Intratumoral injection of IL-12-encoding mRNA targeted to CSFR1 and PD-L1 exerts potent anti-tumor effects without substantial systemic exposure

IL-12 is a potent cytokine for cancer immunotherapy. However, its systemic delivery as a recombinant protein has shown unacceptable toxicity in the clinic. Currently, the intratumoral injection of IL-12-encoding mRNA or DNA to avoid such side effects is being evaluated in clinical trials. In this study, we aimed to improve this strategy by further favoring IL-12 tethering to the tumor. We generated in vitro transcribed mRNAs encoding murine single-chain IL-12 fused to diabodies binding to CSF1R and/or PD-L1. These targeted molecules are expressed in the tumor microenvironment, especially on myeloid cells. The binding capacity of chimeric constructs and the bioactivity of IL-12 were demonstrated in vitro and in vivo. Doses as low as 0.5 μg IL-12-encoding mRNA achieved potent antitumor effects in subcutaneously injected B16-OVA and MC38 tumors. Treatment delivery was associated with increases in IL-12p70 and IFN-γ levels in circulation. Fusion of IL-12 to the diabodies exerted comparable efficacy against bilateral tumor models. However, it achieved tethering to myeloid cells infiltrating the tumor, resulting in nearly undetectable systemic levels of IL-12 and IFN-γ. Overall, tethering IL-12 to intratumoral myeloid cells in the mRNA-transferred tumors achieves similar efficacy while reducing the dangerous systemic bioavailability of IL-12.

Mouse IgG2a isotype therapeutic antibodies elicit superior tumor growth control compared to mIgG1 or mIgE

In the last decades, antibody based tumor therapy has fundamentally improved the efficacy of treatment for cancer patients. Currently, almost all tumor-antigen targeting antibodies approved for clinical application are of IgG1 Fc-isotype. Similarly, the mouse homolog mIgG2a is the most commonly used in tumor mouse models. However, in mice the efficacy of antibody based tumor therapy is largely restricted to a prophylactic application. Direct isotype comparison studies in mice in a therapeutic setting are scarce. In this study, we assessed the efficacy of mouse tumor-targeting antibodies of different isotypes in a therapeutic setting using a highly systematic approach. To this end, we engineered and expressed antibodies of the same specificity but different isotypes, targeting the artificial tumor antigen CD90.1 / Thy1.1 expressed by B16 melanoma cells. Our experiments revealed that in a therapeutic setting mIgG2a was superior to both mIgE and mIgG1 in controlling tumor growth. Furthermore, the observed mIgG2a anti-tumor effect was entirely Fc-mediated as the protection was lost when antibodies with a Fc silenced mIgG2a isotype (LALA-PG mutations) was used. These data confirm mIgG2a superiority in a therapeutic tumour model.

Shortened Hinge Design of Fab x sdAb-Fc Bispecific Antibodies Enhances Redirected T-Cell Killing of Tumor Cells

T cell engager (TCE) antibodies have emerged as promising cancer therapeutics that link cytotoxic T-cells to tumor cells by simultaneously binding to CD3E on T-cells and to a tumor-associated antigen (TAA) expressed by tumor cells. We previously reported a novel bispecific format, the IgG-like Fab x sdAb-Fc (also known as half-IG_VH-h-CH2-CH3), combining a conventional antigen-binding fragment (Fab) with a single domain antibody (sdAb). Here, we evaluated this Fab x sdAb-Fc format as a T-cell redirecting bispecific antibody (TbsAbs) by targeting mEGFR on tumor cells and mCD3E on T cells. We focused our attention specifically on the hinge design of the sdAb arm of the bispecific antibody. Our data show that a TbsAb with a shorter hinge of 23 amino acids (TbsAb.short) showed a significantly better T cell redirected tumor cell elimination than the TbsAb with a longer, classical antibody hinge of 39 amino acids (TbsAb.long). Moreover, the TbsAb.short form mediated better T cell-tumor cell aggregation and increased CD69 and CD25 expression levels on T cells more than the TbsAb.long form. Taken together, our results indicate that already minor changes in the hinge design of TbsAbs can have significant impact on the anti-tumor activity of TbsAbs and may provide a new means to improve their potency.

Opportunities and challenges of bi-specific antibodies

The recent clinical approval of different Bi-specific antibodies (BsAbs) has revealed the great therapeutic potential of this novel class of biologicals. For example, the bispecific T-cell engager (BiTE), Blinatumomab, demonstrated the unique capacity of BsAbs to link T-cells with tumor cells, inducing targeted tumor cell removal. Additionally, Amivantamab, recognizing the EGFR and cMet in cis, revealed a substantial improvement of therapeutic efficacy by concomitantly targeting two tumor antigens. Cis-targeting BsAbs furthermore allow discerning cell populations which concurrently express two antigens, for which each antigen expression pattern in itself might not be selective. In this way, BsAbs harbor the great prospect of being more specific and showing fewer side effects than monoclonal antibodies. Nevertheless, BsAbs have also faced major obstacles, for instance, in ensuring reliable assembly and clinical-grade purification. In this review, we summarize the different available antibody platforms currently used for the generation of IgG-like and non-IgG-like BsAbs and explain which approaches have been used to assemble those BsAbs which are currently approved for clinical application. By focusing on the example of regulatory T-cells (Tregs) and the different, ongoing approaches to develop BsAbs specifically targeting Tregs within the tumor microenvironment, our review highlights the huge potential as well as the pitfalls BsAb face in order to emerge as one of the most effective therapeutic biologicals targeting desired cell populations in a highly selective way. Such BsAb may improve treatment efficacy and reduce side effects, thereby opening novel treatment opportunities for a range of different diseases, such as cancer or autoimmune diseases.

Generation and characterization of novel co-stimulatory anti-mouse TNFR2 antibodies

Tumor necrosis factor receptor 2 (TNFR2) has gained much research interest in recent years because of its potential pivotal role in autoimmune disease and cancer. However, its function in regulating different immune cells is not well understood. There is a need for well-characterized reagents to selectively modulate TNFR2 function, thereby enabling definition of TNFR2-dependent biology in human and mouse surrogate models. Here, we describe the generation, production, purification, and characterization of a panel of novel antibodies targeting mouse TNFR2. The antibodies display functional differences in binding affinity and potency to block TNFα. Furthermore, epitope binding showed that the anti-mTNFR2 antibodies target different domains on the TNFR2 protein, associated with varying capacity to enhance CD8⁺ T-cell activation and costimulation. Moreover, the anti-TNFR2 antibodies demonstrate binding to isolated splenic mouse Tregs ex vivo and activated CD8+ cells, reinforcing their potential use to establish TNFR2-dependent immune modulation in translational models of autoimmunity and cancer.

Advances in mRNA-based drug discovery in cancer immunotherapy

INTRODUCTION

Immune checkpoint inhibitors and adoptive T-cell therapy based on chimeric antigen receptors are the spearhead strategies to exploit the immune system to fight cancer. To take advantage of the full potential of the immune system, cancer immunotherapy must incorporate new biotechnologies such as mRNA technology that may synergize with already approved immunotherapies and act more effectively on immune targets.

AREAS COVERED

This review describes the basics of mRNA biotechnology and provides insight into the recent advances in the use of mRNA for the local and systemic delivery of immunostimulatory antibodies, proinflammatory cytokines or for optimizing adoptive T-cell therapy.

EXPERT OPINION

mRNA-based nanomedicines have great potential to expand the arsenal of immunotherapy tools due to their ability to simplify and accelerate drug development and their suitability for transient and local expression of immunostimulatory molecules, whose systemic and sustained expression would be toxic. The success of mRNA-based COVID-19 vaccines has highlighted the feasibility of this approach. Continuous advances in the delivery and construction of RNA-based vectors hold promise for improvements in clinical efficacy.