Designing and testing the efficacy of recombinant idiotype-mycobacterial HSP70 fusion protein as a vaccine model against B-cell lymphomas

Objectives. Variable regions of immunoglobulin molecule (Ig) on B-cell lymphoma constitute tumor specific antigenic determinants collectively designated as idiotype (Id). Idiotypic determinants are nominally antigenic in tumor bearing hosts. Mycobacterial heat shock protein 70 (mycHSP70) is known for its ability as immunoadjuvant to activate anigen-presenting cells such as dendritic cells (DCs) through a toll-like receptor, TLR4. The objective of this study is to utilize mycHSP70 to enhance immunogenicity of two different B-lymphoma specific idiotopes. We accomplished this by using mycHSP70 fused to idiotypes of two tumors A20 and 2C3 as recombinant protein vaccine. Methods. By using standard molecular techniques we constructed plasmids encoding idiotype-mycHSP70 recombinant proteins (A20Id-mycHSP70, 2C3Id-mycHSP70). Purified recombinant proteins were tested for their efficacy as vaccines. Results. Our study showed that A20Id-mycHSP70 as vaccine elicited significantly higher anti-idiotype humoral responses which were predominantly IgG2a type. This suggests activation/involvement of T-helper type 1 cells. Tumor-challenged mice also experienced long-term protection (mean survival rate 40% higher than control groups) with prophylactic vaccination using A20Id-mycHSP70 protein. Concomitant with this increased survival rate, there was a significant increase in idiotype-specific cytotoxic T-cell responses. In contrast, no significant differences were observed between 2C3Id-mycHSP70 and control groups in terms of humoral and cellular immune responses as well as by survival studies. Conclusion. Immunogenicity of A20 idiotype but not 20 idiotype can be significantly enhanced by its covalent coupling with mycobacterial HSP70. The differences can be explained on the basis of presence or absence of MHC class I binding epitopes in 2C3 idiotype but not in A20 idiotype. However, both the idiotypes were found to have potential MHC II epitopes. In essence, this study suggests that mycHSP70 can be used as an adjuvant to enhance Id immunogenicity provided, the antigen has appropriate MHC epitopes.