De-orphanizing CD271: a novel regulator of T cell function 2300697

Abstract Introduction Co-signaling molecules are central regulators of the immune system, positively and negatively tuning immune cell activation. Many co-signaling molecules belong to the immunoglobulin or tumor necrosis factor receptor superfamilies and are being targeted in the clinic to reinvigorate anti-tumor immunity. However, the cognate receptor of several family members with co-inhibitory activity remains unknown. Among these, CD271, the low-affinity nerve growth factor receptor, is expressed by immunomodulatory cells and cancer cells. While CD271 expression in melanoma correlates with a poor response to immune checkpoint blockade, its impact on T cell function is not well characterized. Therefore, we sought to determine if CD271 directly interacts with T cells to modulate their activation. Methods The impact of CD271 on T cell activation was assessed in vitro. We stimulated mouse and human T cells with plate-bound αCD3/αCD28 in the presence or absence of CD271-Fc. T cell proliferation and cytokine production were assessed by flow cytometry. To identify CD271 partners, we performed cell-based binding assays as well as a CRISPRa-based protein interaction screen. Results We find that CD271 inhibits T cell proliferation in vitro. We confirmed that CD271 binds to human CD80, but that this interaction does not account for the inhibitory effect of CD271. To further investigate which receptor interacts with CD271, we optimized a CRISPRa protein interaction platform that enables robust expression of all known surface receptors. Using CD271-coated beads, we enrich cells expressing CD271 ligands. Conclusion We identified CD271 as a novel immunoregulatory protein that can directly inhibit T cell activation in vitro. We are developing scalable, cell-based assays to systematically identify CD271 binding partners as well as de-oprhanize co-signaling molecules within the immunoglobulin and tumor necrosis factor receptor superfamilies, offering insights into immune regulation and new targets for immune checkpoint blockade. Funding Source Canadian Institutes of Health Research Topic Categories Immune Response Regulation: Molecular Mechanisms (IRM)