Biosafety in the laboratory - VIB

Animal and human cells
Animal and human cells cannot spread to the environment just like that. In addition, noncontaminated
cells are unable to spread genetic material to the environment by accident.
Animal and human cells cannot survive in non-sterile surroundings. Cells that are specially
designed to survive in non-sterile surroundings, such as fish or frog eggs, are an exception
to this rule. As regards non-contaminated cells, the measures that are taken to prevent the
cell culture from being contaminated are sufficient to prevent the cells from being spread
to the environment. Genetic material of animal or human origin can only be spread to the
environment when the cells involved are infected by biological agents, such as viruses, that
are able to mobilize their genetic material. From a biosafety point of view, the question
whether or not cells are infected by biological agents is very important. Any viruses present
may represent a danger to the researcher or to the environment, and any safety
measures should take account of this.
‘Contaminated’ animal or human cells
With regard to activities involving the use of animal or human cells, a distinction
can be made between primary cells and established cell cultures.
Primary cell cultures are created by growing cells directly from a biopsy. It
is often not possible to determine beforehand whether or not these cells
are contaminated by an infectious agent, such as a virus. For this reason,
primary cell cultures should always be handled with care. Established cell
lines are cultures that have been growing for longer periods of time and
which are immortalised, so that they keep dividing infinitely. In most cases
it is known whether they are free of contaminating biological agents. The
immortalisation of such cells may have been achieved in different ways:
•spontaneously (as in NIH-3T3 cells)
• as a result of a natural viral infection (for instance HELA cells in which a
few HPV virus genes, which cause immortalisation, are present)
• or by deliberate transfection of a factor that causes immortalisation.
When using virally immortalised cells in combination with vectors containing
viral sequences, one should always check whether or not viral particles
might be formed. If so, the cell line should be considered to belong to the
same risk class as the virus concerned.
Viruses
A distinction can be made between wild type viruses and viral vectors (constructions derived
from viruses). The use of viruses or viral vectors always implies the use of host cells.
Without host cells no virus can be replicated. In practice, there are three types of activity:
(1) the growing of cells to produce viral particles, (2) the handling of viral particle-containing
supernatants (for quality controls, etc.), and (3) the transduction of a cell line, test
animal or plant. Especially supernatants may contain very high levels of viral particles.
These supernatants should be handled carefully. Once the cell, animal or plant has been
infected, the danger depends on the virus’ or viral particle’s ability to replicate. In some
The spread of organisms in the laboratory 17