Compsn. comprises a pure human-like immunoglobulin (Ig) which (a) reacts specifically with p55 Tac protein and/or (b) inhibits binding of human interleukin-2 (IL-2) to its receptor. Also new are (1) human-like Ig having 2 pairs of light/heavy chains and able to react specifically with an epitope of a human IL-2 receptor with affinity at least 10 power 8 per mole, the chains including complementarily determg. regions (CDR's) and human-like framework regions (FR's), the CDR's being from different Ig molecules than FR's； (2) humanised Ig (hIg) which can bind to IL-2 receptors and contain at least one CDR from anti-Tac antibody in a human-like FR contg. at least one amino acid from the anti-Tac antibody； (3) nucleic acid encoding for human-like FR and at least one murine CDR, and (4) cells transfected with nucleic acid.
