Complement convertase imaging techniques for optimization of complement therapeutic amelioration of antibody mediated rejection

The National Institute of Allergy and Infectious Diseases awarded Northwestern University $3,267,712 under Project Grant R01AI196453 on April 1, 2026, to develop non-invasive fluorescence imaging techniques for detecting complement activation in antibody-mediated rejection (AMR) following lung transplantation.

The recipient will develop novel fluorogenic probes adept at detecting complement convertase activity in real time as a strategy to enable non- or minimally invasive diagnosis and monitoring of AMR. Current clinical approaches rely on invasive biopsy to confirm complement deposition products such as C4D, which persist for weeks at deposition sites. The proposed work uses murine models of transplant rejection in concert with complement inhibitors acting at different points in the complement cascade to optimize imaging and therapeutic intervention.

The award is funded under the Allergy and Infectious Diseases Research program (CFDA 93.855), which supports biomedical research and research training in infectious diseases and related areas. The period of performance runs through March 31, 2030, with work performed in Chicago, Illinois.

Masonic Medical Research Institute serves as a sub-recipient, receiving sub-award R01AI196453-60073636 issued June 12, 2026, to participate in the complement convertase imaging research.

Abstract

Therapeutic strategies to halt antibody-mediated rejection (AMR) following lung transplantation are lacking, due in large part to the complex pathophysiology of the immune process and the multi-faceted approach that must be taken to establish a defined diagnosis. IT is becoming increasingly clear that AMR has many endotypes, with donor-specific antibodies mediating a host of complement dependent and independent functions. Thus, the development of strategies to stratify patients based upon endotype has the potential to revolutionize the treatment of AMR. Pre-clinically, fluorescence imaging has been used to investigate a wide array of diseases and disorders. In transplantation, the focus has primarily been T cell-mediated rejection, detecting leukocyte trafficking to the graft via phagocyte-specific approaches or fluorogenic probes for inflammatory signatures, such as cathepsin B. In our own previous work, we developed a fluorogenic probe specific to granzyme B and reported its utility in monitoring therapeutic intervention in a murine model of myocarditis, a surrogate for cardiac transplant rejection. As such, there is a great unmet need to develop agents capable of non-invasively diagnosing or monitoring AMR. To this end, we have developed novel fluorogenic probes adept at detecting complement activation in real time, via the examination of complement convertase activity, as opposed to deposition products such as C4D, which persist for weeks at the site of deposition and can only be confirmed by invasive biopsy procedures. Thus, the goals of this proposal are to develop non- or minimally invasive techniques to image ongoing complement activation in-vivo. To accomplish this, we will use murine models of transplant rejection in concert with an assortment of complement inhibitors that act at different points in the complement activation pathway to characterize the extent to which these probes can determine complement activation. We will concomitantly examine their efficacy in a novel porcine EX-vivo perfusion system in which human complement activation can be modeled to investigate the potential clinical applicability in the setting of lung transplantation. To accomplish these goals, we propose the following specific aims: aim 1: examination of the extent to which fluorogenic convertase imaging can characterize AMR endotype, and aim 2: investigation of the translatability of convertase imaging to the stratification of AMR patients. On the completion of these studies, we will have validated a cadre of novel protease activatable complement specific imaging agents for use in the examination of AMR. We will have further dissected the significance of complement pathway specific proteins in mediating and modulating AMR. By using rodent analogues of clinically available FDA complement inhibitors, should our studies prove efficacious, our results could be rapidly translated.