Anti-TIGIT antibody improves PD-L1 blockade through myeloid and Treg cells

Tiragolumab, an anti-TIGIT antibody with an active IgG1κ Fc, demonstrated improved outcomes in the phase 2 CITYSCAPE trial (ClinicalTrials.gov: NCT03563716 ) when combined with atezolizumab (anti-PD-L1) versus atezolizumab alone1. However, there remains little consensus on the mechanism(s) of response with this combination2. Here we find that a high baseline of intratumoural macrophages and regulatory T cells is associated with better outcomes in patients treated with atezolizumab plus tiragolumab but not with atezolizumab alone. Serum sample analysis revealed that macrophage activation is associated with a clinical benefit in patients who received the combination treatment. In mouse tumour models, tiragolumab surrogate antibodies inflamed tumour-associated macrophages, monocytes and dendritic cells through Fcγ receptors (FcγR), in turn driving anti-tumour CD8+ T cells from an exhausted effector-like state to a more memory-like state. These results reveal a mechanism of action through which TIGIT checkpoint inhibitors can remodel immunosuppressive tumour microenvironments, and suggest that FcγR engagement is an important consideration in anti-TIGIT antibody development.

Public Health Dashboards in Overdose Prevention: The Rhode Island Approach to Public Health Data Literacy, Partnerships, and Action

As the field of public health rises to the demands of real-time surveillance and rapid data-sharing needs in a postpandemic world, it is time to examine our approaches to the dissemination and accessibility of such data. Distinct challenges exist when working to develop a shared public health language and narratives based on data. It requires that we assess our understanding of public health data literacy, revisit our approach to communication and engagement, and continuously evaluate our impact and relevance. Key stakeholders and cocreators are critical to this process and include people with lived experience, community organizations, governmental partners, and research institutions. In this viewpoint paper, we offer an instructive approach to the tools we used, assessed, and adapted across 3 unique overdose data dashboard projects in Rhode Island, United States. We are calling this model the "Rhode Island Approach to Public Health Data Literacy, Partnerships, and Action." This approach reflects the iterative lessons learned about the improvement of data dashboards through collaboration and strong partnerships across community members, state agencies, and an academic research team. We will highlight key tools and approaches that are accessible and engaging and allow developers and stakeholders to self-assess their goals for their data dashboards and evaluate engagement with these tools by their desired audiences and users.

SOMAScience: A Novel Platform for Multidimensional, Longitudinal Pain Assessment

Chronic pain is one of the most significant health issues in the United States, affecting more than 20% of the population. Despite its contribution to the increasing health crisis, reliable predictors of disease development, progression, or treatment outcomes are lacking. Self-report remains the most effective way to assess pain, but measures are often acquired in sparse settings over short time windows, limiting their predictive ability. In this paper, we present a new mobile health platform called SOMAScience. SOMAScience serves as an easy-to-use research tool for scientists and clinicians, enabling the collection of large-scale pain datasets in single- and multicenter studies by facilitating the acquisition, transfer, and analysis of longitudinal, multidimensional, self-report pain data. Data acquisition for SOMAScience is done through a user-friendly smartphone app, SOMA, that uses experience sampling methodology to capture momentary and daily assessments of pain intensity, unpleasantness, interference, location, mood, activities, and predictions about the next day that provide personal insights into daily pain dynamics. The visualization of data and its trends over time is meant to empower individual users' self-management of their pain. This paper outlines the scientific, clinical, technological, and user considerations involved in the development of SOMAScience and how it can be used in clinical studies or for pain self-management purposes. Our goal is for SOMAScience to provide a much-needed platform for individual users to gain insight into the multidimensional features of their pain while lowering the barrier for researchers and clinicians to obtain the type of pain data that will ultimately lead to improved prevention, diagnosis, and treatment of chronic pain.

Type I interferon activates MHC class I-dressed CD11b+ conventional dendritic cells to promote protective anti-tumor CD8+ T cell immunity

Tumor-infiltrating dendritic cells (DCs) assume varied functional states that impact anti-tumor immunity. To delineate the DC states associated with productive anti-tumor T cell immunity, we compared spontaneously regressing and progressing tumors. Tumor-reactive CD8+ T cell responses in Batf3-/- mice lacking type 1 DCs (DC1s) were lost in progressor tumors but preserved in regressor tumors. Transcriptional profiling of intra-tumoral DCs within regressor tumors revealed an activation state of CD11b+ conventional DCs (DC2s) characterized by expression of interferon (IFN)-stimulated genes (ISGs) (ISG+ DCs). ISG+ DC-activated CD8+ T cells ex vivo comparably to DC1. Unlike cross-presenting DC1, ISG+ DCs acquired and presented intact tumor-derived peptide-major histocompatibility complex class I (MHC class I) complexes. Constitutive type I IFN production by regressor tumors drove the ISG+ DC state, and activation of MHC class I-dressed ISG+ DCs by exogenous IFN-β rescued anti-tumor immunity against progressor tumors in Batf3-/- mice. The ISG+ DC gene signature is detectable in human tumors. Engaging this functional DC state may present an approach for the treatment of human disease.

683 Type-I-interferon activates cross-dressed CD11b+conventional dendritic cells to enhance anti-tumor immunity

Background

Conventional dendritic cells (cDC) are critical mediators of protective anti-tumor CD8+ T-cell responses.1 Batf3-driven DC1 are the predominant cDC subset driving anti-tumor immunity due to their specialized ability to cross-present antigens for T-cell activation.2–4 However, the contribution of other tumor-infiltrating DC subsets such as CD11b+ DC2 to anti-tumor immunity remains poorly characterized. Recent studies suggest that under inflammation, DC subsets can exist in various functional states with differential impacts on their stimulatory potential.5–7 In this study, we sought to dissect the contributions of distinct DC states during a productive or dysfunctional anti-tumor immune response. A nuanced understanding of DC activation states in tumors and the signals that drive them carries therapeutic potential to modulate anti-tumor immunity and enhance immunotherapy responses.

Methods

We compared the DC infiltrate of a regressing tumor and a progressing tumor to study DC states. Flow immunophenotyping and RNA-sequencing was performed to profile the intratumoral DC compartment. Sorted DC subsets were co-cultured with T-cells ex vivo to evaluate their stimulatory capacity. Cross-dressing (in vivo/ex vivo) was assayed by staining for transfer of tumor-derived H-2b MHC complexes to MHC-mismatched or β2M-deficient DC.

Results

Anti-tumor CD8+ T-cell responses in Batf3-/- mice lacking DC1 were maintained in regressor tumors but not progressor tumors, suggesting DC1-independent anti-tumor immunity. Functional assays and RNA-sequencing of the intratumoral DC compartment of regressor tumors revealed a Zbtb46-dependent CD11b+ cDC activation state expressing an interferon-stimulated gene signature (ISG+ DC) that was critical for driving optimal anti-tumor CD8+ T-cell responses. Sorted ISG+ DC could activate CD8+ T-cells similar to DC1. Unlike cross-presenting DC1, however, ISG+ DC acquired antigens by cross-dressing with tumor-derived peptide-MHC, thereby bypassing the requirement for cross-presentation to initiate CD8+ T-cell-immunity. Interestingly, ISG+ DC were enriched in regressor tumors compared to progressor tumors, and this was attributable to constitutive tumor cell-intrinsic type-I-interferon (IFN-I) production in regressor tumors. Ablation of tumor cell-derived IFN-I in regressor tumors led to complete loss of anti-tumor T-cell responses in Batf3-/- mice. Conversely, addition of IFNβ to progressor tumors induced ISG+ DC and rescued anti-tumor T-cell responses in Batf3-/- mice.

Conclusions

We identified a novel IFN-I-induced activation state of CD11b+ cDC, called ISG+ DC, that was capable of driving anti-tumor CD8+ T cell immunity by cross-dressing with tumor-derived pMHC complexes in the absence of DC1. Engaging additional functional states of DC, such as ISG+ DC, will strengthen anti-tumor immunity and may improve immunotherapy responses.

References

Merad M, et al. The dendritic cell lineage: ontogeny and function of dendritic cells and their subsets in the steady state and the inflamed setting. Annu Rev Immunol 2013;31:563–604

Hildner K, et al. Batf3 deficiency reveals a critical role for CD8alpha+ dendritic cells in cytotoxic T cell immunity. Science 2008;322(5904)1097–100.

Broz ML, et al. Dissecting the tumor myeloid compartment reveals rare activating antigen-presenting cells critical for T cell immunity. Cancer Cell 2014;26(5):638–52.

Roberts EW, et al. Critical role for CD103(+)/CD141(+) dendritic cells bearing CCR7 for tumor antigen trafficking and priming of T cell immunity in Melanoma. Cancer Cell 2016;30(2):324–336.

Maier B, et al. A conserved dendritic-cell regulatory program limits antitumour immunity. Nature 2020;580(7802):257–262.

Bosteels C, et al. Inflammatory Type 2 cDCs acquire features of cDC1s and macrophages to orchestrate immunity to respiratory virus infection. Immunity 2020;52(6):1039–1056.e9.

Zilionis R, et al. Single-cell transcriptomics of human and mouse lung cancers reveals conserved myeloid populations across individuals and species. Immunity 2019;50(5):1317–1334.e10.

320 Tumor cell-intrinsic signaling mediates T cell exclusion and promotes resistance to checkpoint blockade therapy in non-small cell lung cancer

Background

Lung cancer is the leading cause of cancer-related death worldwide.1 Immunotherapies such as checkpoint blockade therapy (CBT) can be an effective approach to treat patients with metastatic tumors. However, only a fraction of patients is responsive to CBT treatments.2Patients with a non-T cell-infiltrated tumor microenvironment correlate with a poor response to CBT and T cell infiltration can be influenced by tumor cell-intrinsic signaling pathways.3 4 Therefore, understanding the tumor cell-intrinsic mechanisms affecting anti-tumor immune response will aid us to design better treatments for lung cancer patients. Preliminary work in our group showed that patients with non-small cell lung cancer (NSCLC) can be segregated according to the expression of a T cell gene signature into T cell-infiltrated and non-T cell-infiltrated cohorts. Using an unbiased pathway analysis, we identified that upregulation of specific gene modules significantly correlate with low expression of the T cell gene signature gene (non-T cell-infiltration). In this project, we aim to investigate how the overexpression of one specific pathway in NSCLC cells impacts the anti-tumor immune responses.

Methods

We used a lung cancer cell line derived from a KrasG12D/+ and Tp53-/- mouse (KP) to overexpressed our gene of interest (KP-A). Tumors were induced by subcutaneous or orthotopic implantation and were treated with anti-PD-L1 and anti-CTLA-4 blocking antibodies and analyzed for tumor burden. Infiltration of cytotoxic T cells and regulatory T cells were evaluated by fluorescence microscopy. Additionally, we engineered the KP-A and KP cell lines to express the model antigen SIY which allowed us to characterize tumor-specific T cell responses and utilize SIY-reactive TCR-transgenic T cells.

Results

We identified that the overexpression of our gene of interest in KP cells impairs the response to CBT mediated by T cell exclusion from the tumor. Analyses of tumor-reactive T cells indicated that T cell activation and differentiation into effector T cells was not affected, however, effector T cells failed to infiltrate KP-A tumors. We are currently investigating the molecular mechanism whereby our gene of interest mediates T cell exclusion.

Conclusions

Our results strongly suggest that tumor cell-intrinsic activation of specific pathways in NSCLC promote immune evasion and contribute to immunotherapy resistance. Understanding the molecular and immunological mechanisms mediating T cell exclusion from the lung tumor microenvironment will facilitate the development of novel combination treatment strategies for NSCLC patients.

Acknowledgements

This work was supported by a postdoctoral fellowship from the Ludwig Center at MIT’s Koch Institute for Integrative Cancer Research

References

Chen Z, Fillmore CM, Hammerman PS, Kim CF, Wong KK. Non-small-cell lung cancers: a heterogeneous set of diseases. Nat Rev Cancer 2014;14:535–546.

Hellmann MD, Paz-Ares L, Bernabe Caro R, Zurawski B, Kim SW, Carcereny Costa E, Park K, Alexandru A, Lupinacci L, de la Mora Jimenez E, Sakai H, Albert I, Vergnenegre A, Peters S, Syrigos K, Barlesi F, Reck M, Borghaei H, Brahmer JR, O’Byrne KJ, Geese WJ, Bhagavatheeswaran P, Rabindran SK, Kasinathan RS, Nathan FE, Ramalingam SS. Nivolumab plus ipilimumab in advanced non-small-cell lung cancer. N Engl J Med 2019;381:2020–2031.

Chen DS, Mellman I. Elements of cancer immunity and the cancer-immune set point. Nature 2017;541:321–330.

Nguyen KB, Spranger S. Modulation of the immune microenvironment by tumor-intrinsic oncogenic signaling. J Cell Biol 2020;219.

Ethics Approval

All mouse experiments in this study were approved by MIT’s Committee on Animal Care (CAC) - DHHS Animal Welfare Assurance # D16-00078

Impact of anatomic site on antigen-presenting cells in cancer

Checkpoint blockade immunotherapy (CBT) can induce long-term clinical benefits in patients with advanced cancer; however, response rates to CBT vary by cancer type. Cancers of the skin, lung, and kidney are largely responsive to CBT, while cancers of the pancreas, ovary, breast, and metastatic lesions to the liver respond poorly. The impact of tissue-resident immune cells on antitumor immunity is an emerging area of investigation. Recent evidence indicates that antitumor immune responses and efficacy of CBT depend on the tissue site of the tumor lesion. As myeloid cells are predominantly tissue-resident and can shape tumor-reactive T cell responses, it is conceivable that tissue-specific differences in their function underlie the tissue-site-dependent variability in CBT responses. Understanding the roles of tissue-specific myeloid cells in antitumor immunity can open new avenues for treatment design. In this review, we discuss the roles of tissue-specific antigen-presenting cells (APCs) in governing antitumor immune responses, with a particular focus on the contributions of tissue-specific dendritic cells. Using the framework of the Cancer-Immunity Cycle, we examine the contributions of tissue-specific APC in CBT-sensitive and CBT-resistant carcinomas, highlight how these cells can be therapeutically modulated, and identify gaps in knowledge that remain to be addressed.

ICOS agonism by JTX-2011 (vopratelimab) requires initial T cell priming and Fc cross-linking for optimal T cell activation and anti-tumor immunity in preclinical models

Immunotherapy checkpoint inhibitors, such as antibodies targeting PD-1 and CTLA-4, have demonstrated the potential of harnessing the immune system to treat cancer. However, despite encouraging results particularly with respect to survival, only a minority of patients benefit from these therapies. In clinical studies aimed at understanding changes in the immune system following immunotherapy treatment, ICOS (Inducible T cell CO-Stimulator) was shown to be significantly up-regulated on CD4+ T cells and this was associated with clinical activity, indicating that ICOS stimulatory activity may be beneficial in the treatment of solid tumors. In this report, we describe the generation of specific, species cross-reactive, agonist antibodies to ICOS, including the humanized clinical candidate, JTX-2011 (vopratelimab). Preclinical studies suggest that the ICOS stimulating antibodies require Fc receptor cross-linking for optimal agonistic activity. Notably, the ICOS antibodies do not exhibit superagonist properties but rather require T cell receptor (TCR)-mediated upregulation of ICOS for agonist activity. Treatment with the ICOS antibodies results in robust anti-tumor benefit and long-term protection in preclinical syngeneic mouse tumor models. Additional benefit is observed when the ICOS antibodies are administered in combination with anti-PD-1 and anti-CTLA-4 therapies. Based on the preclinical data, JTX-2011 is currently being developed in the clinical setting for the treatment of solid tumors.

A team effort: natural killer cells on the first leg of the tumor immunity relay race

Recent work by Böttcher and colleagues defines a new role for Natural Killer cells in the anti-tumor immune response, arriving early into the tumor microenvironment before passing the baton to DC1 dendritic cells. DC1 dendritic cells subsequently activate CD8+ T cells resulting in effective anti-tumor immunity. This work highlights the cooperative nature of anti-tumor immunity set in motion by Natural Killer cells, and immune evasion by tumors through their exclusion.

Abstract SY03-02: Preclinical assessment of JTX-2011, an agonist antibody targeting ICOS, supports evaluation in ICONIC clinical trial

ICOS (the inducible T-cell co-stimulator) is a co-stimulatory molecule expressed on the surface of T cells and a member of the CD28 family, which includes clinically validated targets of cancer immunotherapies, such as PD-1 and CTLA-4. Clinical data identified ICOS as a potentially key molecule in providing optimal antitumor benefit following anti-CTLA-4 therapy. We have developed a species cross-reactive humanized IgG1 agonist antibody, JTX-2011, that binds ICOS and is designed to induce an antitumor immune response. Our preclinical data suggest that JTX-2011 functions through a dual mechanism of action, by stimulating T effector cells (Teff) and depleting intratumoral T regulatory cells (Tregs). The ICOS antibody is efficacious as a single agent in mouse syngeneic tumor models and demonstrates enhanced activity when administered in combination with anti-PD-1. Single-agent activity in the preclinical models appears to correlate with ICOS expression, with greater efficacy observed in tumor models that exhibit a higher percentage of ICOS-expressing immune cell infiltrate. An integrated expression analysis of human tumors identified non-small cell lung cancer (NSCLC) and head and neck squamous cell carcinoma (HNSCC) as indications with higher percentages of ICOS-expressing cell infiltrate. Preclinical studies performed in rodent and monkeys evaluated safety, pharmacokinetics, and pharmacodynamics of JTX-2011 to inform the first in-human study. The ICONIC phase I/II clinical trial is currently ongoing for evaluation of JTX-2011 alone or in combination with the anti-PD-1 antibody Nivolumab in patients with advanced solid tumors and incorporates a patient enrichment strategy design based on the preclinical and translational findings.

Citation Format: Jennifer S. Michaelson, Christopher Harvey, Kutlu Elpek, Ellen Duong, Lindsey Shallberg, Matthew Wallace, Robert Mabry, Jenny Shu, Amit Deshpande, Tong Zi, Stephen Sazinsky, Joshua Apgar, Barbara Mounho-Zamora, Michael Briskin, Elizabeth Trehu, Jason Reeves, Heather Hirsch, Sriram Sathyanarayanan, Deborah Law. Preclinical assessment of JTX-2011, an agonist antibody targeting ICOS, supports evaluation in ICONIC clinical trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr SY03-02. doi:10.1158/1538-7445.AM2017-SY03-02

Abstract 573: Preclinical evaluation of JTX-2011, an anti-ICOS agonist antibody

ICOS (inducible co-stimulator molecule) is a co-stimulatory molecule and a member of the CD28 superfamily expressed primarily on T lymphocytes. Analysis of cancer patient samples as well as rodent preclinical data have implicated a role for the ICOS pathway in cancer immunotherapy. We have generated a panel of anti-ICOS monoclonal antibodies with in vitro agonistic properties. The anti-ICOS antibodies are efficacious as monotherapies and in combination with anti-PD1 in multiple syngeneic tumor models. Mechanistic studies demonstrate that tumor regression is associated with enhanced ratios of cytotoxic CD8:T regulatory (Treg) cells as well as preferential reduction in ICOS-high Tregs in the tumor microenvironment. JTX-2011, a species cross-reactive high affinity humanized agonist monoclonal antibody, has been selected for development. Evaluation of JTX-2011 in nonhuman primate models will be presented, including data informing safety and PK parameters. Our preclinical data provides rational for clinical development of JTX-2011 as a cancer immunotherapeutic to be tested as both a monotherapy as well as in combination with immunotherapies in solid tumor indications.

Citation Format: Jennifer S. Michaelson, Christopher J. Harvey, Kutlu G. Elpek, Ellen Duong, Matthew Wallace, Chengyi J. Shu, Sriram Sathyanarayanan, Robert Mabry, Lindsey Shallberg, Tong Zi, Amit Deshpande, Stephen L. Sazinsky, Joshua Apgar, Deborah Law. Preclinical evaluation of JTX-2011, an anti-ICOS agonist antibody. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 573.

Abstract A059: Efficacy of anti-ICOS agonist monoclonal antibodies in preclinical tumor models provides a rationale for clinical development as cancer immunotherapeutics

ICOS (inducible co-stimulator molecule) is a T cell encoded member of the extended B7/CD28 superfamily that is up-regulated upon early T cell activation. Previous studies have shown that higher ICOS expression on circulating T cells, post treatment with ipilimumab, is associated with better clinical outcome. In complementary pre-clinical studies, efficacy observed with a whole cell vaccine consisting of ICOS-L expressing B16 melanoma (IVAX) suggests that agonism of this pathway could provide therapeutic benefit in the cancer setting.

In accordance with these observations, we generated a panel of anti-ICOS monoclonal antibodies with in vitro agonist properties. A lead series of mAbs were shown to be efficacious as monotherapies in syngeneic tumors models with enhanced tumor inhibition observed in combination with anti-PD1. Mechanistic studies demonstrate that tumor regression is associated with enhanced ratios of cytotoxic CD8/regulatory T (Tregs) cells and that this change is related to preferential reduction in ICOS high Tregs in the tumor microenvironment.

These data provided the rationale for development of a high affinity humanized agonist monoclonal antibody to be tested in both mono therapy and in combination with other T cell checkpoints. Our lead anti-ICOS antibody is currently in IND-enabling studies and will be tested for activity in solid tumor indications.

Citation Format: Kutlu Elpek, Christopher Harvey, Ellen Duong, Tyler Simpson, Jenny Shu, Lindsey Shallberg, Matt Wallace, Sriram Sathy, Robert Mabry, Jennifer Michaelson, Michael Briskin. Efficacy of anti-ICOS agonist monoclonal antibodies in preclinical tumor models provides a rationale for clinical development as cancer immunotherapeutics. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr A059.

Variable processing and cross-presentation of HIV by dendritic cells and macrophages shapes CTL immunodominance and immune escape

Dendritic cells (DCs) and macrophages (Møs) internalize and process exogenous HIV-derived antigens for cross-presentation by MHC-I to cytotoxic CD8⁺ T cells (CTL). However, how degradation patterns of HIV antigens in the cross-presentation pathways affect immunodominance and immune escape is poorly defined. Here, we studied the processing and cross-presentation of dominant and subdominant HIV-1 Gag-derived epitopes and HLA-restricted mutants by monocyte-derived DCs and Møs. The cross-presentation of HIV proteins by both DCs and Møs led to higher CTL responses specific for immunodominant epitopes. The low CTL responses to subdominant epitopes were increased by pretreatment of target cells with peptidase inhibitors, suggestive of higher intracellular degradation of the corresponding peptides. Using DC and Mø cell extracts as a source of cytosolic, endosomal or lysosomal proteases to degrade long HIV peptides, we identified by mass spectrometry cell-specific and compartment-specific degradation patterns, which favored the production of peptides containing immunodominant epitopes in all compartments. The intracellular stability of optimal HIV-1 epitopes prior to loading onto MHC was highly variable and sequence-dependent in all compartments, and followed CTL hierarchy with immunodominant epitopes presenting higher stability rates. Common HLA-associated mutations in a dominant epitope appearing during acute HIV infection modified the degradation patterns of long HIV peptides, reduced intracellular stability and epitope production in cross-presentation-competent cell compartments, showing that impaired epitope production in the cross-presentation pathway contributes to immune escape. These findings highlight the contribution of degradation patterns in the cross-presentation pathway to HIV immunodominance and provide the first demonstration of immune escape affecting epitope cross-presentation.

Pathogens such as HIV can enter cells by fusion at the plasma membrane for delivery in the cytosol, or by internalization in endolysosomal vesicles. Pathogens can be degraded in these various compartments into peptides (epitopes) displayed at the cell surface by MHC-I. The presentation of pathogen-derived peptides triggers the activation of T cell immune responses and the clearance of infected cells. How the diversity of compartments in which HIV traffics combined with the diversity of HIV sequences affects the degradation of HIV and the recognition of infected cells by immune cells is not understood. We compared the degradation of HIV proteins in subcellular compartments of dendritic cells and macrophages, two cell types targeted by HIV and the subsequent presentation of epitopes to T cells. We show variable degradation patterns of HIV according to compartments, and the preferential production and superior intracellular stability of immunodominant epitopes corresponding to stronger T cell responses. Frequent mutations in immunodominant epitopes during acute infection resulted in decreased production and intracellular stability of these epitopes. Together these results demonstrate the importance of protein degradation patterns in shaping immunodominant epitopes and the contribution of impaired epitope production in all cellular compartments to immune escape during HIV infection.

Different antigen-processing activities in dendritic cells, macrophages, and monocytes lead to uneven production of HIV epitopes and affect CTL recognition

Dendritic cells (DCs), macrophages (MPs), and monocytes are permissive to HIV. Whether they similarly process and present HIV epitopes to HIV-specific CD8 T cells is unknown despite the critical role of peptide processing and presentation for recognition and clearance of infected cells. Cytosolic peptidases degrade endogenous proteins originating from self or pathogens, exogenous Ags preprocessed in endolysosomes, thus shaping the peptidome available for endoplasmic reticulum translocation, trimming, and MHC-I presentation. In this study, we compared the capacity of DCs, MPs, and monocyte cytosolic extracts to produce epitope precursors and epitopes. We showed differences in the proteolytic activities and expression levels of cytosolic proteases between monocyte-derived DCs and MPs and upon maturation with LPS, R848, and CL097, with mature MPs having the highest activities. Using cytosol as a source of proteases to degrade epitope-containing HIV peptides, we showed by mass spectrometry that the degradation patterns of long peptides and the kinetics and amount of antigenic peptides produced differed among DCs, MPs, and monocytes. Additionally, variable intracellular stability of HIV peptides prior to loading onto MHC may accentuate the differences in epitope availability for presentation by MHC-I between these subsets. Differences in peptide degradation led to 2- to 25-fold differences in the CTL responses elicited by the degradation peptides generated in DCs, MPs, and monocytes. Differences in Ag-processing activities between these subsets might lead to variations in the timing and efficiency of recognition of HIV-infected cells by CTLs and contribute to the unequal capacity of HIV-specific CTLs to control viral load.

A real-time killing assay to follow viral epitope presentation to CD8 T cells

The ability of cytotoxic T lymphocytes (CTL) to clear virus-infected cells requires the presentation of viral peptides intracellularly processed and displayed by major histocompatibility complex class I. Assays to measure CTL-mediated killing often use peptides exogenously added onto target cells--which does not account for epitope processing--or follow killing of infected cells at a single time point. In this study we established a real-time fluorogenic cytotoxic assay that measures the release of the Glucose-6-phosphate-dehydrogenase by dying target cells every 5 min after addition of CTL. It has comparable sensitivity to (51)chromium-based killing assay with the additional advantage of incorporating the kinetics of epitope presentation. We showed that HIV infection of immortalized or primary CD4 T cells leads to asynchronous killing by two CTL clones specific for epitopes located in different proteins. Real-time monitoring of killing of virus-infected cells will enable identification of immune responses efficiently preventing virus dissemination.

A simple methodology to assess endolysosomal protease activity involved in antigen processing in human primary cells

BACKGROUND

Endolysosomes play a key role in maintaining the homeostasis of the cell. They are made of a complex set of proteins that degrade lipids, proteins and sugars. Studies involving endolysosome contribution to cellular functions such as MHC class I and II epitope production have used recombinant endolysosomal proteins, knockout mice that lack one of the enzymes or purified organelles from human tissue. Each of these approaches has some caveats in analyzing endolysosomal enzyme functions.

RESULTS

In this study, we have developed a simple methodology to assess endolysosomal protease activity. By varying the pH in crude lysate from human peripheral blood mononuclear cells (PBMCs), we documented increased endolysosomal cathepsin activity in acidic conditions. Using this new method, we showed that the degradation of HIV peptides in low pH extracts analyzed by mass spectrometry followed similar kinetics and degradation patterns as those performed with purified endolysosomes.

CONCLUSION

By using crude lysate in the place of purified organelles this method will be a quick and useful tool to assess endolysosomal protease activities in primary cells of limited availability. This quick method will especially be useful to screen peptide susceptibility to degradation in endolysosomal compartments for antigen processing studies, following which detailed analysis using purified organelles may be used to study specific peptides.

Variable processing and presentation of HIV epitopes in HIV-infectable cell subsets (106.8)

HIV-specific CD8 T cells (CTL) play a major role in reducing viral load in acute HIV infection and in the spontaneous control of HIV viremia. HIV infects CD4 T cells, monocytes, macrophages and dendritic cells. Whether these subsets have equivalent capacity to produce and present MHC-I restricted epitopes is unknown. We analyzed the effect of TLR agonist-mediated maturation on the processing and presentation of antigens in monocyte-derived dendritic cells (DC) and macrophages (MP). LPS-induced maturation decreased significantly the proteasomal tryptic activity and lysosomal activities in DC whereas in mature MP these activities were increased. Using cytosolic extracts of DC and MP as a source of peptidases we showed by mass spectrometry that degradation of 3-ISW9 in LPS-matured DC yielded 2-fold more epitope HLA-B57-restricted ISW9 than in immature DC. Using recombinant p24 as an exogenous antigen cross-presented by DC or MP expressing HLA-B57 we observed reduced killing of cells by ISW9-specific CTL compared to TW10- or KF11-specific CTL. The lower ISW9-specific killing of target cells was partly rescued by preincubation of cells with protease inhibitor, suggesting that lower cross-presentation may be due to higher intracellular degradation of ISW9. Differences in antigen processing activities in DC and MP upon maturation, and differences in HIV sequences sensitivity to intracellular degradation may affect the production and presentation of HIV epitopes to CTL.

Proteomic analysis of lipid raft-enriched membranes isolated from internal organelles

The mitochondria-associated membrane (MAM) is a sub-region of the endoplasmic reticulum (ER) that facilitates crosstalk between the ER and mitochondria. The MAM actively influences vital cellular processes including Ca(2+) signaling and protein folding. Detergent-resistant microdomains (DRMs) may localize proteins to the mitochondria/MAM interface to coordinate these events. However, the protein composition of DRMs isolated from this region is not known. Lipid-raft enriched DRMs were isolated from a combined mitochondria/MAM sample and analyzed using two-dimensional reversed-phased tandem mass spectrometry. Strict post-acquisition filtering of the acquired data led to the confident identification 250 DRM proteins. The majority (58%) of the identified proteins are bona fide mitochondrial or ER proteins according to Gene Ontology annotation. Additionally, 74% of the proteins have previously been noted as MAM-resident or -associated proteins. Furthermore, ∼20% of the identified proteins have a documented association with lipid rafts. Most importantly, known internal LR marker proteins (inositol 1,4,5-trisphosphate receptor type 3, erlin-2, and voltage-dependent anion channel 1) were detected as well as most of the components of the mitochondrial/MAM-localized Ca(2+) signaling complex. Our study provides the basis for future work probing how the protein activities at the mitochondrion/MAM interface are dependent upon the integrity of these internal lipid-raft-like domains.