In vitro antitumor reactivity of mononuclear leukocytes from cancer patients receiving immunotherapy with BCG

Mononuclear cell‐mediated cytotoxicity (MCMC) against cultured tumor target cells was studied sequentially in melanoma and breast cancer patients before and during BCG administration. MCMC showed temporary fluctuations. In patients with locally advanced melanoma and carcinoma of the breast after tumor load reduction, the administration of BCG may increase the MCMC. This did not always correlate with a favorable clinical course. Potentiating serum factors appeared in 50% of these patients during BCG therapy, while blocking factors were rare. Neither correlated with prognosis. In patients with disseminated melanoma receiving chemoimmunotherapy, increases in MCMC may be related to clinical course. Blocking serum factors frequently developed in this group of patients and potentiating factors were rare. Neither correlated with the clinical course. Significant MCMC among normal donors and the apparent lack of specificity suggest a common non‐specific (? natural) cellular reactivity against cultured tumor target cells.