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Abstract Introduction We report a case of pulmonary metastatic recurrence of renal adenocarcinoma soon after radical nephrectomy that was followed by renal transplant and immunosuppressive medication. Increased risk of metastatic recurrence of renal cell carcinoma should be considered in the immediate post-transplant period when immunosuppressive medication is administered, even if nephrectomy had been performed many years earlier. Case presentation In 1986 the patient demonstrated renal insufficiency secondary to mesangial glomerulonephritis. In 1992 he underwent left side radical nephrectomy with histopathological diagnosis of clear cell adenocarcinoma. Mesangial glomerulonephritis in the remaining right kidney progressed to end-stage renal failure. In October 2000 he received a kidney transplant from a cadaver and commenced immunosuppressive medication. Two months later, several nodules were found in his lungs, which were identified as metastases from the primary renal tumor that had been removed with the diseased kidney 8 years earlier. Conclusion Recurrence of renal cell carcinoma metastases points to tumor dormancy and reflects a misbalance between effective tumor immune surveillance and immune escape. This case demonstrates that a state of tumor dormancy can be interrupted soon after administration of immunosuppressant medication.

Abstract Background The inability of cancer cells to present antigen on the cell surface via MHC class I molecules is one of the mechanisms by which tumor cells evade anti-tumor immunity. Alterations of Jak-STAT components of interferon (IFN)-mediated signaling can contribute to the mechanism of cell resistance to IFN, leading to lack of MHC class I inducibility. Hence, the identification of IFN-γ-resistant tumors may have prognostic and/or therapeutic relevance. In the present study, we investigated a mechanism of MHC class I inducibility in response to IFN-γ treatment in human melanoma cell lines. Methods Basal and IFN-induced expression of HLA class I antigens was analyzed by means of indirect immunofluorescence flow cytometry, Western Blot, RT-PCR, and quantitative real-time RT-PCR (TaqMan® Gene Expression Assays). In demethylation studies cells were cultured with 5-aza-2'-deoxycytidine. Electrophoretic Mobility Shift Assay (EMSA) was used to assay whether IRF-1 promoter binding activity is induced in IFN-γ-treated cells. Results Altered IFN-γ mediated HLA-class I induction was observed in two melanoma cells lines (ESTDAB-004 and ESTDAB-159) out of 57 studied, while treatment of these two cell lines with IFN-α led to normal induction of HLA class I antigen expression. Examination of STAT-1 in ESTDAB-004 after IFN-γ treatment demonstrated that the STAT-1 protein was expressed but not phosphorylated. Interestingly, IFN-α treatment induced normal STAT-1 phosphorylation and HLA class I expression. In contrast, the absence of response to IFN-γ in ESTDAB-159 was found to be associated with alterations in downstream components of the IFN-γ signaling pathway. Conclusion We observed two distinct mechanisms of loss of IFN-γ inducibility of HLA class I antigens in two melanoma cell lines. Our findings suggest that loss of HLA class I induction in ESTDAB-004 cells results from a defect in the earliest steps of the IFN-γ signaling pathway due to absence of STAT-1 tyrosine-phosphorylation, while absence of IFN-γ-mediated HLA class I expression in ESTDAB-159 cells is due to epigenetic blocking of IFN-regulatory factor 1 (IRF-1) transactivation.

Major histocompatibility complex (MHC) class-I molecules (or Human Leucocyte Antigen class-I) play a key role in adaptive immunity against cancer. They present specific tumor neoantigens to cytotoxic T cells and provoke an antitumor cytotoxic response. The total or partial loss of HLA molecules can inhibit the immune system's ability to detect and destroy cancer cells. Loss of heterozygosity (LOH) is a common irreversible genetic alteration that occurs in the great majority of human tumors, including breast cancer. LOH at chromosome 6, which involves HLA genes (LOH-HLA), leads to the loss of an HLA haplotype and is linked to cancer progression and a weak response to cancer immunotherapy. Therefore, the loss of genes or an entire chromosomal region which are critical for antigen presentation is of particular importance in the search for novel prognostic and clinical biomarkers in breast cancer. Here, we review the role of LOH-HLA in breast cancer, its contribution to an understanding of cancer immune escape and tumor progression, and discuss how it can be targeted in cancer therapy.

Background: Loss of human leukocyte antigen (HLA) class I expression and loss of heterozygosity (LOH) are common events implicated in the primary resistance of non-small cell lung cancer (NSCLC) to immunotherapy. However, there is no data on perioperative chemoimmunotherapy (ChIO) efficacy or response mechanisms in the context of HLA class I defects., Methods: Baseline HLA class I tumor status (HLA-deficient (HLA-DEF) or HLA-proficient (HLA-PRO)) was determined by DNA LOH combined with immunohistochemistry for protein levels in tissue of 24 patients with NSCLC treated with perioperative nivolumab plus chemotherapy from NADIM trial (NCT03081689). We integrated HLA tumor status with molecular data (programmed death-ligand 1 (PD-L1), TMB, TCR repertoire, TILs populations, bulk RNA-seq, and spatial transcriptomics (ST)) and clinical outcomes (pathological response and survival data) to study the activity of perioperative ChIO considering HLA class I defects., Results: HLA-DEF tumors comprised 41.7% of analyzed tumors and showed a desert-like microenvironment at baseline, with lower PD-L1 levels and reduced immune infiltrate. However, perioperative ChIO induced similar complete pathological response (CPR) rates in both HLA-DEF and PRO tumors (50% and 60% respectively, p=0.670), as well as 3-year survival rates: Progression-free survival (PFS) and overall survival (OS) of 70% (95% CI 32.9% to 89.2%) for HLA-DEF, and PFS 71.4% (95% CI 40.6% to 88.2%) and OS 92.9% (95% CI 59.1% to 99.0%) for HLA-PRO (log-rank PFS p=0.909, OS p=0.137). Proof-of-concept ST analysis of a CPR HLA-DEF tumor after ChIO showed a strong immune response with tertiary lymphoid structures (TLS), CD4+T cells with HLA class II colocalization, and activated CD8+T cells., Conclusions: Our findings highlight the activity of perioperative ChIO, and the potential role of TLS and T-cell immune response, in NSCLC HLA-DEF tumors., Competing Interests: Competing interests: VC reports consulting fees from Roche, AstraZeneca, MSD, BMS, Takeda, Sanofi, Agmen; payment or honoraria from Roche, AstraZeneca, MSD, BMS, Takeda, Sanofi, Agmen, Janssen, Regeneron and Pfizer; and support for attending meetings and/or travel from Roche, AstraZeneca, MSD, and Takeda outside the submitted work. EN reports grants from Roche, BMS, Pfizer, and Merck Serono; consulting fees and payment or honoraria form Roche, BMS, MSD, Merck Serono, Sanofi, Pfizer, Lilly, Amgen, Janssen, Daiichi Sankyo, Boehringer Ingelheim, AstraZeneca, Takeda, Sanofi, Pierre Fabre, Qiagen; payment or honoraria from Bayer; and advisory board from MSD, Roche, Apollomics, Daiichi and Transgene outside the submitted work. AM-M reports consulting fees, payment or honoraria and support for attending meetings and/or travel from AstraZeneca/MedImmune, BMS, F Hoffmann-La Roche AG, MSD, MSD Oncology, Pfizer; Steering Committee Member of AstraZeneca/MedImmune; support for attending meetings and/or travel from Lilly; and advisory board from AstraZeneca/MedImmune, MSD, BMS, and F Hoffmann-La Roche AG outside the submitted work. AI reports consulting fees from Pfizer, Amgen, AstraZeneca, and Roche; payment form expert testimony form BMS, Roche, Pfizer, AstraZeneca, and Takeda; support for attending meetings and/or travel from Roche, Takeda, and Pfizer; and advisory abroad from Roche and BMS outside the submitted work. BM reports payment or honoraria from Roche, BMS, MSD, Boehringer Ingelheim, and Pfizer outside the submitted work. SV reports payment or honoraria from Merck GmbH, MSD, BMS, Takeda, AstraZeneca, and Roche; support for attending meetings and/or travel from OSE Immunotherapeutics, Roche, and GMS; and advisory board from Merck GmbH, Puma Biotech, Takeda, Ipsen, AbbVie, Roche, and AstraZeneca outside the submitted work. IBA reports payment or honoraria from AstraZeneca, BMS, Janssen Cilag, Lilly, MSD, Roche, Sanofi, and Takeda; as well as support for attending meetings and/or travel from MSD and AstraZeneca outside the submitted work. JdC reports consulting fees from AstraZeneca, BMS, Roche, MSD, Boehringer Ingelheim, Janssen, Lilly, Sanofi, Takeda, Pfizer, and Glaxo; payment or honoraria from AstraZeneca, BMS, Roche, MSD, Pfizer, Janssen, Takeda, and Sanofi; support for attending meetings and/or travel from AstraZeneca, MSD, and Roche; and advisory Board fees from AstraZeneca, BMS, Roche, MSD, Glaxo, Janssen, and Gilead outside the submitted work. MCo reports consulting fees from Novartis, AstraZeneca, Boehringer Ingelheim, Roche, BMS, Lilly, MSD, Takeda, Pfizer, Kyowa, Sanofi, and Janssen, as well as payment or honoraria from Novartis, AstraZeneca, Boehringer Ingelheim, Roche, BMS, Lilly, MSD, Takeda, Kyowa, Pierre Fabre, Novocure, Sanofi, and Janssen outside the submitted work. JM-L reports payment or honoraria from Roche, BMS, and EUSA Pharma, as well as support for attending meetings and/or travel from Roche outside the submitted work. MP reports consulting fees from BMS, AstraZeneca, MSD, Roche, Takeda. Support for attending meetings and/or travel and payment or honoraria from BMS, AstraZeneca, MSD, Roche, and Takeda outside the submitted work. No disclosures were reported by the other authors., (© Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

HLA class I molecules are key in tumor recognition and T cell-mediated elimination. Loss of tumor HLA class I expression with different underlying molecular defects results in reduced antigen presentation and facilitates cancer immune evasion. It is also linked to significant changes in tumor microenvironment and tissue architecture. In this review, we summarize the current advances and future perspectives in the understanding of the mechanisms of MHC/HLA class I alterations during the natural history of tumor progression from a primary lesion to distant metastases. We also focus on recent clinical and experimental data demonstrating that lack of response to cancer immunotherapy frequently depends on the molecular nature of tumor HLA class I aberrations. Finally, we highlight the relevance of detecting and correcting the absence of tumor HLA expression to improve immunotherapy protocols., (©2022 American Association for Cancer Research.)

Breast cancer is the most common type of malignancy and leading cause of cancer death among women worldwide. Despite the current revolutionary advances in the field of cancer immunotherapy, clinical response in breast cancer is frequently below expectations, in part due to various mechanisms of cancer immune escape that produce tumor variants that are resistant to treatment. Thus, a further understanding of the molecular events underlying immune evasion in breast cancer may guarantee a significant improvement in the clinical success of immunotherapy. Furthermore, nanomedicine provides a promising opportunity to enhance the efficacy of cancer immunotherapy by improving the delivery, retention and release of immunostimulatory agents in targeted cells and tumor tissues. Hence, it can be used to overcome tumor immune escape and increase tumor rejection in numerous malignancies, including breast cancer. In this review, we summarize the current status and emerging trends in nanomedicine-based strategies targeting cancer immune evasion and modulating the immunosuppressive tumor microenvironment, including the inhibition of immunosuppressive cells in the tumor area, the activation of dendritic cells and the stimulation of the specific antitumor T-cell response.

Total or partial loss of HLA class I antigens reduce the recognition of specific tumor peptides by cytotoxic T lymphocytes favoring cancer immune escape during natural tumor evolution. These alterations can be caused by genomic defects, such as loss of heterozygosity at chromosomes 6 and 15 (LOH-6 and LOH-15), where HLA class I genes are located. There is growing evidence indicating that LOH in HLA contributes to the immune selection of HLA loss variants and influences the resistance to immunotherapy. Nevertheless, the incidence and the mechanism of this chromosomal aberration involving HLA genes has not been systematically assessed in different types of tumors and often remains underestimated. Here, we used SNP arrays to investigate the incidence and patterns of LOH-6 and LOH-15 in a number of human cancer cell lines and tissues of different histological types. We observed that LOH in HLA is a common event in cancer samples with a prevalence of a copy neutral type of LOH (CN-LOH) that affects entire chromosome 6 or 15 and involves chromosomal duplications. LOH-6 was observed more often and was associated with homozygous HLA genotype and partial HLA loss of expression. We also discuss the immunologic and clinical implications of LOH in HLA on tumor clonal expansion and association with the cancer recurrence after treatment.

Cancer eradication and clinical outcome of immunotherapy depend on tumor cell immunogenicity, including HLA class I (HLA-I) and PD-L1 expression on malignant cells, and on the characteristics of the tumor microenvironment, such as tumor immune infiltration and stromal reaction. Loss of tumor HLA-I is a common mechanism of immune escape from cytotoxic T lymphocytes and is linked to cancer progression and resistance to immunotherapy with the inhibitors of PD-L1/PD-1 signaling. Here we observed that HLA-I loss in bladder tumors is associated with T cell exclusion and tumor encapsulation with stromal elements rich in FAP-positive cells. In addition, PD-L1 upregulation in HLA-I negative tumors demonstrated a correlation with high tumor grade and worse overall- and cancer-specific survival of the patients. These changes define common immuno-morphological signatures compatible with cancer immune escape and acquired resistance to therapeutic interventions across different types of malignancy. They also may contribute to the search of new targets for cancer treatment, such as FAP-expressing cancer-associated fibroblasts, in refractory bladder tumors.

T cell-mediated immune therapies have emerged as a promising treatment modality in different malignancies including colorectal cancer (CRC). However, only a fraction of patients currently respond to treatment. Understanding the lack of responses and finding biomarkers with predictive value is of great importance. There is evidence that CRC is a heterogeneous disease and several classification systems have been proposed that are based on genomic instability, immune cell infiltration, stromal content and molecular subtypes of gene expression. Human leukocyte antigen class I (HLA-I) plays a pivotal role in presenting processed antigens to T lymphocytes, including tumour antigens. These molecules are frequently lost in different types of cancers, including CRC, resulting in tumour immune escape from cytotoxic T lymphocytes during the natural history of cancer development. The aim of this review is to (i) summarize the prevalence and molecular mechanisms behind HLA-I loss in CRC, (ii) discuss HLA-I expression/loss in the context of the newly identified CRC molecular subtypes, (iii) analyze the HLA-I phenotypes of CRC metastases disseminated via blood or the lymphatic system, (iv) discuss strategies to recover/circumvent HLA-I expression/loss and finally (v) review the role of HLA class II (HLA-II) in CRC prognosis.

Tumours can escape T-cell responses by losing major histocompatibility complex (MHC)/ human leucocyte antigen (HLA) class I molecules. In the early stages of cancer development, primary tumours are composed of homogeneous HLA class I-positive cancer cells. Subsequently, infiltration of the tumour by T cells generates a vast diversity of tumour clones with different MHC class I expressions. A Darwinian type of T-cell-mediated immune selection results in a tumour composed solely of MHC class I-negative cells. Metastatic colonization is a highly complex phenomenon in which T lymphocytes and natural killer cells play a major role. We have obtained evidence that the MHC class I phenotype of metastatic colonies can be highly diverse and is not necessarily the same as that of the primary tumour. The molecular mechanisms responsible for MHC/HLA class I alterations are an important determinant of the clinical response to cancer immunotherapy. Hence, immunotherapy can successfully up-regulate MHC/HLA class I expression if the alteration is reversible ('soft'), leading to T-cell-mediated tumour regression. In contrast, it cannot recover this expression if the alteration is irreversible ('hard'), when tumour cells escape T-cell-mediated destruction with subsequent cancer progression. This review summarizes clinical and experimental data on the complexity of immune escape mechanisms used by tumour cells to avoid T and natural killer cell responses. We also provide in-depth analysis of the nature of MHC/HLA class I changes during metastatic colonization and contribute evidence of the enormous diversity of MHC/HLA class I phenotypes that can be produced by tumour cells during this process., (© 2019 John Wiley & Sons Ltd.)

Background: Tumor human leukocyte antigen class I (HLA-I) expression plays an important role in T cell-mediated tumor rejection. Loss of HLA-I is associated with cancer progression and resistance to immunotherapy, including antibodies blocking programmed death-1/programmed death-ligand 1 (PD-1/PD-L1) signaling. Our objective was to analyze a correlation between HLA-I, tumor immune infiltration, and PD-L1/PD-1 axis in bladder cancer in association with the clinicopathologic features of patients., Methods: We analyzed 85 cryopreserved bladder tumors by immunohistochemistry to investigate the expression of HLA-I, PD-L1, PD-1, CD3, CD8, and CXC chemokine receptor 4 (CXCR4). The results were correlated with tumor stage and other clinicopathologic variables of patients., Results: We found a strong positive correlation between tumor HLA-I expression and infiltration with CD3+ and CD8 + T cells. PD-L1 expression was positive in 15.5% of tumors and heterogeneous in 40.5%, and was linked to a more advanced tumor stage. The majority of HLA-I-positive/heterogeneous tumors also expressed PD-L1 and PD-1, which were significantly correlated with each other and with lymphocyte infiltration. Interestingly, the analysis of the simultaneous expression of both markers revealed that 85.2% of tumors with a positive/heterogeneous HLA-I phenotype and negative for PD-L1 were mostly non-invasive, representing a 'tumor rejection' immune phenotype., Conclusions: High tumor HLA-I expression with absence of PD-L1 provides bladder cancer with an immune rejection mechanism. Evaluation of PD-L1 and HLA-I together should be considered in bladder cancer and may provide a new predictive biomarker of tumor invasiveness and of the response to 'immune checkpoint' therapy.

HLA class I (HLA-I) molecules play a crucial role in the presentation of tumor antigenic peptides to CD8+ T cells. Tumor HLA-I loss provides a route of immune escape from T cell-mediated killing. We analyzed HLA-I expression in 98 cryopreserved breast cancer tissues using a broad panel of anti-HLA-I antibodies. Genomic HLA-I typing was performed using DNA obtained from autologous normal breast tissue. Analysis of the loss of heterozygosity (LOH) in the HLA-I region of chromosome 6 (LOH-6) and in the β2-microglobulin (B2M) region of chromosome 15 (LOH-15) was done by microsatellite amplification of DNA isolated from microdissected tumor areas. B2M gene sequencing was done using this DNA form HLA-I-negative tumors. Immunohistological analysis revealed various types of HLA-I alterations in 79 tumors (81%), including total HLA-I loss in 53 cases (54%) and partial loss in 16 samples (14%). In 19 cases (19%), HLA-I expression was positive. Using microsatellite analysis, we detected LOH in 36 cases out of 92 evaluated (39%), including 15 samples with only LOH-6, 14 with LOH-15, and seven tumors with LOH-6 and LOH-15 at the same time. Remarkably, we detected LOH-6 in eight tumors with positive HLA-I immunolabeling. We did not find any B2M mutations in HLA-I-negative breast tumors. In conclusion, LOH at chromosomes 6 and 15 has a high incidence in breast cancer and occurs in tumors with different HLA-I immunophenotypes. This common molecular mechanism of HLA-I alterations may reduce the ability of cytotoxic T lymphocytes  to kill tumor cells and negatively influence the clinical success of cancer immunotherapy.

MHC/HLA class I loss in cancer is one of the main mechanisms of tumor immune escape from T-cell recognition and destruction. Tumor infiltration by T lymphocytes (TILs) and by other immune cells was first described many years ago, but has never been directly and clearly linked to the destruction of HLA-I positive and selection of HLA-I negative tumor cells. The degree and the pattern of lymphocyte infiltration in a tumor nest may depend on antigenicity and the developmental stages of the tumors. In addition, it is becoming evident that HLA-I expression and tumor infiltration have a direct correlation with tumor tissue reorganization. We observed that at early stages (permissive Phase I) tumors are heterogeneous, with both HLA-I positive and HLA-negative cancer cells, and are infiltrated by TILs and M1 macrophages as a part of an active anti-tumor Th1 response. At later stages (encapsulated Phase II), tumor nests are mostly HLA-I negative with immune cells residing in the peri-tumoral stroma, which forms a granuloma-like encapsulated tissue structure. All these tumor characteristics, including tumor HLA-I expression pattern, have an important clinical prognostic value and should be closely and routinely investigated in different types of cancer by immunologists and by pathologists. In this review we summarize our current viewpoint about the alterations in HLA-I expression in cancer and discuss how, when and why tumor HLA-I losses occur. We also provide evidence for the negative impact of tumor HLA-I loss in current cancer immunotherapies, with the focus on reversible ('soft') and irreversible ('hard') HLA-I defects., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Immune-checkpoint inhibitors show encouraging results in cancer treatment, but the clinical benefit is limited exclusively to a subset of patients. We analyzed the density and composition of tumor T-cell infiltration in non-small-cell lung carcinoma (NSCLC) in relation to PD-L1 and HLA class I (HLA-I) expression. We found that positive HLA-I expression, independently on PD-L1 status, is the key factor determining the increased density of the immune infiltrate. When both markers were analyzed simultaneously, we identified four phenotypes of HLA-I and PD-L1 co-expression. They demonstrated different patterns of tumor infiltration and clinicopathologic characteristics, including the tumor size and lymphatic spread. All HLA-I+/PD-L1+ tumors had a high degree of intratumoral infiltration with CD8+T-lymphocytes, whereas HLA-I loss was associated with a significantly reduced number of tumor infiltrating T-lymphocytes mostly restrained in the stroma surrounding the tumor nest. HLA-I-negative/PD-L1-positive tumors had bigger size (T) and lower grade of infiltration with CD8+T-cells. It represents a cancer immune escape phenotype that combines two independent mechanisms of immune evasion: loss of HLA-I and upregulation of PD-L1. Using GCH-array analysis of human lung cancer cell lines we found that the loss of heterozygosity (LOH) with complete or partial deletion of HLA-I genes is the principal mechanism of HLA-I alterations. This irreversible defect, which could potentially decrease the clinical efficacy of lung cancer immunotherapy, appears to be underestimated. In conclusion, our results suggest that the analysis of HLA-I is very important for the selection of potential responders to cancer immunotherapy., Competing Interests: CONFLICTS OF INTEREST The authors have no conflicts of interest to disclose.

Tumor immune escape is associated with the loss of tumor HLA class I (HLA-I) expression commonly found in malignant cells. Accumulating evidence suggests that the efficacy of immunotherapy depends on the expression levels of HLA class I molecules on tumors cells. It also depends on the molecular mechanism underlying the loss of HLA expression, which could be reversible/"soft" or irreversible/"hard" due to genetic alterations in HLA, β2-microglobulin or IFN genes. Immune selection of HLA-I negative tumor cells harboring structural/irreversible alterations has been demonstrated after immunotherapy in cancer patients and in experimental cancer models. Here, we summarize recent findings indicating that tumor HLA-I loss also correlates with a reduced intra-tumor T cell infiltration and with a specific reorganization of tumor tissue. T cell immune selection of HLA-I negative tumors results in a clear separation between the stroma and the tumor parenchyma with leucocytes, macrophages and other mononuclear cells restrained outside the tumor mass. Better understanding of the structural and functional changes taking place in the tumor microenvironment may help to overcome cancer immune escape and improve the efficacy of different immunotherapeutic strategies. We also underline the urgent need for designing strategies to enhance tumor HLA class I expression that could improve tumor rejection by cytotoxic T-lymphocytes (CTL).

Most tumor cells derive from MHC-I-positive normal counterparts and remain positive at early stages of tumor development. T lymphocytes can infiltrate tumor tissue, recognize and destroy MHC class I (MHC-I)-positive cancer cells ("permissive" phase I). Later, MHC-I-negative tumor cell variants resistant to T-cell killing emerge. During this process, tumors first acquire a heterogeneous MHC-I expression pattern and finally become uniformly MHC-I-negative. This stage (phase II) represents a "non-permissive" encapsulated structure with tumor nodes surrounded by fibrous tissue containing different elements including leukocytes, macrophages, fibroblasts, etc. Molecular mechanisms responsible for total or partial MHC-I downregulation play a crucial role in determining and predicting the antigen-presenting capacity of cancer cells. MHC-I downregulation caused by reversible ("soft") lesions can be upregulated by TH1-type cytokines released into the tumor microenvironment in response to different types of immunotherapy. In contrast, when the molecular mechanism of the tumor MHC-I loss is irreversible ("hard") due to a genetic defect in the gene/s coding for MHC-I heavy chains (chromosome 6) or beta-2-microglobulin (B2M) (chromosome 15), malignant cells are unable to upregulate MHC-I, remain undetectable by cytotoxic T-cells, and continue to grow and metastasize. Based on the tumor MHC-I molecular analysis, it might be possible to define MHC-I phenotypes present in cancer patients in order to distinguish between non-responders, partial/short-term responders, and likely durable responders. This highlights the need for designing strategies to enhance tumor MHC-I expression that would allow CTL-mediated tumor rejection.

Immune escape strategies aimed to avoid T-cell recognition, including the loss of tumor MHC class I expression, are commonly found in malignant cells. Tumor immune escape has proven to have a negative effect on the clinical outcome of cancer immunotherapy, including treatment with antibodies blocking immune checkpoint molecules. Hence, there is an urgent need to develop novel approaches to overcome tumor immune evasion. MHC class I antigen presentation is often affected in human cancers and the capacity to induce upregulation of MHC class I cell surface expression is a critical step in the induction of tumor rejection. This review focuses on characterization of rejection, escape, and dormant profiles of tumors and its microenvironment with a special emphasis on the tumor MHC class I expression. We also discuss possible approaches to recover MHC class I expression on tumor cells harboring reversible/'soft' or irreversible/'hard' genetic lesions. Such MHC class I recovery approaches might well synergize with complementary forms of immunotherapy., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Intratumor heterogeneity among cancer cells is promoted by reversible or irreversible genetic alterations and by different microenvironmental factors. There is considerable experimental evidence of the presence of a variety of malignant cell clones with a wide diversity of major histocompatibility class I (MHC-I) expression during early stages of tumor development. This variety of MHC-I phenotypes may define the evolution of a particular tumor. Loss of MHC-I molecules frequently results in immune escape of MHC-negative or -deficient tumor cells from the host T cell-mediated immune response. We review here the results obtained by our group and other researchers in animal models and humans, showing how MHC-I intratumor heterogeneity may affect local oncogenicity and metastatic progression. In particular, we summarize the data obtained in an experimental mouse cancer model of a methylcholanthrene-induced fibrosarcoma (GR9), in which isolated clones with different MHC-I expression patterns demonstrated distinct local tumor growth rates and metastatic capacities. The observed "explosion of diversity" of MHC-I phenotypes in primary tumor clones and the molecular mechanism ("hard"/irreversible or "soft"/reversible) responsible for a given MHC-I alteration might determine not only the metastatic capacity of the cells but also their response to immunotherapy. We also illustrate the generation of further MHC heterogeneity during metastatic colonization and discuss different strategies to favor tumor rejection by counteracting MHC-I loss. Finally, we highlight the role of MHC-I genes in tumor dormancy and cell cycle control., (© 2014 UICC.)

Reduced expression of HLA class I is an important immune escape mechanism from cytotoxic T cells described in various types of malignancy. It often correlates with poor prognosis and resistance to therapy. However, current knowledge about the frequency, underlying molecular mechanisms, and prognostic value of HLA class I and II alterations in prostate cancer (PC) is limited. Immunohistochemical analysis demonstrated that 88 % of the 42 studied cryopreserved prostate tumors have at least one type of HLA alteration as compared to adjacent normal prostate epithelium or benign hyperplasia. Total loss of HLA-I expression found in 50 % of tumors showed an association with increased incidence of tumor relapse, perineural invasion, and high D'Amico risk. The remaining HLA-I-positive tumors demonstrated locus and allelic losses detected in 26 and 12 % of samples, respectively. Loss of heterozygosity at chromosome 6 was detected in 32 % of the studied tumors. Molecular analysis revealed a reduced expression of B2M, TAP2, tapasin and NLRC5 mRNA in microdissected HLA-I-negative tumors. Analysis of twelve previously unreported cell lines derived from neoplastic and normal epithelium of cancerous prostate revealed different types of HLA-I aberration, ranging from locus and/or allelic downregulation to a total absence of HLA-I expression. The high incidence of HLA-I loss observed in PC, caused by both regulatory and structural defects, is associated with more aggressive disease development and may pose a real threat to patient health by increasing cancer progression and resistance to T-cell-based immunotherapy.

Cancer cells escape T-cell-mediated destruction by losing human leukocyte antigen (HLA) class I expression via various mechanisms, including loss of beta2-microglobulin (β2m). Our study illustrates the immune escape of HLA class I-negative tumor cells and chronological sequence of appearance of tumor β2m gene mutation in successive lesions obtained from a patient with metastatic melanoma. We observed a gradual decrease in HLA expression in consecutive lesions with few HLA-negative nodules in the primary tumor and the emergence of a totally negative lesion at later stages of the disease. We detected loss of β2m in β2m-negative nests of the primary tumor caused by a combination of two alterations: (i) a mutation (G to T substitution) in codon 67 in exon 2 of β2m gene, producing a stop codon and (ii) loss of the second gene copy by loss of heterozygosity (LOH) in chromosome 15. The same β2m mutation was found in a homogeneously β2m-negative metastasis 10 months later and in a cell line established from a biopsy of a postvaccination lymph node. Microsatellite analysis revealed the presence of LOH in chromosomes 6 and 15 in tumor samples, showing an accumulation of chromosomal loss at specific short tandem repeats in successive metastases during disease progression. HLA loss correlated with decreased tumor CD8+ T-cell infiltration. Early incidence of β2m defects can cause an immune selection and expansion of highly aggressive melanoma clones with irreversible genetic defects causing total loss of HLA class I expression and should be taken into consideration as a therapeutic target in the development of cancer immunotherapy protocols., (© 2013 UICC.)

The immune system is a critical element involved in the control of tumor development and progression. While professionals have learned how to manipulate the immune system to generate tumor-specific immune responses, cancer immunotherapy has not yet delivered substantial clinical benefits. It has become increasingly clear that tumor-induced abnormalities in the immune system not only hamper tumor immunosurveillance, but also limit the efficacy of cancer immunotherapy. Meanwhile, the results of recent studies allow the belief that one is on the edge of a real breakthrough in this promising direction in cancer therapy. The 2(nd) International Conference 'Cancer Immunotherapy and Immunomonitoring (CITIM)' was the second meeting in Eastern Europe to specifically focus on the issue of immune regulation in the tumor environment, cancer immunotherapy, and immunomonitoring of immunotherapeutic clinical trials. This CITIM Conference held in Budapest, Hungary, was comprised from 12 plenary sessions, Best Abstract Award session, Poster session, and four Keynote lectures. Outstanding presentations and numerous productive discussions summarized the current place of the field and opened new directions for improving monitoring and therapy for patients with cancer.

Bacillus Calmette-Guerin (BCG) immunotherapy is a standard treatment for high-risk non-muscle-infiltrating bladder cancer patients. Although the outcomes are good, cancer relapse is observed in around 40% of patients. We present the comparative analysis of human leukocyte antigen (HLA) class I expression in recurrent bladder tumors in patients treated with mitomycin or BCG. HLA class I expression was analyzed by RT-Q-PCR and immunohistochemical techniques. Loss of heterozygosity (LOH) was determined by microsatellite amplification of markers in chromosome 6 and 15. More profound alterations in HLA class I expression were found in post-BCG recurrent tumors than in pre-BCG lesions, whereas mitomycin treatment did not change the HLA class I expression pattern. Post-BCG recurrent tumors also showed a higher incidence of structural defects underlying altered HLA class I expression. We hypothesize that the immunotherapy-activated immune system recognizes and eliminates tumor cells with reversible ("soft") HLA class I changes but not transformed cells with additional, irreversible ("hard") alterations. To our knowledge, this is the first clinical evidence of immunotherapy-induced immunoselection of HLA class I loss tumor variants in bladder cancer, although the study involved a small number of patients., (Copyright © 2010 UICC.)

Downregulation or total loss of HLA class I expression on tumor cells is known as a mechanism of cancer immune escape. Alterations of the HLA phenotype are frequently due to mutations affecting genes encoding the HLA class I heavy chains located on chromosome 6p21 or the β2-microglobulin (β2m) gene encoding the light chain of the HLA complex located on chromosome 15q21. Frequently irreversible total loss of HLA class I molecules is due to the coincidence of two molecular events, the mutation of one β2m gene and the loss of the second copy. The latter is detectable as loss of heterozygosity (LOH) of microsatellite markers in the β2m region on chromosome 15q21 (LOH-15q21). Thus, LOH-15q21 might be an important event in the processes of HLA class I downregulation and total loss. Here we studied the frequency of LOH-15q21 in tumor tissues of different entities. By determining the status of heterozygosity of two microsatellite markers we detected LOH-15q21 in 44% of bladder carcinomas (n = 69), in 35% of colon carcinomas (n = 95), in 16% of melanomas (n = 70) but only in 7% of renal cancers (n = 45). Moreover, we observed a frequent coincidence of LOH-15q21 and LOH-6p21 in colorectal carcinoma, bladder carcinoma and melanoma, but not for renal carcinoma. We believe that the high incidence of LOH-15q21 in some malignancies and especially the coincidence of LOH-15q21 and LOH-6p21 might have a strong impact on tumor immunogenicity and on the efficiency of cancer immunotherapy.

The ability of cancer cells to escape from the natural or immunotherapy-induced antitumor immune response is often associated with alterations in the tumor cell surface expression of Major Histocompatibility Complex (MHC) Class I antigens. Considerable knowledge has been gained on the prevalence of various patterns of MHC Class I defects and the underlying molecular mechanisms in different types of cancer. In contrast, few data are available on the changes in MHC Class I expression happening during the course of cancer immunotherapy. We have recently proposed that the progression or regression of a tumor lesion in cancer patients undergoing immunotherapy could be predetermined by the molecular mechanism responsible for the MHC Class I alteration and not by the type of immunotherapy used, i.e., interleukin-2 (IL-2), Bacillus Calmette-Guèrin (BCG), interferon-alpha (IFN-alpha), peptides alone, dendritic cells loaded with peptides, protein-bound polysaccharide etc. If the molecular alteration responsible for the changes in MHC Class I expression is reversible by cytokines ("soft" lesion), the MHC Class I expression will be upregulated, the specific T cell-mediated response will increase and the lesion will regress. However, if the molecular defect is structural ("hard" lesion), the MHC Class I expression will remain low, the escape mechanism will prevail and the primary tumor or the metastatic lesion will progress. According to this idea, the nature of the preexisting MHC Class I lesion in the cancer cell has a crucial impact determining the final outcome of cancer immunotherapy. In this article, we discuss the importance of these two types of molecular mechanisms of MHC Class I-altered expression.

Altered HLA class I and class II cell surface expression has been reported in many types of malignancy and represents one of the major mechanism by which tumour cells escape from T lymphocytes. In this report, we review the results obtained from the study of constitutive and IFN-gamma-induced expression of HLA class I and II molecules in 91 human melanoma cell lines from the European Searchable Tumour Cell Line Database, and compare them with published data on HLA expression in other types of cancer. Various types of alterations in HLA class I cell surface expression were found in a high percentage (67%) of the studied cell lines. These alterations range from total to selective HLA class I loss and are associated with beta2-microglobulin gene mutations, transcriptional downregulation of HLA class I genes and antigen processing machinery components, or with the loss of heterozygosity in chromosome 6. The most frequently observed phenotype is selective downregulation of HLA-B locus, reversible after treatment with IFN-gamma. The expression of constitutive- or IFN-gamma induced-surface expression of at least one HLA class II locus is positive in 71.5% of the analysed cell lines. Four different HLA class II expression phenotypes were defined, and a positive correlation between the expression of class I and II molecules is discussed. More detailed information on the HLA expression patterns and others immunological characteristics of these melanoma cell lines can be found on the following website http://www.ebi.ac.uk/ipd/estdab .

Despite the significant efforts to enhance immune reactivity against malignancies the clinical effect of anti-tumor vaccines and cancer immunotherapy is still below expectations. Understanding of the possible causes of such poor clinical outcome has become very important for improvement of the existing cancer treatment modalities. In particular, the critical role of HLA class I antigens in the success of T cell based immunotherapy has led to a growing interest in investigating the expression and function of these molecules in metastatic cancer progression and, especially in response to immunotherapy. In this report, we illustrate that two types of metastatic lesions are commonly generated in response to immunotherapy according to the pattern of HLA class I expression. We found that metastatic lesions, that progress after immunotherapy have low level of HLA class I antigens, while the regressing lesions demonstrate significant upregulation of these molecules. Presumably, immunotherapy changes tumor microenvironment and creates an additional immune selection pressure on tumor cells. As a result, two subtypes of metastatic lesions arise from pre-existing malignant cells: (a) regressors, with upregulated HLA class I expression after therapy, and (b) progressors with resistance to immunotherapy and with low level of HLA class I. Tumor cells with reversible defects (soft lesions) respond to therapy by upregulation of HLA class I expression and regress, while tumor cells with structural irreversible defects (hard lesions) demonstrate resistance to immunostimulation, fail to upregulate HLA class I antigens and eventually progress. These two types of metastases appear independently of type of the immunotherapy used, either non-specific immunomodulators (cytokines or BCG) or autologous tumor vaccination. Similarly, we also detected two types of metastatic colonies in a mouse fibrosarcoma model after in vitro treatment with IFN-gamma. One type of metastases characterized by upregulation of all MHC class I antigens and another type with partial IFN-gamma resistance, namely with lack of expression of L(d)-MHC class I molecule. Our observations may shed new light on the understanding of the mechanisms of tumor escape and might have implications for improvement of the efficacy of cancer immunotherapy.

Background: Altered HLA class I cell surface expression is one of the major mechanisms by which tumor cells escape from T lymphocytes. Immunohistochemistry-defined phenotypes of lost HLA class I expression have been described in human solid tumors, nut less information is available on melanoma cell lines., Objectives: To describe the frequency and distribution of different types of HLA class I antigen alterations in 91 melanoma cell lines from the European Searchable Tumour Cell and Databank (ESTDAB)., Methods: The HLA class I expression was assessed by flow cytometry and HLA genotyping., Results: We found various types of HLA class I cell surface alterations in about 67% of the melanoma cell lines. These alterations range from total to selective HLA class I loss due to loss of heterozygosity (LOH), haplotype loss, beta2-microglobulin gene mutation, and/or total or selective down-regulation of HLA class I molecules. The most frequently observed phenotype is down-regulation of HLA-B locus that was reversible after treatment with IFN -gamma., Conclusions: In general, HLA class I alterations in the majority of the cells analyzed were of regulatory nature and could be restored by IFN-gamma. Analysis of the frequency of distinct HLA class I altered phenotypes in these melanoma cell lines revealed specific differences compared to other types of tumors.