MHC antigens and cancer: implications for T-cell surveillance

PD-L1 expression as a potential predictor of immune checkpoint inhibitor efficacy and survival in patients with recurrent or metastatic nasopharyngeal cancer: a systematic review and meta-analysis of prospective trials

Background

The predictive value of programmed death-ligand 1 (PD-L1) expression in nasopharyngeal cancer (NPC) patients receiving immune checkpoint inhibitors (ICIs) remains controversial. This study aimed to evaluate the optimal threshold of PD-L1 expression in predicting the efficacy of ICIs in patients with recurrent or metastatic (R/M) NPC.

Methods

A meta-analysis was performed by retrieving relevant literature from PubMed, EMBASE, and Cochrane Library databases. Data on the pooled risk ratio (RR), mean overall survival (OS), progression-free survival (PFS), overall response rate (ORR) with 95% confidence interval, and 1%, 10%, and 25% PD-L1 expression cutoff points were obtained to examine the role of PD-L1 as a biomarker in R/M NPC patients receiving immunotherapy.

Results

In total, 1,312 patients from 14 studies were included. An improvement in PFS was observed in both patients with PD-L1 ≥ 1% (RR = 0.76, 95% CI 0.62-0.92, P = 0.005) and those with PD-L1 < 1% (RR = 0.68, 95% CI: 0.35-1.32, P = 0.26) who received first-line treatment with immunotherapy, with no significant difference between these subgroups. The pooled ORR was significantly higher in patients with PD-L1 ≥ 1% (ORR = 0.37) than in those with PD-L1 < 1% (ORR = 0.22) (P < 0.01) undergoing subsequent-line treatment. However, when we used the PD-L1 cutoff values of 10% and 25%, there was no significant difference between the positive (PD-L1 expression ≥ the cutoff value) and negative (PD-L1 expression < the cutoff value) subgroups. PD-L1 ≥ 1% also tended to be associated with better PFS and OS.

Conclusions

Our meta-analysis suggested that first-line immunotherapy could significantly improve PFS in R/M NPC patients, regardless of the PD-L1 expression levels. Positive PD-L1 expression (≥ 1%) might be a potential predictive biomarker for a better overall response to immunotherapy in R/M NPC patients in subsequent-line setting.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42024495841 PROSPERO, identifier CRD42024495841.

Immune microenvironment in tumor progression: characteristics and challenges for therapy

The tumor microenvironment plays a critical role in cancer development, progression, and control. The molecular and cellular nature of the tumor immune microenvironment influences disease outcome by altering the balance of suppressive versus cytotoxic responses in the vicinity of the tumor. Recent developments in systems biology have improved our understanding of the complex interactions between tumors and their immunological microenvironment in various human cancers. Effective tumor surveillance by the host immune system protects against disease, but chronic inflammation and tumor “immunoediting” have also been implicated in disease development and progression. Accordingly, reactivation and maintenance of appropriate antitumor responses within the tumor microenvironment correlate with a good prognosis in cancer patients. Improved understanding of the factors that shape the tumor microenvironment will be critical for the development of effective future strategies for disease management. The manipulation of these microenvironmental factors is already emerging as a promising tool for novel cancer treatments. In this paper, we summarize the various roles of the tumor microenvironment in cancer, focusing on immunological mediators of tumor progression and control, as well as the significant challenges for future therapies.

Inflammation and immune surveillance in cancer

Chronic inflammation is a risk factor for tumor development. However, understanding the effect of the immune system on tumor development has only been significantly advanced over the past two decades. We now appreciate that the immune system, in addition to tumor-suppressive function by eliminating nascent transformed tumor cells, can also exert selection pressure on tumor cells and facilitate tumor growth by providing a favorable tumor microenvironment. Yet, the distinctions between tumor-promoting inflammation and tumor-suppressive immunity are still not clear due to the dual role of some cytokines and other molecules in the immune system. The danger signal hypothesis has shaped our view of the role of immunity in cancer development, but still little is known about the exact role of danger signal receptors in cancer progression. In this review, we introduce the processes of cancer immunoediting and inflammation-induced cancer and discuss what is currently known about the role of danger signal receptors in cancer development and progression.

Alternative mechanism by which IFN-gamma enhances tumor recognition: active release of heat shock protein 72

IFN-gamma exhibits differential effects depending on the target and can induce cellular activation and enhance survival or mediate cell death via activation of apoptotic pathways. In this study, we demonstrate an alternative mechanism by which IFN-gamma enhances tumor recognition, mediated by the active release of Hsp72. We demonstrate that stimulation of 4T1 breast adenocarcinoma cells and K562 erythroleukemic cells with IFN-gamma triggers the cellular stress response, which results in the enhanced expression of total Hsp72 expression without a significant increase in cell death. Intracellular expression of Hsp72 was abrogated in cells stably transfected with a mutant hsf-1 gene. IFN-gamma-induced Hsp72 expression correlated with enhanced surface expression and consequent release of Hsp72 into the culture medium. Pretreatment of tumors with compounds known to the block the classical protein transport pathway, including monensin, brefeldin A, tunicamycin, and thapsigargin, did not significantly block Hsp72 release. However, pretreatment with intracellular calcium chelator BAPTA-AM or disruption of lipid rafts using methyl beta-cyclodextrin completely abrogated IFN-gamma-induced Hsp72 release. Biochemical characterization revealed that Hsp72 is released within exosomes and has the ability to up-regulate CD83 expression and stimulate IL-12 release by naive dendritic cells. Pretreatment with neutralizing mAb or depletion of Hsp72 completely abrogated its chaperokine function. Taken together, these findings are indicative of an additional previously unknown mechanism by which IFN-gamma promotes tumor surveillance and furthers our understanding of the central role of extracellular Hsp72 as an endogenous adjuvant and danger signal.

Genome-wide analysis of molecular changes in IL-12-induced control of mammary carcinoma via IFN-gamma-independent mechanisms

IL-12 is a major activator of tumor-killing NK cells and CTL. IFN-gamma mediates most of the well-known immunological activities of IL-12. In this study, we report IFN-gamma-independent activities induced by therapeutic application of rIL-12 in restricting tumor growth and metastasis in the 4T1 murine mammary carcinoma model. IFN-gamma-deficient mice carrying 4T1 tumor exhibit no gross defect in the number of tumor-infiltrating lymphocytes but have exaggerated angiogenesis in the tumor. Administration of IL-12 is able to constrict blood vessels in the tumor in the absence of IFN-gamma, and retains certain therapeutic efficacy even when applied late during tumor progression. IL-12 exposure in vivo does not irreversibly alter the immunogenicity of the tumor. Finally, global gene expression analysis of primary tumors reveals IL-12-induced molecular patterns and changes, implicating a number of novel genes potentially important for IFN-gamma-independent immune responses against the tumor, for IL-12-mediated antiproliferation, antimetastasis, and antiangiogenesis activities.

Gene expression analysis in Interleukin-12-induced suppression of mouse mammary carcinoma

Interleukin-12 (IL-12) has potent antitumor activities via natural killer cells and cytotoxic T lymphocytes. However, the molecular mechanisms whereby IL-12 induces tumoricidal activities are poorly understood. Here, we report the genome-wide analysis of gene expression in a primary murine mammary carcinoma model that resembles human breast cancer, following the therapeutic application of recombinant IL-12, which restricted tumor growth and metastasis. IL-12 was able to curtail neovascularization in the tumor as well as enhance the number of tumor-infiltrating lymphocytes. Comprehensive examination of global gene expression revealed IL-12-induced molecular changes associated with tumor regression and reduced lung metastasis, thus providing a high-resolution snapshot of a host response against a developing malignancy and a rich source of potential targets for therapeutic intervention of breast cancer.

Amino acid modifications in the wild type sequence p53 232-240 overcome the poor immunogenicity of this self tumour epitope

A major limitation in antigen-specific cancer vaccines is that most of the tumour antigens that are potent candidates for broad applicability originate from self proteins. The peptides presented by tumour cells are derived from tissue-specific differentiation proteins, from proteins altered by genetic mutation or by non mutated proteins that are normally silent in most adult tissues. As a consequence, T-cell responses elicited against those antigens are rather weak. Several data showed that amino acid modifications could enhance the immunogenicity of such antigens by priming T-cells that have escaped central tolerance based on a poor avidity. In this regard, this strategy could be powerful for inducing immunity against tumours. The present report focuses on the murine wild type epitope p53 232-240 that is poorly immunogenic. It shows that substitution of the two cysteine residues by serine or amino butyric acid derivatives and substitution of the two methionine residues by norleucine residues resulted in enhanced stability of the MHC/peptide complex. The MHC binding affinity of analogue peptides was enhanced between 10 and 100 fold. They were also potent immunogens, stronger than was the original wild type epitope; T-cell responses were increased up to 50 times. Moreover, the effector T-cells elicited by three of these peptides cross reacted with the natural epitope. These observations have important implications for strategies that use the modified-peptide epitope.

Chronic immune activation and inflammation in the pathogenesis of AIDS and cancer

Infection with the human immunodeficiency virus (HIV) invariably leads to the development of acquired immunodeficiency syndrome (AIDS) in most infected humans, yet does so rarely, if at all, in HIV-infected chimpanzees. The differences between the two species are not due to differences in cellular receptors or an inability of the chimpanzee to be infected, but rather to the lack of pan-immune activation in the infected primate. This results in reduced apoptotic death in CD4+ T-helper lymphocytes and a lower viral load. In humans the degree of chronic immune activation correlates with virus load and clinical outcome with high immune activation leading to high viral loads and the more rapid progression to AIDS and death. The type of immune perturbation seen in HIV-associated AIDS is similar to that of chronic graft-versus-host disease (GVHD) where reduced cell-mediated immune (CMI) responses occur early in the course of the disease and where humoral responses (HI) predominate. A reduced CMI response occurs in a number of chronic infectious diseases, including tuberculosis and leishmaniasis. More recently, it has become increasingly apparent that the CMI response is suppressed in virtually all malignant diseases, including melanoma and colorectal and prostate cancer. This raises the possibility that, as the malignant process develops, the cancer cells evolve to subvert the CMI response. Moreover, the reduced CMI response seen in colorectal cancer (CRC) patients is completely reversed following curative surgery strongly supporting the hypothesis that CRC can suppress the systemic immune response. Wound healing, ovulation, embryo implantation, and fetal growth are all associated with suppressed CMI and neovascularization (the formation of new blood vessels) or angiogenesis (the formation of new blood vessels from an existing vasculature). If unresolved, wound healing results in chronic inflammation, which can give rise to the phenomenon of "scar cancers." Indeed all the chronic inflammatory conditions known to be associated with the subsequent development of malignant disease, including chronic obstructive airway disease (COPD), ulcerative colitis (UC), and asbestosis, give rise to similar proangiogenic, suppressed CMI, and HI-predominant environments. In keeping with this CMI-associated cytokines such as interleukin (IL)-2 and interferon (IFN)-gamma tend to be antiangiogenic, whereas HI cytokines such as IL-6 tend to be proangiogenic. Furthermore, chronic immune activation leads to the synthesis and release of factors such as macrophage inflammatory protein (MIP)-1 that inhibit apoptosis through suppression of p53 activity. The "Golden Triangle" of suppressed CMI, angiogenesis, and reduced apoptosis would provide the ideal environment for the serial mutations to occur that are required for the development of malignant disease. If the observed association is relevant to carcinogenesis, then treatments aimed at reducing the components of these inflammatory conditions may be useful both in the setting of chemoprevention and the therapeutic management of established disease.

CD8+ T cells are crucial for the ability of congenic normal mice to reject highly immunogenic sarcomas induced in nude mice with 3-methylcholanthrene

An attempt was made to identify the selection pressures put upon a growing tumour by CD8+ T cells. To this end tumours induced with 3-methylcholanthrene in T cell-deficient nude mice and in congenic T cell-competent nu/+ mice were transplanted to nu/+ recipients. The rejection rate of the sarcomas from nude mice was almost twice that of the sarcomas from nu/+ mice. Depletion of CD8+ T cells from nu/+ recipients prior to transplantation made them accept nude tumours that were consistently rejected by untreated nu/+ recipients. These findings suggest that a methylcholanthrene sarcoma during its growth in a T cell-competent host adapts to the T cell system through a selective elimination of highly immunogenic tumour cells that are susceptible to CD8+ T cell-mediated lysis.

Synergistic induction of HLA class I expression by RelA and CIITA

The major histocompatibility complex (MHC) class I genes are induced synergistically by interferons (IFN) and tumor necrosis factor (TNF) , a response thought to involve the cooperative action of Rel/NF-kB and interferon regulatory factor (IRF) transcription factors. The IFN-γ–inducible class II transcriptional activator (CIITA) has recently been shown to transactivate MHC class I as well as class II genes, and this investigation shows that CIITA synergizes strongly with RelA to stimulate HLA class I expression. The functional interaction of CIITA and RelA requires both promoter elements and the upstream Rel binding site and is not seen with a class II reporter. The promoter elements necessary for CIITA action are also required for induction by IFN-. HLA-A and HLA-B loci respond differentially to IFNs, and we identify locus-specific differences in critical promoter elements in addition to known polymorphisms in the Rel and IRF binding sites. The HLA-A promoter is transactivated relatively poorly by CIITA and does not interact detectably with CREB proteins implicated in CIITA recruitment, but the synergism with RelA can compensate for this weakness. The present findings illustrate that multiple transcription factors cooperate to regulate class I expression and that their relative importance differs according to the locus and cell type examined.

Synergistic induction of HLA class I expression by RelA and CIITA

The major histocompatibility complex (MHC) class I genes are induced synergistically by interferons (IFN) and tumor necrosis factor (TNF) , a response thought to involve the cooperative action of Rel/NF-kB and interferon regulatory factor (IRF) transcription factors. The IFN-γ–inducible class II transcriptional activator (CIITA) has recently been shown to transactivate MHC class I as well as class II genes, and this investigation shows that CIITA synergizes strongly with RelA to stimulate HLA class I expression. The functional interaction of CIITA and RelA requires both promoter elements and the upstream Rel binding site and is not seen with a class II reporter. The promoter elements necessary for CIITA action are also required for induction by IFN-. HLA-A and HLA-B loci respond differentially to IFNs, and we identify locus-specific differences in critical promoter elements in addition to known polymorphisms in the Rel and IRF binding sites. The HLA-A promoter is transactivated relatively poorly by CIITA and does not interact detectably with CREB proteins implicated in CIITA recruitment, but the synergism with RelA can compensate for this weakness. The present findings illustrate that multiple transcription factors cooperate to regulate class I expression and that their relative importance differs according to the locus and cell type examined.

The relationship between angiogenesis and the immune response in carcinogenesis and the progression of malignant disease

Recent studies have demonstrated that angiogenesis and suppressed cell-mediated immunity (CMI) play a central role in the pathogenesis of malignant disease facilitating tumour growth, invasion and metastasis. In the majority of tumours, the malignant process is preceded by a pathological condition or exposure to an irritant which itself is associated with the induction of angiogenesis and/or suppressed CMI. These include: cigarette smoking, chronic bronchitis and lung cancer; chronic oesophagitis and oesophageal cancer; chronic viral infections such as human papilloma virus and ano-genital cancers, chronic hepatitis B and C and hepatocellular carcinoma, and Epstein-Barr virus (EBV) and lymphomas; chronic inflammatory conditions such as Crohn's disease and ulcerative colitis and colorectal cancer; asbestos exposure and mesothelioma and excessive sunlight exposure/sunburn and malignant melanoma. Chronic exposure to growth factors (insulin-like growth factor-I in acromegaly), mutations in tumour suppressor genes (TP53 in Li Fraumeni syndrome) and long-term exposure to immunosuppressive agents (cyclosporin A) may also give rise to similar environments and are associated with the development of a range of solid tumours. The increased blood supply would facilitate the development and proliferation of an abnormal clone or clones of cells arising as the result of: (a) an inherited genetic abnormality; and/or (b) acquired somatic mutations, the latter due to local production and/or enhanced delivery of carcinogens and mutagenic growth factors. With progressive detrimental mutations and growth-induced tumour hypoxia, the transformed cell, to a lesser or greater extent, may amplify the angiogenic process and CMI suppression, thereby facilitating further tumour growth and metastasis. There is accumulating evidence that long-term treatment with cyclo-oxygenase inhibitors (aspirin and indomethacin), cytokines such as interferon-alpha, anti-oestrogens (tamoxifen and raloxifene) and captopril significantly reduces the incidence of solid tumours such as breast and colorectal cancer. These agents are anti-angiogenic and, in the case of aspirin, indomethacin and interferon-alpha have proven immunomodulatory effects. Collectively these observations indicate that angiogenesis and suppressed CMI play a central role in the development and progression of malignant disease.

The role of cytotoxic T-lymphocytes in the prevention and immune surveillance of tumors--lessons from normal and immunodeficient mice

The idea of immunological surveillance against cancer has existed for nearly 100 years but as no conclusive evidence has yet been published the importance of the cellular immune defense in the detection and removal of incipient or existing tumors is still a hotly debated subject. However, in order to select a relevant immunotherapeutic strategy in the treatment of cancer, a fundamental understanding of the basic immunologic conditions under which a tumor develops and exists is a prerequisite. Therefore, a murine model was set up that we hoped would enable us to confirm or reject the theory of immunological surveillance. A large panel of methylcholanthrene induced tumors was established in T-cell immunodeficient nude mice and congenic normal mice to study the influence of the immune system on developing tumors. As nude mice developed tumors fastest and with the highest incidence, we concluded that in this model the immune system constituted a 'tumor-suppressive factor' delaying and sometimes abrogating tumor growth, i.e. performing immune surveillance. Immunogenicity of the tumors was assessed by transplantation back to normal histocompatible mice. Tumors originating from the immunodeficient nude mice turned out to be far more immunogenic than tumors from normal mice, resulting in a high rejection rate. CD8+ cytotoxic T cells were found to be indispensable for this rejection, leading to the conclusion that the cytotoxic T cells perform immune selection in normal mice, eliminating immunogenic tumor cell variants in the incipient tumor. In this review, we discuss the difficulties facing immunotherapy when conclusions are drawn from the presented observations and hypotheses.

First comparative delineation of the T cell receptor repertoire in primary and multiple subsequent/coexisting metastatic melanoma sites

At present, very little is known about the types and heterogeneity of T cell responses and immunodominant epitopes of melanoma-associated antigens at coexisting sites of primary melanoma and metastatic lesions. To address this issue, we compared the T cell receptor (TCR) gene usage, complementary-determining region 3 diversity, and melanoma-associated antigens expression patterns of primary and metastatic melanoma specimens from three patients with partially homologous HLA class-1 types. Results obtained showed an overall predominance of a very limited number of TCRV regions with AV13 and BV14 being most frequently overexpressed. Sequencing of the dominating TCR transcripts confirmed the restricted usage of certain TCR specificities and, in two of the three patients, identified several identical TCR clonotypes at more than one metastatic site. Nevertheless, we failed to detect TCR transcripts that were common to all tumor deposits in a given patient and, within the majority of coexisting metastases, tumor-infiltrating lymphocytes preferentially used individual site-specifically expanded TCR beta-chain VJ segment combinations. This occurrence of individual responses simultaneously executed at and influenced in their specificity by the different sites of tumor growth, has important implications for the type of strategies chosen in the development of efficacious vaccines for patients with metastatic melanoma.

High MHC class I expression correlates with slow growth in UV-induced skin carcinomas in hairless mice

An experiment was set up to investigate the relationship, if any, between cell surface MHC class I expression and the growth rate for skin tumors induced by two different UV radiation regimens in hairless mice. Two groups of 20 hairless mice were each irradiated with either a UVA radiation source (2 SED per session) or broad-spectrum UV radiation (UVB) (8.1 SED per session) 5 days a week during the entire experiment. In the UVA group, 17 out of 20 animals developed tumors, and 10 of these grew to a diameter of > or = 5 mm. In the UVB group, 19 out of 20 animals developed tumors, and 15 of these grew to a diameter of > or = 5 mm. The tumor induction time, i.e. the time from the start of UV treatment to tumor appearance, was found to be significantly longer (p<0.01) in the UVA than in the UVB group. This is in accordance with previous findings. Of the 25 tumors growing to a diameter of > or = 5 mm, 11 were established as cultured cell lines (4 UVA and 7 UVB tumors). These uncloned cell lines were analyzed for surface expression of major histocompatibility complex class I by FACS analysis. There was a clear correlation between high MHC class I expression and slow growth of the individual tumors (p<0.05). This suggests a role for the MHC class I governed, i.e. cytotoxic T-cell-mediated, reactions in deciding the fate of UV-induced skin cancers. No correlation was found between MHC class I expression and tumor induction time.

The complement regulatory proteins CD46 and CD59, but not CD55, are highly expressed by glandular epithelium of human breast and colorectal tumour tissues

Three of the proteins protecting cells from autologous lysis by complement are: membrane cofactor protein (MCP; CD46), an inhibitor of the membrane attack complex formation (CD59), and decay accelerating factor (DAF; CD55). We have investigated the expression of these proteins in breast and colorectal carcinoma by immunohistochemistry and immunoblotting of breast tissue for CD46. CD46 was consistently and strongly expressed in the epithelial compartment in 26/28 ductal carcinomas of the breast, 9/9 fibroadenomas, and 9/11 cases of control non-neoplastic breast tissue. CD59 showed a similar degree of expression in the fibroadenomas (9/9), but was less strongly expressed in carcinomatous (22/28) and control (5/11) tissues. In marked contrast, no CD55 expression was detected in tissue from 15 ductal carcinomas. Immunoblotting of breast tissue for CD46 showed the same size of the molecule as for lymphocytes. It had however considerably stronger expression in tumour tissue than in non-neoplastic tissue. CD46 and CD59 were either lacking or only weakly expressed in the epithelial component of control colorectal mucosa: 2/15 and 5/15, respectively. In contrast, tissue samples from colorectal adenocarcinomas showed clear staining for both CD59 (10/18) and, more markedly, CD46 (15/18). There was no association between the pattern or intensity of CD46 and CD59 expression and tumour differentiation. As the complement regulatory proteins CD46 and CD59 are also strongly expressed by trophoblast at the feto-maternal tissue interface, these results support the concept that similar mechanisms are employed both by the genetically dissimilar fetus and certain tumours to evade immune attack by their host.

Lymphocyte apoptosis induced by Fas ligand- expressing ovarian carcinoma cells. Implications for altered expression of T cell receptor in tumor-associated lymphocytes

We have recently reported that tumor-associated lymphocytes obtained from ascitic fluids of women with ovarian carcinoma (OvCA) demonstrate a marked decrease in expression of cytoplasmic CD3-zeta and surface CD3-epsilon chains, which is associated with altered function of T cell receptor (TcR). We now demonstrate that OvCAs in situ and in culture express functional Fas ligand (FasL), capable of triggering an intrinsic cell death program in Fas-expressing T cells. The possibility of a relationship between cell death and altered expression of TcR was examined. The data indicate that alterations in expression of CD3-zeta and CD3-epsilon chains in T cells coincubated with OvCA are related to tumor-induced apoptosis, as the addition of pan-caspase inhibitors, DEVD-cho or YVAD-cho, prevents both the in vitro induction of T cell death by OvCA cells and the changes in the level of expression of CD3-zeta and CD3-epsilon chains. In the presence of Fas-Fc fusion protein, but not Fc-control protein, the loss in expression of CD3-zeta and CD3-epsilon chains induced in T cells by FasL+ OvCA cells was prevented. These results suggest that the loss in expression of CD3-zeta and CD3-epsilon chains in T lymphocytes interacting with OvCA cells is associated with apoptosis mediated by FasL-expressing tumor cells.

Tumour surveillance: missing peptides and MHC molecules

Immunotherapy involving CTL is an attractive alternative for treatment of various malignancies. One of the approaches currently being explored for immune targeting of human cancers involves potentiation of immunogenicity of malignant cells by gene transduction. This strategy is undoubtedly influenced by the ability of the malignant cells to endogenously process and present target epitopes on their cell surface for immune recognition by CTL. However, there is increasing evidence to suggest that a large proportion of human cancers escape CTL-mediated immune surveillance by selectively down-regulating the expression of MHC class I molecules and peptide transporter genes. Understanding and molecular analysis of these immunologically relevant genetic defects in tumours is very important before translating preclinical studies of immunotherapy to rational clinical trials. Careful consideration of these potential limitations may lead to the development of novel immunotherapeutic strategies and, potentially, prevention of tumour progression or development.

Accumulation of the p53 Protein Allows Recognition by Human CTL of a Wild-Type p53 Epitope Presented by Breast Carcinomas and Melanomas

The p53 protein is accumulated in tumor cells of many human cancers and can elicit in vivo humoral and proliferative responses. Rare reports about p53-mediated tumor recognition by CTLs have remained questioned. We therefore studied a panel of breast tumor and melanoma cell lines that we assayed for the presence of accumulated p53 and surface HLA-A2 and for the presentation of p53 epitopes. From PBMC of a healthy donor, we have generated a CTL line, D5/L9V, directed against HLA-A2-restricted peptide 264–272 from wild-type p53. It efficiently lysed breast adenocarcinomas MCF-7, MCF7/RA1, and MDA-MB-231, and melanoma M8, which all accumulate the p53 protein. Using competition assays, we made sure that tumor lysis by D5/L9V was due to recognition of endogenously produced p53 peptide 264–272 associated with the HLA-A2.1 molecule on the surface of these tumor cells. Cells with undetectable levels of wild-type p53, such as lymphoblastoid cells and melanoma M74, were not recognized by D5/L9V. Neither were breast tumor cell line MCF7/ADR nor melanoma line M44 because of HLA loss. This study therefore shows that it is possible to obtain in vitro CTL lines that specifically recognize a p53 epitope spontaneously presented by a variety of HLA-A2+ transformed cell lines provided they display abnormal patterns of p53 expression. This work points out that breast tumors and melanomas share a p53 epitope, and raises hopes for future immunotherapeutic approaches.

Dendritic cells transduced with an adenoviral vector encoding a model tumor-associated antigen for tumor vaccination

Evaluation of the potential role of dendritic cells (DCs) as adjuvants for tumor vaccination has focused primarily on techniques that load DCs with peptide tumor antigens. Our aim has been to optimize the induction of antitumor immunity by enhancing the ability of DCs to present tumor-associated antigens endogenously to the afferent lymphatic system in the appropriate major histocompatibility complex (MHC)-restricted context. We have used replication-defective adenovirus vectors (Ads) to transduce DCs with various genes, including tumor antigen genes. We found that 90% of murine bone marrow derived-DCs could be infected with an Ad vector expressing the beta-galactosidase gene and still retain their physiologic and phenotypic characteristics. Furthermore, we demonstrated that transgene expression was detectable in the spleen for at least 3 days following intravenous injection of Ad-transduced DCs. Using a polyoma middle T (PymT) transgenic murine mammary carcinoma model, we have shown that a single injection of 10(5)-4 x 10(6) DCs transduced with an Ad vector expressing PymT provided complete and specific protection against tumor cell challenge in 100% of vaccinated animals. Immunization against the PymT tumor by injection with the PymT expressing Ad vector alone resulted in varying degrees of effectiveness, was highly dependent upon the route of administration, and led to significant hepatic toxicity that was not seen in mice immunized with DC transduced with the Ad vector. Our results suggest that: (i) DCs can be very efficiently modified by ex vivo Ad transduction to express tumor-specific antigens, (ii) such modified DCs appear nontoxic and stimulate a potent antitumor response.

CD8+ tumor-specific Tc cells primed in vivo or in vitro against the BALB/c plasmacytoma ADJ-PC-5 use the same TcR V beta families but display distinct TC1 or TC2 characteristics

The involvement of counteractive CD8+ T cell subsets in tumor-specific unresponsiveness was analyzed in a syngeneic murine tumor model. CD8+ cytotoxic T cells against the IL-10 producing BALB/c plasmacytoma ADJ-PC-5 can be easily induced in vitro, in a primary syngeneic mixed lymphocyte tumor cell culture (MLTC), or in vivo, by repeated immunization of syngeneic BALB/c mice with high doses of X-irradiated ADJ-PC-5 tumor cells. Long term cultivated CD8+ ADJ-PC-5-specific Tc lines use either TcR of the V beta 6 or V beta 8.1/8.2 type, irrespective if the lines were derived from a primary MLTC or from immunized mice. While most of the Tc lines produce type-1 cytokines (IFN-gamma, no IL-4) upon stimulation, at least two of them, which were derived from a primary MLTC, display a type-2 cytokine spectrum (IL-4, no IFN-gamma). The primary in vitro Tc response against ADJ-PC-5 cells shows characteristics of a TC2 response: CD8+ Tc cells which are induced in a primary MLTC do not produce IFN-gamma, and the tumor-specific Tc response is enhanced by IL-4 but suppressed by IFN-gamma or IL-12. In contrast, ADJ-PC-5-specific CD8+ Tc cells from immunized mice are IFN-gamma producing TC1 cells. Since the primary in vitro Tc response against the tumor is suppressed even by lowest numbers of irradiated ADJ-PC-5-specific TC1 cells via IFN-gamma, these TC1 cells behave similar to a previously described regulatory subset of IFN-gamma producing CD8+ T cells, which are induced during early stages of ADJ-PC-5 tumorigenesis and inhibit the induction of a tumor-specific Tc response from naive BALB/c spleen cells in vitro.

Immunostimulatory cytokines in somatic cells and gene therapy of cancer

The use of immunostimulatory cytokines has become an increasingly promising approach in cancer immunotherapy. The major goal is the activation of tumour-specific T lymphocytes capable of rejecting tumour cells from patients with low tumour burden or to protect patients from a recurrence of the disease. Strategies that provide high levels of immunostimulatory cytokines locally at the site of antigen have demonstrated pre-clinical and occasional clinical efficacy. Animal models using poorly immunogenic tumours revealed that tumour cells genetically engineered to produce cytokines like IL-2, IL-4, IL-7, IL-12, IFNs, GM-CSF or TNF-alpha were found to be effective in eradicating disseminated tumours. Experimental data obtained from these different animal models are reviewed here to provide an overview of this rapidly evolving field. The data obtained so far from clinical trials involving cytokine gene-modified cells have provided important information regarding the feasibility, safety, immunological effects and occasional clinical responses.

Immunotherapy III: Combinatorial molecular immunotherapy--a synthesis and suggestions

Animal models have clearly shown that tumor cells may be amenable to molecular manipulation which can result in immune activation and rejection of unmodified cells (Chapters 4 and 5). The challenge now is to design clinical trials which have a realistic chance of success, (although the definition of 'success' is itself an important issue [see Chapter 9]. How should such a strategy be formulated? A review of the previous fifteen years since the first (immune) gene transfer studies were reported, encompasses a great wealth of data. Unfortunately, far from crystallising a set of unifying principles, these diverse reports shroud us in a fog of uncertainty as to how best to proceed. However, if this technology is to have practical, widespread application in the treatment of cancer patients, it is necessary to identify certain critical immunological goals which any protocols should achieve. Clear elucidation of these goals, by unifying the huge amount of disparate experimental data, must eventually be accomplished. In this chapter, we have reviewed the literature covering the era of molecular immunotherapy. We propose four general goals around which widely applicable clinical protocols, not necessarily dependent upon tumour type or experimental bias, might be based and suggest how they may be achieved in the context of gene transfer.

Methylcholanthrene-induced sarcomas in nude mice have short induction times and relatively low levels of surface MHC class I expression

In order to study the role of the T-cell-mediated immune defense in tumor development, a total of 93 sarcomas were induced using different doses (8 micrograms (0.1%), 40 micrograms (0.5%) and 400 micrograms (5%)) of 3-methylcholanthrene in athymic nude Balb/c mice and phenotypically normal immunocompetent Balb/c mice. A shorter tumor induction time and a higher tumor incidence after treatment with low doses of methylcholanthrene were seen in nude mice than in immunocompetent mice, indicating that they have a lower resistance to the carcinogen. Contrary to expectations we found that the MHC class I expression of tumors from nude mice was lower than that of tumors from normal mice. Higher surface expression of MHC class I was demonstrated on high dose tumors from normal mice than on low dose tumors from normal mice. The cellular composition of the individual tumors raised in nude mice was more heterogeneous with respect to MHC class I expression. Since the mice differ genetically only with respect to the nu gene, these results indicate that a lack of T-cell-mediated defense mechanisms may confer upon the bearer a lower resistance to 3-methylcholanthrene and a different MHC profile of the ensuing tumor.

Chemically induced sarcomas from nude mice are more immunogenic than similar sarcomas from congenic normal mice

To detect possible differences in immunogenicity between tumors induced in T cell-deficient mice and phenotypically normal congenic mice, 16 sarcomas, 8 having developed in nude BALB/c mice and 8 having developed in congenic normal (nu/+) mice, were transplanted to normal BALB/c recipients and the rates of rejection or acceptance were registered. The 16 tumors were chosen randomly from a panel of 39 sarcomas induced with 0.5% or 0.1% 3-methylcholanthrene and maintained as cell lines in culture. Out of the tumors originating from nude mice, 66% were rejected by the normal BALB/c recipients, while only 30% of the tumors originating from normal mice were rejected. Tumors with short induction times from normal mice were more readily accepted than tumors with long induction times. Tumors originating from nude mice had significantly longer mean latency times after transplantation to both normal and nude recipients than tumors originating from normal mice. Contrary to what has been reported by others, there was no correlation between the rejection rates of the individual tumors and their Kd, Dd or Ld major histocompatibility complex (MHC) class I surface expression as measured by flow cytometric analysis of cultured tumor cells. The Kd, Dd and Ld proteins of the transplanted tumor lines were analyzed by isoelectric focusing for the occurrence of mutations resulting in altered charge of the MHC protein. No such mutations were found, ruling out MHC mutations of that kind as the source of immunogenicity in the cell lines used in these experiments. Our results suggest the existence of a T cell-mediated selection in the original tumor cell mass of tumors induced in normal mice, adapting the tumor to growth in a host with a functional T cell system, but apparently there is no connection between this loss of immunogenicity and loss of MHC class I expression.

Peptide transporter (TAP-1 and TAP-2)-independent endogenous processing of Epstein-Barr virus (EBV) latent membrane protein 2A: implications for cytotoxic T-lymphocyte control of EBV-associated malignancies

Major histocompatibility [correction of histocampatability] complex (MHC) class I-restricted cytotoxic T lymphocytes (CTLs) recognizing Epstein-Barr virus (EBV) latent antigens play a pivotal role in restricting the proliferation of EBV-infected normal B cells. However, it is now well established that most of the EBV-associated malignancies escape this potent CTL response in vivo. This resistance to immune surveillance is not due to an obvious CTL dysfunction but has been partly attributed to the down-regulation of the peptide transporters, TAP-1 and TAP-2, thus restricting the endogenous loading of MHC class I molecules with peptides derived from viral nuclear antigens. In the present study we have explored the possibility that EBV latent membrane protein 2A (LMP2A), which is often expressed in many of the EBV-associated malignancies, such as nasopharyngeal carcinoma and Hodgkin's disease tumors, can be endogenously processed through an alternative, TAP-1- and TAP-2-independent pathway. The data presented in this study clearly demonstrate not only that LMP2A can be processed by a TAP-independent mechanism but also that tumor cells with down-regulated TAP expression can be efficiently recognized by LMP2A-specific T cells following infection with recombinant vaccinia virus encoding this protein. We propose that since LMP2A is a membrane protein, it is directly translocated into the secretory pathway and the processing enzymes present in the endoplasmic reticulum are capable of generating the relevant peptide epitopes for MHC binding. The present finding of TAP-1- and TAP-2-independent presentation of LMP2A epitopes suggests a novel mechanism for immune targeting of EBV-positive malignancies, such as nasopharyngeal carcinoma and Hodgkin's disease tumors.

H-2Ld-alloreactive T cell hybridomas utilize diverse V alpha and V beta T cell receptor chains

We have sequenced the TCRs from Ld-specific alloreactive T cell hybridomas, whose reactivities we have found to be quite representative of those of a primary dm2 anti-BALB/cJ mixed lymphocyte reaction. We find V beta 6, V beta 7, V beta 8 and V beta 10 gene segments. V alpha usage is diverse, although closely related to that from peptide-specific Ld-restricted CTLs. V alpha-V beta selection provides evidence of preferential pairing. Amino acid frequency analysis shows that the alpha CDR2 region is rich in charged amino acids, in contrast to the beta CDR2 region. Our data suggests the beta chain may be more immunoglobulin-like than the alpha chain, and that charge complementarity may be important in TCR-MHC interactions. We do not consider our results to be contradictory to those previously reported but rather they may represent an early, more diverse response.

IL-2 gene therapy of solid tumors: an approach for the prevention of signal transduction defects in T cells

The identification of tumor-associated antigens has focused attention on the mechanisms that underlie the failure of T cells to destroy tumor cells. A deeper understanding of the process of signal transduction following the binding of ligand by the T cell receptor can help to identify underlying defects that may be involved. Gene therapy using tumor cells genetically modified to express cytokines or surface determinants is a promising technique for stimulating antitumor responses. A potential pitfall in its application to cancer, however, is that some patients' T cells are immune suppressed and may resist stimulation by such genetically engineered vaccines. Recent studies have demonstrated that T cells from tumor-bearing patients exhibit abnormalities in signal transduction events, possibly rendering them unable to respond to activation signals. Gene therapy with interleukin 2 secreting tumor cells in an animal model has been shown effective in preventing the onset of signaling defects. A more precise definition of the molecular mechanisms that enable cytokine-secreting tumor cells to stimulate specific antitumor responses may make it feasible to optimize immunotherapeutic approaches resulting in better clinical results.

The impact of gene therapy on T cell function in cancer

Studies of signal transduction by T cells are slowly identifying the intracellular messengers that must be generated for full T cell activation to take place. The recent, convincing identification of several tumor-associated antigens (TAA) has transformed our task into trying to define the mechanisms that underlie the failure of T cells to destroy antigenic tumor cells. Although there are a variety of hypotheses that explain why tumors grow progressively, even if they are antigenic, recent evidence suggests that T cells from tumor-bearing patients exhibit abnormalities in signal transduction that render them unable to respond to appropriate activation signals, even following proper stimulation. Gene therapy with interleukin-2 (IL-2)-secreting tumor cells in an animal model has been effective in preventing the onset of these signaling defects. Discovery of the molecular mechanisms by which such cytokine-secreting tumor cells induce immune responses and how they may best be applied clinically may provide clearer indications of the directions to pursue to alter the balance between the T cell and the tumor cell in the patient's favor.

A HLA class I cis-regulatory element whose activity can be modulated by hormones

To elucidate the basis of the down-regulation in major histocompatibility complex (MHC) class I gene expression and to identify possible DNA-binding regulatory elements that have the potential to interact with class I MHC genes, we have studied the transcriptional regulation of class I HLA genes in human breast carcinoma cells. A 9 base pair (bp) negative cis-regulatory element (NRE) has been identified using band-shift assays employing DNA sequences derived from the 5'-flanking region of HLA class I genes. This 9-bp element, GTCATGGCG, located within exon I of the HLA class I gene, can potently inhibit the expression of a heterologous thymidine kinase (TK) gene promoter and the HLA enhancer element. Furthermore, this regulatory element can exert its suppressive function in either the sense or anti-sense orientation. More interestingly, NRE can suppress dexamethasone-mediated gene activation in the context of the reported glucocorticoid-responsive element (GRE) in MCF-7 cells but has no influence on the estrogen-mediated transcriptional activation of MCF-7 cells in the context of the reported estrogen-responsive element (ERE). Furthermore, the presence of such a regulatory element within the HLA class I gene whose activity can be modulated by hormones correlates well with our observation that the level of HLA class I gene expression can be down-regulated by hormones in human breast carcinoma cells. Such interactions between negative regulatory elements and specific hormone trans-activators are novel and suggest a versatile form of transcriptional control.

Analysis of the nucleotide sequence variation of the antigen-binding domain of DR alpha and DQ alpha molecules as related to the evolution of papillomavirus-induced warts in rabbits

We previously found that regression of skin warts induced by the Shope cottontail rabbit papillomavirus in New Zealand White rabbits, as well as malignant conversion of persistent warts, are linked to a restriction fragment length polymorphism of the major histocompatibility complex class II DR alpha and DQ alpha genes. To find out whether this immunogenetic control could be connected with the antigen binding and presentation function of the alpha 1 domain of class II molecules, we have sequenced the exon 2 of the four DR alpha EcoRI and six of the seven DQ alpha PvuII restriction fragment length polymorphism alleles identified, and deduced the encoded amino acid sequences. We found no amino acid polymorphism among DR alpha alleles, indicating that the alpha 1 domain of the DR alpha chain does not condition wart regression or cancer development. In contrast, 27 of the 82 amino acids of the DQ alpha 1 domain were found variable, defining five amino acid sequence alleles. The restriction fragment length polymorphism allele linked to regression and another allele not linked to regression share the same alpha 1 domain, indicating that wart regression is rather conditioned by a closely linked gene. The most divergent DQ alpha 1 allele, however, was that associated with a higher risk of cancer. Alignment of rabbit and human DQ alpha exon 2 alleles disclosed that amino acid charge variations occur at positions assumed to be important for peptide binding in humans. By modulating the affinity for tumor-specific antigenic peptides, such transitions could affect immune surveillance and, thus, condition the risk for progression to carcinoma of papillomavirus-associated lesions.

Expression of classical and non-classical MHC class I antigens in murine hair follicles

Not all keratinocytes in human and rat hair follicles express MHC class I antigens (MHC I). In the present study, we report the first immunohistological profile of classical and non-classical MHC I expression in the skin of adolescent C57 BL-6 mice during the induced hair cycle. MHC I immunoreactivity (H-2b, H-2Db) is absent in the matrix and inner root sheath of growing (= anagen) hair follicles, and the dermal papillae are H-2b negative during catagen and telogen. This lack of normal MHC I expression may serve to sequester potentially damaging autoantigens from immune recognition. In addition, we present the first evidence of non-classical MHC class I antigen expression in normal mammalian skin: during the entire hair cycle, the distal hair follicle shows strong Qa-2 immunoreactivity, which appears to be restricted to an epithelial follicle compartment densely populated by gamma-delta T cells with which Qa-2 molecules may interact as part of a primitive antibacterial defense system of the follicle. The murine hair cycle is an attractive model for dissecting the functional roles of H-2b and Qa-2 molecules in hair biology and in related tissue-interaction systems.

Major histocompatibility complex-restricted recognition of autologous chronic lymphocytic leukemia by tumor-specific T cells

From the peripheral blood of a patient with chronic lymphocytic leukemia (CLL) we generated a T-cell line and clones which recognized autologous CLL. The line comprised T-cell clones which responded to the CLL as well as to autologous Epstein-Barr virus (EBV)-transformed B cells in an HLA-DR-restricted fashion. In addition, the line comprised clones which were CLL-specific and showed no reactivity against EBV-transformed B cells and against autologous peripheral blood mononuclear cells obtained during remission. The proliferative response of the CLL-specific T-cell clone was inhibited by monoclonal antibodies to HLA-DR11, the major histocompatibility complex (MHC)-restrictive element. These results indicate that the MHC class-II molecule of CLL binds a tumor-specific peptide which is recognized by autologous T cells in an MHC class-II-restricted fashion. Such a peptide may serve as a target for immunotherapy.

Expression of CD59, a complement regulator protein and a second ligand of the CD2 molecule, and CD46 in normal and neoplastic colorectal epithelium

CD59 (protectin) and CD46 (membrane cofactor protein, MCP) are membrane-bound complement regulator proteins which inhibit complement-mediated cytolysis of autologous cells. CD59, a phosphatidyl-inositol-anchored glycoprotein, inhibits the formation of the terminal membrane attack complex (MAC) of complement and was found to be a second ligand for CD2 contributing to T-cell activation. In 20 colorectal normal mucosa samples, in ten adenomas, 71 carcinomas and in ten liver metastases derived thereof, CD59 was inconsistently expressed in the epithelial compartment. In carcinomas CD59 expression in the whole neoplastic compartment was more often found in well- and moderately differentiated tumours. By contrast, focal expression or even complete lack of CD59 was more often found in poorly differentiated tumours (P = 0.021). In addition, carcinomas without metastases at the time of operation (Dukes A/B) more often expressed CD59 in the entire neoplastic population compared to those carcinomas which had already metastasised (P = 0.018). There was no correlation between the mode of CD59 expression in colorectal carcinomas and the tumour type or location. CD46 has C3b/C4b binding and factor-I dependent cofactor activity and is broadly expressed in various cells and tissues. In the epithelial compartment of normal colorectal mucosa, of all adenomas, carcinomas and their liver metastases, CD46 was expressed throughout the epithelial compartment. Since CD46 was consistently expressed in colorectal carcinomas the low expression or even lack of CD59 in a subset of tumours might not lead to critical complement-mediated attack of CD59-negative tumour cells. Regarding CD59 as a natural T-cell ligand involved in cognate T-cell-target-cell interaction, however, loss of CD59 might well be a selection advantage, provided that tumour antigen-mediated T-cell toxicity in colorectal carcinoma exists.

Potential immunogenicity of oncogene and tumor suppressor gene products

The immunogenicity of viral oncoproteins has been established beyond doubt. Cytotoxic T lymphocytes directed against viral oncogene products can eradicate large established tumor masses. This stage has not yet been reached for cellular oncogene and tumor suppressor gene products, but T cells have been raised against MHC-binding peptides encoded by both mutant and wild-type alleles of the ras oncogene and the p53 tumor suppressor gene. In addition, T cells specific for joining region peptides of abnormal fusion proteins resulting from chromosome translocation in tumor cells have been generated. Some of these peptides are processed in cells infected with, for example, vaccinia-ras, but direct anti-tumor effects of peptide specific T lymphocytes remain to be demonstrated.

Analysis of antigens recognized on human melanoma cells by A2-restricted cytolytic T lymphocytes (CTL)

We have pursued our analysis of potential tumor-rejection antigens recognized on human melanoma by autologous cytolytic T lymphocytes (CTL). We reported previously that 3 distinct antigens (A,B,C) were recognized on melanoma cell line SK29-MEL in association with HLA-A2. Selection for melanoma-cell variants resistant to anti-A CTL revealed that antigen A consists of at least 2 determinants (Aa, Ab) which can be lost separately. Genetic linkage between Aa and Ab was suggested by concomitant loss of Aa and Ab in an immunoselected tumor-cell variant. This variant was also resistant to an autologous CTL clone restricted by HLA-B45, indicating that this CTL may also recognize a determinant of antigen A. Of 11 allogeneic HLA-A2 melanoma cell lines that were tested, 5 expressed both Aa and Ab, 1 expressed only Aa, and 1 only Ab. None of them was lysed by anti-B or anti-C CTL clones. A CTL clone derived from another HLA-A2-melanoma patient was found to have exactly the same lytic pattern as the anti-Ab CTL of the first patient. This suggested that it may be possible to elicit an anti-Ab response in many HLA-A2 patients. We conclude that there are at least 2 distinct antigens presented in association with HLA-A2 that are common to many melanomas and therefore constitute promising targets for specific immunotherapy.

Highly lytic CD8+, alpha beta T-cell receptor cytotoxic T cells with major histocompatibility complex (MHC) class I antigen-directed cytotoxicity in beta 2-microglobulin, MHC class I-deficient mice

Targeted disruption of the beta 2-microglobulin (beta 2m) gene results in major histocompatibility complex (MHC) class I deficiency and virtual disappearance of functional CD8+ cytotoxic T lymphocytes (CTLs) in beta 2m-deficient (beta 2m-/-) mice. We asked whether the beta 2m-/- mice are able to reject tumor cells injected i.p. and what is the cellular composition of peritoneal exudate leukocytes (PELs) from such mice. We found that beta 2m-/- mice do reject MHC class I-bearing tumor cells injected i.p. Surprisingly, analysis of PEL CTLs obtained from i.p. tumor-injected beta 2m -/- mice revealed the presence of a large proportion of functional, tumor-destroying CD8+, CD4-, alpha beta T-cell receptor-positive, CD3+, Thy-1+, MHC class I-negative CTLs with strong MHC class I-directed cytotoxic activity. These results call for careful studies of local accumulation of CD8+ CTLs in beta 2m -/- mouse models and suggest that the dramatic decrease in MHC class I expression caused by beta 2m gene disruption does not prevent CD8+/CD4- cell selection and expansion.

Tissue typing the HLA-A locus from genomic DNA by sequence-specific PCR: comparison of HLA genotype and surface expression on colorectal tumor cell lines

A system devised for tissue typing the HLA-A locus by PCR from genomic DNA has been used to investigate abnormalities of HLA expression in a panel of 30 colorectal tumor cell lines, by comparing the HLA-A locus genotype with surface expression of HLA. Three cell lines showed complete lack of HLA expression associated with failure to express beta 2-microglobulin. In two other cell lines, loss of expression of HLA-A2 was observed, in spite of the presence of the gene in genomic DNA. Eleven cell lines gave a single HLA-A locus specificity on PCR typing. In one of these cell lines we have demonstrated the loss of an HLA-A locus gene in the tumor cell by comparison with DNA from a lymphoblastoid B-cell line derived from the same patient. These data indicate that at least three independent mechanisms were involved in the loss of HLA expression on the colorectal tumor cell lines.