Background Central nervous system (CNS) tumors are characterized by the paucity of T-cell infiltration Only T-cells that are able to recognize the cognate antigens presented by antigen presenting cells (APCs) in the perivascular or leptomeningeal cerebral spinal fluid (CSF) can cross the glia limitans and infiltrate the CNS parenchyma. While peripheral vaccinations can expand the number of tumor antigen-specific T-cells in circulation, most activated T-cells are confined to the perivascular CSF space and cannot penetrate CNS tumors. We have developed a novel cholesteryl pullulan (CHP) nanogel as a highly biocompatible and efficient vaccine delivery system targeting tumor-associated myeloid cells. In this study, we examined whether delivery of CHP nanogel loaded with the melanoma antigen glycoprotein (gp) 100 peptide along with immunoadjuvant to APCs in the CSF (‘intra-CSF vaccine’) will enhance the homing of antigen-specific T-cells to the tumors in the brain parenchyma, thereby improving the efficacy of T-cell-based therapy for brain tumors.

Methods Mice bearing intracerebral SB28 glioblastoma (GBM) received either an intravenous (i.v) (50µg/mouse) or intra-CSF (5µg) administration of the CHP nanogel along with poly-ICLC, a Toll-like receptor 3 agonist. Tumors and spleens were harvested at 24 hours following the vaccination. CD11b+ myeloid cells isolated from the tumors and spleens were co-cultured with CFSE-labeled pmel-1 CD8+ T-cells or for 96 hours. T-cell response were analyzed by T cell proliferation based on CFSE with flowcytmetry. For the survival study, mice bearing intracerebral gp100+ SB28 GBM received an i.v. infusion of pmel-1 T-cells 24hrs after either an i.v. or intra-CSF vaccination along with intramuscular poly-ICLC.

Results Both Intra-CSF and i.v vaccination induced antigen-specific T-cell responses ex vivo and extended the overall survival compared to control groups in vivo. However, only intra-CSF vaccination group significantly increased the T-cell infiltration into gliomas compared to with or without intravenous vaccination. To enhance the intra-CSF vaccination effect, it is worth considering repeating the experiment with higher dosages or increased treatment frequency.

Conclusions These results suggest that the intra-CSF vaccination of antigen-loaded CHP nanogel can promote the antigen presentation by myeloid cells to T-cellsand represent a promising approach for improving the efficacy of adoptive T-cell therapy for gliomas.

Ethics Approval All animal experiments are approved by UCSF IACUC committee, the protocol number is AN200257–00.