By David N. Leff
Viruses trigger interferon, and interferon clobbers viruses.
Ever since its discovery in 1957, interferon has been haunting immunology research laboratories, looking for diseases to treat. Early hope-filled targets ran from osteosarcoma to the common cold.
In recent years, recombinant Type I interferon (which embraces its alpha and beta persuasions) has been approved for therapy of certain leukemias, lymphomas and myelomas plus hepatitis and some solid tumors ¿ melanoma, Kaposi¿s sarcoma, renal and breast cancer. But multiple sclerosis (MS) is the predominant disorder for which interferon (INF) is prescribed.
That hasn¿t made it a miracle drug. The fly in INF¿s ointment is toxic.
¿Interferon therapy,¿ observed research immunologist Arthur Krieg, ¿causes a lot of side effects in most patients, from flu-like syndrome ¿ fever, muscle ache, joint ache, headache, loss of appetite ¿ to more serious adverse reactions, including extreme depression, even suicide. And it can trigger autoimmune disease. Some patients who are treated with interferon tolerate it fine,¿ Krieg continued, ¿but there¿s a relatively high proportion of them who have moderate to severe side effects that can be so extreme they simply can¿t tolerate the medication, even though it may be having therapeutic activity.¿
Krieg is chief scientific officer of a company with a potential INF alternative. The firm is Coley Pharmaceuticals Group Ltd. Inc., with offices in Wellesley, Mass., and Munich, Germany. It has developed an insulin-releasing Type I interferon, based on licenses to patents invented by Krieg, when he was on the faculty of the University of Iowa in Iowa City.
In the early 1990s, he discovered in E. coli¿s bacterial genome DNA sequences that lead to INF release by the immune system. Krieg determined that immune defenses detect invading viruses and bacteria not only by the invaders¿ antigenic protein coats, but also by motifs in their microbial DNA. The motif he invented is an oligonucleotide that goes by the acronym CpG ¿ standing for cytosine-phosphate-guanine.
Potential In A Four-Letter Word
Krieg explained: ¿It means a cytosine nucleotide with a phosphate bonding to a guanine nucleotide. And with the viral infection or bacterial infection, one of the key things that the immune system detects is CpGs in the DNA of the organism. When I was in high school,¿ Krieg recalled, ¿they taught us that all forms of life on earth use the same bases ¿ A, C, G, T, and the DNA of a bacterium is supposed to be composed of those same four letters as our own human DNA.
¿That¿s true up to a point,¿ he went on. ¿But one of the things that makes CpG special is that when you have CpG in your own DNA, the C followed by the G is usually methylated. That changes its appearance as seen by the immune system, which thus recognizes that DNA as self-DNA ¿ nonthreatening, noninfective. So the presence of these methyl groups avoids activating our immune system in response to our own DNA. And because it¿s not methylated, it allows the immune system to detect foreign DNA.¿
Krieg is a co-author of an article in the July 2001 issue of the European Journal of Immunology. It¿s titled: ¿Identification of CpG oligonucleotide sequences with high induction of IFN-a/b in plasmacytoid dendritic cells.¿
¿We know that there is a type of white blood cell,¿ Krieg told BioWorld Today, ¿that used to be called interferon-producing cell,¿ or IPC ¿ the major cell type that produces interferon in response to infection. IPC is actually a type of immune system cell, called the plasmacytoid dendritic cell, or PDC. And just very recently,¿ Krieg went on, ¿it was discovered that PDCs are activated by CpG to make interferon.
¿For years,¿ he continued, ¿people have wondered where the interferon came from when you have a viral infection. It was tracked to the IPC, which was then identified as PDC, and people could show that infecting PDCs with virus would lead them to produce interferon. But we still didn¿t know what it was about the virus that causes it to produce interferon. Now we¿ve been able to show, in the journal paper, that actually these synthetic DNA oligonucleotide molecules that mimic viral DNA are sufficient to induce INF.¿
He pointed out why CpG avoids and evades prescription IFN¿s dire adverse reactions: ¿We believe that when you give interferon exogenously ¿ the way they treat with recombinant interferon ¿ you get big peaks and valleys in the level of interferon in your body. That may be responsible for a lot of the toxicity. In addition, that recombinant interferon you¿re getting is just a single type of the molecule. The body actually has a dozen or so different genes for interferon, and when we induce the immune system to produce interferon itself, endogenously, it makes this in a more coordinated fashion. We hope it will not have as much of a peak-and-trough effect on the body as giving those pharmaceutical doses of interferon recombinantly.¿
Preclinical Trial Looking Good; Clinicals Next
Krieg and his team have tested their therapeutic oligo in vitro and in vivo.
¿The in vitro assays that we¿ve done,¿ he recounted, ¿are very simple. We just took cells from human blood, from normal donors, and added a little bit of CpG, or control oligo. Then we put them in culture, and incubated them overnight. The next day we took the supernatant from those cultures and tested for the concentration of interferon. With a couple of hundred thousand of those dendritic cells, we got roughly 50,000 nanograms of INF per milliliter. Those are the highest levels, we believe, that have ever been recorded, simply using the synthetic DNA molecules.¿
Krieg continued: ¿We¿ve already performed animal trials with these, and submitted a paper showing the effect of these oligos on curing mice of melanoma. We injected a standard mouse melanoma tumor under the rodents¿ skin, let the tumor start growing, then gave them this interferon-inducing oligo. We were able to get as high as a 100 percent cure rate, but typically 70 percent in mice with established melanoma tumors, using only this immunotherapy. Those experiments were done over the last year,¿ Krieg observed, ¿and we submitted the manuscript for publication just a few weeks ago.¿
He concluded, ¿We¿re hoping to start clinical trials by late 2002 or early 2003.¿