-9 in the setting of BTCs is not completely understood. Methods: We examined expression patterns of total cellular Gal-9 and TIM-3 in a panel of human BTC cell lines with diverse molecular profiles via immunoblot. Soluble Gal-9 (sGal-9) was measured by enzyme-linked immunoassay (ELISA). Tetrazolium-based MTT assay was utilized to evaluate cell viability following Ab-mediated Gal-9 neutralization. Pre-treatment peripheral blood was obtained from patients with metastatic BTCs enrolled in a randomized phase II clinical trial (NCI10139) and sGal-9 levels were measured. ROC curve analysis was employed to identify an optimal concentration cut-point value. Kaplan-Meier models were used to assess the association between sGal-9 levels and overall survival. Results: Human BTC cells demonstrate detectable and differential expression levels of total Gal-9 and TIM-3 proteins in vitro, with greater expression among intrahepatic cell lines (HUCCT-1, HUH28, SNU478). TIM-3 expression was not detected among extrahepatic (MzChA-1) and gallbladder cancer (WITT) cell lines. sGal-9 is secreted at variable levels between cell lines and its neutralization does not affect viability. Pre-treatment peripheral blood was obtained from 73 patients with metastatic BTCs (53% (n = 39) intrahepatic cholangiocarcinoma, 22% (n = 16) extrahepatic cholangiocarcinoma, 25% (n = 18) gallbladder cancer). There was no significant difference in sGal-9 levels between disease sites (p = 0.08). Patients were dichotomized by low and high sGal-9 levels. High baseline plasma levels of sGal-9 were associated with worse overall survival among patients with advanced BTCs (p = 0.03). Conclusions: Biliary tract cancer cells differentially express galectin-9 and its ligand, TIM-3, in vitro. Higher plasma levels of soluble galectin-9 are associated with worse overall survival, suggesting galectin-9 expression may be related to a more aggressive disease state. Additional work is needed to better inform the mechanistic role of the galectin-9/TIM-3 axis on disease progression and how best to leverage this pathway as a therapeutic target in the management of biliary tract cancers.

Integrated biomarker study of neoadjuvant pepinemab and nivolumab in patients with resectable metastatic melanoma

10061

Background: SEMA4D has broad immunomodulatory effects in the tumor microenvironment (TME); blocking SEMA4D in combination with checkpoint inhibitors (CI) promotes immune infiltration, reduces recruitment of myeloid cells, enhances T cell activity, and promotes tumor regression. We hypothesized that adding pepinemab (VX15/2503), which targets SEMA4D, to CI would increase immunomodulatory effects and augment response in melanoma (NCT03769155). Methods: Patients with resectable stage IIIB/C/D melanoma were enrolled to control (no neoadjuvant therapy) or treatment cohorts (n = 8 in four cohorts of pepinemab plus nivolumab, ipilimumab, nivolumab/ipilimumab or alone). Here we report results from patients receiving two doses of nivolumab (360mg) and pepinemab (15mg/kg) every three weeks followed by surgery. Primary endpoint was T cell infiltration into the TME; secondary endpoints include pathologic response rates, peripheral immune profile, and safety. Results: Ten patients are reported: two were controls, eight received neoadjuvant therapy. Two patients had pathologic complete response, one had a near-complete pathologic response ( < 1% viable tumor), one had a partial response (41% viable tumor) and four had stable disease (73-90% viable tumor). All neoadjuvant patients underwent surgery without delay; one patient experienced grade 3 post-operative cellulitis. There were two treatment-related grade 3 adverse events (weakness and arthralgia). Pharmacodynamic studies confirmed saturation of PD-1 and SEMA4D in peripheral and tumor-infiltrating T cells. T/B cell (CD8+/CD20+) ratios, a surrogate for T cell infiltration, were higher in post-treatment tumors compared to pre-treatment and were higher in the tumor bed compared to normal adjacent tissue. Flow cytometric evaluation identified an increase in CD26hi CD4+ and CD8+ tumor-infiltrating effectors in treated patients compared to controls and an increase in peripheral frequencies of the PD-1-responsive effector HLA-DR+CD38+Ki67+ CD4+ and CD8+ T cells following treatment. Treatment increased infiltration of myeloid populations into the TME, increased expression of PD-L1 on TME myeloid populations, and increased expression of the SEMA4D receptor Plexin-B2 on the surface of TME CD45− and M2 macrophages and MDSC. Conclusions: Neoadjuvant nivolumab and pepinemab results in increased T cell infiltration with excellent major response rate (38%) and expected safety profile. We continue to enroll patients using other rational combinations of pepinemab and CI. Clinical trial information: NCT03769155.