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I found the following sentence in the this paper- Safety and immunogenicity of an inactivated SARS-CoV-2 vaccine, BBV152: a double-blind, randomised, phase 1 trial

An imidazoquinoline molecule, which is a toll-like receptor (TLR) 7/8 agonist, has been used to stimulate cell-mediated responses. Algel-IMDG (an imidazoquinoline molecule chemisorbed on alum [Algel]) has been designed to traffic vaccine antigen directly to draining lymph nodes without diffusing into the systemic circulation.

My question is- what is the significance of trafficking vaccine antigen to draining lymph nodes? What will be the consequence if the vaccine diffuses into systemic circulation?

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This paper, Controlling timing and location in vaccines, explains the concept in detail. The TL:DR version is that immune response is affected by the amount of antigen that reaches lymphatic tissue, that is, the tissue where the cells ultimately determining antibody production reside.

With a "non-lymph node-targeting adjuvant" vaccine given intramuscularly, the antigen in the vaccine must diffuse through more tissue, essentially with less reaching lymphatic tissue. With a targeted vaccine, more antigen goes directly where it's most effective, thus hopefully improving immune response.

As antigen availability plays a deterministic role in the strength and type of B cell and T cell responses induced by immunization, optimizing targeting of vaccines to lymph nodes and prolonging antigen availability over an optimal temporal window become key parameters shaping the immune response. As illustrated by recent studies, these are not just “nice to have” features, but can determine the difference between a vaccine inducing neutralizing antibodies or not.

Another theoretical benefit of targeted vaccines is that lower levels of antigen are required to produce the same response, meaning more vaccines can be made from the same amount of antigenic material.

The paper also nicely describes the benefits of nucleic acid vaccines (e.g. the mRNA vaccine).

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