According to a study performed over a -year time period and reported in the Annals of Surgery, 151 patients with malignant melanoma were treated with BCG immunotherapy (NB. BCG is a weakened but live strain of Mycobacterium bovis used as part of the "childhood vaccination regime in European countries", but not in the US.) alone or as an adjunct to surgical therapy. One finding in these studies was that direct injection of metastatic melanoma lesions limited to the skin resulted in 90% regression of the injected lesions and 17% regression of uninjected lesions in immunocompetent patients. Approximately 25% of these patients remained free of disease for 1 to 6 years. Contrastingly, however, direct injections of BCG into the melanomic nodules of patients with subcutaneous metastases resulted in a lower incidence of local control and no long-term survivors.
Give what you know about the immune system, to date, and specifically in respect to the Type IV DTH, how would you interpret these clinical results in terms of the immune mechanism(s) and the differences observed in the two test groups?