IN 1953 John Kidd1 reported a series of experiments showing that subcutaneous mouse lymphomata of two types regressed promptly following intraperitoneal injection of normal guinea pig serum into the mice. The tumor grew normally in untreated controls and in mice injected with rabbit or horse serum. The guinea pig serum had no discernible effect on the tumor cells in vitro. This was the first report of a naturally occurring substance which would cause tumor regression in a single type of cancer without harm to the injected animal.
The experiments reported in this paper were designed to assess the effects of direct contact between sarcoma-180 cells and various animal and human sera on the growth of and immunologic reactions to this tumor in mice. Kidd's experiments suggested that incubation of cancer cells with foreign sera, especially guinea pig serum, might cause the cells to become inactive without discernible effects on