Recent reports on gene-therapy trials described attempts to insert non-CF Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) DNA into epithelial cells using viruses as the delivery vehicle. Now, an article in the premier issue of Nature Medicine, published in January, describes an experiment using liposomes to deliver the corrected DNA ("Liposome-mediated CFTR gene transfer to the nasal epithelium of patients with cystic fibrosis," by Natasha J. Caplen, et al., Nature Medicine, Volume 1, Number 1, January 1995, pages 39-46). This is the first placebo-controlled trial of genetic therapy, and the first experiment to use liposomes to deliver genetic material to people with CF. It was the result of a collaboration between researchers in London and Edinburgh in the United Kingdom, and in Pittsburgh in the United States.
Fifteen CF males between the ages of 20 and 38, all with the same CF genetic makeup, double x-F508, volunteered to be the human guinea pigs. Nine received a nasal aerosol containing the DNA-liposome complex, and six received a placebo containing just liposome. The researchers chose to use an aerosol spray instead of nebulization to avoid accidentally getting any DNA-liposome into the lungs, since before this experiment, no one had yet established its safety, and the aerosol closely resembles nebulization. Biopsies performed four days after administration revealed no clinical changes that might have been due to the treatment.
To determine the functional effect of the treatment, the researchers measured the volunteers' nasal electrical potential difference (PD), in millivolts, under four conditions:
Figures 1 through 3 [only available in hardcopy] plot PD starting with the perfusion with the low-chloride solution, which lasts for five minutes, followed by five minutes of perfusion with isoprenaline. That is why some of the traces show a jag at the five-minute point.
One of the traces in each of the figures shows the typical time course of PD in a person who does not have CF, a response that only increases and reaches its maximum lasting level four or five minutes after the low-chloride perfusion. Figure 1 contrasts this with the same type of measurement in a person with CF who has not been treated. It shows a rapid initial response but returns to the baseline, or lower, within five minutes. Such plots for people with CF treated with the placebo were indistinguishable from untreated people with CF.
Now consider Figure 2. After DNA-liposome treatment, the volunteers displayed an elevated PD that, rather than returning to baseline, settled after five minutes to a continuous value some two millivolts, on average, above baseline. This effect became largest when measured three days after treatment, but disappeared by the seventh day. Finally, Figure 3 shows the best response of any person with CF recorded in this experiment after treatment, again plotted with the corresponding PD for a person who does not have CF, for comparison.
In an interview with BioWorld, Natasha Caplen, the lead author of the study published in Nature Medicine, said, "The primary goal of any Phase I trial is to look at safety. We saw no adverse clinical effects consistent with the treatment any of the patients received, up to the doses that were given.
"Then we come to the assessment of gene transfer efficacy," she continued. "The majority of patients had both DNA and messenger RNA present in their nasal epithelia that was plasmid-specific. Overall, five of eight subjects who were available for assessment by nasal biopsy had evidence of transgene expression. In patients who received the CFTR cDNA, we saw a 20 percent improvement in chloride secretion, but no change at all in those who received the placebo."
The reason for the interest in chloride secretion, Dr. Caplen said, was "because of this lack of chloride secretion, you get disruption in water movement, which leads to the build up of thick mucus in the lungs, which leads to infection and then pathology." She also noted, "We feel we have definitely seen some efficacy."
Finally, concerning future work, Dr. Caplen said, "Our Phase I nasal trial bears an obviously interesting relationship to assessing the basic cellular defect, but is not going to be of therapeutic use. For therapy, the lung's the main thing. The situation at the moment is that we have ethical permission to conduct a DNA-nebulization trial to the lungs of 12 CF patients. We're hoping we'll start this study next summer , and suspect it will probably take about a year from start to publication. Meanwhile, we're doing a full safety study."
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