An approved in vitro approach to preclinical safety and efficacy evaluation of engineered T cell receptor anti-CD3 bispecific (ImmTAC) molecules

Robust preclinical testing is essential to predict clinical safety and efficacy and provide data to determine safe dose for first-in-man studies. There are a growing number of examples where the preclinical development of drugs failed to adequately predict clinical adverse events in part due to their assessment with inappropriate preclinical models. Preclinical investigations of T cell receptor (TCR)-based immunotherapies prove particularly challenging as these biologics are human-specific and thus the conventional testing in animal models is inadequate. As these molecules harness the full force of the immune system, and demonstrate tremendous potency, we set out to design a preclinical package that would ensure adequate evaluation of these therapeutics. Immune Mobilising Monoclonal TCR Against Cancer (ImmTAC) molecules are bi-specific biologics formed of an affinity-enhanced TCR fused to an anti-CD3 effector function. ImmTAC molecules are designed to activate human T lymphocytes and target peptides within the context of a human leukocyte antigen (HLA), thus require an intact human immune system and peptidome for suitable preclinical screening. Here we draw upon the preclinical testing of four ImmTAC molecules, including IMCgp100, the first ImmTAC molecule to reach the clinic, to present our comprehensive, informative and robust approach to in vitro preclinical efficacy and safety screening. This package comprises a broad range of cellular and molecular assays using human tissues and cultured cells to test efficacy, safety and specificity, and hence predict human responses in clinical trials. We propose that this entirely in vitro package offers a potential model to be applied to screening other TCR-based biologics.

Polyfunctional response by ImmTAC (IMCgp100) redirected CD8+ and CD4+ T cells

The success of immune system-based cancer therapies depends on a broad immune response engaging a range of effector cells and mechanisms. Immune mobilizing monoclonal T cell receptors (TCRs) against cancer (ImmTAC™ molecules: fusion proteins consisting of a soluble, affinity enhanced TCR and an anti-CD3 scFv antibody) were previously shown to redirect CD8⁺ and CD4⁺ T cells against tumours. Here we present evidence that IMCgp100 (ImmTAC recognizing a peptide derived from the melanoma-specific protein, gp100, presented by HLA-A*0201) efficiently redirects and activates effector and memory cells from both CD8⁺ and CD4⁺ repertoires. Using isolated subpopulations of T cells, we find that both terminally differentiated and effector memory CD8⁺ T cells redirected by IMCgp100 are potent killers of melanoma cells. Furthermore, CD4⁺ effector memory T cells elicit potent cytotoxic activity leading to melanoma cell killing upon redirection by IMCgp100. The majority of T cell subsets belonging to both the CD8⁺ and CD4⁺ repertoires secrete key pro-inflammatory cytokines (tumour necrosis factor-α, interferon-γ, interleukin-6) and chemokines (macrophage inflammatory protein-1α-β, interferon-γ-inducible protein-10, monocyte chemoattractant protein-1). At an individual cell level, IMCgp100-redirected T cells display a polyfunctional phenotype, which is a hallmark of a potent anti-cancer response. This study demonstrates that IMCgp100 induces broad immune responses that extend beyond the induction of CD8⁺ T cell-mediated cytotoxicity. These findings are of particular importance because IMCgp100 is currently undergoing clinical trials as a single agent or in combination with check point inhibitors for patients with malignant melanoma.

Abstract 3655: Biomarker strategy to guide the clinical development of ImmTACTM molecules, a novel class of bispecific T cell engaging biologic drugs

IMCgp100, a first in class immunotherapy, is a T cell redirecting bispecific biologic comprising an affinity enhanced T-cell receptor specific for gp100 and an anti-CD3 scFV. Phase I/IIa data has provided evidence of a favourable safety profile, and durable responses in both cutaneous and uveal melanoma have been observed. To complement the clinical studies we have developed a comprehensive biomarker strategy to aid our understanding of pharmacodynamics, patient response and potential mechanisms of resistance which includes analysis of markers in both the tumour and periphery. The data obtained to date provide evidence of the pharmacodynamic effects of the molecule including chemokine/cytokine release, in both the tumor and periphery, and lymphocyte infiltration into tumors. In addition, changes in the levels of certain chemokines following the first dose of IMCgp100 were associated with tumor shrinkage. The biomarker strategy we have developed forms the basis for the support of the on-going Ph II development of IMCgp100 in both cutaneous and uveal melanoma and for other ImmTAC molecules, as single agents and in combination, for the treatment of solid tumours.

Citation Format: Cheryl McAlpine, David Krige, Sandra Herrero-Gonzalez, Sarah Franklin, Jacob Hurst, William Shingler, Sanjay Patel, Andy Johnson, Debbie Parker, Christina M. Coughlin, Namir J. Hassan, Bent K. Jakobsen. Biomarker strategy to guide the clinical development of ImmTACTM molecules, a novel class of bispecific T cell engaging biologic drugs [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 3655. doi:10.1158/1538-7445.AM2017-3655

Abstract 2900: IMCgp100: A novel bi-specific biologic for the treatment of malignant melanoma

Despite significant advances in the treatment of metastatic melanoma, long-term remission for the majority of patients remains elusive. Kinase inhibitors provide potent but short-term responses for a significant proportion of patients and immunotherapy elicits long-term responses with the prospect of cure, but only in a minority.

IMCgp100 is a novel bi-specific immunotherapy comprising a soluble, affinity enhanced, T cell receptor (TCR) specific for the melanoma-associated antigen gp100, fused to an anti-CD3 specific antibody fragment (scFv). The engineered TCR portion of the drug targets and binds the gp100 peptide 280-288 antigen, which is over-expressed and presented by HLA-A2 on the surface of melanoma cells. The anti-CD3 scFv portion captures and redirects T cells to kill the melanoma cells, while normal antigen negative tissues are unaffected. Here, we present data which provides the foundation for the clinical observations. In vitro, IMCgp100 is demonstrated to potently redirect T cells from late stage cancer patients to target melanoma tumors exhibiting HLA-down regulation, even in the presence of high numbers of regulatory T cells. Target cell killing is observed within hours and is specific for gp100. In addition killing is associated with the release of various pro-inflammatory cytokines and chemokines as well as cross-presentation of gp100 and other melanoma-associated antigens by dendritic cells. Thus, IMCgp100 demonstrates the potential to elicit potent short-term responses and trigger longer-term anti melanoma activity in vivo.

IMCgp100 is undergoing Phase I clinical testing in patients with advanced malignant melanoma; with the maximum tolerated dose having been established. The drug is well tolerated with evidence of tumor shrinkage. Analyses of serum samples obtained from patients on the trial demonstrate T cell mobilisation and transient drug mediated increases in various cytokines and chemokines, some of which are reported to play a key role in anti-melanoma responses. These data support the potential of IMCgp100 as an effective treatment for malignant melanoma.

Citation Format: Namir J. Hassan, Giovanna Bossi, Debbie Baker, Katherine Adams, Jane Harper, Joseph Dukes, Nathaniel Liddy, Samantha Paston, Yvonne McGrath, Tara Mahon, Peter Molloy, Malkit Sami, Emma Baston, Brian Cameron, Andrew Johnson, Annelise Vuidepot, Gerry Linette, Michael Kalos, Carl June, Bent Jakobsen. IMCgp100: A novel bi-specific biologic for the treatment of malignant melanoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2900. doi:10.1158/1538-7445.AM2014-2900

Identification of a Titin-derived HLA-A1-presented peptide as a cross-reactive target for engineered MAGE A3-directed T cells

MAGE A3, which belongs to the family of cancer-testis antigens, is an attractive target for adoptive therapy given its reactivation in various tumors and limited expression in normal tissues. We developed an affinity-enhanced T cell receptor (TCR) directed to a human leukocyte antigen (HLA)-A*01-restricted MAGE A3 antigen (EVDPIGHLY) for use in adoptive therapy. Extensive preclinical investigations revealed no off-target antigen recognition concerns; nonetheless, administration to patients of T cells expressing the affinity-enhanced MAGE A3 TCR resulted in a serious adverse event (SAE) and fatal toxicity against cardiac tissue. We present a description of the preclinical in vitro functional analysis of the MAGE A3 TCR, which failed to reveal any evidence of off-target activity, and a full analysis of the post-SAE in vitro investigations, which reveal cross-recognition of an off-target peptide. Using an amino acid scanning approach, a peptide from the muscle protein Titin (ESDPIVAQY) was identified as an alternative target for the MAGE A3 TCR and the most likely cause of in vivo toxicity. These results demonstrate that affinity-enhanced TCRs have considerable effector functions in vivo and highlight the potential safety concerns for TCR-engineered T cells. Strategies such as peptide scanning and the use of more complex cell cultures are recommended in preclinical studies to mitigate the risk of off-target toxicity in future clinical investigations.

ImmTAC-redirected tumour cell killing induces and potentiates antigen cross-presentation by dendritic cells

Antigen cross-presentation by dendritic cells (DCs) is thought to play a critical role in driving a polyclonal and durable T cell response against cancer. It follows, therefore, that the capacity of emerging immunotherapeutic agents to orchestrate tumour eradication may depend on their ability to induce antigen cross-presentation. ImmTACs [immune-mobilising monoclonal TCRs (T cell receptors) against cancer] are a new class of soluble bi-specific anti-cancer agents that combine pico-molar affinity TCR-based antigen recognition with T cell activation via a CD3-specific antibody fragment. ImmTACs specifically recognise human leucocyte antigen (HLA)-restricted tumour-associated antigens, presented by cancer cells, leading to T cell redirection and a potent anti-tumour response. Using an ImmTAC specific for a HLA-A*02-restricted peptide derived from the melanoma antigen gp100 (termed IMCgp100), we here observe that ImmTAC-driven melanoma-cell death leads to cross-presentation of melanoma antigens by DCs. These, in turn, can activate both melanoma-specific T cells and polyclonal T cells redirected by IMCgp100. Moreover, activation of melanoma-specific T cells by cross-presenting DCs is enhanced in the presence of IMCgp100; a feature that serves to increase the prospect of breaking tolerance in the tumour microenvironment. The mechanism of DC cross-presentation occurs via 'cross-dressing' which involves the rapid and direct capture by DCs of membrane fragments from dying tumour cells. DC cross-presentation of gp100-peptide-HLA complexes was visualised and quantified using a fluorescently labelled soluble TCR. These data demonstrate how ImmTACs engage with the innate and adaptive components of the immune system enhancing the prospect of mediating an effective and durable anti-tumour response in patients.

Examining the presentation of tumor-associated antigens on peptide-pulsed T2 cells

Peptide-pulsed T2 cells are routinely used to study T-cell activation by MHC-restricted peptides derived from tumor-associated antigens (TAAs). Nevertheless, the capacity of T2 cells to present antigenic epitopes remains to be precisely quantified, primarily due to the detection limits imposed by available methods. Since naturally-processed TAA-derived epitopes have been shown to be displayed at levels as low as 10–150 copies per cell, highly sensitive detection and quantification techniques are essential to assess the natural degree of T-cell sensitivity. Here, we report the use of soluble, high-affinity T-cell receptors (TCRs) coupled with single-molecule fluorescence microscopy to quantify three reported TAA-derived epitopes on peptide-pulsed T2 cells, dissecting the relationship between concentration of exogenous peptide, number of epitopes presented, and activation of epitope-specific T cells. Our findings indicate that peptide concentrations in the low nanomolar range are required for T2 cells to present TAAs in extents that are comparable to those of malignant cells.

Bi-specific TCR-anti CD3 redirected T-cell targeting of NY-ESO-1- and LAGE-1-positive tumors

NY-ESO-1 and LAGE-1 are cancer testis antigens with an ideal profile for tumor immunotherapy, combining up-regulation in many cancer types with highly restricted expression in normal tissues and sharing a common HLA-A*0201 epitope, 157–165. Here, we present data to describe the specificity and anti-tumor activity of a bifunctional ImmTAC, comprising a soluble, high-affinity T-cell receptor (TCR) specific for NY-ESO-1_157–165 fused to an anti-CD3 scFv. This reagent, ImmTAC-NYE, is shown to kill HLA-A2, antigen-positive tumor cell lines, and freshly isolated HLA-A2- and LAGE-1-positive NSCLC cells. Employing time-domain optical imaging, we demonstrate in vivo targeting of fluorescently labelled high-affinity NYESO-specific TCRs to HLA-A2-, NY-ESO-1_157–165-positive tumors in xenografted mice. In vivo ImmTAC-NYE efficacy was tested in a tumor model in which human lymphocytes were stably co-engrafted into NSG mice harboring tumor xenografts; efficacy was observed in both tumor prevention and established tumor models using a GFP fluorescence readout. Quantitative RT-PCR was used to analyze the expression of both NY-ESO-1 and LAGE-1 antigens in 15 normal tissues, 5 cancer cell lines, 10 NSCLC, and 10 ovarian cancer samples. Overall, LAGE-1 RNA was expressed at a greater frequency and at higher levels than NY-ESO-1 in the tumor samples. These data support the clinical utility of ImmTAC-NYE as an immunotherapeutic agent for a variety of cancers.

Abstract 3528: IMCmage1: A novel bi-specific biologic re-directing T cells to kill MAGE-A3/A6 presenting cancers

In a minority of cancer patients immunotherapy has shown the capacity to eradicate tumours leading to clinical remission and the promise of a cure. In the majority of patients however, a cure remains elusive due to active immune evasion by cancers; HLA-down-regulation and immunosuppression are two of the known mechanisms adopted by cancers to promote their survival and proliferation. To overcome these challenges we have developed bi-specific soluble biologics termed ImmTACs (Immune mobilising mTCR against cancer) to re-direct the immune system to recognise and kill cancers. Antigenic peptide fragments presented by HLA molecules on the surface of cancer cells constitute the largest class of cancer associated targets. T cells scan the HLA-peptide (pHLA) antigens being presented to them; sufficient recognition by the harboured T Cell Receptor (TCR) will result in T cell activation and killing of the antigen presenting cell. In cancer patients this process is inefficient partly due to the low affinity TCRs expressed by tumour specific T cells and the low abundance of pHLA on cancers. ImmTACs comprise a soluble TCR with an enhanced affinity for cancer associated pHLA (targeting end) fused to an anti-CD3 scfv, enabling potent T cell re-direction (effector end). Our pipeline constitutes a number of ImmTACs targeting various antigen pHLA complexes relevant to numerous cancer indications. IMCmage1 is a novel ImmTAC targeting MAGE-A3168-176 in the context of HLA-A1. MAGE-A3 is a well validated cancer testis antigen expressed in a variety of cancers including myeloma, NSCLC, prostate cancer, melanoma, bladder cancer, oesophageal cancer and others. IMCmage1 re-directs T cells from cancer patients or healthy donors to kill a range of MAGE positive cell-lines in vitro; this activity is observed against cells presenting as few as 40 epitopes per cell and is coupled with the release of pro-inflammatory cytokines including IFNα, TNFα, IL-2, MIP1α and others. We also demonstrate that IMCmage1 specifically targets and kills the myeloma associated population within CD138+ cells extracted from the marrow of a stage III myeloma patient. IMCmage1 specificity was confirmed by exposure to a panel of HLA-A1 MAGE negative primary cells derived from various organs such as the heart, skin, lung and others; no significant activity was detected. A phase I clinical trial in multiple myeloma to assess tolerability and establish a maximum tolerated dose is planned to commence in Q2 2012.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3528. doi:1538-7445.AM2012-3528

Abstract 4744: Soluble, high affinity TCRs fused to anti-CD3 redirect T cells to kill cancer cells presenting MAGE-A3 and NY-ESO antigens

In the last decade, major efforts in the fight against cancer have focused on galvanizing the adaptive immune system to kill tumors. Many of these endeavors are based on the development and clinical use of monoclonal antibodies (mAb) which are the most successful class of immune modulating agent identified to date. While mAbs show promise against certain cancers, their specificity is limited to integral membrane proteins; this hinders their extensive development for the purposes of targeting cancer cells. In contrast to mAbs, T cell receptors (TCRs) recognize peptides bound to major histocompatibility complex class I (MHC I) molecules. These peptides are derived from endogenously processed proteins, and therefore represent a different repertoire of targets to those recognized by mAbs. This alternate spectrum of antigens provides the potential to target cancers using an untapped source of well-validated epitopes. Naturally occurring TCRs, however, have relatively low affinities for their antigen compared to antibody binding. Advances in engineering techniques have allowed the generation of high affinity monoclonal TCRs (mTCRs) with picomolar affinities for their antigen. Using targeted mutagenesis and phage display, we have generated a number of soluble, high affinity mTCRs specific for several reported tumor-associated antigens. Through mTCR fusion to an anti-CD3 single chain variable fragment (scfv), we produced bifunctional proteins that redirect T cell immune specificity. These novel proteins are termed ImmTACs (Immune-mobilizing mTCRs Against Cancer).

We present data showing the potential of two such ImmTACs, NY-ESO-ImmTAC and MAGE-A3-ImmTAC, to treat certain cancers. NY-ESO1 and MAGE-A3 are cancer testes antigens and therefore represent potentially very clean molecular targets. We demonstrate that both NY-ESO- and MAGE-A3-ImmTACs are capable of potently redirecting unstimulated CD8+ T cells against multiple myeloma, colorectal carcinoma and non-small cell lung cancer cell lines despite the presentation of extremely low antigen numbers (<100 epitopes/cell) on the cell surface. ImmTAC-redirected T cells respond with multiple effector functions including production of granzyme B, IFNγ and IL-2. Using the NY-ESO-ImmTAC we observed significant redirected degranulation of T cells against a primary lung tumor sample which was shown to express NY-ESO. We also present data from an established tumor model using the OV-79 cell line derived from an ovarian tumor which is shown to express MAGE. Administration of MAGE-A3-ImmTAC to animals with established tumors resulted in inhibition of tumor growth in all ImmTAC treated animals with regression or cure in some. Thus both MAGE-A3 and NY-ESO-ImmTACs possess the potential to be highly specific, potent cancer immunotherapies offering a targeting and therapeutic approach distinct from any other biologic in development.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4744. doi:10.1158/1538-7445.AM2011-4744

High-yield production and characterization of biologically active GST-tagged human topoisomerase IIα protein in insect cells for the development of a high-throughput assay

DNA topoisomerase type II enzymes are well-validated targets of anti-bacterial and anti-cancer compounds. In order to facilitate discovery of these types of inhibitors human topoisomerase II in vitro assays can play an important role to support drug discovery processes. Typically, human topoisomerase IIα proteins have been purified from human cell lines or as untagged proteins from yeast cells. This study reports a method for the rapid over-expression and purification of active GST-tagged human topoisomerase IIα using the baculovirus mediated insect cell expression system. Expression of the GST fused protein was observed in the nuclear fraction of insect cells. High yields (40 mg/L i.e. 8 mg/10(9) cells) at >80% purity of this target was achieved by purification using a GST HiTrap column followed by size exclusion chromatography. Functional activity of GST-tagged human topoisomerase IIα was demonstrated by ATP-dependent relaxation of supercoiled DNA in an agarose gel based assay. An 8-fold DNA-dependent increase in ATPase activity of this target compared to its intrinsic activity was also demonstrated in a high-throughput ATPase fluorescence based assay. Human topoisomerase IIα inhibitors etoposide, quercetin and suramin were tested in the fluorescence assay. IC(50) values obtained were in good agreement with published data. These inhibitors also demonstrated ≥ 30-fold potency over the anti-bacterial topoisomerase II inhibitor ciprofloxacin in the assay. Collectively these data validated the enzyme and the high-throughput fluorescence assay as tools for inhibitor identification and selectivity studies.

Abstract 5616: Soluble, high affinity TCRs fused to anti-CD3 redirect T cells to kill cancer cells presenting MAGE-A3 and NY-ESO antigens

In the last decade, major efforts in the fight against cancer have focussed on galvanising the adaptive immune system to kill tumours. Many of these endeavours are based on the development and clinical use of monoclonal antibodies (mAb) which are the most successful class of immune modulating agent identified to date. However, while mAbs show promise against certain cancers, their specificity is limited to integral membrane proteins; this hinders their extensive development for the purposes of targeting cancer cells.

In contrast to mAbs, T cell receptors (TCRs) recognise peptides bound to major histocompatibility complex class I (MHC I) molecules. These peptides are derived from endogenously processed proteins, and therefore represent a different repertoire of targets to those recognised by mAbs. This alternate spectrum of antigens provides the potential to target cancers using an untapped source of well-validated epitopes. Naturally occurring TCRs, however, have relatively low affinities for their antigen compared to antibody binding. Advances in engineering techniques have allowed the generation of high affinity monoclonal TCRs (mTCRs) with picomolar affinities for their antigen. Using targeted mutagenesis and phage display, we have generated a number of soluble, high affinity mTCRs specific for several reported tumour-associated antigens. Through mTCR fusion to an anti-CD3 single chain variable fragment (scfv), we produced bifunctional proteins that redirect T cell immune specificity. These novel proteins are termed ImmTACs (Immune-mobilising mTCRs Against Cancer). We present data demonstrating the potential of two such ImmTAC molecules, NY-ESO-ImmTAC and MAGE-A3-ImmTAC, to treat certain cancers. NY-ESO1 and MAGE-A3 are both cancer testes antigens and therefore represent potentially very clean molecular targets. We demonstrate that both NY-ESO-ImmTAC and MAGE-A3-ImmTAC are capable of potently redirecting unstimulated peripheral blood mononuclear cells (PBMC) or CD8+ T cells against multiple myeloma, colorectal carcinoma and non-small cell lung cancer cell lines despite the presentation of extremely low antigen numbers (<100 epitopes/cell) on the surface of these cells. ImmTAC-redirected T cells respond with multiple effector functions including the production of granzyme B, IFNγ and IL-2, resulting in a high level of antigen-specific cancer cell killing over the course of 24 hours. The mechanism of killing is at least partly contributed by the caspase-3/7 apoptotic pathway. We also show that NY-ESO-ImmTAC and MAGE-A3-ImmTAC were inert by all our measures in the presence of normal primary cells including melanocytes, hepatocytes and astrocytes. Thus both MAGE-A3 and NY-ESO-ImmTACs possess the potential to be highly specific, potent cancer immunotherapies offering a targeting and therapeutic approach distinct from any other biologic in development.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5616.

Development of an insect-cell-based assay for detection of kinase inhibition using NF-kappaB-inducing kinase as a paradigm

Identification of small-molecule inhibitors by high-throughput screening necessitates the development of robust, reproducible and cost-effective assays. The assay approach adopted may utilize isolated proteins or whole cells containing the target of interest. To enable protein-based assays, the baculovirus expression system is commonly used for generation and isolation of recombinant proteins. We have applied the baculovirus system into a cell-based assay format using NIK [NF-kappaB (nuclear factor kappaB)-inducing kinase] as a paradigm. We illustrate the use of the insect-cell-based assay in monitoring the activity of NIK against its physiological downstream substrate IkappaB (inhibitor of NF-kappaB) kinase-1. The assay was robust, yielding a signal/background ratio of 2:1 and an average Z' value of >0.65 when used to screen a focused compound set. Using secondary assays to validate a selection of the hits, we identified a compound that (i) was non-cytotoxic, (ii) interacted directly with NIK, and (iii) inhibited lymphotoxin-induced NF-kappaB p52 translocation to the nucleus. The insect cell assay represents a novel approach to monitoring kinase inhibition, with major advantages over other cell-based systems including ease of use, amenability to scale-up, protein expression levels and the flexibility to express a number of proteins by infecting with numerous baculoviruses.

CD6 regulates T-cell responses through activation-dependent recruitment of the positive regulator SLP-76

Deciphering the role of lymphocyte membrane proteins depends on dissecting the role of a protein in the steady state and on engagement with its ligand. We show that expression of CD6 in T cells limits their responsiveness but that engagement by the physiological ligand CD166 gives costimulation. This costimulatory effect of CD6 is mediated through phosphorylation-dependent binding of a specific tyrosine residue, 662Y, in its cytoplasmic region to the adaptor SLP-76. A direct interaction between SLP-76 and CD6 was shown by binding both to a phosphorylated peptide (equilibrium dissociation constant [K(D)] = 0.5 muM at 37 degrees C) and, using a novel approach, to native phosphorylated CD6. Evidence that CD6 and SLP-76 interact in cells was obtained in coprecipitation experiments with normal human T cells. Analysis of human CD6 mutants in a murine T-cell hybridoma model showed that both costimulation by CD6 and the interaction between CD6 and SLP-76 were dependent on 662Y. The results have implications for regulation by CD6 and the related T-cell surface protein, CD5.

BacMam recombinant baculovirus in transporter expression: A study of BCRP and OATP1B1

Human BCRP and OATP1B1 have recently been identified as important transporters in the absorption, distribution, and elimination of clinically significant drugs. In this report, we illustrate the use of modified baculoviruses, termed BacMam viruses for the expression of functional BCRP and OATP1B1 in mammalian cells. We show a variety of host cells efficiently transduced to express BCRP including HEK 293, LLC-PK, and U-2 OS, where protein levels on the cell-surface were modulated by titrating different amounts of viral inoculum. In addition, using the BODIPY-prazosin efflux assay and the BacMam reagent we illustrate inhibition of BCRP activity with GF120918 or Fumitremorgin C. Furthermore, we present data demonstrating simultaneous expression of BCRP and OATP1B1 in BacMam transduced mammalian cells by simply adding viral inoculum of each transporter. Thus these results indicate that BacMam mediated gene delivery provides a novel and efficient research tool for the investigation of single or multiple transporters in vitro.

Frontline: Optimal T cell activation requires the engagement of CD6 and CD166

The T cell surface glycoprotein, CD6 binds CD166 in the first example of an interaction between a scavenger receptor cysteine-rich domain and an immunoglobulin-like domain. We report that in human these proteins interact with a K(D) =0.4-1.0 microM and K(off) > or =0.4-0.63 s(-1), typical of many leukocyte membrane protein interactions. CD166 also interacts in a homophilic manner but with around 100-fold lower affinity (K(D) =29-48 microM and K(off) > or = 5.3 s(-1)). At concentrations, that will block the CD6/CD166 interaction, soluble monomeric CD6 and CD166 inhibit antigen-specific human T cell responses. This is consistent with extracellular engagement between CD6 and CD166 being required for an optimal immune response.

Characterization of human HtrA2, a novel serine protease involved in the mammalian cellular stress response

Human HtrA2 is a novel member of the HtrA serine protease family and shows extensive homology to the Escherichia coli HtrA genes that are essential for bacterial survival at high temperatures. HumHtrA2 is also homologous to human HtrA1, also known as L56/HtrA, which is differentially expressed in human osteoarthritic cartilage and after SV40 transformation of human fibroblasts. HumHtrA2 is upregulated in mammalian cells in response to stress induced by both heat shock and tunicamycin treatment. Biochemical characterization of humHtrA2 shows it to be predominantly a nuclear protease which undergoes autoproteolysis. This proteolysis is abolished when the predicted active site serine residue is altered to alanine by site-directed mutagenesis. In human cell lines, it is present as two polypeptides of 38 and 40 kDa. HumHtrA2 cleaves beta-casein with an inhibitor profile similar to that previously described for E. coli HtrA, in addition to an increase in beta-casein turnover when the assay temperature is raised from 37 to 45 degrees C. The biochemical and sequence similarities between humHtrA2 and its bacterial homologues, in conjunction with its nuclear location and upregulation in response to tunicamycin and heat shock suggest that it is involved in mammalian stress response pathways.