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Summary.-The leucocyte adherence inhibition (LAI) test, previously described for the detection of cell mediated immunity and serum blocking factors associated with murine tumours, has now been adapted for use with human cancer patients. Blood leucocytes from these patients, mixed in vitro with antigenic extracts of tumours of the same type, had their normal adherence to glass surfaces diminished. This inhibition was reversed (blocked) by the addition of the patients' own sera. Both LAI and blocking were tumour-type specific, but showed complete cross-reactivity within each type of tumour (melanoma, colon carcinoma, mammary carcinoma).The LAI test could be of great value in diagnosis and evaluation of treatment, since it seems to reproduce consistently the findings made by more elaborate techniques but has the advantage of being simple, rapid and inexpensive.

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The leukocyte adherence inhibition (LAI) test has been used to assess specific anti-tumour immunoreactivity in 80 patients with malignant melanoma, 21 of whom had apparently been successfully treated by surgery, and 44 control subjects. Reaction with melanoma extracts in vitro enabled the activity of blood leukocytes to be detected by inhibition of their adherence to glass, while serum was tested for factors which modified this inhibition. Of the patients with tumours (ranging from primary melanoma in situ to advanced disseminated disease), 22/24 had active leukocytes and 50/58 has serum blocking factor; two of the sera, from patients with regressing tumours were unblocking. After surgery with no clinical recurrence, leukocytes continued to be active except when tested several years after operation. Blocking factor rapidly disappeared in 16/20 patients tested, and in several patients examined serially the serum became unblocking. In three cases, persistence of serum blocking was followed by clinical diagnosis of metastases. Leukocyte activity was nerver detected in control subjects (0/10), many of whom had other kinds of tumours or skin lesions. Blocking activity in serum was found in only 3/38 controls with no history of melanoma (1 had a fibrosing cellular blue naevus and 2 had liver disease). Thus the LAI test correlated well with clinical and pathological findings, and shows great promise for the reliable, rapid and specific immunodiagnosis of malignant melanoma.