It is understood that naïve CD4 and CD8 T cells express the TNF receptor superfamily member CD27, while dendritic cells or activated T cells express the CD27 ligand, CD70. The co-stimulatory interaction of CD27 with its ligand, CD70, enhances the activation and proliferation of naive T cells. Following such activation in humans, there is an upregulation of CD70 on T cells, which can interact with CD27 on other T cells, leading to further enhancement of proliferation. Upon blocking of human CD70, there is a reduction in the proliferation of CD8 T cells, and thus, suggests that CD70 on T cells may serve a role in T cell expansion. This contribution of T cell expressed CD70 has not been well described in mice. As CD70 blocking reduced the proliferation of human T cells, we expected a similar response when stimulating murine T cells. However, we find no reduction in murine lymphocyte expansion when stimulating cells in vitro with anti-CD3 and anti-CD28 while blocking CD70 with FR70 antibody. Furthermore, we see no effect of CD70 blocking when enriching for and stimulating CD4 T cells alone. In vivo, there is no reduction in activation and expansion of CD8 T cells when adoptively transferring CD70 knockout OTI cells to B6 mice. Together, these data lead us to conclude that murine T cells do not exploit CD70 for expansion. In brief, human and mouse T cells differ in their utilization of T cell expressed CD70.