Generation in vivo of peptide-specific cytotoxic T cells and presence of regulatory T cells during vaccination with hTERT (class I and II) peptide-pulsed DCs

Abstract

BackgroundOptimal techniques for DC generation for immunotherapy in cancer are yet to be established. Study aims were to evaluate: (i) DC activation/maturation milieu (TNF-α +/- IFN-α) and its effects on CD8+ hTERT-specific T cell responses to class I epitopes (p540 or p865), (ii) CD8+ hTERT-specific T cell responses elicited by vaccination with class I alone or both class I and II epitope (p766 and p672)-pulsed DCs, prepared without IFN-α, (iii) association between circulating T regulatory cells (Tregs) and clinical responses.MethodsAutologous DCs were generated from 10 patients (HLA-0201) with advanced cancer by culturing CD14+ blood monocytes in the presence of GM-CSF and IL-4 supplemented with TNF-α [DCT] or TNF-α and IFN-α [DCTI]. The capacity of the DCs to induce functional CD8+ T cell responses to hTERT HLA-0201 restricted nonapeptides was assessed by MHC tetramer binding and peptide-specific cytotoxicity. Each DC preparation (DCT or DCTI) was pulsed with only one type of hTERT peptide (p540 or p865) and both preparations were injected into separate lymph node draining regions every 2–3 weeks. This vaccination design enabled comparison of efficacy between DCT and DCTI in generating hTERT peptide specific CD8+ T cells and comparison of class I hTERT peptide (p540 or p865)-loaded DCT with or without class II cognate help (p766 and p672) in 6 patients. T regulatory cells were evaluated in 8 patients.Results(i) DCTIs and DCTs, pulsed with hTERT peptides, were comparable (p = 0.45, t-test) in inducing peptide-specific CD8+ T cell responses. (ii) Class II cognate help, significantly enhanced (p < 0.05, t-test) peptide-specific CD8+T cell responses, compared with class I pulsed DCs alone. (iii) Clinical responders had significantly lower (p < 0.05, Mann-Whitney U test) T regs, compared with non-responders. 4/16 patients experienced partial but transient clinical responses during vaccination. Vaccination was well tolerated with minimal toxicity.ConclusionAddition of IFN-α to ex vivo monocyte-derived DCs, did not significantly enhance peptide-specific T cell responses in vivo, compared with TNF-α alone. Class II cognate help significantly augments peptide-specific T cell responses. Clinically favourable responses were seen in patients with low levels of circulating T regs.

MHC Class II Tetramers

“…Although most tumor Ags are self-Ags or modified self-Ags, intentional immunization with these Ags is conducted for therapeutic benefit. For example, class II tetramer studies in patients with malignant melanoma after experimental vaccine therapies documented evidence of immunogenicity, measured the effects of adjuvant on T cell lineage, and have been used to evaluate shifts in T cell subsets (56)(57)(58)(59). Indeed, because the pMHC complex is itself a surrogate for Ag recognition, it is feasible that tetramers might be considered for therapeutic expansion of Ag-specific effector T cells (60).…”

Combined TLR7/8 and TLR9 Ligands Potentiate the Activity of a Schistosoma japonicum DNA Vaccine

“…A potential issue limiting the immune response to vaccination is the presence of regulatory T cells (Tregs) that suppress T cell activation [8], [9]. Multiple studies in mice have shown that Tregs dampen the immune response against pathogens, including S. japonicum [10], [11].…”

Potential Targets for Pancreatic Cancer Immunotherapeutics

“…In similar studies with a telomerase peptide-pulsed DC vaccine, an antigen-specific CD8 + T-cell response was generated in patients who developed various cancers following vaccination. This response was enhanced when DCs were also pulsed with class II telomerase peptides, illustrating the importance of CD4 + T cells in fighting tumor [58]. Pulse can also be performed with peptides from multiple tumor antigens, as was performed in a Phase I clinical study by Carbone et al Patients with various cancers, including pancreatic cancer, immunized with p53 and K-Ras peptide-pulsed PBMCs saw increased survival [59].…”