New research has identified an approach to mapping the immune response in people critically ill with sepsis, which could lead to more targeted and timely treatment for patients.

The research was led by a multidisciplinary team which included King’s College London’s Matthew Fish, a PhD student and Professor Manu Shankar-Hari, who is a consultant in critical care medicine at Guy’s and St Thomas’ and an NIHR clinician scientist. Dr Richard Ellis, head of the NIHR Guy’s and St Thomas’ Biomedical Research Centre’s cutting-edge Flow Cytometry platform, and his team also contributed to this research published in British Journal of Anaesthesia.

It is recognised that critically ill patients have rapidly changing immune responses to infection and tissue injury (immune trajectory). If the path of a patient’s immune response can be identified accurately, then treatments that stimulate or depress the immune system can be timed to mirror the dominant immune signal at distinct stages of critical illness. This is called immunomodulation.

Due to the rapid changes in the immune responses of critically ill patients over time, clinical scientists are presented with major challenges when carrying out research in this area. This is particularly relevant to sepsis, where the natural immune system is profoundly altered and there is currently no standardised system for immune phenotyping. Immune phenotyping uses antibodies to identify cells based on the types of antigens or markers on the surface of the cells, and is a process used to help diagnose diseases. When carrying out the research scientists must also be able to successfully separate the signal for illness specific changes from inter experimental variations in the study. Only when these challenges are addressed alongside the poorly characterised yet rapidly changing sepsis specific immune trajectory, will allow optimal immunomodulation.

To address the challenge of inter-sample and inter experiment variability and to enable simultaneous leucocyte phenotyping to determine path of a patient’s immune response, the team developed a multiplexing approach using the stably expressed pan-leucocyte cluster of differentiation 45 (CD45) antigen as the target (referred to as barcoding), and cytometry by time of flight (CyTOF) as the phenotyping method. To address the non-standardised phenotyping challenge, the team used markers proposed in the standardised human immune phenotyping panel and included selected immune state markers that are treatment targets such as checkpoint molecules and the human leucocyte antigen DR isotype (HLADR).

By using these methods the team developed a feasible CD45 barcoding approach for standardised immune phenotyping. This allows for mapping out how the immune response will progress in critically ill patients.

Matthew Fish said: “We are extremely excited about the development of this feasible barcoding system.  Mapping out the leucocyte immune trajectory in sepsis patients will inform the next stage of our work – the development of immune phenotyping tests to provide targeted and timely immunomodulation in sepsis.”

Utilising mass cytometry with CD45 barcoding and standardised leucocyte phenotyping for immune trajectory assessment in critically ill patients was funded by the National Institute of Academic Anaesthesia (NIAA), the National Institute for Health Research (NIHR) Clinician Scientist Award to Professor Shankar-Hari and the NIHR Guy’s and St Thomas’ Biomedical Research Centre.