Background:  The central nervous system (CNS) is a source of active viral replication and a target for disease. As a consequence of HIV-1 infection, mononuclear phagocytes generate a neuroimmune response that elicits neuronal damage and the generation of a chemokine gradient responsible for cognitive impairment and the recruitment of macrophages from blood into sites of disease. We reasoned that the same macrophages that carry virus and disease into the CNS could be used as vehicles for anti-retroviral drug delivery carried through nanoparticles (NP).

Methods:  Fluorescence-labeled nanoparticles indinavir (fNP-IDV) or superparamagnetic iron oxide (SPIO) were loaded into bone marrow-derived macrophages (BMM) to track cell-drug-formats migration into the brain. HIV-1 encephalitis (HIVE) was induced in severe combined immune deficient (SCID) mice by stereotactic brain injection with HIV-1-infected human monocyte-derived macrophages (MDM). SPIO- or fNP-IDV-BMM were administered intravenously following induction of HIVE. The SPIO-BMM were tracked by magnetic resonance imaging (MRI) and validated by histological co-registration. Animals were sacrificed and coronal brain sections were stained with Prussian blue and HIV-1p24 to identify the distribution of SPIO-BMM and co-localization of virus. Frozen brain sections were used to evaluate fIDV-NP-BMM by confocal microscopy. Brain IDV levels were assessed by high performance liquid chromatography (HPLC). The percentage of HIV-1p24⁺ MDM was used to determine levels of viral infection after a single dose of IDV-NP-BMM.

Results:  BMM migrated only to areas of active encephalitis. This was shown by histology and confirmed by MRI. On day 7, BMM density was robust within and around the site of disease as compared with other brain areas. No BMM were found in the contralateral hemisphere. When compared with free IDV treatment, IDV-NP-BMM produced sustained brain drug levels over 10 days (2 to 16 ng). The levels of infected MDM were 55, 24, and 44 in untreated, NP-IDV-BMM and free IDV-treated HIVE animals, respectively.

Conclusions: These results demonstrate proof of concept for the use of BMM as vehicles for delivery of anti-retroviral nanoformulated drugs across the brain blood barrier. The macrophage-based nanoformulated delivery system showed higher local brain drug concentrations and significant anti-viral activities in this murine HIVE model. The system suppports the potential use of this novel treatment paradigm for an infected human host.