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First-ever video reveals how HIV spreads between immune cells
Editor’s note:
Reporters can request access to videos showing the cell-to-cell transfer
of HIV by contacting SciPak at scipak@aaas.org or (202) 326-6440.
CONTACTS:
Karen Finney, UC Davis Health System
(916) 734-9064, karen.finney@ucdmc.ucdavis.edu
Tod Stoltz, UC Davis Center for Biophotonics Science and Technology
(916) 734-8447, tod.stoltz@cbst.ucdavis.edu
First-ever video reveals how HIV spreads between immune cells
Cell-to-cell transmission
could explain why experimental vaccines have yet to work
(SACRAMENTO, Calif.)
— For the first time, scientists at UC Davis and Mount Sinai School
of Medicine have captured video footage showing the transfer of the
human immunodeficiency virus (HIV) from an infected T-cell to an uninfected
one through an adhesive structure called a virological synapse. The
researchers hope their breakthrough findings, which appear in the March
27 issue of Science, will lead to a new era in HIV treatment
and revive hope of developing a vaccine to halt the virus that leads
to AIDS.
“Our findings may explain
why attempts to develop an HIV vaccine have so far been unsuccessful,”
said Thomas Huser, one of the study’s authors and chief scientist
at the UC Davis Center for Biophotonics Science and Technology (CBST),
where the video images were produced using advanced, live-cell video
imaging microscopy.
While previous efforts to create
an HIV vaccine have focused on priming the immune system to recognize
and attack surface proteins of free-circulating virus, the current results
indicate that HIV avoids recognition by being directly transferred between
cells.
“We should be developing
vaccines that help the immune system recognize proteins involved in
virological synapse formation and antiviral drugs that target the factors
required for synapse formation,” explained Huser, who is also an associate
professor in the UC Davis Department of Internal Medicine.
For decades, scientists believed
that HIV mainly spreads in the body through free-circulating particles
that attach to a cell, take over its replication machinery and make
multiple copies of themselves. Once in the bloodstream, the new particles
attach to target cells and continue the process.
In 2004, scientists discovered
that cell-to-cell transfer of HIV also occurred via virological synapses.
This was considered to be an effective method of transferring the infection,
but the reasons were unclear. The current study, however, reveals that
the synapse is providing the essential structure by which viral proteins
are gathered and relocated to uninfected cells.
“Direct T-cell to T-cell
transfer through a virological synapse is a highly efficient avenue
of HIV infection, and it could be the predominant mode of dissemination,”
said study senior author Benjamin Chen, assistant professor of medicine
and infectious diseases at the Mount Sinai School of Medicine.
Chen made the study possible
when he created a molecular clone of infectious HIV by inserting into
its genetic code a gene that codes for the green fluorescent protein
(GFP), a molecule originally isolated from a species of jellyfish. The
protein glows when exposed to blue light, making it visible on digital
video.
Chen, however, required the
expertise of UC Davis researchers to record the behavior of live cells.
Using the video microscopy developed at CBST, the researchers filmed
interactions between cells infected with GFP-labeled HIV-infected T
cells and uninfected ones, generating 19 hours of video footage.
In the videos, the researchers
observed an infected cell coming into contact with a healthy one. Huser
said that the two cells appear to struggle as a virological synapse
is formed at the point where they connect, and, within minutes, fluorescent
viral particles in the infected cell move toward the synapse and into
the healthy cell.
According to Huser, the technology
developed at CBST and the unique infrastructure available at the Oak
Park Research Building on the Sacramento campus of UC Davis made the
current study possible.
“We were able to determine
the physical parameters of HIV transfer because of our ability to observe
these interactions in real time and in three dimensions,” Huser said.
In creating a key technology
used in this study, Huser and his colleagues modified a commercially
available spinning disk confocal microscope so that it could be used
to image live infected cells. The technology allowed the capture of
30 images per second from various angles and at various depths of field.
Computer programs then merged the images, creating a 3-D movie.
“CBST’s interdisciplinary
team was key to the successful collaboration with Mount Sinai,” Huser
said. “Few facilities have both virologists with experience handling
live HIV samples and experts in high-speed, high-resolution imaging.”
The Mount Sinai-UC Davis team
is now planning to find out as much as they can about how HIV transfer
through virological synapses works. For example, the team will be working
to identify the exact process involved in the movement of viral particles,
which they believe involves the scaffolding of the cell – or its cytoskeleton.
New super-resolution microscopy at CBST will make that possible.
They will also be working out
the details of what happens to viral particles once they are transferred
into a newly infected cell.
“We saw that particles are
released into compartments,” Huser said. “We will be looking carefully
at how the virus particles are freed from these compartments, since
it could be another mechanism to target with new treatments.”
The overall goal for Huser,
Chen and their colleagues is to fully understand the process of HIV
transfer so scientists can use this knowledge in the fight against AIDS.
“The more we know about this
mode of transfer, the better chance we have of figuring out how to block
it and the spread of HIV and AIDS,” Huser said.
In addition to Chen and Huser,
study authors were Wolfgang Hübner, Ping Chen, Benjamin Dale and Ronald
Gordon of the Mount Sinai School of Medicine; and Gregory McNerney,
Frank Y. S. Chuang, Xiao-Dong Li and David Asmuth
of UC Davis. The study was funded by the National Institutes of Health,
Burroughs Wellcome, Hirschl Weill-Caulier, the National Science Foundation
through the Center for Biophotonics Science and Technology, Mount Sinai
School of Medicine and UC Davis.
About the UC Davis Center for Biophotonics Science and Technology:
The National Science Foundation
commissioned the UC Davis Center for Biophotonics Science and Technology
in 2002 with a mission to harness the power of light to solve major
challenges in the life sciences and medicine. CBST research teams are
world-renowned for their ability to image, analyze and manipulate cellular
processes to speed progress in biomedical research and development.
From its headquarters on the Sacramento campus of UC Davis, CBST coordinates
activities with a core group of eight university campuses, a national
laboratory, industrial partners and other research centers. For more
information, visit www.cbst.ucdavis.edu.
About the UC Davis Health System Department of Internal Medicine:
The UC Davis Department of Internal Medicine is one of the country’s most productive and dynamic centers of academic medicine as well as the largest clinical department in the UC Davis Health System. The team provides comprehensive patient services and cutting-edge research in a variety of specialties, including infectious and immunologic diseases, cardiovascular medicine, endocrinology and critical care. The department’s physicians and staff are dedicated to the compassionate practice of medicine — a continuum of care that extends from preventive medicine to acute care to palliative care. For more information, visit www.ucdmc.ucdavis.edu/internalmedicine.
JOURNAL ARTICLE: Quantitative 3D Video Microscopy of HIV Transfer Across T Cell Virological Synapses