long shape line in tSNE plot
Welcome to the community Dalide!

There is a sequential pattern in your data. As a non-Bioinformatics guy, I simply googled and saw that biomarker are also vastly used for learning the Progression of a disease (e.g. Alzheimer). I hope I am right about example and if I am, then it is not a big surprise that you see those curves which might indicate the progress of something. If you need more precise answer you better give some more info about the origin of data (or a link to your data if it is publicly available). 

From ML point of view, about which I fortunately know a bit, those curves in tSNE are caused by sequential patterns. 

Fun: As an equally surprising example, once I found sequential pattern in characteristics of different Wines!! (each row a Wine and each column a wine property like Alcohole%, density, etc.)