Chimeric macaque/human Fab molecules neutralize simian immunodeficiency virus.

A collection of simian immunodeficiency virus (SIV) neutralizing recombinant Fab fragments was generated using the combinatorial antibody library approach. Functional antibody fragments efficiently expressed in Escherichia coli were identified only in the form of chimeric macaque heavy chain gamma 1 and human light chain kappa. The gamma 1 and kappa chains were derived from a clinically healthy long-term surviving SIVsm-infected cynomolgus macaque and from an asymptomatic HIV-2 seropositive individual, respectively. The combinatorial library was constructed on the surface of filamentous phage using the pComb3 phagemid vector and screened against purified SIVsm surface glycoprotein (gp148). Twelve chimeric clones reacting with the antigen were isolated. Six of these clones showed a pronounced neutralizing activity against SIVsm with effects at concentrations of 0.01-0.1 micrograms/ml. All neutralizing Fab fragments were clonally unrelated as demonstrated by nucleic acid sequencing. These potent neutralizing reagents will be used for prophylactic and therapeutic immune intervention of lentivirus infection in macaques and to map neutralizing determinants of SIV.