Histocompatibility antigens acting as helper determinants for tumor-associated antigens of murine lymphosarcoma

Analysis of Rabbit and Guinea PIG Complement Efficiency in Cytotoxicity Tests against Fibrosarcoma and Lymphosarcoma Cells

In a complement-dependent 51Cr cytotoxicity assay, using as target murine fibrosarcoma or lymphosarcoma cells, the rabbit complement (RC) was more efficient than guinea pig complement (GPC) when tested either with strong antisera, such as anti-histocompatibility sera, or with weak sera, such as sera from normal mice shown previously to possess a natural antitumor response. The high efficiency of RC was not due to activation by antibodies of a different class or specificity than those activating GPC. In fact, both 2-mercaptoethanol (2-Me)-sensitive or-resistant immunoglobulins could activate both RC and GPC, and the results of absorption tests indicated that the antibodies detected using either of the 2 complements were directed against the same specificities. In addition, the results of tests searching for cooperative antibodies excluded that a cooperative effect might be responsible for the high efficiency of RC. With weak antisera, sera of different rabbits were found to have different complement activity.

Immunity to B16 melanoma in mice immunized with IL-2-secreting allogeneic mouse fibroblasts expressing melanoma-associated antigens

Co-presentation of weak tumour-associated antigens along with strongly immunogenic determinants leads to the development of an anti-tumour immune response in recipients syngeneic with the tumour. Tumour immunity develops in mice immunized with tumour cells modified by the introduction of cDNA for interleukin-2 (IL-2). Here, we report the anti-tumour response following immunization with an IL-2-secreting cell construct that expresses tumour-associated antigens, along with allogeneic major histocompatibility antigens. The construct was prepared by transfecting LM(TK-) mouse fibroblasts (H-2k) with genomic DNA from B16 melanoma cells syngeneic in C57BL/6J mice (H-2b). Transfectants expressing melanoma-associated antigens (MAA) were then infected with an expression-competent retroviral vector containing a cDNA specifying human IL-2. Cytotoxicity toward B16 cells was detected for as long as 5 months in both spleen and macrophage cell populations in C57BL/6J mice immunized with the IL-2-secreting cells. Mice immunized with non-IL-2-secreting, MAA-positive allogeneic cells developed melanoma immunity as well, but to a lesser extent. Immunity to 2 tumour-cell lines expressing the H-2d haplotype and to YAC-1 cells was detected in peritoneal macrophages, but not in spleen cells from C57BL/6J mice immunized with the cell construct, indicating that the response to B16 cells was only partially specific. C57BL/6J mice immunized with the IL-2-secreting cell construct survived significantly longer, following an injection of viable B16 cells, than mice in various control groups. The contribution of allogeneic antigens to the melanoma immunity was indicated by the failure of mice syngeneic with LM(TK-) cells to develop melanoma immunity following immunization with non-IL-2-secreting, MAA-positive cell constructs. The formation of IL-2 partially compensated for the lack of allogeneic antigens.

Persistence of the immunoprotective effects of leukemia X fibroblast hybrid cells toward leukemia in histocompatible mice

Hybrids of ASL-1 murine leukemia cells and LM(TK-) cells, a cultured line of mouse fibroblast origin, stimulate partial immunity toward ASL-1 cells in (A/J X C3H/HeJ)F1 mice (F1 mice). Such mice ordinarily exhibit no resistance to the malignant proliferation of ASL-1 cells. Unprotected animals invariably die within 14-18 days after receiving as few as 200 ASL-1 cells. The hybrid cells, the mice used in the experimental studies and the leukemia cells used for challenge all share the same histocompatibility antigens. ASL-1 cells are H-2a; LM(TK-) cells are H-2k, both ASL-1 X LM(TK-) hybrid cells and A/J X C3H/HeJ)F1 mice are H-2a/k. The long-term persistence of the immunoprotective properties of the hybrid cells toward murine leukemia was investigated by using cells that had been in continuous culture for approx. 36 months. (A/J X C3H/HeJ)F1 mice injected previously with hybrid cells in continuous culture and then challenged with up to 10(7) ASL-1 cells survived longer (p less than 0.001) than mice who had not received hybrid cells previously. Some mice challenged with lesser number of ASL-1 cells survived indefinitely (greater than 200 days). The median survival time of F1 mice injected simultaneously with 10(7) hybrid cells and 200 or 2000 ASL-1 cells was significantly (p less than 0.001) prolonged as well, although the differences between experimental and control groups are less pronounced than if the hybrid cells were injected before challenge with ASL-1 cells. The hybrid cells like those freshly prepared continue to be rejected by histocompatible precipients. In no instance has there been evidence of a progressively growing tumor of hybrid cells in immunocompetent F1 mice. Hybrid cells like those investigated previously do form rapidly growing metastasizing tumors in immunodeficient nu/nu (BALB/c) or X-irradiated (550 R) F1 mice. The cells possess approx. 70 chromosomes (reduced from 85) including chromosomes identified as having originated in each parental source. Like (A/J X C3H/HeJ)F1 animals, they continue to express both H-2a and H-2k antigenic determinants.

Role of the B-G-region antigen in the humoral immune response to the B-F-region antigen of chicken MHC

In the chicken MHC there exist two regions, designated F and G, which were separated by crossing-over. The F region contains genes controlling all functions characteristic of the MHC. So far only one gene has been assigned to the G region and it is responsible for the presence of an RBC antigen. When cross-immunizing animals of the congenic lines CB and CC with erythrocytes, we have found that both F- and G-specific antibodies were produced. By using the recombinant haplotypes Br1 and Br2 we were able to dissociate the F from the G antigen and immunize with them separately. It was found that production of F antibodies required the copresence of the G antigen, whereas G antibodies were formed regardless of the presence of absence of the F-region antigen. It could be demonstrated that a prerequisite of the role of the G antigen with respect to the F antigen was the localization of both antigens on the same erythrocyte. Possible mechanisms underlying this phenomenon are discussed.

In Vivo Resistance and in Vitro Cellular Reactivity against Lymphosarcoma Cells in Immunized Mice

In an earlier report we have shown that an allogeneic but not a syngeneic immunization of mice with lymphoma cells evoked a humoral complement-dependent cytotoxic response against lymphoma cells syngeneic with the serum. Here we report the results of an investigation, using the same experimental model, on the cellular antitumor response in vitro and the in vivo tumor resistance. Both the allogeneic and the syngeneic antitumor immunizations induced a cellular immune response that was detectable in vitro and that was not inhibited by the correspondent antiserum that was obtained with the same type of immunization. The humoral and cellular immune responses evoked in our system seem, therefore, directed against different antigenic determinants. In the in vivo experiments the maximal antitumor protection was obtained in mice immunized syngeneically, whereas the allogeneic immunization gave a protection that was similar to that obtained in mice immunized with normal allogeneic thymus cells. However, mitomycin-C-blocked thymus cells were unable to induce any protection against the tumor challenge, whereas blocked allogeneic tumor cells conferred the same degree of protection as that obtained with untreated cells. The in vivo transfer in untreated mice of sera obtained with syngeneic or allogeneic antitumor immunization did not give any protection against the tumor challenge.

Increased growth of Rous sarcomas in chickens pretreated with formalinized syngeneic tumor cells

The effect of inoculating formalinized syngeneic or allogeneic Rous sarcoma cells on the growth of Rous sarcoma virus (RSV)-induced tumors in two related inbred strains of chickens was studied. Chickens from both strains that received three weakly inoculations of syngeneic tumor cells had a significant increase in tumor growth and mortality after subsequent challenge with RSV. Development of RSV-induced tumors in chickens pretreated with formalinized allogeneic tumor cells (i.e. incompatible for major histocompatibility complex (MHC) antigens) was similar to what we observed in nonpretreated control chickens. The finding that the tumor-host relationship is altered only in chickens pretreated with formalinized syngeneic RSV-transformed cells, suggests that tumor-associated antigens of Rous sarcomas are modified MHC antigens analogous to "altered self" antigens thought to be present on certain virus-infected cells. If this hypothesis is correct, the results we obtained with formalin-killed syngeneic tumor cells can be explained on the basis of three possible mechanisms: immunological enhancement, immune tolerance or induction of antibody to anti-tumor idiotype. The merits of each mechanism in accounting for the results are discussed.