Lymphoma development from transplanted murine leukemia virus infected organ cultured thymuses: inhibitory effect of in vitro interferon treatment.

Thymuses of 14-day-old AKR mouse embryos were infected with Gross murine leukemia virus (MuLV) and then maintained in organ culture for 3 weeks. When they were transplanted to 3-week-old (AKR X C3H)F1 mice, approximately 50% of these developed T lymphomas within 3-4 months. Most (22/23) tumors were of host, F1-hybrid, origin while only one was of donor AKR type. No clear evidence for in vitro MuLV-induced lymphoma cells was therefore obtained. Exposure of MuLV-infected embryonic thymuses to interferon during the organ culture period significantly reduced the incidence of lymphomas in mice receiving such thymus transpalnts. Interferon also prevented the appearance of detectable numbers of MuLV antigen-containing lymphocytes in infected organ-cultured thymuses. In contrast, despite the use of very high interferon concentrations, no effects were seen on the number of viable thymic lymphocytes, their proliferation or responsiveness to the polyclonal T-cell mitogens concanavalin A (Con A) and leukoagglutinin (LA). Thus interferon, presumably through an antiviral effect, can limit the MuLV infection in the thymus and its consequence, i.e. development of a lymphoma.

Natural cell-mediated immunity to lymphoma cells. I. Characteristics of effector cells in a cytostasis assay in vitro.

Spleen cells from normal, nonimmune, CBA or (CBA X AKR)F1 mice markedly and rapidly inhibited the incorporation of [3H]thymidine by two different T-cell lymphomas in an in vitro cytostasis assay. These were the I-529 lymphoma of spontaneous AKR origin and the Moloney murine leukemia virus-induced YAC lymphoma of A mouse origin. Spleen cells were the most efficient inhibitors for both types of target cells, whereas lymph node cells were much less active and thymus cells showed little or no activity. Granulocytes, as well as conventional T- and B-lymphocytes, were excluded as important contributors to the cytostatic cell population. Spleen cells were separated on nylon wool, Sephadex G-10 columns, or plastic petri dishes and tested for activity in the cytostasis assay or for cytotoxicity against 51Cr-labeled lymphoma target cells. Adherent cells carried almost all cytostatic activity against the AKR lymphoma but also showed significant cytotoxic activity against these target cells. In addition, the cytostatic activity against the YAC lymphoma was mainly due to adherent spleen cells, but nonadherent cells were relatively more active against this target than against I-529 cells. Such nonadherent spleen cells further showed increased cytotoxic activity, compared to the whole spleen cell population.

In vitro establishment and some properties of AKR thymoma cell lines.

Lymphoid cell lines could easily be directly established in vitro from spontaneous thymomas of aged AKR mice. The established lines all carried the Thy-1.1 antigenic marker of T lymphocytes. They differed markedly, however, from one another in several respects. Thus, they showed high or low quantity of Thy-1.1 antigens per cell, high or low sensitivity to cortisone and thymidine, as well as differing morphology and growth rate. The observed heterogeneity suggests that such AKR thymoma cell lines may provide a valuable tool to study T lymphocyte properties and the biology of the AKR thymoma, in particular non-immune and immune mechanisms influencing thymoma cell growth.

Spontaneous and induced appearance of murine leukemia virus antigen containing cells in organ cultures of embryonic mouse thymus.

The potential of embryonic thymus organ cultures for studies on relations of endogenous MuLV, lymphoid cells and thymic microenvironment to lymphoma development were evaluated. Four main findings are reported. First, thymuses of 14-day-old CBA and AKR embryos could be maintained in organ cultures for at least 9 weeks with sustained production of lymphocytes. Lymphopoiesis in CBA and AKR thymuses were not grossly different. Secondly, an indirect immunofluorescence (IF) technique demonstrated spontaneous appearance of MuLV-antigen-containing cells in AKR, but not in CBA thymuses. Such spontaneous MuLV expression first occurred after 16 days of organ culture, thereafter infrequently and at random in individual thymus cultures. Thirdly, incubation of AKR and CBA thymuses in lymphoma extract containing AKR-type MuLV at initiation of organ cultures induced MuLV-antigen-containing cells. These were first detected after 7-14 days in culture, somewhat earlier and initially more frequently in AKR than in CBA thymuses. In the former, induction was accompanied by a clear reduction in the number of lymphocytes per thymus. Fourthly, iododeoxyuridine (IdUrd) treatment of AKR thymuses on cultute day 0, 3 or 7 decreased the number of lymphocytes per thymus and induced appearance of MuLV-antigen containing cells, assayed 8-20 days later. The IdUrd effect was most marked on day 0, and decreased sucessively on days 3 and 7. IdUrd had a much slighter effect on CBA thymuses, causing a lower reduction in cell numbers and inducing few MuLV-antigen cells. These main results clearly demonstrate the potential usefulness of the organ culture system for studied on leukemogenesis. It may be directly applied to answer several questions raised by detailed findings in our study.