Cell-mediated Immune Surveillance Research Articles

Uveal melanoma expression of indoleamine 2,3-deoxygenase: Establishment of an immune privileged environment by tryptophan depletion

The enzyme indoleamine 2,3-dioxygenase (IDO) catalyzes degradation of tryptophan, an essential amino acid required for lymphocyte activation and proliferation. Many tumors express IDO which implies that it acts as a mechanism to evade T cell-mediated immune attack, and also to establish an immunosuppressive tumor microenvironment. The purpose of this study was to determine whether primary and metastatic uveal melanoma expressed the IDO gene and whether uveal melanoma cells could deplete tryptophan. In situ expression of IDO in primary uveal melanoma from tumor bearing eyes and metastatic uveal melanoma liver tissues was determined by immunohistostaining with IDO-specific antibody. Reverse transcription PCR was used to assess IDO gene transcription by primary and metastatic uveal melanoma cell lines. IDO protein expression was determined by Western blot of uveal melanoma cell protein lysate. IDO catalytic activity was assessed by measuring the presence of kynurenine, a product generated by tryptophan degradation, in uveal melanoma culture supernatants. Primary uveal melanoma from tumor-bearing eyes and metastatic uveal melanoma from the liver did not express IDO in situ. IDO was not constitutively expressed in either primary or metastatic uveal melanoma cell lines. However, stimulation of primary and metastatic uveal melanoma cell cultures with interferon-gamma (IFN-γ) universally upregulated both IDO gene and protein expression. Culture supernatants from IFN-γ treated primary and metastatic uveal melanoma cell cultures contained elevated levels of kynurenine. Addition of the IDO inhibitor 1-methyl dl-tryptophan significantly diminished kynurenine levels in IFN-γ treated uveal melanoma cell cultures. The results from this study suggest that IFN-γ inducible IDO upregulation by primary and metastatic uveal melanoma may generate a local immune privileged microenvironment to promote escape from T cell-mediated immune surveillance.

T-helper 1 versus T-helper 2 lymphocyte immunodysregulation is the central factor in genesis of Burkitt lymphoma: hypothesis.

BackgroundThe HIV epidemic has challenged our previous understanding of endemic Burkitt's lymphoma. Despite the strong association of Burkitt's lymphoma and HIV infection in the Developed world, and against previous postulations that the cancer is due to immunosupression among African children, the HIV epidemic in the Malaria belt has not been associated with a corresponding increase in incidence of childhood Burkitt's lymphoma. Even outside the context of HIV infection, there is substantial evidence for a strong but skewed immune response towards a TH2 response in genesis of Burkitt lymphoma.Presentation of the hypothesisRather than a global and/or profound immunosupression, the final common pathway in genesis of Burkitt's lymphoma is the dysregulation of the immune response towards a TH2 response dominated by B-lymphocytes, and the concomitant suppression of the TH1 cell-mediated immune surveillance, driven by various viral/parasitic/bacterial infections.Testing the hypothesisCase control studies comparing TH2 and TH1 immune responses in Burkitt lymphoma of different etiological types (sporadic, HIV-related, endemic and post-transplant) to demonstrate significant dominance of TH2 immune response in presence of poor CMI response as a common factor. Immunological profiling to evaluate differences between immune states that are associated (such as recurrent Malaria infection) and those that are not associated (such as severe protein-energy malnutrition) with Burkitt lymphoma. Prospective cohorts profiling chronology of immunological events leading to Burkitt lymphoma in children with EBV infection.Implications of the hypothesisThe dysregulation of the immune response may be the missing link in our understanding of Burkitt lymphomagenesis. This will provide possibilities for determination of risk and for control of development of malignancy in individuals/populations exposed to the relevant infections.

JNK2 negatively regulates CD8+ T cell effector function and anti‐tumor immune response

JNK1 and JNK2 have distinct effects on activation, differentiation and function of CD8+ T cells. Our early studies demonstrated that JNK1 is required for CD8+ T cell-mediated tumor immune surveillance. However, the role of JNK2 in CD8+ T cell response and effector functions, especially in anti-tumor immune response, is unknown. To define the role of JNK2 in antigen-specific immune response, we have investigated CD8+ T cells from OT-1 CD8+ transgenic mice in response to either high- or low-affinity peptides. JNK2-/- CD8+ T cells proliferated better in response to both peptides, with more cell division and less cell death. In addition, JNK2-/- CD8+ T cells produced higher levels of IFN-gamma, which is associated with increased expression of T-bet and Eomesodermin (Eomes). Moreover, JNK2-/- CD8+ T cells expresses high levels of granzyme B and show increased CTL activity. Finally, the enhanced expansion and effector function of JNK2-/- CD8+ T cells was further evidenced by their capacity to delay tumor growth in vivo. In summary, our results demonstrate that JNK2 negatively regulates antigen-specific CD8+ T cell expansion and effector function, and thus selectively blocking JNK2 in CD8+ T cells may potentially enhance anti-tumor immune response.

Expression of Glucocorticoid-Induced TNF Receptor Ligand on Acute Myeloid Leukemia Cells Mediates the Release of Immunosuppressive Cytokines and Impairs NK Cell-Mediated Immune Surveillance.

NK cells play an important role in the reciprocal interaction of tumor cells with the immune system and participate in the surveillance of hematological malignancies including acute myeloid leukemia (AML). Among the molecules influencing host-tumor interaction are many members of the TNF superfamily, which mediate multiple cellular functions including cellular proliferation, differentiation and cell death. The TNF family member Glucocorticoid-induced TNF Receptor (GITR) costimulates effector T cells, modulates apoptosis and nuclear factor kappa B and abrogates suppression of murine but not human regulatory T cells. Its cognate ligand GITRL has been found in various healthy tissues. Recently we reported that NK cells express GITR, while solid tumors express GITR ligand (GITRL), and GITR/GITRL interaction downregulates NK cell cytotoxicity and IFN-γ production. Here we analyzed the role of GITR and its ligand in AML. We report for the first time that GITRL is expressed on primary AML cells in 18 of 30 patients as determined by FACS and RT-PCR analysis. Reverse signaling through GITRL using a recombinant GITR-Ig fusion protein induces the release of the immunoregulatory cytokines IL-10 and TNF as determined by ELISA. GITRL-mediated cytokine production of AML cells is abrogated by inhibition of mitogen activated protein kinase (MAPK) pathways as demonstrated by addition of the specific p38 MAPK inhibitor SB202190, the specific JNK inhibitor SP600125 and the specific ERK Inhibitor II. Furthermore, binding of AML-expressed GITRL to GITR on NK cells downregulates cellular cytotoxicity and IFN-γ production in AML-NK cell cocultures, which can be overcome by addition of GITR-blocking antibodies as determined by cytotoxicity assays and ELISA. Thus, our data indicate that GITRL expression in AML substantially influences tumor immunoediting and enables the escape of leukemia cells from NK cell-mediated immunosurveillance.

JNK1 Is Essential for CD8+ T Cell-Mediated Tumor Immune Surveillance

JNK1 has divergent roles in regulating the effector functions of CD4+ and CD8+ T cells. However, the function of JNK1 in tumor immune surveillance is unknown. In this study, we show that similar to IFN-gamma-/- mice, JNK1-/- mice are highly susceptible to tumor development after inoculation of both melanoma cell line B16 and lymphoma cell line EL-4. Using T cell depletion and reconstitution approaches, we show that CD8+ T cells, but not CD4+ T cells, from JNK1-/- mice are responsible for tumor susceptibility. JNK1-/- CD8+ T cells have an intrinsic defect in early IFN-gamma gene transcription and production after activation by either anti-CD3/anti-CD28 Abs or dendritic cells loaded with specific Ag in vitro. The impaired IFN-gamma production in JNK1-/- CD8+ T cells is associated with reduced expression of both T-bet and Eomesodermin, indicating that JNK1 regulates the transcription program of CD8+ T cells. Finally, JNK1-/- CD8+ T cells showed reduced perforin expression and impaired CTL function. Taken together, our results demonstrate that JNK1 plays an important role in tumor immune surveillance through regulating the effector functions of CD8+ T cells.

Inherited Perforin and Fas Mutations in a Patient with Autoimmune Lymphoproliferative Syndrome and Lymphoma.

We report the case of an autoimmune lymphoproliferative syndrome (ALPS) patient who developed a non-Hodgkin lymphoma, in whom we identified, in addition to a previously never described fas mutation, a mutation in the perforin (Prf1) gene. In this 27-yr old patient with multiple recurrent adenopathies a diagnosis of ALPS was made. ALPS is a rare disorder characterized by splenomegaly and early-onset massive lymphadenopathy, autoimmune manifestations, and increased incidence of solid and hematological malignancies, including Hodgkin and non-Hodgkin lymphomas. Fas mutations were previously reported as the genetic defect responsible for this syndrome. Fas gene sequencing demonstrated a novel point mutation in intron 7, affecting a canonical splicing site (IVS7nt1 G->A). This mutation produced skipping of exon 7 and a frameshift in exon 8. The frameshift revealed a stop codon in exon 8. Abnormally spliced products lacking exon 7 were demonstrated by cDNA analysis. The predicted protein would then lack the death domain, which is required for apoptosis induction. The same mutation was found in his father and brother, who were both healthy. Two years later, cervical adenopathy recurred; lymph node biopsy was diagnostic for a T-cell/histiocyte-rich large B-cell lymphoma. Disease staging demonstrated multiple sites of involvement (nodes, liver, bone marrow), and an elevated LDH. After four cycles of chemotherapy, worsening of liver function tests precluded further treatment, and the patient died shortly thereafter of disease progression. The mechanisms implicated in lymphomagenesis in ALPS are unclear. The particularly aggressive clinical course of lymphoma in this patient prompted us to investigate whether mutations in other genes might be associated to the identified Fas gene mutation. In this regard, the integrity of the perforin/granzyme pathway of cell-mediated killing appears to be critical. Perforin, a pore-forming molecule expressed in granules of cytotoxic effector lymphocytes, has been implicated in T and NK cell-mediated immune surveillance against viral infections and tumors. Indeed, increased lymphoma incidence has been associated with perforin deficiency in mice. We analyzed the sequence of the Prf1 gene in the patient and in his family. Prf1 gene sequencing in our patient demonstrated a point mutation in exon 3 (g755a) resulting in a change, at position 252, from a medium sized and polar aminoacid (asparagin) to a small sized and polar aminoacid (serin). This mutation occurs within the membrane-attack-complex, a region critically involved in the pore-forming activity of the molecule. The same mutation was found in his healthy mother. In conclusion, we propose that the family described in the present report represents a new genetic model that can explain the development of ALPS and lymphoma, due to a synergistic effect of the mutations in different genes: the family members who carry a heterozygous mutation in a single gene (either Fas or Prf1) are healthy, while the member with mutations in both genes developed ALPS and lymphoma. Perforin mutation may be one of the additional defects contributing to the development of lymphoma in ALPS patients, possibly in conjunction with other unknown factors.

Patients with Lymphoma May Harbor Mutations of the Perforin Gene.

Perforin (PRF), a pore-forming molecule expressed in granules of cytotoxic effector lymphocytes, has been implicated in T and NK cell-mediated immune surveillance against viral infections and tumors. Indeed, increased lymphoma incidence has been associated with PRF deficiency in mice. In view of these experimental findings, we reasoned that also some patients with lymphomas might harbor mutations of the PRF gene and thus we investigated the presence of mutations of the gene in a group of lymphoma patients with pre-defined clinical characteristics. Bi-allelic mutations of the PRF gene were found in 4 out of the 30 patients examined. A female (19 y.) had been successfully cured of her T-cell lymphoblastic lymphoma, when her brother(22 y), 2 years later, developed HLH. The 2 siblings shared the same mutations. The first one, (272 C>T), changes arginine at position 91 into valine; the second one (1122 G>A), changes tryptophan at position 374 into a stop codon. The second patient (7 y), with EBV-positive Hodgkin lymphoma,three years later, developed a large B-cell non-Hodgkin lymphoma. Two mutations were identified: the first one, (1304 C>T), changes threonine at position 435 into methionine. The second one, (1349C>T), changes threonine at position 450 to methionine. The third patient (7 y), a female, presented, with multiple reddish non-ulcerated subcutaneous nodules and B-symptoms. Two surgical lesion biopsies were performed and a rare form of subcutaneous, panniculitis-like, T-cell lymphoma was diagnosed. Sequencing of the PRF gene disclosed the following 2 mutations: the first one, (272 C>T), changes arginine at position 91 into valine; the second one, (1262 T>G), changes phenylalanine at position 421 into cysteine. An female (18 y)presented with fever, malaise and massive hepato-splenomegaly. A peripheral T-cell lymphoma, associated with bone marrow infiltration, was diagnosed and 6 months after diagnosis, she was transplanted from an HLA-identical sibling. PRF gene sequencing showed two novel mutations: the first one (g914a) changes at position 305 glycine in aspartic acid, the second one (c1066a) changes arginine in tryptophan at position 356. Present data, point to a more complex disregulation of the immune system when PRF is absent, which may be associated with quite different clinical presentations indicating that the resulting effect of PRFmutations is likely to be more complex than previously anticipated and may vary among individuals, possibly depending on additional genetic and/or environmental factors.

IL-21 induces the functional maturation of murine NK cells.

IL-21 is a recently identified cytokine that stimulates mouse NK cell effector functions in vitro. In this study we demonstrate that IL-21 achieves its stimulatory effect by inducing the development of mature NK cells into a large granular lymphocyte phenotype with heightened effector function. IL-21 treatment results in increased cell size and granularity and a corresponding decrease in cell viability and proliferative potential. These cells up-regulate the expression of the inhibitory CD94-NKG2A receptor complex and the activation markers CD154 and killer cell, lectin-like-receptor G1. Surprisingly, IL-21 treatment also results in down-regulation of the pan-NK marker, NK1.1. Coinciding with these cellular changes IL-21 enhances cytolytic capacity across a spectrum of target sensitivities and induces IL-10 and IFN-gamma production. In vivo treatment with IL-21 results in a very similar activation and phenotypic maturation of NK cells as well as a potent increase in NK cell-mediated anti-tumor immunity that is perforin dependent. These developmental changes suggested that IL-21 functions to induce the terminal differentiation of mouse NK cells, resulting in heightened NK cell-mediated cytotoxicity and immune surveillance.

Escape of monocyte-derived dendritic cells of HIV-1 infected individuals from natural killer cell-mediated lysis.

To verify whether the in vitro sensitivity of immature dendritic cells (iDC) to lysis by autologous natural killer (NK) cells from HIV-infected individuals might be correlated with HIV disease progression. Both dendritic cells (DC) and interlekin (IL)-2 activated NK cells were obtained from 13 HIV-infected individuals early after seroconversion and not receiving highly active antiretroviral therapy (HAART) and from 14 individuals with chronic HIV infection under HAART. The rate of NK cell-mediated killing of autologous iDC was correlated with classical parameters of HIV evolution. Peripheral blood monocytes obtained from the Ficoll-derived leukocyte fraction after adherence to plastic were stimulated with granulocyte-macrophage colony stimulating factor plus IL-4 to induce their differentiation into iDC to be used as target cells in a standard 4-h cytotoxicity assay. A fraction of autologous leukocytes was stimulated with IL-2 to induce activation of NK cells to be used as effector cells. During early HIV infection the extent of ex vivo lysis of monocyte-derived DC by activated autologous NK cells was inversely and directly correlated with the levels of viraemia and with the percentage of circulating CD4 T cells, respectively. In contrast, the capacity of NK cells to kill iDC was lost independently of the levels of plasma viraemia or the concurrence of HAART in chronically infected individuals. Addition of exogenous HIV Tat during the cytotoxicity assay inhibited NK cell-mediated lysis of DC. NK cell-mediated immune surveillance against infected DC may be effective only during early HIV infection and may not be restored by HAART.

Chemical Carcinogens as Foreign Bodies and Some Pitfalls Regarding Cancer Immune Surveillance

Interferon-gamma-receptor (IFN-gammaR)-deficient mice are more susceptible to tumor induction by methylcholanthrene (MCA) in comparison to control littermates. The cellular source of IFNgamma is not known, but the absence of T cells does not significantly increase the incidence of MCA-induced tumors. However, it appears that the presence of T cells in combination with unknown, perhaps environmental, factors can decrease MCA-induced tumor incidence, indicating that IFN-gamma of unknown origin contributes to the protective response. The current knowledge of cancer biology, immune regulation, and tumor-promoting effects of inflammation are difficult to reconcile with the concept of immune surveillance against non-virus-associated cancer. Analysis of the primary MCA-treated mouse indicates, as one protective mechanism, a tissue repair response against MCA-induced damage, in the course of which MCA is encapsulated and persists for long time in tumor-free mice, termed foreign-body reaction. The protection from DNA damage could simultaneously diminish tissue injury and malignant transformation. We argue that inhibition of MCA-induced carcinogenesis is mechanistically different from tumor transplantation immunity and that a longer latency in MCA-treated mice is unlikely due to T cell-mediated tumor recognition and selection of less immunogenic variants. We discuss that the IFNgammaR-dependent mechanism against MCA is unrelated to the original concept of T cell-mediated immune surveillance and that the increased spontaneous tumor incidence observed in some immune-deficient mice is likely to be explained by opportunistic infection and tumor-promoting chronic inflammation.

The role of CC chemokine receptor 5 in antiviral immunity

The CC chemokine receptor CCR5 is an important coreceptor for human immunodeficiency virus (HIV), and there is a major thrust to develop anti-CCR5-based therapies for HIV-1. However, it is not known whether CCR5 is critical for a normal antiviral T-cell response. This study investigated the immune response to lymphocytic choriomeningitis virus in mice lacking CCR5 (CCR5(-/-) mice). This infection is a classical model for studying antiviral immunity, and influx of CCR5-expressing CD8(+) T cells and macrophages is essential for both virus control and associated immunopathology. Results showed that the virus-induced clonal expansion of antigen-specific T cells was augmented in CCR5(-/-) mice especially with regard to the CD4(+) subset. Despite absence of CCR5, intracerebral infection invariably resulted in lethal T cell-mediated meningitis, and quantitative and qualitative analysis of the inflammatory exudate cells did not reveal any significant differences between gene-targeted mice and wild-type controls. CCR5 was also found to be redundant regarding the ability to eliminate virus from internal organs. Using delayed-type hypersensitivity to evaluate CD8(+) T cell-mediated inflammation, no significant influence of CCR5 was found, not even when viral peptide was used as local trigger instead of live virus. Finally, long-term CD8(+) T cell-mediated immune surveillance was efficiently sustained in CCR5(-/-) mice. Taken together, these results indicate that expression of CCR5 is not critical for T cell-mediated antiviral immunity, and this molecule may therefore constitute a logic and safe target for anti-HIV therapies.

Murine cytomegalovirus m02 gene family protects against natural killer cell-mediated immune surveillance.

The murine cytomegalovirus m02 gene family encodes putative type I membrane glycoproteins named m02 through m16. A subset of these genes were fused to an epitope tag and cloned into an expression vector. In transfected and murine cytomegalovirus-infected cells, m02, m04, m05, m06, m07, m09, m10, and m12 localized to cytoplasmic structures near the nucleus, whereas m08 and m13 localized to a filamentous structure surrounding the nucleus. Substitution mutants lacking the m02 gene (SMsubm02) or the entire m02 gene family (SMsubm02-16) grew like their wild-type parent in cultured cells. However, whereas SMsubm02 was as pathogenic as the wild-type virus, SMsubm02-16 was markedly less virulent. SMsubm02-16 produced less infectious virus in most organs compared to wild-type virus in BALB/c and C57BL/6J mice, but it replicated to wild-type levels in the organs of immunodeficient gamma(c)/Rag2 mice, lacking multiple cell types including natural killer cells, and in C57BL/6J mice depleted of natural killer cells. These results argue that one or more members of the m02 gene family antagonize natural killer cell-mediated immune surveillance.

Expression and prognostic significance of immunoregulatory molecules in esophageal cancer.

Major histocompatibility complex molecules (HLA), the co-stimulatory molecule B7 and the intercellular adhesion molecule 1 (ICAM-1) are key molecules involved in T cell-mediated immune surveillance. We aimed at assessing the expression pattern of these immunoregulatory molecules on primary esophageal carcinomas and evaluating their prognostic significance. Representative samples of primary tumors were obtained from 53 patients who had undergone radical en bloc esophagectomy without residual tumor. Cryostat sections of these tumors were stained with monoclonal antibodies (MAbs) directed against either HLA class I, HLA class II, B7 or ICAM-1. The median follow-up was 19 months (range, 6-43). We found that HLA class I expression was deficient on 27 tumors, while a significant neo-expression of HLA class II, B7 and ICAM-1 (> or =25% positive tumor cells) was observed on 17, 29 and 25, tumors, respectively. Kaplan-Meier analyses revealed a significant beneficial influence on relapse-free survival for patients with tumors expressing HLA class I, HLA class II and B7. Cox's regression analyses demonstrated that co-expression of HLA class I and ICAM-1 was a significant and independent predictor of a reduced risk of developing tumor recurrence, whereas expression of ICAM-1 on HLA class I negative tumors was correlated with an increased risk of tumor relapse.

Expression and prognostic significance of immunoregulatory molecules in esophageal cancer

Major histocompatibility complex molecules (HLA), the co-stimulatory molecule B7 and the intercellular adhesion molecule 1 (ICAM-1) are key molecules involved in T cell-mediated immune surveillance. We aimed at assessing the expression pattern of these immunoregulatory molecules on primary esophageal carcinomas and evaluating their prognostic significance. Representative samples of primary tumors were obtained from 53 patients who had undergone radical en bloc esophagectomy without residual tumor. Cryostat sections of these tumors were stained with monoclonal antibodies (MAbs) directed against either HLA class I, HLA class II, B7 or ICAM-1. The median follow-up was 19 months (range, 6–43). We found that HLA class I expression was deficient on 27 tumors, while a significant neo-expression of HLA class II, B7 and ICAM-1 (≥25% positive tumor cells) was observed on 17, 29 and 25, tumors, respectively. Kaplan-Meier analyses revealed a significant beneficial influence on relapse-free survival for patients with tumors expressing HLA class I, HLA class II and B7. Cox's regression analyses demonstrated that co-expression of HLA class I and ICAM-1 was a significant and independent predictor of a reduced risk of developing tumor recurrence, whereas expression of ICAM-1 on HLA class I negative tumors was correlated with an increased risk of tumor relapse. Int. J. Cancer 74:582–587, 1997.© 1997 Wiley-Liss, Inc.

Expression of a candidate cadherin in T lymphocytes.

Cadherins are homotypic adhesion molecules that classically mediate interactions between cells of the same type in solid tissues. In addition, E-cadherin is able to support homotypic adhesion of epidermal Langerhans cells to keratinocytes (Tang, A., Amagai, M., Granger, L. G., Stanley, J. R. & Udey, M. C. (1993) Nature (London) 361, 82-85) and heterotypic adhesion of mucosal epithelial cells to E-cadherin-negative intestinal intraepithelial T lymphocytes. Thus, we hypothesized that cadherins may play a wider role in cell-to-cell adhesion events involving T lymphocytes. We searched for a cadherin or cadherins in T lymphocytes with a pan-cadherin antiserum and antisera against alpha- or beta-catenin, molecules known to associate with the cytoplasmic domain of cadherins. The anti-beta-catenin antisera coimmunoprecipitated a radiolabeled species in T-lymphocyte lines that had a molecular mass of 129 kDa and was specifically immunoblotted with the pan-cadherin antiserum. Also, the pan-cadherin antiserum directly immunoprecipitated a 129-kDa radiolabeled species from an 125I surface-labeled Jurkat human T-cell leukemic cell line. After V8 protease digestion, the peptide map of this pan-cadherin-immunoprecipitated, 129-kDa species exactly matched that of the 129-kDa species coimmunoprecipitated with the beta-catenin antiserum. These results demonstrate that T lymphocytes express a catenin-associated protein that appears to be a member of the cadherin superfamily and may contribute to T cell-mediated immune surveillance.

Endoplasmic reticulum signal sequence facilitated transport of peptide epitopes restores immunogenicity of an antigen processing defective tumour cell line.

The identification of MHC-restricted and tumour-specific cytotoxic T lymphocytes (CTLs) provides strong evidence in support of T cell-mediated immune surveillance against human tumour cells. These CTLs recognize short peptides derived from tumour-associated antigens in conjunction with class I molecules expressed on tumour cells. In contrast to these observations there are now numerous examples to suggest that a number of tumours escape this CTL-mediated control either by down-regulating accessory molecules or by blocking the intracellular processing of tumour-specific antigens. Recently a number of tumour cell lines have been identified which display a transcriptional deficiency of transporters associated with antigen processing (also referred to as TAP). The Epstein-Barr virus (EBV)-associated tumour, Burkitt's lymphoma (BL), is a classic example in this category. In the present study we have restored class I-restricted antigen processing in a BL cell line by transfecting a minigene expression vector encoding a CTL epitope derived from EBV linked to an endoplasmic reticulum translocation signal sequence. These minigene transfected BL cells were not only susceptible to lysis by virus-specific CTL but were also capable of efficiently activating an antigen-specific CTL response. Interestingly, the immunogenicity of these BL cells was not affected by the significantly down-regulated expression of adhesion molecules such as LFA1 alpha, LFA1 beta and LFA3. These findings suggest that resistance of tumour cells to CTL-mediated immune control can be reversed if the relevant peptide epitopes are appropriately presented on the cell surface.

Toward a Genetic Analysis of Tumor Rejection Antigens

Publisher Summary This chapter presents an integrated account of a genetic approach to the identification of tumor rejection antigens that has been pursued mainly in the laboratory. These results are presented in the context of the present understanding of antigen recognition by T lymphocytes. Considerable progress has been achieved recently in our understanding of antigen recognition by T lymphocytes. The major histocompatibility complex and the structures of its major protein products are known with a remarkable degree of precision both for mouse and for humans. Several viral antigens that induce tumor rejection have been identified with a great degree of precision because purified viral proteins and genomes are readily obtained. Biochemical fractionations of the tumor cell extracts in order to obtain purified tumor rejection antigens have been attempted. The fractions were tested for their ability to immunize mice so as to make them resistant to tumor challenge. The chapter focuses on the possibility of using a direct genetic approach to identify tumor rejection antigens encoded by the cellular genome. It describes the analysis of the genes coding for these antigens and its implications for T cellmediated immune surveillance, and a similar analysis of a gene coding for a tumor rejection antigen has been described.

Absence of age-resistance in neonatally thymectomised chickens as evidence for cell-mediated immune surveillance in Marek's disease.

MAREK'S disease virus (MDV) of chickens induces lymphomas and other lymphoproliferative changes, which, depending on the virulence of the strain used, may terminate in paralysis and death. Chickens genetically selected for resistance, however, are refractory to clinical MD and most chickens that are fully susceptible when young develop resistance as they become older. Resistance acquired with age is expressed through lesion regression1,2. Our studies with genetic and age resistance established that humoral immunity did not play a major role in either type of resistance3,4 and now we present evidence that the thymus-dependent immune system is of principal importance in the natural resistance of old chickens.