International collaboration comparing neutralization and binding assays for monoclonal antibodies to simian immunodeficiency virus.

Thirteen laboratories characterized a coded panel of 10 MAbs to SIVmac251 envelope protein in a collaboration organized by the National Institute of Allergy and Infectious Diseases (NIAID). The MAbs were examined against SIV isolates in neutralization and radioimmune precipitation, immunoblot, enzyme-linked immunosorbent, and radioimmune assays. Although laboratories employed diverse neutralization assays that varied in sensitivity there was agreement on the relative ability of the MAbs to neutralize SIVmac251. Additionally, even though the quantity of any single MAb required to neutralize SIVmac251 varied between laboratories, there was agreement on the rank-order strength fo the five neutralizing MAbs. Based on the data from this study, the MAbs were classified according to their neutralization potential as high efficiency (MAb concentration, < 5 micrograms/ml), low efficiency (MAb concentration, 5-100 micrograms/ml), or nonneutralizing (MAb concentration, > 100 micrograms/ml). The MAbs could be assigned to four serological groups based on ability to cross-neutralize and bind different SIV isolates. The distinction between groups I, II, and III were based on the limited neutralization data obtained with the sooty mangabey isolate.