# HIV-1 and HIV-2 interaction results in reduced cell infectivity and viral replication in vitro

## TL;DR

This study shows that when HIV-1 and HIV-2 infect cells together, HIV-1 infectivity and replication are reduced in laboratory experiments.

## Contribution

The study experimentally demonstrates that HIV-2 inhibits HIV-1 infectivity and replication in vitro across multiple subtypes.

## Key findings

- Dual infection with HIV-2 significantly reduced HIV-1 infectivity and replication in cell culture.
- HIV-1 transcription and splicing were reduced in the presence of HIV-2, leading to lower viral loads.
- Subtype-specific variations were observed, but overall infectivity was consistently lower in dual infections.

## Abstract

During dual infection, HIV-1 and HIV-2 may infect the same cell, either simultaneously or sequentially. When these closely related lentiviruses co-infect, HIV-2 has been found to inhibit HIV-1 replication in vitro. In-patient infection data suggests that dual infection attenuates disease progression. Mechanisms underlying this inhibition have not been fully elucidated. Here, we assessed HIV-1 infectivity in presence or absence of HIV-2 in cell culture.

HIV-1 subtypes A, B, C, and CRF02_AG were used to infect TZM-bl reporter cells as single infections or as dual infections with HIV-2. Infectious titer concentrations were determined by cytopathic effect-based method (TCID50) and P24 ELISA was used to determine p24 concentration in supernatant. Infectivity was determined using luminescence assay, while qPCR was used to determine expression of cell-associated unspliced and multiply spliced HIV-1 RNA. HIV-1 cell free viral RNA (vRNA) levels were quantified in cell supernatants.

Dual infections (simultaneous and sequential) resulted in reduced HIV-1 infectivity and replication relative to single infections. The reduction in infectivity varied among HIV-1 subtypes. Additionally, evaluation of expression levels of unspliced (us) and multiply spliced (ms) HIV-1 RNAs revealed lower expression of these RNA species in simultaneous dual infections for all the four subtypes tested. The same trend was observed for sequential dual infection with the exception of subtype B, which showed a slight increase in levels of usRNA. In both simultaneous and sequential dual infections, expression of msRNA was lower relative to HIV-1 mono-infection. Again, subtype B maintained the same trend as observed in usRNA during sequential dual infection. Despite the observed subtype specific variations, lower HIV-1 infectivity in dual infections coincided with reduced HIV-1 viral loads.

In summary, this study demonstrates a significant reduction in HIV-1 infectivity in the presence of HIV-2. Reduced infectivity was characterized by lower viral loads and coincided with reduced HIV-1 transcription and splicing. These findings pave way for future mechanistic studies to understand the drivers of reduced infectivity in dual infection.

The online version contains supplementary material available at 10.1186/s12985-026-03077-6.