LAUSR

OBJECTIVE Neuroimmune activation is a putative driver of cognitive impairment in people with HIV (PWH), even in the age of modern antiretroviral therapy. Nevertheless, imaging of the microglial marker, the 18kDa translocator protein (TSPO), with positron emission tomography (PET) in treated PWH has yielded inconclusive findings. One potential reason for the varied TSPO results is a lack of cell-type specificity of the TSPO target. DESIGN [11C]CPPC is a radiotracer for use with PET to image the colony stimulating factor 1 receptor (CSF1R). The CSF1R is expressed on microglia and central nervous system macrophages, with little expression on other cell types. We used [11C]CPPC PET in virally-suppressed- (VS)-PWH and HIV-uninfected individuals to estimate the effect sizes of higher CSF1R in the brains of VS-PWH. METHODS Sixteen VS-PWH and 15 HIV-uninfected individuals completed [11C]CPPC PET. [11C]CPPC binding (VT) in nine regions was estimated using a one-tissue compartmental model with a metabolite-corrected arterial input function, and compared between groups. RESULTS Regional [11C]CPPC VT did not significantly differ between groups after age- and sex- adjustment (unstandardized beta coefficient [B] = 1.84, standard error [SE] = 1.18, P = 0.13). The effect size was moderate (Cohen's d = 0.56, 95%confidence interval [CI] -0.16, 1.28), with strongest trend of higher VT in VS-PWH in striatum and parietal cortex (each P = 0.04; Cohen's d = 0.71 and 0.72 respectively). CONCLUSIONS Group difference in [11C]CPPC VT was not observed between VS-PWH and HIV-uninfected individuals in this pilot, although the observed effect sizes suggest the study was underpowered to detect regional group differences in binding.