Characterization of HIV-1 gp120.

Cecilia GRAZIOSI, Elisa DE CRIGNIS

The goal of developing an effective vaccine strategy against AIDS remains unattained, due to HIV's enormous sequence diversity. With more than 33 million people currently infected with HIV, a full understanding of the mechanisms underlying HIV variability represents a major milestone in HIV research.

In this perspective, we have investigated sequence variation in hypervariable regions V3 and V4 of HIV-1 gp120. Our data show that V4 derived from both plasma RNA and proviral DNA is highly heterogeneous within a single patient, due to insertion/deletions (indels) of various sizes. Indels affect the number and distribution of potential N-glycosylation (PNG) sites, resulting in the coexistence, within the same patient, of V4 subsets each characterized by different PNG site patterns. Based on these data, we have proposed that V4 exists within the same host as a swarm of molecules with varying glycan shields, thus enabling the virus to constantly replenish the viral load with new Env variants, as existing variants are neutralized by the host immune response.

One of the most direct consequences of this model is that no matter how much virus is cleared, the mechanism responsible for the generation of these mutations will keep running, producing “new” virus at a faster rate than the immune system can neutralize, as predicted by the model of the glycan shield.

Analysis of the nucleotide sequence of V4 in our cohort of patients indicates that indels are associated to the presence of palindromic sequences, short repeats and region-specific duplications spanning up to 15 base pairs, suggesting that they may be the product of strand-slippage misalignment mechanism. The finding of elements of misalignment in association with indels in V4 indicates that the occurrence of these mutations is not random but is directed by the presence and distribution of elements of misalignment in the HIV genome. Further studies will be necessary to ascertain whether they occur in HIV-1 genomic RNA due to RT errors, or in HIV proviral DNA due to strand-slippage of the host-cell DNA polymerases.

Project 1:

Characterization of variable regions (V1-V5) of gp120 in plasma RNA and proviral DNA of patients with early HIV-1 infection

Elisa DE CRIGNIS

Analysis of V3 and V4 has shown marked divergence between these two regions in both plasma RNA and proviral DNA derived from the same individual, with highly polymorphic V4 associated to fairly constant V3. We are now investigating the behavior of all the variable regions of gp120 (V1 through V5) to see whether the patterns of sequence diversity identified in V4 can also be recognized in other variable regions of gp120 (i.e., V1/v2 and V5).

 
Project 2:

Characterization of variable regions (V1-V5) of Env glycoprotein gp105 derived from plasma RNA and proviral DNA of patients infected with HIV2

Elisa DE CRIGNIS

HIV-2 represents a significant minority of all HIV infections in some countries, such as Guinea-Bissau and Portugal. Given the devastating pandemic nature of HIV-1 infection and the restricted endemicity of HIV-2, it is understandable that the majority of research studies have fallen on HIV-1 and not HIV-2. However, valuable insights into HIV-1 immunopathogenesis can be gained by investigating differences between these two viruses, such as reduced pathogenicity of HIV-2 relative to HIV-1 and enhanced immune control of HIV-2 infection. We are in the process of sequencing the Env glycoprotein gp105 of HIV-2 in both plasma RNA and proviral DNA. Our goal is to compare the Env sequences in both HIV-1 and HIV-2, to see whether differences exist in patterns of potential N-glycosylation, distribution and frequency of indels and of elements of misalignment, such as those described in V4 of HIV-1 gp120.

Dernière modification le 29.06.2010 - Impressum - Informations juridiques