Induction of cytotoxicity from fresh splenocytes after in vivo administration of cyclophosphamide. Importance of long-term culture with high-dose recombinant interleukin-2

L-BLP25 vaccine plus letrozole induces a TH1 immune response and has additive antitumor activity in MUC1-expressing mammary tumors in mice

PURPOSE

In this study, we examine the immunomodulatory effects and antitumor activity of tamoxifen and letrozole when combined with the human epithelial mucin (hMUC1)-specific vaccine, L-BLP25, in the hMUC1-expressing mammary tumor (MMT) mouse model.

EXPERIMENTAL DESIGN

Dose-finding studies were conducted for both tamoxifen and letrozole. Letrozole and L-BLP25 combination studies used 69 MMT female mice assigned to five groups: untreated, cyclophosphamide + placebo, cyclophosphamide + L-BLP25, letrozole 0.8 mg/kg, and cyclophosphamide + L-BLP25 + letrozole. Tamoxifen and L-BLP25 combination studies used 48 MMT female mice assigned to five treatment groups: untreated, cyclophosphamide + placebo, cyclophosphamide + L-BLP25, tamoxifen 50 mg/kg, and cyclophosphamide + L-BLP25 + tamoxifen 50 mg/kg group. Mice were injected subcutaneously with L-BLP25 (10 μg) weekly for 8 weeks. Serum cytokines were serially measured using a Luminex assay, whereas splenocytes at termination were analyzed by ELISpot to determine T-helper (T(H))1/T(H)2 polarization of immune response.

RESULTS

Daily oral doses of 50 and 0.8 mg/kg of tamoxifen and letrozole, respectively, resulted in a significant survival advantage over controls (P < 0.05). A predominant T(H)1-polarized immune response in vaccinated mice was seen with or without tamoxifen or letrozole treatments. In the L-BLP25 plus letrozole treatment group, statistically significant (P < 0.05) additive antitumor activity was observed, whereas tamoxifen plus L-BLP25 was not significantly different (P > 0.05).

CONCLUSION

The results of this study show that hormonal therapy does not interfere with L-BLP25-induced predominant T(H)1 response, and the combination of L-BLP25 with letrozole has additive antitumor activity in the MMT mouse model.

Chemotherapy-induced modulation of natural killer and lymphokine-activated killer cell activity in euthymic and athymic mice

Combinations of chemotherapy and interleukin-2 (IL-2) aimed at improving therapeutic efficacy in cancer patients have generally proved disappointing. Although chemotherapy blocks tumor growth and sometimes boosts immune functions, most drugs are immunosuppressive, at least transiently. Therefore, it is reasonable to assume that maximal exploitation of the immunostimulatory and antitumor activity of both modalities requires careful coordination of chemotherapy and IL-2 timing. We analyzed the temporal effect of 5-fluorouracil (5-FU, 100-120 mg/kg), cyclophosphamide (CY, 100 mg/kg), Adriamycin (8 mg/kg) and dacarbazine (100 mg/kg) on the activation of natural killer/lymphokine-activated killer (NK/LAK) cells by IL-2 in several strains of euthymic mice and in athymic nude mice. Following in vivo or in vitro exposure to IL-2 1-15 days after chemotherapy, the total lytic activity of the spleen and the number of LAK precursors (LAK-p) were measured. In euthymic mice injected with IL-2 (5 x 10(4) Cetus units twice daily for 4-5 days), 5-FU augmented (up to 37-fold, days 1-9) and CY reduced (up to day 6) LAK activity, as compared with that in the IL-2 control. In bulk cultures containing IL-2 (1000 CU/ml, 3-4 days), both 5-FU and CY reduced LAK activity of euthymic mice splenocytes for up to 6 days after chemotherapy, which was followed on day 9 by full recovery. In splenocytes of nude mice, 5-FU increased and CY diminished LAK activation in bulk cultures, starting 3 days after chemotherapy. In athymic mice, 5-FU markedly augmented the total number of LAK-p/spleen (up to 30-fold, days 3-9), as determined by limiting-dilution cultures with IL-2 (for 7-8 days). In euthymic mice, in contrast, LAK-p levels decreased for up to 6-9 days after treatment with 5-FU, Adriamycin or decarbazine, later recovering to pretreatment levels, whereas CY markedly increased LAK-p (up to 15-fold) when administered 6-12 days before limiting-dilution culture initiation. The effect of chemotherapy on LAK and NK activity was essentially similar. In other experiments, a subset of asialoGM1- LAK-p was found in the spleens of 5-FU-treated mice, but not in untreated mice. Our results suggest that the immunomodulatory effect of chemotherapy on NK/LAK activity in mice is variable and largely depends on the drug itself, the interval between chemotherapy and IL-2 administration, the strain of mice and the assay used.

Systemic chemotherapy combined with local adoptive immunotherapy cures rats bearing 9L gliosarcoma

Survival of Fischer rats bearing 9L gliosarcoma in the brain was measured to determine the efficacy of 1) systemically administered chemotherapy with local adoptive immunotherapy (chemo-adoptive immunotherapy) or 2) systemically administered chemo-immunotherapy. Winn assays, where tumor instillation coincided with the start of treatment, and one-week established tumor assays were conducted. Survival of chemo-adoptive immunotherapy treated groups given intraperitoneal cyclophosphamide and intracranial lymphokine activated killer cells and recombinant Interleukin-2 was significantly extended when compared to sham treated control groups, to groups given chemotherapy with intraperitoneal cyclophosphamide, and to groups treated by local adoptive immunotherapy with intracranial lymphokine activated killer cells and Interleukin-2. The killer cells were generated from spleens of donor rats that either had or had not been given cyclophosphamide 24 h earlier. Long-term survivors (9/39), sacrificed at day 70, were obtained only in the chemo-adoptive immunotherapy treated groups; 7/39 had no histologic evidence of tumor and had focal sterile abscesses at the site of killer cell instillation. Average group weight plotted over time showed that there was acceptable toxicity with chemo-adoptive immunotherapy; the toxicity was identical to that obtained with systemic cyclophosphamide treatment. In contrast, survival of chemo-immunotherapy treated groups given systemic cyclophosphamide and Interleukin-2 was not significantly extended from groups which were sham treated or treated only with systemic Interleukin-2. Rapid decline of average group weight plotted over time and early deaths following chemo-immunotherapy treatment indicated that the regimen was toxic. The effect of cyclophosphamide administration on the splenocytes of donor rats and the LAK cells generated from them was determined by in vitro studies analyzing cell number, viability, phenotypic expression and cytotoxicity against 9L tumor. In the treatment of this intracranial neoplasm, the beneficial effects of cyclophosphamide were determined to occur in situ in the tumor-bearing host. No benefit resulted from cyclophosphamide treatment of donor rats that supplied splenocytes for LAK cell production.

Importance in timing of cyclophosphamide on the enhancement of interleukin-2-induced cytolysis

We investigated the in vivo effects of cyclophosphamide (CY) on interleukin-2(IL-2)-induced cytolytic function and spleen cell immunophenotype. Pretreatment of A/J mice with CY (25 mg/kg or 75 mg/kg) i.p. on days -10 and -15 followed by IL-2 (50,000 U i.p. on days 0 to +3) resulted in increased lysis of YAC-1 target cells compared to the group receiving IL-2 without previous CY therapy. In contrast, when CY was given on day -5, the cytotoxicity against YAC-1 was not enhanced. Phenotypic analysis of splenocytes obtained from mice treated with CY on day -10 or -15 revealed a relative decrease in L3T4- and Lyt2-positive T cells. In vivo depletion of natural killer (NK) cells by anti-asialoGM1, prior to IL-2 therapy, abrogated the enhancing effect of CY on cytolysis while in vivo elimination of T cells by anti-L3T4 and anti-Lyt2 monoclonal antibodies did not, indicating that in the absence of T cell antigenic challenge, the increased cytolytic function after CY administration is probably mediated through NK cells. These findings provide evidence that CY may be used more effectively in IL-2-based immunotherapy protocols, if consideration is given to timing of CY and IL-2 administration.