Reevaluation of the Superiority of Polyethylene GlycolModified Interleukin-2 Over Regular Recombinant Interleukin-2

Other groups have reported a superior antitumor efficacy of polyethylene glycol-modified interleukin-2 (PEG-IL-2) compared with regular recombinant interleukin-2 (rIL-2). However, detailed comparison of the antitumor efficacies of locally applied PEG-IL-2 and rIL-2 in the well-established DBA/2-SL2 model shows a higher antitumor efficacy of PEG-IL-2 only at doses < 800 μg IL-2 protein/kg body weight. At doses > 800 μg IL-2 protein/kg body weight, rIL-2 has better therapeutic efficacy. The superiority of rIL-2 at doses > 800 μg IL-2 protein/kg body weight is a result of the toxicity of PEG-IL-2 at these doses. With either IL-2 preparation, cure rates of approximately 90% can be obtained at nontoxic doses. We conclude that PEG-IL-2 does not have superior antitumor efficacy to rIL-2. The main advantage of PEG-IL-2 is that for optimal therapeutic efficacy a daily injection schedule is not required as seems to be the case for rIL-2.