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ISIS Report 13/12/05
Field-Testing a DNA Canine Melanoma Vaccine
A proposal that uses “confidential business information” to conceal the
most critical aspects with regard to safety while dismissing genuine safety
concerns. Prof. Joe Cummins
This report has been submitted to US Department of Agriculture-Animal
and Plant Inspection Service on behalf of the Independent Science Panel
The United States Department of Agriculture-Animal and
Plant Health Inspection Service (APHIS)
is considering granting authorization to ship an unlicensed DNA canine melanoma
vaccine for field-testing, as requested by Merial, Inc., Athens, Georgia.
The company wants to conduct clinical
studies that will provide efficacy and safety data in dogs administered this
vaccine. Efficacy will be measured by the sparing effect of the vaccine in
dogs diagnosed with melanoma; and the safety of the vaccine will be evaluated
in all animals participating in the studies. The Assessment for Field Testing
Canine Melanoma Vaccine, DNA 11/15/2005 is open for public comment
before 15 December 2005 at: http://www.regulations.gov/fdmspublic-bld61/component/main
The environmental assessment dealt
with the novel features of DNA vaccines. But with large sections of the assessment
blacked out as “confidential business information”
(CBI), full evaluation of the assessment is impossible; and this is not in the public interest. Nevertheless,
the use of DNA vaccines to treat canine melanoma has been discussed in the scientific literature.
DNA vaccines are normally delivered by intramuscular injection or a biolistic
device, or orally administered. The vaccines are normally bacterial plasmids
into which are spliced a promoter active in mammals, such as the cytomegalovirus
promoter, driving the coding sequence for an antigen. The plasmid is taken up
by the mammalian cells and reaches the nucleus of some of those cells. There
it is transcribed into RNA, which is translocated to the cytoplasm and translated
into antigen protein. The bacterial plasmid sequences are rich in CpG sequences
which act as adjuvant to enhance the immune response. The DNA vaccines induce
the full spectrum of immune responses including antibodies, T helper cells and
cytotoxic T lymphocytes ; but concerns have been expressed over the induction
of autoimmunity and anti-DNA antibodies, which were observed in rabbits immunized
with plasmids bearing a HIV reverse transcriptase gene .
A phase one clinical trial of a DNA vaccine using a plasmid modified with two
peptides from human tyrosinase - an enzyme on the path to melanin formation
that is greatly elevated in melanoma cancer cells - was undertaken on human
subjects with stage IV melanoma, in which the melanoma has spread from its site
of origin. Plasmid DNA was injected into the groin lymph nodes; and 16 of 24
patients survived for 12 months .
Metastatic (spreading) canine malignant melanoma is common and resistant to
chemotherapy. A clinical study of dogs with malignant melanoma involved treatment
with plasmids containing peptides from human or mouse tyrosinase. The study
showed that the inoculations were safe and resulted in anti-tyrosinase antibodies
. Dogs with advanced malignant melanoma survived for more than a year when
inoculated with a plasmid containing a gene for a peptide from human tyrosinase.
The trial supported the use of the vaccine in both dogs and humans with advanced
The report “Nucleic Acid-Mediated (Genetic) Vaccines Risk Analysis for Melanoma
DNA Vaccine (Product Code 9240.D0, Unlicensed)”  indicated that the DNA vaccine
was derived from a bacterial plasmid, but all of the pertinent information about
the antigen sequence and antibiotic selection markers was blacked out presumably
deemed confidential business information (CBI). The only information on the
plasmid not blacked out was that it was an E coli plasmid.
Among the issues considered in the review was the chance that the vaccine antigen
would recombine with genes in the dog chromosomes causing mutations. No effort
was made to measure integration of the vaccine DNA, the proponents and APHIS
argued that the chance of integration was low based on studies of antigen integration
from the malaria parasite  or influenza virus or HIV virus . But the dog
melanoma vaccines have all been based on genes present in the mammalian genomes
with high levels of DNA homology, allowing legitimate recombination at a much
higher frequency than the antigen genes from parasites or viruses that have
little or no homology with the mammalian genome, and must depend on illegitimate
recombination. It is surprising that APHIS and the proponent failed to mention
this important point.
The proponent and APHIS argue that immuno-modulator sequences such as the CpG
motif are not known to be present in something blacked out related to the plasmid
vaccine DNA. This point is clearly in error, for the CpG motif is present
in E. coli plasmids, and is certainly active in dogs and cats .
The problem of auto-immunity and anti-DNA antibodies was dealt with in a cursory
manner; and so was the handling and escape of plasmid bearing bacteria, with
no data provided to support conclusions. The dissemination of the vaccine plasmid
in the environment was also considered in the absence of experimental data.
The conclusion that the plasmid ingested by animals would be of no consequence
was similarly based on no experimental data, as was the dismissal of horizontal
The report claims that there is little or no chance of problems arising from
accidental spills of solutions containing the plasmid, because the plasmid is
not infectious and is unstable in the environment. Again, no data were supplied
to support that conclusion, which would appear at odds with what we now know
about the stability of DNA in all environment. The report maintains that plasmid
shed or released from test animals posed no concern because the levels of plasmid
released by those animals would be low. But no data were provided to support
that conclusion; and there was no indication that feces, urine or vomited materials
would be handled in any special way to prevent dispersal of the plasmid in the
environment. The antibiotic resistance markers associated with the plasmid were
designated CBI, and hence unavailable to any member of the public exposed to
the plasmid from surface or groundwater, in air associated with dust particles
or in bacteria. Many bacteria are capable of taking up DNA molecules and integrating
them into the bacterial chromosome; there are at least 87 species of naturally
transformable bacteria in the soil alone .
In conclusion, the proposal for a field trial of a DNA vaccine to treat canine
melanoma suffers from serious defects, chief among which, using CBI to conceal
the most critical aspects of the proposal with regard to safety while dismissing
genuine safety concerns with no empirical evidence. This proposal must be rejected
and given no further consideration unless and until those defects are made good.
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