Exploring Viral Interference Using Peptides: Molecular Determinants of HIV-1 Inhibition by a Peptide Derived from Human Pegivirus-1 Envelope Protein E2

A Case of Persistent Human Pegivirus Infection in Two Separate Pregnancies of a Woman

Human pegivirus (HPgV) is best known for persistent, presumably non-pathogenic, infection and a propensity to co-infect with human immunodeficiency virus or hepatitis C virus. However, unique attributes, such as the increased risk of malignancy or immune modulation, have been recently recognized for HPgV. We have identified a unique case of a woman with high levels HPgV infection in two pregnancies, which occurred 4 years apart and without evidence of human immunodeficiency virus or hepatitis C virus infection. The second pregnancy was complicated by congenital heart disease. A high level of HPgV infection was detected in the maternal blood from different trimesters by RT-PCR and identified as HPgV type 1 genotype 2 in both pregnancies. In the second pregnancy, the decidua and intervillous tissue of the placenta were positive for HPgV by PCR but not the chorion or cord blood (from both pregnancies), suggesting no vertical transmission despite high levels of viremia. The HPgV genome sequence was remarkably conserved over the 4 years. Using VirScan, sera antibodies for HPgV were detected in the first trimester of both pregnancies. We observed the same anti-HPgV antibodies against the non-structural NS5 protein in both pregnancies, suggesting a similar non-E2 protein humoral immune response over time. To the best of our knowledge, this is the first report of persistent HPgV infection involving placental tissues with no clear indication of vertical transmission. Our results reveal a more elaborate viral-host interaction than previously reported, expand our knowledge about tropism, and opens avenues for exploring the replication sites of this virus.

Human Pegivirus Type 1: A Common Human Virus That Is Beneficial in Immune-Mediated Disease?

Two groups identified a novel human flavivirus in the mid-1990s. One group named the virus hepatitis G virus (HGV) and the other named it GB Virus type C (GBV-C). Sequence analyses found these two isolates to be the same virus, and subsequent studies found that the virus does not cause hepatitis despite sharing genome organization with hepatitis C virus. Although HGV/GBV-C infection is common and may cause persistent infection in humans, the virus does not appear to directly cause any other known disease state. Thus, the virus was renamed “human pegivirus 1” (HPgV-1) for “persistent G” virus. HPgV-1 is found primarily in lymphocytes and not hepatocytes, and several studies found HPgV-1 infection associated with prolonged survival in people living with HIV. Co-infection of human lymphocytes with HPgV-1 and HIV inhibits HIV replication. Although three viral proteins directly inhibit HIV replication in vitro, the major effects of HPgV-1 leading to reduced HIV-related mortality appear to result from a global reduction in immune activation. HPgV-1 specifically interferes with T cell receptor signaling (TCR) by reducing proximal activation of the lymphocyte specific Src kinase LCK. Although TCR signaling is reduced, T cell activation is not abolished and with sufficient stimulus, T cell functions are enabled. Consequently, HPgV-1 is not associated with immune suppression. The HPgV-1 immunomodulatory effects are associated with beneficial outcomes in other diseases including Ebola virus infection and possibly graft-versus-host-disease following stem cell transplantation. Better understanding of HPgV-1 immune escape and mechanisms of inflammation may identify novel therapies for immune-based diseases.

Clinical and molecular aspects of human pegiviruses in the interaction host and infectious agent

Background

Human pegivirus 1 (HPgV-1) is a Positive-sense single-stranded RNA (+ ssRNA) virus, discovered in 1995 as a Flaviviridae member, and the closest human virus linked to HCV. In comparison to HCV, HPgV-1 seems to be lymphotropic and connected to the viral group that infects T and B lymphocytes. HPgV-1 infection is not persuasively correlated to any known human disease; nevertheless, multiple studies have reported a connection between chronic HPgV-1 infection and improved survival in HPgV-1/HIV co-infected patients with a delayed and favorable impact on HIV infection development. While the process has not been thoroughly clarified, different mechanisms for these observations have been proposed. HPgV-1 is categorized into seven genotypes and various subtypes. Infection with HPgV-1 is relatively common globally. It can be transferred parenterally, sexually, and through vertical ways, and thereby its co-infection with HIV and HCV is common. In most cases, the clearance of HPgV-1 from the body can be achieved by developing E2 antibodies after infection.

Main body

In this review, we thoroughly discuss the current knowledge and recent advances in understanding distinct epidemiological, molecular, and clinical aspects of HPgV-1.

Conclusion

Due to the unique characteristics of the HPgV-1, so advanced research on HPgV-1, particularly in light of HIV co-infection and other diseases, should be conducted to explore the essential mechanisms of HIV clearance and other viruses and thereby suggest novel strategies for viral therapy in the future.

Exploring Viral Interference Using Peptides: Molecular Determinants of HIV-1 Inhibition by a Peptide Derived from Human Pegivirus-1 Envelope Protein E2

Co-infection with the human pegivirus 1 (HPgV-1) often has a beneficial effect on disease progression in HIV-1-infected individuals. Several HPgV-1 proteins and peptides, including a 20-mer peptide (P6-2) derived from the N-terminal region of the HPgV-1 surface protein E2, have been associated with this phenomenon, which is referred to as viral interference. We identified the cysteine residues, the hydrophobic core tetrapeptide, as well as the C-terminal negative charge as key factors for the HIV-1 inhibitory activity of P6-2. Analysis of mutations in P6-2-resistant HIV-1 indicated a binding site for the peptide in the HIV-1 envelope glycoprotein gp120. In fact, P6-2 was shown to bind to soluble gp120, as well as to a peptide presenting the gp120 V3 loop. Furthermore, the HIV-1 inhibitory activity of P6-2 could be revoked by the V3 loop peptide, thus indicating a molecular mechanism that involves interaction of P6-2 with the gp120 V3 loop.