Allo-Specific Humoral Responses: New Methods for Screening Donor-Specific Antibody and Characterization of HLA-Specific Memory B Cells.

Antibody-mediated allograft rejection (AMR) causes more kidney transplant failure than any other single cause. AMR is mediated by antibodies recognizing antigens expressed by the graft, and antibodies generated against major histocompatibility complex (MHC) mismatches are especially problematic. Most research directed towards the management of clinical AMR has focused on identifying and characterizing circulating donor-specific HLA antibody (DSA) and optimizing therapies that reduce B-cell activation and/or block antibody secretion by inhibiting plasmacyte survival. Here we describe a novel set of reagents and techniques to allow more specific measurements of MHC sensitization across different animal transplant models. Additionally, we have used these approaches to isolate and clone individual HLA-specific B cells from patients sensitized by pregnancy or transplantation. We have identified and characterized the phenotypes of individual HLA-specific B cells, determined the V(D)J rearrangements of their paired H and L chains, and generated recombinant antibodies to determine affinity and specificity. Knowledge of the BCR genes of individual HLA-specific B cells will allow identification of clonally related B cells by high-throughput sequence analysis of peripheral blood mononuclear cells and permit us to re-construct the origins of HLA-specific B cells and follow their somatic evolution by mutation and selection.

Human Amnion Epithelial Cells Impair T Cell Proliferation: The Role of HLA-G and HLA-E Molecules.

The immunoprivilege status characteristic of human amnion epithelial cells (hAECs) has been recently highlighted in the context of xenogenic transplantation. However, the mechanism(s) involved in such regulatory functions have been so far only partially been clarified. Here, we have analyzed the expression of HLA-Ib molecules in isolated hAEC obtained from full term placentae. Moreover, we asked whether these molecules are involved in the immunoregulatory functions of hAEC. Human amnion-derived cells expressed surface HLA-G and HLA-F at high levels, whereas the commonly expressed HLA-E molecule has been measured at a very low level or null on freshly isolated cells. HLA-Ib molecules can be expressed as membrane-bound and soluble forms, and in all hAEC batches analyzed we measured high levels of sHLA-G and sHLA-E when hAEC were maintained in culture, and such a release was time-dependent. Moreover, HLA-G was present in extracellular vesicles (EVs) released by hAEC. hAEC suppressed T cell proliferation in vitro at different hAEC:T cell ratios, as previously reported. Moreover, inhibition of T cell proliferation was partially reverted by pretreating hAEC with anti-HLA-G, anti-HLA-E and anti-ß2 microglobulin, thus suggesting that HLA-G and -E molecules are involved in hAEC-mediated suppression of T cell proliferation. Finally, either large-size EV (lsEV) or small-size EV (ssEV) derived from hAEC significantly modulated T-cell proliferation. In conclusion, we have here characterized one of the mechanism(s) underlying immunomodulatory functions of hAEC, related to the expression and release of HLA-Ib molecules.

Epigallocatechin-3-gallate Inhibits Cu(II)-Induced ß-2-Microglobulin Amyloid Formation by Binding to the Edge of Its ß-Sheets.

Epigallocatechin-3-gallate (EGCG) is a catechin found in green tea that can inhibit the amyloid formation of a wide variety of proteins. EGCG's ability to prevent or redirect the amyloid formation of so many proteins may reflect a common mechanism of action, and thus, greater molecular-level insight into how it exerts its effect could have broad implications. Here, we investigate the molecular details of EGCG's inhibition of the protein ß-2-microglobulin (ß2m), which forms amyloids in patients undergoing long-term dialysis treatment. Using size-exclusion chromatography and a collection of mass spectrometry-based techniques, we find that EGCG prevents Cu(II)-induced ß2m amyloid formation by diverting the normal progression of preamyloid oligomers toward the formation of spherical, redissolvable aggregates. EGCG exerts its effect by binding with a micromolar affinity (Kd ≈ 5 µM) to the ß2m monomer on the edge of two ß-sheets near the N-terminus. This interaction destabilizes the preamyloid dimer and prevents the formation of a tetramer species previously shown to be essential for Cu(II)-induced ß2m amyloid formation. EGCG's binding at the edge of the ß-sheets in ß2m is consistent with a previous hypothesis that EGCG generally prevents amyloid formation by binding cross-ß-sheet aggregation intermediates.

In silico-guided identification of potential inhibitors against ß2m aggregation in dialysis-related amyloidosis.

In dialysis-related amyloidosis (DRA), misfolding of ß2-microglobulin (ß2m) leads to amyloid fibril deposition mainly in the skeletal joints seriously affecting their functionality. The identification and characterization of small-molecules that bind ß2m and possibly inhibit its aggregation remain unexplored. In the present study, a ligand-based virtual screening approach and molecular dynamics (MD) simulations were employed to explore potent small-molecule inhibitors against ß2m aggregation. The compounds were screened from various small-molecule databases by applying ligand-based virtual screening with rifamycin SV (RSV) as a reference compound. The molecular docking analysis was performed to filter out lead compounds with a higher binding affinity than RSV from a library of ∼800 compounds. Three compounds, ChEBI68321 (C1), ChEMBL360190 (C2) and ZINC3091144 (C3), displaying excellent binding free energies of -51.29, -36.51 and -34.36 kcal/mol, respectively, with ß2m were subjected to MD simulations to get insights into the binding locations, key interactions and structural stability of the ß2m-ligand complexes. The hydrogen bond analysis highlight higher structural stability and reduced flexibility of the loop regions of ß2m in presence of C1, C2 and C3. The integrated computational approach employed in the present study identify promising lead compounds against ß2m aggregation in DRA. Abbreviationsß2mß2-microglobulin3Dthree dimensionalADAlzheimer's diseaseADTAutoDock ToolsDRADialysis-related amyloidosisDSSPdictionary of secondary structure of proteinsFELfree energy landscapeGROMACSGROningen MAchine for Chemical SimulationsLGALamarckian Genetic AlgorithmLINCSLINear Constraint SolverMCmain chainMDmolecular dynamicsMHC-Imajor histocompatibility complex class IMM-PBSAmolecular mechanics Poisson-Boltzmann surface areaPMEnanometer (nm); particle mesh ewaldPCAprincipal component analysisPDBprotein data bankRgradius-of-gyrationRSVrifamycin SVRMSDroot-mean-square deviationRMSFroot-mean-square fluctuationSCside chainSPCsimple point chargeSASASolvent accessible surface areaVMDvisual molecular dynamicsCommunicated by Ramaswamy H. Sarma.

High Expression Achievement of Active and Robust Anti-ß2 microglobulin Nanobodies via E.coli Hosts Selection.

Nanobodies (VHHs) overcome many of the drawbacks of conventional antibodies, and the related technologies represent state-of-the-art and advanced applications in scientific research, pharmaceuticals, and therapies. In terms of productivity and economic cost, the cytoplasmic expression of VHHs in Escherichia coli (E. coli) is a good process for their recombinant production. The cytoplasmic environment of the host is critical to the affinity and stability of the recombinant VHHs in soluble form, yet the effects have not been studied. For this purpose, recombinant anti-ß2 microglobulin VHHs were constructed and expressed in four commercialized E. coli hosts, including BL21 (DE3), Rosetta-gami B (DE3) pLysS, Origami 2 (DE3) and SHuffle T7 Express. The results showed that anti-ß2 microglobulin (ß2MG) VHHs expressed in different hosts exhibited distinctive differences in the affinity and structural characteristics. The VHHs expressed in Rosetta-gami B (DE3) pLysS possessed not only the greatest affinity of (equilibrium dissociation constant) KD = 4.68 × 10-8 M but also the highest yields compared with the VHHs expressed in BL21 (DE3), Origami 2 (DE3) and SHuffle T7 Express. In addition, the VHHs expressed in Rosetta-gami B (DE3) pLysS were more stable than the VHHs expressed in the rest three hosts. Thus far, we have successfully realized the high expression of the active and robust anti-ß2MG VHHs in Rosetta-gami B (DE3) pLysS. The underlying principle of our study is able to guide the expression strategies of nanobodies on the context of industrial large-scale production.

Sequential treatment failures in response to BRAF/MEK and immune checkpoint inhibitors mediated by MAP2K2 and B2M mutations in melanoma.

Although the treatment of metastatic melanoma has been significantly improved by both anti-BRAF/MEK and checkpoint immunotherapies, resistance to these treatment modalities remains a substantial clinical problem. Multiple clinical studies are addressing the optimal sequencing of these agents in larger patient cohorts, but successful long-term individualized treatment will likely require the elucidation of resistance mechanisms from post-progression samples. Here, we describe a patient with BRAF-V600E-positive metastatic melanoma who was sequentially treated with BRAF/MEK inhibitors (dabrafenib/trametinib) and checkpoint inhibitor immunotherapy (nivolumab, followed by pembrolizumab). After the emergence of resistance, whole exome sequencing was performed, implicating MAP2K2 and B2M mutations in loss of response to anti-BRAF/MEK and anti-PD1 therapies, respectively.

Genomic Profiling of Patient-Derived Xenografts for Lung Cancer Identifies B2M Inactivation Impairing Immunorecognition.

Purpose: We aimed to maximize the performance of detecting genetic alterations in lung cancer using high-throughput sequencing for patient-derived xenografts (PDXs).Experimental Design: We undertook an integrated RNA and whole-exome sequencing of 14 PDXs. We focused on the genetic and functional analysis of ß2-microglobulin (B2M), a component of the HLA class-I complex.Results: We identified alterations in genes involved in various functions, such as B2M involved in immunosurveillance. We extended the mutational analysis of B2M to about 230 lung cancers. Five percent of the lung cancers carried somatic mutations, most of which impaired the correct formation of the HLA-I complex. We also report that genes such as CALR, PDIA3, and TAP1, which are involved in the maturation of the HLA-I complex, are altered in lung cancer. By gene expression microarrays, we observed that restitution of B2M in lung cancer cells upregulated targets of IFNα/IFNγ. Furthermore, one third of the lung cancers lacked the HLA-I complex, which was associated with lower cytotoxic CD8+ lymphocyte infiltration. The levels of B2M and HLA-I proteins correlated with those of PD-L1. Finally, a deficiency in HLA-I complex and CD8+ infiltration tended to correlate with reduced survival of patients with lung cancer treated with anti-PD-1/anti-PD-L1.Conclusions: Here, we report recurrent inactivation of B2M in lung cancer. These observations, coupled with the mutations found at CALR, PDIA3, and TAP1, and the downregulation of the HLA-I complex, indicate that an abnormal immunosurveillance axis contributes to lung cancer development. Finally, our observations suggest that an impaired HLA-I complex affects the response to anti-PD-1/anti-PD-L1 therapies. Clin Cancer Res; 23(12); 3203-13. ©2016 AACR.

Anti-ß2-microglobulin monoclonal antibodies overcome bortezomib resistance in multiple myeloma by inhibiting autophagy.

Our previous studies showed that anti-ß2M monoclonal antibodies (mAbs) have strong and direct apoptotic effects on multiple myeloma (MM) cells, suggesting that anti-ß2M mAbs might be developed as a novel therapeutic agent. In this study, we investigated the anti-MM effects of combination treatment with anti-ß2M mAbs and bortezomib (BTZ). Our results showed that anti-ß2M mAbs enhanced BTZ-induced apoptosis of MM cell lines and primary MM cells. Combination treatment could also induce apoptosis of BTZ-resistant MM cells, and the enhanced effect depended on the surface expression of ß2M on MM cells. BTZ up-regulated the expression of autophagy proteins, whereas combination with anti-ß2M mAbs inhibited autophagy. Sequence analysis of the promoter region of beclin 1 identified 3 putative NF-κB-binding sites from -615 to -789 bp. BTZ treatment increased, whereas combination with anti-ß2M mAbs reduced, NF-κB transcription activities in MM cells, and combination treatment inhibited NF-κB p65 binding to the beclin 1 promoter. Furthermore, anti-ß2M mAbs and BTZ combination treatment had anti-MM activities in an established MM mouse model. Thus, our studies provide new insight and support for the clinical development of an anti-ß2M mAb and BTZ combination treatment to overcome BTZ drug resistance and improve MM patient survival.

Systemic amyloidosis: lessons from ß2-microglobulin.

ß2-Microglobulin is responsible for systemic amyloidosis affecting patients undergoing long-term hemodialysis. Its genetic variant D76N causes a very rare form of familial systemic amyloidosis. These two types of amyloidoses differ significantly in terms of the tissue localization of deposits and for major pathological features. Considering how the amyloidogenesis of the ß2-microglobulin mechanism has been scrutinized in depth for the last three decades, the comparative analysis of molecular and pathological properties of wild type ß2-microglobulin and of the D76N variant offers a unique opportunity to critically reconsider the current understanding of the relation between the protein's structural properties and its pathologic behavior.

Anti-ß2M monoclonal antibodies kill myeloma cells via cell- and complement-mediated cytotoxicity.

Our previous studies showed that anti-ß2M monoclonal antibodies (mAbs) at high doses have direct apoptotic effects on myeloma cells, suggesting that anti-ß2M mAbs might be developed as a novel therapeutic agent. In this study, we investigated the ability of the mAbs at much lower concentrations to indirectly kill myeloma cells by utilizing immune effector cells or molecules. Our results showed that anti-ß2M mAbs effectively lysed MM cells via antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC), which were correlated with and dependent on the surface expression of ß2M on MM cells. The presence of MM bone marrow stromal cells or addition of IL-6 did not attenuate anti-ß2M mAb-induced ADCC and CDC activities against MM cells. Furthermore, anti-ß2M mAbs only showed limited cytotoxicity toward normal B cells and nontumorous mesenchymal stem cells, indicating that the ADCC and CDC activities of the anti-ß2M mAbs were more prone to the tumor cells. Lenalidomide potentiated in vitro ADCC activity against MM cells and in vivo tumor inhibition capacity induced by the anti-ß2M mAbs by enhancing the activity of NK cells. These results support clinical development of anti-ß2M mAbs, both as a monotherapy and in combination with lenalidomide, to improve MM patient outcome.

Inhibition of ß2-microglobulin/hemochromatosis enhances radiation sensitivity by induction of iron overload in prostate cancer cells.

BACKGROUND: Bone metastasis is the most lethal form of several cancers. The ß2-microglobulin (ß2-M)/hemochromatosis (HFE) complex plays an important role in cancer development and bone metastasis. We demonstrated previously that overexpression of ß2-M in prostate, breast, lung and renal cancer leads to increased bone metastasis in mouse models. Therefore, we hypothesized that ß2-M is a rational target to treat prostate cancer bone metastasis. RESULTS: In this study, we demonstrate the role of ß2-M and its binding partner, HFE, in modulating radiation sensitivity and chemo-sensitivity of prostate cancer. By genetic deletion of ß2-M or HFE or using an anti-ß2-M antibody (Ab), we demonstrate that prostate cancer cells are sensitive to radiation in vitro and in vivo. Inhibition of ß2-M or HFE sensitized prostate cancer cells to radiation by increasing iron and reactive oxygen species and decreasing DNA repair and stress response proteins. Using xenograft mouse model, we demonstrate that anti-ß2-M Ab sensitizes prostate cancer cells to radiation treatment. Additionally, anti-ß2-M Ab was able to prevent tumor growth in an immunocompetent spontaneous prostate cancer mouse model. Since bone metastasis is lethal, we used a bone xenograft model to test the ability of anti-ß2-M Ab and radiation to block tumor growth in the bone. Combination treatment significantly prevented tumor growth in the bone xenograft model by inhibiting ß2-M and inducing iron overload. In addition to radiation sensitive effects, inhibition of ß2-M sensitized prostate cancer cells to chemotherapeutic agents. CONCLUSION: Since prostate cancer bone metastatic patients have high ß2-M in the tumor tissue and in the secreted form, targeting ß2-M with anti-ß2-M Ab is a promising therapeutic agent. Additionally, inhibition of ß2-M sensitizes cancer cells to clinically used therapies such as radiation by inducing iron overload and decreasing DNA repair enzymes.

Benefit of doxycycline treatment on articular disability caused by dialysis related amyloidosis.

Abstract Doxycycline inhibits amyloid formation in vitro and its therapeutic efficacy is under evaluation in clinical trials for different protein conformational diseases, including prion diseases, Alzheimer's disease and transthyretin amyloidosis. In patients on chronic hemodialysis, a persistently high concentration of ß2-microglobulin causes a form of amyloidosis (dialysis-related amyloidosis, DRA) localized in bones and ligaments. Since doxycycline inhibits ß2-microglobulin fibrillogenesis in vitro and accumulates in bones, DRA represents an ideal form of amyloidosis where doxycycline may reach a therapeutic concentration at the site of amyloid deposition. Three patients on long-term dialysis with severe articular impairment and uncontrollable pain due to DRA were treated with 100 mg of doxycycline daily. Pharmacokinetics and safety of treatment were conducted. Plasmatic levels of the drug reached a plateau after one week (1.1-2.3 µg/ml). Treatment was well tolerated in two patients for a year, while one was suspended after 5 months due to mild esophagitis. Treatment was associated with a significant reduction in articular pain and with a significant and measurable improvement in passive and active movements in all cases, despite the persistence of unchanged amyloid deposits measured by magnetic resonance imaging.

ß2-microglobulin induces epithelial to mesenchymal transition and confers cancer lethality and bone metastasis in human cancer cells.

Bone metastasis is one of the predominant causes of cancer lethality. This study demonstrates for the first time how ß2-microglobulin (ß2-M) supports lethal metastasis in vivo in human prostate, breast, lung, and renal cancer cells. ß2-M mediates this process by activating epithelial to mesenchymal transition (EMT) to promote lethal bone and soft tissue metastases in host mice. ß2-M interacts with its receptor, hemochromatosis (HFE) protein, to modulate iron responsive pathways in cancer cells. Inhibition of either ß2-M or HFE results in reversion of EMT. These results demonstrate the role of ß2-M in cancer metastasis and lethality. Thus, ß2-M and its downstream signaling pathways are promising prognostic markers of cancer metastases and novel therapeutic targets for cancer therapy.

Insight into the mechanism of human herpesvirus 7 U21-mediated diversion of class I MHC molecules to lysosomes.

The U21 open reading frame from human herpesvirus-7 encodes a membrane protein that associates with and redirects class I MHC molecules to the lysosomal compartment. The mechanism by which U21 accomplishes this trafficking excursion is unknown. Here we have examined the contribution of localization, glycosylation, domain structure, and the absence of substrate class I MHC molecules on the ability of U21 to traffic to lysosomes. Our results suggest the existence of a cellular protein necessary for U21-mediated rerouting of class I MHC molecules.

A combined high-resolution mass spectrometric and in silico approach for the characterisation of small ligands of beta2-microglobulin.

Beta(2)-microglobulin (beta(2)-m) is a protein responsible for a severe complication of long-term hemodialysis, known as dialysis-related amyloidosis, in which initial beta(2)-m misfolding leads to amyloid fibril deposition, mainly in the skeletal tissue. Whereas much attention is paid to understanding the complex mechanism of amyloid formation, the evaluation of small molecules that may bind beta(2)-m and possibly inhibit the aggregation process is still largely unexplored mainly because the protein lacks a specific active site. Based on our previous findings, we selected a pilot set of sulfonated molecules that are known to either bind or not to the protein, including binders that are anti-amyloidogenic. We show how a complementary approach, using high-resolution mass spectrometry and in silico studies, can offer rapid and precise information on affinity, as well as insight into the structural requisites that favour or disfavour the inhibitory activity. Overall, this approach can be used for predictive purposes and for a rapid screening of fibrillogenesis inhibitors.

Generation of HLA-deficient platelets from hematopoietic progenitor cells.

BACKGROUND: Exposure to allogeneic blood products often leads to the development of human leukocyte antigen (HLA) antibodies. Refractoriness to platelet (PLT) transfusion caused by alloimmunization against HLA Class I antigens constitutes a significant clinical problem. STUDY DESIGN AND METHODS: We developed an RNA interference (RNAi)-based approach to silence the expression of HLA Class I molecules on PLTs derived from CD34+ progenitor cells. A lentiviral-based system was used to express short-hairpin RNA (shRNA) targeting ß2-microglobulin (ß2m) transcripts in CD34+ progenitor cells. Differentiation to PLTs was performed by incubating progenitor cells in the presence of thrombopoietin and interleukin-3. RESULTS: The transduction of RNAi cassettes containing the sequences for shRNAs targeting ß2m caused up to 85% reduction of progenitor cells HLA Class I antigen expression, which was maintained in the culture-derived PLTs. The HLA-deficient PLTs derived from HLA-silenced CD34+ cells proved to be fully functional in in vitro tests when compared to peripheral blood-derived PLTs. CONCLUSIONS: Our data show that in vitro generating HLA Class I-deficient PLTs from hematopoietic progenitor cells prove to be feasible. As malignancy risks associated with insertional mutagenesis are not to be expected in anucleated PLTs, provision of HLA-deficient PLTs from large-scale production units may become reality in the management of patients suffering from PLT transfusion refractoriness.

Identification of beta2-microglobulin as a potential target for ovarian cancer.

Ovarian cancer is one of the most lethal gynecological cancers. Antibody-based therapy has emerged as an important therapeutic approach for an increasing number of malignancies. Here, we prepared an antibody pool against SKOV3 ovarian cancer cells, which could induce apoptosis of SKOV3 cells in a dose- and time-dependent manner. Through SEREX analysis, beta 2-microglobulin (b2M) was identified as the potential target molecules of functional antibodies. The immune IgG (i-IgG) of antibody pool had little effects on other kinds of cancer cells, maybe because of the more secretion of b2M by SKOV3. Further studies indicated that specific antibody of b2M indeed also can inhibit the growth of SKOV3. In addition, overexpression of b2M could promote the growth of SKOV3 cells in vitro, by colony formation and anchorage-independent growth assay, at least partially through the activation of PI3K/Akt pathway. Thus, b2M could be a potential therapeutic target in ovarian cancer.

Overexpression of beta2-microglobulin is associated with poor survival in patients with oral cavity squamous cell carcinoma and contributes to oral cancer cell migration and invasion.

beta2-Microglobulin (beta2M), a component of MHC class I molecules, is believed to be associated with tumour status in various cancers. In this study, we examined the expression of beta2M at different malignant stages of oral cavity squamous cell carcinoma (OCSCC). To determine the possible correlation between beta2M expression and various clinical characteristics, 256 samples from patients with OCSCC were evaluated by immunohistochemical staining. Strong beta2M expression was significantly correlated with a relatively advanced tumour stage (P<0.001), positive nodal status (P<0.001), and TNM stage (P<0.001). The cumulative 5-year survival rate was significantly correlated with a relatively advanced tumour stage (P<0.001), positive nodal status (P<0.001), TNM stage (P<0.001), and strong expression of beta2M (P<0.001). Thus, elevated beta2M expression is an indicator of poor survival (P<0.001). In addition, we extended our analysis of beta2M expression to the FaDu and SCC25 oral cancer cell lines. beta2-Microglobulin expression was positively correlated with cell migration and invasion in beta2M-overexpressing transfectants in Transwell chambers. The suppression of beta2M expression using small interfering RNA (siRNA) was sufficient to decrease cell migration and invasion in vitro. Taken together, our results suggest that beta2M expression in the tissues is associated with survival and may be involved in tumour progression and metastasis in OCSCC.

Anti beta2-microglobulin monoclonal antibodies induce apoptosis in myeloma cells by recruiting MHC class I to and excluding growth and survival cytokine receptors from lipid rafts.

We recently showed that monoclonal antibodies (mAbs) against beta2-microglobulin (beta2M) have a remarkably strong apoptotic effect on myeloma cells. The mAbs induced apoptosis by recruiting major histocompatibility complex (MHC) class I to lipid rafts, activated c-Jun N-terminal kinase (JNK), and inhibited phosphatidylinositol 3-kinase (PI3K)/Akt and extracellular signal-regulated kinase (ERK) pathways. Growth and survival cytokines such as interleukin-6 (IL-6) and insulin-like growth factor-I (IGF-I), which could protect myeloma cells from dexamethasone-induced apoptosis, did not affect mAb-mediated cell death. This study was undertaken to elucidate the mechanisms underlying anti-beta2M mAb-induced PI3K/Akt and ERK inhibition and the inability of IL-6 and IGF-I to protect myeloma cells from mAb-induced apoptosis. We focused on lipid rafts and confirmed that these membrane microdomains are required for IL-6 and IGF-I signaling. By recruiting MHC class I into lipid rafts, anti-beta2M mAbs excluded IL-6 and IGF-I receptors and their substrates from the rafts. The mAbs not only redistributed the receptors in cell membrane, but also abrogated IL-6- or IGF-I-mediated Janus kinase/signal transducer and activator of transcription 3 (JAK/STAT3), PI3K/Akt, and Ras/Raf/ERK pathway signaling, which are otherwise constitutively activated in myeloma cells. Thus, this study further defines the tumoricidal mechanism of the mAbs and provides strong evidence to support the potential of these mAbs as therapeutic agents for myeloma.

Complex interplay of activating and inhibitory signals received by Vgamma9Vdelta2 T cells revealed by target cell beta2-microglobulin knockdown.

Tumor cells often escape immunosurveillance by down-regulating MHC class I molecule expression. For human Vgamma9Vdelta2 T cells, a major peripheral blood T cell subset with broad antitumor reactivity, this down-regulation can affect signals transmitted by both the inhibitory and the activating MHC class I and Ib-specific NK receptors (NKRs) that these lymphocytes frequently express. To assess the overall impact of MHC down-regulation on Vgamma9Vdelta2 T cell activation, we used stable beta(2)-microglobulin knockdown to generate tumor cells with a approximately 10-fold down-modulation of all MHC class I molecules. This down-modulation had little effect on T cell proliferation or cytokine production, but modified tumor cell killing efficiency. Ab-blocking studies identified ILT2 as an important inhibitor of tumor cell killing by Vgamma9Vdelta2 T cells. Down-modulation of MHC class I and Ib molecules severely reduced ILT2 inhibitory signaling, but still allowed signaling by activating CD94-based receptors. It also unveiled a frequent enhancing effect of NKG2D on tumor killing by Vgamma9Vdelta2 T cells. Current models suggest that activating NKRs have less affinity for their MHC ligands than homologous inhibitory NKRs. Our results show that, despite this, activating NKRs recognizing MHC class I molecules play an important role in the increased killing by Vgamma9Vdelta2 T cells of tumor cells with down-regulated MHC class I molecule expression, and suggest that these T cells will best lyse tumor cells combining MHC class I molecule expression down-regulation with up-regulated NKG2D ligand expression.