Diagnosis of breast implant associated anaplastic large cell lymphoma by analysis of cytokines in peri-implant seromas.

More than 1300 women with breast implants have developed an anaplastic large cell lymphoma (ALCL) in fluid (seroma) around their implant. More often, seromas are due to benign causes, for example, capsule contracture, leakage, or trauma. Our report in American Journal of Hematology identified several cytokines (IL-9, IL-10, IL-13) as significantly elevated only in seromas due to ALCL. We further showed that the most robust biomarker, IL-10, could be detected by a lateral flow assay (similar to COVID detection) within minutes allowing physicians to quickly plan management, eliminate or reduce costly testing and patient time away from family. Early detection of ALCL in seromas before infiltration may avoid need for cytotoxic or immunotherapy and is possibly life-saving.

MHC Class I Deficiency in Solid Tumors and Therapeutic Strategies to Overcome It.

It is now well accepted that the immune system can control cancer growth. However, tumors escape immune-mediated control through multiple mechanisms and the downregulation or loss of major histocompatibility class (MHC)-I molecules is a common immune escape mechanism in many cancers. MHC-I molecules present antigenic peptides to cytotoxic T cells, and MHC-I loss can render tumor cells invisible to the immune system. In this review, we examine the dysregulation of MHC-I expression in cancer, explore the nature of MHC-I-bound antigenic peptides recognized by immune cells, and discuss therapeutic strategies that can be used to overcome MHC-I deficiency in solid tumors, with a focus on the role of natural killer (NK) cells and CD4 T cells.

Spatial and Temporal Changes in PD-L1 Expression in Cancer: The Role of Genetic Drivers, Tumor Microenvironment and Resistance to Therapy.

Immunotherapies blocking immune inhibitory receptors programmed cell death-1 (PD-1) and cytotoxic T-lymphocyte-associated protein-4 (CTLA-4) on T-cells have dramatically improved patient outcomes in a range of advanced cancers. However, the lack of response, and the development of resistance remain major obstacles to long-term improvements in patient outcomes. There is significant interest in the clinical use of biomarkers to improve patient selection, and the expression of PD-1 ligand 1 (PD-L1) is often reported as a potential biomarker of response. However, accumulating evidence suggests that the predictive value of PD-L1 expression in tumor biopsies is relatively low due, in part, to its complex biology. In this review, we discuss the biological consequences of PD-L1 expression by various cell types within the tumor microenvironment, and the complex mechanisms that regulate PD-L1 expression at the genomic, transcriptomic and proteomic levels.

Anti-PD-1-induced high-grade hepatitis associated with corticosteroid-resistant T cells: a case report.

Effective treatment or prevention of immune side effects associated with checkpoint inhibitor therapy of cancer is an important goal in this new era of immunotherapy. Hepatitis due to immunotherapy with antibodies against PD-1 is uncommon and generally of low severity. We present an unusually severe case arising in a melanoma patient after more than 6 months uncomplicated treatment with anti-PD-1 in an adjuvant setting. The hepatitis rapidly developed resistance to high-dose steroids, requiring anti-thymocyte globulin (ATG) to achieve control. Mass cytometry allowed comprehensive phenotyping of circulating lymphocytes and revealed that CD4+ T cells were profoundly depleted by ATG, while CD8+ T cells, B cells, NK cells and monocytes were relatively spared. Multiple abnormalities in CD4+ T cell phenotype were stably present in the patient before disease onset. These included a population of CCR4-CCR6- effector/memory CD4+ T cells expressing intermediate levels of the Th1-related chemokine receptor CXCR3 and abnormally high multi-drug resistance type 1 transporter (MDR1) activity as assessed by a rhodamine 123 excretion assay. Expression of MDR1 has been implicated in steroid resistance and may have contributed to the severity and lack of a sustained steroid response in this patient. The number of CD4+ rhodamine 123-excreting cells was reduced > 3.5-fold after steroid and ATG treatment. This case illustrates the need to consider this form of steroid resistance in patients failing treatment with corticosteroids. It also highlights the need for both better identification of patients at risk and the development of treatments that involve more specific immune suppression.

Pro- and anti-tumour effects of B cells and antibodies in cancer: a comparison of clinical studies and preclinical models.

The primary immune role of B cells is to produce antibodies, but they can also influence T cell function via antigen presentation and, in some contexts, immune regulation. Whether their roles in tumour immunity are similar to those in other chronic immune responses such as autoimmunity and chronic infection, where both pro- and anti-inflammatory roles have been described, remains controversial. Many studies have aimed to define the role of B cells in antitumor immune responses, but despite this considerable body of work, it is not yet possible to predict how they will affect immunity to any given tumour. In many human cancers, the presence of tumour-infiltrating B cells and tumour-reactive antibodies correlates with extended patient survival, and this clinical observation is supported by data from some animal models. On the other hand, T cell responses can be adversely affected by B cell production of immunoregulatory cytokines, a phenomenon that has been demonstrated in humans and in animal models. The isotype and concentration of tumour-reactive antibodies may also influence tumour progression. Recruitment of B cells into tumours may directly reflect the subtype and strength of the anti-tumour T cell response. As the response becomes chronic, B cells may attenuate T cell responses in an attempt to decrease host damage, similar to their described role in chronic infection and autoimmunity. Understanding how B cell responses in cancer are related to the effectiveness of the overall anti-tumour response is likely to aid in the development of new therapeutic interventions against cancer.

Tumour-specific CD4 T cells eradicate melanoma via indirect recognition of tumour-derived antigen.

The importance of CD4 T cells in tumour immunity has been increasingly recognised, with recent reports describing robust CD4 T cell-dependent tumour control in mice whose immune-regulatory mechanisms have been disturbed by irradiation, chemotherapy, immunomodulatory therapy and/or constitutive immunodeficiency. Tumour control in such models has been attributed in large part to direct Major Histocompatibility Complex (MHC) class II-dependent CD4 T cell killing of tumour cells. To test whether CD4 T cells can eradicate tumours without directly killing tumour cells, we developed an animal model in which tumour-derived antigen could be presented to T-cell receptor (TCR)-transgenic CD4 T cells by host but not tumour MHC class II molecules. In I-E(+) mice bearing I-E(null) tumours, naive I-E-restricted CD4 T cells proliferated locally in tumour-draining lymph nodes after recognising tumour-derived antigen on migratory dendritic cells. In lymphopaenic but not immunosufficient hosts, CD4 T cells differentiated into polarised T helper type 1 (Th1) cells expressing interferon gamma (IFNγ), tumor necrosis factor alpha (TNFα) and interleukin (IL)-2 but little IL-17, and cleared established tumours. Tumour clearance was enhanced by higher TCR affinity for tumour antigen-MHC class II and was critically dependent on IFNγ, as demonstrated by early tumour escape in animals treated with an IFNγ blocking antibody. Thus, CD4 T cells and IFNγ can control tumour growth without direct T-cell killing of tumour cells, and without requiring additional adaptive immune cells such as CD8 T cells and B cells. Our results support a role for effective CD4 T cell-dependent tumour immunity against MHC class II-negative tumours.

CD326(lo)CD103(lo)CD11b(lo) dermal dendritic cells are activated by thymic stromal lymphopoietin during contact sensitization in mice.

The cytokine thymic stromal lymphopoietin (TSLP) is produced by epithelia exposed to the contact sensitizer dibutyl phthalate (DBP), and it is critical for the induction of Th2 immune responses by DBP-FITC. TSLP is thought to act on dendritic cells (DC), but the precise DC subsets involved in the response to TSLP remain to be fully characterized. In this study we show that a subset of CD326(lo)CD103(lo)CD11b(lo) dermal DC, which we termed "triple-negative (TN) DC," is highly responsive to TSLP. In DBP-FITC-treated mice, TN DC upregulated expression of CD86 and rapidly migrated to the draining lymph node to become the most abundant skin-derived DC subset at 24 and 48 h after sensitization. None of these responses was observed in TSLPR-deficient mice. In contrast, TN DC numbers were not increased after treatment with the allergen house dust mite or the bacteria Escherichia coli and bacillus Calmette-Guérin, which increased other DC subsets. In vivo, treatment with rTSLP preferentially increased the numbers of TN DC in lymph nodes. In vitro, TN DC responded to rTSLP treatment with a higher level of STAT5 phosphorylation compared with other skin-derived DC subsets. The TN DC subset shared the morphology, phenotype, and developmental requirements of conventional DC, depending on FLT3 expression for their optimal development from bone marrow precursors, and CCR7 for migration to the draining lymph node. Thus, TN DC represent a dermal DC subset that should be considered in future studies of TSLP-dependent contact sensitization and skin immune responses.

IL-2 is a critical regulator of group 2 innate lymphoid cell function during pulmonary inflammation.

BACKGROUND: Group 2 innate lymphoid cells (ILC2) have been implicated in the pathogenesis of allergic lung diseases. However, the upstream signals that regulate ILC2 function during pulmonary inflammation remain poorly understood. ILC2s have been shown to respond to exogenous IL-2, but the importance of endogenous IL-2 in ILC2 function in vivo remains unclear. OBJECTIVE: We sought to understand the role of IL-2 in the regulation of ILC2 function in the lung. METHODS: We used histology, flow cytometry, immunohistochemistry, ELISA, and quantitative PCR with knockout and reporter mice to dissect pulmonary ILC2 function in vivo. We examined the role of ILC2s in eosinophilic crystalline pneumonia, an idiopathic type 2 inflammatory lung condition of mice, and the effect of IL-2 deficiency on this disease. We determined the effect of IL-2 administration on pulmonary ILC2 numbers and function in mice in the steady state and after challenge with IL-33. RESULTS: We discovered an unexpected role for innate cell-derived IL-2 as a major cofactor of ILC2 function during pulmonary inflammation. Specifically, we found that IL-2 was essential for the development of eosinophilic crystalline pneumonia, a type 2 disease characterized by increased numbers of activated ILC2s. We show that IL-2 signaling serves 2 distinct functions in lung ILC2s, namely promoting cell survival/proliferation and serving as a cofactor for the production of type 2 cytokines. We further demonstrate that group 3 innate lymphoid cells are an innate immune source of IL-2 in the lung. CONCLUSION: Innate cell-derived IL-2 is a critical cofactor in regulating ILC2 function in pulmonary type 2 pathology.

Langerhans cells are precommitted to immune tolerance induction.

Antigen-dependent interactions between T lymphocytes and dendritic cells (DCs) can produce two distinct outcomes: tolerance and immunity. It is generally considered that all DC subsets are capable of supporting both tolerogenic and immunogenic responses, depending on their exposure to activating signals. Here, we tested whether epidermal Langerhans cells (LCs) can support immunogenic responses in vivo in the absence of antigen presentation by other DC subsets. CD4 T cells responding to antigen presentation by activated LCs initially proliferated but then failed to differentiate into effector/memory cells or to survive long term. The tolerogenic function of LCs was maintained after exposure to potent adjuvants and occurred despite up-regulation of the costimulatory molecules CD80, CD86, and IL-12, but was consistent with their failure to translocate the NF-κB family member RelB from the cytoplasm to the nucleus. Commitment of LCs to tolerogenic function may explain why commensal microorganisms expressing Toll-like receptor (TLR) ligands but confined to the skin epithelium are tolerated, whereas invading pathogens that breach the epithelial basement membrane and activate dermal DCs stimulate a strong immune response.

MHCII restriction demonstrates B cells have very limited capacity to activate tumour-specific CD4+ T cells in vivo.

There has been growing interest in the role of B cells in antitumour immunity and potential use in adoptive cellular therapies. To date, the success of such therapies is limited. The intrinsic capacity of B cells to specifically activate tumour-specific CD4+ T cells in vivo via TCR-dependent interactions remains poorly defined. We have developed an in vivo tumour model that utilizes MHCII I-E restriction which limits antigen presentation to tumour-specific CD4 T cells to either tumour-specific B cells or host myeloid antigen presenting cells (APCs) in lymphopenic RAG-/-mice. We have previously shown that these naive tumour-specific CD4+ T cells can successfully eradicate established tumours in this model when activated by host APCs. When naïve tumour-specific B cells are the only source of I-E+ APC, very limited proliferation of naïve CD4+ T cells is observed, whereas host I-E+ APCs are potent T cell activators. B cells pre-activated with an anti-CD40 agonistic antibody in vivo support increased T cell proliferation, although far less than host APCs. CD4+ T cells that have already differentiated to an effector/central memory phenotype proliferate more readily in response to naïve B cells, although still 100-fold less than in response to host APCs. This study demonstrates that even in a significantly lymphopenic environment, myeloid APCs are the dominant primary activators of tumour-specific T cells, in contrast to the very limited capacity of tumour-specific B cells. This suggests that future anti-tumour therapies that incorporate activated B cells should also include mechanisms that activate host APCs.

IFN-γ Signaling Sensitizes Melanoma Cells to BH3 Mimetics.

Immunotherapy targeting PD-1 and/or CTLA4 leads to durable responses in a proportion of patients with melanoma. However, many patients will not respond to these immune checkpoint inhibitors, and up to 60% of responding patients will develop treatment resistance. We describe a vulnerability in melanoma driven by immune cell activity that provides a pathway towards additional treatment options. This study evaluated short-term melanoma cell lines (referred to as PD1 PROG cells) derived from melanoma metastases that progressed on PD-1 inhibitor-based therapy. We show that the cytokine IFN-γ primes melanoma cells for apoptosis by promoting changes in the accumulation and interactions of apoptotic regulators MCL-1, NOXA, and BAK. The addition of pro-apoptotic BH3 mimetic drugs sensitized PD1 PROG melanoma cells to apoptosis in response to IFN-γ or autologous immune cell activation. These findings provide translatable strategies for combination therapies in melanoma.

The molecular and functional landscape of resistance to immune checkpoint blockade in melanoma.

Resistance to immune checkpoint inhibitor therapies in melanoma is common and remains an intractable clinical challenge. In this study, we comprehensively profile immune checkpoint inhibitor resistance mechanisms in short-term tumor cell lines and matched tumor samples from melanoma patients progressing on immune checkpoint inhibitors. Combining genome, transcriptome, and high dimensional flow cytometric profiling with functional analysis, we identify three distinct programs of immunotherapy resistance. Here we show that resistance programs include (1) the loss of wild-type antigen expression, resulting from tumor-intrinsic IFNγ signaling and melanoma de-differentiation, (2) the disruption of antigen presentation via multiple independent mechanisms affecting MHC expression, and (3) immune cell exclusion associated with PTEN loss. The dominant role of compromised antigen production and presentation in melanoma resistance to immune checkpoint inhibition highlights the importance of treatment salvage strategies aimed at the restoration of MHC expression, stimulation of innate immunity, and re-expression of wild-type differentiation antigens.

Intratumoral CD16+ Macrophages Are Associated with Clinical Outcomes of Patients with Metastatic Melanoma Treated with Combination Anti-PD-1 and Anti-CTLA-4 Therapy.

PURPOSE: This study characterizes intratumoral macrophage populations within baseline melanoma biopsies from patients with advanced melanoma who received either anti-PD-1 monotherapy or a combination with anti-CTLA-4. Particularly, FcγRIIIa (CD16)-expressing macrophage densities were investigated for associations with response and progression-free survival. EXPERIMENTAL DESIGN: Patients with advanced melanoma who received either anti-PD-1 monotherapy or combination anti-PD-1 and anti-CTLA-4 were retrospectively identified. Macrophage populations were analyzed within baseline melanoma biopsies via multiplex IHC in relation to treatment outcomes. RESULTS: Patients who responded to combination immune checkpoint inhibitor contained higher CD16+ macrophage densities than those who did not respond (196 vs. 7 cells/mm2; P = 0.0041). There was no diffidence in CD16+ macrophage densities in the PD-1 monotherapy-treated patients based on response (118 vs. 89 cells/mm2; P = 0.29). A significantly longer 3-year progression-free survival was observed in combination-treated patients with high intratumoral densities of CD16+ macrophages compared with those with low densities (87% vs. 42%, P = 0.0056, n = 40). No association was observed in anti-PD-1 monotherapy-treated patients (50% vs. 47%, P = 0.4636, n = 50). Melanoma biopsies with high densities of CD16+ macrophages contained upregulated gene expression of critical T-cell recruiting chemokines (CXCL9, CXCL10, and CXCL11). CONCLUSIONS: Our data demonstrate that tumor microenvironments enriched with CD16+ macrophages are favorable for response to combination anti-PD-1 and anti-CTLA-4 therapy but not anti-PD-1 monotherapy. These data provides a potential biomarker of response for combination immunotherapies in patients with metastatic melanoma. See related commentary by Smithy and Luke, p. 2345.

SERS characterization of colorectal cancer cell surface markers upon anti-EGFR treatment.

Colorectal cancer (CRC) is the third most diagnosed and the second lethal cancer worldwide. Approximately 30-50% of CRC are driven by mutations in the KRAS oncogene, which is a strong negative predictor for response to anti-epidermal growth factor receptor (anti-EGFR) therapy. Examining the phenotype of KRAS mutant and wild-type (WT) CRC cells in response to anti-EGFR treatment may provide significant insights into drug response and resistance. Herein, surface-enhanced Raman spectroscopy (SERS) assay was applied to phenotype four cell surface proteins (EpCAM, EGFR, HER2, HER3) in KRAS mutant (SW480) and WT (SW48) cells over a 24-day time course of anti-EGFR treatment with cetuximab. Cell phenotypes were obtained using Raman reporter-coated and antibody-conjugated gold nanoparticles (SERS nanotags), where a characteristic Raman spectrum was generated upon single laser excitation, reflecting the presence of the targeted surface marker proteins. Compared to the KRAS mutant cells, KRAS WT cells were more sensitive to anti-EGFR treatment and displayed a significant decrease in HER2 and HER3 expression. The SERS results were validated with flow cytometry, confirming the SERS assay is promising as an alternative method for multiplexed characterization of cell surface biomarkers using a single laser excitation system.

Durable Responses to Anti-PD1 and Anti-CTLA4 in a Preclinical Model of Melanoma Displaying Key Immunotherapy Response Biomarkers.

Immunotherapy has transformed the management of patients with advanced melanoma, with five-year overall survival rates reaching 52% for combination immunotherapies blocking the cytotoxic T-lymphocyte-associated antigen-4 (CTLA4) and programmed cell death-1 (PD1) immune axes. Yet, our understanding of local and systemic determinants of immunotherapy response and resistance is restrained by the paucity of preclinical models, particularly those for anti-PD1 monotherapy. We have therefore generated a novel murine model of melanoma by integrating key immunotherapy response biomarkers into the model development workflow. The resulting YUMM3.3UVRc34 (BrafV600E; Cdkn2a-/-) model demonstrated high mutation burden and response to interferon (IFN)γ, including induced expression of antigen-presenting molecule MHC-I and the principal PD1 ligand PD-L1, consistent with phenotypes of human melanoma biopsies from patients subsequently responding to anti-PD1 monotherapy. Syngeneic immunosufficient mice bearing YUMM3.3UVRc34 tumors demonstrated durable responses to anti-PD1, anti-CTLA4, or combined treatment. Immunotherapy responses were associated with early on-treatment changes in the tumor microenvironment and circulating T-cell subsets, and systemic immunological memory underlying protection from tumor recurrence. Local and systemic immunological landscapes associated with immunotherapy response in the YUMM3.3UVRc34 melanoma model recapitulate immunotherapy responses observed in melanoma patients and identify discrete immunological mechanisms underlying the durability of responses to anti-PD1 and anti-CTLA4 treatments.

Antigen load governs the differential priming of CD8 T cells in response to the bacille Calmette Guerin vaccine or Mycobacterium tuberculosis infection.

One reason proposed for the failure of Mycobacterium bovis bacille Calmette Guérin (BCG) vaccination to adequately control the spread of tuberculosis is a limited ability of the vaccine to induce effective CD8 T cell responses. However, the relative capacity of the BCG vaccine and virulent Mycobacterium tuberculosis to induce activation of CD8 T cells, and the factors that govern the initial priming of these cells after mycobacterial infection, are poorly characterized. Using a TCR transgenic CD8 T cell transfer model, we demonstrate significant activation of Ag-specific CD8 T cells by BCG, but responses were delayed and of reduced magnitude compared with those following infection with M. tuberculosis. The degree of CD8 T cell activation was critically dependent on the level of antigenic stimulation, as modifying the infectious dose to achieve comparable numbers of BCG or M. tuberculosis in draining lymph nodes led to the same pattern of CD8 T cell responses to both strains. Factors specific to M. tuberculosis infection did not influence the priming of CD8 T cells, as codelivery of M. tuberculosis with BCG did not alter the magnitude of BCG-induced T cell activation. Following transfer to RAG-1(-/-) recipients, BCG and M. tuberculosis-induced CD8 T cells conferred equivalent levels of protection against M. tuberculosis infection. These findings demonstrate that BCG is able to prime functional CD8 T cells, and suggest that effective delivery of Ag to sites of T cell activation by vaccines may be a key requirement for optimal CD8 T cell responses to control mycobacterial infection.

Melanoma Cell State-Specific Responses to TNFα.

Immune checkpoint inhibitors that target the programmed cell death protein 1 (PD1) pathway have revolutionized the treatment of patients with advanced metastatic melanoma. PD1 inhibitors reinvigorate exhausted tumor-reactive T cells, thus restoring anti-tumor immunity. Tumor necrosis factor alpha (TNFα) is abundantly expressed as a consequence of T cell activation and can have pleiotropic effects on melanoma response and resistance to PD1 inhibitors. In this study, we examined the influence of TNFα on markers of melanoma dedifferentiation, antigen presentation and immune inhibition in a panel of 40 melanoma cell lines. We report that TNFα signaling is retained in all melanomas but the downstream impact of TNFα was dependent on the differentiation status of melanoma cells. We show that TNFα is a poor inducer of antigen presentation molecules HLA-ABC and HLA-DR but readily induces the PD-L2 immune checkpoint in melanoma cells. Our results suggest that TNFα promotes dynamic changes in melanoma cells that may favor immunotherapy resistance.

Tumor MHC Expression Guides First-Line Immunotherapy Selection in Melanoma.

Immunotherapy targeting T-cell inhibitory receptors, namely programmed cell death-1 (PD-1) and/or cytotoxic T-lymphocyte associated protein-4 (CTLA-4), leads to durable responses in a proportion of patients with advanced metastatic melanoma. Combination immunotherapy results in higher rates of response compared to anti-PD-1 monotherapy, at the expense of higher toxicity. Currently, there are no robust molecular biomarkers for the selection of first-line immunotherapy. We used flow cytometry to profile pretreatment tumor biopsies from 36 melanoma patients treated with anti-PD-1 or combination (anti-PD-1 plus anti-CTLA-4) immunotherapy. A novel quantitative score was developed to determine the tumor cell expression of antigen-presenting MHC class I (MHC-I) molecules, and to correlate expression data with treatment response. Melanoma MHC-I expression was intact in all tumors derived from patients who demonstrated durable response to anti-PD-1 monotherapy. In contrast, melanoma MHC-I expression was low in 67% of tumors derived from patients with durable response to combination immunotherapy. Compared to MHC-I high tumors, MHC-I low tumors displayed reduced T-cell infiltration and a myeloid cell-enriched microenvironment. Our data emphasize the importance of robust MHC-I expression for anti-PD-1 monotherapy response and provide a rationale for the selection of combination immunotherapy as the first-line treatment in MHC-I low melanoma.

Transcriptional downregulation of MHC class I and melanoma de- differentiation in resistance to PD-1 inhibition.

Transcriptomic signatures designed to predict melanoma patient responses to PD-1 blockade have been reported but rarely validated. We now show that intra-patient heterogeneity of tumor responses to PD-1 inhibition limit the predictive performance of these signatures. We reasoned that resistance mechanisms will reflect the tumor microenvironment, and thus we examined PD-1 inhibitor resistance relative to T-cell activity in 94 melanoma tumors collected at baseline and at time of PD-1 inhibitor progression. Tumors were analyzed using RNA sequencing and flow cytometry, and validated functionally. These analyses confirm that major histocompatibility complex (MHC) class I downregulation is a hallmark of resistance to PD-1 inhibitors and is associated with the MITFlow/AXLhigh de-differentiated phenotype and cancer-associated fibroblast signatures. We demonstrate that TGFß drives the treatment resistant phenotype (MITFlow/AXLhigh) and contributes to MHC class I downregulation in melanoma. Combinations of anti-PD-1 with drugs that target the TGFß signaling pathway and/or which reverse melanoma de-differentiation may be effective future therapeutic strategies.

Interferon Signaling Is Frequently Downregulated in Melanoma.

Immune checkpoint inhibitors that block the programmed cell death protein 1/PD-L1 pathway have significantly improved the survival of patients with advanced melanoma. Immunotherapies are only effective in 15-40% of melanoma patients and resistance is associated with defects in antigen presentation and interferon signaling pathways. In this study, we examined interferon-γ (IFNγ) responses in a large panel of immune checkpoint inhibitor-naïve melanoma cells with defined genetic drivers; BRAF-mutant (n = 11), NRAS-mutant (n = 10), BRAF/NRAS wild type (n = 10), and GNAQ/GNA11-mutant uveal melanomas (UVMs) (n = 8). Cell surface expression of established IFNγ downstream targets PD-L1, PD-L2, HLA-A, -B, and -C, HLA-DR, and nerve growth factor receptor (NGFR) were analyzed by flow cytometry. Basal cellular expression levels of HLA-A, -B, -C, HLA-DR, NGFR, and PD-L2 predicted the levels of IFNγ-stimulation, whereas PD-L1 induction was independent of basal expression levels. Only 13/39 (33%) of the melanoma cell lines tested responded to IFNγ with potent induction of all targets, indicating that downregulation of IFNγ signaling is common in melanoma. In addition, we identified two well-recognized mechanisms of immunotherapy resistance, the loss of ß-2-microglobulin and interferon gamma receptor 1 expression. We also examined the influence of melanoma driver oncogenes on IFNγ signaling and our data suggest that UVM have diminished capacity to respond to IFNγ, with lower induced expression of several targets, consistent with the disappointing response of UVM to immunotherapies. Our results demonstrate that melanoma responses to IFNγ are heterogeneous, frequently downregulated in immune checkpoint inhibitor-naïve melanoma and potentially predictive of response to immunotherapy.