Immunotoxin with mistletoe lectin I A-chain and ricin A-chain directed against CD5 antigen of human T-lymphocytes; comparison of efficiency and specificity.

Monoclonal anti-CD5 antibody was coupled to the enzymatically active subunit of plant toxin [either mistletoe lectin I (ML) or ricin]. The obtained conjugates proved to be selectively toxic to CD5-bearing target cells. The immunotoxin prepared from ML A-chain (MLA) was as toxic as native ML and approximately 80-fold more active than the corresponding conjugate with ricin A-chain (RTA). The comparative studies of the structural properties of isolated MLA and RTA were carried out using intrinsic fluorescence spectroscopy. The results showed similar properties for both proteins. No antigenic cross-reactivity against both toxins was detected when using polyclonal antibodies. The results suggest that MLA-antibody conjugates may be potential candidates for therapeutical use.