Influence of factors derived from EMT6 tumors and from bone marrow of tumor-bearing mice on tumor and bone marrow stem cell kinetics.

Untreated EMT6 tumors in BALB/c mice were used to assess the regulatory mechanisms of tumor growth in these animals. This tumor can be quantitated for clonogenic cells by in vitro techniques, and the hydroxyurea suicide method makes it possible to determine the kinetic status of the clonogenic cells. The untreated EMT6 tumor does not seem to have internal humoral regulatory mechanisms explaining tumor growth kinetics. However, the exponentially growing EMT6 experimental tumor releases a factor capable of stimulating quiescent splenic colony-forming units into cycle. This is also true of bone marrow taken from tumor-bearing mice. This study was made possible using an in vivo-in vitro technique which separates the effector cells from the responder cells by a Millipore filter floating on the culture medium. The relationship between tumor growth and normal hematopoietic tissue of the tumor-bearing animal is discussed.