As a possible alternate to existing in vitro assays of cell mediated host responsiveness to tumour, a modification of the leucocyte adherence inhibition test employing peripheral blood lymphocytes (PBL), has been evaluated in patients with adenocarcinoma of the prostate. PBL from patients with prostatic cancer reacted to varying degrees with 3 M KCl extracts of autologous and allogeneic prostatic tumours when cultured in the presence of homologous serum. When sensitized PBL and tumour extract were cultured in autologous serum, inhibition ('blocking') of the interaction of PBL and antigen was observed. 'Blocking' was not observed when the tumour extract was allogeneic with respect to the origin of PBL and serum. Cross reactivity between individual tumours within a given tumour type is in keeping with observations of anti tumour immunity in patients with other tumours. Observations suggestive of a specificity of 'blocking' for autologous tumour only, is somewhat unique and will require further confirmation. While preliminary, these results provide further evidence suggestive of anti tumour cell mediated immunity in prostatic cancer patients previously observed by inhibition of leucocyte migration. The observed 'blocking' effect of autologous serum may be analogous to that observed in the technically more complex colony inhibition and lymphocyte cytotoxicity tests and may be indicative of one means by which the potential effects of sensitized PBL are inhibited in vivo.
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