Fab-drug conjugates in transplant

About This Grant

SUMMARY Current treatments for the suppression of allograft rejection have remained largely unchanged over the last several decades, relying on systemic calcineurin inhibition, anti-metabolites, and steroids. Although effective in curtailing alloimmune responses, these systemic therapies produce significant undesired off-target effects, which often lead to early organ loss and patient mortality. There is an urgent need for innovative strategies to mitigate these critical side effects, extend transplant survival, and improve organ recipient lifespans. Among nanotherapies, antibody-drug conjugates (ADCs), represent a cutting-edge technology that combines biologics with small molecules to target specific cells. ADCs have been successful in cancer, where they leverage antibody specificity to deliver cytotoxic drugs directly to target cells, achieving impressive tumor efficacy with reduced systemic toxicity compared to chemotherapy. However, their application to the field of organ transplantation has been hindered by the high immunogenicity of the Fc portion, poor tissue penetration, and the absence of tools to track cargo delivery to the target cells, essential for controlling immunosuppression. We hypothesize that Fab-fragment drug conjugates (FDCs), which lack the limitations of ADCs, can be utilized to selectively deliver immunosuppressive drugs both intracellularly to T cells (intra-FDCs) and locally to sites of allograft inflammation (local-FDCs), while maintaining low drug systemic levels of free drug. Our approach, supported by our preliminary results, introduces an innovative design for these nanotherapies, which enables precise monitoring of drug release both in vitro and in vitro, combining both therapeutic and diagnostic (theranostic) purposes. In Aim 1 we will design and optimize an FDCs-based platform for the targeted delivery of the calcineurin inhibitor Tacrolimus, and the anti-metabolite mycophenolic acid (MPA) directly into T cells (Intra-FDCs). In Aim 2 we will establish an FDCs-based strategy to locally release the corticoid methylprednisolone at inflamed allograft sites (local-FDCs). While both intra-FDCs and local-FDCs utilize Fab fragments, they rely on independent mechanisms of action and drug-release triggers. This independence ensures that each approach can be pursued separately. This R21 application will generate intra-FDCs and local-FDCs leveraging a fluorescent theranostic platform to enable real-time tracking of their delivery and activity. This approach, while technically challenging (high-risk), offers a potentially transformative solution to a critical unmet need in transplant immunosuppression and other contexts, such as autoimmune disease (high-reward). Successful outcomes will set a clear path forward for developing these FDC strategies for human use and will constitute the basis for applications to other funding mechanisms. 1