Abstract

Exosomes and Viruses: A Tale of Two Overlapping Worlds

Fatah Kashanchi, Professor, George Mason University

Extracellular vesicles (EVs) play a significant role in intercellular communication by serving as a carrier for the transfer of membrane and cytosolic proteins, lipids, and RNA between cells.  In recent years, using state of art technologies such as RNA seq, RPMA, and single cell omics, we have found that virally infected cells including HIV-1, HTLV-1, Rift Valley Fever, Zika, Ebola, and Coronavirus infected cells secret exosomes that contain biomarker of these infections in urine, saliva, CSF, and blood. We have been able to separate and characterize EVs from several different viruses including HIV-1.  These EVs are not infectious and have a different density than infectious virions using gradients.  They contain various viral RNAs including TAR (non-coding RNA), Nef, gp120/160 and Tat.  The origin of these EVs are infected cells, especially when treated with cART or Interferons.  They are present in patient samples tested (plasma and CSF, 33%-95%) to date (4 cohorts of 5-20 patients each). The EVs contribute to pro-inflammatory signals in the naïve recipient cells using TLR3 signaling.  Recently, we have asked about the timing difference between EV and virus release from infected cells using serum starvation experiments from cells followed by release. Results from supernatants of uninfected cells showed a peak of tetraspanin proteins (CD63, CD81, and CD9) at 6 hours and a gradual decrease of all EV associated proteins by 24 hours. However, the EV from HIV-1 infected cells showed all three tetraspanins present at 3 hours and expression gradually increased up to 24 hours. HIV-1 viral proteins (p24, gp120, Nef) expression was present at 6 hours and continued to increase and peaked at 24 hours.  HIV-1 supernatant 6- hour sample was found not to be infectious. However, infectious HIV-1 was successfully rescued from 24-hour sample.

Our data indicates that EV release may occur prior to viral release in infected cells, thereby implicating a potentially significant effect of EVs on uninfected recipient cells prior to subsequent viral infection.