A novel digital enzyme-linked immunosorbent assay (ELISA) could be a tool used to further understand HIV central nervous system (CNS) involvement by having high sensitivity for the HIV p24 antigen in human cerebrospinal fluid (CSF), according to a study published in Clinical Infectious Diseases.
A better understanding of all anatomic reservoirs is needed to eradicate HIV, given the viral persistence despite combination antiretroviral therapy. Low HIV RNA levels in the CNS reservoir are evident, but additional markers are needed to measure viral persistence and reactivation. The most abundant HIV protein, p24, has shown potential as another marker but has not been valuable because of the low sensitivity of previous p24 assays. Therefore, new tools are needed to understand HIV CNS involvement. A novel digital ELISA showed high p24 sensitivity and has detected early HIV infection and measured HIV latency reactivation in vitro. Using digital ELISA, this exploratory study determined whether low levels of HIV p24 antigen in human CSF could be quantified.
Adult outpatients (n=15) with chronic HIV infection were enrolled at Emory University Center for AIDS Research from March 2011 to October 2016. A neuropsychological (NP) battery of 9 commonly used tests of cognition and HIV infection was administered. Plasma and CSF HIV RNA concentrations were quantified (lowest limit of detection, 40 copies/mL). CNS virologic escape was defined as either detectable CSF HIV RNA in the setting of plasma HIV RNA <40 copies/mL or CSF HIV RNA >1 log10 copies/mL higher than plasma HIV RNA.
Results demonstrate that digital ELISA is able to quantify p24 at low levels in CSF. CSF p24 was detected in 10/11 cases (91%) with CSF HIV RNA >1000 copies/mL. Plasma p24 was detected in only 6/11 cases (54.5%) with plasma HIV RNA >1000 copies/mL. However, despite p24 assay sensitivity, all samples with CSF HIV RNA <1000 copies had undetectable CSF p24, suggesting further assay optimization research for maximum sensitivity is needed.
CSF p24 concentration correlated strongly with CSF HIV RNA concentration (P <.001), but not with plasma HIV RNA (P =.15). Plasma p24 did not significantly correlate with either plasma HIV RNA (P =.21) or CSF p24 (P =.22). These results suggest that HIV p24 is locally produced in the CSF.
CSF p24 more closely correlated with worse NP performance than CSF HIV RNA. Mean NPT-9 score was 41.3 (standard deviation, 9.4). CSF HIV RNA and composite global neuropsychological score (NPT-9) showed a low correlation (P =.37), but CSF p24 and NPT-9 showed a strong correlation trend (P =.055). Therefore, p24 presence may indicate a “translationally competent” HIV infection of CNS cells. Other viral proteins associated with neurotoxicity are likely being produced along with p24 in the CNS as well.
Overall, findings support the longstanding interest in measuring HIV viral proteins in the CNS. Due to the small sample size, study authors concluded that “more comprehensive research will be needed to further investigate CSF p24 by high sensitivity assay as a marker for neurocognitive impairment during poorly controlled HIV and as a marker for HIV CNS reactivation during latency reversal therapy.”
Anderson AM, Tyor WR, Mulligan MJ, Waldrop-Valverde D, Lennox JL, Letendre SL. Measurement of human immunodeficiency virus p24 antigen in human cerebrospinal fluid with digital enzyme-linked immunosorbent assay and association with decreased neuropsychological performance [published online January 29, 2018]. Clin Infect Dis. doi: 10.1093/cid/ciy056