Introduction: Current glioblastoma multiforme (GBM) immunotherapeutic vaccines rely largely on bulk tumor-associated antigen (TAA) sources from limited patient tumor samples or specific GBM peptide antigens susceptible to immunoediting. This study examined the ability to exploit allogeneic GBM cell line lipid rafts, enriched in specific TAAs as well as immunogenic chaperone proteins, as a renewable antigen source for dendritic cell (DC) vaccines for GBM.
Methods: Whole cell lysates, total membrane fractions, lipid raft fractions, or non-lipid raft membrane fractions were isolated from a syngeneic murine glioma cell line transfected with model antigen ovalbumin (GL261-OVA). For each membrane fraction, we measured levels of protein heterogeneity, TAA expression, and immunogenic chaperone protein by Western blot. DCs cultured from C57BL/6 mice were pulsed with the various lysate fractions, and DC maturity was assessed by CD83 staining. Stimulation of TAA-specific CD8+ T-cells by pulsed DCs was determined by Kb-OVA-specific tetramer staining and IFNg ELISA.
Results: Lipid rafts had markedly reduced overall protein heterogeneity but were enriched for multiple TAAs and immunogenic chaperone proteins (OVA, MAGE A3, ErbB2, Grp94). DCs pulsed with GBM lipid rafts were more mature (CD83+) and demonstrated enhanced OVA antigen cross-presentation to CD8+ T-cells compared to DCs pulsed with standard whole cell lysate (13.11%+/-2.93% vs. 2.44%+/-0.58%; p=0.02) or other membrane fractions. Furthermore, increased IFNg was released by CD8+ T-cells co-cultured with DCs pulsed with lipid raft as compared to those pulsed with whole cell lysate (53.42 pg/mL vs. unmeasurable) or other membrane fractions.
Conclusions: Our findings suggest that GBM lipid rafts from established glioma cell lines may be a potent renewable antigen source for glioma vaccines. Further studies are underway characterizing vaccine efficacy in mouse studies, as well as stimulating HLA-A2+ human T-cells by autologous DCs pulsed with lipid rafts from allogeneic human Good Manufacturing Practice-grade GBM cell lines.
Patient Care: Current glioblastoma vaccines rely largely on bulk antigen sources from limited patient samples or specific GBM antigens that are susceptible to immunoediting. Our study examines the ability of utilizing lipid raft fractions from GBM cell lines as renewable antigen source for DC vaccines.
Learning Objectives: Develop understanding of obstacles faced by current GBM immunotherapeutic approaches.
Be able to discuss potential strategies to improve dendritic cell vaccines in areas of developing reliable tumor-antigen presentation and maximal induction of antitumor activity.