Microglial cells are the main reservoir for HIV-1 within the brain and potential exists for negative immune checkpoint blockade therapies to purge this viral reservoir. Here, we investigated cytolytic responses of CD8+ T lymphocytes against microglia loaded with peptide epitopes. Initially, flow cytometric analysis demonstrated efficient killing of HIV-1 p24 AI9 or YI9 peptide-loaded splenocytes in MHC-matched recipients. Cytolytic killing of microglia was first demonstrated using ovalbumin (OVA) as a model antigen for in vitro cytotoxic T lymphocyte (CTL) assays. Peptide-loaded primary microglia obtained from programmed death ligand (PD-L) 1 knockout (KO) animals showed significantly more killing than cells from wild-type (WT) animals when co-cultured with activated CD8+ T-cells isolated from rAd5-OVA primed animals. Moreover, when peptide loaded-microglial cells from WT animals were treated with neutralizing α-PD-L1 Ab, significantly more killing was observed compared to either untreated or IgG isotype-treated cells. Most importantly, significantly increased in vivo killing of HIV-1 p24 YI9 peptide-loaded microglia from PD-L1 KO animals, as well as AI9 peptide-loaded BALB/c microglial cells treated with α-PD-L1, was observed within brains of rAd5-p24 primed-CNS boosted C57BL/6 or BALB/c mice, respectively. Finally, ex vivo responses of brain CD8+ T-cells in response to AI9 stimulation showed significantly increased IFN-γ and IL-2 production when treated with α-PD-1 Abs. Greater proliferation of CD8+ T-cells from the brain was also observed following blockade. Taken together, these studies demonstrate that PD-L1 induction on microglia restrains CTL responses and indicate that immune checkpoint blockade targeting this pathway may be beneficial in clearing viral brain reservoirs.
Bibliographical noteFunding Information:
This project was supported by grants from the National Institute of Mental Health (MH‐066703) and the National Institute of Neurological Disorders and Stroke (NS‐038836). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. We thank Jessica Fiege, Department of Microbiology, University of Minnesota, for valuable input regarding CTL assays.
This project was supported by grants from the National Institute of Mental Health (MH-066703) and the National Institute of Neurological Disorders and Stroke (NS-038836). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. We thank Jessica Fiege, Department of Microbiology, University of Minnesota, for valuable input regarding CTL assays.
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- HIV-associated neurocognitive disorders
- brain-resident memory T-cells
- cytotoxic T lymphocyte
- programmed death (PD)-1: PD-L1 pathway
PubMed: MeSH publication types
- Journal Article