An Albumin-binding Polypeptide Both Targets Cytotoxic T Lymphocyte Vaccines to Lymph Nodes and Boosts Vaccine Presentation by Dendritic Cells

Rationale: Albumin-binding carriers have been shown to target cytotoxic T lymphocyte (CTL) vaccines to lymph nodes (LNs) and improve the efficacy of the vaccines. However, it was not clear whether the improved efficacy is solely due to the LN targeting, which prompted this study. Methods: First, we generated a fusion protein consisting of an albumin-binding domain (ABD) and an immune-tolerant elastin-like polypeptide (iTEP). Then, we examined the binding between this fusion protein, termed ABD-iTEP, and mouse serum albumin (MSA). Next, we evaluated the accumulation of ABD-iTEP in LNs and dendritic cells (DCs) in the LNs. We also analyzed antigen presentation and in vitro T cell activation of vaccines that were delivered by ABD-iTEP and investigated possible underlying mechanisms of the presentation and activation results. Last, we measured CTL responses induced by ABD-iTEP-delivered vaccines in vivo. Results: ABD-iTEP bound with MSA strongly with an affinity of 1.41 nM. This albumin-binding carrier, ABD-iTEP, accumulated in LNs 3-fold more than iTEP, a control carrier that did not bind with albumin. ABD-iTEP also resulted in 4-fold more accumulation in DCs in the LNs than iTEP. Most importantly, ABD-iTEP drastically enhanced the antigen presentation of its vaccine payloads and the T cell activation induced by its payloads. The enhancement was dependent on the formation of the complex between MSA and ABD-iTEP. Meanwhile, the MSA/ABD-iTEP complex was found to have increased stability in acidic subcellular compartments and increased cytosolic accumulation in DCs, which might explain the enhanced vaccine presentation resulting from the complex. Finally, when ABD-iTEP was used to deliver CTL vaccines derived from both self-and non-self-antigens, it boosted the vaccine-induced responses by 2-fold in either case. Conclusion: ABD-iTEP not only targets vaccines to LNs but also promotes the presentation of the vaccines by DCs. Albumin-binding carriers have more than one mechanism to boost the efficacy of CTL vaccines.