Protective CD8 T Cell Immunity Triggered by CpG-Protein Conjugates Competes with the Efficacy of Live Vaccines

Abstract

In contrast to infectious (live) vaccines are those based on subunit Ag that are notoriously poor in eliciting protective CD8 T cell responses, presumably because subunit Ags become insufficiently cross-presented by dendritic cells (DCs) and because the latter need to be activated to acquire competence for cross-priming. In this study, we show that CpG-Ag complexes overcome these limitations. OVA covalently linked to CpG-DNA (CpG-OVA complex), once it is efficiently internalized by DCs via DNA receptor-mediated endocytosis, is translocated to lysosomal-associated membrane protein 1 (LAMP-1)-positive endosomal-lysosomal compartments recently shown to display competence for cross-presentation. In parallel, CpG-OVA complex loaded DCs become activated and acquire characteristics of professional APCs. In vivo, a single s.c. dose of CpG-OVA complex (10 μg of protein) induces primary and secondary clonal expansion/contraction of Ag-specific CD8 T cells similar in kinetics to live vaccines; examples including Listeria monocytogenes genetically engineered to produce OVA (LM-OVA) and two viral vector-based OVA vaccines analyzed. Interestingly, CpG-OVA complex induced almost equal percentages of Ag-specific memory CD8 T cells as did infection with LM-OVA. A single dose vaccination with CpG-OVA complex protected mice against lethal doses of LM-OVA. These data underscore that the synergy imparted by CpG-OVA complex-mediated combined triggering of innate and specific immunity might be key to initiate CD8 T cell-based immunoprotection by synthetic vaccines based on subunit Ag.

Intracellular Cleavable CpG Oligodeoxynucleotide-Antigen Conjugate Enhances Anti-tumor Immunity

“…The dose of 10 mg antigen per injection was based on previous studies that also reported strong induction of cytotoxicity by both stable conjugates as well as mixtures of antigen and adjuvant. 10,11 In our study, very high cytotoxicity of 99% was observed following vaccination of the mice with the conjugates as well as a boost injection of the conjugates after 3 weeks. The strong cytotoxicity induced by SS comparable to both HYN and HYN-SS that was higher than that induced by the mixture of CpG and OVA was unexpected.…”

“…9,11 We hypothesize that if the antigen adjuvant components of the conjugate are released from each other once the conjugate has entered, the cell the antigen and adjuvant will be more readily available for processing. In this study we describe the enhancement of the immune response of the OVA-CpG conjugate when the OVA and CpG are linked via a disulphide bond that was shown in vitro to be specifically cleaved by the higher intracellular GSH concentration of the cytosol.…”

“…[6][7][8][9][10] In soluble conjugates, the tumor antigen is directly conjugated to a vaccine adjuvant as a means for co-delivery and has been shown to induce a strong immune response. 9,11,12 However, the direct conjugation of antigen to adjuvant may obstruct both the processing of the antigen for presentation to T cells as well as the binding of the adjuvant to the target toll-like receptor (TLR) for complete activation of the APC.…”

Structure and Immune Adjuvant Properties of CPG-D

“…Со-вместное введение, комплексирование антигена и CpG-ОДН может оптимизировать индукцию антиген-специфического иммунного ответа [16]. Кроме того, для повышения адъювантной активности CpG-ОДН компоненты вакцины возможно вводить в комплексе с различны-ми носителями: наночастицами, микросфера-ми, липосомами, что способствует активации сильного антиген-специфического иммунного ответа [31].…”

Dendritic cells in cancer immunotherapy

“…Differential expression of receptors might allow targeting of select DC subsets and ''tailor-made'' immunization [19,20]. Effective immunization was also observed following delivery of TLR ligand-antigen conjugates, which contain the maturation stimulus but are not as precise in cell targeting [21]. Although the in situ targeting strategy is clearly a promising approach, one caveat is that in diseased patients, DC subsets and precursors as well as their receptor expression may be variable and even abnormal so that translation into the clinic might hold unexpected surprises.…”