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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 [1]; 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 [2].

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 [3].

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 [4]. 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 melanoma [5].

The report “Nucleic Acid-Mediated (Genetic) Vaccines Risk Analysis for Melanoma DNA Vaccine (Product Code 9240.D0, Unlicensed)” [6] 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 [7] or influenza virus or HIV virus [8]. 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 [9].

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 gene transfer.

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 [10].

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.

References

  1. Kowalczyk D and Ertl H. Immune response to DNA vaccines.  CMLS Cell. Mol. Life Sci. 1999, 55, 751-70.
  2. Isaguliants MG, Iakimtchouk K, Petrakova NV, Yermalovich MA, Zuber AK,        Kashuba VI, Belikov SV, Andersson S, Kochetkov SN, Klinman DM and  Wahren B. Gene immunization may induce secondary antibodies reacting with DNA. Vaccine 2004, 22(11-12),1576-85.
  3. Tagawa ST, Lee P, Snively J, Boswell W, Ounpraseuth S, Lee S, Hickingbottom B, Smith J, Johnson D and  Weber JS. Phase I study of intranodal delivery of a plasmid DNA vaccine for patients with Stage IV melanoma.  Cancer 2003, 98,144-54.
  4. Bergman PJ, Camps-Palau MA, McKnight JA, Leibman NF, Craft DM, Leung C, Liao J, Riviere I, Sadelain M, Hohenhaus AE, Gregor P, Houghton AN, Perales MA and Wolchok JD. Development of a xenogeneic DNA vaccine program for canine malignant melanoma at the Animal Medical Center.  Vaccine 2005 Sep 23; [Epub ahead of print]
  5. Bergman PJ, McKnight J, Novosad A, Charney S, Farrelly J, Craft D, Wulderk M, Jeffers Y, Sadelain M, Hohenhaus AE, Segal N, Gregor P, Engelhorn M, Riviere I, Houghton AN and Wolchok JD. Long-term survival of dogs with advanced malignant melanoma after DNA vaccination with xenogeneic human tyrosinase: a phase I trial. Clin Cancer Res. 2003, 9(4), 1284-90.
  6. Merial, Inc. Environmental Assessment for Field Testing Canine Melanoma Vaccine, DNA 2005  Nucleic Acid-Mediated (Genetic) Vaccines Risk Analysis for Melanoma DNA Vaccine (Product Code 9240.D0, Unlicensed)”  http://www.regulations.gov/fdmspublic-bld61/component/main
  7. Martin T, Parker SE, Hedstrom R, Le T, Hoffman SL, Norman J, Hobart P and  Lew D. Plasmid DNA malaria vaccine: the potential for genomic integration after intramuscular injection. Hum Gene Ther. 1999, 10(5), 759-68.
  8. Ledwith BJ, Manam S, Troilo PJ, Barnum AB, Pauley CJ, Griffiths TG 2nd, Harper LB, Beare CM, Bagdon WJ and Nichols WW. Plasmid DNA vaccines: Investigation of integration into host cellular DNA following intramuscular lnjection in mice.  Intervirology 2000, 43(4-6), 258-72.
  9. Krieg A. CpG Motifs in bacterial DNA and their immune effect.  Ann Rev. Immunol. 2002, 20, 709-60.
  10. de Vries J, Meier P and Wackernagel W. Microbial horizontal gene transfer and the DNA release from transgenic crop plants. Plant and Soil 2004, 266, 91-104.
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