CSF2 and Acidosis: Acidosis-exposed MSCs also stimulate the invasive and clonogenic capacities of osteosarcoma (OS) cells via the secretion of a variety of factors, including colony-stimulating factor 2 (CSF2, also referred to as GM-CSF), CSF3 (also known as G-CSF), bone morphogenetic protein 2 (BMP2), and interleukins 6 and 8 (IL6 and IL8) (46).