Supercharged protein-surfactant bioconjugates for next-generation cell therapies

Artificial membrane binding proteins (AMBPs) have the potential to impact on the efficacy of adoptive cell therapies, as the introduction of exogenous proteins to provide additional functionality to therapeutic cells could be highly advantageous for site-directed tissue repair. The methodology is centred on the rational design of modular bifunctional supercharged protein-polymer surfactant complexes that spontaneously insert into the plasma membrane of stem cells to impart oxygen delivery and chemotropic homing properties. This could address many of the challenges in cell therapies, including the lack of viable cell engraftment, which results in limited functional integration. Several cell therapy studies have shown that intravenous or intra-arterial infusion of stem cells leads to accumulation in tissue sinks, such as the lungs and spleen. These off-target effects reduce the efficiency of systemic delivery and increase the likelihood of producing lethal microemboli. Accordingly, this research programme describes the rational design of a new class of bifunctional AMBPs with responsive oxygen delivery and chemotrophic homing properties that will help overcome these limitations and have far-reaching implications in cell therapies for disease and regenerative medicine.

The new approach circumvents the need for covalent cell-surface chemistry, and offers a high degree of flexibility, as the approach can be applied to a wide range of proteins for use on potentially any cell type. The AMBP methodology pioneered by the PI involves the rational design of an AMBP in two key steps: (i) supercharging the AMBP anchor to amplify the positive surface charge density (ii) electrostatic grafting of polymer surfactant chains to the cationic sites on the membrane anchor. The resulting polymer surfactant corona allows the cell membrane affinity to be systematically tuned to facilitate spontaneous insertion of the AMBP into the cell membrane, whilst retaining the native function of the cell-bound protein. The PI has successfully applied this methodology to the oxygen-binding protein myoglobin, as well as supercharged green fluorescent protein fused to the fibronectin binding domain of a bacterial adhesin motif CshA. Here, the AMBPs rapidly inserted into the membranes of adult bone-marrow derived hMSCs and provided either responsive oxygen delivery or chemotactic stem cell homing to cardiac tissue.

The research programme has a strong (but not exclusive) focus on developing AMBPs for cardiac stem cell therapies, as cardiovascular disease (CVD) is the leading cause of death globally (2021 World Health Organisation estimate is 17.9 million deaths p.a.). Here, the conceptual advance is centred on developing humanised bifunctional AMBP chimeras that can responsively deliver oxygen to the cells via a supercharged myoglobin anchor module (to improve cell viability in hypoxic in vivo environments), fused to a module that provides cardiac extracellular matrix targeting. Accordingly, the ability to display multiple copies of these AMBPs, which can deliver oxygen and have been evolutionarily optimised to recognise and bind specific molecular targets in the cardiac endothelium, has the potential to advance cardiac cell therapy.

The AMBP platform is likely to have clinical impact beyond cell therapies for CVD, as it could be readily applied to other cell types and vesicles (e.g., monocytes, natural killer cells, exosomes, or lipid nanoparticles) and involve other homing protein- or peptide-based molecules (e.g., integrins, nanobodies, or other bacterial adhesins). The research programme describes a scientific methodology that combines both in-house techniques for biophysics, synthetic biology and regenerative medicine, as well as cutting-edge techniques available at large-scale facilities. As there is a strong medical focus within the programme, the applicant has engaged clinical scientists and industrial partners to aid with medical translation.