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Lindsey Penner
Dr. LeFebvre
Cluster 7-Biomedical Sciences
27 July 2015
The History of Gene Therapy
Gene therapy has been a rising and continually evolving field since the 1960s. The
development of gene therapy (and its various techniques) has been a long and laborious
process, defined by trial and error, modification, and worthwhile success. Although it has
nearly unlimited potential, progress is blocked not only by technological barriers, but by
ethical ones as well. Many may object to the editing of the genome of individuals created
by a much higher force, but it is often the last remaining hope for many individuals
suffering from heritable and non-heritable diseases alike.
Melanoma tumors shrinking right before a patient’s very eyes, a restored immune system
and the ability to socialize normally without having to worry about contracting what could
develop into a fatal infection, and even complete remission for multiple leukemia patients; all of
these miraculous medical innovations, and many more, have been made possible through the
emerging field of gene therapy. “Researchers have concluded that virtually all human illness,
even infectious disease, has some relationship to genetic endowment…For eons, genetic diseases
have remained incurable, and…untreatable…” (Lyon, Jeff, and Gorner 28). Fast forward to the
20th century, in which new technologies were able to forge a different path from that decided by
one’s genes, and were designed to, “…introduce normal genes into a patient’s cell nuclei to
repair, replace, or compensate for the defective ones,” (Lyon, Jeff, and Gorner 32). The history
of gene therapy presented in this research will follow gene therapy from its origins in the 1900s,
to the initial trials, to a surge of popularity for gene therapy in the 1990s, through the difficulties
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and disappointments the field has endured, and finally into the modifications and
successes that will guide the ongoing development of gene therapy.
1. The Origins of Gene Therapy
The overarching scientific branch that gave birth to gene therapy, genetic
engineering, is considered to have appeared around 1932. The idea of “gene correction” through
genetic engineering led to the development of “gene therapy” by Clyde E. Keeler in 1947,
although the concept was only initially considered for application exclusively in plants and
animals (Scherman 17). By the 1960s however, and extending into the 1970s, Stanfield Rogers
executed the first gene transfer into humans to try and treat an arginase deficiency with doses of
Shope rabbit papilloma virus, but was ultimately not successful. Almost a decade later, in July of
1980, Martin Cline attempted to alleviate a patient’s β-thalassemia by removing bone marrow
cells, transforming them in vitro utilizing plasmids with β-globulin gene along with herpes
simplex thymidine kinase (to help marrow cells when reinserted) until the trial was stopped, with
no net effect on the patient. Both trials were not considered successful and both were heavily
scrutinized (Scherman 17-18).
2. The First Trials
Then in 1985, Dr. French Anderson, considered to be to the “chief pioneer” in gene
therapy (Lyon, Jeff, and Gorner, 18), collaborated with Dr. Michael Blaese to prove that a
retroviral vector could be used to transfer a functioning human ADA (adenosine deaminase)
gene to cells belonging to ADA deficient patients to correct the disorder. In 1986, the “safe[ty]
and efficien[cy] of the gene transfer into animal cells were observed, but had too few uptakes of
the correct genes for the procedure to progress as a treatment,” (Gene Therapy-National
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Institutes of Health). Two years later, the scientists switched to white blood cells, specifically Tcells, which yielded a much higher rate of gene transfer into the animal cells as compared to the
bone marrow cells (Gene Therapy- A Revolution).
Soon after, Anderson, Blaese, and Dr. Steven Rosenberg wanted to apply gene therapy to
cancer patients, particularly those afflicted with melanoma, using “tumor infiltrating
lymphocytes (TIL cells)”, “cells isolated from a malignant tumor, cultured with interleakin-2,
and injected back into patient as a tumor-killing cell that has greater toxicity,” (Gene Therapy- A
Revolution). They utilized a virus to insert DNA marker into TIL cells that would indicate to the
scientists “which TIL cells work best for cancer treatment; and that the engineered virus can be
safely used in humans,” (Gene Therapy- A Revolution). The first patient to be treated with this
method was a middle aged man named Maurice Kuntz who had been diagnosed with advanced
melanoma. Although Kuntz is reported by his wife to have been slightly disoriented from the
first infusion of his own cells, he soon recovered and willingly continued to the gene transfer
stage which took place on May 22, 1989. Initially, the treatment appeared to be working: Kuntz
was pain free and the tumors that had been inhabiting his spleen and liver “had disappeared”
(Lyon, Jeff, and Gorner 171). However, by November, new tumors were discovered in his brain
and others had reformed in his spleen. Despite multiple rounds of radiation, Kuntz’s health
continued to decline, and he passed away in April of 1990. (Lyon, Jeff, and Gorner 162-172).
Kuntz was principally treated by Anderson, while Rosenberg focused on his first five
patients. Many experienced the same initial shrinking of their tumors, with one woman even
completely cured of all cancer and related tumors, but many then went down the same path that
Kuntz had. Rosenberg concluded that, “‘In general, about half our patients are unaffected by
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TIL therapy,’” (Lyon, Jeff, and Gorner 174). This mixed success, however, did not deter these
scientists in any way, and they eagerly requested more trials for the 1990s (Lyon, Jeff, and
Gorner, 173-176).
3. The Gene Therapy Hype
The 1990s became host to hundreds of new trials in gene therapy. In 1990, for example,
the world saw the complete licensing of the first veterinary gene therapy vaccine produced by
Transage SA, licensed to Merial, and registered under RABORAL V-RG®. The vaccine would be
administered through the mouth and would contain a “recombinant vaccinia virus” that had
rabies glycoprotein G instead of thymidine kinase, and was primarily used for Western European
foxes and North American raccoons and coyotes (Scherman 19). Not only did the use of this
gene therapy vaccine decrease the prevalence of wildlife rabies infection and the risk for the
human population, but it also contributed to the elimination of rabies in France and Belgium by
2001 (Scherman 19).
Also in 1990, Anderson, Blaese, and Dr. Kenneth Culver moved to treat ADA in two
young girls, starting with a four-year-old named Ashanthi DeSilva (Lyon, Jeff, and Gorner, 229),
by withdrawing a minimum of half her number of white blood cells, despite her already severely
depleted supply, because, “one needed a good supply [of T cells]” to be replicated (Lyon, Jeff,
and Gorner 229). Anderson constantly monitored her pulse by hand after the infusion had begun,
and soon Ashanthi had “hundreds of thousands of her own cells, reconditioned with the addition
of the absent ADA gene…flowing though her veins,” (Lyon, Jeff, and Gorner 238). Ashanthi
would have numerous and increasingly sized infusions (Lyon, Jeff, and Gorner, 229-239) for the
next two years (Gene Therapy- A Revolution) as would the other patient, Cynthia Cutshall
(Lyon, Jeff, and Gorner, 239).Three years later, in 1993 gene therapy was applied to
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newborns with ADA, inserting corrected genes into “immature red blood cells isolated from the
babies’ umbilical cords,” (Gene Therapy- A Revolution). Today, it is reported that the first two
child ADA patients, Ashanthi and Cynthia, live “normal lives” “and that just one gene therapy
treatment proved enough to raise ADA levels in the newborns’ immune system cells,” (Gene
Therapy- A Revolution). The relative success of these trials led to various gene therapy attempts
at a myriad of hereditary diseases (A History).
4. Difficulties Along the Way
Despite the growing numbers of trials in gene therapy in the 1990s, “only 1% of
protocols” endured to Phase III (Scherman 19), a large scale trial with hundreds of people to
observe the work of the vaccine in normal conditions. If proven to be successful and safe, the
trials/ methods being evaluated could then apply for licensure and manufacture for human
application (Stages of Vaccine Development). Any substantial progress, however, was blocked
by the “inefficiency of vectors” used to administer the genes (A History), and the fact that the
“theraputic DNA” must be inserted directly “into the host cell genome” or given in numerous
treatments to accommodate for the continual process of cell division (Scherman 20). In addition,
the use of promotors or gene sequences that do not naturally synchronize with codons in the
receiving host may not prove to be functional (Scherman 20).
Other problems that have hindered the advancement of gene therapy include “insertional
mutagenesis” (Scherman 21), in which the addition of “new genetic material into a normal gene”
results in a “mutation” (Scherman 21). This was seen in the cases of “5 out of 20” “X-linked
severe combined immunodeficiency (SCID-X1) patients whose hematopoietic stem cells were
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transduced with the gamma-chain interleukin 2…receptor gene using a retrovirus,” and who
subsequently “developed T-cell leukemia,” (Scherman 21). Although a majority of the affected
patients were successfully administered “anti-leukemia treatment”, the clinical trials were paused
for a short duration of time in 2002 before resuming with considerable results in many countries,
with at least “100 immunodeficient children…successfully treated” (Scherman 21). The success
of these trials allowed different immunodeficiencies to be studied. So far, the utilization of
“integrative vectors to treat bone marrow stem cells represent the most successful application of
gene therapy,” (Scherman 21).
Another difficulty that arises in gene therapy treatments are the patients’ “immune
response[s] either to the viral vector or the newly expressed transgenes” (Scherman 21) which
appears to be similar to patients undergoing organ transplants. Additional obstacles are gene
control and targeting, both requiring extreme precision. Having the capacity to manufacture
sufficient amounts of vector for “large clinical trials”, especially viral vectors, has also proven to
be an impediment to continual progress (Scherman 22).
5. Disappointments and Modifications
What would be known as a decade of disappointments in gene therapy culminated in the
death of an 18-year-old male, Jesse Gelsinger, in September of 1999. Gelsinger had been being
treated with gene therapy for OTCD, a hereditary liver disease, before passing away from an
“inflammatory response” to the viral vector used to deliver the corrected genes, in what would be
the first death to be “directly related to gene therapy” (Stolberg). Even though the other patients
in the trial did not experience significant adverse effects, Gelsinger’s death dealt a severe blow to
the reputation of gene therapy (Scherman 19). His passing, however, was not in vain, as it
encouraged more attention to enforcing patient safety protocols in “medical research” (A
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History-British Society for Gene and Cell Therapy), in addition to work with genetically
modified, weaker forms of the virus (Scherman 20).
This research led to the first human gene therapy product on the market, Gendicine® , “a
recombinant adenovirus vector 5 expressing tumor suppressor gene p53,” that was designed by a
Chinese firm to target “ head-and-neck squamous cell carcinoma” (Scherman 20). In November
of 2005, Chinese officials also approved Oncorine® that could eliminate tumor cells expressing
“dysfunctional p53 genes” (Scherman 20). Cerepro® , a new brain cancer treatment featuring the
application of HSVtk through an “intravenous” injection of prodrug granciclovir that is
transformed to kill only “dividing tumor cells” after interaction with tumor-produced thymine
kinase, is currently being tested in Europe.
6. Fine-Tuning, Success, and Onward
Advancements and triumphs, however, have been made in recent years to allow
continued research into the increasing applications of gene therapy. For example, insertional
mutagenesis is now mitigated through the use of “self-complimentary lentiviral vectors” or by
using specific sequences “to direct the site of integration to specific chromosomal sites”
(Scherman 22). Less dangerous forms of gene therapy have also been developed: gene targeting,
and the removal of certain genes with designed nucleases (an example being zinc-finger
nucleases). Work is currently being done in the “envelope protein pseudotyping of viral vectors”
that would affect host cell ranges and require less vector (Scherman 22).
In a recent trial, a small group of adults and a larger pool of children afflicted with acute
lymphocytic leukemia were treated with a method similar to that of the ADA patients in the
1990s. The patients’ T-cells were extracted and modified to become attackers of the cancer cells
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within their own bodies. Aside from a few instances of relapse, most of the participants in the
trial have experienced complete remission. One in particular being Emily Whitehead, an 8 yearold-girl and the first child recipient of that particular gene therapy that, before treatment was
deemed by doctors to be at death’s doorstep, but remains cancer free two years after the
treatment (Gene Therapy Scores).
Methods of gene delivery have also been fine-tuned. The limited success of earlier
intramuscular injection of naked DNA led to more research that generated new techniques like
electroporation, sonoporation, and the gene gun. Genetic neuromuscular disorders, however, are
harder to treat, as seen in the minimal gene expression in the Phase I trials for DMD (Duchenne
Muscular Dystrophy) that inserted coding sequence for dystrophin gene through a low dose of
plasmid DNA (Scherman 22).
Success of the first gene therapy trial for Leber congenital amaurosis (hereditary
“blindness disease caused by mutations in the RPE65 gene” (Scherman 24)) in 2007 and its
announcement in 2008 led to research of more eye-related disorders. Other types of gene
therapy, however, either don’t operate on the DNA level, cause discrepancies in transcriptions or
siRNA, or use oligodeoxynucleotides to mimic transcription factors of specific genes, in addition
to oligonucleotides (“short nucleic acid polymers…designed to hybridize specifically to DNA or
RNA sequences” (Mandal)) that function in gene repair (Scherman 24).
One technique in particular, exon skipping, developed as a result of studies of Duchene
Muscular Dystrophy in 1991. “Splicing therapy” should be able to fix many frameshift mutations
by using antisense nucleotides to skip over the faulty part of a gene and allow a better form of
dystrophin to function as opposed to none at all (Scherman 25). The year 2006 would see the
first trial in humans with intravenous injection of an “antisense phosphorothioate
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oligodeoxynucleotide” that would “skip exon 19” in a young DMD patient that lacked exon 20
(Scherman 25). The requirement that the “splice” must be designed to the genome of each
individual patient, however, requires more investigations of “trans-splicing and skipping multiple
exons” (Scherman 25). While some cases are limited by a reduced ability to treat the heart and
patients not being able to spare certain parts of their proteins for deletion, this can serve as an
advantage in non-heritable diseases that rely on “oncogenes or viral proteins” (Scherman 25)
The pattern of the development of gene therapy is viewed by many as the struggle to
meet the high potential set for it, and resultant doubt that it ever will. While they toil to solve the
current issues hindering gene therapy’s wider application, however, scientists are constantly
working with the future in mind. On the horizon of gene therapy lie concepts such as germ line
gene therapy (an extremely controversial endeavor) and preventative gene therapy. The
opportunities to transform these visions into a medical reality for prospective patients, however,
“will depend upon the ability of private companies to solve technological… and business…
issues” and to expand their sources of “collaboration” (Scherman 27).
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2013. Web. 19 July 2015.
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York Times, 27 Nov. 1999. Web. 19 July 2015.