Oral Selective TLR8 Agonist Selgantolimod Induces Multiple Immune Cell Responses in Humans

TLR8 agonists have the potential for use as immunomodulatory components in therapeutic modalities for viral infections such as chronic HBV (CHB) and HIV. In this study, using peripheral blood samples from a phase 1a clinical trial, we examined the acute effects of a single oral administration of a selective TLR8 agonist on immune cell phenotypes. Administration of the TLR8 agonist selgantolimod (SLGN) in healthy individuals resulted in alteration in frequencies of peripheral blood monocytes, pDCs, mDCs and MAIT cells. Frequencies of mDCs and lymphoid cells significantly reduced after 8 h of SLGN administration, whereas pDC frequencies significantly increased, with changes possibly reflecting migration of different cell types between peripheral and tissue compartments in response to the agonist. Myeloid cell activation was evident by an upregulated expression of co-stimulatory molecules CD40 and CD86 accompanied by the production of IL-6 and IL-18 from these cells. Concomitantly, there was induction of the early activation marker CD69 on innate and adaptive lymphoid cells, including MAIT and NK cell subsets. Further, these activated lymphoid cells had enhanced expression of the effector molecules granzyme B and perforin. Microarray analysis of isolated lymphocytes and monocytes from baseline and post-SLGN treatment revealed changes in expression of genes involved in cellular response to cytokine stimulus, innate immune response, myeloid cell differentiation and antigen receptor-mediated signaling pathway. In a preliminary analysis of samples from CHB patients treated with selgantolimod, activation of innate and adaptive lymphocytes was evident. In conclusion, this first in-human study shows that selgantolimod administration in humans results in activation of multiple immune cell responses with antiviral potential.