J. W. Pearson

Chemo-adoptive immunotherapy against a guinea-pig leukemia

SummaryStrain-2 guinea-pigs bearing the transplantable L2C leukemia were treated with cytoxan 24 h prior to receiving an injection of either allogeneic or syngeneic spleen cells from donors preimmunized to the leukemia. Treatment with the drug alone produced a remission period which lasted for 4–5 weeks before eventual relapse and death. An IP transfer of spleen or peritoneal exudate (PE) cells from syngeneic strain-2 guinea-pigs hyperimmunized to the leukemia greatly extended the survival times of drug-treated animals beyond that observed in animals receiving normal strain-2 cells. Long-term survivors were refractory to a subsequent challenge with a lethal inoculum of L2C cells. A reduced tumor load was essential for an immunotherapeutic effect of adoptively transferred cells. The use of sensitized lymphocytes alone failed to control the established disease. Hyperimmune spleen cells from strain-13 and Hartley guinea-pigs also demonstrated a slight capacity to inhibit the proliferation of leukemia cells when injected into diseased animals previously treated with the drug. Due to inadequate drug suppression, however, the injection of allogeneic cells from either immune strain-13 or Hartley guinea-pigs did not prolong the latent period for the appearance of the leukemia to the same extent as either immune strain-2 spleen or PE cells. A marked delay in the onset of disease was noted when immune spleen cells from either syngeneic or allogeneic sources were mixed in vitro with L2C leukemia cells at a ratio of 200:1 before injection back into normal strain-2 animals. However, an exposure of L2C blast cells in vitro with heat-inactivated serum obtained from L2C-immune strain-2 animals significantly enhanced the onset of disease.

Therapeutic application of various immunostimulators on the L2C guinea-pig leukemia

SummaryImmunostimulators such as Corynebacterium parvum (C. parvum), Bacillus Calmette-Guerin (BCG), pyran copolymer, and glucan were examined in the guinea pig L2C lymphoblastic leukemia model to determine their capacity for therapeutic modulation of the immune response of the host toward controlling leukemic cell proliferation. The dose, route, and frequency of administration of the stimulators were also evaluated as a function of time in order to obtain an optimal antileukemic effect. Results indicated that only C. parvum and BCG were capable of significantly increasing host survival when given 1 day after an inoculation of 1.5×104 viable leukemic cells. Administration of BCG or C. parvum, alone or in combination with irradiated blast cells on either days 4 or 7, was totally ineffective in prolonging survival. In the majority of cases, enhanced leukemic growth was observed on these days. The combination of BCG and/or C. parvum with irradiated syngeneic blast cells given 24 h after leukemia inoculation promoted a synergistic response with a significant increase in median survival time and a number of long-term survivors.

The use of immunotherapy to enhance tumor rejection immunity in leukemic (L2C) guinea pigs following remission induction with MeCCNU

Abstract Employing a transplantable guinea pig leukemia (L 2 C), animals treated with MeCCNU were completely free of disease 180 days post chemotherapy. However, these animals were not refractory to a subsequent challenge with viable L 2 C leukemic blast cells. In an attempt to augment the hosts immune response to tumor associated antigens (TAA) while enhancing the immunogenicity and expression of the TAA on the surface of the blast cell, guinea pigs were injected with either irradiated syngeneic blast cells, immunostimulators (BCG or C. parvum ) or combinations of both. Guinea pigs treated with either BCG or C. parvum plus irradiated cells were now resistant to tumor re-inoculation. Use of irradiated blast cells or BCG or C. parvum alone was ineffective and did not protect against a bio-challenge. Therapeutic benefit was only observed following the mixture of vaccine with the immunostimulator. Application of immunostimulation at sites separate from the vaccine was less effective. Maximum stimulation of the immune response in the form of tumor rejection immunity occurred following repeated immunization (3 times vs 1 time) every other week with the vaccine-immunostimulator mixture. These results were substantiated by in vitro studies in which significant increases in both cellular and humoral mediated immunity were noted in only those animals receiving the combined mixture of irradiated blasts plus immunostimulator. These data suggest the need for enhancing tumor-specific recognition in situations where the host is immunologically competent but the TAA are too weak to elicit an immune response beneficial to the host.

Busulfan versus cyclophosphamide treatment in the early and late stages of granulocytic leukemia in guinea pigs

A transplantable granulocytic leukemia (GL-13-BC) in strain 13 guinea pigs, which has many similarities to human CML, was used to test the antineoplastic effects of two alkylating agents, busulfan and cyclophosphamide, administered in the late and early stages of the disease. Busulfan had a pronounced cytoreductive effect on circulating leukemic cells in the late, pre-blast crisis stage of this disease but all treated animals, succumbed to the leukemia with only a marginal increase in survival time relative to that of untreated controls. In this respect the guinea pig model resembles human CML. Survival time was moderately increased with early busulfan treatment but, as in the late treatment group, all animals succumbed to the leukemia. A pronounced cytoreductive action on leukemic cells was also observed in guinea pigs treated with cyclophosphamide. Late treatment with this drug produced highly variable effects on the survival time of leukemic guinea pigs; of the nine animals treated, no effect was observe in five, three showed a significant increase in survival time and one animal was still in remission without treatment when the experiment was concluded. Early treatment with cyclophosphamide produced the most striking finding of this study. Two treatments with this drug produced a complete remission in all of the treated guinea pigs. This remission lasted without further treatment for the duration of the study (greater than 200 days) while all untreated controls died within 27-37 days after receiving leukemic cell transplants. The relevance of these findings to the treatment of human CML is discussed.