An open-trial evaluation of mitoxantrone in the treatment of progressive MS.

We treated 13 patients with progressive MS with mitoxantrone. All patients received a standard IV dose of mitoxantrone (8 mg/m2) every 3 weeks for a total of seven infusions, with dosage adjustments depending on the hematologic profile at the nadir. The treatment was well tolerated, with the most common side effect being mild nausea. Four of seven women developed transient secondary amenorrhea. The postenrollment clinical behavior of these patients was generally more favorable than during the 18 months prior to enrollment (only three of 13 patients developed an increase in the Expanded Disability Status Scale of more than 0.5 points), suggesting a possible treatment effect, but comparison with two historical control groups (both the active and placebo groups from the Canadian Cooperative Trial of Cyclophosphamide and Plasma Exchange) does not suggest that mitoxantrone was efficacious. Eight of 12 patients had evidence of MRI activity on 13 of 29 follow-up visits. This small, open-labeled pilot study did not provide strong support for proceeding with a randomized, controlled trial of this dosage regimen of mitoxantrone in patients with progressive MS.

Experience in Canada with the new revised monkey neurovirulence test for oral poliovirus vaccine.

Nine years of experience in our laboratory, using more than 1500 cynomolgus monkeys in 138 tests, has shown that the new neurovirulence test (NVT) adopted by the World Health Organization (WHO) for live, oral monovalent vaccine of each poliovirus type, was a reproducible and sensitive assay likely to ensure the safety of this vaccine in humans. Our findings were the following: (1) when the test vaccine and the appropriate homotypic reference vaccine were tested in a single group of monkeys, the concurrent use of the reference vaccine considerably increased the reproducibility of the NVT; (2) in the assessment of the degree of attenuation of each lot of vaccine, the use of 12 monkeys for types 1 and 2 vaccines and 20 monkeys for type 3 vaccine (inoculated intraspinally each for reference and test vaccine) was satisfactory; (3) the virus dose used per monkey (10(5.6) to 10(6.6) pfu per monkey) was found not to be critical, i.e. the lower virus dose yielded mean lesion scores in the central nervous system of monkeys at least as high or higher than the tenfold higher virus dose; (4) the statistical analysis of our data showed that the old intrathalamic (IT) assay was considerably less sensitive than the new intraspinal (IS) assay, i.e., a test vaccine with a twofold increase in monkey neurovirulence would have a 41% chance of failing in the IT test (using 30 monkeys per vaccine), while this chance increased to 99% in the WHO IS assay (using 12 or 20 monkeys per vaccine). Since the introduction of the WHO NVT in Canada, the laboratory findings in monkeys were confirmed by vaccine experience in humans; the number of vaccine-associated paralytic poliomyelitis cases in the population showed a further decline.

Immunosuppression by spleen cells from Moloney leukemia. III. Evidence for a suppressor cell that is not the leukemic, virus-producing cell.

Spleens of mice bearing MuLV (Moloney)-induced leukemia contain cells that inhibit the antibody response of normal syngeneic lymphocytes to sheep RBC in Marbrook cultures. In order to determine whether these immunosuppressive cells are virus-infected tumor cells or normal cells we pretreated leukemic spleen cell suspensions with syngeneic mouse antiserum to Moloney leukemia antigen(s) (plus complement) and with rat anti-Moloney serum (plus complement). The cytotoxic treatment killed approximately 20% to 30% and 60% to 70% of the cells, respectively. The remaining viable cell population was tested for MuLV production (in an infectious center assay on S+L-fibroblasts), for lethal effect on newborn mice, and for immunosuppressive activity. After the treatment with anti-Moloney sera the number of MuLV-releasing cells decreased 10-fold and the leukemogenic potential in vivo decreased 100-fold as compared to leukemic spleen cells pretreated with nonimmune mouse and rat sera (plus complement). In contrast, the ability of the antisera-treated cells to inhibit anti-SRBC response remained undiminished. This indicates that, in part, the immunosuppressive cells in the leukemic spleen are normal, noninfected cells, involved, perhaps, in immune regulation.

Tumor-mediated immunosuppression: prevention by inhibitors of prostaglandin synthesis.

The addition of MC16 tumor cells (a prostaglandin E2-producing cell line induced in C57BL/6J mice by methylcholanthrene) to cultures of cells to sheep red blood cells. This inhibition can be blocked by adding to the cultures prostaglandin synthetase inhibitors, such as indomethacin, flufenamic acid and aspirin. These MC16 tumor cells are also immunosuppressive in vivo. Mice bearing the syngeneic MC16 tumor become unresponsive to sheep red blood cells as the tumor grows. As in the in vitro test system, inhibitors of prostaglandin synthetases seem to block the immunosuppressive activity of MC16 cells in vivo since tumor-bearing mice, treated therapeutically with indomethacin, responded normally in their production of antibody to sheep red blood cells.

Subversive activity of syngeneic tumor cells as an escape mechanism from immune surveillance and the role of prostaglandins.

Mice bearing a syngeneic tumor become increasingly immunodepressed during growth of the tumor, being unable to develop both cellular and humoral immunity to a histoincompatible tumor allograft and to reject the allograft. This failure to reject a strongly antigenic tumor allograft suggests that immunodepression associated with growth of a weakly antigenic syngeneic tumor provides the syngeneic tumor with an escape mechanism. This immunodepression is also manifest by the suppression of the response of spleen cells to mitogen stimulation by syngeneic tumor cells, both in vivo and in vitro. T cells that are stimulated by PHA, a T-cell mitogen, are the primary targets, and their suppression is the result of the direct subversive activity of the tumor cells. Subversion of T cells by tumor cells seems to be mediated through the prostaglandin pathway, because the prostaglandin PGE2 is itself suppressive, and an antagonist of PGE2 and an inhibitor of prostaglandin synthetases both inhibit the subversive activity of tumor cells. Several tumor cell lines tested, of different etiology and histologic type, all were subversive. This suggests that this subversive activity may be a general property of tumor cells and may be a key element in their ability to thwart the immunological system of the host. For this reason, any therapeutic regimen of cancer, based on immunostimulating drugs, should include drugs that can inhibit active subversion of the immune system by the tumor itself. Antagonists of prostaglandins and inhibitors of prostaglandin synthetases show promise in this regard.

Subversion of immune system by tumor cells and role of prostaglandins.

Mice bearing syngeneic tumors, chemical and virus-induced, became immunologically unresponsive to sheep erythrocytes. The increase in the degree of unresponsiveness with tumor growth suggested a causal relationship. Immunosuppression was in fact caused by the tumor cells because the addition of tumor cells to in vitro cultures of spleen cells and sheep erythrocytes resulted in suppression of antibody response. Suppression was dose dependent with a ratio of 1 to 1000 of tumor cells to spleen cells sufficient to produce significant suppression. Prostaglandins were found to have a role in immunosuppression by tumor cells in that PGE2 was itself immunosuppressive and in that indomethacin and aspirin, inhibitors of prostaglandin synthetases, blocked immunosuppression in vitro and retarded tumor growth in vivo. These findings suggest that tumors, although antigenic, may be able to escape immuno-sureillance by their host by means of subverting the immune system. Thus, success of immunotherapy may well depend on our ability to prevent or block the immunosuppressive activity of tumors.