Developing immunostimulatory antibodies to deliver agonism without toxicity

• Background Monoclonal antibodies (mAb) targeting immune checkpoints such as CTLA-4 and PD-1/PD-L1 have transformed therapy for some types of cancer in a proportion of patients. Despite these advances, the majority of patients have tumours which are resistant to this form of immunotherapy. Recent studies suggest that most tumours which respond to checkpoint therapy display a ‘hot’ T-cell rich signature.

Immunostimulatory antibodies (ISA) targeting TNF receptor superfamily members are capable of activating immune cells to deliver enhanced T cell priming, expansion, secretion of inflammatory cytokines and tumour cell killing. Notably, ISA synergise with checkpoint mAb to improve anti-tumour responses in preclinical models.

To date clinical development of ISA has been hindered by two key issues.

First, their activity on human cells has been variable, with only a minority demonstrating potent immunostimulation, in contrast to their more active murine counterparts.

Secondly, severe adverse events are frequently seen with strong ISA agonists, necessitating new approaches to mitigate these effects.

In the last five years, we have made important advances in understanding how to generate potent ISA that operate through either FcgR-dependent or -independent mechanisms.

We are now ideally-placed to bring this understanding to bear on a range of existing and new targets to deliver next-generation ISA for clinical application. • Aims 1) Optimise human ISA to deliver agonism with and without FcgR cross-linking. 2) Develop novel ‘conditional’ ISA formats that mitigate adverse events 3) Evaluate a new class of ISA that promote lymphocyte recruitment to tumours • Methods The programme will benefit from interactions with structural biologists, experts in antibody engineering as well as specialists in receptor biology and tumour microenvironment.

A unique panel of transgenic and humanised mouse models will allow appropriate evaluation of newly developed agents.

By combining techniques, including X-ray crystallography, SAXS and molecular dynamics together with protein engineering we will define the relationship between key mAb properties (affinity, hinge-rigidity, epitope) and immunostimulatory activity.

Furthermore, we will develop novel mAb formats and ISA against new targets to minimise adverse events associated with conventional ISA and improve T cell access to tumours. • How the results of this research will be used This programme will generate deeper mechanistic understanding of ISA, specifically detailing the factors which determine potency and toxicity in existing and new formats.

We will apply this knowledge to generate new optimised ISA for clinical testing that could extend the benefit of immunotherapy to more people with cancer.