Infection risk small in
~ some DNA experiments

Studies by the National Institutes
of Health to assess the risk of infec-
tion from working with recombinant

. DNA find that risk very small.
Virologists Malcolm A. Martin,

Wallace P. Rowe, and associates at

ae

the National Institute of Allergy &
Infectious Diseases find that highly
infectious polyoma virus is not
transmitted to mice when the mice
are fed or injected bacteria infected

with polyoma DNA in recombinant
DNA molecules.

However, two of five mice that were
injected with purified recombinant
DNA having more than one copy 0!
the polyoma DNA became infectec
with the virus.

The scientists conclude that poly-
oma DNA contained in recombinant
DNA molecules is between 10 million
and 1 billion times less infectious than
free Pelyoma virus. When adminis-
tered by mouth or in live bacteria, it
was never observed to cause infection.
And free virus growth was not ob-
served in bacteria carrying the re-
combinant DNA molecules.

Rowe says these findings show “our
intuitive fears over the safety of these

‘experiments were greatly exagger-
ated.”

Rowe cautions that the experi-
ments so far have examined the safety
of only one host system—that of the
bacterium Escherichia coli K-12.

Similar experiments must be done |
with each host to establish its safety. |

But speaking only for experiments in
E. coli K-12, Rowe says, “I personally
believe that any recombinant DNA
research is safe except that involving
toxin genes, which should not be
transferred willy-nilly.” £. coli K-12

has been the host for nearly all re-
combinant DNA experiments per-
formed so far.

. owe and Martin’s experiments
use DNA from polyoma_virus—a
small, well-characterized DNA that
replicates readily in its natural host,
the mouse, but is not infectious in
humans. '

Using recombinant DNA tech-
niques, polyoma DNA was spliced
into DNA from either £. coli plas-
mids or bacteriophage lambda, a virus
that infects E. coli. Then the recom-
binant DNA was introduced into E.
coli, propagated there, and either the
infected bacteria fed to or injected
into mice, or the recombinant D

isolated fism the bacteria and in-
_ jected into mice.

~ Polyoma antibodies were never

‘ observed when mice or mouse cells in

culture were exposed to bacteria

_ carrying the recombinant molecules,
- the researchers say.

When the re-
combinant DNA molecules isolated
from bacteria were injected into mice,
the systems in which a single copy of

the polyoma DNA was contained in

‘the recombinant molecule also did
-not cause infection.

The only cases of infection that
occurred came when recombinant
DNA carrying double copies of the

polyoma segment was injected di-.
rectly into mice. Such double-copy
DNA is not likely to be produced in
recombinant DNA experiments, the
scientists say. When it is produced, it
frequently will revert to a single-copy
form in the bacteria as it propagates.
And, when part of the whole bacteri-
um, even this double-copy DNA is not |
infectious, according to Martin and

Rowe. Oo