Immunization strategies for the production of rat monoclonal anti-idiotope antibodies

Anti-idiotypic response to antigrowth factor receptor monoclonal antibodies

The immunogenicity of the idiotypic portions of two antigrowth factor receptor monoclonal antibodies (MAbs) was studied. Immunisation of allogeneic but not syngeneic mice with antihuman epidermal growth factor receptor (EGF-R) MAb MINT5 or anti-HER-2/neu MGR6 MAb elicited a detectable titre of circulating antibodies, particularly when the MAb was coupled with the keyhole limpet haemocyanin and administered together with Freund's adjuvant. The anti-Ab1 response to MAb MINT5 was slightly delayed as compared with the response obtained with MAb MGR6 and was mainly directed to the variable regions. In both cases, all anti-Ab1-positive sera specifically competed with the binding of homologous radiolabelled Ab1 to the relevant EGF-R+ or HER-2/neu+ target cells. Fusion of splenocytes from MINT5-immunised animals failed to produce MAb, whereas cell fusion was successful in generating a paratope-related MAb in the case of MGR6. The anti-MGR6 MAb-produced IdM6.4 inhibited the binding of MAb MGR6 on breast carcinoma cells, suggesting that it recognises an idiotope in or near the antigen combining site, and can be considered useful in the identification and purification of the Ab1 or its derivatives. We analysed whether a possible recognition of murine EGF-R by MAb MINT5 or a mimicry of EGF by the MAb idiotype prevented or delayed the development of an idiotypic cascade in mice. MINT5 inhibited human and murine EGF binding to the human EGF-R, whereas the anti-Ab1 response competed with MINT5 but not with murine EGF binding to A431 human epidermoid carcinoma cells. Moreover, MINT5 did not recognise the murine EGF-R. In a phase I clinical study, no detectable levels of human antimouse antibody response were observed in 5 of the 6 treated cancer patients. The ability of MAb MINT5 to block human EGF-R function, together with its low immunogenicity in patients, raise the possibility of its application in carcinoma immunotherapy.

Rapid induction of anti-idiotypic responses to unmodified monoclonal antibodies from syngeneic mice following primary immunization

A single foot-pad immunization in adjuvant of BALB/c mice with non-modified BALB/c monoclonal antibodies (HyHEL 5, 9 and 10) specific for hen egg lysozyme permitted isolation of anti-idiotypic monoclonal antibodies 10 days later. An evaluation of different screening tests revealed that antibodies were detected more easily by isotype-specific or direct binding assays than by cross-linking ELISA procedures. These results were confirmed by a direct cell-binding assay on B cells transgenic for one of the immunizing antibodies. The use of these cells also permitted an evaluation of the ability of these antibodies to inhibit antigen binding under conditions in which the target antibody, in its cell-surface configuration, is minimally modified by potential artifacts induced by purification or fixation to a solid support. This study demonstrates that anti-idiotypic responses to anti-protein antibodies may be rapidly generated in syngeneic animals.