RICHMOND, Calif. ( TheStreet) -- An experimental HIV gene therapy from Sangamo BioSciences ( SGMO) knocked down the virus to undetectable levels in one patient, according to results from an early stage trial. Five other HIV patients in the same trial, however, did not benefit as much.

Sangamo shares were up 8% to $6.50 in Monday pre-market trading. The stock closed Friday at $6.

The Sangamo gene therapy, known as SB-728, is designed to genetically alter a patient's T cells to eliminate a protein known as CCR5 that is commonly used by HIV to invade and infect cells.

If successful and ultimately approved, the SB-278 gene therapy might be a "functional cure" for HIV, meaning patients would no longer need to take daily regimens of anti-retroviral drugs to keep the virus in check.

Sangamo is still a long way from proving that SB-728 is safe and effective. The data presented Sunday came from a small phase I study in which six HIV patients were infused with the genetically modified T cells and then stopped taking their anti-retroviral drugs for 12 weeks. The study was designed to determine if the modified T cells could take up residence safely in the patients; and then to see if the patients' newly altered immune system could fight off HIV on its own.

Results from the study found a "statistically significant" relationship between the number of genetically modified immune cells in the patients and suppression of viral load, or the amount of HIV in the body.

In one SB-278-treated patient, viral load increased initially after anti-retroviral medicines were stopped. After about six weeks, however, viral loads began falling, a sign that the patient's genetically altered T cells were fighting off HIV. At 12 weeks, the patient's viral load returned to baseline levels and was undetectable.

Further analysis showed that this patient had the highest level of modified T cells in his blood of all the patients enrolled. Importantly, this patient already carried a naturally occurring genetic mutation against the CCR5 protein that gave him a built-in advantage against the virus.

Between 5-10% of HIV patients have this innate genetic mutation that makes them less susceptible to HIV infection.

The other five patients in the study all had normal CCR5 proteins that are the most susceptible to HIV and as a result, these patients did not fare as well.

Like the first patient, the remaining five all saw their viral loads increase after being infused with the modified T cells and the cessation of anti-retroviral therapy. After about six weeks, viral loads in these patients also began falling but never returned to baseline levels, meaning their viral loads were higher at the end of the study than when they started.

Two of the five patients re-started taking their anti-retroviral medicines earlier than planned.

Based on these data, Sangamo plans to push SB-728 into further, more advanced studies that will include trials of patients with built-in CCR5 mutation. The company also believes it will get better results if it can increase and maintain a higher number of genetically modified T cells in the patients.

Sangamo will provide more details on SB-728's future at an investment conference on Wednesday.

Anti-retroviral drugs, including those made by Gilead Sciences ( GILD), GlaxoSmithKline ( GSK), Abbott Labs ( ABT) and Bristol-Myers Squibb ( BMY), among others, are the standard treatment for patients with HIV. The disease, today, has no cure.

The phase I data on SB-728 were presented Sunday at the Interscience Conference on Antimicrobial Agents and Chemotherapy in Chicago.

--Written by Adam Feuerstein in Boston.

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