Abstract LB-297: HER2-targeted antibody drug conjugates induce host immunity and target cancer stem cells and the efficacy can be enhanced by anti-PD-L1
Authors: Xia Leiming , Wen Lu , Lin Ming , Frank Comer , Jane Hinrichs Mary , Michael Oberst , Steven Coats , Bao Yangyi , Chang Alfred E. , Wicha Max , Li Qiao 
Published: August 2018

Abstract
HER2 represents an ideal target for cancer immunotherapy. HER2-targeted antibody drug conjugate (ADC) was tested in immunocompromised (SCID) host, which doesn't allow the evaluation of the ADC-induced immune responses. In addition, no potential impact of ADC on cancer stem cells (CSCs) has been reported. Furthermore, tumor cells with PD-L1 expression may escape immune attack by converting PD-1 positive immune effector cells into anergy. We hypothesized that HER2-targeted ADC could modulate host immune response, target HER2high CSCs, and the efficacy of ADC could be enhanced by anti-PD-L1. To test this hypothesis, we used two immunocompetent murine models: mouse breast tumor D2/F2 and TNBC 4T1 with enforced expression of HER2, D2F2/E2 and HER2-4T1 respectively. Both D2F2/E2 and HER2-4T1 could generate tumor in immunocompetent Balb/c mice, which allowed us to test the efficacy and specificity of HER2-targeted ADC, and to evaluate host immune responses. In D2F2/E2 mouse model, we found that HER2-targeted ADC significantly inhibited D2F2/E2 tumor growth, but not the parental D2F2 tumors, in a dose dependent manner. The specificity was confirmed in HER2-4T1 model because we observed significant suppression of HER2-targted ADC on HER2-4T1 tumor growth, but not on the parental 4T1 tumor. In parallel, we observed that HER2-targeted ADC treatment reduced the number of HER2 positive cells, and ALDHhigh cells. ALDHhigh cells have been identified as cancer stem cells in multiple malignancies. We have characterized the stemness of ALDHhigh 4T1 cells. In the present study, we confirmed that the ALDHhigh sub-population of D2F2/E2 cells are highly tumorigenic compared to ALDHlow cells. Next, we tested and observed that PD-L1 expression increased in D2F2/E2 and HER2-4T1 fresh tumor cells than in cell lines. Anti-PD-L1 mAb significantly augmented the therapeutic efficacy of HER2-targeted ADC in both D2F2/E2 and HER2-4T1 tumor models. In addition, anti-PD-L1 plus HER2-targeted ADC further reduced the number of HER2 positive cells, and ALDHhigh cells, but increased the number of CD3+ and CD19+ tumor infiltrating lymphocytes (TILs). Expanded CD3+ TILs from the tumor subjected to HER2-targeted ADC plus anti-PD-L1 treatment killed tumor cells significantly more than mono-treatment. Expanded CD19+ TILs from tumor subjected to HER2-targeted ADC plus anti-PD-L1 produced more IgG than all the controls. Importantly, the IgG could specifically bind to tumor cells, resulting in the highest cytotoxicity of the tumor cells via ADCC. Together, our data indicate that HER2-targeted ADC could induce significant host immune responses, which was evidenced by the detection of anti-tumor CD3+ and CD19+ TILs. We first show that HER2-targeted ADC could target ALDHhigh cancer stem cells, and such effect was significantly enhanced by anti-PD-L1 administration.
Citation Format: Leiming Xia, Lu Wen, Ming Lin, Comer Frank, Hinrichs Mary Jane, Oberst Michael, Coats Steven, Yangyi Bao, Alfred E. Chang, Max Wicha, Qiao Li. HER2-targeted antibody drug conjugates induce host immunity and target cancer stem cells and the efficacy can be enhanced by anti-PD-L1 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-297.