411 Dichotomy in Cross-clade Reactivity of Sera: Implications for the Development of Active and Passive Immunotherapy L. Cavacini*1, M. Duval1, C. Wood2, K. Mayer3, M. Posner1 1Beth Israel Deaconess Med Ctr and Harvard Med Sch, Boston, MA; 2Univ of Nebraska at Lincoln; and 3Fenway Community Hlth, Boston, MA
Background: Using sera and virions from clade B infected individuals, we have shown previously that serum antibodies reactive with primary isolate virions correlates with virus neutralization and stable disease. While clade B is responsible for the vast majority of infections in North America and parts of Europe, infection with clade C virus is more prevalent in other parts of the world. We have evaluated the reactivity of sera from clade C infected individuals for reactivity and neutralization of clade C virus. Furthermore, we have analyzed sera from clade B and clade C infected individuals for cross-clade reactivity and will be analyzing cross-clade neutralization.
Methods: Sera IgG was captured onto ELISA plates coated with goat anti-human IgG Fc specific prior to the addition of clade B (2 each R5, R5X4 and X4) virus or clade C (2 R5) virus which were prepared in PHA stimulated PBMC. Unbound virus was removed by washing, and virus captured determined by p24 were released from captured virus lysed using triton. Neutralization of virus was determined using a 7-day PHA stimulated PBMC assay with 100 TCID50/ml.
Results: Clade B sera reacted more frequently with X4 virus and captured more X4 virus than R5 and R5X4 virus. Clade C sera reacted equally with X4, R5, and R5X4 viruses, although slightly more X4 virus was captured. When tested for cross-clade reactivity, less than 50% of clade B sera reacted with clade C virus. Of those sera reactive with clade C virus, significantly less clade C virus was captured as compared to other R5 viruses. In contrast, over 90% of clade C sera reacted with clade B virus. Of interest, more than 75% of the clade C sera reactive with clade B virus captured more clade B virus than clade C virus.
Conclusions: These studies suggest that while there are some similarities, there are also distinct differences in cross-clade reactivity of antibodies induced in response to clade C infection versus clade B infection. Further studies of antibodies from clade C infected individuals and their interaction with env may provide important information on the design of immunogens for effective active immunization.