Molecular Mechanism of HIV-1 Infection: Role of Viral and Host Determinants

by Sundaravaradan, Vasudha.

Most neonates and infants acquire HIV-1 infection as a result of mother-to-infant (vertical) transmission and are infected with the minor genotype with macrophage-tropic (R5) phenotype of the mother. Several studies suggest that infected infants have a higher viral load and develop AIDS more rapidly than infected adults, but the mechanisms of this differential HIV-1 infection are not known. The hypothesis of my dissertation is that viral determinants and differential cellular gene expression profiles influence differential HIV-1 replication and disease progression seen in neonates vs. adults. This work includes characterization of viral determinants, including reverse transcriptase (RT) and envelope gp120, and host determinants, including cellular transcription factors and cytokines that may be associated with differential HIV-1 replication in infants and adults. The characterization of HIV-1 RT gene from five mother-infant pairs following vertical transmission revealed a low degree of viral heterogeneity and a high conservation of intact open reading frames comprising functional domains and CTL epitopes. Biological characterization of HIV-1 subtype C (predominant subtype worldwide) envelope gp120 from infected patients from India was performed by constructing chimeras with HIV-1 subtype B that is prevalent in the United States. Infection of cell lines and primary cells with chimeric subtype C/B virus showed that the subtype C env gp120 from patients contributed to an increased rate of virus entry, which correlated with higher replication efficiencies and virus production in subtype C env chimeras compared with subtype B env chimeras ( in subtype B molecular clone) and subtype B primary isolates. Higher level of viremia with subtype C infection compared with subype B may be responsible 17 for its rapid disease progression and spread. More importantly, the mechanisms of HIV-1 replication in neonatal and adult cells was determined and found that differential HIV-1 replication in neonatal and adult cells is influenced at the level of HIV-1 gene expression. Evaluation of cellular gene expression profile of neonatal and adult mononuclear cells performed by microarray analysis identified several factors, including transcription factors, cytokines and matrix metalloproteinases that may be associated with increased HIV-1 gene expression and replication in neonates and infants. Taken together, these results provide new insights into the understanding of mecahnsims of HIV-1 vertical transmission, pathogenesis and disease progression in infected neonates and infants. 18 1. INTRODUCTION Claiming the lives of about 25 million people worldwide, acquired immune deficiency syndrome or AIDS is one of the biggest pandemics mankind has faced. The Centers for Disease Control identified this syndrome in 1981 among young homosexual men who died of infections that a functional immune system would normally eliminate with ease. This disease was characterized by drastic loss of CD4+ T- cells in these individuals accompanied by the presence of opportunistic infections and immune abnormalities normally associated with a defective immune system (5). Since then, human immunodeficiency virus (HIV) has been identified as the causative agent of