| Summary: | Depending on their state of maturation, dendritic cells (DCs) might initiate immune suppression or immune activation in DC-targeted therapies. In cases where immune activation is desired, adjuvants are often co-administered to augment the immune response. But adjuvants that rely on the use of pathogen-associated molecular patterns (PAMPS) pose the potential threat of toxicity. Thus, we explored antibody receptors in the body and found that we can utilize the Tripartite Motif-containing 21 (TRIM21) pathway. TRIM21 is a cytosolic receptor of the Fragment Cystallizable (Fc) region of antibodies. Antibodies bound to cell-invading pathogens can in some cases enter the cytosol as an immune complex (IC) and recruit TRIM21. Following the binding to IC, TRIM21 mediates intracellular neutralization of the pathogen and immune signaling pathways. We postulated that improving the affinity of antibody Fc to TRIM21 should enhance TRIM21-mediated activity and possibly improve the activation status of DCs. In this study, we have designed and generated modified antibodies carrying an Fc region that was engineered for enhanced binding to human TRIM21. As an investigative model, adenovirus was used as an infection model that carries anti-adenovirus antibody into the cytosolic compartment of human monocyte-derived DC (moDC). Adenoviruses complexed with modified antibodies promoted heightened moDC maturation, which was independent of FcγR binding. The matured moDCs led to an increase in IFN-γ production and adenovirus-specific T cell proliferation in a co-culture containing T cells. Co-immunoprecipitation of antibodies revealed intracellular interaction between antibody and TRIM21, but only antibody bearing the engineered Fc was massively retained within the cell. This likely augmented moDC activation. Transcriptomic data suggests that modified antibody boosted immune-related signaling in human moDCs, which was supported by the upregulation of TRIM21-dependent NF-κB signaling response observed in HEK293T cells. Further work is required to elucidate the involvement of TRIM21 in antibody retainment. Preliminary results on hTRIM21-transgenic mouse model indicated that antigen-conjugated anti-DEC205 with engineered Fc might lead to the expansion of antigen-specific CD8 T cells and modulate anti-tumor immune response. Our study presents a novel alternative to conventional adjuvants, and can be translated for application with DC-targeted therapies.
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