Correlation between in vitro and in vivo sensitivity to human leucocyte interferon in patients with multiple myeloma.

26 of 32 patients with multiple myeloma (MM) were successfully tested in vitro for human leucocyte interferon (IFN) sensitivity by use of the human tumour stem cell assay (HTCA) and/or 3H-thymidine incorporation (LI). Altogether, 12 patients were sensitive to IFN in vitro and 14 were resistant. All patients received treatment with leucocyte IFN. 8 patients were classified as responders, 3 as partial responders and 15 as non-responders. Correlating the in vitro/in vivo results, we found that the in vitro tests of the myeloma cells reflected a true sensitivity in 9 patients (75%) and a true resistance in 12 patients (86%). Furthermore, stimulation by IFN was found in 9 in vitro tests, of which 8 were obtained from non-responsive patients. Our results show that in vitro testing for IFN sensitivity is of clinical importance in predicting response to IFN treatment. Also, a stimulating effect by IFN in vitro will imply an unfavourable response in vivo.