Antibodies directed against the MHC-I molecule H-2Dd complexed with an antigenic peptide: similarities to a T cell receptor with the same specificity

Opportunities and Challenges for Antibodies against Intracellular Antigens

Therapeutic antibodies are one most significant advances in immunotherapy, the development of antibodies against disease-associated MHC-peptide complexes led to the introduction of TCR-like antibodies. TCR-like antibodies combine the recognition of intracellular proteins with the therapeutic potency and versatility of monoclonal antibodies (mAb), offering an unparalleled opportunity to expand the repertoire of therapeutic antibodies available to treat diseases like cancer. This review details the current state of TCR-like antibodies and describes their production, mechanisms as well as their applications. In addition, it presents an insight on the challenges that they must overcome in order to become commercially and clinically validated.

TCR-like antibody drug conjugates mediate killing of tumor cells with low peptide/HLA targets

The currently marketed antibody-drug conjugates (ADC) destabilize microtubule assembly in cancer cells and initiate apoptosis in patients. However, few tumor antigens (TA) are expressed at high densities on cancer lesions, potentially minimizing the therapeutic index of current ADC regimens. The peptide/human leukocyte antigen (HLA) complex can be specifically targeted by therapeutic antibodies (designated T cell receptor [TCR]-like antibodies) and adequately distinguish malignant cells, but has not been the focus of ADC development. We analyzed the killing potential of TCR-like ADCs when cross-linked to the DNA alkylating compound duocarmycin. Our data comprise proof-of-principle results that TCR-like ADCs mediate potent tumor cytotoxicity, particularly under common scenarios of low TA/HLA density, and support their continued development alongside agents that disrupt DNA replication. Additionally, TCR-like antibody ligand binding appears to play an important role in ADC functionality and should be addressed during therapy development to avoid binding patterns that negate ADC killing efficacy.

Therapeutic Antibodies against Intracellular Tumor Antigens

Monoclonal antibodies are among the most clinically effective drugs used to treat cancer. However, their target repertoire is limited as there are relatively few tumor-specific or tumor-associated cell surface or soluble antigens. Intracellular molecules represent nearly half of the human proteome and provide an untapped reservoir of potential therapeutic targets. Antibodies have been developed to target externalized antigens, have also been engineered to enter into cells or may be expressed intracellularly with the aim of binding intracellular antigens. Furthermore, intracellular proteins can be degraded by the proteasome into short, commonly 8-10 amino acid long, peptides that are presented on the cell surface in the context of major histocompatibility complex class I (MHC-I) molecules. These tumor-associated peptide-MHC-I complexes can then be targeted by antibodies known as T-cell receptor mimic (TCRm) or T-cell receptor (TCR)-like antibodies, which recognize epitopes comprising both the peptide and the MHC-I molecule, similar to the recognition of such complexes by the TCR on T cells. Advances in the production of TCRm antibodies have enabled the generation of multiple TCRm antibodies, which have been tested in vitro and in vivo, expanding our understanding of their mechanisms of action and the importance of target epitope selection and expression. This review will summarize multiple approaches to targeting intracellular antigens with therapeutic antibodies, in particular describing the production and characterization of TCRm antibodies, the factors influencing their target identification, their advantages and disadvantages in the context of TCR therapies, and the potential to advance TCRm-based therapies into the clinic.

Engineering chimeric human and mouse major histocompatibility complex (MHC) class I tetramers for the production of T-cell receptor (TCR) mimic antibodies

Therapeutic monoclonal antibodies targeting cell surface or secreted antigens are among the most effective classes of novel immunotherapies. However, the majority of human proteins and established cancer biomarkers are intracellular. Peptides derived from these intracellular proteins are presented on the cell surface by major histocompatibility complex class I (MHC-I) and can be targeted by a novel class of T-cell receptor mimic (TCRm) antibodies that recognise similar epitopes to T-cell receptors. Humoural immune responses to MHC-I tetramers rarely generate TCRm antibodies and many antibodies recognise the α3 domain of MHC-I and β2 microglobulin (β2m) that are not directly involved in presenting the target peptide. Here we describe the production of functional chimeric human-murine HLA-A2-H2D^d tetramers and modifications that increase their bacterial expression and refolding efficiency. These chimeric tetramers were successfully used to generate TCRm antibodies against two epitopes derived from wild type tumour suppressor p53 (RMPEAAPPV and GLAPPQHLIRV) that have been used in vaccination studies. Immunisation with chimeric tetramers yielded no antibodies recognising the human α3 domain and β2m and generated TCRm antibodies capable of specifically recognising the target peptide/MHC-I complex in fully human tetramers and on the cell surface of peptide pulsed T2 cells. Chimeric tetramers represent novel immunogens for TCRm antibody production and may also improve the yield of tetramers for groups using these reagents to monitor CD8 T-cell immune responses in HLA-A2 transgenic mouse models of immunotherapy.

Opportunities and challenges for TCR mimic antibodies in cancer therapy

INTRODUCTION

Monoclonal antibodies (mAbs) are potent cancer therapeutic agents, but exclusively recognize cell-surface targets whereas most cancer-associated proteins are found intracellularly. Hence, potential cancer therapy targets such as over expressed self-proteins, activated oncogenes, mutated tumor suppressors, and translocated gene products are not accessible to traditional mAb therapy. An emerging approach to target these epitopes is the use of TCR mimic mAbs (TCRm) that recognize epitopes similar to those of T cell receptors (TCR).

AREAS COVERED

TCRm antigens are composed of a linear peptide sequence derived from degraded proteins and presented in the context of cell-surface MHC molecules. We discuss how the nature of the TCRm epitopes provides both advantages (absolute tumor specificity and access to a new universe of important targets) and disadvantages (low density, MHC restriction, MHC down-regulation, and cross-reactive linear epitopes) to conventional mAb therapy. We will also discuss potential solutions to these obstacles.

EXPERT OPINION

TCRm combine the specificity of TCR recognition with the potency, pharmacologic properties, and versatility of mAbs. The structure and presentation of a TCRm epitope has important consequences related to the choice of targets, mAb design, available peptides and MHC subtype restrictions, possible cross-reactivity, and therapeutic activity.

T cell receptor mimic antibodies for cancer therapy

The major hurdle to the creation of cancer-specific monoclonal antibodies (mAb) exhibiting limited cross-reactivity with healthy human cells is the paucity of known tumor-specific or mutated protein epitopes expressed on the cancer cell surface. Mutated and overexpressed oncoproteins are typically cytoplasmic or nuclear. Cells can present peptides from these distinguishing proteins on their cell surface in the context of human leukocyte antigen (HLA). T cell receptor mimic (TCRm) mAb can be discovered that react specifically to these complexes, allowing for selective targeting of cancer cells. The state-of-the-art for TCRm and the challenges and opportunities are discussed. Several such TCRm are moving toward clinical trials now.

Vaccination with single chain antigen receptors for islet-derived peptides presented on I-A(g7) delays diabetes in NOD mice by inducing anergy in self-reactiveT-cells

To develop a vaccination approach for prevention of type 1 diabetes (T1D) that selectively attenuates self-reactive T-cells targeting specific autoantigens, we selected phage-displayed single chain antigen receptor libraries for clones binding to a complex of the NOD classII MHC I-A(g7) and epitopes derived from the islet autoantigen RegII. Libraries were generated from B-cell receptor repertoires of classII-mismatched mice immunized with RegII-pulsed NOD antigen presenting cells or from T-cell receptor repertoires in pancreatic lymph nodes of NOD mice. Both approaches yielded clones recognizing a RegII-derived epitope in the context of I-A(g7), which activated autoreactive CD4(+) T-cells. A receptor with different specificity was obtained by converting the BDC2.5 TCR into single chain form. B- but not T-cells from donors vaccinated with the clones transferred protection from diabetes to NOD-SCID recipients if the specificity of the diabetes inducer cell and the single chain receptor were matched. B-cells and antibodies from donors vaccinated with the BDC2.5 single chain receptor induced a state of profound anergy in T-cells of BDC2.5 TCR transgenic NOD recipients while B-cells from donors vaccinated with a single chain receptor specific for I-A(g7) RegII peptide complexes induced only partial non-responsiveness. Vaccination of normal NOD mice with receptors recognizing I-A(g7) RegII peptide complexes or with the BDC2.5 single chain receptor delayed onset of T1D. Thus anti-idiotypic vaccination can be successfully applied to T1D with vaccines either generated from self-reactive T-cell clones or derived from antigen receptor libraries.

The promise of the anti-idiotype concept

A basic tenet of antibody-based immunity is their specificity to antigenic determinates from foreign pathogen products to abnormal cellular components such as in cancer. However, an antibody has the potential to bind to more than one determinate, be it an antigen or another antibody. These observations led to the idiotype network theory (INT) to explain immune regulation, which has wax and waned in enthusiasm over the years. A truer measure of the impact of the INT is in terms of the ideas that now form the mainstay of immunological research and whose roots are spawned from the promise of the anti-idiotype concept. Among the applications of the INT is understanding the structural implications of the antibody-mediated network that has the potential for innovation in terms of rational design of reagents with biological, chemical, and pharmaceutical applications that underlies concepts of reverse immunology which is highlighted herein.

T cell receptor-like recognition of tumor in vivo by synthetic antibody fragment

A major difficulty in treating cancer is the inability to differentiate between normal and tumor cells. The immune system differentiates tumor from normal cells by T cell receptor (TCR) binding of tumor-associated peptides bound to Major Histocompatibility Complex (pMHC) molecules. The peptides, derived from the tumor-specific proteins, are presented by MHC proteins, which then serve as cancer markers. The TCR is a difficult protein to use as a recombinant protein because of production issues and has poor affinity for pMHC; therefore, it is not a good choice for use as a tumor identifier outside of the immune system. We constructed a synthetic antibody-fragment (Fab) library in the phage-display format and isolated antibody-fragments that bind pMHC with high affinity and specificity. One Fab, fE75, recognizes our model cancer marker, the Human Epidermal growth factor Receptor 2 (HER2/neu) peptide, E75, bound to the MHC called Human Leukocyte Antigen-A2 (HLA-A2), with nanomolar affinity. The fE75 bound selectively to E75/HLA-A2 positive cancer cell lines in vitro. The fE75 Fab conjugated with ⁶⁴Cu selectively accumulated in E75/HLA-A2 positive tumors and not in E75/HLA-A2 negative tumors in an HLA-A2 transgenic mouse as probed using positron emission tomography/computed tomography (PET/CT) imaging. Considering that hundreds to thousands of different peptides bound to HLA-A2 are present on the surface of each cell, the fact that fE75 arrives at the tumor at all shows extraordinary specificity. These antibody fragments have great potential for diagnosis and targeted drug delivery in cancer.

TCR-like biomolecules target peptide/MHC Class I complexes on the surface of infected and cancerous cells

The human leukocyte antigen (HLA; also called major histocompatibility, or MHC) class I system presents peptides that distinguish healthy from diseased cells. Therefore, the discovery of peptide/MHC class I markers can provide highly specific targets for immunotherapy. Over the course of almost two decades, various strategies have been used, with mixed success, to produce antibodies that have recognition specificity for unique peptide/MHC class I complexes that mark infected and cancerous cells. Using these antibody reagents, novel peptide/MHC class I targets have been directly validated on diseased cells and new insight has been gained into the mechanisms of antigen presentation. More recently, these antibodies have shown promise for clinical applications such as therapeutic targeting of cancerous and infected cells and diagnosis and imaging of diseased cells. In this review, the authors comprehensively describe the methods used to identify disease-specific peptide/MHC class I epitopes and generate antibodies to these markers. Finally, they offer several examples that illustrate the promise of using these antibodies as anti-cancer agents.

Short communication: generation of recombinant monoclonal antibodies against an immunodominant HLA-A*2402-restricted HIV type 1 CTL epitope

Molecular interaction between the peptide/MHC class I complexes (pMHCs) and T cell receptor (TCR) is fundamental to the effector function of cytotoxic T lymphocytes (CTLs). Monoclonal antibody against pMHC with TCR-like specificity is a possible research tool for the antigen presentation. However, it is notoriously difficult to isolate monoclonal antibodies against pMHCs by the conventional hybridoma technique. To isolate monoclonal antibodies against an immunodominant HIV-1-derived CTL epitope in the nef gene, we panned phage clones from a human scFv phage display library. Eight Nef138-10/HLA-A*24(A24)-specific scFv clones were isolated and two of them (scFv#3 and scFv#27) were selected for further analysis. The clones stained A24-positive cells pulsed with Nef138-10 peptides specifically. We reconstituted humanized immunoglobulin Gs (IgGs) using a baculovirus expression system. Reconstituted IgGs kept the original specificities of the parental scFvs. The dissociation constants were 23 microM and 20 microM by Biacore, respectively. This is the first report of a successful generation of monoclonal antibodies against an HIV-1 CTL epitope loaded on an MHC class I molecule.

Can oligomeric T-cell receptor be used as a tool to detect viral peptide epitopes on infected cells?

We have utilized soluble HIV Gag-specific T-cell receptor (TCR) D3 with low affinity and TCR-like antibody 25-D1.16 recognizing its natural peptide-MHC (pMHC) ligand with high affinity to determine how affinity and off-rate of the receptor-pMHC interactions affect the sensitivity of pMHC detection on the cell surface. We found that with soluble TCR cognate pMHCs can be detected only at relatively high cell surface densities when the TCR was oligomerized using either Streptavidin or quantum dot (QD) scaffolds. While the higher affinity probe led to a greater sensitivity of pMHC detection, monomers and oligomers of the probe showed essentially the same detection limit, which is restricted by the sensitivity of standard flow cytometry technique. We have also shown that imaging of QD/TCR specifically bound to cognate pMHC on the cell surface yielded a very bright fluorescent signal that can enhance the sensitivity of viral peptide detection on infected cells.

Estimation of low frequency antigen-presenting cells with a novel RELISPOT assay

Adequate presentation of self and foreign antigens is a key factor for efficient T-cell immunosurveillance against pathogens and tumors. Cells presenting foreign antigens usually comprise a rare population and are difficult to detect even at the peak of infection. Here we demonstrate a CD8(+) T-cell-based approach that allows detection of specific antigen-presenting cells (APC) at a frequency of less than 0.0005%. When T cells are in excess, they form rosettes with rare APCs, which appear as single spots in an IFN-gamma ELISPOT assay. Using this RELISPOT (Rosette ELISPOT) method we demonstrate the dynamic interplay between CD8 T cells and professional and non-professional APCs following virus challenge.

Epitopes of the class I major histocompatibility complex (MHC-I) recognized in the syngeneic or allogeneic context predominantly linked to antigenic peptide loading to its binding groove

Class 1 major histocompatibility complex (MHC-I)-antigenic peptide exposed at the target cell surface is crucial for the adaptive immune response exerted in the self/syngeneic context by cytotoxic T lymphocyte (CTL). Such a complex also provides epitopes in the allogeneic context for antibody response directed against the MHC-I polymorphic determinant. In the present report we examined the formation of the MHC-I-peptide complex leading predominantly to the expression of T and/or B cell epitopes in a process of internal versus external antigenic peptide loading onto the binding groove of MHC-I. Analyses using antibodies specific to complex MHC-I-peptide generated in the syngeneic context to mimic T cell receptor (TCR) in comparison with antibodies specific to the MHC-I polymorphic determinant allowed the observation that the external peptide loading to MHC-I, while remaining necessary for inducing the formation of B cell epitopes, was less efficient than the internal one for generating T cell epitopes. Thus, external loading of peptide to the MHC-I appeared to match more closely the allogeneic situation and the humoral immunity in general, while internal peptide loading corresponded with the self/syngeneic context of the cellular CTL response.

T-cell receptor-like antibodies: novel reagents for clinical cancer immunology and immunotherapy

Major histocompatibility complex class I molecules play a central role in the immune response against a variety of cells that have undergone malignant transformation by shaping the T-cell repertoire and presenting peptide antigens from endogeneous antigens to CD8+ cytotoxic T-cells. Diseased tumor or virus-infected cells are present on class I major histocompatibility complex molecule peptides that are derived from tumor-associated antigens or viral-derived proteins. Due to their unique specificity, such major histocompatibility complex-peptide complexes are a desirable target for novel approaches in immunotherapy. Targeted delivery of toxins or other cytotoxic drugs to cells which express specific major histocompatibility complex-peptide complexes that are involved in the immune response against cancer or viral infections would allow for a specific immunotherapeutic treatment of these diseases. It has recently been demonstrated that antibodies with the antigen-specific, major histocompatibility complex-restricted specificity of T-cells can be generated by taking advantage of the selection power of phage display technology. In addition to their tumor targeting capabilities, antibodies that mimic the fine specificity of T-cell receptors can serve as valuable research reagents that enable study of human class I peptide-major histocompatibility complex ligand presentation, as well as T-cell receptor peptide-major histocompatibility complex interactions. T-cell receptor-like antibody molecules may prove to be useful tools for studying major histocompatibility complex class I antigen presentation in health and disease as well as for therapeutic purposes in cancer, infectious diseases and autoimmune disorders.

Dendritic Cells in Human Thymus and Periphery Display a Proinsulin Epitope in a Transcription-Dependent, Capture-Independent Fashion

The natural expression of tissue-specific genes in the thymus, e.g., insulin, is critical for self-tolerance. The transcription of tissue-specific genes is ascribed to peripheral Ag-expressing (PAE) cells, which discordant studies identified as thymic epithelial cells (TEC) or CD11c+ dendritic cells (DC). We hypothesized that, consistent with APC function, PAE-DC should constitutively display multiple self-epitopes on their surface. If recognized by Abs, such epitopes could help identify PAE cells to further define their distribution, nature, and function. We report that selected Abs reacted with self-epitopes, including a proinsulin epitope, on the surface of CD11c+ cells. We find that Proins+ CD11c+ PAE cells exist in human thymus, spleen, and also circulate in blood. Human thymic Proins+ cells appear as mature DC but express CD8alpha, CD20, CD123, and CD14; peripheral Proins+ cells appear as immature DC. However, DC derived in vitro from human peripheral blood monocytes include Proins+ cells that uniquely differentiate and mature into thymic-like PAE-DC. Critically, we demonstrate that human Proins+ CD11c+ cells transcribe the insulin gene in thymus, spleen, and blood. Likewise, we show that mouse thymic and peripheral CD11c+ cells transcribe the insulin gene and display the proinsulin epitope; moreover, by using knockout mice, we show that the display of this epitope depends upon insulin gene transcription and is independent of Ag capturing. Thus, we propose that PAE cells include functionally distinct DC displaying self-epitopes through a novel, transcription-dependent mechanism. These cells might play a role in promoting self-tolerance, not only in the thymus but also in the periphery.

Design of Soluble Recombinant T Cell Receptors for Antigen Targeting and T Cell Inhibition

The use of recombinant T cell receptors (TCRs) to target therapeutic interventions has been hindered by the naturally low affinity of TCR interactions with peptide major histocompatibility complex ligands. Here, we use multimeric forms of soluble heterodimeric alphabeta TCRs for specific detection of target cells pulsed with cognate peptide, discrimination of quantitative changes in antigen display at the cell surface, identification of virus-infected cells, inhibition of antigen-specific cytotoxic T lymphocyte activation, and identification of cross-reactive peptides. Notably, the A6 TCR specific for the immunodominant HLA A2-restricted human T cell leukemia virus type 1 Tax(11-19) epitope bound to HLA A2-HuD(87-95) (K(D) 120 microm by surface plasmon resonance), an epitope implicated as a causal antigen in the paraneoplastic neurological degenerative disorder anti-Hu syndrome. A mutant A6 TCR that exhibited dramatically increased affinity for cognate antigen (K(D) 2.5 nm) without enhanced cross-reactivity was generated; this TCR demonstrated potent biological activity even as a monomeric molecule. These data provide insights into TCR repertoire selection and delineate a framework for the selective modification of TCRs in vitro that could enable specific therapeutic intervention in vivo.

Human CTLs to Wild-Type and Enhanced Epitopes of a Novel Prostate and Breast Tumor-Associated Protein, TARP, Lyse Human Breast Cancer Cells

Vaccine therapy for prostate and breast cancer may have potential for treating these major causes of death in males and females, respectively. Critical to the development of tumor-specific vaccines is finding and characterizing novel antigens to be recognized by CD8(+) T cells. To define new CD8(+) T-cell tumor antigens, we determined two wild-type HLA-A2 epitopes from a recently found tumor-associated protein, TARP (T-cell receptor gamma alternate reading frame protein), expressed in prostate and breast cancer cells. We were also able to engineer epitope-enhanced peptides by sequence modifications. Both wild-type and enhanced epitopes induced peptide-specific CD8(+) T-cell responses in A2K(b) transgenic mice. In vitro restimulation of human CD8(+) T cells from a prostate cancer patient resulted in CD8(+) T cells reactive to the peptide epitopes that could lyse HLA-A2(+) human breast cancer cells (MCF-7) expressing TARP. Epitope-specific human CD8(+) T cells were also enumerated in patients' peripheral blood by tetramer staining. Our data suggest that HLA-A2-binding TARP epitopes and enhanced epitopes discovered in this study could be incorporated into a potential vaccine for both breast and prostate cancer.

Tax and M1 peptide/HLA-A2-specific Fabs and T cell receptors recognize nonidentical structural features on peptide/HLA-A2 complexes

Both TCRs and Ab molecules are capable of MHC-restricted recognition of peptide/MHC complexes. However, such MHC restriction is the predominant mode of recognition by T cells, but is extremely rare for B cells. The present study asks whether the dichotomy in Ag recognition modes of T and B cells could be due to fundamental differences in the methods by which TCRs and Abs recognize peptide/MHC complexes. We have compared MHC and peptide recognition by panels of CTL lines specific for the Tax and M1 peptides presented by HLA-A2 plus Tax and M1 peptide/HLA-A2-specific human Fabs that were selected from a naive phage display library. Collectively, the results indicate both striking similarities and important differences between Fab and TCR recognition of MHC and peptide components of the Tax and M1/HLA-A2 complexes. These findings suggest that these two classes of immunoreceptors have solved the problem of specific recognition of peptide/MHC complexes by nonidentical mechanisms. This conclusion is important in part because it indicates that Ab engineering approaches could produce second-generation Ab molecules that more closely mimic TCR fine specificity. Such efforts may produce more efficacious diagnostic and therapeutic agents.

Recombinant antibodies with MHC-restricted, peptide-specific, T-cell receptor-like specificity: new tools to study antigen presentation and TCR-peptide-MHC interactions

The advent in recent years of the application of tetrameric arrays of class I peptide-MHC complexes now enables us to detect and study rare populations of antigen-specific CD8+ T cells. However, available methods cannot visualize or determine the number and distribution of these TCR ligands on individual cells or detect antigen-presenting cells (APCs) in tissues. Here we describe a new approach that enables study of human class I peptide-MHC ligand-presentation as well as TCR-peptide-MHC interactions. Such studies are facilitated by applying novel tools in the form of peptide-specific, HLA-A2-restricted human recombinant antibodies directed toward a large variety of tumor-associated as well as viral T-cell epitope peptides. Using a large human antibody phage display library, a large panel of recombinant antibodies that are specific for a particular peptide-MHC class I complex in a peptide-dependent, MHC-restricted manner was isolated. These antibodies were used to directly visualize the specific MHC-peptide complex on tumor cells, antigen-presenting cells or virus-infected cells by flow cytometry. They enabled direct quantitation of the number of MHC-peptide complexes as well as in situ detection of the complex on the surface of APCs after naturally occurring active intracellular processing of the cognate antigen. These studies will enable also the development of a new class of targeting molecules to deliver drugs or toxins to tumor or virus-infected cells. Thus, we demonstrate our ability to transform the unique fine specificity but low intrinsic affinity of TCRs into high-affinity soluble antibody molecules endowed with a TCR-like specificity toward human tumor or viral epitopes. These molecules may prove to be crucial useful tools for studying MHC class I antigen presentation in health and disease as well as for therapeutic purposes in cancer, infectious diseases and autoimmune disorders.

TCR-like human antibodies expressed on human CTLs mediate antibody affinity-dependent cytolytic activity

The permanent genetic programming via gene transfer of autologous T cells with cell surface receptors directed toward tumor-related Ags holds great promise for the development of more-specific tumor therapies. In this study we have explored the use of Abs directed to MHC-peptide complexes (or TCR-like Abs) to engraft CTLs with exquisite specificity for cancer cells. First, we affinity matured in vitro a previously selected TCR-like Ab, Fab-G8, which is highly specific for the peptide melanoma-associated Ag-A1 presented by the HLA-A1 molecule. A combination of L chain shuffling, H chain-targeted mutagenesis, and in vitro selection of phage display libraries yielded a Fab-G8 Ab derivative, Fab-Hyb3, with an 18-fold improved affinity yet identical peptide fine specificity. Fab-G8 and Fab-Hyb3 were expressed on primary human T lymphocytes as cell surface-anchored Fab, demonstrating that T cells expressing the high-affinity Fab-Hyb3 molecule eradicate tumor cells much more effectively. Furthermore, the gain in ligand-binding affinity resulted in a 2-log improvement in the detection of peptide/MHC complexes on melanoma-associated Ag-A1 peptide-loaded cells. In summary, an affinity-matured Ab specifically recognizing a cancer-related peptide/MHC complex was generated and used to improve the tumor cell killing capacity of human T cells. This strategy, based on engraftment of T cells with in vitro engineered Abs, is an attractive alternative to the laborious, and in many cases unsuccessful, generation of highly potent tumor-specific T lymphocytes.

Binding of the natural killer cell inhibitory receptor Ly49A to its major histocompatibility complex class I ligand. Crucial contacts include both H-2Dd AND beta 2-microglobulin

Ly49A, an inhibitory C-type lectin-like mouse natural killer cell receptor, functions through interaction with the major histocompatibility complex class I molecule, H-2D(d). The x-ray crystal structure of the Ly49A.H-2D(d) complex revealed that homodimeric Ly49A interacts at two distinct sites of H-2D(d): Site 1, spanning one side of the alpha1 and alpha2 helices, and Site 2, involving the alpha1, alpha2, alpha3, and beta(2)m domains. Mutants of Ly49A, H-2D(d), and beta(2)-microglobulin at intermolecular contacts and the Ly49A dimer interface were examined for binding affinity and kinetics. Although mutations at Site 1 had little affect, several at Site 2 and at the dimer interface hampered the Ly49A.H-2D(d) interaction, with no effect on gross structure or T cell receptor interaction. The region surrounding the most critical residues (in H-2D(d), Asp(122); in Ly49A, Asp(229), Ser(236), Thr(238), Arg(239), and Asp(241); and in beta(2)-microglobulin, Gln(29) and Lys(58)) of the Ly49A.H-2D(d) interface at Site 2 includes a network of water molecules, suggesting a molecular basis for allelic specificity in natural killer cell recognition.

Activating CTL precursors to reveal CTL function without skewing the repertoire by in vitro expansion

Detection of the functional CD8(+) CTL response usually requires in vitro restimulation. The differences between the CD8(+) CTL repertoire in freshly isolated precursor cells and CD8(+) CTL after short-term in vitro expansion have been generally assumed to be minimal, but have never been defined experimentally. Using staining with P18-I10/H-2D(d) tetramers and monoclonal antibodies (mAb) against Vbeta, we show the surprising result that there was significant skewing of the CD8(+) CTL repertoire after just 7 days of stimulation. In contrast, we found that overnight incubation of precursor cells with peptide allows the functional assessment of CD8(+) CTL (which cannot be detected ex vivo from freshly isolated cells) without changing the absolute number of antigen-specific CTL as measured by tetramer staining or the repertoire of TCR analyzed with mAb. This study affords a better understanding of the differences between the ex vivo and in vitro stimulated CTL repertoire, and provides an approach to reveal a more faithful representation of the functional in vivo CTL response without skewing of the repertoire of T cells detected.

Survey of the year 2000 commercial optical biosensor literature

We have compiled a comprehensive list of the articles published in the year 2000 that describe work employing commercial optical biosensors. Selected reviews of interest for the general biosensor user are highlighted. Emerging applications in areas of drug discovery, clinical support, food and environment monitoring, and cell membrane biology are emphasized. In addition, the experimental design and data processing steps necessary to achieve high-quality biosensor data are described and examples of well-performed kinetic analysis are provided.

Competitive inhibition in vivo and skewing of the T cell repertoire of antigen-specific CTL priming by an anti-peptide-MHC monoclonal antibody

We have recently described a mAb, KP15, directed against the MHC-I/peptide molecular complex consisting of H-2D(d) and a decamer peptide corresponding to residues 311-320 of the HIV IIIB envelope glycoprotein gp160. When administered at the time of primary immunization with a vaccinia virus vector encoding gp160, the mAb blocks the subsequent appearance of CD8(+) CTL with specificity for the immunodominant Ag, P18-I10, presented by H-2D(d). This inhibition is specific for this particular peptide Ag; another H-2D(d)-restricted gp160 encoded epitope from a different HIV strain is not affected, and an H-2L(d)-restricted epitope encoded by the viral vector is also not affected. Using functional assays and specific immunofluorescent staining with multivalent, labeled H-2D(d)/P18-I10 complexes (tetramers), we have enumerated the effects of blocking of priming on the subsequent appearance, avidity, and TCR Vbeta usage of Ag-specific CTL. Ab blocking skews the proportion of high avidity cells emerging from immunization. Surprisingly, Vbeta7-bearing Ag-specific TCR are predominantly inhibited, while TCR of several other families studied are not affected. The ability of a specific MHC/peptide mAb to inhibit and divert the CD8(+) T cell response holds implications for vaccine design and approaches to modulate the immune response in autoimmunity.