Antibodies elicited by naked DNA vaccination against the complementary-determining region 3 hypervariable region of immunoglobulin heavy chain idiotypic determinants of B-lymphoproliferative disorders specifically react withpatients' tumor cells

Several reports have suggested that the mechanism of protection induced by antiidiotypic vaccination against low-grade lymphoproliferative disorders i s likely to be antibody mediated. Here we test the hypothesis that DNA vacc ination with the short peptide encompassing the complementary-determining r egion 3 hypervariable region of immunoglobulin heavy chain (VH-CDR3) may el icit a specific antibody immune response able to recognize the native antig ens in the form required for therapy, As a test system, we used the VH-CDR3 sequences derived from two patients with non-Hodgkin's B lymphomas (PA, AS ) and one patient with hairy cell leukemia (BA) to immunize outbred Swiss m ice. This experimental model could mimic a clinical setting in which differ ent patients present distinct HLA haplotypes, Individual tumor-specific VH- CDR3 sequences were amplified by a two-step procedure and directly cloned i nto multigenic plasmid vectors (pRC100 and derived) with and without mouse interleukin 2 (mIL-2). Each tumor-specific sequence was characterized by se quencing. Female Swiss mice were vaccinated i.m. with plasmids expressing t he tumor-specific VH-CDR3 sequence alone (pRC101-PA), mIL-2 plus the VH CDR 3 sequence (pRC111-PA), or a different unrelated antigen (NS3 of hepatitis C virus; pRC112), the sole mIL-2 (pRC110), and the empty plasmid (pRC100), Boost injections were performed at 3 and 16 weeks from the first vaccinatio n, and sera were drawn before each vaccination and at 6, 9, and 19 weeks. I nduction of anti-VH-CDR3s antibodies in the sera and their ability to recog nize native antigens on patients' tumor cells were evaluated by FACS analys is. Up to 56% (n = 25) of mice vaccinated with pRC111-PA plasmid and 20% (n = 15) of mice vaccinated with pRC101-PA developed a specific immune respon se that was maintained throughout 19 weeks of observation in 40% of pRC111- PA-vaccinated mice. No response was detected in sera obtained from mice vac cinated with the other plasmids (n = 45). pRC111-PA injection s.c. was less effective (13%, n = 15) than i.m. injection (53%, n = 15). Indeed, we demo nstrated that antibodies elicited by naked DNA vaccination against three di fferent patient-derived VH-CDR3 peptides (pRC111-PA or BA or AS) readily re acted with binding epitopes on the idiotypic proteins expressed on the surf ace of tumor cells derived from each patient; 60, 40, and 40% of, respectiv ely, PA-, BA-, and AS-vaccinated mice developed specific antibodies. No cro ss-reactivity was detected among the three different CDR3s against tumor ce lls derived from the other two patients, The outbred mouse strategy confirm ed the significant matching potential of three different VH-CDR3 peptides t o be efficaciously presented through different MHCs, We conclude that indiv idual VH-CDR3 DNA vaccination can result in a potentially effective specifi c immune response against non-Hodgkin's B lymphoma cells by a rapid and low -cost therapeutic approach.