Microcytotoxicity and serum blocking factors in malignant melanoma and halo nevus

Microcytotoxicity assays of patients with malignant melanoma and halo nevi were performed. No good correlation could be found between percent cell inhibition and histopathological level of melanoma or the clinical staging. The percent cell inhibition was usually an index of response to vaccinia virus immunotherapy. Actively regressing halo nevi showed high levels of percent cell inhibition, whereas inactive halo nevi had low levels of percent cell inhibition and blocking factor. Immunologic reactivity to melanoma cells may be a common feature of melanoma and halo nevus.