Adhesion molecules involved in the trafficking of normal and malignant leukocytes

Adhesion molecules involved in leukocyte recruitment and lymphocyte recirculation impact on several aspects of tumor biology--the primary host response, the delivery of effective adoptive immunotherapy and the hematogenous spread of malignant cells. Common to all three processes are receptor-mediated adhesive interactions between circulating cells and the vessel wall. Recruitment of circulating lymphocytes, monocytes and natural killer cells is essential for an effective host response or successful adoptive immunotherapy. Thus poor induction or blockade of leukocyte binding sites on the microvasculature of tumor implants may help malignancies evade natural defenses. In addition, perturbation of adhesion receptor function during ex vivo expansion may alter the behavior of infused cells in adoptive immunotherapy protocols. Finally, circulating malignant cells may utilize receptors normally involved in recruitment and recirculation. This paper reviews the function and regulation of adhesion molecules involved in normal leukocyte trafficking. The evidence implicating specific adhesion receptors in the spread of lymphoid malignancies through the bloodstream is then discussed.