Anti-idiotypic antibodies induced by genetic immunisation are directed exclusively against combined VL/VH determinants

DNA vaccines encoding the idiotype of immunoglobulins of tumour B cells were shown to induce protection in several mouse lymphoma models. The mechanism of rejection of tumour cells has not been fully understood, but there is strong evidence suggesting that engagement of the idiotype by anti-idiotypic antibodies may directly result in inhibition of tumour growth. In this study, we have investigated the structural basis of the idiotypic/anti-idiotypic interaction following immunisation with DNA vaccines. scFvs containing only one of the two tumour-derived V regions recombined to an irrelevant V region partner were generated. These constructs encoding a secretory form of the scFv were used as immunogens to induce anti-ld antibodies. The same scFvs were expressed as membrane-bound molecules on the surface of mammalian cells. Analysis of immune sera on the membrane-displayed idiotypes revealed that DNA immunisation induced a polyclonal antibody response restricted to conformational combined epitopes formed by the parental V-L/V-H association. Immune sera raised by scFv DNA vaccination did not show any detectable reactivity towards chimeric scFvs containing only one of the two immunising V regions, indicating that the response against combined V-L/V-H determinants is highly dominant. Remarkably, the same immunogen, delivered as scFv protein, induced antibodies also directed against chain-specific determinants. These findings indicate that presentation of properly folded idiotypes results in a highly specific antibody response directed exclusively to private idiotypic determinants of the V-L/V-H combination of the immunogen.