Immune mechanisms in homotransplantation. II. Quantitative assay of the immunologic activity of lymphoid cells stimulated by tumor homografts

Summary A technique for quantitatively assaying the activity of immunologically activated lymphoid cells is described. The technique consists in mixing the lymphoid cells with cells of an appropriate tumor and injecting the mixtures into mice of a) the strain of origin of the tumor, b) the strain of origin of the lymphoid cells, or c) the F 1 hybrid obtained in matings between mice of types (a) and (b). Subsequently, these recipients are killed and the tumors are dissected out and weighed. In a given donor-host combination the tumor weights were found to be inversely proportional to the numbers of immune lymphoid cells contained in the mixture. Except at very large cell doses, normal lymphoid tissues were inactive in this respect. The antitumor activity was shown to be immunologically specific and to depend on the continued functioning of the lymphoid cells in their new hosts. Incubation of the cell mixtures prior to injecting them into the host mice has no effect on the level of activity observed, and the available evidence indicates that the two cell types do not react with each other in vitro . The technique is extremely sensitive, being capable of detecting the activity of less than 0.1% of the cells harvested from the draining lymph nodes of a single mouse previously implanted with a tumor homograft. Very high activity has been found in the spleens of mice bearing subcutaneous tumor homografts on the right flank; much smaller amounts were detected in contralateral nodes and only occasional weak activity was detected in the thymus. It is concluded that the lymph node cells are immunologically immature at the time of excision, that they mature in their new host at subcutaneous sites as well as in lymphoid organs and that they attack their target cells directly rather than through the elaboration of a serumborne antibody.