Tumor Immunotherapy: The mechanism of action of anti-CTLA-4 antibodies requires FcgR-dependant TREG depletion

Ipilimumab is an anti-CTLA-4 antibody used for treatment of metastatic melanoma, one of only two cancer immunotherapeutic drugs approved to date by the FDA.  CTLA-4 is a negative regulatory molecule expressed by activated T cells as well as by negative regulatory T cells (TREGs).  CTLA-4 is related to the T cell co-stimulatory receptor CD28, and acts to suppress T cell function by competing with CD28 for binding to CD80 and CD86 on antigen presenting cells and recruiting inhibitory molecules into the TCR signaling synapse.  Thus, the mechanism of action of Ipilimumab has been presumed to involve releasing anti-tumor effector T cells from CTLA-4-inhibition and/or limiting TREG activity in the tumor and therefore resulting in an increase in the ratio of effector T cells/ TREGs within the tumor.   However, two recent articles demonstrate that Ipilimumab has an additional mechanism of action: FcgR-dependant depletion of intra-tumoral TREGs.

Fcg receptors are a multi-family class of immunoglobulin (IgG)-binding receptors that initiate either activating or inhibitory signals when engaged.  Activating receptors contain cytoplasmic immunoreceptor tyrosine-based activation motifs (ITAM) and activate the FcgR-expressing cell to mediate functions including antibody-dependant cell mediated cytotoxicity (ADCC) and phagocytosis of the antibody-labeled target cell.  FcgRIIB is the single inhibitory Fcg receptor in mice and humans and contains a cytoplasmic immunoreceptor tyrosine-based inhibitory motif (ITIM) which instead downregulates cellular responses.  There are four classes of IgG molecules in both humans and mice, and each bind to different Fcg receptors with varying affinity.  Thus differential affinities of IgG subclasses to functionally different Fcg receptors are thought to mediate the variation in clinical effectiveness of different antibodies targeting the same antigen.

Ipilimumab functions to increase the ratio of effector T cells to TREGS in the tumor microenvironment and has been shown to require binding to both types of T cells for maximal anti-tumor effectiveness.  However, how Ipilimumab differentially modulates these cell types remains to be understood.  A recent study published in The Journal of Experimental Medicine by Simpson et. al sought to clarify the mechanism by which Ipilimumab functions to alter the ratio of effector T cells/ TREGs in a murine tumor model.   Interestingly, the effects of Ipilimumab were found to be tissue-dependant.  In tumors which had high levels of infiltrating CD11b+ macrophages expressing the ADCC-activating FcgRIV, TREGS were selectively depleted in an FcgR-dependant manner, while effector T cells were instead expanded.  In lymph nodes lacking significant levels of these macrophages, frequencies of both effector T cells and TREGS were increased.  Tumor-associated TREGS expressedhigher levels of CTLA-4 than their effector T cell counterparts, or than TREGS present in the lymph node, indicating that higher CTLA-4 expression levels mediate ADCC via macrophages in the tumor.  Furthermore, the presence of FcgRs and hence TREG depletion was required for Ipilimumab’s effects.   Thus is appears that the mechanism of action of Ipilimumab on the effector T cell compartment is two-fold: directly targeting effector T cells to release inhibition via blocking CTLA4 activity, as well as by ADCC-mediated depletion of TREGS.

A second article in the same issue of The Journal of Experimental Medicine by Bulliard et al also explored the role of FcgR engagement on the effects of Ipilimumab as well as an agonistic antibody (DTA-1) targeting the T cell activating receptor GITR (TNFR glucocorticoid-induced TNFR-related protein), which is also expressed on both activated T cells and TREGs.  This study concluded that a major mechanism of action for both antibodies involved engagement of activating FcgRs leading to ADCC-mediated TREG depletion from the tumor.  Even though GITR-activation in effector T cells promotes activities including cytokine production and proliferation, the agonistic properties of this antibody alone were not effective in the absence of activating FcgR engagement.  Thus, even for functionally different (antagonistic versus agonistic) immunotherapeutic antibodies targeting these same T cell populations, FcgR-mediated ADCC of TREGs appears to be a critical mechanism for anti-tumor effects.

These studies highlight several important principles for the field of tumor immunotherapeutics.  Antibody targeting can elicit multiple effects, dependant on expression levels of the target, the isotype of the antibody, and the FcgR-expressing cell types present in the tissue.  Thus knowing the nature of the immune populations present in various types of tumors that are able to mediate ADCC, the FcgRs expressed by these cells, and the expression levels of the target molecule on immune populations that would be ideally targeted for elimination versus activation/inhibition will be critical areas for the forwarding of this field.  Furthermore, as FcgRs are polymorphous in humans, and affect IgG binding affinities, taking these genetic variations into account will be critical in the future of personalized medicine.

Further reading:

Fc-dependent depletion of tumor-infiltrating regulatory T cells co-defines the efficacy of anti-CTLA-4 therapy against melanoma.  Simpson TR, Li F, Montalvo-Ortiz W, Sepulveda MA, Bergerhoff K, Arce F, Roddie C, Henry JY, Yagita H, Wolchok JD, Peggs KS, Ravetch JV, Allison JP, Quezada SA. J Exp Med. 2013 Jul 29.

Activating Fc γ receptors contribute to the antitumor activities of immunoregulatory receptor-targeting antibodies.  Bulliard Y, Jolicoeur R, Windman M, Rue SM, Ettenberg S, Knee DA, Wilson NS, Dranoff G, Brogdon JL. J Exp Med. 2013 Jul 29.

Fcgamma receptors as regulators of immune responses.  Nimmerjahn F, Ravetch JV. Nat Rev Immunol. 2008 Jan;8(1):34-47.

Progranulin Antibodies a Common Link in Vasculitis, Lupus, and RA

Patients with autoimmune rheumatic diseases (ARD) such as rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) have a significantly increased risk of developing cardiovascular disease (CVD) and often develop CVD earlier than those without underlying autoimmunity, although it is not clear whether CVD is a general consequence of RA and SLE or only affects a subgroup of patients.  Control of autoimmune inflammation by disease-modifying anti-rheumatic drugs (DMARD), especially those that target immune factors also involved in vasculitis (e.g., T and B cells), is believed to have a protective effect.  One area of current research is focused on identifying commonalities across multiple ARD that suggest specific mechanisms of ARD-related CVD in order to develop diagnostics, preventatives, and treatments for those at greatest risk.

IgG2 antibody
IgG2 antibody

A recent article in the Journal of Autoimmunity suggests anti-progranulin antibodies as one potential mechanism.  Thurner and colleagues used a protein macro-array to screen serum from patients with anti-neutrophil cytoplasmic antibody (ANCA)-associated systemic vasculitides for novel autoantibodies specific to these diseases.  Of the six candidate autoantigens reactive with pooled vasculitis patient serum, progranulin was the only autoantigen appearing in every one of the vasculitides studied.  However, extended screenings showed that a positive progranulin antibody titer was not specific for vasculitides; although the prevalence was low in healthy controls (1/97 or 1%) and patients with melanoma (0/98) or sepsis (0/22), progranulin antibodies were also detectedin serum from patients with RA (16/44 or 36%) and SLE (39/91 or 43%).

Progranulin, also called proepithelin, granulin-epithelin precursor, or acrogranin, is a glycoprotein secreted by epithelial cells, neurons, and certain leukocytes.  In addition to growth factor-like activity, progranulin has immunomodulatory effects in vitro and in vivo.  Full-length progranulin decreases oxidant production by activated neutrophils, blocks TNFα-induced immune responses via binding to TNFR-1 and -2, and promotes up-regulation of IL-4, IL-5, and IL-10.  Progranulin deficiency in mice results in greater inflammation in collagen-induced arthritis (CIA) and collagen antibody-induced arthritis models of human RA; treatment of either progranulin-deficient or wild-type mice with recombinant human progranulin ameliorates CIA inflammation.

Progranulin is cleaved by several proteases into mature granulins.  Neither recombinant nor proteolytically released granulins antagonize TNFα.  Rather, granulins increase expression of pro-inflammatory cytokines IL-1β, IL-8, and TNFα.  SLPI and apolipoprotein A-I binding to progranulin protects it from cleavage by matrix metalloproteinases and other proteases.  However, during inflammation, neutrophils and macrophages release serine proteases that increase progranulin digestion.  In the context of ongoing inflammation in ARD, this may result in increased cleavage of anti-inflammatory progranulin to pro-inflammatory granulin.

Thurner et al. are the first to report the presence of neutralizing anti-progranulin antibodies in RA, SLE, and small- and medium-vessel vasculitides, which may represent a pro-inflammatory mechanism common to several autoimmune diseases.  Their findings provide additional support for exploration of the progranulin/granulin pathway as a therapeutic target and suggest the potential use of anti-progranulin antibodies as a diagnostic and/or prognostic tool in ARD.  Further studies using sera of patients with known autoimmune disease states are needed to confirm these findings and address the additional questions raised, such as –  What causes the failure of self-tolerance to progranulin and the generation of anti-progranulin antibodies, as seen in ~20-40% of the patients in this study?  Are these anti-progranulin antibodies common to all autoimmune diseases?  Could the development of progranulin-neutralizing antibodies even become a biomarker in ARD, for example as a predictor of responsiveness to DMARD therapy, or an indicator of future progression to ARD-related CVD?  We await the results of these and other studies in this area with great interest.

Further Reading:

Progranulin antibodies in autoimmune diseases.  Thurner L, Preuss KD, Fadle N, Regitz E, Klemm P, Zaks M, Kemele M, Hasenfus A, Csernok E, Gross WL, Pasquali JL, Martin T, Bohle RM, Pfreundschuh M.  J Autoimmun. 2013 May; 42:29-38.

Insights into the role of progranulin in immunity, infection, and inflammation.  Jian J, Konopka J, Liu C.  J Leukoc Biol. 2013 Feb; 93(2):199-208.

Cardiovascular disease in autoimmune rheumatic diseases.  Hollan I, Meroni PL, Ahearn JM, Cohen Tervaert JW, Curran S, Goodyear CS, Hestad KA, Kahaleh B, Riggio M, Shields K, Wasko MC.  Autoimmun Rev. 2013 Aug; 12(10):1004–1015.

PD-1 re-expression is differentially regulated by IL-12 vs IFNα in CD8 T cells

TUMOR_immunotherapyDownregulation of immune functions following responses to pathogen infections is critical for limiting damage to the host by the immune system.  T cell activity is known to be downregulated by a variety of negative regulatory mechanisms including negative checkpoint regulatory proteins, a family of CD28-related molecules.  PD-1 is one such molecule that is transiently expressed on activated T cells.   The ligands for PD-1 are PD-L1 and PD-L2, members of the B7 family of molecules which are upregulated on antigen presenting cells and tumor cells.  Interaction of PD-1 with its ligand leads to inhibition of TCR-mediated signaling via recruitment of SHP1 and SHP2 phosphatases to the TCR synapse.  In the August 2013 edition of The Journal of Immunology, Gerner et al., demonstrate that CD8 T cells initially activated in the presence of IL-12 and IFNα differentially re-express PD-1 upon antigen restimulation.

Cytokines play roles in regulation of nearly every aspect of immune responses.  The cytokine milieu present during T cell activation directs differentiation into the different functional classes of CD4 T helper or CD8 T cells.  This study sought to determine the differences in anti-tumor CD8 T cell effector functions mediated when T cells are activated in the presence of various cytokines.  IL-12 and IFNα activate both overlapping and distinct gene programs and promote cytotoxic CD8 T cell responses.  Thus, these cytokines were chosen for comparison in this study.

In this system, CD8+ OT-1 cells were activated ex-vivo in the presence of either IL-12 or IFNα, and transferred into B16-OVA tumor-bearing mice.  T cells activated in the presence of IL-12 were found to mediate tumor-growth inhibition significantly better than if they had been activated in the presence of IFNα.  Over time in tumor-bearing mice, transferred IFNα-matured OT-1 cells were observed to decline in number and lost the ability to produce IFNγ ex vivo upon restimulation, indicating these cells may be exhausted.

Because PD-1 is known to be a marker and mediator of T cell exhaustion, PD-1 expression was examined.  Initial induction levels of PD-1 were comparable on OT-1 cells following ex vivo activation with IFNα or IL-12.  Following transfer into tumor-bearing mice, PD-1 levels declined over time on both types of cells isolated from the spleen and on IL-12 matured cells isolated from the tumor.  However, PD-1 expression was high on transferred IFNα-matured cells when isolated from the tumor.  Similar results were seen when cells were transferred into mice that subsequently received an injection of the OVA peptide.  Thus, CD8+ T cells matured in the presence of IFNα appear to re-express significantly higher levels of PD-1 upon antigen restimulation than IL-12 matured T cells.

PD-1 and PD-L1 targeting with inhibitory antibodies have emerged as promising avenues in tumor immunotherapy.  In this study, anti-PD-1 antibody administration had no additional anti-tumor effect in mice that received IL-12-matured T cells, while in mice that received IFNα-matured T cells, anti-PD-1 antibodies led to inhibition of tumor-growth to a level similar to that in mice that had received IL-12-matured T cells.  Thus, the relatively poor ability of IFNα-matured T cells to efficiently inhibit tumor growth appears to be largely due to PD-1 upregulation.  Finally, when T cells were matured with both IL-12 and IFNα, the effect of IL-12 was dominant.

Many questions remain regarding the mechanisms mediating PD-1 re-expression in IFNα vs. IL-12 matured T cells.  However, since IL-12 activity was dominant over IFNα on regulating PD-1 expression, IL-12 administration during immunotherapy regimens may enhance anti-tumor T cell responses by blocking the mechanisms by which IFNα enhances PD-1 re-expression.

Further Reading:

Cutting Edge: IL-12 and Type I IFN Differentially Program CD8 T Cells for Programmed Death 1 Re-expression Levels and Tumor Control.  Gerner MY, Heltemes-Harris LM, Fife BT, Mescher MF. J Immunol. 2013 Aug 1;191(3):1011-5. doi: 10.4049/jimmunol.1300652. Epub 2013 Jun 26.

CD20-Negative Circulating Plasmablasts Are Target for New B Cell Therapies in Anti-CCP Positive RA

Diagnosis of rheumatoid arthritis (RA) is based on meeting several of the criteria established by the American College of Rheumatology and the European League Against Rheumatism.  One of these criteria is the presence of anti-citrullinated protein antibodies (ACPA).  ACPA seropositivity is currently tested using a filaggrin-derived peptide (anti-cyclic citrullinated peptide [anti-CCP]) ELISA, although other ELISAs in development such as mutated citrullinated vimentin (MCV) show promising results.


While myelin basic protein, filaggrin, and several histone proteins are naturally citrullinated, other proteins such as fibrin and vimentin can become citrullinated during an inflammatory response.  Citrullination, enzymatic conversion of arginine residues into citrulline, increases protein hydrophobicity, which can change its structure.  In RA, these citrullinated proteins are recognized as “non-self” by immune cells, leading to production of ACPA.  Recent studies suggest these autoantibodies are not merely convenient diagnostic markers resulting from the autoimmune response, but instead may play a role in RA pathogenesis. Current research in this area includes identifying subtypes of RA based on ACPA positivity and specificity, and determining the roles and mechanisms of action for ACPA in RA autoimmunity.

Little is known about the B cells which produce these ACPA.  However, in a recent report in Annals of Rheumatic Disease, Kerkman and her colleagues used B cells isolated from the peripheral blood of ACPA-positive and -negative RA patients, as well as healthy individuals, to examine ACPA production in vitro and identify the ACPA-producing cell populations.

Initially, the authors stimulated peripheral B cells with B cell activating factor (BAFF) and anti-IgM F(ab′)2-fragments to induce ACPA production.  Although total IgG production was equivalent across the cultures, only B cells from ACPA-positive RA patients produced ACPA.  There was good correlation of ACPA titers obtained from in vitro culture with in vivo patient ACPA titers, underscoring the utility of this model system.  Next, the authors examined spontaneous ACPA production in unstimulated peripheral blood mononuclear cells (PBMC) from ACPA-positive RA patients.  In this case, total IgG was up to 100x lower than that seen in their studies with stimulated B cells; however, the amount of ACPA produced was equivalent.

Were ACPA in PBMC cultures generated solely by circulating plasmablasts, or were antigen presenting cells (APC) present in the PBMC population also stimulating production of ACPA by memory or even naïve B cells?  Kerkman et al. used FACS to selectively deplete ACPA-positive RA patient PBMC of plasmablast/plasma cell or naïve/memory populations, as well as to sort the CD19+ B cell subpopulations.  Naïve B cells (CD20+CD27-) did not produce any ACPA, even when stimulated with BAFF and IgM F(ab′)2.  Memory B cells (CD20+CD27+) produced ACPA upon stimulation, indicating CCP-specific memory cells are present in the circulation of ACPA-positive RA patients; however, ACPA production in CD20-depleted PBMC remained essentially unchanged, while unstimulated PBMCs depleted of plasmablasts/plasma cells produced significantly less ACPA.

acpa b cells

This study demonstrates the presence of circulating ACPA-producing plasmablasts/plasma cells in the peripheral blood of patients with ACPA-positive RA.  This is a novel and unexpected finding, since the plasmablast population is typically a transient population within PBMCs following antigen exposure, with antibody production continuing from mature plasma cells in the spleen and lymph nodes.
Circulating ACPA-producing B cells may persist in RA due to plasmablast replication and/or to memory B cell activation in response to persistent systemic citrullinated antigens.  Currently approved RA therapies which target the CD20+ B cell population, such as rituximab, would affect the memory B cell population, but not CD20- plasmablasts.  New therapies targeting circulating plasmablasts/plasma cells in addition to memory B cells could significantly limit ACPA production and subsequent immunological damage in RA, including that due to ACPA-induced TNFα production and complement activation.  Delineating circulating plasmablasts as a major source of ACPA is therefore a step forward in the quest to determine the roles and mechanisms of action for ACPA in RA pathogenesis, and underscores the possibility of developing effective new therapies by targeting specific B cell populations in RA.

Further Reading:

Circulating plasmablasts/plasma cells as a source of anti-citrullinated protein antibodies in patients with rheumatoid arthritis.  Kerkman PF, Rombouts Y, van der Voort EIH, Trouw LA, Huizinga TWJ, Toes REM, Scherer HU.  Ann Rheum Dis 2013 Jul; 72:1259–1263.

The effect of targeted rheumatoid arthritis therapies on anti-citrullinated protein autoantibody levels and B cell responses.  Modi S, Soejima M, Levesque MC.  Clin Exp Immunol 2013 Jul; 173(1):8-17.

B effector cells in rheumatoid arthritis and experimental arthritis.  Finnegan A, Ashaye S, Hamel KM.  Autoimmunity 2012 Aug; 45(5):353-63.

New Research Points the Way Towards Mechanism of Action, Receptor for MS Copolymer Drugs

Multiple_sclerosis_T_cellsNeurological damage in multiple sclerosis (MS) is caused by autoreactive immune cells, which attack myelin sheathing on axons of the brain and spinal cord, leading to inflammation and myelin loss.  The MS drug Copaxone is a copolymer of glutamic acid, lysine, alanine, and tyrosine (YEAK) that is thought to impair myelin attack by inhibiting MBP self antigen presentation to autoreactive T cells; a related copolymer in which phenylalanine replaces glutamic acid (YFAK) has been developed based on MBP binding to class II MHC.  However, little is known about these drugs’ molecular targets or mechanisms of actionIn vitro studies suggest IL-10 secretion by B cells or regulatory and Th2-CD4+ T cells is involved.  Recent data demonstrate YEAK and YFAK also have MHC-independent effects on macrophages and dendritic cells, although the receptor which mediates these effects is unknown.  In a recent article in The Journal of Immunology, Koenig and colleagues isolated YEAK- and YFAK-interacting proteins from macrophage lysates and identified structures required for copolymer interaction with cells.

Following incubation with RAW264.7 macrophage lysate, biotinylated copolymers were recovered using avidin-coated beads and the associated cellular proteins were identified using mass spectroscopy.  One high-frequency hit with known surface expression and involvement in immune signaling was gp96.  Cell surface gp96 directly activates innate immune cell cytokine production, acts as a class I MHC antigen chaperone, and has been proposed as a Th2-specific co-stimulatory molecule.  CD91 has been implicated in gp96 stimulation of antigen-presenting cells (APC) and is involved in signaling and endocytosis of several ligands.  App was also identified as a surface protein that interacts with YEAK and YFAK.  A β-amyloid species precursor in Alzheimer’s disease, its function on myeloid cells is not well understood.

Macrophages secrete CCL22, a chemoattractant for regulatory and Th2 T cells, in response to YEAK or YFAK.  Koenig et al. studied this response in wild-type versus gp96-, CD91-, and App-deficient cells and found no impairment in any of the knock-out cell lines, indicating that despite their interactions with YEAK and YFAK, neither gp96, CD91, nor App are involved in cell signaling by these copolymers.

Lysine confers a positive charge on these copolymers, leading Koenig et al. to propose that cellular binding may be mediated by electrostatic interaction rather than conformation.  Indeed, increasing salt concentration reduced protein interactions with biotinylated copolymer.  Importantly, using cell lines lacking specific sulfation enzymes, the authors demonstrated that YEAK and YFAK bind to negatively charged heparan sulfate proteoglycans (HSPG).  This interaction is functional: RAW264.7 cells stimulated with YFAK in the presence of heparin sulfate, a structurally similar competitor of HSPG, did not produce CCL22.

HSPG are glycoproteins which contain one or more covalently attached heparin sulfate (HS) chains.  Membrane HSPG are known to act as co-receptors for many growth factors and could therefore play a role in the cellular effects of YEAK by activating cell signaling through an associated receptor or preventing signaling by that receptor’s natural ligand.  For example, YEAK binding to HS, a co-receptor for gp96 binding to CD91, may alter cellular uptake of gp96-peptide complexes via CD91, affecting self antigen cross-presentation and T cell activation by APC.

Alternatively, HSPG also function as receptors for constitutive as well as ligand-induced endocytosis.  YEAK interaction with HSPG may promote its fluid-phase uptake and delivery to intracellular target(s) in a manner similar to that of cationic cell-penetrating peptides.  In fact, gene ontology term enrichment analysis highlights “RNA binding” as a molecular function of YEAK- and YFAK-interacting proteins identified in this study, supporting a potential cytosolic or nuclear site of action.

Significant work remains to define the receptors and molecular mechanisms of action for these copolymers and aid rational design of future immune-modulating drugs.  The authors’ list of 222 copolymer-interacting proteins and characterization of sulfated glycosaminoglycans as the moieties responsible for functional interaction of these copolymers with innate immune cells serve as a solid foundation for further research in this area.

Further Reading:

Amino acid copolymers that alleviate experimental autoimmune encephalomyelitis in vivo interact with heparan sulfates and glycoprotein 96 in APCs.  Koenig PA, Spooner E, Kawamoto N, Strominger JL, Ploegh HL.  J Immunol.  2013 Jul 1; 191(1):XXX.  Epub ahead of print 2013 June 5.

Heparan sulphate proteoglycans fine-tune mammalian physiology.  Bishop JR, Schuksz M, Esko JD.  Nature. 2007 Apr 26; 446(7139):1030-7.

Interactions between heparan sulfate and proteins – design and functional implications.  Lindahl U, Li JP.  Int Rev Cell Mol Biol. 2009; 276:105-59.

Cell surface heparan sulfate proteoglycans influence MHC class II-restricted antigen presentation.  Léonetti M, Gadzinski A, Moine G.  J Immunol. 2010 Oct 1; 185(7):3847-56.



Upcoming Immunology Conferences: October – December, 2013

I previously posted on Immunology Conferences: July – September, 2013 and 2013 Conferences in Tumor Immunology and Cancer ImmunotherapyThis post lists upcoming Immunology-related conferences from October – December, 2013.

Aegean Conference: 6th International Conference on Autoimmunity: Mechanisms & Novel Treatments

October 2 – 7, 2013.

Corfu, Greece

Early registration deadline: July 25, 2013.

Abstract submission deadline: July 25, 2013.

Travel award application deadline: June 30, 2013.


IL-1-mediated inflammation and diabetes: From basic science to clinical applications

October 10 – 11, 2013.

Nijmegen, The Netherlands

Abstract submission deadline: August 1, 2013.


European Macrophage & Dendritic Cell Society Meeting: Myeloid Cells: Microenvironment, Microorganisms & Metabolism From Basic Science to Clinical Applications

October 10 – 12, 2013.

Erlangen, Germany


13th International Workshop on Langerhans Cells

October 10-13, 2013

Royal Tropical Institute, Amsterdam, The Netherlands

Early Registration deadline: August 1, 2013.

Abstract submission deadline: August 19, 2013.


The International Symposium on Immunotherapy

October 11-12, 2013

London, UK

Early Registration deadline: August 9, 2013.

Abstract submission deadline: August 9, 2013.


46th Annual Meeting of the Society for Leukocyte Biology

October 20-22, 2013

Newport Marriott, Newport, RI, USA

Late Breaking Abstract submission deadline: August 6, 2013.

Online Registration deadline: October 7, 2013.


16th Annual New York State Immunology Conference

October 20-23, 2013

Sagamore Resort and Conference Center, Bolton Landing, NY, USA

Abstract submission deadline: July 31, 2013.

Registration deadline: September 6, 2013.


Cold Spring Harbor Asia Conference: Tumour Immunology and Immunotherapy

October 28 – November 1, 2013.

Suzhou, China

Abstract submission deadline: August 16, 2013.

Early Registration deadline: August 16, 2013.


Keystone Symposium: Advancing Vaccines in the Genomics Era

October 31 – November 4, 2013.

Rio de Janeiro, Brazil

Abstract Deadline: July 30, 2013.

Early Registration Deadline: August 29, 2013.



The Lancet and Cell: What Will it Take to Achieve an AIDS-free World?

November 3–5, 2013.

San Francisco, California, USA.

Abstract submission deadline: July 26, 2013.

Early Registration Deadline: September 13, 2013.


International Primary Immunodeficiencies Congress

November 7–8, 2013.

Lisbon, Portugal

Early Registration deadline: July 19, 2013.


Asia Pacific Congress of Allergy, Asthma and Clinical Immunology

November 14–17, 2013.

Taipei City, Taiwan

Abstract Submission Deadline: July 31, 2013.

Early Registration: August 30, 2013.

Registration Deadline: October 25, 2013.


Cold Spring Harbor Asia Conference: Bacterial Infection and Host Defence

November 18–22, 2013.

Suzhou, China

Abstract submission deadline: September 6, 2013.

Early Registration Deadline: September 6, 2013.


6th Autoimmunity Congress Asia

November 20–22, 2013.

Hong Kong

Abstract Submission Deadline: July 20, 2013.

Early Registration deadline: August 6, 2013.


Harnessing Immunity to Prevent and Treat Disease

November 20–23, 2013.

Cold Spring Harbor Laboratory, New York, USA

Abstract submission deadline: September 6, 2013.


11th Annual UC Irvine Immunology Fair
November 21–22, 2013.

Irvine, California, USA

Abstract submission deadline: October 19, 2013.

Poster contest deadline: November 2, 2013.



EMBO Workshop: Complex Systems in Immunology

December 2–4, 2013.

Biopolis, Singapore

Abstract submission deadline: September 1, 2013.

Registration deadline: September 1, 2013.


British Society for Immunology Congress

December 2–5, 2013.

Liverpool, UK

Abstract submission deadline: September 6, 2013.

Early Registration deadline: September 30, 2013.


Annual Scientific Meeting of the Australasian Society for Immunology

December 2–5, 2013.

Wellington, New Zealand

Abstract submission deadline: September 1, 2013.

Early Registration deadline: September 1, 2013.


UK Primary Immunodeficiency Network Forum

December 6–7, 2013.

Liverpool, UK

Abstract submission deadline: September 6, 2013.

Early Registration deadline: September 30, 2013.


2013 American Society for Cell Biology Annual Meeting

December 14-18, 2013

New Orleans, LA, USA

Abstract submission deadline (Minisymposium Talk, ePoster Talk, and/or Poster Presentation): July 30, 2013.

Abstract submission deadline (Poster Presentation Only): September 4, 2013.

Early Registration deadline: October 10, 2013.


Websites that list upcoming Conferences & Events in Immunology, Tumor Immunology, and Cancer Immunotherapy:

The American Association of Immunologists (AAI) Meetings and Events Calendar

Nature Reviews Immunology’s list of conferences

Cancer Immunity Journal’s List of Conferences

FASEB Scientific Research Conferences Calendar

Highlight: A silver bullet against bacteria?

The development of multi-resistant bacterial strains is a major medical problem, especially in hospitals. New antibiotics are constantly under development, but the success rate seems to have slowed down in recent years. However, two recent publications suggest that instead of finding novel antibiotics, an alternative strategy could be to increase the sensitivity of the bacteria to the antibiotics already in use.s12sIn the first report [1], the authors demonstrated that silver ions interfered with several metabolic pathways and increased the permeability of the cell membrane, both made the bacteria much more susceptible to antibiotics. The use of silver to combat bacteria is not unprecedented and actually has been used at least since Grecian times to treat wounds and to preserve water. However, with the advent of potent antibiotics in the 1940s their use fell out of favor.

The authors uncovered two independent mechanisms of how silver is beating up bacteria. They studied E. coli a Gram-negative bacteria that is especially difficult to treat with many drugs due to its thick cell wall.

First, when exposed to silver ions the bacteria produced more reactive oxygen species (ROS). ROS are chemically highly reactive molecules that can bind unspecifically to closeby proteins and DNA and thereby irreversibly alter or damage those structures. Small amounts of ROS are constantly produced during several chemical reactions of the normal metabolism, but cell stress in any of its forms can greatly increase their production. The widespread damage that ROS can inflict weakens the cell and if the damage is too severe it can ultimately lead to cell death.

The second mechanism of silver is its ability to affect two metabolic pathways of the bacterial cells. On the one hand, the ability of the bacteria to maintain their iron level was disturbed. On the other hand, the formation of disulfide bonds, which are crucial for the structural integrity and function of many proteins, was affected in the presence of the silver ions. Both of these actions can be understood as severe forms of cell stress.

As a result of the ROS production and the metabolic impairment, the bacterial cell wall became more permeable. This is important as Gram-negative bacteria have a thick extra cell coating that prevents large molecules to enter. Many antibiotics are too big to enter through this bacterial cell wall, but the silver treatment allowed the antibiotic to enter the cells. By gaining access to the cell, the gram-negative bacteria became sensitive to large molecule antibiotics that usually work only with Gram-positive bacteria that lack such a thick cell coating. This finding greatly expands the arsenal of antibiotics that can be used against Gram-negative bacteria.

Importantly, bacteria that were weakened and made permeable by the silver ions became highly susceptible to even low amounts of antibiotics. The authors tested this in vivo with a mouse model of urinary tract infection. When the antibiotic treatment of the infected mice was supplemented with small amounts of silver ions, the silver greatly augmented the efficiency of the antibiotic: 10 fold to up to 1,000 fold. In one experiment, only 10% of the infected mice that were treated with the antibiotic alone survived, but when treated additional with the silver ions 90% survived!

This silver sensitization was also effective with two types of infections that are particular difficult to treat: dormant bacteria that remain inactive during the antibiotic treatment and rebound afterwards, and bacteria that produce slime layers, called biofilms. Biofilms can be visualized as huge amounts of extra coating produced by the bacteria that make them stick to surfaces (e.g. catheters in the clinic) and provides them with an extra shielding against antibiotics.

However, before somebody now starts grinding his silver spoons into his food, the caveat has to be noted that silver has some side effects: it can accumulate in your body, e.g. in the skin and when it is then exposed to sun can turn you into a smurf, quite literally, as the skin turns irreversible blue-grayish. The medical term is ‘Argyria’ and one stunning example is Paul Karason. Although the concentrations of silver used by Morones-Ramirez et al. were much lower, it still shows that the use of silver will likely be very limited in humans.

In a similar vein to the report by Morones-Ramirez et al., another recent study [2] showed that very high doses of vitamin C also could trigger the production of above-mentioned ROS in the bacterium Mycobacterium tuberculosis, the causative agent of tuberculosis. Thereby, vitamin C was able to kill the bacteria, either directly or in concert with antibiotics. Similar to the case above, the efficiency of the antibiotic was greatly increased when applied together with the vitamin C. However, starting to eat now vitamin C in bucket loads might be a bit premature too.

Vitamin C structure
Vitamin C structure

Nonetheless, both reports can be viewed as proof-of-principle studies. In both studies agents that by themselves are rather harmless to bacteria could massively increase their sensitivity towards antibiotics! Having established such potential it is likely that other substances will be described in the near future that are safer and still have this prominent potential to boost the efficiency of antibiotics.


[1] Morones-Ramirez, J. R., Winkler, J. A., Spina, C. S. & Collins, J. J. Silver Enhances Antibiotic Activity Against Gram-Negative Bacteria. Science Translational Medicine 5, 190ra81–190ra81 (2013).

[2] Vilchèze, C., Hartman, T., Weinrick, B. & Jacobs, W. R. Mycobacterium tuberculosis is extraordinarily sensitive to killing by a vitamin C-induced Fenton reaction. Nat Commun 4, 1881 (2013).

Using Mass Spectrometry for Mass T cell Epitope Discovery

Time of Flight Mass Cytometry (CyTOF) is a relatively new multiparametric technology that is far outpacing standard fluorescence-based flow cytometry in the number of parameters that can be simultaneously assessed on a single cell.  In CyTOF, rare transition element isotope-conjugated antibodies are used to label cellular antigens of interest, the magnitude of which is then quantitated by a time of flight mass cytometer, as discussed previously. Previous studies assessing 34 cell surface and intracellular proteins by this technology demonstrated the existence of high dimensional complexity in the heterogeneity of human bone marrow and CD8+ T cell populations.  In a July 2013 article in Nature Biotechonology, Newell et al., move CyTOF and the field of immunology another technological step forward by utilizing CyTOF to measure the frequencies of Rotavirus antigen-specific T cells in human peripheral blood mononuclear cells (PBMCs) and jejunal tissue with peptide-MHC tetramers.

In CyTOF, the theoretical maximum number of simultaneously assessable parameters is 100-200 depending on the instrument.  This vastly outnumbers the assessable parameters of standard fluorescence-based flow cytometry.  To date however, only approximately 40 metal ions have been utilized for antibody labeling, and the development of further metal-chelating technologies is awaited in order to utilize the maximum capacity of the CyTOF instrument.  In the current study, the authors circumvent this limitation by using a “bar-coding” methodology in which a variant combination of three out of ten metal ions are used for labeling each tetramer, allowing for up to 120 different metal combinations.

In this study, the authors sought to identify Rotavirus epitopes recognized by human CD8+ T cells in the context of the MHC class I allele, HLA-A*0201.  To date, only two Rotavirus epitopes recognized by T cells have been identified, and little is known about the phenotypic and functional diversity of antigen-specific T cells for any particular pathogen.  The technical difficulties in proper epitope prediction along with the limited number of cells attainable from human blood samples contribute to these issues.  Thus, this method represents a huge leap forward in the potential to identify significantly more antigen-specific T cell epitopes and to extensively classify these cells functionally.  Using an MHC-prediction algorithm, 77 possible Rotavirus peptides were identified that bound to HLA-A*0201.  An additional 32 positive and negative control tetramers were added for a total of 109 labeled tetramers used to stain each sample simultaneously.  This was further combined with 23-27 metal-chelated antibodies specific for cell surface and intracellular antigens to phenotypically characterize the T cells. A specialized Matlab script was used to analyze the high-dimensional data obtained following mass spectrometry of PBMC and jejunal samples.

On average, CD8 T cell populations specific for two Rotavirus-peptides plus 6-7 peptides from other viruses including influenza, EBV, and CMV, were identified on average across PBMCs from the 17 healthy donors analyzed.  These antigen-specific T cell populations were further phenotypically characterized by expression of surface and intracellular markers.   CD8 T cells specific for six Rotavirus epitopes that included the two previously identified epitopes, were recurrently detected in PBMCs from at least two individuals.  Of these, CD8 cells specific for a Rotavirus peptide from the VP3 protein were most common among healthy donor PBMCs and were phenotypically unique, being of the effector memory subtype compared with a central memory phenotype typical of the T cells specific for the other Rotavirus peptides.  VP3-specific T cells were also uniquely present in jejunal tissue obtained from obese patients that had undergone gastric bypass surgeries.  Thus, this methodology discovered at least 4 new Rotavirus peptides as well as unique characteristics of the different antigen-specific CD8 T cell populations.

In summary, this methodology of combining CyTOF technology with tetramer “bar-coding” paves the way for a vast expansion over fluorescent-based flow cytometry techniques for identifying antigen-specific T cell populations.  As vaccine strategies are an ongoing goal for treatment and prevention of infectious diseases and cancer, it is important to not only identify the peptides that can elicit T cell responses, but also functionally characterize these T cells in order to maximally promote desired immune responses.

Further  Reading:

Combinatorial tetramer staining and mass cytometry analysis facilitate T-cell epitope mapping and characterization.  Newell EW, Sigal N, Nair N, Kidd BA, Greenberg HB, Davis MM. Nat Biotechnol. 2013 Jul;31(7):623-9. doi: 10.1038/nbt.2593. Epub 2013 Jun 9.

Cracking the code of human T-cell immunity.  Harvey CJ, Wucherpfennig KW. Nat Biotechnol. 2013 Jul 9;31(7):609-10. doi: 10.1038/nbt.2626.

Cytometry by time-of-flight shows combinatorial cytokine expression and virus-specific cell niches within a continuum of CD8+ T cell phenotypes. Immunity. 2012 Jan 27;36(1):142-52. doi: 10.1016/j.immuni.2012.01.002.

Single-cell mass cytometry of differential immune and drug responses across a human hematopoietic continuum.  Bendall SC, Simonds EF, Qiu P, Amir el-AD, Krutzik PO, Finck R, Bruggner RV, Melamed R, Trejo A, Ornatsky OI, Balderas RS, Plevritis SK, Sachs K, Pe’er D, Tanner SD, Nolan GP. Science. 2011 May 6;332(6030):687-96. doi: 10.1126/science.1198704.

Whole Blood Phospho-flow: Direct Ex Vivo Measurement of Signaling in PBMC

I previously discussed phospho-flow cytometry, a method to study intracellular protein phosphorylation events in peripheral blood mononuclear cells (PBMC) at the single cell level.  In standard phospho-flow cytometry protocols, prior to performing assays, PBMCs are first isolated from blood using density gradient centrifugation methods such as Ficoll.  However, there may be times when it is advantageous to study signaling pathways in relatively unmanipulated cells directly ex vivo.  For this, Chow et al. have established a protocol for performing phospho-flow cytometry on PBMCs directly in whole blood.


There are many advantages to isolating and cryopreserving PBMCs with the intention of later studying signaling events by methods including standard phospho-flow cytometry.  In particular, when comparisons are desired between patient groups and healthy controls, there is likely to be less confounding contributions of experimental variability to the results if all of the comparative samples are assayed together.  However, as discussed by Chow et al., pharmacodynamic monitoring as well as evaluation of constitutively activated signaling pathways in PBMCs would be best studied on cells having undergone the least manipulation.  Some signaling pathway responses may be more robust in whole blood PBMCs as well.  For example, I have found in my own assays that signaling responses to IL-6 are strongest in whole blood PBMCs compared with PBMCs following Ficoll or culture in the incubator for any amount of time.  This method can also be used to study bone marrow immune cell signaling as well as expression of intracellular molecules that are exposed by the permeabilization method chosen. In addition, looking at signaling events in murine PBMCs is difficult to do if PBMCs need to be isolated first, given the very small amount of blood that can be obtained from a mouse.  In these cases, anti-coagulated whole blood phospho-flow cytometry should be considered.

Whole blood phospho-flow cytometry is a relatively easy method.  Using 100 ul of whole blood is enough for this assay, and the stimulus (cytokine or other activating signaling molecule) is added directly to the whole blood for the preferred amount of time.  PBMCs are then fixed with formaldehyde and a Triton X-100 based buffer is added to lyse the red blood cells and permeabilize the white blood cells.  This is followed with a few washes and finally the cells can be treated with methanol to unmask phospho-epitopes, similarly to the standard phospho-flow cytometry method by Nolan and colleagues.  Chow et al. include an optional step in which the PBMCs can be stored in a freezing buffer prior to methanol treatment.  However, I have successfully stored PBMCs in 90-100% methanol at -20 or -80 ºC until staining for flow cytometry, similarly to what is done for the standard phospho-flow cytometry method by Nolan and colleagues.

As with all protocols involving treatment of cells with reagents such as methanol or Triton X-100, some epitopes may be lost and thus will not be evaluable if staining is done following these treatments.  Thus, there is an alternate method included in the protocol to stain for some antigens up front.  As a reminder however, some fluorophores are sensitive to methanol, for instance V500, and thus cannot be used to stain PBMCs prior to such treatments.  Finally, in a prior article, Chow et al. (2005), tested different methods of fixation, permeabilization and alcohol unmasking, and I have included the link to that article below as an excellent reference in the case that modulation of the protocol is required for optimal assessment of your antigens of interest.

Further Reading:

Whole blood processing for measurement of signaling proteins by flow cytometry.  Chow S, Hedley D, Shankey TV. Curr Protoc Cytom. 2008 Oct;Chapter 9:Unit 9.27.

Whole blood fixation and permeabilization protocol with red blood cell lysis for flow cytometry of intracellular phosphorylated epitopes in leukocyte subpopulations.  Chow S, Hedley D, Grom P, Magari R, Jacobberger JW, Shankey TV. Cytometry A. 2005 Sep;67(1):4-17.

Single-cell phospho-protein analysis by flow cytometry. Schulz KR, Danna EA, Krutzik PO, Nolan GP.Curr Protoc Immunol. 2012 Feb;Chapter 8:Unit 8.17.1-20.