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New research presented at the 26th International AIDS Conference in Rio de Janeiro suggests that HIV may leave a detectable immune footprint in the central nervous system even when the virus is fully suppressed in the blood. The findings come from a 16-year study of South African adolescents born with HIV who began antiretroviral therapy (ART) during infancy.

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The study, as reported by AllAfrica, analyzed paired blood and cerebrospinal fluid (CSF) samples from 79 adolescents. Of these, 75% had achieved viral suppression in their blood—meaning the virus was undetectable by standard measures. However, 11 of the 59 adolescents with suppressed virus—nearly one in five—still showed evidence of detectable HIV-specific immune activity in their CSF, the fluid surrounding the brain and spinal cord.

This discrepancy between blood and CSF findings forms the core of the study's implications. The research suggests that blood-based measures of viral suppression may not capture all HIV-related biology in other compartments of the body.

Key Claims

  • A 16-year study of South African adolescents with HIV found that nearly one in five still showed signs of detectable HIV-specific immune activity in their cerebrospinal fluid despite having achieved viral suppression in their blood.
  • The study analyzed paired blood and cerebrospinal fluid samples from 79 adolescents.
  • 75% of participants had achieved viral suppression in their blood, but 11 of the 59 adolescents with suppressed virus still had evidence of detectable HIV-specific immune activity in their cerebrospinal fluid.
  • The findings suggest that viral suppression in blood may not capture all HIV-related biology in other compartments.
  • The study has implications for HIV cure research, suggesting that scientists may need to look beyond the bloodstream when evaluating new therapies.
The central nervous system is a distinct anatomical and immunological compartment, as noted in the research. A therapy that appears effective in the bloodstream may not have the same penetration or biological effect within the brain and surrounding CSF. The blood-brain barrier can limit the entry of some drugs, while long-lived cells within the central nervous system may harbour HIV or continue producing viral material that sustains an immune response.

Shalena Naidoo, a researcher involved in the study, highlighted the value of the long-running cohort, saying, "This unique cohort provides a rare opportunity to understand the long-term effects of early treatment." The research drew on the PAVE-80 cohort, a group of children who acquired HIV around birth and began ART during infancy, followed for 16 years.

Antiretroviral therapy has transformed HIV from a fatal disease into a manageable chronic condition, and achieving viral suppression remains one of medicine's greatest successes. Yet these findings complicate that picture, suggesting that viral suppression in blood may not be the whole story.

The study's authors suggest the immune activity in the CSF may be caused by ongoing HIV transcription, antigen production, or low-level viral activity within a central nervous system reservoir. They also noted that a history of treatment interruption was more common among adolescents with this CSF antibody response.

These results have particular relevance for HIV cure research, which often relies on blood-based markers to evaluate the effectiveness of new therapies. The findings imply that scientists may need to look beyond the bloodstream when assessing whether a therapy is truly clearing HIV from all parts of the body.