Receptor binding ligands, their use in the detection of cells with biological interest

A method for determining a physiological state of target cells taking place at a given time or during a given time interval, comprising:

• contacting the target cells with at least two soluble receptor binding ligands comprising the totality of the receptor binding domains (RBD) of at least two glycoproteins of at least two enveloped viruses that interacts with a cellular cognate receptor,
• each of said at least two receptor binding ligands having a tag, detectable molecule or label coupled thereto, each of said at least two soluble receptor binding ligands containing the totality of one of the RBD of said glycoprotein, wherein said RBD does not comprise a transmembrane domain;
• and,
• wherein complexes are formed between each of said at least two soluble receptor binding ligands and each of at least two distinct membrane receptors, and the complexes are detectable by the tag, the detectable molecule or the label coupled to each of said at least two receptor binding ligands,
• wherein all receptor binding ligands contacting the cells contain the totality of RBD of said glycoprotein, and said all receptor binding ligands do not comprise a transmembrane domain, and
• wherein said at least two glycoproteins belong to viruses selected from the group consisting of:
• Amphotropic MLV (ampho, SEQ ID NO:1), Gibbon Ape Leukemia virus (GALV, SEQ ID NO:2), Feline endogenous virus (RD114, SEQ ID NO:3), vesicular stomatitis virus (VSV, SEQ ID NO:4), Xenotropic Murine Leukaemia Virus (NZB, Xeno, SEQ ID NO:
• 10), Feline Leukaemia Virus C (FeLV, SEQ ID NO:
• 19), Env Koala Retrovirus (KoV, SEQ ID NO:
• 20), Env Porcine Endogeneous Retrovirus-B (Perv B, SEQ ID NO:
• 22), Human T Leukaemia Virus-1 (HTLV1, SEQ ID NO:27), Human T Leukaemia Virus-2 (HTLV2, SEQ ID NO:28), Human T Leukaemia Virus-4 (HTLV4, SEQ ID NO:
• 31), and Env Bovine Leukaemia Virus (BLV, SEQ ID NO:
• 30).