Reports in the journal Nature show infusions of so-called broadly neutralising antibodies could suppress the amount of HIV in a patient's blood.
The approach uses clones of immune proteins taken from a rare individual who has natural control of the disease.
Scientists hope with further work this could bolster current treatments.
People naturally mount a defence against the virus by producing an army of protein based weapons - antibodies. But in most cases these are not powerful enough to defeat it.
The international research team harvested copies of unusually potent ones, capable of neutralising many different strains of HIV.
Patients given the highest concentrations were able to fight the virus for some time, dampening the replication of HIV in their blood.
The strength of this protection varied - in some it lasted more than four weeks.
In the journal the authors said: "Our data establish that passive infusion of single broadly neutralising antibodies can have profound effects on HIV viraemia in humans."
But because of the virus's ability to mutate rapidly, in some patients it was able to outwit the therapy by changing structure over time.
To overcome this scientists suggest using this treatment alongside current drugs or together with other antibodies.
Prof Michel Nussenzweig of the Rockefeller University in New York, told BBC News: "This is different to treatment out there already on two counts.
"First because it comes from a human - so it is natural in that respect.
"And secondly it opens up the possibility of giving the patient's own weakened immune system a jolt.
"One part of the antibody could act as a red flag - pointing out to the body where the virus is hiding and sending signals to kill it."
They are now exploring whether the infusion could shield people from getting the disease in the first place.
But he cautioned that studies into the antibody are still small and at an early stage.
"We have shown the approach is safe and effective.
"What this trial is telling us is that it is now time to look at the possibilities - from prevention and treatment to even cure," he said.
Commenting on the findings, Prof Vincent Piguet from Cardiff University, said: "This exciting novel study shows for the first time that antibodies may have a place in the line of therapies directed against HIV."
He described it as an "important development in the fight against HIV" but said the costs of antibody therapy and the emergence of resistance must be taken into account.

The £1.471bn spent shooting movies like Star Wars: The Force Awakens and Avengers: Age of Ultron in 2014 represents a 35% increase on 2013.
Money spent on homegrown UK films also increased, with £188m spent making films budgeted at £500,000 and above.
Box office takings, though, were down 2% on the previous year.
Overall, 157.5 million tickets were sold, representing a 5% dip in attendances compared with 2013.
Yet the BFI's figures show an increased market share for UK independent films, thanks in part to the box office success of Paddington and The Inbetweeners 2.
The former title took £34.7m in 2014 and has now made more than £35.5m at UK and Ireland box offices.
"The UK film industry is a powerhouse for growth and I'm delighted that 2014 saw an all-time high spend on film production," culture secretary Sajid Javid said.
"The huge amount of inward investment we are seeing is a sure-fire sign that the UK is the best place in the world to make films."
BFI chief executive Amanda Nevill said its report "illuminates a dynamic and vibrant story of success for the screen industries in the UK".
The £1.471bn spend represents the highest figure since statistics were first recorded 20 years ago.
The first human trial of a new type of HIV therapy suggests it could be a promising weapon in the fight against the virus.
[NEXT_CONCEPT]
More money was spent making films in the UK last year than in any other year since measurements began, figures from the British Film Institute have shown.