Release of soluble "blocking" and "suppressor" factors from normal lymphocytes treated with RNA from spleens of tumour-bearing mice

RNA extracted from the spleens of tumour-bearing (TLRNA) and tumour-immune (ILRNA) mice was shown to transfer to normal lymphocytes (NL) the ability to produce factors that blocked specific tumour-cell cytotoxicity and mediated specific antibody-dependent cell cytotoxicity (ADCC). Aliquots of normal C3H mouse lymphocytes were treated with TLRNA or ILRNA and cultured in vitro in the absence of tumour antigen. Supernatants were collected at 24h intervals and tested in a microcytotoxicity assay for blocking and ADCC activities. Factors that inhibited tumour destruction by specifically sensitized lymphocytes at the level of both the tumour cells and effector cells were demonstrable in culture supernatants of NL pretreated with TLRNA (50 or 100 microgram/4 X 10(6) cells) but not ILRNA. However, treatment of NL with either RNA resulted in the production factors that mediated tumour-specific ADCC. Cytotoxicity testing and absorption studies of the tumour cell and a control cell (LM) indicated that factors mediating ADCC and blocking at the target-cell level were specific for the tumour. Suppressor activity at the effector-cell level was not absorbed by tumour cells and represents a separate and distinct mechanism of immunosuppression. These data indicate that RNA faithfully transfers "suppressive" as well as "positive" types of immune responses that have been reported previously for lymphocytes obtained directly from tumour-bearing and tumour-immune animals.

Immunotherapy of a murine sarcoma using specific antitumor immune RNA

The effect of IRNA therapy in a polyoma-induced fibrosarcoma of C3H mice has been studied. Although a protocol that transferred in vitro cytotoxicity was used, no reduction in incidence of tumors, tumor size, or survival was demonstrated. In one experiment, enhancement of tumor growth occurred. It is concluded that cytotoxicity does not reflect in vivo changes and that therapeutic trials of IRNA are premature.

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.