In a paper published in Nature Scientific Reports last week, researchers from the Human Protein Atlas describe a method for stratification of responders towards the drug eculizumab that allows for precision medicine and should be applicable to several other diseases and therapeutics.

The term precision medicine describes the idea of providing effective treatment based on a patient´s molecular make up. Recent advances in molecular diagnostic tools and handling of large data sets allow for the stratification of patients based on e.g. genetic or protein information and make it possible to provide tailored treatment for these sub-groups. In this report, the researchers describe how epitome information, exemplified by binding of the therapeutic antibody eculizumab on its target complement component 5 (C5) can be used to guide treatment.

The complement system is an important part of the human immunity. It fulfills an important role in fighting bacterial infections and provides a link between innate adaptive immune responses. Such powerful functions require a tight regulation to prevent the complement system from attacking the host´s cells. Paroxymal nocturnal hemoglobinuria (PNH) and atypical hemolytic uremic syndrome (aHUS) are two disorders associated with a malfunctioning complement system.

The monoclonal antibody eculizumab is a therapeutic antibody for treatment of PNH and aHUS, targeting C5, a central protein in the complement system cascade. Despite the proven relevance of the drug, reports on non- or poorly responding patients have been published, suggesting mutations in the C5 gene which changes the C5 protein so that it can no longer be bound to the drug.

Here, the researchers use an epitope mapping strategy based on deep mutational scanning of surface-displayed protein domains to explore in detail the structural epitope properties of eculizumab. Their workflow includes the identification of a binding domain, creation of a mutant display library, identification and sorting of surface expressed non-binding domain mutants using flow cytometry and sequencing of them. The researchers present six residues on the complement protein C5 that are essential for the binding and function of eculizumab and suggest that other means of treatment should be considered for individuals carrying mutations in these positions.

Comparing the patient´s gene sequence with the epitope of available drugs enables stratification into treatment groups. The work presented in this report outlines a general strategy for stratification of responders and non-responders for treatment with therapeutic antibodies and more specifically analyses the underlying molecular mechanism for patients´ response to the therapeutic antibody eculizumab.

Read the whole report here >>