Toll-like receptor agonist therapy augments the antitumor activity of adoptively transferred CD8+ T cells without host preconditioning

Abstract

Lymphodepletion enhances adoptive T cell transfer (ACT) therapy by activating the innate immune system via microbes released from the radiation-injured gut. Microbial LPS is a key mediator of lymphodepletion enhancement, but our ability to use these TLR agonists to bolster the potency of T cell-based cancer therapies remains elusive. Herein, we used LPS as a tool to address how and when to use TLR agonists to improve cancer immunotherapy. We utilized the pmel-1 melanoma mouse model. B16F10-bearing mice were lymphodepleted with 5Gy total body irradiation (TBI) and given a tripartite ACT therapy (consisting of transferred pmel-1 CD8+ T cells, vaccination with fowlpox encoding gp100, and IL-2) along with TLR4 agonist LPS. The timing of LPS administration and the requirement of individual components of the tripartite therapy were evaluated. We discovered that while exogenous administration of LPS was able to enhance CD8+ T cells’ tumor destruction, LPS treatment alone did not replace individual components of the tripartite regimen. Interestingly, administering LPS one day before ACT compromised tumor regression. Conversely, administering LPS after ACT potentiated the antitumor effectiveness of the regimen, thereby supporting the expansion of transferred CD8+ T cells over host Treg cells. Non-toxic TLR agonists MPL and CpG also improved ACT therapy. Finally, TBI preconditioning was no longer needed to regress tumors in mice depleted of host CD4+ T cells, given a tripartite ACT regimen and then treated with a TLR agonist. Collectively, our results identify how and when to administer TLR agonists to augment ACT in the absence of host preconditioning. These findings have implications for the design of next generation T cell therapies.