Evasion of cytotoxic T lymphocytes is a functional constraint maintaining HIV-1 Nef expression

Abstract

Nef expression is not required for HIV-1 replication and is highly targeted by CD8 + CTL, raising the question of why Nef expression is not lost in order to evade immunity in vivo. We explore whether MHC class I (MHC-I) down-regulation to evade CTL in general is a selective pressure maintaining Nef. HIV-1 with functional Nef (wild type, WT) is compared to virus containing a Nef point mutation (M20A) that selectively ablates MHC-I down-regulation. WT-infected cells are relatively resistant to cytolysis and less suppressed for viral replication by Gag-and RT-specific CTL compared to M20A. These viruses grow similarly in vitro in the absence of CTL, but the presence of Gag-or RTspecific CTL strongly favors WT overgrowth of M20A. Finally, while in vitro selection by Nef-specific CTL readily drives disruption of the nef reading frame, the addition of Gagor RT-specific CTL markedly limits such escape. These data indicate that MHC-I downregulation is an important function favoring Nef maintenance due to a net selective advantage in the setting of the general CTL response.

Novel Nipah Virus Immune-Antagonism Strategy Revealed by Experimental and Computational Study

“…However, the suppression of MHC-I upregulation suggests a potent deficiency in initiating the adaptive response. Suppression of antigen presentation by MHC-I is employed by multiple virus types to evade immune clearance, thereby promoting persistent infections (1,2,5,6,18,51,61). The identification of viral antigen in the brains of NiV encephalitis patients postmortem indicates the spread of the virus past the presumed respiratory route of entry (13,27).…”

HIV-1 Gag Cytotoxic T Lymphocyte Epitopes Vary in Presentation Kinetics Relative to HLA Class I Downregulation

“…It has been demonstrated that the early-killing phenomenon first described by Sacha et al (5) varies, depending on the virus inoculum, and that CTLs targeting different epitopes require different amounts of input virus to achieve early killing (28). Our earlier data obtained with a virus suppression assay have suggested that most Gag-specific CTLs are susceptible to Nef (10,11,21). In these assays, a low initial inoculum of virus is allowed to spread, and thus the dose of virus for each infected cell is unclear in comparison to controlled single-round infections such as those used by Sacha et al (5).…”

“…Additionally, a version of HIV-1 Nef containing the Gag SL9 epitope was created through substitution mutations between residues 40 and 55 of Nef. Epitope mutations known to disrupt CTL recognition were generated in the p83-2.1 Gag reading frame by site-directed mutagenesis (Agilent Technologies), and the M20A mutation, which ablates HLA-I downregulation by Nef (20,21), also was generated by site-directed mutagenesis in plasmid p83-10. (Table 2) containing the murine CD24 reporter gene in the vpr locus, followed by flow cytometric analysis as previously described (18,21).…”

“…Epitope mutations known to disrupt CTL recognition were generated in the p83-2.1 Gag reading frame by site-directed mutagenesis (Agilent Technologies), and the M20A mutation, which ablates HLA-I downregulation by Nef (20,21), also was generated by site-directed mutagenesis in plasmid p83-10. (Table 2) containing the murine CD24 reporter gene in the vpr locus, followed by flow cytometric analysis as previously described (18,21). Briefly, the cells were costained with antimurine CD24 -fluorescein isothiocyanate and anti-HLA-A*02-phycoerythrin antibodies (BD Biosciences) 5 days after infection.…”

HIV induced suppression of host immunity: relevance to <i>Mycobacterium tuberculosis</i> infections

“…Though, direct effects of HIV on CD8+ population and its function(s) are also reported. HIV is known to manipulate the expression of MHC class I using Nef expression and in turn evade the CTL response [72,73]. Nef is also known to downregulate the expression of CD80 and CD86 on infected cells, which leads to defective priming, activation, and further the function of CD8+ CTL cells [66].…”