Enhanced dendritic cell immunotherapy to treat glioblastoma

Abstract

Introduction: Glioblastoma (GBM) patients have a poor survival and are inevitably treatment refractory. The power of enhancing the immune system to combat the chemo-radiotherapy resistant tumour, melanoma, affirms the potential for re-directing the immune response against GBM. Furthermore, immunotherapy combines anti-cancer cytotoxicity with durable memory responses. Dendritic cells (DC) orchestrate a central role in the adaptive immune response by antigen uptake, presentation and co-stimulation to effector T-cells. However, tumours have evolved mechanisms to evade immune recognition by DC. Here we focussed on the myeloid CD1c+ (cDC2) subset, the most abundant circulating DC, to assess the feasibility of adoptive transfer in the next generation of DC vaccines. We also study the novel use of p38 mitogen-activated protein kinase inhibitor (p38i) as an adjunct to improve DC dysfunction and combination therapy with immune checkpoint blockade (ICB). Method: 6-colour flow cytometry of whole blood was used to enumerate and phenotype 4 circulating DC subsets in GBM patients (n=16) and healthy controls (n=16). Following magnetic bead isolation of DC, the cytokines IL-12 and IL-10 were measured post maturation from GBM patients (n=6) and modelled using healthy DC co-cultured with dexamethasone (Dex) and GBM tumour-derived lysate (TDL). A mixed lymphocyte reaction (MLR) measured T-cell stimulatory ability and phenotype. Migration was assessed using a transwell 5M pore membrane towards a CCL21 gradient and antigen presentation measured using an autologous DC, lymphocyte and peptide co-culture expansion system. Peptide-specific responses were analysed by IFN- ELISPOT. cDC2 ability to cross present gp100 peptides was analysed using transfected gp100280-288 T-cell receptor-Jurkat cell line. The p38i, BIRB0796, was added as an adjunct prior to maturation to assess response and ICB added to determine synergy in a MLR. Results: GBM patients had reduced cDC2 and plasmacytoid DC, with an immature phenotype, compared to controls. Likewise, cDC2 isolated from patients, showed significantly suppressed IL-12 secretion. This was modelled in healthy DC by co-culture with Dex and TDL. Treatment with p38i reversed cDC2 dysfunction with increased co-stimulation expression, IL-12 secretion and allo-stimulation. In addition, IL-10 was suppressed, migration towards CCL21 improved and cross-presentation ability maintained. Patient-derived cDC2 showed improved IL-12:IL-10 ratio, similar to healthy controls. There was a superior and synergistic Th1 proliferation when combined with ICB. Conclusions: Circulating DC from GBM patients are dysfunctional and this represents a potential mechanism of immune evasion. Here we establish that p38i restores phenotype and function to activate a Th1 response. We have also shown favourable characteristics of a combination ICB treatment strategy. This is the first study in GBM patients to investigate the use of cDC2 in the next generation of vaccines with a p38i adjunct. We are in the process of establishing the first cDC2 vaccine trial in GBM patients