Download General Information About Mammalian Virus Vectors

General Information
About Mammalian Virus Vectors
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All use of mammalian recombinant viral systems at UR must be approved by the IBC through the
registration process. The NIH Guidelines stipulate that Institutional Biosafety Committee approval be
obtained prior to the use of recombinant mammalian viral systems..
Overview of selected viral systems
General comment on containment:
Suggested biosafety containment levels are provided for each viral system. Note, however, that use of
a high-level containment facility may be required in some cases, depending on the specific properties
of the vector and/or insert. Special care should be given to the design, risk assessment and handling of
virus vectors containing genes that make growth-regulating products, products released into circulation
and products that may have a general effect on the host-immune system (See Section II of the NIH
Guidelines).
Gene Insert:
Depending on the gene expressed, containment may be increased from the initial assignment levels
described below- depending on the initial vector designation, the nature of the insert and other
experimental considerations. Please note that if the insert codes for a toxin, and oncogene, or is
suspected to be tumorigenic, then the biosafety assessment will most likely contain precautions of the
next higher biosafety level to the usual set of precautions.
BSL3 containment for the viral systems listed here would be a very rare occurrence, and would only
occur if the full IBC felt this was necessary to protect public and worker safety.
Adeno-associated virus
Lab: BSL1 (generally)
These are infectious human viruses with no known disease association. Some AAV types are common
in the general population, and these viruses have the ability to integrate into the host chromosome.
The NIH Guidelines (Appendix B) state that "adeno-associated viruses (AAV) all serotypes and
recombinant or synthetic recombinant AAV constructs, in which the transgene does not encode either
a potentially tumorigenic gene product or a toxin molecule and are produced in the absence of a
“helper virus" can in most cases be handled at biosafety level 1 (BL1). This level of containment may
be modified by other considerations.
Animal: ABSL1 (generally, for mice)
See above
General Information
About Mammalian Virus Vectors
Adenovirus
See Adenovirus Vector Safety Guidelines for additional information.
LAB: BSL2 (generally)
Adenoviruses are infectious human viruses, which often cause mild respiratory illness. Rare cases of
severe disease can occur, and its use as a genetic vector therefore requires the use of adequate
containment equipment and practices. Biosafety Level 2 (BL2) is appropriate for many constructs.
Particular care should be given to vectors containing genes that make products that may be similar to
products made by the deleted adenovirus genes.
Animal: ABSL1 (generally, for mice)
Mice are not a permissive host for human adenoviruses and do not shed virus. Thus, virus inoculation
should be done at BSL2, but animal housing and husbandry at ABSL1 is appropriate. Exceptions
would include mice engrafted with human cells, in which the adenovirus could replicate. Also, specific
inserts that might enhance virus replication, very high viral doses, or skin or mucosal surface contact
with the virus might drive a desire to house animals at ABSL2.
Herpes Simplex Virus
LAB: BLS2 (generally)
Herpes viruses include infectious human viruses such as herpes simplex virus type-1 (HSV-1), which
is the most commonly used vector system. HSV-1 is common in the general population, but can cause
encephalitis in rare cases; its utility as a vector system stems from its broad host cell range, ability to
transduce neurons, and its large insert capacity. Biosafety Level 2 (BL2) is appropriate for many
constructs.
Animal: ABSL1 (generally for mice, for helper-defective amplicon vectors)
Wild-type HSV-1 CAN replicate in mice and should be handled at ABSL2. However, helper-free HSV1 amplicon vectors contains <2/3 of the virus genome and do not contain detectable levels of
replication-competent HSV-1 (<1 in 108). Thus, vector inoculation should be done at BSL2, but animal
housing and husbandry at ABSL1 is appropriate. Very high virus doses might drive a desire to house
animals at ABSL2, as might particularly dangerous inserts, or the use of a helper virus for
propagation/production of amplicons.
General Information
About Mammalian Virus Vectors
Lentivirus
Lentiviruses are a subset of retroviruses, with the ability to integrate into host chromosomes, and to
infect non-dividing cells. These viruses can cause severe immunologic and neurologic disease in their
natural hosts. Lentivirus vector systems can include viruses of non-human origin (feline
immunodeficiency virus, equine infectious anemia virus) as well as simian viruses (simian
immunodeficiency virus) and human viruses (HIV). Typical lentivirus vectors take the form of virus
pseudotypes bearing envelope proteins from vesicular stomatitis virus (VSV). It is usually
recommended that work with non-human lentiviruses that are incapable of establishing productive
infections in humans (FIV, EIAV) be conducted at biosafety level 2 (BSL2).
Work with simian or human lentiviruses (SIV, HIV) is typically conducted at a higher containment level
(please consult the IBC).
See Lentiviral Vector Safety Guidelines for additional information.
Feline Immunodeficiency Virus (FIV)
See FIV Vector Safety Guidelines for additional information.
LAB: BSL2 (generally)
FIV is a BSL1 agent. However, replication-defective FIV vectors in which a heterologous envelope
(such as VSV-G) is used for vector packaging should be handled at BSL2. These vectors have the
potential to transducer human cells, and thus a risk for insertional mutagenesis.
Animal: ABSL1 (generally, for mice)
Mice are not a permissive host for FIV, even if replication-competent virus were present. Thus, vector
inoculation should be done at BSL2, but animal housing and husbandry at ABSL1 is appropriate.
Human Immunodeficiency Virus (HIV)
LAB: BSL2 (generally)
At UR, small amounts of HIV-1 are generally handled under BSL2+ containment (BSL3 work practices
and equipment in a BSL2 facility). MOST (but not all) replication-defective HIV-1 vectors contain <2/3
of the viral genome, and do not yield detectable levels of replication-competent virus (<1 in 108; based
on published data). This is due to the deletion of most of the viral structural genes (and often Tat/Rev
also), including HIV-1 Env. Vectors are typically packaged using heterologous evelope (such as VSVG) and can be safely handled at BSL2 in the lab setting.
General Information
About Mammalian Virus Vectors
The sequences in VSV-G have no homology to HIV-1 sequences, and thus cannot recombine with the
vector. The major risk is therefore insertional mutagenesis.
Animal: ABSL 1 (generally for mice)
All commercially available, replication-defective HIV-1 vectors include <2/3 of the viral genome. Mice
are not a permissive host for HIV-1, even if replication-competent virus were present. In most cases,
therefore, the initial vector inoculation can be performed at BSL2, but subsequent animal housing and
husbandry can be done at ABSL1 (provided that the local site of injection is appropriately
decontaminated and no local shedding/release is anticipated). Exceptions would include mice
engrafted with human cells, in which virus could replicate. Also specific inserts or very high viral doses
might drive the desire to house the animals at ABSL2, specific routes of delivery (e.g., skin or mucosal
surface contact) might also drive a reconsideration of containment issues.
Retrovirus
LAB: BSL2 (generally)
These are infectious viruses which can integrate into transduced cells with high frequency, and which
may have oncogenic potential in their natural hosts. Retrovirus vector systems are typically based on
murine viruses -- most commonly, these systems include ecotropic viruses (which can infect only
murine cells), amphotropic viruses (which can infect human cells) or pseudotyped viruses (which can
also infect human cells). Containment for vectors with the ability to infect human cells and thus present
a reisk for insertional mutagenesis will usually be recommended at biosafety level 2 (BSL2), as per
NIH Guidelines (appendix B) ("For agents that are infectious to human cells, e.g., amphotropic and
xenotropic strains of murine leukemia virus, a containment level appropriate for RG2 human agents is
recommended."), whereas for ecotropic vectors with no ability to infect human cells, BL1 containment
may be appropriate ("[ecotropic] murine retroviral vectors....that contain less than 50% of their
respective parental viral genome and that have been demonstrated to be free of detectable replication
competent retrovirus can be maintained, handled, and administered, under BL1 containment").
Animal: ABSL1 (generally, for mice)
Vector systems in which a heterologous envelope is used for vector production will yield very low
levels of replication-competent retrovirus, if any. In most cases, vector inoculation should be done at
BSL2, but animal housing and husbandry can be performed at ABSL1 (provided that the local site of
injection is appropriately decontaminated and no local shedding/release is anticipated). As noted for
lentiviral vectors (HIV), specific inserts, or very high doses might drive a desire to house animals at
ABSL2; specific routes of delivery (e.g., skin or mucosal surface contact) might also drive a
reconsideration of containment requirements.
General Information
About Mammalian Virus Vectors
Poxvirus
Poxvirus vectors include avian viruses (avipox vectors) such as NYVAC and ALVAC, which cannot
establish productive infections in humans, as well as mammalian poxviruses, which can productively
infect humans -- such as vaccinia virus (VV) and modified vaccinia viruses (MVA). Poxviruses are
highly stable, and vaccinia virus can ( although rarely) cause severe infections in immunocompromised
persons, persons with certain underlying skin conditions, or pregnant women. Such individuals should
not work with vaccinia virus (see Policy on Vaccinia Virus ). The use of biosafety Level 2 (BL2) is
appropriate for many poxvirus and constructs.
Vaccinia Virus (regular VV)
LAB: BSL2 (generally)
Wild-type VV is a BSL2 agent. Attenuated virus (TK deleted) is also handled at BSL2. The vaccinia
virus vaccine must be offered to lab workers, but vaccination is not a requirement for handling the
virus. It is important that lab workers with immunodeficiency be counseled.
Animals: ABSL2 (generally, for mice)
VV can replicate in mice, and thus ABSL2 housing and husbandry is appropriate.
Modified Vaccinia Virus (MVA)
LAB: BSL1 (generally)
Wild-type VV is a BSL2 agent. However, MVA is a derivative of wild-type VV that lacks many viral
genes, due to serial passage, and undergoes abortive infection in human and mouse cells. It can
therefore be handled under BSL1 containment in a lab setting, typically. The vaccinia virus vaccine
can be offered to lab workers, but it is not a required vaccination and may present more of a risk than
working with the agent.
Animal: ABSL1 (generally, for Mice)
MVA is not able to replicate in mice, and thus ABSL1 housing and husbandry is appropriate.
Updated 10/16/13: dd
10/18/13: ji