Around 40% of humans and Tasmanian devils (Sarcophilus harrisii) develop cancer in their lifetime, compared to less than 10% for most species. In addition, devils are affected by two of the three known transmissible cancers in mammals. Immune checkpoint immunotherapy has transformed human medicine, but a lack of species-specific reagents has limited checkpoint immunology in most species. We developed a cut-and-paste reagent development system and used the fluorescent fusion protein system to show that immune checkpoint interactions are conserved across 160,000,000 years of evolution, CD200 is highly expressed on transmissible tumor cells, and coexpression of CD200R1 can block CD200 surface expression. The system’s versatility across species was demonstrated by fusing a fluorescent reporter to a camelid-derived nanobody that binds human programmed death ligand 1. The evolutionarily conserved pathways suggest that naturally occurring cancers in devils and other species can be used to advance our understanding of cancer and immunological tolerance.

This protocol provides a step-by-step method to create recombinant fluorescent fusion proteins that can be secreted from mammalian cell lines. This builds on many other recombinant protein and fluorescent protein techniques, but is among the first to harness fluorescent fusion proteins secreted directly into cell culture supernatant. This opens new possibilities that are not achievable with proteins produced in bacteria or yeast, such as direct use of the fluorescent protein-secreting cells in live coculture assays. The Fluorescent Adaptable Simple Theranostic (FAST) protein system includes a histidine purification tag and a tobacco etch virus (TEV) cleavage site, allowing the purification tag and fluorescent protein to be removed for therapeutic use. This protocol is split into five parts: (A) In silico characterization of the gene-of-interest (GOI) and protein-of-interest (POI); (B) design of the expression vector; (C) assembly of the expression vector; (D) transfection of a eukaryotic cell line with the expression vector; (E) testing of the recombinant protein. This extensive protocol can be completed with only polymerase chain reaction (PCR) and cell culture training. Additionally, each part of the protocol can be used independently.

A series of layered peripheral checkpoints maintain self-reactive B cells in an unresponsive state. Autoantibody production occurs when these checkpoints are breached; however, when and how this occurs is largely unknown. In particular, how self-reactive B cells are restrained during bystander inflammation in otherwise healthy individuals is poorly understood. A weakness has been the unavailability of methods capable of dissecting physiologically relevant B cell responses without the use of an engineered BCR. Resolving this will provide insights that decipher how this process goes awry during autoimmunity or could be exploited for therapy. In this study, we use a strong adjuvant to provide bystander innate and adaptive signals that promote B cell responsiveness in conjunction with newly developed B cell detection tools to study in detail the ways that peripheral tolerance mechanisms limit the expansion and function of self-reactive B cells activated under these conditions. We show that although self-reactive B cells are recruited into the germinal center, their development does not proceed, possibly because of rapid counterselection. Consequently, differentiation of plasma cells is blunted, and Ab responses are transient and devoid of affinity maturation. We propose this approach, and these tools can be more widely applied to track Ag-specific B cell responses to more disease-relevant Ags, without the need for BCR transgenic mice, in settings where tolerance pathways are compromised or have been genetically manipulated to drive stronger insights into the biology underlying B cell-mediated autoimmunity.