Potent anti‐tumor responses to immunization with dendritic cells loaded with tumor tissue and an NKT cell ligand

Abstract

Cancer immunotherapy is well tolerated and specific, but its efficacy remains variable. To enhance anti-tumor CD8 + T-cell responses induced by immunization with antigen-loaded dendritic cells (DCs), we explored the impact of eliciting a potent source of T-cell help from activated invariant natural killer (NK)-like T cells (iNKT cells) using the specific glycolipid ligand a-galactosylceramide (a-GalCer). As cytokines released by iNKT cells may drive proliferation of CD4 + CD25 + regulatory T cells (Tregs), we assessed this immunization strategy in animals treated with anti-CD25 antibody to inactivate Treg function. Combining DC immunization with iNKT cell activation was found to significantly enhance anti-tumor activity, which was improved further by the prior inactivation of Tregs. The improved anti-tumor activity with Treg inactivation was associated with a prolonged proliferative burst of responding CD8 + T cells. We could find no evidence that inclusion of a-GalCer in the vaccine enhanced Treg numbers, or that the 'helper' function of iNKT cells was improved in the absence of Treg activity. Rather, the two activities appeared to act independently to improve the tumor-specific T-cell response. Inactivating regulatory T cells and eliciting iNKT cell activation are therefore two useful strategies that can be used in combination to improve anti-tumor immunization with antigen-loaded DCs.

Functional invariant natural killer T-cell and CD1d axis in chronic lymphocytic leukemia: implications for immunotherapy

“…Subsequently, 1x10 5 to 1x10 6 CLL cells were thawed, washed, and added back to 1x10 6 autologous B cell-depleted PBMC cultured with 1 ng/mL interleukin-7. After two further weekly stimulations, iNKT cell frequency was determined by flow cytometry.…”

“…An interferon-g enzyme-linked immunosorbent spot (ELISpot) assay was performed using a commercial kit (BD Biosciences) according to the manufacturer's instructions: 1x10 6 B-cell-depleted PBMC were washed, resuspended in complete Iscove's modified Dulbecco's medium (cIMDM) and dispensed into coated ELISpot plates. α-GalCer 200 ng/mL, phosphate-buffered saline/Tween vehicle (as a negative control), or protein phytohemagglutinin (PHA-P) 1 mg/mL (Sigma-Aldrich) (as a positive control) were added, and plates cultured for 18 h at 37°C.…”

“…1 In preclinical models, co-administration of the prototypical iNKT agonist α-galactosylceramide (α-GalCer) 2 with tumor-associated antigens leads to enhanced proliferation of peptide-specific CD4 + and CD8 + T cells, 3 and protective immunity against subsequent tumor challenge. [4][5][6][7] The mechanism of this adjuvant activity involves presentation of α-GalCer to iNKT cells by resident dendritic cells (DC), 8 DC maturation, 4 and enhanced DC production of interleukin-12. 9 Chronic lymphocytic leukemia (CLL) represents an attractive target for cellular immunotherapy: a graft-versusleukemia effect can be observed after allogeneic stem cell transplantation, 10 peptide vaccination can induce leukemiaspecific cytotoxic T cells, 11 and remission can be induced using autologous T cells bearing a chimeric antigen receptor directed against CD19.…”

Vaccination with Irradiated Tumor Cells Pulsed with an Adjuvant That Stimulates NKT Cells Is an Effective Treatment for Glioma

“…Although it has also been reported that activated iNKT cells can unexpectedly expand Tregs (51), it is unlikely that the Glioma/Gal vaccine induced Treg activity because Treg depletion was not required for successful prophylactic vaccination. In addition, we have previously shown that an a-GalCer-pulsed dendritic cell vaccine did not alter Treg number or function (13).…”

“…Anticancer vaccines that activate iNKT cells with a-GalCer are highly effective in animal studies, with long-lasting immunity induced in response to coadministration of tumor antigens and a-GalCer (10)(11)(12)(13). This approach has yet to be tested directly in patients with cancer.…”