An isotope-release assay and terminal-labeling assay for measuring cell-mediated allograft and tumor immunity to small numbers of adherent target cells

Growth arrest of proadipocytes at a distinct predifferentiation G1 state associated with cytotoxic responsiveness to 8-bromo cyclic AMP

The control of cell proliferation can result from the coupling of growth arrest and differentiation. In this regard, we recently demonstrated that growth arrest which precedes the differentiation of 3T3 T proadipocytes must occur at a distinct state in the G1 phase of the cell cycle (GD). Cells arrested at GD differ in several biological parameters from cells arrested in G1 at other states induced by either serum deprivation (GS) or nutrient deficiency (GN). Specifically, GD-arrested cells can differentiate in the absence of DNA synthesis and GD-arrested cells can be induced to proliferate when stimulated with 1-methyl-3-isobutylxanthine; GS- and GN-arrested cells cannot. In addition, GD-, GS- and GN-arrested cells reside at topographically distinct states in G1. We now report that GD-arrested proadipocytes are also distinct in that they are highly sensitive to a cytotoxic effect of 8-bromocyclic AMP, whereas GS- and GN-arrested cells are not.

Some characteristics of natural cytostatic mouse splenocytes

Murine B16 melanoma cells and metastasis variants of this tumor are resistant to NK activity mediated by normal splenocytes. The B16 cells are, however, sensitive to splenocyte-mediated cytostasis. Cytostasis was measured by a [125I]UDR incorporation-inhibition [(125I]UDR I-I) assay. The main characteristics of the [125I[UDR I-I assay and of the cells mediating it are as follows: The activity is mediated by splenocytes but not by thymocytes, it is not syngeneically restricted and it does not decrease with age. The presence of effector cells is required as splenocyte supernatants or supernatants of effector-target cell mixtures do not cause [125I]UDR I-I. The activity is probably mediated by at least 2 populations of non-phagocytic splenocytes. The first population adheres to plastic surfaces and to Sephadex G-10 columns while the other does not. The sensitivity to [125I]UDR I-I of the high metastasis B16 variant was similar to that of the low metastasis variant.

Treatment of feline leukemia and reversal of FeLV by ex vivo removal of IgG: a preliminary report

Cats that were spontaneously infected with feline leukemia virus (FeLv) were treated with a combination of low-dose irradiation and extracorporeal immunosorption using formalin and heat-fixed S. aureus as a non-specific immunosorbent to remove plasma IgG and immune complexes. The treatment resulted in reduction of circulating lymphoblasts within two weeks and clinical improvement of three of the five animals. A reversal of the FeLV status is reported in five of five cats. Two of the five cats remain FeLV negative and completely tumor free seven and eight months post-therapy at the time of writing (July 1979). A third cat returned to an FeLV positive state but remained tumor free for 24 weeks. Another cat responded to the therapy by reduction of lymphoblasts and became FeLV negative but died of a hemorrhage during an immunosorption. The last cat's status was FeLV positive, then FeLV negative, and finally FeLV positive again. He died 20 weeks after initiation of therapy. During the treatment there was a weight gain in the three cats responding by tumor regression. The results are discussed in terms of a removal of some type of immunoinhibiting factors such as antigen-antibody complexes or suppressor molecules.

T-T hybridoma product specifically suppresses tumor immunity

Culture supernatants of spleen or thymus cells from BALB/c mice bearing transplanted, syngeneic, methylcholanthrene-induced sarcomas suppress T lymphocyte-mediated lysis of cells from the tumor borne by the donor of the spleen or thymus cells. On this basis, we hybridized thymus cells from mice bearing sarcoma MCA-1490 with cells from the T lymphoma BW5147. The hybrids (hybridomas) formed were tested for production of factors that could suppress T lymphocyte-mediated lysis of MCA-1490 cells. One hybridoma, and a clone derived from it, produced factors that suppressed the lysis of MCA-1490 cells in vitro. In addition, these factors enhanced the growth of MCA-1490 in immune mice and prevented the destruction of MCA-1490 cells by immune lymphocytes in tumor neutralization (Winn) assays. In vitro lysis of cells from another MCA-induced sarcoma by immune lymphocytes was not suppressed. The suppressor factors did not affect the proliferative response of BALB/c lymphocytes to mitogens or the generation of a cytotoxic response to C57BL/6 alloantigens. Neither did they inhibit the generation of primary or secondary cytotoxic responses to murine leukemia virus-related antigens present on a BALB/c lymphoma line, LSTRA. Although our findings suggest that these suppressor factors are specific for MCA-1490, their specificity for antigens restricted to this tumor needs further definition.

Susceptibility of adherent versus suspension target cells derived from adherent tissue culture lines to cell-mediated cytotoxicity in rapid 51Cr-release assays

Preparation of target cells from tissue culture lines which grow adherent to tissue culture vessels is often desirable for tests of cell-mediated cytotoxicity (CMC). In the present study we used cells derived from adherent tissue culture lines to compare the merits of suspension vs. adherent target cells in short-term 51Cr-release assays. Cytotoxic activity of murine spleen cells sensitized in vitro against allogeneic spleen cells or syngeneic sarcoma cells was tested with fibroblast or sarcoma target cells. In parallel tests, aliquots of tissue culture lines were detached and used as either suspension or adherent target cells in CMC assays, matching the concentrations of suspension and adherent target cells. In both allogeneic and syngeneic combinations adherent target cells released less 51Cr spontaneously and were more susceptible to CMC than their suspension counterparts.

A sensitive assay for the detection cytotoxic antibodies to mammalian cell surface antigens

A microcytotoxicity assay for the detection of complement-dependent serum toxicity against adherent cells has been modified to include post-labeling of the target cells with [3H]leucine or [3H]thymidine. The adaptation represents a significant improvement over the visual counting of residual cells. The technique is more objective and less tedious than the original procedure, while retaining the features of economy of cells and sera, reproducibility, and sensitivity. Examples are given which demonstrate the suitability of the modified assay for the analysis of human and mouse tumor antigens using autologous, allogeneic, and syngeneic sera.

Cell-mediated reactivity to antigens shared by Moloney-virus-induced lymphomas (LSTRA) and certain 3-methylcholanthrene-induced mouse sarcomas

Spleen cells (SC) both from BALB/c mice whose primary Moloney sarcoma virus (MSV)-induced sarcomas had spontaneously regressed and from normal, untreated BALB/c mice, were co-cultivated for 5 days with mitomycin-C-treated LSTRA cells; LSTRA is a BALB/c Moloney lymphoma which shares cell surface antigens with MSV-indiced sarcomas. These SC, referred to as CMR and CU cells, respectively, were shown to be cytotoxic to LSTRA cells in 3 h 51Cr-release assays; CMR cells showed, in most cases, the greatest lytic activity against LSTRA targets. The same SC were also reactive, in 20-h microcytotoxicity and 51Crassays, against target cells from a variety of transplanted sarcomas indiced by 3-methylcholanthrene (MCA) in Balb/c mice. The highest reactivity was seen when CMR or CU cells were tested against target cells from sarcoma lines that expressed an NB-ecotropic MuLV cross-reacting serologically with Moloney virus. Reactivity against isotope-labelled tumor cells expressing MuLV-associated cell surface antigens could be competititively inhibited by adding unlabelled tumor cells expressing such antigens. Finally, Winn assays were performed in which CMR cells strongly inhibited the outgrowth of cells from three sarcoma lines that express the NB-ecotropic MuLV. There was less but significant inhibition of cells from some other MCA sarcomas, either negative for the expression of MuLV-associated antigens or expressing the N-ecotropic endogenous BALB/c MuLV. CU cells enhanced tumor outgrowth in Winn assays at least as often as they inhibited it.