EFFECTS OF NATURAL SEQUENCE VARIATION ON RECOGNITION BY MONOCLONAL-ANTIBODIES THAT NEUTRALIZE SIMIAN IMMUNODEFICIENCY VIRUS INFECTIVITY

The determinants of immune recognition by five monoclonal antibodies ( KK5, KK9, KK17, Senv7.1, and Senv1O1.1) that neutralize simian immunod eficiency virus infectivity were analyzed. These five neutralizing mon oclonal antibodies were generated to native SIVmac251 envelope glycopr otein expressed by a vaccinia virus recombinant vector. All five recog nize conformational or discontinuous epitopes and require native antig en for optimal recognition. These monoclonal antibodies also recognize SIVmac239 gp120, but they do not recognize gp120 of two natural varia nts of SIVmac239, 1-12 and 8-22, which evolved during the course of pe rsistent infection in vivo (D. P. W. Burns and R. C. Desrosiers, J. Vi rol. 65:1843-1854, 1991). Recombinant viruses which were constructed b y exchanging variable regions between SIVmac239 and variant 1-12 were used to define domains important for recognition. Radioimmunoprecipita tion analysis demonstrated that sequence changes in variable regions 4 and 5 (V4/V5) were primarily responsible for the loss of recognition of the 1-12 variant. Site-specific mutants were used to define precise changes that eliminate recognition by these neutralizing antibodies. Changing N-409 to D, deletion of KPKE, and deletion of KEQH in V4 each resulted in loss of recognition by all five monoclonal antibodies. SI Vs with these natural sequence changes are still replication competent and viable. Changing A-417 to T or A/N-417/418 to TK in V4 or Q-477 t o K in V5 did not alter recognition detectably. These results define s pecific, naturally occurring sequence changes in V4 of SIVmac that res ult in loss of recognition by one class of SIVmac neutralizing antibod ies.