Abstract 3660: Blocking the DC-HIL receptor reverses the T-cell suppression induced by proliferating myeloid-derived suppressor cells in common cancer types

Myeloid-derived suppressor cells (MDSC) are the most potent suppressors of T-cell function, and their exponential proliferation in cancer states counteracts the benefits of immunotherapy given to these patients. Having discovered the T cell-inhibitory DC-HIL receptor, we showed that DC-HIL is responsible for MDSC’s T-cell suppressive function. We found that melanoma patients (but not healthy controls) harbor in the blood an expanded population of DC-HIL+ MDSC, whose suppressor effects in vitro can be blocked by our 3D5 anti-DC-HIL mAb. To determine whether similar outcomes apply to non-melanoma cancers, we recruited patients with metastases from bladder (BL, n=4), breast (BR, n=11), colon (CO, n=44), kidney (KI, n=6), lung (LU, n=20), pancreatic (PA, n=17), and prostate (PR, n=9) cancer. FACS analysis of blood samples showed all cancer types (except LU) were associated with elevated blood HLA-DRno/low CD14+ MDSC vs. age-matched controls (n=21, median of 0.5%). % DC-HIL+ MDSC in PBMC was also significantly high in all cancer types; median of 2.5% for BL; 1.7% for BR; 3.5% for CO; 3.6% for KI; 0.3% for LU; 1.8% for PA; and 4.8% for PR, vs. 0.04% for healthy controls. MDSC in all cancer types showed high DC-HIL-positivity (20-90% vs. 8% for controls). We assayed T-cell suppressor activity by purifying MDSC and T-cells from the same patient and co-culturing them at varying cell ratios, with co-stimulators. Activity was determined by % suppression in IFN-γ secretion, which was correlated with % DC-HIL-positivity of MDSC. MDSC from KI (n=3) were more suppressive than those from CO and PA, with suppressor activity correlating with DC-HIL-positivity: Pearson’s r for 0.5 for CO (n=13) and 0.73 for PA (n=8). We evaluated effects of anti-DC-HIL mAb on co-cultures of MDSC/ T-cells from cancer patients (n=25). The mAb restored IFN-γ secretion by >30% in 8/15 cases of CO; 4/8 of PA, and 2/2 of KI. To determine whether DC-HIL+ MDSC migrate into cancer sites, lesional specimens from CO patients (n=5) with high blood counts of DC-HIL+ MDSC were immunohistochemically stained for CD14 and DC-HIL expression: DC-HIL was absent from all cancer cells, but present strongly in many CD14+ cells surrounding the cancers. This outcome contrasts starkly with melanoma, in which DC-HIL was expressed highly by the cancer cells surrounded by only a few DC-HIL+ CD14+ cells. Finally we evaluated in vivo effects of blocking DC-HIL using a mouse model of MC38 colon cancer, which is DC-HILneg. MC38 tumor challenge induced DC-HIL+ Gr1lowLy6Chigh MDSC in the tumor site. Intravenous infusion of anti-DC-HIL mAb into mice with pre-established MC38 tumor significantly inhibited tumor growth by 50-70%, reduced blood levels of MDSC, and enhanced cytotoxic T-lymphocyte response. Our findings support DC-HIL blockade as a potential treatment for metastatic cancers, with high blood levels of DC-HIL+ MDSC as a prognostic marker for the best responders. Citation Format: Masato Kobayashi, Jin-Sung Chung, Muhammad Beg, Yull Arriaga, Udit Verma, Kevin Courtney, John Mansour, Barbara Haley, Saad Khan, Yutaka Horiuchi, David Harker, Purva Gopal, Ponciano D. Cruz, Kiyoshi Ariizumi. Blocking the DC-HIL receptor reverses the T-cell suppression induced by proliferating myeloid-derived suppressor cells in common cancer types [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3660. doi:10.1158/1538-7445.AM2017-3660