Preclinical and Clinical Observations Implying Combination Therapy to Enhance the Efficacy of the Her-2/neu B-Cell Peptide-Based Vaccine HER-Vaxx and to Prevent Immune Evasion

Her-2/neu-targeting therapy by passive application with trastuzumab is associated with acquired resistance and subsequent metastasis development, which is attributed to the upregulation of tumoral PD-L1 expression and the downregulation of Her-2/neu. We aimed to investigate this association, following active immunization with our recently constructed B-cell peptide-based Her-2/neu vaccines in both preclinical and clinical settings. Immunohistochemistry (IHC), fluorescence in situ hybridization (FISH), and combined positive score (CPS) were applied to evaluate Her-2/neu and PD-L1 expression using a murine syngeneic tumor model for Her-2/neu lung metastases and tumor biopsies from a gastric cancer patient with disease progression. A significant and concomitant reduction in Her-2/neu and the upregulation of PD-L1 expression was observed in vaccinated mice after 45 days, but not after 30 days, of metastases development. A significant increase in tumor-infiltrating B lymphocytes was observed at both time points. The downregulation of Her-2/neu and the upregulation of PD-L1 were observed in a patient's primary tumor at the disease progression time point but not prior to vaccination (Her-2/neu IHC: 3 to 0, FISH: 4.98 to 1.63; PD-L1 CPS: 0% to 5%). Our results further underline the need for combination therapy by targeting PD-L1 to prevent metastasis formation and immune evasion of Her-2/neu-positive and PD-L1-negative tumor cells.

A New Strategy Toward B Cell-Based Cancer Vaccines by Active Immunization With Mimotopes of Immune Checkpoint Inhibitors

Therapeutic monoclonal antibodies (mAbs), targeting tumor antigens, or immune checkpoints, have demonstrated a remarkable anti-tumor effect against various malignancies. However, high costs for mono- or combination therapies, associated with adverse effects or possible development of resistance in some patients, warrant further development and modification to gain more flexibility for this immunotherapy approach. An attractive alternative to passive immunization with therapeutic antibodies might be active immunization with mimotopes (B-cell peptides) representing the mAbs' binding epitopes, to activate the patient's own anti-tumor immune response following immunization. Here, we identified and examined the feasibility of inducing anti-tumor effects in vivo following active immunization with a mimotope of the immune checkpoint programmed cell death 1 (PD1), alone or in combination with a Her-2/neu B-cell peptide vaccine. Overlapping peptides spanning the extracellular domains of human PD1 (hPD1) were used to identify hPD1-derived mimotopes, using the therapeutic mAb Nivolumab as a proof of concept. Additionally, for in vivo evaluation in a tumor mouse model, a mouse PD1 (mPD1)-derived mimotope was identified using an anti-mPD1 mAb with mPD1/mPDL-1 blocking capacity. The identified mimotopes were characterized by in vitro assays, including a reporter cell-based assay, and their anti-tumor effects were evaluated in a syngeneic tumor mouse model stably expressing human Her-2/neu. The identified PD1-derived mimotopes were shown to significantly block the mAbs' capacity in inhibiting the respective PD1/PD-L1 interactions. A significant reduction in tumor growth in vivo was observed following active immunization with the mPD1-derived mimotope, associated with a significant reduction in proliferation and increased apoptotic rates in the tumors. Particularly, combined vaccination with the mPD1-derived mimotope and a multiple B-cell epitope Her-2/neu vaccine potentiated the vaccine's anti-tumor effect. Our results suggest active immunization with mimotopes of immune checkpoint inhibitors either as monotherapy or as combination therapy with tumor-specific vaccines, as a new strategy for cancer treatment.