Host Restriction of Immune Escape HIV-1 Mutants

Project Summary
Neither a vaccine nor a scalable cure is available to end the HIV/AIDS pandemic. A feasible “functional
cure” approach entails durable antiretroviral therapy-free control of HIV, a characteristic exhibited by HIV elite
controllers (ECs). In certain ECs carrying human leukocyte antigen B27, potent CD8+ cytotoxic T-lymphocyte
(CTL) response targeting the HIV-1 capsid protein (CA) epitope KK-10 establishes a functional cure-like
status. The selection of CTL escape CA mutation R264K significantly diminishes virus replication, which
intriguingly is contingent on two critical CA-binding host dependency factors—cyclophilin A (CypA) and
cleavage and polyadenylation specificity factor subunit 6 (CPSF6). Eventually, selection of compensatory CA
mutation S173A restores R264K-harboring virus replication to WT levels in these ECs. The underlying virus-
host cell dynamics remains largely undetermined. Our long-term goal is to understand the molecular
mechanisms that impose immune control of HIV-1 and that enable HIV-1’s counter response and immune
escape. Our previous work demonstrated that R264K-linked infectivity defect results from CypA-dependent
impairment of viral DNA integration but is restored by the presence of CA mutation S173A or the absence of
CypA.
The objective of this proposal is to determine the mechanistic basis of the novel host dependency
factor-dictated R264K-imposed virus integration block and the S173A-associated restoration of viral
integration. Our central hypothesis is that the R264K-harboring virus integration impairment is imposed by the
human anti-HIV restriction protein TRIM5αhu in a CypA- or CPSF6-dependent manner and that the
compensatory CA mutation S173A restores viral integration by altering R264K capsid conformation that
renders it inaccessible to TRIM5αhu restriction. The rationale is based on our published data demonstrating
direct functional role for CA, CypA, and CPSF6 in HIV-1 integration as well as published findings by other
research groups. Our work is innovative as it probes a host dependency factor-guided HIV restriction by
nuclear-localized TRIM5αhu.
In the proposed project, we will study the effect of HIV-1 nuclear PIC-associated CypA or CPSF6 on
R264K-imposed impairment of viral integration (Aim 1), the proposed role of nuclear TRIM5αhu in R264K-
imposed virus integration block (Aim 2), and the predicted consequence of S173A-associated capsid core
conformational changes on TRIM5αhu restriction and the restoration of R264K-harboring virus integration (Aim
3). The proposed research is significant because of its potential to yield fundamental insights into novel
mechanisms of virus/host cell dynamics governing the replication outcomes of clinically significant immune
escape HIV-1 mutants and will broadly impact the field by supporting the development of innovative cure and
treatment strategies for controlling the HIV/AIDS pandemic.
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Grant Number: 1R56AI200599-01
NIH Institute/Center: NIH
Principal Investigator: Muthukumar Balasubramaniam