Structured treatment interruptions

May 2008      View PDF      En español

Using an STI to reinvigorate the immune response

Some observations suggest that HIV disease progression may be due in part to the loss of a potent type of immune cell, called an HIV-specific cytotoxic lymphocyte (CTL). These cells seek out and destroy HIV-infected cells. Some findings indicate that some long-term non-progressors — people who stay well for many years without HIV therapy — maintain their CTLs while those who progress more rapidly do not.

Although not all research supports the loss of CTLs as a cause for disease progression, several studies were planned or started. These included giving treatment within the first few weeks or months after infection (acute infection) followed by an STI as well as STIs taken with therapeutic vaccines to enhance a person’s immune response against HIV.

Ultimately, the goal of this type of STI is to preserve and enhance the body’s natural immune responses in early HIV infection. In theory, this would help a person’s immune system to better control HIV on its own for longer, and perhaps indefinitely, without therapy. For those with established HIV infection, the goal is to enhance or restore their immune responses, hopefully doing better in the long-term.

By starting and stopping therapy at regular intervals, it was hoped that with each STI the immune system would become more able to control HIV on its own. This is sometimes called auto-immunization, when enhancing a person’s exposure to HIV in a controlled manner can create a more potent and effective response against it.

However, the results of this research were the opposite of what was expected. People living with HIV the longest were actually more likely to have broader and more potent CTL increases. Those who had started therapy just before or after acute infection had
fairly weak responses with CTLs. The CTLs were boosted somewhat during the STI but then decreased back to lower levels after restarting treatment. Similar results were found in several other studies in people with long-term infection.

Several studies combined STIs with immune therapies, like IL-2 (Interleukin-2) or therapeutic vaccines. The hope here is that these therapies, when used with an STI, would provide the needed “lift” to coordinate a stronger immune response to HIV. The results are not promising. Therefore, people who hope to “boost” their immune systems should not look to STIs as a proven treatment.