Facilitation of Metastatic Growth by Antilymphocyte Serum

Abstract

IN 1967, we described the phenomenon of concomitant immunity evoked by a homotransplantable lymphoma in hamsters¹. Although growing progressively at the site of transplantation, this tumour initiates a strong and specific immune response such that a second (similar) tumour graft is rejected²; the immune response is cell-mediated and is reminiscent of a homograft reaction³. A second important manifestation of concomitant immunity in tumour-bearing hamsters is the apparent suppression of metastatic growth¹: viable tumour cells are demonstrable in the blood and regional lymph nodes⁴, but there are intense reactive changes in the lymphoid tissues^3,5,6 and metastatic deposits are not established. It follows that if concomitant immunity were weakened in some way, foci of metastatic growth would be expected to appear. One way is to remove the main immunogenic stimulus by excising the tumour 7 days after grafting⁷, a procedure which is followed by the development of metastatic deposits in most animals. We now report results indicating that metastatic growth is also favoured by immunosuppression with antilymphocyte serum (ALS).