Abstract: Novel compounds carrying ligands capable of ligating to counter receptors on relevant target cells are disclosed. The compounds possess a number of advantageous features, rendering them very suitable for a wide range of applications, including use as detection systems, detection of relevant target cells as well as in various methods. In particular, novel MHC molecule constructs comprising one or more MHC molecules are disclosed. The affinity and avidity of the MHC molecules of the constructs are surprisingly high. The possibility of presenting to the target cells a plurality of MHC molecules makes the MHC molecule constructs an extremely powerful tool e.g. in the field of diagnosis. The invention relates in general to the field of therapy, including therapeutic methods and therapeutic compositions. Also comprised by the present invention is the sample-mounted use of MHC molecules, MHC molecule multimers, and MHC molecule constructs.