Advantages of Adoptive Chemoimmunotherapy with Polyethylene Glycol-cultured, Antigen-activated, Tumor-infiltrated Spleen Cells for the Complete Eradication of Lethal MOPC-315 Plasmacytomas¹

The incorporation of polyethylene glycol-6000 (PEG) into the culture media of tumor-infiltrated spleen cells (TISpC) and MOPC-315 stimulator tumor cells at a responder to stimulator cell ratio of 30/1 had been shown to lead to the appearance of CD8⁺ T-cells that were effective in adoptive chemoimmunotherapy (ACIT) of mice bearing a barely palpable MOPC-315 tumor (J. A. Wise, M. B. Mokyr, and S. Dray, Cancer Res., 49: 3613–3619, 1989). Here we show that in the presence of substantially fewer added stimulator tumor cells (responder to stimulator cell ratio, 100/1), the inclusion of PEG in the cultures of TISpC also enhanced the appearance of cells that were highly effective in curing such mice by ACIT. Moreover, these PEG-cultured TISpC were more effective in ACIT than TISpC cultured in the presence of an optimal concentration of recombinant interleukin-2 (60 IU/ml). The potency of the tumoreradicating activity of the PEG-cultured TISpC in ACIT was further illustrated by their ability to cause the complete regression of a large (20–22 mm) s.c. MOPC-315 tumor in conjunction with a dose of drug that by itself did not cause tumor regression. PEG-cultured TISpC that were effective in ACIT were capable of exerting a potent, direct, in vitro lytic activity against MOPC-315 tumor cells in an antigen-specific manner. In fact, PEG-cultured TISpC were more effective than recombinant interleukin-2-cultured TISpC, not only in ACIT, but also in their ability to lyse MOPC-315 tumor cells in vitro. Thus, a direct specific lytic activity against the tumor by cytotoxic T-lymphocytes is the apparent mechanism through which the complete regression of the large tumor burden is brought about by the PEG-cultured TISpC. Finally, we suggest that the incorporation of PEG to render ineffective lymphoid cells effective in ACIT may offer some advantages compared with the incorporation of recombinant interleukin-2 and may be suitable for protocols to generate human cytotoxic cells for cancer therapy when there are relatively low numbers of available tumor cells.