Abstract
Abstract During aging, homeostatic maintenance of naïve T cells in secondary lymphoid tissues (SLT) is lost, leading to reduced cell numbers, a loss of stem-like properties and partial differentiation. The underlying mechanisms that drive these changes are unclear. Moreover, mechanistic studies in humans are currently limited by poor T cell homeostasis in standard in vitro culture and in humanized mice. Thus, we sought to develop a robust culture system mimicking SLT that maintains human T cell survival and homeostasis. In our system, we encapsulate human T cells into a bioengineered matrix containing primary fibroblastic reticular cells (FRC), which are stromal cells that support T cell homeostasis within SLT in vivo. Within these SLT-like organoids, resting naïve T cells from young donors exhibited significantly higher viability and dramatically longer survival times (> 3 weeks) compared with two-dimensional (2D) T cell-FRC cultures. Survival was not driven by T cell receptor activation or proliferation. Moreover, naïve T cells maintained a quiescent-like phenotype (CD45RAhighCD27high), which is a phenotype preferentially lost by naïve T cells in 2D culture as well as during aging. Using small molecule screening, we found that inhibition of adenosine receptor signaling caused naïve T cells to break quiescence and acquire a partially differentiated phenotype (CD45RAlow) similar to that of naïve T cells from older individuals. As old naïve T cells expressed similar levels of adenosine receptors as young, these data suggest that the loss of adenosine within SLT may contribute to immune aging. Thus, we have developed a new, malleable model system that allows for mechanistic investigation into human T cell homeostasis and the effects of aging.