Antigenic diversity of tumors chemically induced within the progeny of a single cell

Criteria to make animal studies more relevant to treating human cancer

Certain aspects of experimental tumor models in mice most accurately reflect the biology and immunology of cancer in patients. A survey of experimental cancer immunotherapy papers published in 2020 shows most do not achieve cancer shrinkage although treatment is initiated at an early time point after cancer cell injection, which does not reflect cancer immunotherapy in patients. Even then, few current experimental approaches eradicate the injected malignant cells, most only delay outgrowth. The value of targeting mutation-encoded tumor-specific antigens becomes increasingly evident while problems of finding normal gene-encoded tumor-associated antigens as safe, effective targets persist. It might be time to refocus on realistic experimental settings and truly cancer-specific targets. These antigens are associated with the least risk of side effects.

Mass spectrometry driven exploration reveals nuances of neoepitope-driven tumor rejection

Neoepitopes are the only truly tumor-specific antigens. Although potential neoepitopes can be readily identified using genomics, the neoepitopes that mediate tumor rejection constitute a small minority, and there is little consensus on how to identify them. Here, for the first time to our knowledge, we use a combination of genomics, unbiased discovery mass spectrometry (MS) immunopeptidomics, and targeted MS to directly identify neoepitopes that elicit actual tumor rejection in mice. We report that MS-identified neoepitopes are an astonishingly rich source of tumor rejection-mediating neoepitopes (TRMNs). MS has also demonstrated unambiguously the presentation by MHC I, of confirmed tumor rejection neoepitopes that bind weakly to MHC I; this was done using DCs exogenously loaded with long peptides containing the weakly binding neoepitopes. Such weakly MHC I–binding neoepitopes are routinely excluded from analysis, and our demonstration of their presentation, and their activity in tumor rejection, reveals a broader universe of tumor-rejection neoepitopes than presently imagined. Modeling studies show that a mutation in the active neoepitope alters its conformation such that its T cell receptor–facing surface is substantially altered, increasing its exposed hydrophobicity. No such changes are observed in the inactive neoepitope. These results broaden our understanding of antigen presentation and help prioritize neoepitopes for personalized cancer immunotherapy.

Neoepitopes identified by mass spectrometry are a rich source of tumor rejection antigens, including those with a weak binding to MHC I.

Harnessing the antigenic fingerprint of each individual cancer for immunotherapy of human cancer: genomics shows a new way and its challenges

The idea that individual tumors are antigenically unique has been around since the very dawn of our recognition of adaptive immune response to tumors. That idea has inspired a small number of attempts at individualized immunotherapy of human cancers. Such previous attempts for solid tumors have been hobbled by an inability to define the individually unique antigenic repertoire of tumors because of technological difficulties. The new availability of rapid and cheap high throughput DNA sequencing promises to overcome that hurdle. Using this new ability, coupled with bio-informatic tools, it is now possible to define the immunogenic repertoire of any tumor to a high degree of granularity within a practical time frame and an acceptable cost. The development of these ideas, and a small number of such studies that underscore this promise, is discussed. This new way--of characterizing the tumor immunome through characterization of the tumor genome--has distinct challenges, including selection of the appropriate peptides, choosing methods of immunizations that can incorporate tens of epitopes, and addressing issues of antigenic heterogeneity of tumors. However, tools for meeting these challenges exist and are emergent.

The flip side of immune surveillance: immune dependency

The growths of many and perhaps all tumors may be stimulated rather than inhibited by a quantitatively low level of immunity. The reason tumors have antigens may be that tumors do not develop in vivo in the absence of at least a minimal immune reaction; in this sense, cancer may be considered an autoimmune disease. This review, based largely on the work of our own laboratory, outlines the data showing that the titration of anti-tumor immunity exhibits the phenomenon of hormesis, i.e. the dose-response curve is non-linear such that low levels of immunity are generally stimulatory but larger quantities of the same immune reactants may inhibit tumor growth. Evidence is also reviewed that suggests that the immune response may vary qualitatively and quantitatively during progression, such that there seems to be, during oncogenesis, a very low level of immune reaction that aids initial tumor growth, followed by a larger reaction that may cause remission of early neoplasms, followed, if the neoplasm survives, by a relative immunologic tolerance to the tumor that may be dependent, at least in part, on suppressor cells. This knowledge may help to explain some clinical observations concerning the relationships among tumor types and the organ distribution of metastases.

Antigen(s)-specific tumour-infiltrating lymphocytes from tumour induced by human herpes virus-6 (HHV-6) DNA transfected NIH 3T3 transformants

Tumour infiltrating lymphocytes (TIL) have recently been shown to mediate potent therapeutic effects in certain malignancies in mice and in humans. To understand the mechanism of TIL immunotherapy it would be advantageous to generate tumour-specific TIL and to study a defined system of TIL and target cells in which the tumour epitope(s) recognized by TIL might be identified. We have established tumourigenic cell lines by transfection of NIH 3T3 cells with the entire genome of human herpesvirus-6 (HHV-6) and its small fragment (about 5% of the viral DNA sequence). Injection of these cells into nude mice produced tumours termed G-2T and 14-2T, respectively. Cell lines derived from these tumours when injected in NIH Swiss mice produced tumours, G-2TS and 14-2TS, respectively. We have generated TIL from G-2TS tumour that can kill G-2TS tumour cells in vitro but not other related tumours (14-2TS or MCA-106). These TIL can be expanded between 2-6.5 every 3-5 days. The TIL proliferated in tissue culture in response to recombinant interleukin-2 and interleukin-4 and maintained their tumor specificity for up to 6 months in vitro. Their phenotype was Thy 1.2+, Lyt-2+ and L3T4-. The availability of such tumour-specific stable TIL lines and specific viral-transformed targets will provide an opportunity to characterize the tumour-associated antigen critical for the specific cytotoxicity in this system and thereby to clarify the mechanism of this promising immunological approach to cancer therapy.

Tumor antigens defined by cloned immunological probes are highly polymorphic and are not detected on autologous normal cells

We have isolated UV light-induced and spontaneous tumors along with nonmalignant cells and tissues from each host. CD8+ CTL clones generated to a number of highly immunogenic UV-induced tumors did not react with autologous normal fibroblasts nor with autologous second tumors. Using up to 25 independently induced tumors as targets, these CTL clones were found to be uniquely specific for the particular tumor used for immunization even when multiple tumors isolated from the same animals were used as targets. In addition to this extensive antigenic diversity of independently induced tumors, we found that a single cancer cell can express multiple independent antigens that were uniquely expressed on the tumor but were not detectable on autologous nonmalignant fibroblasts. A poorly immunogenic spontaneous tumor was also found to express an antigen that was uniquely specific for the immunizing tumor in that it was absent from any of 25 other tumors tested. This antigen was recognized by a mAb and not detected on autologous nonmalignant fibroblasts or on an autologous second spontaneous tumor. These findings demonstrate that syngeneic CTL clones or mAbs can define unique antigens on UV-induced or spontaneous tumors. The use of autologous nonmalignant fibroblast targets made it unlikely that these antigens were widely expressed on normal cells. The availability of cloned immunological probes to antigens on tumors isolated with autologous normal cells will allow a reliable identification of the genetic origins of unique antigens on experimentally induced and spontaneous tumors and permit a decisive answer to whether these unique antigens are encoded by normal genes or by genes that have undergone somatic mutations; i.e., whether these antigens are truly tumor specific.

Advances in the immunobiology of the skin. Implications for cutaneous malignancies

Recent advances in cutaneous immunobiology have led to the realization that skin is an important and unique immunologic organ. Studies on the immunobiology of skin cancers induced by ultraviolet radiation indicate that immune mechanisms can play a crucial role in the development of cutaneous tumors. This paper summarizes the evidence linking skin and the immune system and discusses current hypotheses concerning the mechanisms by which UV radiation interferes with cutaneous immunity. The significance of these findings for cutaneous carcinogenesis is discussed.

Tumour-related antigen specificities associated with 3-methylcholanthrene-treated rat embryo cells

Rat embryo cells were treated in vitro for 18 h with 10 micrograms/ml 3-methylcholanthrene (MCA). Syngenetic male rats were immunized with several inocula of treated cells to prepare antisera which were screened for membrane immunofluorescence reactivity against panels of established chemically-induced syngeneic rat tumours. Three separate antiserum pools raised against MCA-treated cells reacted with certain chemically-induced tumours, whereas antisera to control (DMSO-treated) cells were completely negative. The reactions observed were reproducible and highly specific for particular target tumours. Absorption studies indicated that each antiserum contained antibodies to several different antigens, present on different tumours. Antiserum prepared against extranuclear membrane from MCA-treated cells, rather than intact MCA-treated cells, was negative. This suggests that the antibody responses were directed against antigens arising subsequently to MCA treatment and injection into syngeneic hosts. It is postulated that carcinomgen treatment results in the acquisition of multiple neoantigens among a treated cell population, which represent an early change in a sequence of events leading to malignant transformation.

Expression of alien H-2 specificities of a chemically induced BALB/c fibrosarcoma

The presence of alien histocompatibility antigens on the cell surface of the 3-methylcholanthrene-induced BALB/c (H-2d) fibrosarcoma C-1, was investigated by serological and transplantation studied. Absorption experiments with monospecific alloantisera showed that C-1 cells expressed their original private (H-2.4 and 31) and public (H-2.3, 8, 28, and 35) specificities. C-1 cells were also able to absorb monospecific antisera directed to the private specificity H-2.23 of the H-2k haplotype, as well as antisera to the public specificities H-2.1, 5, 11 11 and 25 (H-2k and in part H-2q, H-2a and H-2b haplotypes), which are absent from H-2d normal cells. Conversely, other alien specificities (H-2.2, 17, 30, 32, and 33) were not detected on C-1 cells. The C-1 cells were also unable to absorb the activity of an anti-Ia serum (1-28) directed to 1a.1, 2 and 19 (lak) specificities. Transplantation studies showed that resistance against the challenge of C-1 cells could be induced in syngeneic BALB/c mice by preimmunization with normal tissues from C3Hf and AKR (H-2k), A (H-2a) and C57BL/6J (H-2b) strains (expressing all or some of the extra H-2 antigens of the tumor) whereas no protection was obtained with DBA/2 (H-2d) or with W/Fu rat tissues. The anti-tumor activity could be passively transferred by BALB/c lymphoid cells immune to normal C3Hf, AKR, A, and NIH (H-2q) tissues, but no protection was achieved with lymphoid cells immune to DBA/2 or to W/Fu normal rat tissues. These data indicate that foreign H-2 antigens are expressed on C-1 tumor and that they might function as tumor-associated transplantation antigen which was shown to be present and individually distinct on this sarcoma by appropriate in vivo tests.

Chemical and immunological studies of cell surfaces from normal and transformed cells

Immunological and chemical studies of cell surfaces from normal and transformed BALB/c fibroblasts have shown alterations associated with transformation. The cells studied include normal lines which do not cause tumors when injected into BALB/c mice, viral transformants, and spontaneous transformants which cause tumors that either regress or grow progressively, killing the host. The spontaneously transformed progressors include cell lines which are immunogenic and nonimmunogenic as determined by the ability of tumor excision to protect an animal from subsequent rechallenge by tumor cells. Tumor-bearing mice produce lymphocytes which are nonspecifically cytotoxic for all the normal and transformed lines. Some of the cell lines induce specific antibody formation in BALB/hosts. Antisera have been prepared in rabbits which are specific for the transformed cell lines. These antisera can be used to determine specific surface changes on the transformed cells. Chemical studies have shown glycolipid alterations between the normal cells and some, but not all, of the transformants. Glycoproteins labeled by lactoperoxidase-125I or [3H] glucosamine were compared by SDS gel electrophoresis. Results from these studies do not show changes associated with malignancy. Individual glycoprotein regions from gels were treated with pronase, and the glycopeptides compared by Sephadex G50 chromatography. Alterations in glycopeptides from several cellular glycoproteins are the only changes which appear to be associated with malignancy.

Alien histocompatibility determinants on the cell surface of sarcomas induced by methylcholanthrene. I. In vivo studies

Groups of BALB/c mice were immunized to normal tissues (skin and/or liver plus kidney) of C3Hf, C57Bl/6, DBA/2 and AKR strains and challenged with either of two syngeneic 3-methylcholanthrene-induced immunogenic sarcomas, ST2 and TZ15, or with a "spontaneous" non-immunogenic BALB/c sarcoma, B2. It was found that anti-C3Hf and anti-DBA/2 immune mice were significantly protected against the growth of ST2, whereas anti-AKR immune mice rejected TZ15; no protection was elicited by immunizing with normal tissues of any strain against B2, which lacked individual tumor-associated transplantation antigens (TATA). The reciprocal experiment, i.e. the immunization of BALB/c mice with tumor cells and challenge with skin grafts of different strains, was also carried out with ST2 and TZ15. Accelerated rejection of all the various allogeneic skins was observed in anti-ST2 immune mice and of AKR and C3Hf skin in anti-TZ15 immune animals. In addition the Winn test demonstrated that lymph-node cells of BALB/c mice immune to C3Hf or DBA/2 tissues were specifically inhibitory for ST2, and that lymph-node cells immune to AKR tissues protected against TZ15. In a further experiment both ST2 and TZ15 tumors were left to grow in (C3Hf X BALB/c)F1, (C57Bl/6 X BALB/c)F1, (BALB/c X DBA/2)F1 and (BALB/c X AKR)F1 mice; the tumors were then excised and the "immune" mice challenged with the related tumor to measure their immune response in comparison with that elicited by the same procedure in BALB/c mice. ST2 was highly immunogenic in syngeneic BALB/c mice and in all the hybrid combinations except (C3Hf X BALB/c)F1 mice, where it completely lost its immunogenicity; TZ15 showed a certain loss of immunogenic strength in (BALB/c X AKR)F1 hybrids. It was concluded that TATA of ST2 contain antigenic determinants expressed on the normal cells of C3Hf and DBA/2 strains, and that TATA of TZ15 are likely to share antigens with AKR normal tissues.

Restoration of specific immunity against SV40 tumor-specific transplantation antigen to lymphoid cells from tumor-bearing mice

Specific cell-mediated immunity to SV40 tumor-specific transplantation antigen (TSTA) in BALB/c mice undergoing progressive tumorigenesis by syngeneic SV40-transformed cells (VLM) was investigated in vivo using a tumor-cell neutralization test. Specific cellular reactivity to SV40 TSTA was not detected in BALB/c mice bearing large tumors (10-15 mm mean diameter) but was demonstrable after tumor excision. Specific cytotoxic reactivity against syngeneic SV40-transformed cells in vivo could be restored to lymphoid cells from VLM tumor-bearing mice either by culturing the lymphoid cells in vitro or by treating them with papain or trypsin. Enzyme-treated lymphoid cells from MCA tumor-bearing BALB/c mice had no cytotoxic reactivity against VLM cells. These studies suggest that tumor-bearing hosts possess lymphocytes which are sensitized to the TSTA of the tumor but that the reactivity of these lymphocytes is blocked.

Malignant hemangioendotheliomas produced by subcutaneous inoculation of Balb/3T3 cells attached to glass beads

The Balb/3T3 mouse embryo cell line has been frequently used in cancer research as representative of nontumorigenic cells with the characteristic in vitro properties of postconfluence inhibition of cell division, low saturation density, and anchorage dependence. On the reasoning that anchorage dependence might also apply in vivo, each of nine mice were subcutaneously inoculated with an average of 15,400 Balb/3T3 cells attached to two glass beads 3 millimeters in diameter. After 8 weeks, all the mice had developed large bloody tumors that microscopically proved to be hemangioendotheliomas. Ther inoculation of Balb/3T3 cells alone or beads alone produced no tumors. Transplants of each tumor into normal mice grew to kill the animal within 6 weeks. Tumor cells from collagenase-disaggregated tumor tissue had a plating efficiency of 21.2 percent compared to that of normal adult subcutaneous fibroblasts of less than 0.1 percent. The tumor cells in vitro closely resembled Balb/3T3 cells in appearance and were tumorigenic at a dose of 10-4 cells. A second, repeat experiment produced the same type of tumors grossly and microscopically in 17 of 25 mice between 99 and 211 days after inoculation of the Balb/3T3 cells attached to glass beads. These findings require a reassessment of the postulate that low saturation density, postconfluence of cell division, and anchorage dependence are characteristic in vitro properties only of nonneoplastic cells.

Serologic evidence for cross-reacting antigens in two carcinogen-induced murine sarcomas

Serological evidence is presented that two chemically-induced (by methylcholanthrene and 3,4-benz(a)pyrene) sarcomas of C3HF mice contain cross-reacting tumor-associated cell-surface antigens. Xenogeneic and syngeneic antitumor antisera against the two sarcomas were studied with an isotopic, complement-dependent, antibody-mediated microcytotoxicity assay and an isotopic antiglobulin test for the detection of antibodies to tumor-associated antigens, in vitro. Absorportions with various tissues were performed which consistently revealed that the specific activity of the antitumor antisera could be removed by absorption with cells from either chemically-induced tumor, while absorption with syngeneic normal adult tissues, normal fetal tissues, or cells from a histogenetically unrelated tumor (spontaneous mammary carcinoma) failed to remove any specific activity. In view of the individual character of carcinogen-induced tumor antigens as detected by tumor transplantation techniques, our results suggest that chemically-induced murine sarcomas (even when induced by different carcinogens) contain both private and common cell-surface antigens, the latter detectable by serological methods. These common tumor-associated antigens may be related to a viral genome involved in the nalignant transformation of carcinogen-induced marine sarcomas.