© 1998 by Oxford University Press
But Blaese, chief of the Clinical Gene Therapy Branch at the National Human Genome Research Institute, according to his own "working plan," will move over to Kimeragen, Inc., in Newtown, Pa., in the next few months, while staying involved in clinical protocols at the NIH for at least another year.
Strong Ties
Then who knows? Something in his manner suggests that after 32 years at the NIH, the ties to his many patients, their families, and to the NIH scientific community, are far too strong to sever completely. "I've got the best job in the world right here. . . . I really do," he says, gesturing to "this fabulous place" out a large office picture window in a recent interview. "And I don't have any particular reason to want to leave except this is something that has me so excited, I really wanted to push it."
What so excites Blaese is Kimeragen's technology, a technology based on small molecules known as oligonucleotides, often called "oligos," that work together with a cell's own DNA repair mechanisms to correct misspellings of genes that cause disease. Because these short pieces of synthetic DNA are designed to be complementary to a gene's messenger RNA -- fitting much like a zipper -- they can be targeted to specific errors in gene expression including that of a single base pair mutation. It is that specificity, and oligos' smaller size compared to traditional gene vectors, that Blaese believes gives them "the potential of really making an impact on the lives of thousands of thousands of patients" with genetic diseases.
Totally Seduced
"I am totally seduced by the technology," he readily admits. After having struggled through the "wars of gene therapy" for the last decade and a half, and understanding "what's out there, what's likely to be available, and what the limitations are," Blaese says, "I go back to my roots as a pediatrician taking care of disease for my entire career and realize that what's on the horizon is not going to fix them . . . not going to be very useful."
One reason for his skepticism is that for traditional gene therapy to fix a genetic disease such as sickle cell anemia, whose cause lies in a single nucleotide error, it would be necessary to use a whole gene, "but you can't put in the whole gene because we don't have vectors that are big enough." So a copy of the coding region of the gene (i.e., a DNA sequence complementary to the gene's messenger RNA) would have to suffice.
But by using a gene copy, according to Blaese, important regulatory regions are lost and "you are delivering tens of thousands of base pairs when all you need to do is fix one nucleotide." The resulting delivery problems, he says, are like "enormous delivery vans that are trying to get down a narrow street in Italy -- It doesn't work."
Although delivery problems also plague oligos, Blaese admits, he seems confident that this problem, along with the need to bypass or overcome a cell's defense mechanisms to prevent enzymatic degradation, can be solved. An oligonucleotide, he says, is much more "like a small molecule drug than it is like a biologic" -- making delivery issues, at least, far simpler.
ADA Deficiency
One genetic disease, however, that Blaese feels may eventually be fixed by traditional gene therapy is ADA deficiency, an illness which destroys the body's ability to fight off ordinarily harmless infections, and whose name is inextricably linked to Blaese's own.
On September 14, 1990, at the NIH, Blaese, along with two former NIH researchers W. French Anderson, M.D., and Kenneth Culver, M.D., ushered in a new era of gene therapy when Ashanthi DeSilva, then 4 years old, received a transfusion of her own white blood cells (T cells), which had been genetically altered to carry a healthy ADA gene. Several months later, a second Ohio girl, 9-year-old Cindy Cutshall, also suffering from ADA, underwent the same procedure.
Blaese's belief that the ADA defect may yield to these early genetic manipulations is linked in part to how well both girls appear to be doing 8 years after their initial gene treatments, and in part to the nature of their genetic defect, which lends itself to symptomatic improvement even if only small amounts of the missing adenosine deaminase enzyme can be produced.
pegADA
In fact, because both girls -- and subsequently three infants who were also genetically treated for ADA (see sidebar) -- have remained on a synthetic enzyme, known as pegADA, some critics have contended that the true value of gene therapy may never be known. But Blaese counters that the "theoretical basis for gene therapy -- of using peripheral T cells" did not lend itself to stopping [pegADA] "unless you get absolutely huge numbers of ADA, which we didn't anticipate we could get."
"There was never really a plan to stop it [the pegADA]," he adds, "and that's why we haven't."
Although both girls appear to be leading normal lives, their immunologic responses to the gene treatments have been quite different, says Blaese, and for many years investigators could not figure out why. Ashi, now 12, has not been treated in 6 years -- except for the pegADA -- and 50% of her circulating T cells are still positive for the ADA gene 8 years out from her initial gene treatment. In comparison, Cindy, a high school senior "looking at colleges," has circulating T-cell levels that test positive for ADA in the range of only 2% to 4%, says Blaese -- "even though she got treated the same number of times, with the same number of cells."
Puzzled
Researchers puzzled over this discrepancy in immunologic profiles between the two girls for nearly 5 years, and "all sorts of things" were studied, according to Blaese. "But, ultimately, we discovered, and I think convincingly demonstrated, that what happened to Cindy is -- because she had a much milder defect [than Ashi] and the ability to make some antibodies before we ever gave her the gene therapy -- she actually became immune to fetal calf serum," the mixture in which retroviral vectors are often cultured and grown prior to using them to ferry new [corrective] genes inside cells.
Specifically, a lipoprotein in the calf serum triggered an immune response. "So when Cindy was getting her own T cells [reinfused]," Blaese notes, "she now had a new antigen on their membranes and she had enough immunity to respond to that and make an antibody to this new component on the membrane of her cells."
"Then when she had a next treatment and she had an antibody, she just basically cleared the cells as quickly as they were infused."
Unexpected Snag
The resulting spikes in immune response meant there was initially some effect [of the gene therapy], more effect, and "then nothing," says Blaese. This unexpected snag, which later derailed attempts to genetically alter her stem cells, arose in spite of efforts to wash the cells extensively -- more than 500 volumes of liquid were used -- prior to reinfusion. What happened, Blaese says, is the lipoprotein in the calf serum actually became attached to her cells and it wouldn't wash out -- requiring a new way of doing things. "We've had to do a lot of dancing to try and get the retrovirus produced so we don't have to have bovine serum there." Now that the problem is understood, he says, it can be avoided.
Meanwhile, for Ashi, there are no more plans for T-cell therapy, although Blaese and his colleagues expect to attempt a blood stem cell correction, using gene therapy, within the next 6 months. Because stem cells, which originate in the bone marrow, give rise to all blood cells, a successful insertion of a healthy ADA gene into these cells in theory would provide a cure.
It is clear that the decision to attempt to genetically alter her stem cells is a preemptive strike against new pathogens that may arise unexpectedly. Although she is capable of mounting an immune response, the range of her response is considered limited because of the high level of genetically corrected T cells still detected in her blood even though she has not had a gene treatment since 1992.
"What this tells you," said Blaese, "is that there are no new cells entering the pool, or you would dilute out these cells. But since the number of cells remains relatively constant, you don't have the opportunity to introduce a new repertoire of T cells . . . which is why we haven't stopped pegADA. She needs to be able to respond if she is exposed to something new."
For the impending procedure, there are plans to use a second generation vector, which Blaese estimates is 30 to 50 times more active than its predecessor, and which presumably will allow greater efficiency in inserting the ADA gene into Ashi's stem cells. Additionally, a different cocktail of cytokines will be used to induce better cell growth.
"One of the real difficulties is you don't get a very good concordance between what you see in animal models and what you see in human beings," said Blaese. "So in a way it comes down to -- almost as it did in the beginning. . . . Eventually, you have to do it [gene therapy] in man to see what's going to happen."
-- Susan Jenks
R. Michael Blaese: Still Blazing a Path Of His Own
Reports of his imminent departure, it seems, have been greatly exaggerated. Nearly 7 months after being named chief scientific officer and president of the Molecular Pharmaceuticals Division of a small Pennsylvania biotech company, R. Michael Blaese, M.D. -- one of the world's leading gene therapists -- is still on the National Institutes of Health campus, still a federal employee, and still ensconced in his scenic 10th floor office at the NIH clinical center.
CiteULike 
Connotea 
Del.icio.us What's this?
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||