In the Netherlands, and in most European countries, once people turn 55, they start to be invited every two years to perform a faecal immunochemical test (FIT) [1]. Additionally, in the US, for example, the professional Gastroenterology and Oncology societies suggest that people belonging to high-risk groups, e.g. with a family history of CRC, should start screening by age of 40 [2]. The end-users of our diagnostic tool are precisely the people from the aforementioned high-risk groups: people over 55 years old, and people with family history of CRC, IBD and other risk conditions. After talking to stakeholders, we think people over the age of 45/50 should be included in our programme. This is also confirmed by the fact that CRC incidence in individuals younger than 50 years has been increasing by 2 % per year since 1994 [3]. Hence the final goal of Colourectal: increasing the sensitivity and accessibility of the current national screening programme. Our diagnostic tool is therefore envisioned for its distribution among the previously mentioned risk groups of the population, as part of the national screening programme by replacing the current diagnostic methods.

When invited to the national colorectal screening programme, the person may take the Colourectal self-test. Specifically, the user receives the kit containing four pills directly at home. The first three of these pills allow the test to function for the duration of seven days. The function of the fourth pill is to remove the diagnostic from the colon.

Colourectal is a diagnostic test, so the user should read the provided leaflet before use carefully (click here to read the leaflet). After reading how and when Colourectal should be ingested, the diagnostic process can begin. Pills one, two and three should be taken at days one, two and three, respectively. These pills should be taken every day at the same time, to facilitate the process, an app is available to guide the user through the entire process. The app will also send daily reminders to take the corresponding pills at the right moment.

The third pill contains a built-in mechanism to check whether Colourectal is functioning properly. From day three, the user should see a pink colour in their stool. If not, the test might not have worked correctly, and the user should contact the national screening programme to request an additional test.

During the seven days in which Colourectal is active, the user should keep an eye on their stool, preferably by using the app for tracking and reference. If a blue colour is noticed in the stool anytime during this week, the user might have CRC. If no blue colour is detected during this period, the Colourectal self-test has not detected CRC in the user.

Even though our model predicts that the living diagnostic tool is unlikely to stay in the colon for longer than a week and will gradually disappear, the gut microbiome varies from person to person. Therefore, to make sure that our living diagnostic is removed from the colon, the fourth pill is included in the test. Additionally, if at any time during the testing period the user feels unwell or experiences unfamiliar or unexpected symptoms or side-effects, the fourth pill should be taken immediately to remove the self-test from the user’s colon.

Our self-test comes in the form of pills containing an engineered E. coli Nissle 1917 strain, hence the name ‘living diagnostic’. This system allows to have a laboratory-free testing process for CRC. The pills containing the living diagnostic are made of acid resistant capsules with a pH-based release [4]. This allows for the delivery of Colourectal into the colon. As previously introduced, the test consists of four pills: the first two contain only the living diagnostic, the third contains the living diagnostic and an inducer for the positive control, and the fourth contains the test terminator.

When cancer is detected by the living diagnostic, a blue colour could become visible in the faeces at any time during the test. Additionally, from the third day onwards, a pink colour should be seen to verify that the Colourectal system is functional and has been applied correctly.

To decrease any risk associated with the ingestion of our test, we implemented a fourth pill that can stop the living diagnostic at any time of the process. If anything happens during the test, such as any type of side-effect, our kill-switch will be able to get rid of the living diagnostic. The fourth pill should also be used on day seven to fully get rid of our living diagnostic.

Due to the differences in lifestyle, microbiome, diet, etc. the stool can appear different from person to person, affecting the results of the test. Adding to this, a seven-day continuous test might cause anxiety in the person performing the test. This might mislead the user by, for example, not being able to distinguish the colour of the stool clearly. For this reason, it was highlighted by several stakeholders that our self-test needs supportive material to avoid any misunderstandings as well as causing anxiety in the user. This inspired us to create the Colourectal leaflet and app to help the users step by step.

The Colourectal digital app provides instructions to perform the test and helps the users to recognise the colour of their stool and therefore the outcome of the test. Furthermore, we envision Colourectal to be part of the national screening programme, making it possible to link this app to the users’ digital ID. In this way, the users can get into contact with health professionals in case they are still unsure about their test result, feel anxious as a consequence of the test, or want to make an appointment for further check-ups.

Since Colourectal is a living diagnostic, safety is a priority. For this reason, we dedicated a section on safety considerations of our tool, our safe-by-design approach, and considerations about the possible misuse. Click here to know more.

The main aspects of our proposed implementation for Colourectal are focused on making the test easy, accessible, user-friendly and more effective. To achieve this, we think that our design should be modular. We accomplished modularity, by building our system in a way that if new scientific discoveries come to place, they could be implemented in the current design. Hence, if new potential bacterial strains are discovered, our system could be translated into these. Modularity is also maintained in the components of the various genetic circuits. For example, one step of the three-step inducible system is modular, so that we can introduce new beneficial genetic circuits. Additionally, the lactate sensing mechanism can be exchanged for a chimeric receptor, if a new and more specific biomarker would be found.

Lastly, for a real-world implementation, various aspects of our project still have to be fully investigated. With the help of experts in the field of start-ups, we built a guide that would help us fill the gap and actually give life to Colourectal.