A Highly Active Form of XCL1/Lymphotactin Functions as an Effective Adjuvant to Recruit Cross-Presenting Dendritic Cells for Induction of Effector and Memory CD8+ T Cells

Abstract

The chemokine receptor XCR1 is known to be selectively expressed by cross-presenting dendritic cells (DCs), while its ligand XCL1/lymphotactin is mainly produced by activated CD8+ T cells and natural killer cells. Recent studies have shown that XCL1-antigen fusion proteins efficiently induce CD8+ T cell responses by preferentially delivering antigens to XCR1+ DCs. However, XCL1 per se was found to be a poor adjuvant for induction of CD8+ T cell responses. XCL1 is unique because of its lack of one of the two disulfide bonds commonly conserved in all other chemokines and thus has an unstable structure with a relatively weak chemokine activity. In the present study, we generated a variant form of murine XCL1 termed mXCL1-V21C/A59C that contained a second disulfide bond to stabilize its chemokine structure. We confirmed that mXCL1-V21C/A59C had much more potent chemotactic and calcium mobilization activities than the wild type XCL1 (mXCL1-WT). Intradermal injection of mXCL1-V21C/A59C, but not that of mXCL1-WT, significantly increased the accumulation of XCR1+CD103+ DCs in the injection site, and most of the accumulated XCR1+CD103+ DCs were found to take up co-injected ovalbumin (OVA). Furthermore, recruited XCR1+CD103+ DCs efficiently migrated to the draining lymph nodes and stayed for a prolonged period of time. Consequently, mXCL1-V21C/A59C strongly induced OVA-specific CD8+ T cells. The combination of OVA and mXCL1-V21C/A59C well protected mice from E.G7-OVA tumor growth in both prophylactic and therapeutic protocols. Finally, memory CTL responses were efficiently induced in mice immunized with OVA and mXCL1-V21C/A59C. Although intradermal injection of OVA and polyinosinic-polycytidylic acid (poly(I:C)) as an adjuvant also induced CD8+ T cell responses to OVA, poly (I:C) poorly recruited XCR1+CD103+ DCs in the injection site and failed to induce significant memory CTL responses to OVA. Collectively, our findings demonstrate that a highly active form of XCL1 is a promising vaccine adjuvant for cross-presenting DCs to induce antigen-specific effector and memory CD8+ T cells.

Structure-function guided modeling of chemokine-GPCR specificity for the chemokine XCL1 and its receptor XCR1

“…Our previous work demonstrated that XCL1 CC3 was slightly more potent than XCL1 WT as XCR1 agonist in an intracellular Ca 2+ -flux assay (29). A recent study demonstrated that a murine version of XCL1 CC3 is a more potent XCR1 agonist in vitro than is WT mXCL1 and is more effective in vivo as an adjuvant for the induction of antigen-specific effector CD8 + T cells (35).…”

Tumor-Intrinsic or Drug-Induced Immunogenicity Dictates the Therapeutic Success of the PD1/PDL Axis Blockade

“…Their selective ablation massively impairs T cell mediated tumor regression [40]. In a model of vaccination, adjuvant-driven recruitment of CD103 + DCs was required to induce significant memory CTL responses to ovalbumin [41]. Expression of inhibitory molecules, including PDL1 and PDL2, by DCs mitigates their stimulatory ability in the TME, thus limiting CD8 + T-mediated responses [42].…”

Functional Role of Dendritic Cell Subsets in Cancer Progression and Clinical Implications

“…Although resident CD8α + cDC1s may also be involved, migratory CD103 + cDC1s have unique abilities in tumor-antigen cross presentation [27,32]. The expression of XCR1 is crucial for cDC1 functions, since it favors their localization in response to the ligand (XCL1) produced by CTLs and NK cells and the XCR1/XCL1 axis appears indispensable in the development of efficient cytotoxic immunity [33,34]. cDC1s in turn orchestrate local anti-tumor immunity, being the main producer of CXCL9 and CXCL10, two chemokines active on CXCR3 + effector T and NK cells [28,35].…”