Synthetic peptides as putative therapeutic agents in transplantation medicine: application of PEPSCAN to the identification of functional sequences in the extracellular domain of the interleukin-2 receptor beta chain (IL-2R beta)

A desired treatment strategy in transplantation medicine is the selective t argeting of alloreactive T cells without impairing antileukemic and antivir al activities. One approach is the synthesis of peptides that interfere wit h the binding of interleukin-2 (IL-2) to its high affinity receptor (IL-2R) . This blocks the activation and proliferation of the antigen-activated T c ells and the secretion of IL-2. The latter binds to its receptor, via the e xtracellular domain of the IL-2R beta chain, while its cytoplasmic domain i s required for intracellular signal transduction. In this study, the PEPSCA N method was applied in order to identify antigenic sequences (epitopes) in the extracellular domain of the IL-2R beta. Based on the primary amino aci d (aa) sequence of the IL-2R beta, a total of 239 overlapping dodecapeptide s, spanning the entire sequence of IL-2R beta, were synthesized by PEPSCAN and their immunoreactivity was tested by ELISA using monoclonal antibodies (mAbs) specific for IL-2R beta such as TU11, Mik beta 1, HuMik beta 1 and T U27. TU11 recognized a linear epitope located in the region R-85-Q(96). Non e of the 239 synthetic peptides was recognized by TU27. Mik beta 1 (and HuM ik beta 1) recognized a discontinuous epitope formed by aa located in the I L-2R beta domains L-106 to P-148 and E-170 to A(202). Subsequently, synthet ic peptides corresponding to the identified putative epitopic sequences wer e prepared by solid phase synthesis and their immunogenicity in vivo was as sessed by raising polyclonal antibodies. Given that Mik beta 1 and HuMik be ta 1 inhibit binding of IL-2 on the IL-2R beta, we addressed the question o f whether the identified antigenic sequences serve as putative IL-2 binding domains. Synthetic peptides corresponding to these sequences were tested f or their ability to compete with IL-2 for binding and, thereby, inhibit IL- 2-induced proliferation of mitogen-stimulated human peripheral blood T cell s. Sequences M-107-E-118 and Y-178-Q(199) probably represent functional IL- 2 binding domains on IL-2R beta, since these synthetic peptides significant ly inhibited the proliferation of activated T cells and secretion of IL-2. (C) 2000 Elsevier Science B.V. All rights reserved.