Role of MDA5 and interferon-I in dendritic cells for T cell expansion by anti-tumor peptide vaccines in mice

Abstract

Cytotoxic T lymphocytes (CTLs) are effective components of the immune system capable of destroying tumor cells. Generation of CTLs using peptide vaccines is a practical approach to treat cancer. We have previously described a peptide vaccination strategy that generates vast numbers of endogenous tumor-reactive CTLs after two sequential immunizations (prime-boost) using poly-ICLC adjuvant, which stimulates endosomal toll-like receptor 3 (TLR3) and cytoplasmic melanoma differentiation antigen 5 (MDA5). Dendritic cells (DCs) play an important role not only in antigen presentation but are critical in generating costimulatory cytokines that promote CTL expansion. Poly-ICLC was shown to be more effective than poly-IC in generating type-I interferon (IFN-I) in various DC subsets, through its enhanced ability to escape the endosomal compartment and stimulate MDA5. In our system, IFN-I did not directly function as a T cell costimulatory cytokine, but enhanced CTL expansion through the induction of IL15. With palmitoylated peptide vaccines, CD8α+ DCs were essential for peptide crosspresentation. For vaccine boosts, non-professional antigen-presenting cells were able to present minimal epitope peptides, but DCs were still required for CTL expansions through the production of IFN-I mediated by poly-ICLC. Overall, these results clarify the roles of DCs, TLR3, MDA5, IFN-I and IL15 in the generation of vast and effective antitumor CTL responses using peptide and poly-IC vaccines.

Poly-IC enhances the effectiveness of cancer immunotherapy by promoting T cell tumor infiltration

“…We previously reported that intravenous injections of PICLC into mice resulted in more than 10-fold higher production levels of IFN-I as compared with poly-IC, which was mediated by MDA5 and not TLR3. 32 Several experiments presented here provide evidence that the stromal cells responding to PICLC are VECs, which would make sense since these cells play a critical role in allowing T cell infiltration into tissues where they are needed. It is well-known that VECs express numerous scavenger receptors allowing them to capture molecules such as lipids and nucleic acids.…”

“…In vitro studies with DCs using a proton sponge inhibitor bafilomycin A1 have shown that IFN-I production by PICLC requires endosomal escape via this mechanism. 32 VECs stimulated with PICLC upregulated VCAM-I, CXCL10 and CXCL9, which play an important role in T cell tissue infiltration. 11 12 14 24 Interestingly, systemic administration of PICLC promoted T cell infiltration into tumors while not affecting much T cell infiltration into other organs.…”

The route of administration dictates the immunogenicity of peptide-based cancer vaccines in mice

“…TnTR1 TCR-transnuclear mice (Trp1 455-463 specific CTLs RAG1-KO) were described [23]. Transgenic mice that express the TCR specific for gp100 [25][26][27][28][29][30][31][32][33] (pmel-1 mice) [24], or Ova 257-264 restricted TCR (OT-1 mice), were purchased from The Jackson Laboratory. Trp1-KO B6 mice were generated in our facility by breeding F1 mice of TRP-1 TCR Bw RAG-mice (Jackson Laboratory Stock No.…”

“…In previous studies we reported that peptide vaccines administered with poly-ICLC adjuvant (TLR3 and MDA5 agonist) in a prime-boost protocol induced vast CD8 T cell responses that lead to significant antitumor effects in mice [17,[25][26][27]. Amphiphilic peptides such as those conjugates with palmitic acid chains (pam-peptides), which self-assemble into nanoparticles were more immunogenic than minimal peptide epitopes or long peptides (LPs) [17].…”

In Laboratory Generation and Maturation of Human Monocyte-Derived Dendritic Cells for Cancer Immunotherapy

“…During the T cell activation, DC engages the T-cell receptor (TCR), secrete specific cytokines and stimulate the immune responses toward TH1, TH2, or Tregs depending on the cytokine environment. Due to their proficiency at antigen crosspresentation (i.e., the presentation to both CD4+and CD8+T cells), DC have been used as vaccine platforms to induce anti-tumor cytotoxic T lymphocyte (CTL) CD8 immune responses [8,9].…”