RESUMO
Neuroblastoma treatment with chimeric antidisialoganglioside GD2 Ab ch14.18 showed objective antitumor responses. Production of anti-idiotypic Abs (Ab2) against ch14.18 (Ab1) in some cases was positively correlated with a more favorable prognosis. According to Jerne's network theory, a subset of anti-idiotypic Abs (Ab2beta) carries an "internal image" of the Ag and induces Abs (Ab3) against the original Ag. The molecular origin of an anti-idiotypic Ab response in tumor patients was not investigated previously. To clone anti-idiotypic Abs, B cells of a ch14.18-treated neuroblastoma patient with Ab2 serum reactivity were used to construct Ab phage display libraries. After repeated biopannings on ch14.18 and its murine relative, anti-GD2 mAb 14G2a, we selected 40 highly specific clones. Sequence analysis revealed at least 10 of 40 clones with different Ig genes. Identities to putative germline genes ranged between 94.90 and 100% for V(H) and between 93.90 and 99.60% for V(L). An overall high rate of replacement mutations suggested a strong Ag-driven maturation of the anti-idiotypic Abs. Two clones that were analyzed further, GK2 and GK8, inhibited binding of ch14.18 to GD2 just as the patient's serum did. GK8 alone inhibited >80% of the patient's anti-idiotypic serum Abs in binding to ch14.18. Rabbits vaccinated with GK8 or GK2 (weaker) produced Ab3 against the original target Ag GD2. GK8 may be useful as a tumor vaccine for GD2-positive [corrected] tumors.
