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49   Cell Biology
     The Washington Post, Saturday, June 24, 1967

     I had an opportunity to hear an impromptu seminar by Dr. Hilary
Koprowski, director of the Wistar Institute of Philadelphia, when I
was in Pavia, Italy, recently.

     He recounted his work on the cryptic stages of the life of
certain viruses in cells of human or monkey origin.  This was first
reported in more preliminary form at scientific meetings in Atlantic
City, New Jersey.

     The virus that was the object of these studies is SV-40,
discovered to be endemic in certain wild monkeys after it was revealed
as a contaminant of polio vaccines.  SV-40 has many fascinating
properties, including its potentiality for inducing tumors when
injected into newborn hamsters.

     It is doubtful whether SV-40 plays an important role in human
disease.  However, it is an important experimental tool for
fundamental studies of the way in which other viruses might work.

     When cultured cells are freshly exposed to SV-40, many may be
killed, but others are "transformed" into new varieties of cells.  
These are recognized by altered shapes, by the presence of new
antigenic substances and above all by their malignancy when
inoculated into susceptible animals.

     Persistence of the infecting virus might be blamed for these
changes.  However, it has been possible to purify the transformed
cell lines and cultivate them for years (a thousand cell generations)
without any actual virus being any longer demonstrable.

     Dr. Koprowski applied the technique of somatic cell fusion to
this problem.  He promptly found that SV-40 virus reappeared in
every combination of transformed cells fused with sensitive ones.  It
should be stressed that no cell entering into the fusion showed virus.
The same result was obtained with combinations of monkey and human
cells, and by fusions of cells of the same species.

     This extraordinary result is analogous to previously established
findings on bacterial viruses.  The analogy helps to support the
orientation of future research, as well as some predictions that
relate to its human significance.  In both situations, the key to
further progress is the development of new techniques and understanding
of cell behavior.

     The essential insight is that viruses can enter the genetic
material of the cell and remain there in a cryptic form for an
indefinite number of generations.  Their presence is sometimes
revealed by secondary effects on the cell, which may include
malignant changes.  Many generations later, the virus may reappear
when some drastic change in cell chemistry occurs, as upon somatic
hybridization with an uninfected cell.  Related effects have been
shown upon reinfection with another virus.  The conditions of its
reappearance will be an important target for further research.

     Since fusion can occur between cells of different species,
the whole living world constitutes a potential reservoir of new
viruses, some of which may have been cryptic since pre-human times.

     The technique of cell fusion is now one of the most powerful
methods for studying the role of cryptic viruses in human cancer.
Perhaps even more important, in the long run, is the opportunity
to alter the genetic material by the calculated use of viruses
carefully studied for their specific effects.

     Pavia is one of the oldest scientific universities in the world.
Its ancient buildings now include a leading center of Italy's
scientific renascence in modern biology.
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