A randomized phase II trial of SRL172 (Mycobacterium vaccae) +/- low-dose interleukin-2 in the treatment of metastatic malignant melanoma

We conducted a randomized phase II trial of SRL172 (Mycobacterium vaccae) +/- low-dose interleukin-2 (IL-2) as treatment for stage IV malignant melanoma. The objectives were to establish the safety and efficacy of SRL172 with and without IL-2. All patients had measurable metastatic disease and none received concurrent chemotherapy, radiotherapy, corticosteroids or any other investigational agent. Sixteen patients were randomized into each arm of the trial prior to closure. The trial was halted prematurely when no responses were seen in the first 16 patients receiving SRL172 alone, predicting a response rate of less than 20%. Three partial remissions were seen in the 16 patients receiving SRL172 + IL-2. These patients remained on monthly SRL172 + IL-2, with disease progression at 12, 15 and 23 months. They continued on the trial regimen following surgical management of their disease progression. This trial provides preliminary evidence of a new, non-toxic, immunotherapeutic regimen in the management of malignant melanoma. Further trials are required to establish a definitive response rate and to compare the combination regimen with the regimen of low-dose IL-2 used in this trial. A biological basis for the responses seen in the SRL172 + IL-2 arm also needs to be established.