Studies with a spontaneous murine tumour--I. Indetectibility of host immune resistance with tumour-activated elaboration of T cell stimulatory lymphokines in vitro.

A spontaneous tumour SP/N-1 which arose in a BALB/c female mouse and histologically consistent with breast origin was studied in vivo and in vitro to assess host responses to the tumour. Examination by means of the established methods of tumour cell challenge and cell transfer assays following 'immunization' of the isogeneic host against the tumour failed to provide clear evidence of host recognition and reactivity. Cell transfers conducted using critical numbers of tumour cells in which tumour to spleen cell ratios of up to 1:1000 were employed did not show any sign of antitumour activity within the pretreated host spleen cells. Nor was there any evidence of host resistance when presensitized mice were challenged with graded doses of tumour cells ranging from 10(4) cells, with no take of tumours, to 5 X 10(4) cells, with total acceptance of the tumour by the challenged mice. Despite failures to demonstrate clear immune recognition of tumour by the above criteria, normal spleen cells when incubated with the tumour cells in vitro elaborated factors with stimulatory and possibly suppressive properties. At least one of these factors was shown to stimulate T cells as evidenced by stimulation of DNA synthesis in thymocytes. This could be shown readily in the presence of a submitogenic concentration of Con A.