Red cell exchange for rapid leukoreduction in adults with hyperleukocytosis and leukostasis

ABSTRACT

We show that red cell exchange (RCE) treats hyperleukocytosis in acute leukemia. RCE provided similar leukoreduction to standard therapeutic leukoreduction and could be superior in patients with severe anemia or monocytic leukemias or when requiring rapid treatment.

Mechanisms of inhibition of human monoclonal antibodies in immune thrombotic thrombocytopenic purpura

Antibody binding to a plasma metalloprotease, a disintegrin and metalloproteinase with thrombospondin type 1 repeats 13 (ADAMTS13), is necessary for the development of immune thrombotic thrombocytopenic purpura (iTTP). Inhibition of ADAMTS13-mediated von Willebrand factor (VWF) cleavage by such antibodies clearly plays a role in the pathophysiology of the disease, although the mechanisms by which they inhibit ADAMTS13 enzymatic function are not fully understood. At least some immunoglobulin G-type antibodies appear to affect the conformational accessibility of ADAMTS13 domains involved in both substrate recognition and inhibitory antibody binding. We used single-chain fragments of the variable region previously identified via phage display from patients with iTTP to explore the mechanisms of action of inhibitory human monoclonal antibodies. Using recombinant full-length ADAMTS13, truncated ADAMTS13 variants, and native ADAMTS13 in normal human plasma, we found that, regardless of the conditions tested, all 3 inhibitory monoclonal antibodies tested affected enzyme turnover rate much more than substrate recognition of VWF. Hydrogen-to-deuterium exchange plus mass spectrometry experiments with each of these inhibitory antibodies demonstrated that residues in the active site of the catalytic domain of ADAMTS13 are differentially exposed to solvent in the presence and absence of monoclonal antibody binding. These results support the hypothesis that inhibition of ADAMTS13 in iTTP may not necessarily occur because the antibodies directly prevent VWF binding, but instead because of allosteric effects that impair VWF cleavage, likely by affecting the conformation of the catalytic center in the protease domain of ADAMTS13. Our findings provide novel insight into the mechanism of autoantibody-mediated inhibition of ADAMTS13 and pathogenesis of iTTP.

Anti-BCMA/CD19 CAR T Cells with Early Immunomodulatory Maintenance for Multiple Myeloma Responding to Initial or Later-Line Therapy

We conducted a phase I clinical trial of anti-BCMA chimeric antigen receptor T cells (CART-BCMA) with or without anti-CD19 CAR T cells (huCART19) in multiple myeloma (MM) patients responding to third- or later-line therapy (phase A, N = 10) or high-risk patients responding to first-line therapy (phase B, N = 20), followed by early lenalidomide or pomalidomide maintenance. We observed no high-grade cytokine release syndrome (CRS) and only one instance of low-grade neurologic toxicity. Among 15 subjects with measurable disease, 10 exhibited partial response (PR) or better; among 26 subjects responding to prior therapy, 9 improved their response category and 4 converted to minimal residual disease (MRD)-negative complete response/stringent complete response. Early maintenance therapy was safe, feasible, and coincided in some patients with CAR T-cell reexpansion and late-onset, durable clinical response. Outcomes with CART-BCMA + huCART19 were similar to CART-BCMA alone. Collectively, our results demonstrate favorable safety, pharmacokinetics, and antimyeloma activity of dual-target CAR T-cell therapy in early lines of MM treatment.

SIGNIFICANCE

CAR T cells in early lines of MM therapy could be safer and more effective than in the advanced setting, where prior studies have focused. We evaluated the safety, pharmacokinetics, and efficacy of CAR T cells in patients with low disease burden, responding to current therapy, combined with standard maintenance therapy. This article is highlighted in the In This Issue feature, p. 101.

Development and pharmacokinetic assessment of a fully canine anti-PD-1 monoclonal antibody for comparative translational research in dogs with spontaneous tumors

PD-1 checkpoint inhibitors have revolutionized the treatment of patients with different cancer histologies including melanoma, renal cell carcinoma, and non-small cell lung carcinoma. However, only a subset of patients show a dramatic clinical response to treatment. Despite intense biomarker discovery efforts, no single robust, prognostic correlation has emerged as a valid outcome predictor. Immune competent, pet dogs develop spontaneous tumors that share similar features to human cancers including chromosome aberrations, molecular subtypes, immune signatures, tumor heterogeneity, metastatic behavior, and chemotherapeutic response. As such, they represent a valuable parallel patient population in which to investigate predictive biomarkers of checkpoint inhibition. However, the lack of a validated, non-immunogenic, canine anti-PD-1 antibody for pre-clinical use hinders this comparative approach and prevents potential clinical benefits of PD-1 blockade being realized in the veterinary clinic. To address this, fully canine single-chain variable fragments (scFvs) that bind canine (c)PD-1 were isolated from a comprehensive canine scFv phage display library. Lead candidates were identified that bound with high affinity to cPD-1 and inhibited its interaction with canine PD-L1 (cPD-L1). The lead scFv candidate re-formatted into a fully canine IgGD reversed the inhibitory effects of cPD-1:cPD-L1 interaction on canine chimeric antigen receptor (CAR) T cell function. In vivo administration showed no toxicity and revealed favorable pharmacokinetics for a reasonable dosing schedule. These results pave the way for clinical trials with anti-cPD-1 in canine cancer patients to investigate predictive biomarkers and combination regimens to inform human clinical trials and bring a promising checkpoint inhibitor into the veterinary armamentarium.

A Keratinocyte-Tethered Biologic Enables Location-Precise Treatment in Mouse Vitiligo

Despite the central role of IFN-γ in vitiligo pathogenesis, systemic IFN-γ neutralization is an impractical treatment option owing to strong immunosuppression. However, most patients with vitiligo present with <20% affected body surface area, which provides an opportunity for localized treatments that avoid systemic side effects. After identifying keratinocytes as key cells that amplify IFN-γ signaling during vitiligo, we hypothesized that tethering an IFN-γ‒neutralizing antibody to keratinocytes would limit anti‒IFN-γ effects on the treated skin for the localized treatment. To that end, we developed a bispecific antibody capable of blocking IFN-γ signaling while binding to desmoglein expressed by keratinocytes. We characterized the effect of the bispecific antibody in vitro, ex vivo, and in a mouse model of vitiligo. Single-photon emission computed tomography/computed tomography biodistribution and serum assays after local footpad injection revealed that the bispecific antibody had improved skin retention, faster elimination from the blood, and less systemic IFN-γ inhibition than the nontethered version. Furthermore, the bispecific antibody conferred localized protection almost exclusively to the treated footpad during vitiligo, which was not possible by local injection of the nontethered anti‒IFN-γ antibody. Thus, keratinocyte tethering proved effective while significantly diminishing the off-tissue effects of IFN-γ blockade, offering a safer treatment strategy for localized skin diseases, including vitiligo.

Targeted In Vivo Loading of Red Blood Cells Markedly Prolongs Nanocarrier Circulation

Engineering drug delivery systems for prolonged pharmacokinetics (PK) has been an ongoing pursuit for nearly 50 years. The gold standard for PK enhancement is the coating of nanoparticles with polymers, namely polyethylene glycol (PEGylation), which has been applied in several clinically used products. In the present work, we utilize the longest circulating and most abundant component of blood─the erythrocyte─to improve the PK behavior of liposomes. Antibody-mediated coupling of liposomes to erythrocytes was tested in vitro to identify a loading dose that did not adversely impact the carrier cells. Injection of erythrocyte targeting liposomes into mice resulted in a ∼2-fold improvement in the area under the blood concentration versus time profile versus PEGylated liposomes and a redistribution from the plasma into the cellular fraction of blood. These results suggest that in vivo targeting of erythrocytes is a viable strategy to improve liposome PK relative to current, clinically viable strategies.

Potent suppression of neuroendocrine tumors and gastrointestinal cancers by CDH17CAR T cells without toxicity to normal tissues

Gastrointestinal cancers (GICs) and neuroendocrine tumors (NETs) are often refractory to therapy after metastasis. Adoptive cell therapy using chimeric antigen receptor (CAR) T cells, though remarkably efficacious for treating leukemia, is yet to be developed for solid tumors such as GICs and NETs. Here we isolated a llama-derived nanobody, VHH1, and found that it bound cell surface adhesion protein CDH17 upregulated in GICs and NETs. VHH1-CAR T cells (CDH17CARTs) killed both human and mouse tumor cells in a CDH17-dependent manner. CDH17CARTs eradicated CDH17-expressing NETs and gastric, pancreatic and colorectal cancers in either tumor xenograft or autochthonous mouse models. Notably, CDH17CARTs do not attack normal intestinal epithelial cells, which also express CDH17, to cause toxicity, likely because CDH17 is localized only at the tight junction between normal intestinal epithelial cells. Thus, CDH17 represents a class of previously unappreciated tumor-associated antigens that is 'masked' in healthy tissues from attack by CAR T cells for developing safer cancer immunotherapy.

Development of a fully canine anti-canine CTLA4 monoclonal antibody for comparative translational research in dogs with spontaneous tumors

The immune checkpoint inhibitor (ICI) ipilimumab has revolutionized the treatment of patients with different cancer histologies, including melanoma, renal cell carcinoma, and non-small cell lung carcinoma. However, only a subset of patients shows dramatic clinical responses to treatment. Despite intense biomarker discovery efforts linked to clinical trials using CTLA4 checkpoint blockade, no single prognostic correlate has emerged as a valid predictor of outcome. Client-owned, immune competent, pet dogs develop spontaneous tumors that exhibit similar features to human cancers, including shared chromosome aberrations, molecular subtypes, immune signatures, tumor heterogeneity, metastatic behavior, and response to chemotherapy. As such, they represent a valuable parallel patient population in which to investigate novel predictive biomarkers and rational therapeutic ICI combinations. However, the lack of validated, non-immunogenic, canine ICIs for preclinical use hinders this comparative approach. To address this, fully canine single-chain variable fragments (scFvs) that bind canine CTLA4 were isolated from a comprehensive canine scFv phage display library. A lead candidate for clinical development was selected based on its subnanomolar binding affinity to canine CTLA4 and its ability to prevent CTLA4 binding to CD80/CD86 and promote T cell proliferation and effector function. In vivo mouse studies revealed pharmacokinetics similar to isotype control IgG with no evidence of short-term adverse effects. This work paves the way for in vivo analysis of the first fully canine, anti-canine CTLA4 antibody to promote anti-tumor immunity in dogs with immune-responsive cancers and provide an important comparative tool to investigate correlative biomarkers of response and mechanisms of resistance to CTLA4 checkpoint inhibition.

Red blood cells: The metamorphosis of a neglected carrier into the natural mothership for artificial nanocarriers

Drug delivery research pursues many types of carriers including proteins and other macromolecules, natural and synthetic polymeric structures, nanocarriers of diverse compositions and cells. In particular, liposomes and lipid nanoparticles represent arguably the most advanced and popular human-made nanocarriers, already in multiple clinical applications. On the other hand, red blood cells (RBCs) represent attractive natural carriers for the vascular route, featuring at least two distinct compartments for loading pharmacological cargoes, namely inner space enclosed by the plasma membrane and the outer surface of this membrane. Historically, studies of liposomal drug delivery systems (DDS) astronomically outnumbered and surpassed the RBC-based DDS. Nevertheless, these two types of carriers have different profile of advantages and disadvantages. Recent studies showed that RBC-based drug carriers indeed may feature unique pharmacokinetic and biodistribution characteristics favorably changing benefit/risk ratio of some cargo agents. Furthermore, RBC carriage cardinally alters behavior and effect of nanocarriers in the bloodstream, so called RBC hitchhiking (RBC-HH). This article represents an attempt for the comparative analysis of liposomal vs RBC drug delivery, culminating with design of hybrid DDSs enabling mutual collaborative advantages such as RBC-HH and camouflaging nanoparticles by RBC membrane. Finally, we discuss the key current challenges faced by these and other RBC-based DDSs including the issue of potential unintended and adverse effect and contingency measures to ameliorate this and other concerns.

Pathologically stiff erythrocytes impede contraction of blood clots

BACKGROUND

Blood clot contraction, volume shrinkage of the clot, is driven by platelet contraction and accompanied by compaction of the erythrocytes and their gradual shape change from biconcave to polyhedral, with the resulting cells named polyhedrocytes.

OBJECTIVES

Here, we examined the role of erythrocyte rigidity on clot contraction and erythrocyte shape transformation.

METHODS

We used an optical tracking methodology that allowed us to quantify changes in contracting clot size over time.

RESULTS AND CONCLUSIONS

Erythrocyte rigidity has been shown to be increased in sickle cell disease (SCD), and in our experiments erythrocytes from SCD patients were 4-fold stiffer than those from healthy subjects. On average, the final extent of clot contraction was reduced by 53% in the clots from the blood of patients with SCD compared to healthy individuals, and there was significantly less polyhedrocyte formation. To test if this reduction in clot contraction was due to the increase in erythrocyte rigidity, we used stiffening of erythrocytes via chemical cross-linking (glutaraldehyde), rigidifying Wrightb antibodies (Wrb ), and naturally more rigid llama ovalocytes. Results revealed that stiffening erythrocytes result in impaired clot contraction and fewer polyhedrocytes. These results demonstrate the role of erythrocyte rigidity in the contraction of blood clots and suggest that the impaired clot contraction/shrinkage in SCD is due to the reduced erythrocyte deformability, which may be an underappreciated mechanism that aggravates obstructiveness of erythrocyte-rich (micro)thrombi in SCD.

A human monoclonal antibody against the distal carboxyl terminus of ADAMTS-13 modulates its susceptibility to an inhibitor in thrombotic thrombocytopenic purpura

BACKGROUND

Immune thrombotic thrombocytopenic purpura (iTTP) is a potentially fatal thrombotic microangiopathy, resulting from a severe deficiency of plasma ADAMTS-13 (A Disintegrin And Metalloproteinase with ThromboSpondin type 1 motif, member 13) activity. IgG-type autoantibodies are primarily responsible for the inhibition of plasma ADAMTS-13 activity. However, the mechanism underlying autoantibody-mediated inhibition is not fully understood.

OBJECTIVE

The purpose of the present study is to determine the role of IgG autoantibodies against various carboxyl-terminal domains of ADAMTS-13 in regulating ADAMTS-13 activity and its inhibition.

METHOD

Various human monoclonal antibodies isolated by phage display, recombinant protein expression and purification, and biochemical analyses were employed for the study.

RESULTS

Our results demonstrate for the first time that a human monoclonal antibody fragment, the single chain fragment of the variable region (scFv) isolated from a patient with acute iTTP that binds the distal carboxyl-terminus of ADAMTS-13, is able to activate ADAMTS-13 and increase the proteolytic cleavage of a FRETS-VWF73 substrate; moreover, binding of such a human monoclonal antibody against the carboxyl-terminus of ADAMTS-13 to plasma ADAMTS-13 appears to modulate inhibition by another human monoclonal antibody (i.e., scFv4-20), also isolated from an iTTP patient, that targets the spacer domain of ADAMTS-13. These results provide new insights into our understanding of the pathogenesis of iTTP.

CCR5-edited CD4+ T cells augment HIV-specific immunity to enable post-rebound control of HIV replication

BackgroundWe conducted a phase I clinical trial that infused CCR5 gene-edited CD4+ T cells to determine how these T cells can better enable HIV cure strategies.MethodsThe aim of trial was to develop RNA-based approaches to deliver zinc finger nuclease (ZFN), evaluate the effect of CCR5 gene-edited CD4+ T cells on the HIV-specific T cell response, test the ability of infused CCR5 gene-edited T cells to delay viral rebound during analytical treatment interruption, and determine whether individuals heterozygous for CCR5 Δ32 preferentially benefit. We enrolled 14 individuals living with HIV whose viral load was well controlled by antiretroviral therapy (ART). We measured the time to viral rebound after ART withdrawal, the persistence of CCR5-edited CD4+ T cells, and whether infusion of 10 billion CCR5-edited CD4+ T cells augmented the HIV-specific immune response.ResultsInfusion of the CD4+ T cells was well tolerated, with no serious adverse events. We observed a modest delay in the time to viral rebound relative to historical controls; however, 3 of the 14 individuals, 2 of whom were heterozygous for CCR5 Δ32, showed post-viral rebound control of viremia, before ultimately losing control of viral replication. Interestingly, only these individuals had substantial restoration of HIV-specific CD8+ T cell responses. We observed immune escape for 1 of these reinvigorated responses at viral recrudescence, illustrating a direct link between viral control and enhanced CD8+ T cell responses.ConclusionThese findings demonstrate how CCR5 gene-edited CD4+ T cell infusion could aid HIV cure strategies by augmenting preexisting HIV-specific immune responses.REGISTRATIONClinicalTrials.gov NCT02388594.FundingNIH funding (R01AI104400, UM1AI126620, U19AI149680, T32AI007632) was provided by the National Institute of Allergy and Infectious Diseases (NIAID), the National Institute on Drug Abuse (NIDA), the National Institute of Mental Health (NIMH), and the National Institute of Neurological Disorders and Stroke (NINDS). Sangamo Therapeutics also provided funding for these studies.

Adoptive T cell immunotherapy for medullary thyroid carcinoma targeting GDNF family receptor alpha 4

Metastatic medullary thyroid cancer (MTC) is a rare but often aggressive thyroid malignancy with a 5-year survival rate of less than 40% and few effective therapeutic options. Adoptive T cell immunotherapy using chimeric antigen receptor (CAR)-modified T cells (CAR Ts) is showing encouraging results in the treatment of cancer, but development is challenged by the availability of suitable target antigens. We identified glial-derived neurotrophic factor (GDNF) family receptor alpha 4 (GFRα4) as a putative antigen target for CAR-based therapy of MTC. We show that GFRα4 is highly expressed in MTC, in parafollicular cells within the thyroid from which MTC originates, and in normal thymus. We isolated two single-chain variable fragments (scFvs) targeting GFRα4 isoforms a and b by antibody phage display. CARs bearing the CD3ζ and the CD137 costimulatory domains were constructed using these GFRα4-specific scFvs. GFRα4-specific CAR Ts trigger antigen-dependent cytotoxicity and cytokine production in vitro, and they are able to eliminate tumors derived from the MTC TT cell line in an immunodeficient mouse xenograft model of MTC. These data demonstrate the feasibility of targeting GFRα4 by CAR T and support this antigen as a promising target for adoptive T cell immunotherapy and other antibody-based therapies for MTC.

Bispecific and split CAR T cells targeting CD13 and TIM3 eradicate acute myeloid leukemia

Chimeric antigen receptor (CAR) T cells have radically improved the treatment of B cell-derived malignancies by targeting CD19. The success has not yet expanded to treat acute myeloid leukemia (AML). We developed a Sequentially Tumor-Selected Antibody and Antigen Retrieval (STAR) system to rapidly isolate multiple nanobodies (Nbs) that preferentially bind AML cells and empower CAR T cells with anti-AML efficacy. STAR-isolated Nb157 specifically bound CD13, which is highly expressed in AML cells, and CD13 CAR T cells potently eliminated AML in vitro and in vivo. CAR T cells bispecific for CD13 and TIM3, which are upregulated in AML leukemia stem cells, eradicated patient-derived AML, with much reduced toxicity to human bone marrow stem cells and peripheral myeloid cells in mouse models, highlighting a promising approach for developing effective AML CAR T cell therapy.

Synthetic nucleic acid antibody prophylaxis confers rapid and durable protective immunity against Zika virus challenge

Significant concerns have arisen over the past 3 y from the increased global spread of the mosquito-borne flavivirus, Zika. Accompanying this spread has been an increase in cases of the devastating birth defect microcephaly as well as of Guillain-Barré syndrome in adults in many affected countries. Currently there is no vaccine or therapy for this infection; however, we sought to develop a combination approach that provides more rapid and durable protection than traditional vaccination alone. A novel immune-based prophylaxis/therapy strategy entailing the facilitated delivery of a synthetic DNA consensus prME vaccine along with DNA-encoded anti-ZIKV envelope monoclonal antibodies (dMAb) were developed and evaluated for antiviral efficacy. This immediate and persistent protection strategy confers the ability to overcome shortcomings inherent with conventional active vaccination or passive immunotherapy. A collection of novel dMAbs were developed which were potent against ZIKV and could be expressed in serum within 24-48 h of in vivo administration. The DNA vaccine, from a previous development, was potent after adaptive immunity was developed, protecting against infection, brain and testes pathology in relevant mouse challenge models and in an NHP challenge. Delivery of potent dMAbs protected mice from the same murine viral challenge within days of delivery. Combined injection of dMAb and the DNA vaccine afforded rapid and long-lived protection in this challenge model, providing an important demonstration of the advantage of this synergistic approach to pandemic outbreaks.

B cell maturation antigen-specific CAR T cells are clinically active in multiple myeloma

BACKGROUND

Chimeric antigen receptor (CAR) T cells are a promising therapy for hematologic malignancies. B-cell maturation antigen (BCMA) is a rational target in multiple myeloma (MM).

METHODS

We conducted a phase I study of autologous T cells lentivirally-transduced with a fully-human, BCMA-specific CAR containing CD3ζ and 4-1BB signaling domains (CART-BCMA), in subjects with relapsed/refractory MM. Twenty-five subjects were treated in 3 cohorts: 1) 1-5 x 108 CART-BCMA cells alone; 2) Cyclophosphamide (Cy) 1.5 g/m2 + 1-5 x 107 CART-BCMA cells; and 3) Cy 1.5 g/m2 + 1-5 x 108 CART-BCMA cells. No pre-specified BCMA expression level was required.

RESULTS

CART-BCMA cells were manufactured and expanded in all subjects. Toxicities included cytokine release syndrome and neurotoxicity, which were grade 3-4 in 8 (32%) and 3 (12%) subjects, respectively, and reversible. One subject died at day 24 from candidemia and progressive myeloma, following treatment for severe CRS and encephalopathy. Responses (based on treated subjects) were seen in 4/9 (44%) in cohort 1, 1/5 (20%) in cohort 2, and 7/11 (64%) in cohort 3, including 5 partial, 5 very good partial, and 2 complete responses, 3 of which were ongoing at 11, 14, and 32 months. Decreased BCMA expression on residual MM cells was noted in responders; expression increased at progression in most. Responses and CART-BCMA expansion were associated with CD4:CD8 T cell ratio and frequency of CD45RO-CD27+CD8+ T cells in the pre-manufacturing leukapheresis product.

CONCLUSION

CART-BCMA infusions with or without lymphodepleting chemotherapy are clinically active in heavily-pretreated MM patients.

TRIAL REGISTRATION

NCT02546167.

FUNDING

University of Pennsylvania-Novartis Alliance and NIH.

Proteomic Analysis of Pemphigus Autoantibodies Indicates a Larger, More Diverse, and More Dynamic Repertoire than Determined by B Cell Genetics

In autoantibody-mediated diseases such as pemphigus, serum antibodies lead to disease. Genetic analysis of B cells has allowed characterization of antibody repertoires in such diseases but would be complemented by proteomic analysis of serum autoantibodies. Here, we show using proteomic analysis that the serum autoantibody repertoire in pemphigus is much more polyclonal than that found by genetic studies of B cells. In addition, many B cells encode pemphigus autoantibodies that are not secreted into the serum. Heavy chain variable gene usage of serum autoantibodies is not shared among patients, implying targeting of the coded proteins will not be a useful therapeutic strategy. Analysis of autoantibodies in individual patients over several years indicates that many antibody clones persist but the proportion of each changes. These studies indicate a dynamic and diverse autoantibody response not revealed by genetic studies and explain why similar overall autoantibody titers may give variable disease activity.

Targeting thrombomodulin to circulating red blood cells augments its protective effects in models of endotoxemia and ischemia-reperfusion injury

Endothelial thrombomodulin (TM) regulates coagulation and inflammation via several mechanisms, including production of activated protein C (APC). Recombinant APC and soluble fragments of TM (sTM) have been tested in settings associated with insufficiency of the endogenous TM/APC pathway, such as sepsis. We previously designed a fusion protein of TM [single-chain variable fragment antibody (scFv)/TM] targeted to red blood cells (RBCs) to improve pharmacokinetics and antithrombotic effects without increasing bleeding. Here, scFv/TM was studied in mouse models of systemic inflammation and ischemia-reperfusion injury. Injected concomitantly with or before endotoxin, scFv/TM provided more potent protection against liver injury and release of pathological mediators than sTM, showing similar efficacy at up to 50-fold lower doses. scFv/TM provided protection when injected after endotoxin, whereas sTM did not, and augmented APC production by thrombin ∼50-fold more than sTM. However, scFv/TM injected after endotoxin did not reduce thrombin/antithrombin complexes; nor did antibodies that block APC anticoagulant activity suppress the prophylactic anti-inflammatory effect of scFv/TM. Therefore, similar to endogenous TM, RBC-anchored scFv/TM activates several protective pathways. Finally, scFv/TM was more effective at reducing cerebral infarct volume and alleviated neurological deficits than sTM after cerebral ischemia/reperfusion injury. These results indicate that RBC-targeted scFv/TM exerts multifaceted cytoprotective effects and may find utility in systemic and focal inflammatory and ischemic disorders.-Carnemolla, R., Villa, C. H., Greineder, C. F., Zaitseva, S., Patel, K. R., Kowalska, M. A., Atochin, D. N., Cines, D. B., Siegel, D. L., Esmon, C. T., Muzykantov, V. R. Targeting thrombomodulin to circulating red blood cells augments its protective effects in models of endotoxemia and ischemia-reperfusion injury.

Erythrocytes as Carriers for Drug Delivery in Blood Transfusion and Beyond

Red blood cells (RBCs) are innate carriers that can also be engineered to improve the pharmacokinetics and pharmacodynamics of many drugs, particularly biotherapeutics. Successful loading of drugs, both internally and on the external surface of RBCs, has been demonstrated for many drugs including anti-inflammatory, antimicrobial, and antithrombotic agents. Methods for internal loading of drugs within RBCs are now entering clinical use. Although internal loading can result in membrane disruption that may compromise biocompatibility, surface loading using either affinity or chemical ligands offers a diverse set of approaches for the production of RBC drug carriers. A wide range of surface determinants is potentially available for this approach, although there remains a need to characterize the effects of coupling agents to these surface proteins. Somewhat surprisingly, recent data also suggest that red cell-mediated delivery may confer tolerogenic immune effects. Questions remaining before widespread application of these technologies include determining the optimal loading protocol, source of RBCs, and production logistics, as well as addressing regulatory hurdles. Red blood cell drug carriers, after many decades of progress, are now poised to enter the clinic and broaden the potential application of RBCs in blood transfusion.

Abstract 2295: GDNF family receptor alpha 4 (GFRa4)-targeted adoptive T-cell immunotherapy for medullary thyroid carcinoma

Metastatic medullary thyroid cancer (MTC) is a rare, but often aggressive, thyroid malignancy with a 5-year survival rate of 28% and few effective therapeutic options. Adoptive T-cell immunotherapy using chimeric antigen receptor (CAR)-modified T cells (CARTs) is showing encouraging results in the treatment of cancer, but development is challenged by the availability of suitable target antigens. We identified glial-derived neurotrophic factor (GDNF) family receptor alpha 4 (GFRα4), which associates with the RET receptor tyrosine kinase, as a putative antigenic target for CAR-based therapy of MTC. Using RNA in situ hybridization (RNAscope) and quantitative RT-PCR, we show that GFRα4 is highly expressed in MTC. Normal tissue expression of GFRα4 mRNA is restricted to parafollicular cells (C-cells) within the thyroid, the normal cell type from which MTC originates, and normal thymus.Based upon the highly restricted expression, we generated two high affinity single chain variable fragments (scFvs) targeting GFRα4 isoforms a and b by selecting a naïve rabbit antibody library by phage display. Second generation CARs bearing the CD137 costimulatory domain were constructed using these GFRα4-specific scFvs. GFRα4-specific CARTs trigger antigen-dependent cytotoxicity and cytokine production in vitro, and they are able to control pre-established TT cell tumors in an immunodeficient mouse xenograft model of MTC. These data demonstrate the feasibility of targeting GFRα4 by CARTs, and support this molecule as a promising target for adoptive T cell immunotherapy and other antibody-based therapy of MTC.

Citation Format: Vijay G. Bhoj, Selene Nunez-Cruz, Kenneth Zhou, Dimitrios Arhontoulis, Michael Feldman, Keith Mansfield, Haiyong Peng, Christoph Rader, Don L. Siegel, Michael C. Milone. GDNF family receptor alpha 4 (GFRa4)-targeted adoptive T-cell immunotherapy for medullary thyroid carcinoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2295.

ADAMTS13 autoantibodies cloned from patients with acquired thrombotic thrombocytopenic purpura: 1. Structural and functional characterization in vitro

BACKGROUND

Acquired thrombotic thrombocytopenia purpura (TTP) is a life-threatening illness caused by autoantibodies that decrease the activity of ADAMTS13, the von Willebrand factor-cleaving protease. Despite efficacy of plasma exchange, mortality remains high and relapse is common. Improved therapies may come from understanding the diversity of pathogenic autoantibodies on a molecular or genetic level. Cloning comprehensive repertoires of patient autoantibodies can provide the necessary tools for studying immunobiology of disease and developing animal models.

STUDY DESIGN AND METHODS

Anti-ADAMTS13 antibodies were cloned from four patients with acquired TTP using phage display and characterized with respect to genetic origin, inhibition of ADAMTS13 proteolytic activity, and epitope specificity. Anti-idiotypic antisera raised to a subset of autoantibodies enabled comparison of their relatedness to each other and to polyclonal immunoglobulin (Ig)G in patient plasma.

RESULTS

Fifty-one unique antibodies were isolated comprising epitope specificities resembling the diversity found in circulating patient IgG. Antibodies directed both to the amino terminal domains and to those requiring the ADAMTS13 cysteine-rich/spacer region for binding inhibited proteolytic activity, while those solely targeting carboxy-terminal domains were noninhibitory. Anti-idiotypic antisera raised to a subset of antibody clones crossreacted with and reduced the inhibitory activity of polyclonal IgG from a set of unrelated patients.

CONCLUSIONS

Anti-ADAMTS13 autoantibodies isolated by repertoire cloning display the diversity of epitope specificities found in patient plasma and provide tools for developing animal models of acquired TTP. Shared idiotypes of inhibitory clones with circulating IgG from multiple patients suggest common features of pathogenic autoantibodies that could be exploited for developing more targeted therapies.

Modulation of natural IgM autoantibodies to oxidative stress-related neo-epitopes on apoptotic cells in newborns of mothers with anti-Ro autoimmunity

At birth, the human immune system already contains substantial levels of polymeric IgM, that include autoantibodies to neo-epitopes on apoptotic cells (ACs) that are proposed to play homeostatic and anti-inflammatory roles. Yet the biologic origins and developmental regulation of these naturally arising antibodies remain poorly understood. Herein, we report that levels of IgM-antibodies to malondialdehyde (MDA) protein adducts, a common type of in vivo generated oxidative stress-related neoepitope, directly correlate with the relative binding of neonatal-IgM to ACs. Levels of IgM to phosphorylcholine (PC), a natural antibody prevalent in adults, were relatively scant in cord blood, while there was significantly greater relative representation of IgM anti-MDA antibodies in newborns compared to adults. To investigate the potential interrelationships between neonatal IgM with pathogenic IgG-autoantibodies, we studied 103 newborns born to autoimmune mothers with IgG anti-Ro (i.e., 70 with neonatal lupus and 33 without neonatal lupus). In these subjects the mean levels of IgM anti-Ro60 were significantly higher than in the newborns from non-autoimmune mothers. In contrast, levels of IgM anti-MDA in IgG anti-Ro exposed neonates were significantly lower than in neonates from non-autoimmune mothers. The presence or absence of neonatal lupus did not appear to influence the total levels of IgM in the anti-Ro exposed newborns. Taken together, our studies provide evidence that the immune development of the natural IgM-repertoire may be affected, and become imprinted by, the transfer of maternal IgG into the fetus.

ADAMTS13 autoantibodies cloned from patients with acquired thrombotic thrombocytopenic purpura: 2. Pathogenicity in an animal model

BACKGROUND

Acquired thrombotic thrombocytopenic purpura (TTP) is a potentially fatal disease in which ultralarge von Willebrand factor (UL-VWF) multimers accumulate as a result of autoantibody inhibition of the VWF protease, ADAMTS13. Current treatment is not specifically directed at the responsible autoantibodies and in some cases is ineffective or of transient benefit. More rational, reliable, and durable therapies are needed, and a human autoantibody-mediated animal model would be useful for their development. Previously, TTP patient anti-ADAMTS13 single-chain variable-region fragments (scFv's) were cloned that inhibited ADAMTS13 proteolytic activity in vitro and expressed features in common with inhibitory immunoglobulin G in patient plasma. Here, pathogenicity of these scFv's is explored in vivo by transfecting mice with inhibitory antibody cDNA.

STUDY DESIGN AND METHODS

Hydrodynamic tail vein injection of naked DNA encoding human anti-ADAMTS13 scFv was used to create sustained ADAMTS13 inhibition in mice. Accumulation of UL-VWF multimers was measured and formation of platelet (PLT) thrombi after focal or systemic vascular injury was examined.

RESULTS

Transfected mice expressed physiological plasma levels of human scFv and developed sustained ADAMTS13 inhibition and accumulation of unprocessed UL-VWF multimers. Induced focal endothelial injury generated PLT thrombi extending well beyond the site of initial injury, and systemic endothelial injury induced thrombocytopenia, schistocyte formation, PLT thrombi, and death.

CONCLUSIONS

These results demonstrate for the first time the ability of human recombinant monovalent anti-ADAMTS13 antibody fragments to recapitulate key pathologic features of untreated acquired TTP in vivo, validating their clinical significance and providing an animal model for testing novel targeted therapeutic approaches.

CAR-T Cell Therapies From the Transfusion Medicine Perspective

The use of chimeric antigen receptor (CAR)-T cell therapy for the treatment of hematologic malignancies has generated significant excitement over the last several years. From a transfusion medicine perspective, the implementation of CAR-T therapy as a potential mainstay treatment for not only hematologic but also solid-organ malignancies represents a significant opportunity for growth and expansion. In this review, we will describe the rationale for the development of genetically redirected T cells as a cancer therapeutic, the different elements that are required to engineer these cells, as well as an overview of the process by which patient cells are harvested and processed to create and subsequently validate CAR-T cells. Finally, we will briefly describe some of the toxicities and clinical efficacy of CAR-T cells in the setting of patients with advanced malignancy.

Dog erythrocyte antigen 1: mode of inheritance and initial characterization

BACKGROUND

The dog erythrocyte antigen (DEA) 1 blood group system remains poorly defined.

OBJECTIVES

The purpose of the study was to determine the DEA 1 mode of inheritance and to characterize the DEA 1 antigen and alloantibodies.

ANIMALS

Canine research colony families, clinic canine patients, and DEA 1.2+ blood bank dogs were studied.

METHODS

Canine blood was typed by flow cytometry and immunochromatographic strips using anti-DEA 1 monoclonal antibodies. Gel column experiments with polyclonal and immunoblotting with monoclonal anti-DEA 1 antibodies were performed to analyze select samples. Cross-reactivity of human typing reagents against canine RBC and one monoclonal anti-DEA 1 antibody against human RBC panels was assessed.

RESULTS

Typing of 12 families comprising 144 dogs indicated an autosomal dominant inheritance with ≥ 4 alleles: DEA 1- (0) and DEA 1+ weak (1+), intermediate (2+), and strong (3+ and 4+). Samples from 6 dogs previously typed as DEA 1.2+ were typed as DEA 1+ or DEA 1- using monoclonal antibodies. Human typing reagents produced varied reactions in tube agglutination experiments against DEA 1+ and DEA 1- RBC. Polypeptide bands were not detected on immunoblots using a monoclonal anti-DEA 1 antibody, therefore the anti-DEA 1 antibody may be specific for conformational epitopes lost during processing.

CONCLUSIONS

The autosomal dominant inheritance of DEA 1 with ≥ 4 alleles indicates a complex blood group system; the antigenicity of each DEA 1+ type will need to be determined. The biochemical nature of the DEA 1 antigen(s) appears different from human blood group systems tested.

NY-ESO-1-specific TCR-engineered T cells mediate sustained antigen-specific antitumor effects in myeloma

Despite recent therapeutic advances, multiple myeloma (MM) remains largely incurable. Here we report results of a phase I/II trial to evaluate the safety and activity of autologous T cells engineered to express an affinity-enhanced T cell receptor (TCR) recognizing a naturally processed peptide shared by the cancer-testis antigens NY-ESO-1 and LAGE-1. Twenty patients with antigen-positive MM received an average 2.4 × 10(9) engineered T cells 2 d after autologous stem cell transplant. Infusions were well tolerated without clinically apparent cytokine-release syndrome, despite high IL-6 levels. Engineered T cells expanded, persisted, trafficked to marrow and exhibited a cytotoxic phenotype. Persistence of engineered T cells in blood was inversely associated with NY-ESO-1 levels in the marrow. Disease progression was associated with loss of T cell persistence or antigen escape, in accordance with the expected mechanism of action of the transferred T cells. Encouraging clinical responses were observed in 16 of 20 patients (80%) with advanced disease, with a median progression-free survival of 19.1 months. NY-ESO-1-LAGE-1 TCR-engineered T cells were safe, trafficked to marrow and showed extended persistence that correlated with clinical activity against antigen-positive myeloma.

Carbohydrate sequence of the prostate cancer-associated antigen F77 assigned by a mucin O-glycome designer array

Monoclonal antibody F77 was previously raised against human prostate cancer cells and has been shown to recognize a carbohydrate antigen, but the carbohydrate sequence of the antigen was elusive. Here, we make multifaceted approaches to characterize F77 antigen, including binding analyses with the glycolipid extract of the prostate cancer cell line PC3, microarrays with sequence-defined glycan probes, and designer arrays from the O-glycome of an antigen-positive mucin, in conjunction with mass spectrometry. Our results reveal F77 antigen to be expressed on blood group H on a 6-linked branch of a poly-N-acetyllactosamine backbone. We show that mAb F77 can also bind to blood group A and B analogs but with lower intensities. We propose that the close association of F77 antigen with prostate cancers is a consequence of increased blood group H expression together with up-regulated branching enzymes. This is in contrast to other epithelial cancers that have up-regulated branching enzymes but diminished expression of H antigen. With knowledge of the structure and prevalence of F77 antigen in prostate cancer, the way is open to explore rationally its application as a biomarker to detect F77-positive circulating prostate cancer-derived glycoproteins and tumor cells.

The receptor for advanced glycation end products mediates lung endothelial activation by RBCs

The receptor for advanced glycation end products (RAGE) is a multiligand pattern recognition receptor implicated in multiple disease states. Although RAGE is expressed on systemic vascular endothelium, the expression and function of RAGE on lung endothelium has not been studied. Utilizing in vitro (human) and in vivo (mouse) models, we established the presence of RAGE on lung endothelium. Because RAGE ligands can induce the expression of RAGE and stored red blood cells express the RAGE ligand N(ε)-carboxymethyl lysine, we investigated whether red blood cell (RBC) transfusion would augment RAGE expression on endothelium utilizing a syngeneic model of RBC transfusion. RBC transfusion not only increased lung endothelial RAGE expression but enhanced lung inflammation and endothelial activation, since lung high mobility group box 1 and vascular cell adhesion molecule 1 expression was elevated following transfusion. These effects were mediated by RAGE, since endothelial activation was absent in RBC-transfused RAGE knockout mice. Thus, RAGE is inducibly expressed on lung endothelium, and one functional consequence of RBC transfusion is increased RAGE expression and endothelial activation.

Mannose receptor (MR) engagement by mesothelin GPI anchor polarizes tumor-associated macrophages and is blocked by anti-MR human recombinant antibody

Tumor-infiltrating macrophages respond to microenvironmental signals by developing a tumor-associated phenotype characterized by high expression of mannose receptor (MR, CD206). Antibody cross-linking of CD206 triggers anergy in dendritic cells and CD206 engagement by tumoral mucins activates an immune suppressive phenotype in tumor-associated macrophages (TAMs). Many tumor antigens are heavily glycosylated, such as tumoral mucins, and/or attached to tumor cells by mannose residue-containing glycolipids (GPI anchors), as for example mesothelin and the family of carcinoembryonic antigen (CEA). However, the binding to mannose receptor of soluble tumor antigen GPI anchors via mannose residues has not been systematically studied. To address this question, we analyzed the binding of tumor-released mesothelin to ascites-infiltrating macrophages from ovarian cancer patients. We also modeled functional interactions between macrophages and soluble mesothelin using an in vitro system of co-culture in transwells of healthy donor macrophages with human ovarian cancer cell lines. We found that soluble mesothelin bound to human macrophages and that the binding depended on the presence of GPI anchor and of mannose receptor. We next challenged the system with antibodies directed against the mannose receptor domain 4 (CDR4-MR). We isolated three novel anti-CDR4-MR human recombinant antibodies (scFv) using a yeast-display library of human scFv. Anti-CDR4-MR scFv #G11 could block mesothelin binding to macrophages and prevent tumor-induced phenotype polarization of CD206(low) macrophages towards TAMs. Our findings indicate that tumor-released mesothelin is linked to GPI anchor, engages macrophage mannose receptor, and contributes to macrophage polarization towards TAMs. We propose that compounds able to block tumor antigen GPI anchor/CD206 interactions, such as our novel anti-CRD4-MR scFv, could prevent tumor-induced TAM polarization and have therapeutic potential against ovarian cancer, through polarization control of tumor-infiltrating innate immune cells.

Impact of pre-existing immunity on gene transfer to nonhuman primate liver with adeno-associated virus 8 vectors

Vectors based on the primate-derived adeno-associated virus serotype 8 (AAV8) are being evaluated in preclinical and clinical models. Natural infections with related AAVs activate memory B cells that produce antibodies capable of modulating the efficacy and safety of the vector. We have evaluated the biology of AAV8 gene transfer in macaque liver, with a focus on assessing the impact of pre-existing humoral immunity. Twenty-one macaques with various levels of AAV neutralizing antibody (NAb) were injected intravenously with AAV8 vector expressing green fluorescent protein. Pre-existing antibody titers in excess of 1:10 substantially diminished hepatocyte transduction that, in the absence of NAbs, was highly efficient. Vector-specific NAb diminished liver deposition of genomes and unexpectedly increased genome distribution to the spleen. The majority of animals showed high-level and stable sequestration of vector capsid protein by follicular dendritic cells of splenic germinal centers. These studies illustrate how natural immunity to a virus that is related to a vector can impact the efficacy and potential safety of in vivo gene therapy. We propose to use the in vitro transduction inhibition assay to evaluate research subjects before gene therapy and to preclude from systemic AAV8 trials those that have titers in excess of 1:10.

Homologous regions of autoantibody heavy chain complementarity-determining region 3 (H-CDR3) in patients with pemphigus cause pathogenicity

Pemphigus is a life-threatening autoimmune disease in which antibodies specific for desmogleins (Dsgs) cause loss of keratinocyte cell adhesion and blisters. In order to understand how antibodies cause pathogenicity and whether there are commonalities among antibodies in different patients that could ultimately be used to target specific therapy against these antibodies, we characterized Dsg-specific mAbs cloned by phage display from 3 patients with pemphigus vulgaris and 2 with pemphigus foliaceus. Variable heavy chain gene usage was restricted, but similar genes were used for both pathogenic and nonpathogenic mAbs. However, the heavy chain complementarity-determining region 3 (H-CDR3) of most pathogenic, but not nonpathogenic, mAbs shared an amino acid consensus sequence. Randomization of the H-CDR3 and site-directed mutagenesis indicated that changes in this sequence could block pathogenicity but not necessarily binding. In addition, for 2 antibodies with longer H-CDR3s, a tryptophan was critical for pathogenicity but not binding, a result that is consistent with blocking the tryptophan acceptor site that is thought to be necessary for Dsg-mediated adhesion. These studies indicate that H-CDR3 is critical for pathogenicity of a human autoantibody, that a small region (even 1 amino acid) can mediate pathogenicity, and that pathogenicity can be uncoupled from binding in these antibodies.

Rapid isolation of high-affinity human antibodies against the tumor vascular marker Endosialin/TEM1, using a paired yeast-display/secretory scFv library platform

Endosialin/TEM1 is predominantly expressed on neovasculature, thus ideally suited for diagnostic, targeted imaging and therapy of cancer. To isolate TEM1-specific affinity reagents, we thought to screen a recombinant antibody (scFv) library derived from the repertoire of a patient with thrombotic thrombocytopenic purpura (TTP), as autoimmune disorders may produce self-reactive specificities. The yeast-display scFv library was constructed by homologous recombination of the TTP patient repertoire originally expressed on M13 bacteriophage in the novel vector pAGA2 for yeast-display expression. The TTP yeast-display library (10⁹ members) was screened by magnetic and flow sorting with human TEM1 recombinant protein. A pool of yeast-display scFv able to detect 2nM of TEM1 was obtained and transformed into yeast-secreted scFv by homologous recombination using the novel p416 BCCP vector for yeast secretion of biotinylated scFv. Anti-TEM1 yeast-secreted scFv were independently validated in vitro by flow cytometry analysis and ELISA assays, then in vivo biotinylated in N-termini to produce biobodies. Biobody-78 bound specifically to Endosialin/TEM1-expressing ovarian tumor in vivo, with functional stability over 48 h. Our results suggest that our novel paired display-secretory yeast libraries can serve as an ideal platform for the rapid isolation of high-affinity reagents, and that anti-TEM1 biobody-78 can be used for in vitro assays including flow cytometry analysis, as well as in vivo for targeted imaging and therapy of cancer.

Generation and validation of canine single chain variable fragment phage display libraries

Single chain variable region fragments (scFvs) are composed of an immunoglobulin (Ig) variable heavy (VH) and variable light (VL) chain joined by a flexible serine-glycine linker. They represent the smallest antibody fragments that maintain antigen specificity and they hold significant potential for therapeutic antigen targeting in vivo. Here we report on the design and validation of a series of degenerate primers that amplify the recombined variable regions of canine Ig heavy and light chain genes from lymphocyte cDNA. We show that these VH and VL amplicons can be randomly combined by a flexible linker using splicing by overlap extension PCR to form scFv constructs that can be expressed on the surface of M13 bacteriophage. To demonstrate that scFvs with specificity for previously encountered antigens are contained within these scFv phage display libraries we used simple panning procedures to isolate canine parvovirus (CPV) specific scFvs from a library made from the splenocytes of a dog immunized against CPV. These studies reveal the feasibility of this approach for generating diverse canine scFv libraries and pave the way toward future studies to isolate canine antigen-specific scFv of interest that may be tested as targeting agents for the treatment of infectious, inflammatory and neoplastic diseases in the dog.

Update on the cloning of monoclonal anti-desmoglein antibodies from human pemphigus patients: implications for targeted therapy

Autoantibodies in pemphigus foliaceus (PF) and vulgaris (PV) bind to desmoglein (Dsg) 1 and 3, respectively, and cause loss of keratinocyte adhesion. To characterize the pathogenicity and genetics of such antibodies we have used phage display to isolate monoclonal antibodies (mAbs) from patients. PCR is used to clone the heavy and light chain variable region of the peripheral B cells into a vector that creates a phage particle with the antibody expressed on its surface and the cDNA encoding that antibody inside. The library of phage produced from a PF or PV patient are then panned on a plate containing Dsg1 or Dsg3 to isolate clones. The cDNA of each clone is sequenced to characterize the genetics of the expressed mAb. The mAb from each unique clone is tested for pathogenicity either by injecting into normal human skin organ culture or into neonatal mice. Pathogenic antibodies cause typical pemphigus blisters. In both PV and PF patients the heavy chain (VH) genes used for Dsg-binding antibodies are severely restricted. PV and PF patients have both pathogenic and non-pathogenic mAbs. The immunochemical characteristics of the antibodies (including pathogenicity) sort with the VH, not the VL, gene. These monoclonal pathogenic antibodies can be used to screen peptide libraries to find short peptides that block antibody binding. In summary, the antibody response is restricted and, therefore, it may be feasible to target the specific pathogenic antibodies for therapy.

Antibodies to the desmoglein 1 precursor proprotein but not to the mature cell surface protein cloned from individuals without pemphigus

In pemphigus foliaceus (PF), autoantibodies against desmoglein 1 (Dsg1) cause blisters. Using Ab phage display, we have cloned mAbs from a PF patient. These mAbs, like those from a previous patient, were directed against mature Dsg1 (matDsg1) on the cell surface of keratinocytes and precursor Dsg1 (preDsg1) in the cytoplasm. To determine whether individuals without pemphigus have B cell tolerance to Dsg1, we cloned mAbs from two patients with thrombotic thrombocytopenic purpura and a healthy person. We found mAbs against preDsg1, but not matDsg1. All but 1 of the 23 anti-preDsg1 mAbs from PF patients and those without PF used the VH3-09 (or closely related VH3-20) H chain gene, whereas no PF anti-matDsg1 used these genes. V(H) cDNA encoding anti-preDsg1 had significantly fewer somatic mutations than did anti-matDsg1 cDNA, consistent with chronic Ag-driven hypermutation of the latter compared with the former. These data indicate that individuals without PF do not have B cell tolerance to preDsg1 and that loss of tolerance to matDsg1 is not due to epitope shifting of anti-preDsg1 B cells (because of different V(H) gene usage). However, presentation of peptides from Dsg1 by preDsg1-specific B cells may be one step in developing autoimmunity in PF.

Isolation of high affinity human scFv antibodies against mouse and human tumor endothelial marker 1 (TEM1) using yeast-display scFv library derived from an autoimmune patient. (42.4)

TEM1 is predominantly expressed on neovasculature, thus ideally suited for targeted imaging and therapy for cancer. Yeast has emerged as an alternative technology for display and selection of recombinant antibody fragments (scFv). Because autoimmune disorders may produce self-reactive specificities, an autoimmune repertoire derived from a patient with thrombotic thrombocytopenic purpura (TTP) was screened to isolate anti-TEM1 scFv.

A yeast-display scFv library was constructed by homologous recombination of the TTP patient repertoire originally expressed on M13 bacteriophage. The library (10^9 members) was flow sorted with decreasing antigen concentration until a scFv pool detecting 2 nM of rhTEM1/GST was obtained. Secreted scFv were expressed and 470 scFv were screened by ELISA for binding to rhTEM1/GST. Nearly 50% of the scFv gave colorimetric signals higher than 3 standard deviations above background. No cross-reactivity with GST control protein was detected. Sequencing of 29 scFv identified 8 unique antibodies. Two of these clones exhibited Kd's in the 100 pM range and bound to both mouse and human TEM1. Such cross-reactive anti-mouse/human TEM will facilitate proof of concept for the development of novel anti-angiogenic targeted therapies.

Our data suggest that the use of large scFv libraries derived from autoimmune patient repertoires may provide a rich source of high affinity antibody reagents to therapeutically relevant molecules.

This work was supported by the Claneil Foundation

Post-transplant outcomes of induction therapy for myeloma: thalidomide and dexamethasone versus doxorubicin, vincristine, and dexamethasone prior to high-dose melphalan with autologous stem cell support

High-dose melphalan with autologous stem cell support improves survival as part of initial therapy for myeloma. Previous studies of pre-transplant induction regimens have compared paraprotein response rates but not long-term outcomes after transplant. We reviewed the records of all patients with multiple myeloma who received an autologous stem cell transplant at the University of Pennsylvania Medical Center. We compared outcomes for 69 patients who received high-dose melphalan conditioning after January 1, 2003 as part of initial therapy for myeloma, including 41 patients who received anthracycline-based induction (VAD or DVD) and 28 patients who received thalidomide and dexamethasone induction. Baseline characteristics in these two groups were not different, though potentially clinically important differences were apparent in assignment to post-transplant consolidation and maintenance therapy. Despite similar response rates during induction therapy, thalidomide and dexamethasone induction was associated with better progression-free survival (hazard ratio 0.18, P = 0.011) after transplant. This effect persisted in multivariable regression models including baseline characteristics and post-transplant treatment. Overall survival was not different between the two groups. These results suggest that the use of thalidomide during induction therapy may lead to improved long-term outcomes after transplant. Future trials comparing induction therapies should examine progression-free and overall survival after transplant to confirm this benefit.

Isolation of pathogenic monoclonal anti-desmoglein 1 human antibodies by phage display of pemphigus foliaceus autoantibodies

Pemphigus foliaceus (PF) is a blistering disease caused by autoantibodies to desmoglein 1 (Dsg1) that cause loss of epidermal cell adhesion. To better understand PF pathophysiology, we used phage display to isolate anti-Dsg1 mAbs as single-chain variable fragments (scFvs) from a PF patient. Initial panning of the library isolated only non-pathogenic scFvs. We then used these scFvs to block non-pathogenic epitopes and were able to isolate two unique scFvs, each of which caused typical PF blisters in mice or human epidermis models, showing that a single mAb can disrupt Dsg1 function to cause disease. Both pathogenic scFvs bound conformational epitopes in the N terminus of Dsg1. Other PF sera showed a major antibody response against the same or nearby epitopes defined by these pathogenic scFvs. Finally, we showed restriction of the heavy-chain gene usage of all anti-Dsg1 clones to only five genes, which determined their immunological properties despite promiscuous light-chain gene usage. These mAbs will be useful for studying Dsg1 function and mechanisms of blister formation in PF and for developing targeted therapies and tools to monitor disease activity.

Targeting Pemphigus Autoantibodies through their Heavy-Chain Variable Region Genes

Pemphigus vulgaris (PV) is a potentially fatal blistering disease characterized by autoantibodies against cell surface adhesion proteins desmoglein (Dsg) 3 and Dsg1. Previous studies using phage display to clone Dsg-reactive monoclonal antibodies from a PV patient demonstrated that a limited number of antibody variable region genes encode the autoantibody repertoire, with different genes for pathogenic and non-pathogenic mAbs. Here, we investigated the feasibility of specific autoantibody targeting in pemphigus. We produced rabbit anti-idiotypic antibodies against two pathogenic and two non-pathogenic PV mAbs. Antisera inhibited binding of the immunizing mAb to Dsgs by ELISA as well as pathogenicity against cultured human keratinocytes. Antisera also inhibited other mAbs using the same variable region heavy chain (V(H)) genes, despite different light chains or somatic mutations. Additionally, peptide phage display identified peptide sequences that bound PV mAbs in a V(H)-specific manner. To evaluate the therapeutic potential of V(H) gene-targeted reagents, preimmune sera and antisera were used to adsorb pathogenic antibodies from PV sera. Pooled antisera significantly reduced pathogenic activity from the original PV patient's serum and bound pathogenic antibodies from two other PV sera, suggesting shared autoantibody V(H) gene usage among PV patients. Together, these data suggest novel V(H) gene-targeted approaches toward PV treatment.

Prognostic value of FDG-PET scan imaging in lymphoma patients undergoing autologous stem cell transplantation

We conducted a retrospective analysis of 50 lymphoma patients (Hodgkin's disease and non-Hodgkin's lymphoma) who had an 18F-fluoro-deoxyglucose positron emission tomography (FDG-PET) scan after at least two cycles of salvage chemotherapy and before autologous stem cell transplantation (ASCT) at our institution. The patients were categorized into FDG-PET negative (N = 32) and positive (N = 18) groups. The median follow-up after ASCT was 19 months (range: 3-59). In the FDG-PET-negative group, the median progression-free survival (PFS) was 19 months (range: 2-59) with 15 (54%) patients without progression at 12 months after ASCT. The median overall survival (OS) for this group was not reached. In the FDG-PET-positive group, the median PFS was 5 months (range: 1-19) with only one (7%) patient without progression at 12 months after ASCT. The median OS was 19 months (range: 1-34). In the FDG-PET-negative group, chemotherapy-resistant patients by CT-based criteria had a comparable outcome to those with chemotherapy-sensitive disease. A positive FDG-PET scan after salvage chemotherapy and prior ASCT indicates an extremely poor chance of durable response after ASCT.

Nephrogenic fibrosing dermopathy/nephrogenic systemic fibrosis with diaphragmatic involvement in a patient with respiratory failure

Nephrogenic fibrosing dermopathy/nephrogenic systemic fibrosis (NFD/NSF) is a disorder occurring exclusively in patients with renal disease. Until recently, it has been considered a fibrosing disorder essentially confined to the skin and underlying superficial soft tissue. Recent reports, however, have described patients with involvement of other organ systems, suggesting that this disorder is actually a systemic disease with preferential cutaneous manifestations. We describe a patient with end-stage renal disease with diagnosed NFD/NSF who subsequently developed respiratory failure leading to his death. Autopsy findings showed NFD/NSF involving the skin of all extremities, as well as diffuse diaphragm involvement.

Phage display tools for blood typing

Current technologies used in blood banks for blood group antigen typing and other pretransfusion tests are extraordinarily labor-intensive, prone to human error, and an order of magnitude more expensive per test than those in other clinical laboratories. With a growing shortage of skilled medical technologists, dwindling supplies of human plasma-derived phenotyping reagents, and an inherent difficulty in fully automating agglutination-based methodologies, the ability to perform rapid and accurate pretransfusion testing in a cost-effective manner has become a significant challenge. This paper reviews the latest advances in the use of phage display technologies to address these issues through the development of inexpensive and renewable blood bank testing reagents that are amenable to high-throughput, automatable assay systems.

Long-term event-free survivors after high-dose therapy and autologous stem-cell transplantation for low-grade follicular lymphoma

Although follicular lymphoma (FL) is generally responsive to conventional-dose chemotherapy, improved survival in patients with this disease has been difficult to demonstrate. High-dose chemo/radiotherapy followed by autologous stem-cell transplantation (ASCT) can improve response rates, although its effects on survival remain controversial. Between 1990 and 2003, we transplanted 49 patients with low-grade FL at our institution. Twenty-two patients (45%) had undergone histologic transformation at the time of ASCT. In all, 44 patients (90%) had relapsed disease and five patients (10%) were resistant to chemotherapy at the time of transplantation. After ASCT, 30 patients (61%) were in complete remission (CR). The median overall survival (OS) has not been reached, while the median event-free survival (EFS) is 2.4 years. At a median follow-up of 5.5 years (longest 12.4 years), a plateau has been reached with 56% of patients remaining alive, and 35% event-free. ASCT was well tolerated except for two (4%) treatment-related deaths. In multivariable analysis, CR after ASCT and age less than 60 years are the best predictors of EFS and OS. ASCT is thus a safe therapeutic approach in FL, resulting in long-term EFS and OS for some patients, even with transformed disease.