View All Abstracts for Session 24
120 Structural Features of HIV Envelope Defined by Antibody Escape Mutant Analysis
S. D’Costa*1, K. S. Slobod1, R. G. Webster1, S. White1, and J. Hurwitz1,2
1St Jude Children’s Res. Hosp., Memphis, TN, USA and 2Univ. of Tennessee, Memphis, USA
Background: We characterized antibody (Ab) binding determinants of envelope by generating and analyzing neutralizing Ab (nAb) escape mutants (EM). Results, when analyzed in conjunction with crystallographic data, help describe the structure of intact envelope-core and variable loops together. Understanding this association is important in designing envelope-based vaccines.
Methods: Ab EM from a IIIB founder virus were generated by incubating virus with MT2 cells in the presence of monoclonal nAbs (902 or NM-01) specific for the V3 sequence of HIV (IIIB). Recognition of virus envelope by the mAb was determined by flow cytometric detection of Ab bound to infected MT2 cells. To identify mutations responsible for immune escape, DNA from founder and EM virus was harvested, and the full gp120 sequence of each was cloned, sequenced, and compared.
Results: EM were isolated from virus grown in the presence of nAb, and, in contrast to MT2 cells infected with founder virus, MT2 cells infected with EM failed to bind either V3-specific mAb. Most EM harbored amino acid changes in the V3 region targeted by the nAb. In contrast, 1 variant was identified that differed from the founder virus not in the V3 region, but rather in the C2 region: alanine to valine at position 275 and glutamine to threonine at position 290.
Conclusions: Identification of mutations in C2 that mediate escape from V3-specific nAb indicates an interaction between the C2 and V3 regions of envelope. To explain this association, we propose that the V3 loop extends across the CD4 binding face of gp120 to associate with C2 residues. This association suggests that highly variable loops may provide an important viral defense by shielding vulnerable, more conserved core residues from immune surveillance. Results discourage the design of vaccines based on truncated cores and support vaccines capable of eliciting responses that can cope with highly variable loops.
Contact Author about this Abstract
