Researchers suggested that the failure of the well-publicized HIV vaccine in the STEP trial triggered from extension of CD4 memory cells from prior exposure to the adenoviral vector used to deliver HIV antigens.

Probably the vaccine prompted CD4-positive T cells which is also HIV's main cellular prey to collect in mucous membranes in patients previously exposed to some adenoviruses as per Steven Patterson, PhD, of Imperial College London in England, and colleagues.

The reason why HIV infection rates were increased in vaccinated participants in STEP can be explained by the findings published online in Proceedings of the National Academy of Sciences.

A theory was formed by Patterson and his colleagues that the collection of CD4-positive cells in mucosal tissues increased patients' vulnerability to HIV.

He and his colleagues conducted in-vitro experiments and extracted cells from 20 normal volunteers to study reactions to the vaccine used in STEP.

They found that T cell propagation induced with adenovirus correlated with previous Ad5-specific antibody titers.

In addition to this they also found expression of the a4ß7 integrin molecule, which aids cells to accommodate mucosal tissues in the gut, was up-regulated in adenovirus-specific, CD-4 positive memory T cells after exposure to Ad5 virus.

It is a revelation that about half of the adults in the developed countries and about 90 percent of them in the sub-Saharan Africa have gained immunity to the ad5 adenovirus used in the STEP vaccine. These are the regions where HIV is most common.

They finally concluded that these problems can not be solved only by using rare adenovirus strains to package vaccine antigens, because CD4 epitopes are preserved across viral serotypes.