LIVE POLIO IRUS VACCINES

Application of Genetic Markers to Development and Control of Vaccine 61
its first human passage strains. These preliminary
data seem to indicate that the cold variant
of the W1-P strain retains its infectivity for the
human intestinal tract, as do other attenuated
Type 1 strains, and does not undergo marked
changes in its growth characteristics under different
temperatures after one passage through the
human intestinal tract. It must be emphasized
that these are very preliminary results, obtained
on a small number of individuals and subject to
possible revision when more extensive data are
obtained. Similar data are now being sought for
the Type 3 virus, where development of a new
and improved attenuated strain is much more
imperative than in the case of the two other
types of poliovirus.
Inquiry into the Nature of MS and Temperatare
Markers. Although genetic markers for
poliovirus and other viruses have been employed
in laboratory investigations for some time, the
nature of these markers seems to be somewhat
illusive. As shown in Table 13, the MS cell
monolayer infected with CHAT virus will yield
much smaller quantities of virus than parallel
infection of fresh monkey-kidney culture. However,
if, instead of intact virus, infectious nucleic
acid isolated from the CHAT strain is used as the
inoculum, the yield from MS cells will be greater
than from monkey-kidney cells and similar to
that obtained with either intact virus of the
virulent Mahoney strain or infectious nucleic
acid isolated from this strain. These results
seem to indicate that in the process of attenuation
the protein coat loses some of its ability to attach
itself to the receptors and penetrate the
cells of the established monkey-kidney line. In
contrast, the nucleic acid part of the attenuated
strains, which does not seem to need receptors to
penetrate the cells, infects the MS cells at the
same rate as a virulent intact virus. Thus results
obtained with the CHAT strain and the MS cells
are somewhat similar to those of Holland et al. 6
for cell systems which are resistant to poliovirus.
Obviously, the parallel cannot be drawn too
closely, since ultimately the attenuated poliovirus
can be propagated in the MS line, in contrast to
Log. 10
PFU /ml.
-8-
-6
-1637-
-400 C.
°
C.
/
/
/
/ /
-MA4H
B210
/
B207 .--- e
- - _- _ --- B2 -4
-4-
- -c
-YjW_, - -
------- -
l
2
I·
- i - I
I I
6 10 Hrs.
i
FIG. 1