Abstract
As the entry sites of many pathogens such as human immunodeficiency virus (HIV), mucosal sites are defended by rapidly reacting resident memory T cells (TRM). TRMs represent a special subpopulation of memory T cells that persist long term in non-lymphoid sites without entering the circulation and provide the “sensing and alarming” role in the first-line defense against infection. The rectum and vagina are the two primary mucosal portals for HIV entry. However, compared to vaginal TRM, rectal TRM is poorly understood. Herein, we investigated the optimal vaccination strategy to induce rectal TRM. We identified an intranasal prime–intrarectal boost (pull) strategy that is effective in engaging rectal TRM alongside circulating memory T cells and demonstrated its protective efficacy in mice against infection of Listeria monocytogenes. On the contrary, the same vaccine delivered via either intranasal or intrarectal route failed to raise rectal TRM, setting it apart from vaginal TRM, which can be induced by both intranasal and intrarectal immunizations. Moreover, intramuscular prime was also effective in inducing rectal TRM in combination with intrarectal pull, highlighting the need of a primed systemic T cell response. A comparison of different pull modalities led to the identification that raising rectal TRM is mainly driven by local antigen presence. We further demonstrated the interval between prime and boost steps to be critical for the induction of rectal TRM, revealing circulating recently activated CD8+ T cells as the likely primary pullable precursor of rectal TRM. Altogether, our studies lay a new framework for harnessing rectal TRM in vaccine development.
Highlights
For many human disease-causing pathogens, the first step toward the establishment of a successful infection is to cross the mucosal barrier before getting access to the underlying tissues and, in some cases, further to the systemic circulation
To assess the protectiveness of rectum TRM elicited by the above intranasal prime–intrarectal boost vaccination strategy, we developed a murine model of L. monocytogenes expressing OVA (LM-OVA) infection
We focused on exploring the immunization means to induce a protective rectum TRM response, which might hold the key to a successful human immunodeficiency virus (HIV) vaccine
Summary
For many human disease-causing pathogens, the first step toward the establishment of a successful infection is to cross the mucosal barrier before getting access to the underlying tissues and, in some cases, further to the systemic circulation. An effective immune response against these pathogens constitutes two components: the mucosal response majoring in rapidly detecting the invading pathogens and containing them locally and the systemic immunity, which provides the later enforcement if the frontline mucosal defense is breached [1]. This two-layer defense concept and its implication in vaccine development has been excellently illustrated by the yet unsolved HIV-1 challenge. A reasonable postulation is that systemic immunity, coming into effect after local virus replication, might be “too late and too little” for containing the HIV viruses once they overcome the portal barrier to establish systemic infection [5, 6]
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