Adaptation of Two Primary Human Immunodeficiency Virus Type 1 Isolates to Growth in Transformed T Cell Lines Correlates with Alterations in the Responses of Their Envelope Glycoproteins to Soluble CD4

Abstract

Two sCD4-resistant, primary viruses (P-08 and P-17) were compared with two sCD4-sensitive, T cell line-adapted variants (C-08 and C-17) for their biochemical responses to sCD4. At 37 degrees C, neither primary virus shed gp120 within 8 hr at sCD4 concentrations of up to 500 nM, whereas C-08 and C-17 lost gp120 within minutes of addition of 5-10 nM sCD4. At 4 degrees C, however, P-17 and C-17 shed gp120 at similar rates in response to the same sCD4 concentration. Irrespective of the temperature, gp120 dissociation from both P-17 and C-17 was inhibited by CD4 MAbs 6H10 and 5A8, the latter of which blocks events subsequent to sCD4 binding. Binding of sCD4 to P-17 was greater at 4 degrees C than at 37 degrees C, whereas the converse was found for C-17. Consistent with this, P-17 was neutralized much more potently by sCD4 at 4 degrees C than at 37 degrees C, whereas C-17 was slightly more sensitive to sCD4 at 37 degrees C than at 4 degrees C. Resistance to neutralization by sCD4 is probably determined by kinetic parameters. We suggest that the acquisition of sCD4 neutralization sensitivity and the above biochemical responses to sCD4 are coincidental to the process by which some primary viruses adapt to growth in transformed T cells. Sequence data indicate that there are a limited number of amino acid differences between the Env glycoproteins of the primary viruses and their T cell line-adapted counterparts; the significance of the individual changes is under investigation, but both pairs of viruses have amino acid substitutions in a region of gp41 thought to contact gp120.

Virus Isolates during Acute and Chronic Human Immunodeficiency Virus Type 1 Infection Show Distinct Patterns of Sensitivity to Entry Inhibitors

“…Primary HIV-1 isolates have proven to be relatively resistant to soluble CD4, probably due to the fact that these viruses have adapted to replicate in the presence of neutralizing antibodies to CD4BS, which are highly prevalent in patient sera (3,12,23,37,57,58,60,63,65,86). HIV-1 cultured in the absence of neutralizing antibodies in vitro rapidly adapts, and more-neutralization-sensitive variants emerge (6,56,57,70,100). This change in phenotype has been attributed to an alternate interaction with CD4, potentially generating a greater affinity of the envelope for CD4 while simultaneously exposing neutralization epitopes, particularly those associated with the CD4 binding site (70).…”

Phenotypic Correlates of HIV-1 Macrophage Tropism

“…Early observations revealed that tissue culture-adapted viruses, in the absence of antibody selection, result in the premature exposure of CD4-induced epitopes (88)(89)(90)(91), indicating that the Env protein for these viruses is in a more open conformation that exposes the coreceptor binding site. Furthermore, studies have shown that tissue culture-adapted viruses evolved to use low CD4 for entry (92,93) were more sensitive to sCD4 (94)(95)(96) and had greater sensitivity to antibody neutralization than typical primary isolates (58,89,92,97). Together, these observations raised the possibility that these phenotypes covary and are generated by the same mechanism.…”

A small molecule HIV-1 inhibitor that targets the HIV-1 envelope and inhibits CD4 receptor binding

“…Moreover, two of the selected substitutions, I595F and K655E, were situated at the gp41 region. It is interesting to note that the same I595 residue has been implicated in the development of sCD4 sensitivity (38). The reasons why these gp41 substitutions were selected by BMS-378806 and the impact these changes have on envelope conformation await further studies.…”