Immune cytolysis of murine tumor cells mediated by xenogeneic "immune" RNA

Immune RNA therapy as an effective adjuvant immunotherapy after surgery: an animal model

Transfer of tumor immunity as adjuvant cancer therapy has been a topic of intense interest. We have examined the efficacy of various combinations of surgery, xenogeneic immune RNA, xenogeneic normal RNA, tumor vaccine, and nonspecific splenocytes as adjuvant therapy for B16 melanoma in the C57BL/6J mouse system. B16 melanoma was transplanted by trocar into the right hind limb of 6-week-old mice. The tumors were readily palpable on the ninth day posttransplantation. The tumors were amputated at that time under mild anesthesia. Immune RNA was prepared by hot phenol extraction from immune sheep spleens. Various combinations of immune RNA, normal RNA, and tumor antigen, with or without normal mouse spleen cells, were administered every other day for a total of 10 injections. The survival and mode of death was followed up to 120 days. All mice without any treatment died within 30 days. Immunotherapy had no effect on the survival of mice that did not have surgical therapy. Individual group comparisons between mice that underwent surgery only and mice that had surgery plus immune RNA immunotherapy revealed a striking statistical improvement (P less than 0.01). Comparing all groups that received amputation plus various combinations of adjuvant immunotherapy showed no statistical difference in survival. However, immune RNA appears somewhat superior to normal RNA or antigen only. It appears that adjuvant immune RNA immunotherapy following surgical excision in the B16 melanoma model significantly improves survival and retards the spread of metastases.

Immunotherapy with RNA in cancer

The effect of I-RNA therapy was studied in a B16 melanoma-C57BL/6J mouse system. After having primary B16 isografts excised, mice receiving syngeneic lymphocytes incubated in vitro with specific guinea pig B16 I-RNA showed significantly improved survival as compared to control mice receiving untreated lymphocytes. This therapeutic effect was tumor specific and RNase sensitive. Significant cytotoxicity against B16 cells in vitro was consistently observed with lymphocytes prepared from B16 I-RNA treated animals, whereas lymphocytes from control animals or those treated with RNase-degraded B16 I-RNA or 3LL I-RNA had no effect. Results suggest that the combination of surgery and immunotherapy with I-RNA may be useful in preventing tumor recurrence in certain patients with cancer.

Prevention of death from metastases by immune RNA therapy

The effect of immune RNA treatment on the incidence of death from pulmonary metastases was studied in C57BL/6J mice after excision of a B16 murine melanoma. Immune RNA was extracted from the lymphoid tissues of guinea pigs immunized with B16 tumor and then incubated in vitro with normal C57BL/6J mouse splenocytes. Mice receiving intraperitoneal injections of these RNA-treated syngeneic splenocytes after the primary B16 isograft was resectioned showed significantly improved long-term survival (42 to 67 percent in three successive experiments) as compared to control mice (0 to 20 percent survival) receiving untreated splenocytes. The effect of RNA treatment was tumor-specific and ribonuclease sensitive. The results suggest that immunotherapy with immune RNA may be of benefit to certain patients after surgery for cancer.

Anti-tumour cytotoxicity of poly(A)-containing messenger RNA isolated from tumour-specific immunogenic RNA

The transfer of tumour-specific cytotoxicity against a murine fibrosar-coma has been demonstrated in vitro using xenogeneic RNA extracted from tumour-cell-immune animals. Poly(A)-tailed messenger RNA from immunogenic RNA was isolated by passage through an oligo(dT)-cellulose column, and evaluated to determine whether the same tumour-specific cytotoxicity could be transferred. Aliquots of normal C3H mouse lymphocytes were treated with poly(A)-containing immune RNA, whole-cell immune RNA lacking poly(A) and total cellular immune RNA. Treated cells were tested in vitro using an adaptation of the Takasugi and Klein microcytotoxicity assay. Percent cytotoxicity was calculted using cells treated with fractions of normal RNA as control. An increase in tumour cytotoxicity was found with poly(A)-containing immune RNA. The optimum dose of poly(A)-tailed immune RNA was estimated as 6.5 microgram of RNA per 4 x 10(6) lymphocytes. Populations of lymphocytes were separated using glass and nylon wool. T- and B-enriched populations were treated with various RNA components. The adherent cell population showed no significant cytotoxicity, whilst treatment of the nonadherent population with poly(A)-tailed immune RNA produced high levels of cytotoxicity.

Immunotherapy of cancer with "immune" RNA. A preliminary report

A phase I clinical trial of immunotherapy with "Immune" RNA was undertaken fifteen months ago. Twenty-six cancer patients were treated with RNA extracted from the lymphoid organs of sheep immunized with either autologous tumor cells or allogeneic tumor cells of the same histologic type. Eighteen patients had gross disease and eight had minimum residual disease. RNA was administered weekly, intradermally, at doses up to 9 mg/week without any significant local or systemic toxicity. Four patients improved, thirteen achieved stability of disease or possible improvement, seven were treatment failures, and two are indeterminate. Lymphocyte-mediated cytotoxicity to allogeneic tumor target cells of the same histologic type were monitored in eleven patients. In seven patients, cytotoxicity increased after "Immune" RNA therapy; no change was observed in three patients; a decrease was noted in one patient. There appeared to be a possible correlation between cytotoxicity assessed in vitro and clinical response. There is some evidence that these responses may be specific for the particular tumor used to immunize the RNA donor.

Transfer of tumor specific immunity with "immune" RNA: prospects for the treatment of human cancer

Ribonucleic acids extracted from specifically sensitized lymphoid cells (I-RNA) have been shown to transfer specific immunoreactivity to normal non-immune lymphoid cells. Evidence for the transfer by I-RNA, of immune responses to tumor-associated antigens of animal and human neoplasms, in vivo and in vitro, is reviewed. Results obtained in our laboratory and in other laboratories indicate that xenogeneic, allogeneic and syngeneic I-RNA extracts mediate specific cytotoxicity to tumor cells, in vitro, and mediate transplantation resistance and tumor rejection responses in vivo. Our results suggest that I-RNA preparations fail to elicit immune responses directed against "self" antigens. By contrast, I-RNA's directed against "non-self" tumor-associated antigens appear to induce lymphocytes to effect specific anti-tumor immune responses. The mechanisms responsible for the failure of I-RNA to initiate immune responses against "self" antigens are not known at present and demand investigation. Preliminary results of a clinical Phase I trial of immunotherapy with xenogeneic I-RNA in selected cancer patients are reviewed. I-RNA might offer promise as a new modality for the immunotherapy of human cancer.

Mediation of immune responses to tumor antigens in vitro by immune RNA

It was shown that normal nonimmune C3H mouse spleen cells became specifically cytotoxic to chemically-induced syngeneic C3H tumor cells by incubation with xenogeneic I-RNA extracted from the lymphoid organs of specifically immunized guinea pigs. This response was specific for the tumor used to immunize the I-RNA donor. In a totally syngeneic system, we showed that syngeneic I-RNA extracted from the spleens of tumor-bearing rats mediated cytotoxic immune reactions which were directed specifically against the tumor-associated antigens of syngeneic rat tumor target cells. Active antitumor I-RNA synthesis in the lymphoid organs of I-RNA donor animals reached a maximum between days 14 and 21, depending on the route of administration and the nature of the immunizing tumor. Active I-RNA preparations were insensitive to treatment with deoxyribonuclease or pronase, but were inactivated by ribonuclease treatment; thereby indicating that the active moiety was one or more species of RNA. The active fractions of the I-RNA preparations had sedimentation values in sucrose density gradients of 12-16S, and comprised only a small fraction of the total RNA present in the lymphoid cells. Active antitumor I-RNA appeared to be localized in the cytoplasm of sensitized lymphoid cells, rather than in the nucleus. Lymphocytes from normal human donors as well as from cancer patients, when incubated with xenogeneic or allogeneic I-RNA, became specifically cytotoxic for human tumor cells in vitro. Crossreactivity among tumors of the same histologic type was observed, but not crossreactivity with tumors of other histologic types. Xenogeneic I-RNA extracted from the lymphoid organs of donor animals immunized either iwth tumor cells or normal tissues, following incubation with normal allogeneic lymphocytes, mediated cytotoxic immune reactions which were directed both against tumor-associated antigens and normal transplantation antigens. However, when autologous lymphocytes were used as effector cells, only immune reactions directed against tumor-associated antigens were observed. Allogeneic I-RNA extracted from peripheral blood lymphocytes of human cancer patients mediated specific cytotoxic immune reactions that were directed against common tumor-associated antigens shared by human tumors of similar histologic type. I-RNA's directed against "self" normal cell surface antigens appear to be recognized as self by lymphocytes, and immune responses against these self antigens are not elicited. On the other hand, I-RNA's directed against "nonself" tumor-associated antigens induce lymphocytes to effect specific antitumor immune responses. Our data are consistent with the hypothesis that I-RNA is an information-containing ribonucleic acid molecule capable of mediating immune reactions in vitro which are specific for the tumor-associated antigens of the tumor used to immunize the I-RNA donor.