Specific tumor memory induced by polyethylene-glycol-modified interleukin-2 requires both helper and cytotoxic T cells.

Local polyethylene-glycol (PEG)-modified interleukin-2 (IL-2) immunotherapy of the guinea pig Line 10 (L10) tumor was previously demonstrated to evoke long-lasting systemic immunity after cure of the tumor and metastases. T cells, most likely the helper T cell subpopulation, were demonstrated to be crucial to the antitumor effects. Here we show that systemic immunity is induced within 7 days after the start of PEG-IL-2 therapy, indicating a rapid systemic priming of L10-specific T cells. No in vitro cytotoxic activity was detected in cell suspensions obtained from the primary tumor site, the regional lymph node or the spleen when isolated during (days 21 and 28) intratumoral treatment with 200,000 IU PEG-IL-2. These data confirm our earlier results obtained with 60,000 IU PEG-IL-2. Moreover, no cytolytic activity was observed in the chromium-release assay after in vitro restimulation with irradiated tumor cells. Specific L10 immunity can be transferred using spleen cell suspensions. Depletion of such a suspension of helper T cells resulted in rejection of the primary tumor in two out of four animals, but all the guinea pigs developed lymph node metastases. Removal of the cytotoxic/suppressor phenotype caused rejection of the dermal tumor in four of eight guinea pigs, but the capacity to prevent lymph node metastases was retained in all animals. Thus, depletion of either subtype reduces, but does not abrogate, the capacity to transfer L10 immunity with spleen cells. In conclusion, our data suggest that tumor cell killing through direct T cell cytotoxicity is not the main mode of action in PEG-IL-2-induced L10 tumor regression. PEG-IL-2 therapy induces early systemic immunity, resulting in rejection of a distant tumor, and the transfer of this immunity depends mainly on the presence of helper T cells, although cytotoxic T cells may also play a role.

PEG-IL-2 therapy of advanced cancer in the guinea pig. Impact of the primary tumor and beneficial effect of cyclophosphamide.

The efficacy of tumor therapy using polyethylene-glycol-modified interleukin-2 (PEG-IL-2), alone or in combination with cyclophosphamide, was studied in advanced metastatic disease in the guinea pig. Line 10 (L10) tumor cells appeared in the axillary lymph node only 7 days after intradermal tumor-cell inoculation, and lymph-node leukocytes were almost completely replaced by tumor cells on day 28. Local treatment of the intradermally growing L10 hepatocarcinoma in the guinea pig with a relatively low dose of PEG-IL-2 resulted in regression of the primary tumor and prevention of lymph-node metastases. Therapy was completely curative (4 out of 5 animals) when started on day 7 or 14 after tumor-cell inoculation. When started on day 21, therapy was effective in only some (2 out of 5 cured) of the treated animals. Anti-tumor effects against the primary tumor and against lymph-node metastases were observed only after intratumoral (i.t.) administration of PEG-IL-2. Injection of the agent into or near lymph-node metastases in the absence of the primary tumor had no curative effect. In PBS/BSA-treated control animals the primary tumor and metastases grew progressively. In the treatment of far advanced metastatic disease, the combination of i.t. administration of PEG-IL-2 and i.p. injection of cyclophosphamide (Cy) resulted in improved anti-tumoral effects (5/5 guinea pigs were cured) when compared with monotherapy using either agent (one and none out of 5 animals cured, respectively). PBS/BSA heated controls showed progressive tumor-growth. We conclude that large primary tumors and lymph-node metastases can be treated effectively with PEG-IL-2. The i.t. route of administration is of major importance in the treatment of metastases, since administration of PEG-IL-2 near or into the lymph node had no therapeutic effect. Combination of PEG-IL-2 therapy with systemic injections of Cy significantly improved the curative effects of the treatment of advanced metastatic cancer.

Effects of sequential intravesical administration of mitomycin C and bacillus Calmette-Guérin on the immune response in the guinea pig bladder.

It has been suggested that intravesical treatment with mitomycin C (MMC) before instillation of bacillus Calmette-Guérin (BCG) improves the antitumor activity of BCG in human bladder cancer. Therefore, we studied the immunological effects of sequential intravesical treatment with MMC and BCG in the guinea pig. Four weekly intravesical instillations with MMC preceded six weekly intravesical BCG instillations. The delayed-type hypersensitivity (DTH) skin reaction evoked by tuberculin purified protein derivative (PPD) in guinea pigs receiving BCG intravesically appeared slightly earlier in animals pretreated intravesically with MMC than in phosphate-buffered saline (PBS)-pretreated animals. However, after completing BCG instillations no differences in DTH reaction were observed between these treatment groups. The extent of the local inflammatory reaction in the bladder wall, as well as the parameters measured in the draining iliacal lymph nodes (i.e., the weight, the number of leukocytes, and the composition of leukocyte subpopulations), did not differ in animals treated with BCG alone or in combination with MMC. A slight increase in the MHC class II expression on the bladder urothelium was shown if MMC and BCG treatment was combined. The adherence of mycobacteria to the bladder wall, measured using 3H-labeled mycobacteria, dit not differ between MMC/BCG- and BCG-treated animals. We conclude that MMC does not enhance the immune response against mycobacteria. Therefore, we hypothesize that a possible increased antitumor activity by the combination of MMC and BCG might be due to separate, rather than synergistic, effects of the drugs, namely a cytostatic effect of MMC on tumor cells and a local immune response in the bladder evoked by BCG.

Locoregional therapy with polyethylene-glycol-modified interleukin-2 of an intradermally growing hepatocellular carcinoma in the guinea pig induces T-cell-mediated antitumor activity.

Therapy with repeated intratumoral and perilymphatic administration of relatively low doses of polyethylene-glycol(PEG)-modified interleukin-2 (IL-2) in the syngeneic guinea pig line 10 (L10) hepatocarcinoma results in significant local tumor growth inhibition and a delay in development of regional lymph node metastases of more than 3 weeks when compared to controls. Occasionally animals are cured of tumor. The mechanism of this antitumor activity was studied. The antitumor activity of locoregionally administered PEG-IL-2 was abrogated by pretreatment with polyclonal anti-thymocyte serum, indicating that the observed tumor growth inhibition was a T-cell-mediated phenomenon. Besides the locoregional tumor growth inhibition, a systemic effect was recorded as the growth of a second tumor cell inoculum at the contralateral side was inhibited as well. Furthermore, those animals cured after PEG-IL-2 therapy developed specific immunity against the L10 tumor and this immunity could be transferred to naive animals by spleen cells. Immunohistological observations of the tumor site revealed a slight increase of helper and cytotoxic T cell subpopulations after PEG-IL-2 therapy. More pronounced, however, was the rise in number of eosinophilic granulocytes present in the stroma surrounding the tumor cells. Involvement of cytotoxic cells in the antitumor effects of PEG-IL-2 could not be demonstrated: regional lymph node cells and spleen cells obtained immediately after therapy (day 15) or on day 21 showed no cytotoxic activity in vitro against L10, K562, Daudi and line 1 (L1) target cells. In conclusion, locoregional therapy with PEG-IL-2 induced a a systemic T-cell-mediated antitumor response. As no cytotoxic T cell activity was measured, however, the underlying mechanism is most likely a T-helper response. Eosinophils at the tumor site may be tumoricidal but further experiments must reveal the role of these cells in the PEG-IL-2-induced tumor regression.

Polyethylene-glycol-modified interleukin-2 is superior to interleukin-2 in locoregional immunotherapy of established guinea-pig tumors.

Polyethylene glycol-modified recombinant human interleukin-2 (PEG-IL-2) represents a cytokine with prolonged circulatory half-life and increased antitumor activity as compared to recombinant interleukin-2 (rIL-2) after systemic administration. We studied whether PEG-IL-2 would also be advantageous in locoregional immunotherapy using a syngeneic tumor model. Intradermal inoculation of line-10 tumor cells into the flanks of strain-2 guinea-pigs results in a fast-growing tumor and regional lymph-node metastases. Treatment schedules were started on day 7 after inoculation in animals with established tumors. First, groups of 5-6 animals were treated with repeated intratumoral and perilymphatic rIL-2 or PEG-IL-2 injections. PEG-IL-2 caused significant growth inhibition of both the primary tumor and the regional lymph-node metastases at lower doses and with less frequent administration than rIL-2. The best schedule for PEG-IL-2 was 3 injections a week for 5 weeks, resulting in cure of 4/17 and 5/5 (p less than 0.01) animals at the 2 most efficient dose levels tested. Subsequent experiments indicated that the intratumoral and not the perilymphatic injection route was essential for the obtained antitumor effect. Furthermore, 12/12 animals cured after PEG-IL-2 treatment rejected a rechallenge with line-10 tumor cells, whereas no cures were seen after rIL-2 injections. PEG-IL-2 therefore appears to be a valuable substance for intratumoral immunotherapy.