A unique group of HIV-1-infected individuals remain clinically healthy and do not experience a decline in CD4+ T-cell counts. A recent report has shown that a point mutation, involving the substitution from arginine to glutamine at position 77 in the Vpr gene, affects viral pathogenesis and is involved in the mechanism of long-term non-progression of HIV-1 infection. Similarly to our results, they found that 80% of LTNP had the mutation, whereas only 33% of progressors presented the R77Q .
On the contrary another study did not confirm a correlation between the frequency of the R77Q substitution and different measures of disease intensity .
We analysed the cohort of LTNP enrolled in the Resistant Host Prospective Study (rHoPeS) in Italy and our data support the relevance of the point mutation in preventing disease progression as 86.7% of LTNP bear the substitution compared with only 42.1% of progressors. Both our analysis and the study by Lum et al were performed on HIV-RNA, while the study failing to detect the relevance of the mutation in altering disease progression was done only on HIV-DNA from PBMC.
It is possible that the different results of the studies are related to the different technical approach. HIV-RNA reflects the viral strain currently proliferating and affecting CD4+ T-cell depletion, whereas integrated DNA is not the main replicating strain and represents the archived virus.
As demonstrated for antiretroviral therapy-induced mutations in the Pol gene, HIV mutations in PBMC may persist for a long time, possibly lifelong and re-emerge in the absence of selective pressure [40,41].
Different viral quasispecies variations in the Vpr gene may exist within a single person and it is possible that an epitope-specific immune response is able to maintain the replicating virus in a less cytopathic asset blocking the replication of more aggressive strains that may be archived in PBMC. Moreover other studies have related the C-terminus region of Vpr to disease progression [42,43].
We also analysed the frequency of the Vpr mutation in a peculiar group of patients that, despite dual NRTI therapy, are able to control HIV-1 replication and maintain a stable CD4+ T-cell count for a long period of time and compared them to patients failing antiretroviral therapy and showing a progressive depletion of CD4+ T cells (MEP).
STP patients display a high percentage of R77Q mutation similar to LTNP and significantly higher than progressors and MEP.
The C-terminal region of Vpr induces apoptosis by binding to the adenine nucleotide translocator (ANT) component of the mitochondrial permeability transition pore complex . Mitochondrial membrane permeabilization (MMP) is a key event of apoptotic cell death [45–51]. The MMP-inducing activity of Vpr resides in its COOH-terminal moiety (Vpr 52-96), within an α-helical motif of 12 amino acids (Vpr 71–82) containing several critical arginine (R) residues (R73, R77, R80) strongly conserved among different pathogenic HIV-1 isolates [32–34]. These residues participate in the physical interaction with the first loop of ANT exposed to the mitochondrial intermembrane space. This complex forms a composite ion channel, which dissipates the ΔΨm and thus favors MMP and subsequent apoptosis . The interaction of Vpr with ANT is abrogated by the R77Q mutation and such mutation impairs Vpr capability to induce apoptosis of T lymphocytes .
Among patients in sub-optimal therapy not only patients with viraemia < 50 copies/ml but also patients with persistent low levels of viral replication do not experience CD4+ T-cell depletion confirming a potential role for the Vpr R77Q mutation in impeding CD4+ T-cell apoptosis.
It is noteworthy that the large majority of patients with dual NRTI therapy also present the mutation M184V that has been associated to reduction of viral fitness [52–54]. Thus the co-existence with the R77Q mutation in the Vpr gene might further contribute to allow a long-term control of HIV-1 infection in STP. This is not the case in MEP, further suggesting the potential contribution of a specific immune response to Vpr.
A recent report observed a significantly higher prevalence of the R77Q mutation in subtype A than in subtype B viruses (84 versus 32%) ; our data based mainly on subtype B in all the different groups of patients confirm a similar frequency in patients with progressive disease (42.1%), but a much higher frequency in LTNP (86.7%).
The standard of care of HIV-1 treatment consists of continuous HAART, the criteria for initiation of therapy are not univocal, therefore the identification of a laboratory parameter such as the R77Q Vpr point mutation able to predict disease progression might help addressing such issues in conjunction with CD4+ T-cell count and HIV-RNA.
Clinicians are currently facing the problem of drug toxicity, lack of adherence to therapy and the requests of patients to interrupt therapy. Therefore, treatment interruptions are entering clinical practice, but clear criteria for interruption, monitoring and re-introduction of therapy are not available. Treatment interruptions expose patients to the risk of brisk CD4+ T-cell decline and disease progression, but allow reduction in drug toxicities and preservation of future treatment options. Monitoring the R77Q Vpr mutation might constitute a parameter to stop therapy and decide re-initiation of treatment; clinical trials to evaluate the clinical predictive role of such mutation are to be considered.
We are grateful to Bianca Ghisi for excellent editorial assistance, to all the patients participating in the study and to the staff at the Institute of Infectious Diseases and Tropical Medicine, ‘L. Sacco’ Hospital, who cared for the patients.
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The Resistant Host Prospective Study (rHoPeS) participants are: F. Adorni, B. Allegranza, G.P. Cadeo, G.P. Carosi, M.C. Colombo, E. Concia, G. Cristini, G. Di Perri, M. Galli, E. Gianelli, L. Meroni, G. Migliorino, G. Monolo, S. Pasquinucci, E. Raise, C. Riva, S. Santambrogio, M. Sciandra, A. Sinicco, M.G. Suardi, F. Suter, R. Tambini, M. Violin, A. Valenza.