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

Joshua Tobias,Matthias Preusser,Annika De Sousa Linhares,Katharina Ambroz,Peter Steinberger,Erika Garner-Spitzer,Karin Baier,Christoph C Zielinski,Michael Lebens,Lukas Kenner,Aleksandra Inic-Kanada,Sandra Högler,Ursula Wiedermann,Mirjana Drinić,Claire Battin,Michael Kundi

doi:10.3389/fimmu.2020.00895

Abstract

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.

Highlights

MATERIALS AND METHODSMultiple lines of preclinical and clinical evidence have shown that tumors can evade the immune system by expressing surface ligands, which engage co-inhibitory receptors on tumorspecific T cells resulting in immune tolerance [1, 2]
Following the concept of active immunization with B-cell-derived epitopes, as previously described against Her-2/neu [23, 24], in this study we describe the identification of programmed cell death 1 (PD1)-derived mimotopes, and their use for active immunization to induce the host’s immune system and inhibit tumor growth in vivo
It has been described that Nivolumab binds to the N-terminal loop of human PD1 [29], where the identified and selected mimotope JT–N1 resides

Summary

MATERIALS AND METHODS

Multiple lines of preclinical and clinical evidence have shown that tumors can evade the immune system by expressing surface ligands, which engage co-inhibitory receptors on tumorspecific T cells resulting in immune tolerance [1, 2]. To examine whether the blockade of mPD1/mPD–L1 interaction by rabbit IgG against JT–mPD1 as shown in vitro can be translated to anti-tumor activity in vivo, passive immunization/administration of the rabbit IgG in a syngeneic mouse model, involving BALB/c mice engrafted with BALB/c-derived mammary carcinoma (D2F2/E2) cells expressing human Her-2, was carried out. To evaluate whether active immunization with PD1-derived mimotopes induces an anti-tumor effect, the BALB/c mice, engrafted with the syngeneic tumor cell line D2F2/E2 expressing human Her-2/neu, were immunized with the mimotope JT– mPD1 (conjugated to CRM197 in conjunction with Montanide; 25 μg/dose) (Figure 4A).

DISCUSSION

Findings

ETHICS STATEMENT