FDG-PET imaging in HIV-infected subjects: relation with therapy and immunovirological variables

To characterise tissue sites of immune activation and HIV replication we performed FDG-PET in ART-treated and ART-naive HIV-infected individuals. Specific aims were to establish whether HIV-infected patients can be differentiated on the basis of the detection of specific locations of viral replication, even in the presence of an apparently optimal immunovirological response to ART, and whether these FDG-PET findings can be related to immunovirological variables and AIDS history status.

Patients were divided into five groups as follows: subgroup A1 (full responders, n = 8): current ART treatment, CD4+ T lymphocytes >500/mL, viral load <50 copies/mL; subgroup A2 (full responders, n = 5): same criteria as A-1, but with a previous history of AIDS; subgroup A3 (immunological non responders, n = 5): current ART treatment, viral load <50 copies/mL, low CD4+ T lymphocytes (<200/mL); group B (virological non responders, n = 2): current ART treatment, CD4+ T lymphocytes around 500/mL, viral load >50,000 copies/mL; group C (ART-naïve, n = 5): no current or previous ART treatment, increased viral load.

PET images revealed different patterns of FDG uptake. All ART-treated patients with either suppressed (<50 copies/mL; Group A) or high viremia (group B) showed a normal pattern of FDG uptake. On the contrary, the ART-naïve subjects with high viraemia (group C) displayed multiple foci of increased glucose metabolism in the lymph nodes. In the ART-naïve subjects, FDG uptake, apparently related to viraemia level, was observed in the upper torso mainly in the axillary nodes bilaterally in patients with viraemia below 100,000 copies/mL; in those with viraemia higher than 100,000 copies/mL, FDG uptake was also observed in the inguinal lymph nodes.

The emergence, in our study, of a correlation between the percentage of CD8+/CD38+/RO+ T cells (well established markers of progression to AIDS independently of CD4+ T lymphocytes) and positive FDG-PET in ART-naive patients is a novel finding that seems to confer prognostic value on FDG uptake. FDG uptake is strongly associated with response to ART independently of a previous AIDS diagnosis. Notably, no differences were observed between ART-treated subjects classed as immunological responders and those classed as non responders. Data herewith indicate that FDG uptake and immunological variables are unrelated when ART is being administered. This is evidence of the complementarity of immunological and FDG measures. FDG uptake is a sensitive marker of disease state and its relation with CD8+/CD38+/CD45RO+ T cells indicates that it can be considered a marker of disease status. The lack of a correlation between FDG uptake and immunological variables in patients under ART warrants further investigation.