Immunogenic (tum-) variants obtained by mutagenesis of mouse mastocytoma P815. VIII. Detection of stable transfectants expressing a tum- antigen with a cytolytic T cell stimulation assay

Tools to define the melanoma-associated immunopeptidome

Immunotherapies have been traditionally applied in malignant melanoma, which represent one of the most immunogenic tumours. Recently, immune checkpoint modulation has shown high therapeutic efficacy and may provide long-term survival in a significant proportion of affected patients. T cells are the major players in tumour rejection and recognize tumour cells predominantly in an MHC-dependent way. The immunopeptidome comprises the peptide repertoire presented by MHC class I and II molecules on the surface of the body's cells including tumour cells. To understand characteristics of suitable rejection antigens as well as respective effective T-cell responses, determination of the immunopeptidome is of utmost importance. Suitable rejection antigens need to be further characterized and validated not only to systematically improve current therapeutic approaches, but also to develop individualized treatment options. In this review, we report on current tools to explore the immunopeptidome in human melanoma and discuss current understanding and future developments to specifically detect and select those antigens that may be most relevant and promising for effective tumour rejection.

Behavior of the P1.HTR mastocytoma cell line implanted in the chorioallantoic membrane of chick embryos

The P1.HTR cell line includes highly transfectable cells derived from P815 mastocytoma cells originating from mouse breast tissue. Despite its widespread use in immunogenic studies, no data are available about the behavior of P1.HTR cells in the chick embryo chorioallantoic membrane model. The objective of the present investigation was to study the effects of P1.HTR cells implanted on the chorioallantoic membrane of chick embryos. We inoculated P1.HTR cells into the previously prepared chick embryo chorioallantoic membrane and observed the early and late effects of these cells by stereomicroscopy, histochemistry and immunohistochemistry. A highly angiotropic and angiogenic effect occurred early after inoculation and a tumorigenic potential with the development of mastocytoma keeping well mast cells immunophenotype was detected later during the development. The P1.HTR mastocytoma cell line is a good tool for the development of the chick embryo chorioallantoic membrane mastocytoma model and also for other studies concerning the involvement of blood vessels. The chick embryo chorioallantoic membrane model of mastocytoma retains the mast cell immunophenotype under experimental conditions and could be used as an experimental tool for in vivo preliminary testing of antitumor and antivascular drugs.

Inhibition of RL male 1 tumor growth in BALB/c mice by introduction of the RLakt gene coding for antigen recognized by cytotoxic T-lymphocytes and the GM-CSF gene by in vivo electroporation

A DNA vaccine for inducing a tumor immune response was investigated using a well-characterized murine model tumor antigen. We demonstrated that in vivo electroporation augmented the induction of IFNgamma enzyme-linked immunospot (ELISPOT) and cytotoxic T lymphocyte (CTL) generation against pRL1a peptide in BALB/c spleen cells upon immunization with RLakt plasmid. Immunization without in vivo electroporation resulted in only a marginal induction of IFNgamma ELISPOT and CTL generation. Furthermore, co-injection of GM-CSF and RLakt plasmids significantly enhanced the induction of IFNgamma ELISPOT and CTL generation compared to the injection of RLakt plasmid alone. Inhibition of RL male 1 tumor growth was observed by injecting BALB/c mice with GM-CSF and RLakt plasmids using in vivo electroporation, although no effect was observed against an established tumor using the same treatment. No growth inhibition was observed without in vivo electroporation. Immunization with either RLakt plasmid alone, or GM-CSF and pCIneo control plasmids using in vivo electroporation did not inhibit RL male 1 tumor growth.

Sequential involvement of two distinct CD4+ regulatory T cells during the course of transplantable tumor growth and protection from 3-methylcholanthrene-induced tumorigenesis by CD25-depletion

The involvement of two phenotypically different regulatory T cells in different stages of tumor growth was investigated. Treatment of BALB/c mice with anti-CD25 monoclonal antibody (mAb) (PC61), but not anti-CD4 mAb (GK1.5) before RL male 1 or Meth A inoculation caused tumor rejection. On the other hand, treatment of BALB/c mice with anti-CD4 mAb (GK1.5) but not anti-CD25 mAb (PC61) on day 6 after inoculation of the same tumors caused rejection. The findings suggest that CD4+CD25+ T cells downregulated the rejection response in the early stage of tumor growth. On the other hand, putative CD4+CD25- T cells downregulated the tumor rejection response in the late stage. Both CD4+CD25+ and putative CD4+CD25- T cells appeared to inhibit the efficient generation of cytotoxic T lymphocytes (CTL). The present study also demonstrated that the treatment of BALB/c mice with anti-CD25 mAb (PC61) at 4 or 6 weeks after 3-methylcholanthrene (3-MC) inoculation retarded tumor occurrence and prolonged survival.

Th cell-deficient mice control influenza virus infection more effectively than Th- and B cell-deficient mice: evidence for a Th-independent contribution by B cells to virus clearance

The notion that MHC class I- restricted CD8+ T (Tc) cells are capable of resolving autonomously infections with influenza virus is based largely on studies testing virus strains of low pathogenicity in CD4+ T (Th) cell-deficient/depleted mice. To test whether this holds also for pathogenic strains and to exclude possible contributions by B cells, we analyzed PR8 infection in Th cell-depleted B cell-deficient (muMT) mice. These mice, termed muMT (-CD4), showed 80% mortality after infection with a small dose of PR8, which resulted in insignificant mortality in intact or Th cell-depleted BALB/c mice. Infection of muMT(-CD4) mice with a virus of low pathogenicity was resolved without mortality, but, compared with intact BALB/c mice, with delay of approximately 5 and approximately 20 days from lung and nose, respectively. The low mortality of Th cell-depleted BALB/c mice suggested that B cells contributed to recovery in a Th-independent manner. This was verified by showing that transfer of 8-10 million T cell-depleted naive spleen cells into muMT(-CD4) mice 1 day before infection reduced mortality to 0%. The mechanism by which B cells improved recovery was investigated. We found no evidence that they operated by improving the lung-associated Tc response. Treatment of infected muMT(-CD4) mice with normal mouse serum spiked with hemagglutinin-specific IgM did not reduce mortality. Taken together, the data show that 1) the Tc response is capable of resolving autonomously (in conjunction with innate defenses) influenza virus infections, although with substantial delay compared with intact mice, and 2) B cells can contribute to recovery by a Th-independent mechanism.

Expression of Multiple Unique Rejection Antigens on Murine Leukemia BALB/c RL♂1 and the Role of Dominant Akt Antigen for Tumor Escape

Using the pRL1a Ag-loss RL♂1 tumor variant cell line RM2-1, we demonstrated the presence of tumor Ags other than pRL1a that were recognized by CTLs on RL♂1 cells. Semiallogeneic CB6F1 or syngeneic BALB/c CTLs generated against RM2-1 lysed RM2-1 and RL♂1 cells to a similar extent, but no killing was observed with any other tumor or normal cells examined. Clonal analysis and sensitization with reversed phase-HPLC fractions revealed that there were Dd- and Ld-binding peptides recognized by RM2-1 CTLs. Lysis by bulk CTLs stimulated against RL♂1 and limiting dilution analysis suggested that the pRL1a peptide was dominantly recognized to the RM2-1 peptides by CTLs on RL♂1 cells. The rejection response against the parental RL♂1 tumor was much less than that against RM2-1 cells in either CB6F1 or BALB/c mice, suggesting that the presence of altered Akt molecules from which the dominant pRL1a peptide was derived inhibited the rejection response against RL♂1. Depletion of CD4 T cells caused the regression of RL♂1 at the doses in which the tumor grew in untreated mice. The generation of pRL1a CTLs was inhibited in RL♂1-bearing mice. Thus, immunoregulatory CD4 T cells were most likely activated by the altered Akt molecules and inhibited the efficient generation of CTLs against the dominant pRL1a Ag in RL♂1.

Identification of genes coding for tumor antigens recognized by cytolytic T lymphocytes

Strategies have been developed to characterize tumor antigens recognized by cytolytic T lymphocytes (CTL). We use a genetic approach based on the transfection of HLA genes and cDNA libraries in COS cells to isolate the gene producing the antigenic peptide. The tumor-specific expression of this gene can be evaluated by cDNA synthesis and quantitative PCR amplification. Transfection of fragments of the isolated gene allows the identification of the region encoding the antigenic peptide. Peptides are synthesized and tested for their ability to sensitize target cells to lysis by the CTL.

A pulmonary influenza virus infection in SCID mice can be cured by treatment with hemagglutinin-specific antibodies that display very low virus-neutralizing activity in vitro

We have previously shown that a pulmonary influenza virus infection in SCID mice can be cured by treatment with monoclonal antibodies (MAbs) specific for the viral transmembrane protein hemagglutinin (HA) but not for matrix 2. Since both types of MAbs react with infected cells but only the former neutralizes the virus, it appeared that passive MAbs cured by neutralization of progeny virus rather than reaction with infected host cells. To prove this, we selected a set of four HA-specific MAbs, all of the immunoglobulin G2a isotype, which reacted well with native HA expressed on infected cells yet differed greatly (>10,000-fold) in virus neutralization (VN) activity in vitro, apparently because of differences in antibody avidity and accessibility of the respective determinants on the HA of mature virions. Since the VN activities of these MAbs in vitro were differentially enhanced by serum components, we determined their prophylactic activities in vivo and used them as measures of their actual VN activities in vivo. The comparison of therapeutic and prophylactic activities indicated that these MAbs cured the infection to a greater extent by VN activity (which was greatly enhanced in vivo) and to a lesser extent by reaction with infected host cells. Neither complement- nor NK cell-dependent mechanisms were involved in the MAb-mediated virus clearance.

Immunotherapy for peritoneal ovarian carcinoma metastasis using ex vivo expanded tumor infiltrating lymphocytes

Surgery and chemotherapy have contributed to a modest overall survival in patients with epithelial ovarian carcinoma. It is therefore important to pursue novel therapy strategies for this disease that are different from conventional chemotherapy. Tumor infiltrating lymphocytes (TILs) from patients with ovarian carcinoma may represent an active immune response of the host directed against the tumor cells. These TILs can be expanded in vitro in low concentrations of recombinant interleukin-2 (rIL-2) by a few thousandfold. The resulting T-cell lines comprise CD3+CD4+TCR alpha beta + or CD3+CD8+TCR alpha beta + cells, or mixtures of both. These T-cell lines may exhibit either tumor-specific cytotoxicity against autologous tumor cells, or produce cytokines (interferon-gamma, tumor necrosis factor, and granulocyte stimulating factor) either in antigen-dependent (tumor-specific) or an antigen-independent manner. T-cell lines exhibiting primarily autologous tumor-specific cytotoxicity were developed from approximately 50% of the patients. Blocking experiments using appropriate monoclonal antibodies revealed that the CD3/TCR complex on the effector cells and the MHC class I antigens on the tumor cells were involved in the cytolytic process. We have developed a four-step method for the expansion of TILs to large numbers (1 x 10(10) to 1 x 10(11)) sufficient for clinical trials in patients with ovarian cancer. We have conducted a pilot clinical trial to examine the feasibility and clinical effects of intraperitoneal TILs and low-dose rIL-2 in patients with advanced ovarian carcinoma who were refractory to platinum-based chemotherapy. More recently, procedures have been developed for obtaining large numbers of purified CD8+ rIL-2-expanded TILs for the treatment of patients with ovarian carcinoma. The evolution of clinical trials and correlative studies necessary to develop an effective adoptive immunotherapy approach were discussed.

Immunogenicity and immunosensitivity of ex vivo human carcinomas: interferon gamma and tumour necrosis factor alpha treatment of tumour cells potentiates their interaction with autologous blood lymphocytes

Human carcinoma cells vary appreciably in the expression of MHC class I, class II, ICAM-1 (CD54) and B7 (CD80) molecules. Short-term in vitro exposure of ex vivo carcinoma cells to interferon gamma and tumour necrosis factor alpha elevated/induced the surface expression of MHC class I, class II and ICAM-1, but only rarely of B7. We found that cytokine treatment elevated the cytotoxic susceptibility and the stimulatory potential of ex vivo tumour cells. This was demonstrated (a) by the increased frequency and elevated level of auto-tumour lysis and (b) by induction of DNA synthesis and generation of cytotoxic lymphocytes in autologous mixed lymphocyte/tumour cell culture (MLTC). The MHC class I and ICAM-1 molecules on the tumour cells were required for interaction with the lymphocytes as indicated by the inhibitory effect of specific mAb both in the stimulation and in the cytotoxic tests. While the cytokine-induced increases in MHC and ICAM-1 on the low-expression tumours were probably important for the modification of functional interaction with the autologous lymphocytes, it is likely that alterations in other properties of tumour cells were also induced which contributed to the phenomenon. This was indicated by the results obtained with several tumours, which expressed indigenously high levels of these molecules but activated the autologous lymphocytes only after cytokine treatment. In several experiments the untreated targets that did not activate the lymphocytes were sensitive to the cytotoxicity of the effectors activated in MLTC. The results show that the afferent and efferent arms of the immune response have different requirements for functional interactions between lymphocytes and tumour cells.

Virus-neutralizing antibodies of immunoglobulin G (IgG) but not of IgM or IgA isotypes can cure influenza virus pneumonia in SCID mice

The ability of monoclonal antibodies (MAbs) to passively cure an influenza virus pneumonia in the absence of endogenous T- and B-cell responses was investigated by treating C.B-17 mice, homozygous for the severe combined immunodeficiency (SCID) mutation, with individual monoclonal antiviral antibodies 1 day after pulmonary infection with influenza virus PR8 [A/PR/8/34 (H1N1)]. Less than 10% of untreated SCID mice survived the infection. By contrast, 100% of infected SCID mice that had been treated with a single intraperitoneal inoculation of at least 175 micrograms of a pool of virus-neutralizing (VN+) antihemagglutinin (anti-HA) MAbs survived, even if antibody treatment was delayed up to 7 days after infection. The use of individual MAbs showed that recovery could be achieved by VN+ anti-HA MAbs of the immunoglobulin G1 (IgG1), IgG2a, IgG2b, and IgG3 isotypes but not by VN+ anti-HA MAbs of the IgA and IgM isotypes, even if the latter were used in a chronic treatment protocol to compensate for their shorter half-lives in vivo. Both IgA and IgM, although ineffective therapeutically, protected against infection when given prophylactically, i.e., before exposure to virus. An Fc gamma-specific effector mechanism was not an absolute requirement for antibody-mediated recovery, as F(ab')2 preparations of IgGs could cure the disease, although with lesser efficacy, than intact IgG. An anti-M2 MAb of the IgG1 isotype, which was VN- but bound well to infected cells and inhibited virus growth in vitro, failed to cure. These observations are consistent with the idea that MAbs of the IgG isotype cure the disease by neutralizing all progeny virus until all productively infected host cells have died. VN+ MAbs of the IgA and IgM isotypes may be ineffective therapeutically because they do not have sufficient access to all tissue sites in which virus is produced during influenza virus pneumonia.

An intracisternal A-particle sequence codes for an antigen recognized by syngeneic cytolytic T lymphocytes on a mouse spontaneous leukemia

Cytolytic T lymphocyte (CTL) clones directed against spontaneous mouse leukemia LEC have been obtained. By transfecting a cosmid library into cells which were then tested for their ability to stimulate the CTL, we identified the gene coding for the antigen recognized by one of these CTL clones. It is the gag gene of an endogenous defective retrovirus that belongs to the intracisternal A particle (IAP) family. A gag-encoded nonapeptide presented by the H-2 Dk molecule caused recognition by the anti-LEC CTL clone. Southern blot and polymerase chain reaction analyses indicated that the expression of the antigen by the LEC tumor cell line resulted from the transposition of an IAP sequence into a new genomic location.

Presentation of mouse tum- P91A antigen from chimeric proteins with different subcellular localizations by class I molecules of the major histocompatibility complex

Like many antigens presented by class I molecules the mouse Ld-binding tum- antigen P91A derives from a cytosolic protein. To decide how stringent this localization is for presentation to cytotoxic lymphocytes (CTL) the P91A template has been inserted in the cDNA of rat esterase ES-10, a protein located in the endoplasmic reticulum (ER), and in the cDNA of mouse interleukin-9, a secretory product of lymphocytes. The esterase construct was also engineered to replace the C-terminal leucine by arginine, which causes secretion of the protein, or to delete the N-terminal presequence, which prevents transfer of the nascent chain to the ER. After cell-free transcription-translation, or transfection in COS cells, the products of the chimeric cDNA had the expected size and localization; however, the truncated form of esterase remained undetected in COS cells. The various chimeric templates were transfected in P1.HTR cells (H-2d); upon challenge with Ld-restricted anti-P91A CTL the cells were lyzed almost as efficiently as cells transfected with the full-length P91A cDNA. We conclude that peptide fragments that bind to class I molecules of the major histocompatibility complex can be generated in the ER.

HLA class I expression and HPV-16 sequences in premalignant and malignant lesions of the cervix

A series of 10 normal cervix epithelia, 38 condylomas, 17 CIN (cervical intraepithelial neoplasm) I/II (low-grade CIN), 10 CIN III (high-grade CIN), 27 squamous cell carcinomas and 7 adenocarcinomas of the cervix were studied in paraffin-embedded sections for the expression of MHC class I antigens, using antibodies against HLA antigens and the immunoperoxidase technique. A PCR technique was also used to evaluate the presence of HPV-16 DNA. All samples from normal tissue, benign, premalignant and CIN III lesions expressed HLA class I antigens. However, 15% of the invasive carcinomas completely lacked HLA-B and HLA-C antigen expression, 20% presented a heterogeneous pattern and 2 cases lacked HLA-B and HLA-C heavy chain but retained beta 2-microglobulin. MHC class I antigen expression on tumors was compared with clinical-pathological parameters. The absence of expression of HLA class I molecules was significantly associated with the Glanz histoprognostic index of malignancy. HPV-16 sequences were detected in 60% of the condylomas, 88% of the CIN I/II, 80% of the CIN III and 82% of the cervical carcinomas. Eight-six per cent of the tumors expressing HLA class I antigen presented HPV-16, whereas only 40% of the nonexpressing tumors did. Our results lead us to the following conclusions: a) HLA class I losses occurred when the tumor became invasive, and in tumors of a more aggressive histological type; b) The presence of HPV-16 was associated with tumors expressing HLA class I antigens.

A nonapeptide encoded by human gene MAGE-1 is recognized on HLA-A1 by cytolytic T lymphocytes directed against tumor antigen MZ2-E

We have reported the identification of human gene MAGE-1, which directs the expression of an antigen recognized on a melanoma by autologous cytolytic T lymphocytes (CTL). We show here that CTL directed against this antigen, which was named MZ2-E, recognize a nonapeptide encoded by the third exon of gene MAGE-1. The CTL also recognize this peptide when it is presented by mouse cells transfected with an HLA-A1 gene, confirming the association of antigen MZ2-E with the HLA-A1 molecule. Other members of the MAGE gene family do not code for the same peptide, suggesting that only MAGE-1 produces the antigen recognized by the anti-MZ2-E CTL. Our results open the possibility of immunizing HLA-A1 patients whose tumor expresses MAGE-1 either with the antigenic peptide or with autologous antigen-presenting cells pulsed with the peptide.

Efficient expression of tum- antigen P91A by transfected subgenic fragments

Mutagen treatment of mouse P815 tumor cells produces immunogenic mutants that express new transplantation antigens (tum- antigens) recognized by cytolytic T cells. The gene encoding tum- antigen P91A comprises 12 exons and a mutation located in exon 4 is responsible for the production of a new antigenic peptide. Transfection experiments showed that the expression of the antigen could be transferred not only by the entire gene but also by gene segments comprising only the mutated exon and parts of the surrounding introns. This was observed with subgenic regions that were not cloned in expression vectors. Antigen expression did not require the integration of the transfected gene segment into a resident P91A gene by homologous recombination. It also occurred when the subgenic segment was transfected without the usual selective gene, which comprises an eucaryotic promoter, and also without plasmid sequences, which are known to contain weak promoters. When a stop codon was introduced at the beginning of exon 4, the expression of the antigen was maintained and evidence was obtained that an ATG codon located in this region served as initiation site for the translation of the antigenic peptide. But we have not obtained evidence indicating that antigenic peptides are direct translation products rather than degradation products of entire proteins.

Transfection and expression of a gene coding for a human melanoma antigen recognized by autologous cytolytic T lymphocytes

Human melanoma line MZ2-MEL expresses several antigens recognized by autologous cytolytic T lymphocytes (CTL). As a first step towards the cloning of the gene coding for one of these antigens, we tried to obtain transfectants expressing the antigen. The DNA recipient cell was a variant of MZ2-MEL which had been selected with a CTL clone for the loss of antigen E. It was cotransfected with genomic DNA of the original melanoma line and with selective plasmid pSVtkneo beta. Geneticin-resistant transfectants were obtained at a frequency of 2 x 10(-4). These transfectants were then screened for their ability to stimulate the production of tumor necrosis factor by the anti-E CTL clone. One transfectant expressing antigen E was identified among 70,000 drug-resistant transfectants. Its sensitivity to lysis by the anti-E CTL was equal to that of the original melanoma cell line. When this transfectant was submitted to immunoselection with the anti-E CTL clone, the resulting antigen-loss variants were found to have lost several of the transfected pSVtkneo beta sequences. This indicated that the gene coding for the antigen had been integrated in the vicinity of pSVtkneo beta sequences, as expected for cotransfected DNA.

A gene encoding an antigen recognized by cytolytic T lymphocytes on a human melanoma

Many human melanoma tumors express antigens that are recognized in vitro by cytolytic T lymphocytes (CTLs) derived from the tumor-bearing patient. A gene was identified that directed the expression of antigen MZ2-E on a human melanoma cell line. This gene shows no similarity to known sequences and belongs to a family of at least three genes. It is expressed by the original melanoma cells, other melanoma cell lines, and by some tumor cells of other histological types. No expression was observed in a panel of normal tissues. Antigen MZ2-E appears to be presented by HLA-A1; anti-MZ2-E CTLs of the original patient recognized two melanoma cell lines of other HLA-A1 patients that expressed the gene. Thus, precisely targeted immunotherapy directed against antigen MZ2-E could be provided to individuals identified by HLA typing and analysis of the RNA of a small tumor sample.

Transfer of long-lasting tumor immunity by immune T cells from MHC congenic mice: migration, survival and tumor-protectivity of cytotoxic donor cells

Immunocompetent B10.D2 (H-2d) mice are able to reject the highly malignant lymphoma ESb of DBA/2 (H-2d) origin very effectively. Seven days after intravenous injection of the ESb tumor cells, B10.D2 mice developed a strong tumor-rejection response which was associated with the generation of anti-tumor T cells in their spleens with direct cytotoxic activity. Most of the cytotoxic potential was directed against the minor histocompatibility differences as demonstrated by the lysis of unrelated DBA/2 derived Eb tumor cells and normal DBA/2 but no B10.D2 derived ConA lymphoblasts. A previously performed clonal analysis, however, revealed a minority population of CTL clones which specifically recognized the ESb specific transplantation antigen (ESb-TATA). When transferred systemically into DBA/2 mice, the B10.D2 anti-ESb immune spleen cells could delay the outgrowth of s.c. transplanted ESb tumor cells. When the ESb tumor cells were experimentally distributed in a s.c. implanted sponge-matrix, the i.v. injected B10.D2 immune cells could confer complete protective immunity against the metastatic tumor, provided the recipients were pre-treated with 5 Gy to allow a better take of the allogeneic cells. The distribution of intravenously injected B10.D2 donor spleen cells was assessed in the recipients up to 50 days by cytotoxicity testing and assaying for the expression of the beta 2 microglobulin allelic form b (beta 2mb). These tests revealed a high propensity of donor cells to populate the spleen and lymph nodes of the DBA/2 recipients. Again this was particularly marked in sublethally irradiated mice where a long-lasting lymphoid chimerism was established.

The gene coding for a major tumor rejection antigen of tumor P815 is identical to the normal gene of syngeneic DBA/2 mice

We showed previously that mouse mastocytoma P815 expresses several distinct antigens that are recognized by cytolytic T lymphocytes (CTL) of syngeneic DBA/2 mice. Antigens P815A and P815B are usually lost jointly and are targets for immune rejection responses in vivo. We used a cosmid library and a CTL stimulation assay to obtain transfectants expressing tumor rejection antigen P815A. From these transfectants we retrieved gene P1A which transferred the expression of both P815A and B. This gene is unrelated to three previously isolated genes coding for tum-antigens. It encodes a putative protein of 224 amino acids which contains two highly acidic domains showing homology with similar regions of nuclear proteins. The P1A gene expressed by tumor P815 is completely identical to the gene present in normal DBA/2 cells. Expression of the gene was tested by Northern blots. Cells from liver, spleen, and a number of mast cell lines were negative, but mast cell line L138.8A produced a high level of P1A message and was lysed by CTL directed against antigens P815A and B. We conclude that major tumor rejection antigens of P815 are encoded by a gene showing little or no expression in most normal cells of adult mice.

Human autologous tumor-specific T cells in malignant melanoma

T cell lines and clones with autologous tumor-specific activity have been developed in malignant melanoma by stimulating peripheral blood lymphocytes (PBL), lymph node lymphocytes or tumor-infiltrating lymphocytes (TIL) with autologous melanoma cells in the presence of recombinant interleukin 2 (rIL2). T-cell lines and clones have been developed with specific cytotoxicity and/or proliferative responses for autologous melanoma targets but not for allogeneic melanoma tumor cells, autologous normal cells or natural killer (NK)-sensitive targets. The concentration of rIL2 is critical for the generation of autologous tumor-specific T-cell lines, with low rIL2 concentrations (up to 800 IU/ml) facilitating the growth of T-cell lines with tumor-specific activity. The alpha beta T-cell receptor (TCR) and the CD3 antigen are involved in specific cytotoxicity and/or proliferative responses of these T-cell lines and clones. An oligoclonal pattern of beta-chain TCR gene rearrangements was observed on T-cell lines and clones with autologous tumor-specific cytotoxicity, suggesting that they are comprised of T cells that have undergone a clonal expansion in response to particular antigen. Autologous tumor-specific cytotoxic T cells are HLA-restricted and recognize on the melanoma tumor cells HLA Class I or possibly Class II antigens plus a tumor-specific determinant. TIL from patients with metastatic melanoma have unique characteristics in comparison with PBL and lymph node lymphocytes and they appear to contain substantial proportions of T cells that have been locally sensitized to autologous tumor cells. Single stimulation of TIL with autologous tumor cells in the presence of rIL2 is sufficient for the generation of T cell lines with autologous tumor-specific activity, whereas, multiple stimulation of PBL and lymph node lymphocytes was required to achieve the same purpose. TIL-derived T cell lines have been expanded in rIL2 in vitro by at least 1,500-fold without losing their activity. Approximately, 40% of the patients exhibited complete or partial responses to adoptive immunotherapy with melanoma TIL and rIL2.

Molecular analysis of MHC-class-I alterations in human tumor cell lines

Molecular characterization of HLA-class-I expression was investigated in human tumor cell lines at the protein and mRNA levels using locus-specific monoclonal antibodies (MAbs) and probes. Some cell lines exhibited a differential expression of HLA-A and HLA-B products and also showed differences in the inducibility of HLA-class-I genes by gamma-IFN. Thus, gamma-IFN stimulation induced predominantly HLA-B mRNA in the HeP-2 cell line, which showed imbalances in basal levels of HLA-A and HLA-B expression. This unequal inducibility of HLA genes may imply that locus-specific regulatory mechanisms are involved in the expression of individual HLA products. The specific mechanism controlling the differential expression of HLA subsets appears to be independent of c-myc activity. Northern blot analysis found no relationship between c-myc mRNA levels and specific mRNA for HLA-A and HLA-B antigens.

Cognate peptides induce self-destruction of CD8+ cytolytic T lymphocytes

Cytotoxic T lymphocytes (CTLs) have been shown to be relatively resistant to cytolytic attack by other CTLs. We show here, however, that cloned CTLs, in the absence of other cells, are destroyed by exposure to their cognate peptides (defined as those that in association with major histocompatibility complex proteins are recognized by the antigen-specific receptor of the T cell). Destruction is proportional to peptide concentration and can be prevented by a second peptide that competes with the cognate peptide for presentation by the class I major histocompatibility complex proteins of the CTLs. The speed and extent of peptide-induced changes in the appearance of CTLs suggest that the destruction may be due primarily to self-recognition and self-destruction of individual CTLs (suicide) rather than to the destruction of some CTLs by others of the same clone in the same culture (fratricide). This effect may also take place in vivo because the appropriately timed injection of a cognate peptide into ovalbumin-immunized mice appeared to deplete their spleens of primed anti-ovalbumin CTLs. The results point to a possible physiologic mechanism for postthymic elimination of cytolytic T cells that recognize their own peptides in association with their own major histocompatibility complex protein. The results also raise the possibility that cognate peptides might eventually prove therapeutically useful for eliminating CTL clones that cause pathological cell destruction, as in some autoimmune diseases and some viral infections.

Antigens recognized on a melanoma cell line by autologous cytolytic T lymphocytes are also expressed on freshly collected tumor cells

Peripheral blood lymphocytes of a melanoma patient were stimulated in vitro with a permanent cell line derived from the autologous tumor. Stable cytolytic T lymphocyte (CTL) clones were obtained that lysed the melanoma cell line and did not lyse autologous Epstein-Barr virus-transformed B lymphocytes or K-562 cells. These CTL clones were directed against two distinct antigens on the melanoma line. In view of the possibility that these antigens could be culture artefacts, we tested the stimulatory ability of tumor cells that had been freshly collected from metastatic relapses on the CTL clones. A considerable CTL proliferation was observed and it appeared to be specific. We conclude that the antigens recognized by the autologous CTL clones on the permanent melanoma cell line were expressed by the tumor cells in the patient.

Structure of the gene of tum- transplantation antigen P198: a point mutation generates a new antigenic peptide

Mutagen treatment of mouse tumor cell line P815 produces tum- variants that are rejected by syngeneic mice because they express new transplantation antigens. These tum- antigens are recognized by cytotoxic T lymphocytes (CTL) but induce no detectable antibody response. By transfecting P815 cell line P1.HTR with DNA of tum- variant P198, we obtained transfectants expressing tum- antigen P198 that could be identified on the basis of their ability to stimulate anti-P198 CTL. This was repeated with DNA of a cosmid library derived from variant P198, and a cosmid carrying the sequence encoding antigen P198 was recovered from a transfectant. Gene P198 is 3 kb long and contains eight exons. It shows no homology with previously identified tum- gene P91A, nor with any gene presently recorded in the data banks. The long open reading frame codes for a 23.5-kD protein. The antigenic allele of gene P198 differs from the normal allele by a point mutation located in exon 7. This mutation causes an Ala to Thr change, and was shown by site-directed mutagenesis to be responsible for the expression of the antigen. An 11-amino acid synthetic peptide covering the sequence surrounding the tum- mutation rendered P815 cells sensitive to lysis by anti-P198 CTL. The homologous peptide corresponding to the normal sequence of the gene did not, but it was able to compete for binding to major histocompatibility complex molecule Kd. We conclude that tum- mutation P198 generates a new epitope recognized by syngeneic T cells. As observed with gene P91A, we found that a fragment of gene P198 that contained only exons 3-7, cloned in nonexpression vectors, transferred efficiently the expression of the antigen.

Induction of high-grade anti-tumor immunity by use of a recombinant H-2Kb/avian erythroblastosis virus erbB gene transfectant

The recombinant H-2Kb-erbB gene, encoding for a part of the H-2 class I antigen and the kinase domain of the V-erbB peptide, was successfully introduced into murine mastocytoma P815 variant P1.HTR cells, which resulted in low but significant cell-surface expression of the hybrid gene product. When the chimeric gene transfectant was inoculated into the CDF1 mice, it soon grew but regressed thereafter. The tumorigenicity of this transfectant was lower than the H-2Kb gene transfectant that expressed the H-2Kb antigen at a comparable level. These CDF1 mice that had received the chimeric gene transfectant obtained a high-grade anti-tumor immunity against the challenge of a high dose of parental tumor. Corresponding to these observations, anti-tumor cytotoxic T lymphocytes, which lyse parental P1.HTR cells but not syngeneic L1210 or NS-1 tumor cells, were developed in the peritoneal cavity of mice that had been inoculated with the transfectant and parental tumor. Definite antibody activity binding to parental P1.HTR tumor cells was also demonstrated in the sera of these mice, precipitating 40-kDa, 74-kDa and 98-kDa molecules from the surface of the radiolabeled P1-HTR tumor cells. The results suggested that the chimeric H-2-erB gene transfectant efficiently triggers both cellular and humoral anti-tumor immune responses.

Structure of the gene of tum- transplantation antigen P91A: the mutated exon encodes a peptide recognized with Ld by cytolytic T cells

Mutagen treatment of mouse P815 tumor cells produces immunogenic mutants that express new transplantation antigens (tum- antigens) recognized by cytolytic T cells. We found that the gene conferring expression of tum- antigen P91A contains 12 exons, encoding a 60 kd protein lacking a typical N-terminal signal sequence. The sequence shows no significant similarity with sequences in current data bases. A mutation that causes expression of the antigen is located in exon 4; it is the only apparent difference between the normal and the antigenic alleles. A short synthetic peptide corresponding to a region of exon 4 located around this mutation makes P815 cells sensitive to lysis by anti-P91A cytolytic T cells. The mutation creates a strong aggretope enabling the peptide to bind the H-2 Ld molecule. Several secondary tumor cell variants that no longer express tum- antigen P91A were found to carry deletions in the gene.

Immunological reactivity towards chondrocytes in rat and man: relevance to autoimmune arthritis

Immunological investigation of articular chondrocytes obtained from rat and man have shown the presence of unique differentiation antigens on the cell surface demonstrated by poly- or monoclonal antibodies in both species, and by the analysis of T cell reactivity in the rat. Both species of chondrocytes express Class I antigens in common with all nucleated mammalian cells and, in man, individual specificities of the MHC A, B, and C locus can be identified using standard histocompatibility testing. Class II antigens are strongly expressed in the rat but are expressed poorly in the human specimens we have analyzed. This finding is at variance with the reports of others and may depend upon the antisera we have used or the diseased state of our patient donors. In the rat, T cell reactivity to chondrocyte antigens is strong and can be demonstrated in both proliferation and cytotoxic assay. Moreover, syngeneic reactivity is present in naive animals, suggesting that rats are not tolerant of their own CSDA. The cross-reactivity found on analysis of cytotoxic killing suggests a sharing of differentiation antigens amongst the different strains of rats and possibly a limited polymorphism for this system. In man, conventional assays for T cell reactivity are hampered by the presence of a soluble inhibitor of lymphocyte proliferation released by chondrocytes and as yet unidentified. The poor representation of Class II antigens on our chondrocyte specimens may further contribute to the difficulty in producing proliferation. On the other hand, early success is reported in finding a significant number of T cell clones isolated from the inflammatory membrane of patients with rheumatoid arthritis, which respond to chondrocyte antigens. The possibility that these antigens may play a role in the pathogenesis of inflammatory arthritis may be more readily explored by exploring these approaches.

T cell-recognized antigenic peptides derived from the cellular genome are not protein degradation products but can be generated directly by transcription and translation of short subgenic regions. A hypothesis

It is now widely accepted that cytolytic T cells recognize their antigens in the form of small peptides bound to major histocompatibility complex molecules at the surface of the target cells. We present here the hypothesis that, when these antigenic peptides are derived from the cellular genome, they are not degradation products of cellular proteins but can be generated directly by the autonomous transcription and translation of short subgenic regions that we propose to name "peptons". We discuss some consequences of the notion that antigenic peptides can be produced in the absence of synthesis of messenger RNA and protein from the corresponding genes.

Characterization of variant and parental-cross-protective immunity to immunogenic variants of a murine fibrosarcoma using the local adoptive transfer assay

The purpose of this study was to characterize the lymphocyte populations responsible for rejection of immunogenic (Imm+) tumor variants, and the cross-protective immunity engendered by Imm+ variants against the weakly immunogenic parental tumor. Immunogenic clones of the weakly immunogenic methylcholanthrene-induced fibrosarcoma MCA-F have been generated using 1-methyl-3-nitro-1-nitrosoguanidine, 5-aza-2'-deoxycytidine, or ultraviolet radiation (UV-B; 280-320 nm). These clones grow progressively in immunosuppressed adult-thymectomized irradiated mice, but are rejected by immunocompetent syngeneic hosts. The parental MCA-F tumor grows progressively in both groups. Mice that have rejected a challenge of 1 x 10(5) Imm+ cells show an anamnestic immune response against both the Imm+ clone and the parental MCA-F tumor. Using the local adoptive transfer assay and depletion of T-cell subsets with antibody plus complement, we show that immunity induced by the Imm+ variants against the parent MCA-F was mediated by the Thy1.2+, L3T4a+ population without an apparent contribution by Lyt2.1+ cells. Although antivariant immunity was also dependent upon Thy1.2+ cells, depletion of either the L3T4a+ or the Lyt2.1+ cells failed to abolish immunity against the variant. A role for Lyt2.1+ T lymphocytes in antivariant immunity, but not antiparent immunity, was supported by the results of cytotoxic T lymphocyte (CTL) assays. Following immunization with high numbers (1 x 10(5) to 5 x 10(5) of viable Imm+ cells, antivariant, but not antiparent CTL activity was detected in mixed lymphocyte tumor cell cultures. Immunization with lower numbers (3 x 10(4] of viable Imm+ or with high numbers of mitomycin-C-treated Imm+ engenders only antivariant immunity without parental cross-protection. Under these conditions lymphocytes mediating immunity against the variant in the local adoptive transfer assay were exclusively of the Thy1.2+, L3T4a+ phenotype, with no contribution from the Lyt2.1+ cells. Identical results were obtained for Imm+ clones of MCA-F induced by methylnitronitrosoguanidine, 5-azadeoxycytidine, and UV-B, suggesting that the nature of the antitumor immunity engendered by Imm+ is not significantly affected by the agent used. Furthermore, these results demonstrate that the cross-reactivity and cellular effectors of antitumor immunity in this system are influenced by the immunizing dose of Imm+ cells: the predominant effectors of both antivariant and parental-cross-reactive immunity were of the CD4+ T cell subclass, with a CD8+ cytotoxic population contributing to antivariant immunity only after high-dose immunization.

Immunogenic (tum-) variants of mouse tumor P815: cloning of the gene of tum- antigen P91A and identification of the tum- mutation

Mutagen treatment of mouse P815 tumor cells produces tum- variants that are rejected by syngeneic mice because these variants express new surface antigens. These "tum- antigens" are recognized by cytolytic T lymphocytes but induce no detectable antibody response. Transfection of P815 cell line P1.HTR with DNA of tum- variant P91 yielded transfectants expressing tum- antigen P91A. They were detected by their ability to stimulate proliferation of cytolytic T lymphocytes [Wölfel, T., Van Pel, A., De Plaen, E., Lurquin, C., Maryanski, J. L. & Boon, T. (1987) Immunogenetics 26, 178-187]. A cosmid library of a cell line expressing antigen P91A was transfected into P1.HTR. Transfectants expressing the antigen were obtained. By packaging directly the DNA of a transfectant with lambda phage extracts, we obtained a small cosmid population containing as major component a cosmid that transferred the expression of P91A. The assay of various restriction fragments of this cosmid led to the isolation of an 800-base-pair fragment containing the P91A sequence required for transfection. Comparison with a homologous cDNA showed that this fragment contained only one of the several exons of the P91A gene. The normal and the tum- forms of the gene differ by one nucleotide located in this 137-base-pair exon. The essential role of this mutation, which produces an amino acid change, was confirmed by site-directed mutagenesis. No significant sequence similarity was found between the 800-base-pair fragment and any recorded gene.

Cell-mediated immunity to chemically xenogenized tumors--III. Generation of monoclonal antibodies interfering with reactivity to novel antigens

To develop monoclonal antibodies (MAbs) recognizing drug-mediated tumor antigens on a chemically xenogenized murine lymphoma, hybridomas were constructed with splenocytes from histocompatible mice hyperimmunized with L5178Y cells antigenically altered by triazene treatment in vivo (clone D, derived from a polyclonal L5178Y/DTIC subline). Screening of supernatants with parental and xenogenized cells showed that nine MAbs displayed exclusive or preferential reactivity with clone D cells as detected by immunofluorescence, and failed, as a rule, to bind normal or unrelated malignant cells of the same or different haplotype. Moreover, no reactivity was displayed to the triazene-xenogenized variants of antigenically unrelated tumors. All nine MAbs, however, were capable of binding a panel of L5178Y/DTIC clones in addition to clone D. When the ability of these antibodies to interfere with the development of cell-mediated immunity to clone D cells in vitro was tested, it was found that the proliferative reaction and generation of cytolytic activity by syngeneic lymphocytes were inhibited by addition of several MAbs to the tumor--lymphocyte co-cultures.