Mediation of cytotoxic immune responses against human tumor-associated antigens by xenogeneic immune RNA.

Xenogeneic immune RNA (I-RNA), extracted from the lymphoid organs of sheep or guinea pigs immunized with human tumor cells, mediated in vitro cytotoxic immune responses that were directed specifically against tumor-associated antigens of human tumor target cells. Normal human peripheral blood lymphocytes from healthy donors became markedly more cytotoxic for human tumor target cells after being incubated with I-RNA extracted from the lymphoid organs of animals that had been immunized with that particular tumor. Gastric carcinoma, malignant melanoma, and carcinoma of the breast were studied. Lymphocytes incubated with RNA from animals immunized with only complete Freund's adjuvant evidenced no increased cytotoxic activity. RNA extracted from the lymphoid organs of animals immunized with normal skin fibroblasts that were autologous to the immunizing tumor, when incubated with normal allogeneic lymphocytes, also mediated cytotoxic immune reactions against tumor target cells. These immune responses probably were directed principally against normal transplantation antigens. However, when lymphocytes that were autologous to the immunizing tumor and/or the tumor target cells were incubated with RNA from animals immunized with autologous normal fibroblasts, cytotoxicity did not increase. Only I-RNA extracted from donor animals specifically immunized with tumor cells mediated cytotoxic antitumor immune responses when incubated with autologous lymphocytes.

Specificity of antitumor immune reactions mediated by xenogeneic immune RNA.

Evidence that xenogeneic immune RNA (I-RNA) mediated specific cytotoxic immune responses against human tumor-associated antigens was obtained from in vitro studies in two autologous melanoma systems. In these systems, malignant melanoma target cells, matching normal fibroblast target cells, lymphocyte effector cells, and melanoma and normal skin tissue used to immunize RNA donor animals were derived from the same autochthonous hosts. When incubated with autologous lymphocytes, I-RNA extracted from the lymphoid organs of donor animals immunized with melanoma tissue mediated immune reactions against autologous melanoma target cells in vitro. I-RNA from animals immunized with normal skin tissue from autochthonous hosts did not increase the cytotoxicity of autologous lymphocytes for autologous melanoma cells. Using autologous fibroblasts as target cells, we detected no increase in cytotoxicity when autologous lymphocytes were incubated with RNA from animals immunized either with melanoma tissue or normal skin tissue from the autochthonous host. By contrast, when allogeneic lymphocytes were used as effector cells, RNA extracted from animals immunized either with melanoma tissue or normal skin mediated cytotoxic immune reactions against melanoma target cells and normal fibroblast target cells derived from the same patient.

Production of antisera with specificity for malignant melanoma and human fetal skin.

Complement-dependent cytotoxic antibodies to common cell surface antigens of cultured melanoma cells were produced in guinea pigs. At appropriate dilution, melanoma antisera were cytotoxic only to melanoma target cells. Following absorption with pooled lymphoid cells, additional absorption with melanoma cells but not absorption with fibroblasts or carcinoma cells was found to remove all cytotoxic activity from melanoma antisera. Absorption with human fetal skin cells but not with autologous fetal visceral cells was found to remove cytotoxicity from melanoma antisera. Tissue type-specific antigens may be shared by human malignant melanomas and fetal skin of black racial origin (at 16 to 18 weeks of gestation). The methods may be useful in the production of xenogeneic antisera with "operational monospecificity" for common melanoma-specific antigens. Sera from 47 patients with malignant melanoma failed to evidence specific cytotoxicity for melanoma target cells.

Development of a miniaturized, improved nucleic acid precursor incorporation assay for chemosensitivity testing of human solid tumors.

Two technological problems limit the usefulness of chemosensitivity assays: low success rates (generally 30-60%); and the requirement for large numbers of tumor cells (5 X 10(5)/dish). To solve these problems, we developed a miniaturized, improved, nucleic acid precursor incorporation assay (MINI-assay). In this new assay, 0.3-1.5 X 10(5) tumor cells were plated in double-layer agarose in 16-mm wells of a Costar (No. 3524) 24-well cluster dish. After 72 h of incubation, 5 microCi [3H]thymidine were added to each well. After an additional 24 h of incubation, the trichloroacetic acid-precipitable material was collected and counted by liquid scintillation. We found that 280 of 351 (80%) human solid tumors gave evaluable chemosensitivity results. Labeling efficiency was optimum when the plating density was between 1.5 and 3 X 10(4) cells/well. Radioisotope uptake was less efficient in 35-mm Petri dishes and in the 7-mm wells. The MINI-assay was particularly suitable for small specimens (less than 1 g) and for tumor types that usually yield small numbers of viable tumor cells (19 of 30 breast cancers and 56 of 71 sarcomas were evaluable). The artifacts of colony counting (cell clumps, debris, clots) were also eliminated with this assay. With high evaluability rates, the requirement of fewer cells, a short duration (5 days), and ease of quantitation, the MINI-assay is widely applicable to chemosensitivity testing in human tumors.

A new micromethod for the detection of HL-A antigens on cultured human tumor cells.

A rapid microcytotoxicity assay for the detection of HL-A antigens on tissue culture cells derived from human solid tumors is described. Tumor cells were prelabeled with 125Iododeoxyuridine. Isotopically labeled tumor cells were reacted with up to 37 highly selected HL-A antisera and diluted rabbit complement. Results of the HL-A typing of nine human tumor cell lines are reported. Three melanoma cell lines showed individually distinct HL-A profiles at the first HL-A locus which agreed with the antigenic pattern of the tumor donor's autologous lymphocytes. Less reactivity was noted with HL-A antisera defining second locus specificities on the three melanoma cell lines, whereas some other cell lines showed more HL-A reactions than required to present a "full house". This method obviates the necessity for visually enumerating residual tumor target cells.

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.

A continuous cell line derived from a human primary cutaneous melanoma: morphologic and karyologic properties.

A continuous tissue culture cell line, JD-MEL, derived from a primary cutaneous human malignant melanoma, is described. The cultured cells retain the characteristic epithelial morphology of the tumor of origin. The malignant nature of the cell line was demonstrated by the lack of contact inhibition, multilayered growth pattern and the ability to produce tumors in athymic BALB/c mice. Chromosome analysis revealed a near tetraploidy. Distinctive marker chromosomes and a female karyotype were present. No recognizable melanin pigment was identified in the cultured cells.

Detection of private and common tumor-associated antigens in murine sarcomas induced by different chemical carcinogens.

Two fibrosarcomas of similar histological type, induced in C3Hf mice by either methylcholanthrene or 3,4-benz(a)pyrene, were shown to have individually unique tumor-rejection antigens in classical transplantation-type experiments. By contrast, sera of autochthonous mice, which resisted only transplants of the immunizing sarcoma, were found to contain complement-dependent cytotoxic antibodies, specific for both sarcomas, in vitro. The existence of individually unique as well as common tumor-associated antigens in chemically-induced murine sarcomas is suggested. The private "tumor transplantation-type" antigens elicited tumor rejection responses in vivo. The common tumor-associated antigens, although immunogenic in autochthonous hosts, inducing the production of tumor-specific antibodies, failed to induce transplantation cross-resistance in vivo. This study supports the contention that, in carcinogen-induced murine tumors, and perhaps in human neoplasms as well the evaluation of humoral (and cell-mediated) immune responses in vitro may not reflect tumor rejection-type immune responses in vivo.