**Recent Developments**

Since the completion of our Special Issue, a few interesting biological activities of TCTP have been reported in non-vertebrate organisms. Some examples are its role in the growth, development and differentiation of the slime mold *Dictyostelium discoideum* [21]; the importance in *Drosophila* for epithelial integrity and organ growth [22]; and in *Toxoplasma gondii* for robust growth of the parasite and for the maintenance of its virulence [23]. Recognizing the importance of TCTP for the survival of unicellular parasites, Bossard et al. [24] took the step to test the efficacy of immunizing mice against the parasitic TCTP of *Trypanosoma brucei*. The immunized mice displayed a reduced first peak of parasitemia, a two-fold delay in the onset of the second peak and an increased time of survival, compared to the control animals.

The group of Kyunglim Lee investigated the metabolic importance of TCTP in mice. They generated a TCTP-overexpressing mouse and found that these display an improved metabolic homeostasis, with enhanced glucose tolerance, insulin sensitivity, and energy expenditure, compared to control mice [25]. In another paper, the group studied the importance of TCTP in rheumatoid arthritis (RA) [26]. They found that TCTP levels are increased in the sera and synovial fluids of patients with RA, compared to control groups. Their results indicate that TCTP might serve as a biomarker and a therapeutic target in RA patients. A novel tumor–promoting role of TCTP has just been published in Nature Immunology [27]. The authors observed that the release of TCTP from necrotic cancer cells switches on an immunosuppressive network of myeloid-derived suppressor cells, which substantially contributes to the suppression of antitumor immunity, and thus to tumor progression. All these examples show that we can still expect new facets of TCTP's role to be unraveled, both regarding its biological and its disease-promoting activities.

**Funding:** U.-A.B. received small grants from the Illawarra Health and Medical Research Institute, University of Wollongong. T.K. was supported by the US National Institutes of Health grants, AI146042 and AI153867.

**Acknowledgments:** We thank all authors who contributed to this Special Issue. The guidance by Janet Yan and her colleagues through the editorial process is highly appreciated. We thank the Editorial team of *Cells* for the opportunity to serve as Guest Editors for this Special Issue.

**Conflicts of Interest:** The authors declare no conflict of interest.
