Taming immune suppressor: application of myeloid-derived suppressor cells in anti-cancer gene therapy

Myeloid-derived suppressor cells (MDSCs) are immune regulatory myeloid cells, which have emerged as critical regulators of tumor progression and therapy resistance through promoting immune suppression and contributing to tumor vasculature development mechanisms (1-6). Human and mice MDSCs differ in surface, cytoplasmic and nuclear markers (2,7,8). MDSCs characterization and functions have been updated time-to-time (9). After decades of MDSC discovery, we have gained ample knowledge that how MDSC works to promote cancer associated immune suppression. However, in the translational era, scientist started exploiting old knowledge to develop next generation therapeutic modalities. In the same line of thought, Apolloni et al. developed a MDSC cell line using mouse MDSCs (CD11b⁺/Gr-1⁺) isolated from the spleens of immunosuppressed mice (10). MDSCs were immortalized using a retrovirus encoding the v-myc and v-raf oncogenes, which expressed monocyte/macrophage markers (10). Establishing MDSC cell line has opened a new door for its tremendous applications in cancer therapy.