When VSV∆M51-FLUC was used both as a first and a second treatment, depletion of monocytes by CLL (Fig. 3c) or by administration of anti-CCR2 (Fig. 3d) resulted in less overall infection of the tumor, indicating the enhanced and sustained infectivity observed in response to the second OV dose was inhibited in monocyte-depleted animals. The gene discussed is CCR2; the disease is infection.