RESTRICTED ANTIGENIC VARIABILITY OF THE EPITOPE RECOGNIZED BY THE NEUTRALIZING GP41 ANT BODY 2F5

Objective: To investigate whether variations of the conserved gp41 ami no-acid sequence ELDKWA affect its binding or neutralization by monocl onal antibody (MAb) 2F5. Design and methods: Neutralization assays wer e performed with primary isolates from different HIV-1 subtypes and th e sequences corresponding to the 2F5 epitope region were analysed. Stu dies of MAb 2F5 peptide reactivity were performed by spot analysis, us ing peptides immobilized on cellulose. The frequency of emergence of n eutralization-resistant virus variants was determined by immune select ion experiments in the presence of MAb 2F5. Results: Primary isolates from clades A, B and E were neutralized by MAb 2F5. Neutralization sen sitivity correlated with the presence of the LDKW motif. A K-to-N chan ge in the core sequence was identified in a neutralization-resistant p atient isolate. Neutralization resistant virus variants that were sele cted in the presence of MAb 2F5 were found to contain D-to-N, D-to-E, or K-to-N changes within the LDKW sequence. Neither in natural isolate s nor in variants obtained under immune selection conditions in the la boratory were changes in the L and W positions observed. Studies of MA b 2F5 binding to variations of the ELDKWA peptide confirmed that the c hanges at the first and last positions did not significantly reduce bi nding capacity, whereas amino-acid changes from D to N, D to E, and K to N almost completely abrogated binding of MAb 2F5. Conclusion: Seque nce analysis of a variety of primary isolates suggests that the major determinant of MAb 2F5 binding corresponds to the amino-acid sequence LDKW. Naturally occurring and in vitro selected neutralization-resista nt viruses contained changes in the D and K positions of the ELDKWA mo tif.