The interim results from the study, which tested HIV-positive patients, were presented by Inovio's chief operating officer, Dr. Niranjan Y. Sardesai, at the Vaccine World Summit 2012 in Hyderabad, India.
"We are particularly excited by the positive interim results of the HIV-001 study in HIV-positive subjects," said president and CEO, Dr. J. Joseph Kim.
"This data is a first for DNA vaccines by yielding robust T cell immune responses in people chronically infected with HIV. Even though the HIV viral load of these volunteers was suppressed and brought under control by antiretroviral drugs, their immune systems are not normal and would typically have difficulty generating strong T cell responses to any immune stimulating approach.
"Coupled with positive data from two earlier trials, Inovio's results demonstrate the potency of our synthetic vaccine technology platform and raises the potential for the development of therapeutic vaccines against HIV and other chronic infections."
The HIV-001 open label, phase one study enrolled 12 adult HIV-positive volunteers to assess safety and levels of immune responses generated by Inovio's vaccine delivered with the company's Cellectra electroporation device.
Pennvax-B consists of SynCon immunogens targeting HIV gag, pol, and env proteins from HIV subtype B, which is commonly found in North America and Europe, Inovio said.
Overall, the company said significant vaccine-specific T-cell responses were observed in 75 percent of subjects against at least one of the three vaccine antigens (gag. pol, or env) following vaccination.
Fifty percent of the subjects had strong vaccine-induced antigen-specific responses above the pre-vaccination levels to at least two of the antigens. Importantly, the responses were predominantly antigen-specific CD8+ T-cells, Inovio said, which are considered to be "paramount in clearing chronic viral infections and an important measurement of the performance of a therapeutic vaccine".
"These results are in stark contrast to previously reported studies with other DNA vaccines delivered without electroporation that yielded poor overall T cell immune responses," the company added in a statement.
In the study, 12 eligible subjects were administered a four dose series of the vaccine containing 3 milligrams of DNA/dose via intramuscular electroporation. Inovio said there were no significant adverse events reported, with the vaccine found to be generally well-tolerated.
T-cell responses were measured using a validated ELISpot assay at the University of Pennsylvania Immunology Core Facility. The clinical study was sponsored by Inovio Pharmaceuticals and conducted at the University of Pennsylvania Medical Center.
Kim added: "Together with our HIV prophylactic vaccine programs in collaboration with our partners at DAIDS and HVTN, this HIV therapy trial highlights our commitment to addressing one of the foremost global health issues of our time."
According to the Joint United Nations Programme on HIV/AIDS, nearly 30 million people have died from HIV-related causes and roughly 34 million are living with HIV.
Although a HAART regimen has dramatically transformed the treatment of the disease in developed countries, effective HIV vaccines can be used to stop the spread of disease and perhaps reduce the need for antiretroviral treatments, which generally have harsh side effects and which in many cases lose their efficacy over time.
In a previous trial, Inovio reported strong T-cell immune responses to the Pennvax-B vaccine in health adults in a preventative setting. In that trial, over 89 percent of the vaccinated subjects mounted an antigen-specific T cell response against at least one of the vaccine antigens.
Inovio's SynCon vaccines are designed to provide universal cross-strain protection against known as well as newly emergent unmatched strains of pathogens such as influenza.
These synthetic vaccines, in combination with the company's proprietary electroporation delivery, have been shown in humans to generate strong immune responses with a favorable safety profile.
Inovio's clinical programs include phase two studies for cervical dysplasia, leukemia and hepatitis C virus and phase one studies for influenza and HIV.