Amino acid sequences directed against cellular receptors for viruses and bacteria

An isolated polypeptide comprising

• a) two or more VHH, humanized VHH or camelized VH that specifically bind hCXCR4 (SEQ ID NO:
• 254) and that inhibit HIV entry into a cell, wherein one VHH, humanized VHH or camelized VH consists essentially of 4 framework regions (FR1 to FR4, respectively) and 3 complementarity determining regions (CDR1 to CDR3, respectively), in which CDR1 is the amino acid sequence of SEQ ID NO:
• 142, CDR2 is the amino acid sequence of SEQ ID NO:
• 174, and CDR3 is the amino acid sequence of SEQ ID NO:
• 206
• wherein another VHH, humanized VHH or camelized VH consists essentially of 4 framework regions (FR1 to FR4, respectively) and 3 complementarity determining regions (CDR1 to CDR3, respectively), in which CDR1 is the amino acid sequence of SEQ ID NO:
• 143, CDR2 is the amino acid sequence of SEQ ID NO:
• 175, and CDR3 is the amino acid sequence of SEQ ID NO:
• 207;
• and
• b) a VHH, humanized VHH or camelized VH that specifically binds to hCD4 (SEQ ID NO:
• 268) and that inhibits HIV entry into a cell wherein the VHH, humanized VHH or camelized VH consist essentially of 4 framework regions (FR1 to FR4, respectively) and 3 complementarity determining regions (CDR1 to CDR3, respectively), in which CDR1 is the amino acid sequence of SEQ ID NO:
• 287;
• CDR2 is the amino acid sequence of SEQ ID NO:
• 295;
• and CDR3 is the amino acid sequence of SEQ ID NO:
• 303.