Patent Publication Number: US-2022227872-A1

Title: Anti-tem1 antibodies and antigen-binding portions thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a National Stage Application under 35 U.S.C. § 371 of International Application No. PCT/US2020/035157 filed May 29, 2020, which claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 62/855,559 filed May 31, 2019, the disclosures of all of which are hereby incorporated by reference in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to the field of molecular biology. More particularly, the invention provides antibodies and antigen-binding portions thereof that bind to mammalian tumor endothelial marker 1 (TEM1) and therapeutic compositions thereof, as well as methods of using such antibodies, including methods for treating cancer and methods of diagnosis. 
     BACKGROUND 
     The present disclosure relates to the generation of antibodies and antigen-binding portions thereof that recognize and bind tumor endothelial marker 1 (TEM1), a cell surface antigen characteristic of tumor pericytes and cells of tumor stroma. 
     TEM1, also known as CD248 or endosialin, is a highly restricted 165-kDa cell surface glycoprotein expressed by tumor pericytes and fibroblasts in a broad range of human cancers but not detected in the respective cell types in many normal tissues. TEM1 is a 165-kDa single-pass transmembrane glycoprotein that has been classified as a C type lectin-like membrane receptor. It has multiple extracellular domains consisting of three EGF-like domains, a sushi-like domain, and a C lectin-like domain. TEM1 was shown to interact with proteins of the extracellular matrix (Fibronectin, Collagen I), mediating cell adhesion and migration. TEM1 also interacts with the tumor secreted protein LGALS3BP, a protein involved in cell adhesion and migration, acting also as a pro-angiogenic factor. 
     TEM1 is broadly expressed in human cancer, including but not limited to, sarcomas and carcinomas. Due to the protein&#39;s expression across the stroma of many human tumors, the low to absent expression of TEM1 in normal tissues, and the accessibility of TEM1 from the vascular circulation, TEM1 is an attractive molecule for diagnostics and therapeutics. 
     SUMMARY OF THE INVENTION 
     Provided herein are antibodies and antigen-binding portions thereof that selectively bind to TEM1, as well as methods of using such antibodies and antigen-binding portions thereof. 
     In one aspect, provided is an antibody or antigen-binding portion thereof which binds to TEM1, wherein the antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising three heavy chain CDRs (HCDR1, HCDR2 and HCDR3) and a light chain variable region comprising three light chain CDRs (LCDR1, LCDR2 and LCDR3), and wherein HCDR1 comprises the amino acid sequence of SEQ ID NO:16 or SEQ ID NO:19; HCDR2 comprises the amino acid sequence of SEQ ID NO:17 or SEQ ID NO:20; HCDR3 comprises the amino acid sequence of SEQ ID NO:22 or SEQ ID NO:48; LCDR1 comprises the amino acid sequence of SEQ ID NO:11 or SEQ ID NO:14; LCDR2 comprises the amino acid sequence SNN or the sequence of SEQ ID NO:15; and LCDR3 comprises the amino acid sequence of SEQ ID NO:13. 
     In one aspect, provided is an antibody or antigen-binding portion thereof which binds to TEM1, wherein the antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising three heavy chain CDRs (HCDR1, HCDR2 and HCDR3) and a light chain variable region comprising three light chain CDRs (LCDR1, LCDR2 and LCDR3), and wherein HCDR1 comprises the amino acid sequence of SEQ ID NO:16 or SEQ ID NO:19; HCDR2 comprises the amino acid sequence of SEQ ID NO:17 or SEQ ID NO:20; HCDR3 comprises the amino acid sequence of SEQ ID NO:18 or SEQ ID NO:21; LCDR1 comprises the amino acid sequence of SEQ ID NO:11 or SEQ ID NO:14; LCDR2 comprises the amino acid sequence SNN or the sequence of SEQ ID NO:15; and LCDR3 comprises the amino acid sequence of SEQ ID NO:13. 
     In one aspect, provided is an antibody or antigen-binding portion thereof which binds to TEM1, wherein the antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising three heavy chain CDRs (HCDR1, HCDR2 and HCDR3) and a light chain variable region comprising three light chain CDRs (LCDR1, LCDR2 and LCDR3), and wherein HCDR1 comprises the amino acid sequence of SEQ ID NO:28 or SEQ ID NO:31; HCDR2 comprises the amino acid sequence of SEQ ID NO:29 or SEQ ID NO:32; HCDR3 comprises the amino acid sequence of SEQ ID NO:30 or SEQ ID NO:33; LCDR1 comprises the amino acid sequence of SEQ ID NO:23 or SEQ ID NO:26; LCDR2 comprises the amino acid sequence DAS or the sequence of SEQ ID NO:27; and LCDR3 comprises the amino acid sequence of SEQ ID NO:25. 
     In one aspect, provided is an antibody or antigen-binding portion thereof which binds to TEM1, wherein the antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising three heavy chain CDRs (HCDR1, HCDR2 and HCDR3) and a light chain variable region comprising three light chain CDRs (LCDR1, LCDR2 and LCDR3), and wherein HCDR1 comprises the amino acid sequence of SEQ ID NO:39 or SEQ ID NO:42; HCDR2 comprises the amino acid sequence of SEQ ID NO:40 or SEQ ID NO:43; HCDR3 comprises the amino acid sequence of SEQ ID NO:41 or SEQ ID NO:49; LCDR1 comprises the amino acid sequence of SEQ ID NO:34 or SEQ ID NO:37; LCDR2 comprises the amino acid sequence STY or the sequence of SEQ ID NO:38; and LCDR3 comprises the amino acid sequence of SEQ ID NO:36. 
     In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising a sequence that is at least 90% identical to SEQ ID NO: 6 and a light chain variable region comprising a sequence that is at least 90% identical to SEQ ID NO: 5. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising the sequence of SEQ ID NO: 6 and a light chain variable region comprising the sequence of SEQ ID NO: 5. 
     In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising a sequence that is at least 90% identical to SEQ ID NO: 4 and a light chain variable region comprising a sequence that is at least 90% identical to SEQ ID NO: 3. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising the sequence of SEQ ID NO: 4 and a light chain variable region comprising the sequence of SEQ ID NO: 3. 
     In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising a sequence that is at least 90% identical to SEQ ID NO: 8 and a light chain variable region comprising a sequence that is at least 90% identical to SEQ ID NO: 7. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising the sequence of SEQ ID NO: 8 and a light chain variable region comprising the sequence of SEQ ID NO: 6. 
     In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising a sequence that is at least 90% identical to SEQ ID NO: 10 and a light chain variable region comprising a sequence that is at least 90% identical to SEQ ID NO: 9. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising the sequence of SEQ ID NO: 10 and a light chain variable region comprising the sequence of SEQ ID NO: 9. 
     Provided is an anti-TEM1 antibody or antigen-binding portion thereof, wherein the antibody is selected from antibodies 1C1mut, 1C1, 2B11, and 3B6. Provided is an anti-TEM1 antibody or antigen-binding portion thereof, wherein the antigen-binding portion is provided as a scFv, Fv, Fab′, Fab, F(ab′)2, scFv-Fc fusion, BiTE, tri-lobed bidirectional T-cell engager (Tri-lobed Bi-specific T cell engager (tB)), chimeric antigen receptor, or diabody. 
     Provided herein is an antigen-binding portion of an anti-TEM1 antibody disclosed herein wherein the antigen-binding portion is a scFv. In some embodiments, the scFv is fused to the constant region of a Fab. In some embodiments, the antigen-binding portion is fused to the constant region of a Fab using a linker comprising SEQ ID NO:46 or SEQ ID NO:47. In some embodiments, the Fab comprises a VH-CH1 region or fragment thereof and a VL-CL1 region or fragment thereof, wherein the VH-CH1 region is derived from IgG1, and wherein the VL-CL1 region is derived from a kappa light chain. In some embodiments, the VH-CH1 region is derived from human IgG1 and further comprises a S64E and/or a S66V mutation and the VL-CL1 region is derived from a human kappa light chain and further comprises a S69L and/or a T71S mutation. In some embodiments, the Fab binds to a T-cell antigen. 
     Provided herein is a chimeric antigen receptor (CAR), wherein the CAR comprises an scFv comprising the antigen-binding portion of an anti-TEM1 antibody disclosed herein and further comprises a transmembrane domain and one or more intracellular domains. In some embodiments, the CAR comprises: a spacer derived from CD28, a transmembrane domain derived from CD28, an intracellular domain derived from CD28, and a domain comprising immunoreceptor tyrosine-based activation motifs (ITAMs) derived from CD3-zeta. 
     Provided herein is an anti-TEM1 antibody or antigen-binding portion thereof, wherein the antibody or antigen-binding portion thereof is a multispecific or a bispecific antibody or antigen-binding portion thereof. In some embodiments, the anti-TEM1 antibody or antigen-binding portion thereof has the isotype IgG1. In some embodiments, the anti-TEM1 antibody or antigen-binding portion thereof is deglycosylated. 
     Provided herein is an anti-TEM1 antibody or antigen-binding portion thereof, wherein the antibody or antigen-binding portion is conjugated to a therapeutic moiety, an imaging moiety, and/or an affinity tag. 
     Provided herein is an anti-TEM1 antibody or antigen-binding portion thereof, wherein the antibody or antigen-binding portion thereof competes for binding to TEM1 with an antibody or antigen-binding portion thereof according to according to any of the preceding claims. 
     Provided herein is a nucleic acid molecule encoding an anti-TEM1 antibody or antigen-binding portion thereof disclosed herein. Provided herein is a vector comprising a nucleic acid molecule encoding an anti-TEM1 antibody or antigen-binding portion thereof disclosed herein. Also provided is a cell comprising vector comprising a nucleic acid molecule encoding an anti-TEM1 antibody or antigen-binding portion thereof disclosed herein. 
     Provided herein is a method of treating cancer in a subject in need thereof, the method comprising administering to the subject an effective amount of an anti-TEM1 antibody or antigen-binding portion thereof disclosed herein. In some embodiments, the cancer is sarcoma, carcinoma, melanoma, pancreatic cancer, thyroid cancer, lung cancer, colorectal cancer, squamous cancer, prostate cancer, breast cancer, bladder cancer, or gastric cancer. 
     Provided herein is a method of reducing tumor growth in a subject in need thereof, the method comprising administering to the subject an effective amount of an anti-TEM1 antibody or antigen-binding portion thereof disclosed herein. 
     Provided herein is a method of reducing tumor metastasis in a subject in need thereof, the method comprising administering to the subject an effective amount of an anti-TEM1 antibody or antigen-binding portion thereof disclosed herein. 
     Provided herein is a method of reducing tumor-associated fibrosis in a subject in need thereof, the method comprising administering to the subject an effective amount of an anti-TEM1 antibody or antigen-binding portion thereof disclosed herein. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  illustrates the structures of different anti-TEM1 functional formats described in this disclosure.  FIG. 1A  is a schematic representation of an scFv-Fc fusion molecule.  FIG. 1B  is a schematic representation of an anti-TEM1 scFv-Fc fusion molecule utilized in a recombinant cell assay.  FIG. 1C  is a schematic representation of a Tri-lobed Bi-specific T cell engager (tB) molecule. A tumor antigen-specific scFv is fused to both heavy and light chain of a chimeric humanized anti-CD3 Fab. The human CH1-Ck interface serves as the heterodimerization scaffold and has been reinforced by stabilizing mutations, shown in bold stick representation.  FIG. 1D  is a schematic representation of a chimeric antigen receptor (CAR). 
         FIG. 2  confirms selective binding of anti-TEM1 scFv-Fcs to human and murine TEM1. 1C1 shows preferential binding to human TEM1 +  cells. Binding of reformatted and purified scFv-Fc (hIgG1) clones (2 μg/ml) to human and murine cell lines was determined using fluorescence-activated cell sorting (FACS). A673, human Ewing&#39;s sarcoma; SK-N-AS, human neuroblastoma; 2H11, murine tumor vascular endothelium; TC1, murine lung adenocarcinoma; HEK293-6E, human embryonic kidney; HT-1080, human fibrosarcoma; MDA-MB-231, human mammary carcinoma; MS1, murine pancreatic islet endothelium. 
         FIG. 3  illustrates the apparent 70-80-fold differential affinity of 1C1 and 1C1mut to human TEM1 using two distinct analyte/ligand Surface Plasmon Resonance (SPR) formats. SPR monovalent affinity determination of parental clone 1C1 (upper sensorgrams) and an affinity-matured variant, 1C1mut (lower sensorgrams), formatted as either a BiTE (left) or a scFv-Fc (right), and using either hTEM1-SpyC (left) or 1C1/1C1mut scFv-Fc (right) as the immobilized ligand. Soluble analyte concentration ranges were 100, 50, 25, 12.5 and 0 nM for 1C1, and 5, 2.5, 1.25, 0.625 and 0 nM for 1C1mut experiments. hTEM1-FL=full-length human TEM1 extracellular domain. 
         FIG. 4  illustrates that 1C1mut effectively recognizes both human and murine TEM1 +  cells. Binding of 1C1mut variant scFv-Fc (0.1 μg/ml) to endogenous human (A673) and murine (2H11) TEM1 +  cell lines was determined using FACS. HEK293-6E cells served as TEM1 −  control cells. 
         FIG. 5  illustrates the TEM1 +  selectivity of 1C1 and 1C1mut. Anti-TEM1 scFv-Fc clones (2 μg/ml) bound to HEK293T cells transiently transfected with native FL-hTEM1 (right), but not to cells transfected with an irrelevant cell surface-presented molecule (2nd generation CAR) (left) as determined by FACS. 
         FIG. 6  illustrates that 1C1 effectively recognizes canine TEM1 +  cells. Binding of anti-TEM1 scFv-Fc 1C1 clone (1 μg/ml) to HEK293-6E suspension cells transiently transfected with a native canine full-length FL-TEM1 reporter construct ( FIG. 6A ) was determined using FACS ( FIG. 6B ). 
         FIG. 7  illustrates that 1C1 effectively recognizes canine TEM1 in the context of endogenously expressing tumor cell lines. Binding of anti-TEM1 scFv-Fc 1C1 clone (0.2 μg/ml) to 2 out of 3 canine hemangiosarcoma tumor cell lines was determined using FACS. EFB is a canine hemangiosarcoma cell line derived from a metastatic brain tumor. EFS and FROG are canine hemangiosarcoma cell lines derived from the spleen. 
         FIG. 8  illustrates that anti-TEM1-Tri-lobed Bi-specific T cell engager (tB) specifically activate both CD8 +  and CD4 +  primary human T-cells in the presence of TEM1-expressing A673 cells. Upregulation of early activation markers CD69 and CD25 (upper right gate) was measured by flow cytometry after 16 h of co-culture. Expression of CD69/CD25 by CD8+ T-cells co-cultured with Raji cells (TEM1 − ) is shown as a control. 
         FIG. 9A  illustrates IFN-γ secretion by primary human T-cells activated with anti-TEM1 Tri-lobed Bi-specific T cell engager (tB) variants (1 nM) in the presence of different target cell lines: A673 (hTEM1 + ), SK-N-AS (hTEM1 + ), and AsPC-1 (hTEM1 − ). Cytokine concentration in the supernatant was measured after 24 h of co-culture.  FIG. 9B  illustrates that anti-TEM1 Tri-lobed Bi-specific T cell engager (tB) molecules redirect primary human T-cells to kill TEM1-expressing A673 cells. Tri-lobed Bi-specific T cell engagers (tBs) were added at 1 nM or 0.1 nM and LDH activity was measured after 24 h as a reporter of lysed cells. Specific cell killing was calculated as a percentage of complete lysis achieved with 1% Triton-X 100. 
         FIG. 10  illustrates real-time kinetics of cell killing by primary human T-cells activated with 0.6 nM or 60 pM 1C1mut or sc78 Tri-lobed Bi-specific T cell engager (tB). Image-based acquisition of Cytotox Red signal indicates lysis of TEM1 +  A673 cells (closed symbols and connected lines), while TEM1-negative AsPC-1 cells (open symbols) are spared. 
         FIG. 11  shows a comparison of different Tri-lobed Bi-specific T cell engagers (tBs) (comprising high- or low-affinity scFvs in a mono- or bivalent format) as mediators of cytotoxic T-cell activity. Lysis of hTEM1 +  target cells (A673) by polyclonal human T-cells was quantified based on LDH released from dead cells. Cell killing is expressed as a fraction of maximal lysis achieved with 1 Triton-X 100. 
         FIG. 12  shows that an anti-TEM1 Tri-lobed Bi-specific T cell engager (tB) reduces the growth of TEM1 +  tumors in vivo. Purified human pan-T-cells were activated with CD3 and CD28 and combined with A673 tumor cells prior to co-inoculation at a sub-cutaneous site. For an untreated tumor-only control, no T-cells were used (“untreated”). 1, 24 and 48 h after tumor cell inoculation, mice were injected (I.V., tail vein) with either 1 mg/kg of a Tri-lobed Bi-specific T cell engager (tB) comprising anti-TEM1 scFv 1C1mut or with PBS (“T cells only”).  FIG. 12A  illustrates that injection of the anti-TEM1 Tri-lobed Bi-specific T cell engager (tB) was well tolerated by the mice.  FIG. 12B  (tumor volume over time) and  FIG. 12C  (tumor volume at point of sacrifice) illustrate that bulk human T-cells had a general inhibitory effect on A673 tumor engraftment. However, administration of the anti-TEM1 Tri-lobed Bi-specific T cell engager (tB) completely prevented establishment of tumor (no outgrowth observed a considerable period after the last treatment). 
         FIG. 13  illustrates Jurkat NFAT-mCherry reporter cells transduced with anti-TEM1 CARs (1C1, 1C1m, sc78) and an anti-CD19 positive control CAR (FMC63), and co-cultured with target cells. All CAR constructs incorporated an in-frame C-terminal green fluorescent protein (GFP) reporter. A673 cells (TEM1 + , CD19 − ) were the co-cultured cognate target cells for the anti-TEM1 CARs, and Raji cells (TEM1 − , CD19 + ) were co-cultured as the cognate target for the anti-CD19 (FMC63) CAR. HEK293-6E (TEM1 − , CD19 − ) cells were co-cultured as a negative control for all CARs. NT, non-transduced. 
         FIG. 14  illustrates that primary human T cells transduced with anti-TEM1 CARs expressed the early activation markers CD69 and CD25 when co-cultured in the presence of A673 target cells (TEM1 + , CD19 − ; upper panel). Negative control data was generated using AsPC-1 cells (TEM1 − , CD19 − ; lower panel). Raji cells (TEM1 − , CD19 + ) were used to stimulate the positive control anti-CD19 (FMC63) CAR T-cells (upper panel, plot on the far right). CD69/CD25 expression was quantified by flow cytometry after 16 h of co-culture. NT, non-transduced. 
         FIG. 15  illustrates real-time kinetics of target cell killing (A673 cells; TEM1 + , CD19 − ) by 1C1m anti-TEM1 CAR-T-cells over the course of 48 h. Cell killing was quantified based on the image-based acquisition of Cytotox Red signal. NT, non-transduced; CD19, an anti-CD19 negative control CAR. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Anti-TEM1 Antibodies and Antigen-Binding Portions Thereof 
     Provided herein are antibodies and antigen-binding portions thereof that selectively bind to TEM1, as well as methods of using such antibodies and antigen-binding portions thereof. The sequence of human TEM 1 (endosialin precursor; GenPep Accession NP_065137) is provided in SEQ ID NO:1. The sequence of murine TEM1 (UniprotKB/Swiss-Prot: Q91V98 (CD248 MOUSE)) is provided in SEQ ID NO:2. In some embodiments, the anti-TEM1 antibodies or antigen-binding portions thereof disclosed herein bind to human TEM1, to murine TEM1, and/or to canine TEM1. 
     As used herein, the term “antibody” refers to an immunoglobulin molecule comprising four polypeptide chains, two heavy (H) chains and two light (L) chains inter-connected by disulfide bonds, as well as multimers thereof (e.g., IgM). In a typical antibody, each heavy chain comprises a heavy chain variable region (VH) and a heavy chain constant region. The heavy chain constant region may comprise three domains, CH1, CH2 and CH3. Each light chain may comprise a light chain variable region (VL) and a light chain constant region. The light chain constant region may comprise one domain (CL1). The VH and VL regions can be further subdivided into regions of hypervariability, termed complementarity determining regions (CDRs), interspersed with regions that are more conserved, termed framework regions (FR). Each VH and VL may be composed of three CDRs and four FRs, arranged from amino-terminus to carboxy-terminus in the following order: FR1, CDR1, FR2, CDR2, FR3, CDR3, FR4. 
     As used herein, the term “Complementarity Determining Regions” (CDRs) refers to portions of an antibody variable domain or antigen-binding portion thereof that are (typically) involved in antigen binding. Each variable domain typically has three CDR regions identified as CDR1, CDR2 and CDR3. Each CDR can comprise amino acid residues from a CDR as defined by e.g. Kabat (i.e., about residues 24-34 (L1), 50-56 (L2) and 89-97 (L3) in the light chain variable domain and 31-35 (H1), 50-65 (H2) and 95-102 (H3) in the heavy chain variable domain (Kabat et al., Sequences of Proteins of Immunological Interest, 5th Ed. Public Health Service, National Institutes of Health, Bethesda, Md. (1987, 1991)). Each CDR can also comprise amino acid residues from a “hypervariable loop” (i.e., about residues 26-32 (L1), 50-52 (L2) and 91-96 (L3) in the light chain variable domain and 26-32 (H1), 53-55 (H2) and 96-101 (H3) in the heavy chain variable domain (Chothia &amp; Lesk 196 J. Mol. Biol. 901 (1987)). In some instances, a CDR can include amino acids from both a CDR region defined according to Kabat and a hypervariable loop. The Kabat residue designations do not always correspond directly with the linear numbering of the amino acid residues (primary amino acid sequence). The actual linear amino acid sequence may contain fewer or additional amino acids than in the strict Kabat numbering corresponding to a shortening of, or insertion into, a structural component, whether framework or CDR, of the basic variable domain structure. The correct Kabat numbering of residues may be determined for a given antibody or antigen-binding portion thereof by alignment of residues of homology in the sequence of the antibody or antigen-binding portion thereof with a “standard” Kabat numbered sequence. Alternatively, a CDR can be defined according to the ImMunoGeneTics (IMGT) system (Lefranc, M.-P. et al., Dev. Comp. Immunol., 27, 55-77 (2003)). 
     As used herein, the terms “antigen-binding portion” of an antibody, and the like, include any naturally occurring, enzymatically obtainable, synthetic, or genetically engineered polypeptide or glycoprotein that specifically binds an antigen to form a complex. Antigen-binding portions of an antibody may be derived, e.g., from full antibody molecules using any suitable standard techniques such as proteolytic digestion or recombinant genetic engineering techniques involving the manipulation and expression of DNA encoding antibody variable and optionally constant domains. 
     An antigen-binding portion of an antibody may comprise at least one variable domain. In antigen-binding portion having a VH domain associated with a VL domain, the VH and VL domains may be situated relative to one another in any suitable arrangement. For example, the variable region may be dimeric and contain VH-VH, VH-VL or VL-VL dimers. Alternatively, the antigen-binding portion may contain a monomeric VH or VL domain. 
     In certain embodiments, an antigen-binding portion may contain at least one variable domain covalently linked to at least one constant domain. Non-limiting, exemplary configurations of variable and constant domains that may be found within an antigen-binding portion disclosed herein include: (i) VH-CH1; (ii) VH-CH2; (iii) VH-CH3; (iv) VH-CH1-CH2; (v) VH-CH1-CH2-CH3; (vi) VH-CH2-CH3; (vii) VH-CL; (viii) VL-CH1; (ix) VL-CH2; (x) VL-CH3; (xi) VL-CH1-CH2; (xii) VL-CH1-CH2-CH3; (xiii) VL-CH2-CH3; and (xiv) VL-CL. In any configuration of variable and constant domains, including any of the exemplary configurations listed above, the variable and constant domains may be either directly linked to one another or may be linked by a full or partial hinge or linker region. A hinge region may consist of at least 2 (e.g., 5, 10, 15, 20, 40, 60 or more) amino acids which result in a flexible or semi-flexible linkage between adjacent variable and/or constant domains in a single polypeptide molecule. Moreover, an antigen-binding portion of an antibody provided herein may comprise a homo-dimer or hetero-dimer (or other multimer) of any of the variable and constant domain configurations listed above in non-covalent association with one another and/or with one or more monomeric VH or VL domain (e.g., by disulfide bond(s)). 
     In one embodiment, the antigen-binding portion is provided in the form of a Fab fragment comprising or consisting essentially of a variable (VL) and constant (CL) domain of the light chain and a variable domain (VH) and the first constant domain (CH1) of the heavy chain. 
     In one embodiment, the antigen-binding portion is provided in the form of a Fab′ fragment comprising a free sulfhydryl group. 
     In one embodiment, the antigen-binding portion is provided in the form of F(ab′) 2  fragment, which comprises a bivalent fragment comprising two Fab′ fragments linked by a disulfide bridge at the hinge region. 
     In one embodiment, the antigen-binding portion is provided in the form of a dAb fragment comprising or consisting essentially of a VH domain. 
     In one embodiment, the antigen-binding portion is provided in the form of an Fd fragment comprising or consisting essentially of VH and CH1 domains. 
     In one embodiment, the antigen-binding portion is provided in the form of an Fd′ fragment comprising VH and CH1 domains and one or more cysteine residues at the C-terminus of the CH1 domain. 
     In one embodiment, the antigen-binding portion is provided in the form of a diabody comprising two antigen-binding sites, comprising a heavy chain variable domain (V H ) connected to a light chain variable domain (VL) in the same polypeptide chain. 
     In one embodiment, the antigen-binding portion is provided in the form of an Fv fragment comprising or consisting essentially of the VH and VL domains of antibody, wherein the VH and VL chains of the Fv domains are held together by non-covalent interactions. 
     In one embodiment, the antigen-binding portion is provided in the form of a single-chain Fv or scFv, which comprises or consists essentially of the VH and VL domains of antibody, such that these domains are present in a single polypeptide chain. In one embodiment, the scFv comprises a polypeptide linker between the V H  and V L  domains, which allows the scFv to form the desired structure for antigen binding. See, for example, Pluckthun, 113 Pharmacology Monoclonal Antibodies 269 (Rosenburg &amp; Moore, eds., Springer-Verlag, New York, 1994). In some embodiments, the antigen-binding portion comprises a scFv, which is further fused to an Fc domain. 
     In one embodiment, the antigen-binding portion is provided in the form of a bi-specific T-cell engager (BiTE) comprising two scFv fragments derived from one or two antibodies. 
     In one embodiment, the antigen-binding portion is provided in the form of a tri-lobed bidirectional T-cell engager (Tri-lobed Bi-specific T cell engager (tB)), wherein the Tri-lobed Bi-specific T cell engager (tB) comprises one or more scFv domains that are linked to the constant region of a Fab. Selectivity and T-cell engagement of the Tri-lobed Bi-specific T cell engager (tB) can be modulated, for example, by varying the antigen target of the Fab, the antigen target(s) of the one or more scFv domains, the number of scFv domains present in the Tri-lobed Bi-specific T cell engager (tB) molecule, the affinity of one or more scFv domains to their respective targets, and the length and composition of the linker fusing the one or more scFvs to the Fab constant region. For example, using a higher-affinity scFv can increase the potency of the T-cell engager. Alternatively, strong antigen binding might also be achieved by using more than one low-affinity or medium-affinity scFv, an approach which can further provide for tumor-selective binding of the T-cell engager to target antigens that are expressed at low levels in normal tissues. 
     In one embodiment, the one or more scFvs are derived from the same antibody. In one embodiment, the one or more scFvs bind the same antigen, including, but not limited to, TEM1. In one embodiment, the Tri-lobed Bi-specific T cell engager (tB) comprises scFvs that are derived from more than one antibody. In one embodiment, the Tri-lobed Bi-specific T cell engager (tB) comprises scFvs that bind to different antigens. In one embodiment, the Tri-lobed Bi-specific T cell engager (tB) comprises a single anti-TEM1 scFv. In one embodiment, the Tri-lobed Bi-specific T cell engager (tB) comprises two anti-TEM1 scFv. 
     In one embodiment, the Tri-lobed Bi-specific T cell engager (tB) comprises one high-affinity scFv. In one embodiment, the Tri-lobed Bi-specific T cell engager (tB) comprises two or more low- or medium-affinity scFvs. In one embodiment, the Tri-lobed Bi-specific T cell engager (tB) comprises two low- or medium-affinity scFvs. 
     In one embodiment, the Tri-lobed Bi-specific T cell engager (tB) comprises a Fab comprising a VH1-CH1 domain and a VL-CK domain. In one embodiment, the VH1-CH1 is derived from IgG1. In one embodiment, the VH1-CH1 domain and a VL-C κ  domain are human. In one embodiment, the VH1-CH1 domain comprises an S64E and/or an S66V mutation. In one embodiment, VL-CK comprises an S69L and/or a T71S mutation. 
     In one embodiment, the one or more scFv domains are fused to the C-terminus of the Fab via the constant region of the Fab. In one embodiment, an scFv is fused to the constant region using a linker comprising SEQ ID NOs:46 or 47. In one embodiment, the scFv domain is fused to the VH1-CH1 domain using a linker comprising SEQ ID NO:47. In one embodiment, the scFv domain is fused to the VL-CK domain using a linker comprising SEQ ID NO:46. 
     In one embodiment, the Tri-lobed Bi-specific T cell engager (tB) comprises: (a) a Fab comprising (1) a human VH1-CH1 (IgG1) domain comprising an S64E and an S66V mutation and (2) a human VL-Cκ domain comprising an S69L and an T71S mutation and (b) one or two anti-TEM1 scFvs, wherein the one or more scFv domains are fused to the constant region of the Fab using a linker. 
     In one embodiment, the Tri-lobed Bi-specific T cell engager (tB) comprises: (a) a Fab comprising (1) a human VH1-CH1 (IgG1) domain comprising an S64E and an S66V mutation and (2) a human VL-Cκ domain comprising an S69L and an T71S mutation and (b) an anti-TEM1 scFv, which is fused to the VH1-CH1 domain using a linker comprising SEQ ID NO:47 and/or an anti-TEM1 scFv, which is fused to the VL-Cκ domain using a linker comprising SEQ ID NO:46. In some embodiments, the anti-TEM1 scFv comprises any of the CDRs of any of the anti-TEM1 antibodies or antigen-binding portions thereof disclosed herein. In some embodiments, the anti-TEM1 scFv comprises any of the variable heavy and/or variable light chains of any of the anti-TEM1 antibodies or antigen-binding portions thereof disclosed herein. In one embodiment, the Fab is an anti-CD3 Fab. 
     In one embodiment, the antigen-binding portion is provided in the form of a chimeric antigen receptor (CAR). As used herein, a CAR may refer to artificial T-cell receptor, chimeric T-cell receptor, or chimeric immunoreceptor, for example, and encompass engineered receptors that graft an artificial specificity onto a particular immune effector cell. In some embodiments, CARs direct specificity of the T-cell to a tumor antigen. CARs comprise an intracellular domain, a transmembrane domain, and an extracellular domain comprising a tumor antigen binding region. 
     In one aspect, provided is a CAR comprising an anti-TEM1 binding portion derived from any of the anti-TEM1 antibodies or antigen-binding portions thereof disclosed herein. In one embodiment, provided is a CAR comprising an anti-TEM1 scFv comprising any of the antigen-binding portions thereof disclosed herein. 
     In one aspect, the anti-TEM1 binding portion is fused to a transmembrane domain. Non-limiting examples of transmembrane domains suitable for use in the CAR constructs disclosed herein include transmembrane domains derived from CD3, CD28, CD4, CD8, and ICOS. In some embodiments, the anti-TEM1 binding portion is fused to the transmembrane domain using a spacer. Non-limiting examples of spacers suitable for use in the CAR constructs disclosed herein include spacers derived from CD28, CD4, and CD8a, as well as hinge and constant domains derived from IgG or IgD. 
     In one aspect, the transmembrane domain of the CAR is fused to one or more intracellular domains, wherein at least one of the one or more intracellular domains mediates signal transduction upon antigen binding. Non-limiting examples of intracellular domains to be used in the CARs disclosed herein include intracellular domains derived from CD3ζ, FcR, CD27, CD28, CD137, DAP10, 4-1BB, OX40 and domains comprising immunoreceptor tyrosine-based activation motifs (ITAMs). 
     In one embodiment, provided is an anti-TEM1 CAR comprising: (1) an anti-TEM1 scFV; (2) a spacer derived from CD28, (3) a transmembrane domain derived from CD28, (4) an intracellular domain derived from CD28, and (4) a domain comprising ITAMs derived from CD3. In some embodiments, the anti-TEM1 CAR comprises any of the CDRs of any of the anti-TEM1 antibodies or antigen-binding portions thereof disclosed herein. In some embodiments, the anti-TEM1 CAR comprises any of the variable heavy and/or variable light chains of any of the anti-TEM1 antibodies or antigen-binding portions thereof disclosed herein. 
     In some cases, molecules can be co-expressed with the CAR, including co-stimulatory molecules, reporter genes for imaging (e.g., for positron emission tomography), gene products that conditionally ablate the T-cells upon addition of a pro-drug, homing receptors, chemokines, chemokine receptors, cytokines, and cytokine receptors. 
     In some embodiment, the anti-TEM1 antibodies and antigen-binding portions thereof disclosed herein are provided in a bispecific or multi-specific format. 
     In some embodiments, the anti-TEM1 antibody or antigen-binding portion thereof further comprises one or more an antigen-binding portions directed at second tumor antigen. The term “tumor antigen” as used herein includes both tumor associated antigens (TAAs) and tumor specific antigens (TSAs). A tumor associated antigen means an antigen that is expressed on the surface of a tumor cell in higher amounts than is observed on normal cells or an antigen that is expressed on normal cells during fetal development. A tumor specific antigen is an antigen that is unique to tumor cells and is not expressed on normal cells. The term tumor antigen includes TAAs or TSAs that have been already identified and those that have yet to be identified and includes fragments, epitopes and any and all modifications to the tumor antigens. Not-limiting examples of tumor antigens include CD19, CD20, CD30, CD33, CD38, CD133, BCMA, TEM8, EpCAM, ROR1, Folate Receptor, CD70, MAGE-1, MAGE-2, MAGE-3, CEA, tyrosinase, midkin, BAGE, CASP-8, β-catenin, CA-125, CDK-1, ESO-1, gp75, gp100, MART-1, MUC-1, MUM-1, p53, PAP, PSA, PSMA, ras, trp-1, HER-2, TRP-1, TRP-2, IL13Ralpha, IL13Ralpha2, AIM-2, AIM-3, NY-ESO-1, C9orf112, SART1, SART2, SART3, BRAP, RTN4, GLEA2, TNKS2, KIAA0376, ING4, HSPH1, C13orf24, RBPSUH, C6orf153, NKTR, NSEP1, U2AF1L, CYNL2, TPR GOLGA, BMI1, COX-2, EGFRvIII, EZH2, LICAM, Livin, Livinβ, MRP-3, Nestin, OLIG2, ART1, ART4, B-cycline, Gli1, Cav-1, Cathepsin B, CD74, E-Cadherin, EphA2/Eck, Fra-1/Fosl 1, GAGE-1, Ganglioside/GD2, GnT-V, β1, 6-N, Ki67, Ku70/80, PROX1, PSCA, SOX10, SOX11, Survivin, βhCG, WT1, mesothelin, melan-A, NY-BR-1, NY-CO-58, MN (gp250), telomerase, SSX-2, PRAME, PLK1, VEGF-A, VEGFR2, and Tie-2. 
     In some embodiments, the anti-TEM1 antibodies and antigen-binding portions thereof further comprise one or more antigen-binding portions directed at a T-cell (or other effector immune cell) antigen, including, but not limited to CD3, CD2, CD5, TCRα, TCRβ, CD28, 4-1BB, OX40, GITR, CD16, NKG2D, CD47, and SIRPα. 
     Also provided herein are antigen-binding antibody portions comprising minimal antigen recognition units consisting of the amino acid residues that mimic the hypervariable region of an antibody (e.g., an isolated CDR such as a CDR3 peptide), or a constrained FR3-CDR3-FR4 peptide. 
     Provided herein are anti-TEM1 antibodies or antigen-binding portions thereof, as well as methods of using those anti-TEM1 antibodies or antigen-binding portions thereof, wherein the anti-TEM1 antibody is a chimeric, humanized, or human antibody. 
     As used herein, a “chimeric antibody” refers to a polypeptide comprising at least the antigen-binding portion of an antibody molecule linked to at least part of another protein. 
     As used herein, a “humanized antibody” refers to an antibody with a framework region having substantially the amino acid sequence of a human immunoglobulin and a CDR having substantially the amino acid sequence of a non-human immunoglobulin (the “import” sequences). In certain embodiments, humanization of an antibody can reduce immunogenicity. In certain embodiments, the frameworks of the humanized antibody are a composite of two or more human antibodies. In other embodiments, surface-exposed framework residues of the antibody are replaced with framework residues of a human antibody to form a humanized antibody. In a preferred embodiment, the frameworks are selected to minimize the presence of amino acid sequences predicted to be T-cell epitopes over a wide population range. 
     As used herein, the term “human antibody” refers to an antibody having variable and constant regions derived from human germline immunoglobulin sequences. The human antibodies provided herein may nonetheless include amino acid residues not encoded by human germline immunoglobulin sequences (e.g., mutations introduced by random or site-specific mutagenesis in vitro or by somatic mutation in vivo), for example in the CDRs and in particular CDR3. 
     Provided herein are further other engineered anti-TEM1 molecules, such as domain-specific antibodies, single domain antibodies, domain-deleted antibodies, diabodies, triabodies, tetrabodies, minibodies, nanobodies (e.g., monovalent nanobodies, bivalent nanobodies, etc.), small modular immunopharmaceuticals (SMIPs), and shark variable immunoglobulin new antigen receipt (IgNAR) domains. 
     In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises three heavy chain CDRs (HCDR1, HCDR2 and HCDR3) and three light chain CDRs (LCDR1, LCDR2 and LCDR3), wherein HCDR1 comprises the amino acid sequence of SEQ ID NO:16; HCDR2 comprises the amino acid sequence of SEQ ID NO:17; HCDR3 comprises the amino acid sequence of SEQ ID NO:18; LCDR1 comprises the amino acid sequence of SEQ ID NO:11; LCDR2 comprises the amino acid sequence SNN; and LCDR3 comprises the amino acid sequence of SEQ ID NO:13. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises three heavy chain CDRs (HCDR1, HCDR2 and HCDR3) and three light chain CDRs (LCDR1, LCDR2 and LCDR3), wherein HCDR1 comprises the amino acid sequence of SEQ ID NO:19; HCDR2 comprises the amino acid sequence of SEQ ID NO:20; HCDR3 comprises the amino acid sequence of SEQ ID NO:21; LCDR1 comprises the amino acid sequence of SEQ ID NO:14; LCDR2 comprises the amino acid sequence of SEQ ID NO:15; and LCDR3 comprises the amino acid sequence of SEQ ID NO:13. 
     In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising a sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99%, identical to SEQ ID NO:4. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a light chain variable region comprising a sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99%, identical to SEQ ID NO:3. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising a sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99%, identical to SEQ ID NO:4 and comprises a light chain variable region comprising a sequence that is at least 85% at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99%, identical to SEQ ID NO:3. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising the sequence of SEQ ID NO:4. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a light chain variable region comprising the sequence of SEQ ID NO:3. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising the sequence of SEQ ID NO:4 and a light chain variable region comprising the sequence of SEQ ID NO:3. 
     “Identity” refers to the number or percentage of identical positions shared by two amino acid or nucleic acid sequences, taking into account the number of gaps, and the length of each gap, which need to be introduced for optimal alignment of the two sequences. “Substantially identical” means an amino acid sequence that which differs only (i) by conservative amino acid substitutions, for example, substitution of one amino acid for another of the same class (e.g., valine for glycine, arginine for lysine, etc.) or (ii) by one or more non-conservative substitutions, deletions, or insertions located at positions of the amino acid sequence which do not destroy the function of the protein. Preferably, the amino acid sequence is at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% similar to another amino acid sequence. Methods and computer programs for determining sequence similarity are publically available, including, but not limited to, the GCG program package (Devereux et al., Nucleic Acids Research 12: 387, 1984), BLASTP, BLASTN, FASTA (Altschul et al., J. Mol. Biol. 215:403 (1990), and the ALIGN program (version 2.0). The well-known Smith Waterman algorithm may also be used to determine similarity. The BLAST program is publicly available from NCBI and other sources (BLAST Manual, Altschul, et al., NCBI NLM NIH, Bethesda, Md. 20894; BLAST 2.0 at http://www.ncbi.nlm.nih.gov/blast/). In comparing sequences, these methods account for various substitutions, deletions, and other modifications. Conservative substitutions typically include substitutions within the following groups: glycine, alanine; valine, isoleucine, leucine; aspartic acid, glutamic acid, asparagine, glutamine; serine, threonine; lysine, arginine; and phenylalanine, tyrosine. 
     In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises three heavy chain CDRs (HCDR1, HCDR2 and HCDR3) and three light chain CDRs (LCDR1, LCDR2 and LCDR3), wherein HCDR1 comprises the amino acid sequence of SEQ ID NO:16; HCDR2 comprises the amino acid sequence of SEQ ID NO:17; HCDR3 comprises the amino acid sequence of SEQ ID NO:22; LCDR1 comprises the amino acid sequence of SEQ ID NO:11; LCDR2 comprises the amino acid sequence SNN; and LCDR3 comprises the amino acid sequence of SEQ ID NO:13. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises three heavy chain CDRs (HCDR1, HCDR2 and HCDR3) and three light chain CDRs (LCDR1, LCDR2 and LCDR3), wherein HCDR1 comprises the amino acid sequence of SEQ ID NO:19; HCDR2 comprises the amino acid sequence of SEQ ID NO:20; HCDR3 comprises the amino acid sequence of SEQ ID NO:48; LCDR1 comprises the amino acid sequence of SEQ ID NO:14; LCDR2 comprises the amino acid sequence of SEQ ID NO:15; and LCDR3 comprises the amino acid sequence of SEQ ID NO:13. 
     In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising a sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99%, identical to SEQ ID NO:6. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a light chain variable region comprising a sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99%, identical to SEQ ID NO:5. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising a sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99%, identical to SEQ ID NO:6 and comprises a light chain variable region comprising a sequence that is at least 85% at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99%, identical to SEQ ID NO:5. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising the sequence of SEQ ID NO:6. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a light chain variable region comprising the sequence of SEQ ID NO:5. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising the sequence of SEQ ID NO:6 and a light chain variable region comprising the sequence of SEQ ID NO:5. 
     In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises three heavy chain CDRs (HCDR1, HCDR2 and HCDR3) and three light chain CDRs (LCDR1, LCDR2 and LCDR3), wherein HCDR1 comprises the amino acid sequence of SEQ ID NO:28; HCDR2 comprises the amino acid sequence of SEQ ID NO:29; HCDR3 comprises the amino acid sequence of SEQ ID NO:30; LCDR1 comprises the amino acid sequence of SEQ ID NO:23; LCDR2 comprises the amino acid sequence DAS; and LCDR3 comprises the amino acid sequence of SEQ ID NO:25. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises three heavy chain CDRs (HCDR1, HCDR2 and HCDR3) and three light chain CDRs (LCDR1, LCDR2 and LCDR3), wherein HCDR1 comprises the amino acid sequence of SEQ ID NO:31; HCDR2 comprises the amino acid sequence of SEQ ID NO:32; HCDR3 comprises the amino acid sequence of SEQ ID NO:33; LCDR1 comprises the amino acid sequence of SEQ ID NO:26; LCDR2 comprises the amino acid sequence of SEQ ID NO:27; and LCDR3 comprises the amino acid sequence of SEQ ID NO:25. 
     In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising a sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99%, identical to SEQ ID NO:8. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a light chain variable region comprising a sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99%, identical to SEQ ID NO:7. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising a sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99%, identical to SEQ ID NO:8 and comprises a light chain variable region comprising a sequence that is at least 85% at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99%, identical to SEQ ID NO:7. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising the sequence of SEQ ID NO: 8. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a light chain variable region comprising the sequence of SEQ ID NO:7. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising the sequence of SEQ ID NO:8 and a light chain variable region comprising the sequence of SEQ ID NO:7. 
     In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises three heavy chain CDRs (HCDR1, HCDR2 and HCDR3) and three light chain CDRs (LCDR1, LCDR2 and LCDR3), wherein HCDR1 comprises the amino acid sequence of SEQ ID NO:39; HCDR2 comprises the amino acid sequence of SEQ ID NO:40; HCDR3 comprises the amino acid sequence of SEQ ID NO:41; LCDR1 comprises the amino acid sequence of SEQ ID NO:34; LCDR2 comprises the amino acid sequence STY; and LCDR3 comprises the amino acid sequence of SEQ ID NO:36. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises three heavy chain CDRs (HCDR1, HCDR2 and HCDR3) and three light chain CDRs (LCDR1, LCDR2 and LCDR3), wherein HCDR1 comprises the amino acid sequence of SEQ ID NO:42; HCDR2 comprises the amino acid sequence of SEQ ID NO:43; HCDR3 comprises the amino acid sequence of SEQ ID NO:49; LCDR1 comprises the amino acid sequence of SEQ ID NO:37; LCDR2 comprises the amino acid sequence of SEQ ID NO:38; and LCDR3 comprises the amino acid sequence of SEQ ID NO:36. 
     In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising a sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99%, identical to SEQ ID NO:10. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a light chain variable region comprising a sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99%, identical to SEQ ID NO:9. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising a sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99%, identical to SEQ ID NO:10 and comprises a light chain variable region comprising a sequence that is at least 85% at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99%, identical to SEQ ID NO:9. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising the sequence of SEQ ID NO:10. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a light chain variable region comprising the sequence of SEQ ID NO:9. In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a heavy chain variable region comprising the sequence of SEQ ID NO:10 and a light chain variable region comprising the sequence of SEQ ID NO:9. 
     In one embodiment, the anti-TEM1 antibody or antigen-binding portion thereof comprises a CDR that has one, two, three or more amino acid substitutions as compared to any of the CDR sequences closed herein. 
     Nucleic Acids 
     Also provided herein are nucleic acids encoding anti-TEM1 antibodies and antigen-binding portions thereof, as well as vectors, host cells, and expression systems. 
     The term “nucleic acid” as used herein refers to a polymeric form of nucleotides of any length, either ribonucleotides or desoxyribonucleotides. Thus, this term includes, but is not limited to, single-, double- or multi-stranded DNA or RNA, genomic DNA, cDNA, DNA-RNA hybrids, or a polymer comprising purine and pyrimidine bases, or other natural, chemically or biochemically modified, non-natural, or derivatized nucleotide bases. 
     The nucleic acids encoding anti-TEM1 antibodies and antigen-binding portions thereof may be, e.g., DNA, cDNA, RNA, synthetically produced DNA or RNA, or a recombinantly produced chimeric nucleic acid molecule comprising any of those polynucleotides either alone or in combination. For example, provided is an expression vector comprising a polynucleotide sequence encoding an anti-TEM1 antibodies and antigen-binding portions thereof described herein operably linked to expression control sequences suitable for expression in a eukaryotic and/or prokaryotic host cell. 
     The term “vector” refers to a nucleic acid molecule capable of transporting another nucleic acid to which it has been linked. A “vector” includes, but is not limited to, a viral vector, a plasmid, a RNA vector or a linear or circular DNA or RNA molecule which may consists of a chromosomal, non-chromosomal, semi-synthetic or synthetic nucleic acids. In some embodiments, the employed vectors are those capable of autonomous replication (episomal vector) and/or expression of nucleic acids to which they are linked (expression vectors). Large numbers of suitable vectors are known to those of skill in the art and commercially available. Viral vectors include retrovirus, adenovirus, parvovirus (e.g., adeno associated viruses, AAV), coronavirus, negative strand RNA viruses such as orthomyxovirus (e.g., influenza virus), rhabdovirus (e.g., rabies and vesicular stomatitis virus), paramyxovirus (e.g., measles and Sendai), positive strand RNA viruses such as picornavirus and alphavirus, and double-stranded DNA viruses including adenovirus, herpesvirus (e.g., Herpes Simplex virus types 1 and 2, Epstein-Barr virus, cytomegalovirus), and poxvirus (e.g., vaccinia, fowlpox and canarypox). Other viruses include Norwalk virus, togavirus, flavivirus, reoviruses, papovavirus, hepadnavirus, and hepatitis virus, for example. Examples of retroviruses include: avian leukosis-sarcoma, mammalian C-type, B-type viruses, D type viruses, HTLV-BLV group, lentivirus, and spumavirus. 
     A variety of expression vectors have been developed for the efficient synthesis of antibodies and antigen-binding portions thereof in prokaryotic cells such as bacteria and in eukaryotic systems, including but not limited to yeast and mammalian cell culture systems have been developed. The vectors can comprise segments of chromosomal, non-chromosomal and synthetic DNA sequences. Also provided are cells comprising expression vectors for the expression of the anti-TEM1 antibodies and antigen-binding portions thereof disclosed herein. 
     In one embodiment, the nucleic acid molecule comprises a sequence encoding any of the sequences of SEQ ID NOS:3-10. 
     Also provided are vectors and pairs of vectors comprising the nucleic acid molecules disclosed herein, as well as cells comprising such vectors. 
     Methods of Treatment 
     In one aspect, the invention provides for anti-TEM1 antibodies and antigen binding portions thereof that are also useful for the treatment of subjects in need thereof. 
     In the methods described herein, a therapeutically effective amount of an antibody or antigen-binding portions thereof set forth herein is administered to a mammal in need thereof. Although antibodies or antigen-binding portions thereof set forth herein are particularly useful for administration to humans and canines, they may be administered to other mammals as well. The term “mammal” as used herein is intended to include, but is not limited to, humans, laboratory animals, domestic pets and farm animals. “Therapeutically effective amount” means an amount of antibody or antigen-binding portions thereof set forth herein that, when administered to a mammal, is effective in producing the desired therapeutic effect. 
     As such, also provided herein are methods of treating a subject having a cancer or tumor and/or reducing tumor growth, comprising administering an effective amount of an anti-TEM1 or antigen-binding portion thereof provided herein. “Reducing” includes inhibiting and/or reversing and can refer to, for example, the symptoms of the disorder being treated, the presence or size of metastases or micrometastases, the size of the primary tumor, the presence or the size of the dormant tumor. 
     The term “cancer” refers to or describes the physiological condition in mammals that is typically characterized by unregulated cell growth. Included in this definition are benign and malignant cancers, as well as dormant tumors or micrometastases. Accordingly, the term “cancer” as used herein refers to an uncontrolled growth of cells, which interferes with the normal functioning of the bodily organs and systems, including cancer stem cells and tumor vascular niches. A subject that has a cancer is a subject having objectively measurable cancer cells present in the subject&#39;s body. Included in this definition are benign and malignant cancers, as well as dormant tumors or micrometastases. Cancers that migrate from their original location and seed vital organs can eventually lead to the death of the subject through the functional deterioration of the affected organs. Hematopoietic cancers, such as leukemia, are able to out-compete the normal hematopoietic compartments in a subject, thereby leading to hematopoietic failure (in the form of anemia, thrombocytopenia and neutropenia) ultimately causing death. 
     By “subject” is meant a mammal, including, but not limited to, a human or non-human mam-mal, such as a bovine, equine, canine, ovine, or feline, etc. Individuals and patients are also subjects herein. 
     The terms “treat,” “treated,” “treating,” or “treatment” as used herein refer to therapeutic treatment measures, wherein the object is to slow down (lessen) an undesired physiological condition, disorder or disease, or to obtain beneficial or desired clinical results. For the purposes of this disclosure, beneficial or desired clinical results include, but are not limited to, alleviation of symptoms; diminishment of the extent of the condition, disorder or disease; stabilization (i.e., not worsening) of the state of the condition, disorder or disease; delay in onset or slowing of the progression of the condition, disorder or disease; amelioration of the condition, disorder or disease state; and remission (whether partial or total), whether detectable or undetectable, or enhancement or improvement of the condition, disorder or disease. Treatment includes eliciting a clinically significant response without excessive levels of side effects. Treatment also includes prolonging survival as compared to expected survival if not receiving treatment. 
     The embodiments of the invention may be used for treating metastasis, which relates to the spreading of cancer from its primary site to other places in the body. Cancer cells can break away from a primary tumor, penetrate into lymphatic and blood vessels, circulate through the bloodstream, and grow in a distant focus (metastasize) in normal tissues elsewhere in the body. Metastasis can be local or distant. Metastasis is a sequential process, contingent on tumor cells breaking off from the primary tumor, traveling through the bloodstream, and stopping at a distant site. At the new site, the cells establish a blood supply and can grow to form a life-threatening mass. Both stimulatory and inhibitory molecular pathways within the tumor cell regulate this behavior, and interactions between the tumor cell and host cells in the distant site are also significant. Metastases are most often detected through the sole or combined use of magnetic resonance imaging (MRI) scans, computed tomography (CT) scans, blood and platelet counts, liver function studies, chest X-rays and bone scans in addition to the monitoring of specific symptoms. 
     Cancers that may be treated by the compositions and methods contemplated by the invention include tumors that are not vascularized, or not yet substantially vascularized, as well as vascularized tumors. The cancers may comprise nonsolid tumors (such as hematological tumors, for example, leukemias and lymphomas) or may comprise solid tumors. Types of cancers to be treated include, but are not limited to benign and malignant tumors, and malignancies e.g., sarcomas, carcinomas, and melanomas. Adult tumors/cancers and pediatric tumors/cancers are also included. Examples of cancer include but are not limited to, carcinoma, lymphoma, blastoma, sarcoma, and leukemia. More particular examples of such cancers include, but are not limited to, basal cell carcinoma, biliary tract cancer; bladder cancer; bone cancer; brain and CNS cancer; breast cancer; cancer of the peritoneum; cervical cancer; choriocarcinoma; colon and rectum cancer; connective tissue cancer; cancer of the digestive system; endometrial cancer; esophageal cancer; eye cancer; cancer of the head and neck; gastric cancer (including gastrointestinal cancer); glioblastoma; hepatic carcinoma; hepatoma; intra-epithelial neoplasm; kidney or renal cancer; larynx cancer; leukemia; liver cancer; lung cancer (e.g., small-cell lung cancer, non-small cell lung cancer, adenocarcinoma of the lung, and squamous carcinoma of the lung); lymphoma including Hodgkin&#39;s and non-Hodgkin&#39;s lymphoma; melanoma; myeloma; neuroblastoma; oral cavity cancer (e.g., lip, tongue, mouth, and pharynx); ovarian cancer; pancreatic cancer; prostate cancer; retinoblastoma; rhabdomyosarcoma; rectal cancer; cancer of the respiratory system; salivary gland carcinoma; sarcoma; skin cancer; squamous cell cancer; stomach cancer; testicular cancer; thyroid cancer; uterine or endometrial cancer; cancer of the urinary system; vulval cancer; as well as other carcinomas and sarcomas; as well as B-cell lymphoma (including low grade/follicular non-Hodgkin&#39;s lymphoma (NHL); small lymphocytic (SL) NHL; intermediate grade/follicular NHL; intermediate grade diffuse NHL; high grade immunoblastic NHL; high grade lymphoblastic NHL; high grade small non-cleaved cell NHL; bulky disease NHL; mantle cell lymphoma; AIDS-related lymphoma; and Waldenstrom&#39;s Macroglobulinemia); chronic lymphocytic leukemia (CLL); acute lymphoblastic leukemia (ALL); Hairy cell leukemia; chronic myeloblastic leukemia; and post-transplant lymphoproliferative disorder (PTLD), as well as abnormal vascular proliferation associated with phakomatoses, edema (such as that associated with brain tumors), and Meigs&#39; syndrome. A patient can have more than one type of cancer. 
     In a preferred embodiment, the anti-TEM1 antibodies or antigen-binding portions thereof are used in a method of treating sarcoma, including, but not limited to sarcoma subtypes synovial sarcoma, fibrosarcoma, malignant fibrous histiocytoma (MFH), liposarcoma, and osteosarcoma. In another preferred embodiment, the anti-TEM1 antibodies or antigen binding fragments are used in a method of treating carcinoma, including bladder cancer. 
     The efficacy of the treatment methods for cancer comprising therapeutic formulations of the compositions comprising the antibodies and antigen binding portions thereof described herein can be measured by various endpoints commonly used in evaluating cancer treatments, including but not limited to, tumor regression, tumor weight or size shrinkage, time to progression, duration of survival, progression free survival, overall response rate, duration of response, and quality of life. In the case of cancers, the therapeutically effective amount of the recombinant anti-TEM1 or antigen-binding portion thereof can reduce the number of cancer cells; reduce the tumor size; inhibit (i.e., slow to some extent and preferably stop) cancer cell infiltration into peripheral organs; inhibit (i.e., slow to some extent and preferably stop) tumor metastasis; inhibit, to some extent, tumor growth; and/or relieve to some extent one or more of the symptoms associated with the disorder. In cases where a patient has more than one type of cancer, the therapeutically effective amount of the recombinant anti-TEM1 or antigen-binding portion thereof is an amount effective in treating at least one of the cancers. To the extent the anti-TEM1 antibody or antigen-binding portion thereof acts to prevent growth and/or kill existing cancer cells, it can be cytostatic and/or cytotoxic. For cancer therapy, efficacy in vivo can, for ex-ample, be measured by assessing the duration of survival, duration of progression free survival (PFS), the response rates (RR), duration of response, and/or quality of life. 
     In some embodiments, the anti-TEM1 antibody or antigen-binding portion thereof is administered with a checkpoint inhibitor. Checkpoint proteins interact with specific ligands that send a signal into the T-cell and switch off or inhibit T-cell function. By expressing high levels of checkpoint proteins on their surface, cancer cells can control the function of T-cells that enter the tumor microenvironment, thus suppressing the anticancer immune response. The immune checkpoint protein Programmed Death-1 (PD-1) is a key immune checkpoint receptor ex-pressed by activated T and B cells and mediates immunosuppression. PD-1 is a member of the CD28 family of receptors, which includes CD28, CTLA-4, ICOS, PD-1, and BTLA. Two cell surface glycoprotein ligands for PD-1 have been identified, Programmed Death Ligand-1 (PD-L1) and Programmed Death Ligand-2 (PD-L2), that are expressed on antigen-presenting cells as well as many human cancers and have been shown to downregulate T-cell activation and cytokine secretion upon binding to PD-1 (Freeman et al., 2000; Latchman et al., 2001). Inhibition of the PD-1/PD-L1 interaction can promote potent antitumor activity. Examples of PD-1 inhibitors include, but are not limited to, Pembrolizumab (MK-3475), Nivolumab (MDX-1106), Cemiplimab-rwlc (REGN2810), Pidilizumab (CT-011), Spartalizumab (PDR001), tislelizumab (BGB-A317), PF-06801591, AK105, BCD-100, BI 754091, JS001, LZMO09, MEDI0680, MGA012, Sym021, TSR-042. Examples of PD-L1 inhibitors include, but are not limited to, Atezolizumab (MPDL3280A), Durvalumab (MEDI4736), Avelumab (MSB0010718C), BGB-A333, CK-301, CS1001, FAZ053, KN035, MDX-1105, MSB2311, SHR-1316. 
     Further provided are pharmaceutical compositions comprising one or more of the anti-TEM1 antibodies and antigen-binding portions thereof provided herein and a pharmaceutically acceptable excipient. 
     Diagnostic Methods 
     The anti-TEM1 antibodies and antigen-binding portions thereof provided herein are also useful for diagnostic purposes. As such, also provided herein are methods of selecting a subject for treatment with an anti-TEM1 antibody or antigen-binding portion thereof, the method comprising contacting a sample from a patient with an anti-TEM1 antibody or antigen-binding portion thereof disclosed herein, and determining the presence of TEM1 in the sample. In some embodiments, the method further comprises administering to the patient anti-TEM1 antibody or antigen-binding portion thereof if TEM1 was determined to be present in the sample. In some embodiments, the sample is a tissue, blood, or a tumor sample. 
     In some embodiments, the anti-TEM1 antibodies and antigen-binding portions thereof provided herein are used for the identification and/or isolation of cancer cells. 
     Targeting Methods 
     The anti-TEM1 antibodies and antigen-binding portions thereof provided herein are also useful for targeting a payload to a cell expressing TEM1. In one embodiment, provided is a method of treating and/or preventing a disease in a subject in need thereof, the method comprising administering to the subject an effective amount of one or more anti-TEM1 antibodies or antigen-binding portions thereof, wherein at least one anti-TEM1 antibody or antigen-binding portions thereof is conjugated to a therapeutic moiety. 
     Examples of therapeutic moieties which are useful in the methods and antibodies and antigen binding portions thereof contemplated by the invention include, for example, anti-inflammatory agents, anti-cancer agents, anti-neurodegenerative agents, anti-infective agents, or generally a therapeutic. The functional moiety may also have one or more of the above-mentioned functions. 
     Exemplary therapeutic moieties include radionuclides with high-energy ionizing radiation that are capable of causing multiple strand breaks in nuclear DNA, and therefore suitable for inducing cell death (e.g., of a cancer). Exemplary high-energy radionuclides include:  90 Y,  125 I,  131 I,  123 I,  111 In,  105 Rh,  153 Sm,  67 Cu,  67 Ga,  166 Ho,  177 Lu,  186 Re and  188 Re. These isotopes typically produce high-energy α- or β-particles which have a short path length. Such radionuclides kill cells to which they are in close proximity, for example neoplastic cells to which the conjugate has attached or has entered. They have little or no effect on non-localized cells and are essentially non-immunogenic. 
     Exemplary therapeutic moieties also include cytotoxic agents such as cytostatics (e.g. alkylating agents, DNA synthesis inhibitors, DNA-intercalators or cross-linkers, or DNA-RNA transcription regulators), enzyme inhibitors, gene regulators, cytotoxic nucleosides, tubulin binding agents, hormones and hormone antagonists, anti-angiogenesis agents, and the like. 
     Exemplary therapeutic moieties also include alkylating agents such as the anthracycline family of drugs (e.g., adriamycin, carminomycin, cyclosporin-A, chloroquine, methopterin, mithramycin, porfiromycin, streptonigrin, anthracenediones, and aziridines). In another embodiment, the chemotherapeutic moiety is a cytostatic agent such as a DNA synthesis inhibitor. Examples of DNA synthesis inhibitors include, but are not limited to, methotrexate and dichloromethotrexate, 3-amino-1,2,4-benzotriazine 1,4-dioxide, aminopterin, cytosine β-D-arabinofuranoside, 5-fluoro-5′-deoxyuridine, 5-fluorouracil, ganciclovir, hydroxyurea, actinomycin-D, and mitomycin C. Exemplary DNA-intercalators or cross-linkers include, but are not limited to, bleomycin, carboplatin, carmustine, chlorambucil, cyclophosphamide, cis-diammineplatinum(II) dichloride (cisplatin), melphalan, mitoxantrone, and oxaliplatin. 
     Exemplary therapeutic moieties also include transcription regulators such as actinomycin D, daunorubicin, doxorubicin, homoharringtonine, and idarubicin. Other exemplary cytostatic agents that are compatible with the present invention include ansamycin benzoquinones, quinonoid derivatives (e.g. quinolones, genistein, bactacyclin), busulfan, ifosfamide, mechlorethamine, triaziquone, diaziquone, carbazilquinone, indoloquinone EO9, diaziridinyl-benzoquinone methyl DZQ, triethylenephosphoramide, and nitrosourea compounds (e.g. carmustine, lomustine, semustine). 
     Exemplary therapeutic moieties also include cytotoxic nucleosides such as, for example, adenosine arabinoside, cytarabine, cytosine arabinoside, 5-fluorouracil, fludarabine, floxuridine, ftorafur, and 6-mercaptopurine; tubulin binding agents such as taxoids (e.g. paclitaxel, docetaxel, taxane), nocodazole, rhizoxin, dolastatins (e.g. Dolastatin-10, -11, or -15), colchicine and colchicinoids (e.g. ZD6126), combretastatins (e.g. Combretastatin A-4, AVE-6032), and vinca alkaloids (e.g. vinblastine, vincristine, vindesine, and vinorelbine (navelbine)); anti-angiogenesis compounds such as Angiostatin K1-3, DL-α-difluoromethyl-ornithine, endostatin, fumagillin, genistein, minocycline, staurosporine, and (±)-thalidomide. 
     Exemplary therapeutic moieties also include hormones and hormone antagonists, such as corticosteroids (e.g. prednisone), progestins (e.g. hydroxyprogesterone or medroprogesterone), estrogens, (e.g. diethylstilbestrol), antiestrogens (e.g. tamoxifen), androgens (e.g. testosterone), aromatase inhibitors (e.g. aminogluthetimide), 17-(allylamino)-17-demethoxygeldanamycin, 4-amino-1,8-naphthalimide, apigenin, brefeldin A, cimetidine, dichloromethylene-diphosphonic acid, leuprolide (leuprorelin), luteinizing hormone-releasing hormone, pifithrin-α, rapamycin, sex hormone-binding globulin, and thapsigargin. 
     Exemplary therapeutic moieties also include enzyme inhibitors such as, S(+)-camptothecin, curcumin, (−)-deguelin, 5,6-dichlorobenz-imidazole 1-β-D-ribofuranoside, etoposide, formestane, fostriecin, hispidin, 2-imino-1-imidazolidineacetic acid (cyclocreatine), mevinolin, trichostatin A, tyrphostin AG 34, and tyrphostin AG 879. 
     Exemplary therapeutic moieties also include gene regulators such as 5-aza-2′-deoxycytidine, 5-azacytidine, cholecalciferol (vitamin D3), 4-hydroxytamoxifen, melatonin, mifepristone, raloxifene, trans-retinal (vitamin A aldehydes), retinoic acid, vitamin A acid, 9-cis-retinoic acid, 13-cis-retinoic acid, retinol (vitamin A), tamoxifen, and troglitazone. 
     Exemplary therapeutic moieties also include cytotoxic agents such as, for example, the pteridine family of drugs, diynenes, and the podophyllotoxins. Particularly useful members of those classes include, for example, methopterin, podophyllotoxin, or podophyllotoxin derivatives such as etoposide or etoposide phosphate, leurosidine, vindesine, leurosine and the like. 
     Still other cytotoxins that are compatible with the teachings herein include auristatins (e.g. auristatin E and monomethylauristan E), calicheamicin, gramicidin D, maytansanoids (e.g. maytansine), pyrrolobenzodiazepine (PBD) dimers, neocarzinostatin, topotecan, taxanes, cytochalasin B, ethidium bromide, emetine, tenoposide, colchicin, dihydroxy anthracindione, mitoxantrone, procaine, tetracaine, lidocaine, propranolol, puromycin, and analogs or homologs thereof. Any of these cytotoxins can be conjugated to the anti-TEM1 antibody through cleavable or non-cleavable linkers, the choice of which depends on target and target cell and tissue. 
     In one embodiment, the therapeutic moiety is an immune cell engager, including but not limited to a T-cell, NK cell, and/or macrophage engager. In one embodiment, the therapeutic moiety is a bi-specific T-cell engager (BiTE), which forms a bridge between a cytotoxic T-cell and a tumor cell. In some embodiments, the therapeutic moiety is a cytokine, a chemokine, an interleukin, or an immunomodulatory imide drug. In addition, other molecules that alter the tumor microenvironment in order to increase an immune response against a tumor could be conjugated to the anti-TEM1 antibody, for example a STING agonists such as diABZI. 
     In one embodiment, the therapeutic moiety is a checkpoint inhibitor. 
     In some embodiments, the anti-TEM1 antibody or antigen-binding portion thereof is conjugated to a detectable moiety. In some embodiments, the detectable moiety is fluorescent. In some embodiments, the anti-TEM1 antibody or antigen-binding portion thereof is conjugated to an affinity tag and/or a purification tag or molecule. In some embodiments, the anti-TEM1 antibody or antigen-binding portion thereof is conjugated to a magnetic moiety. 
     It is to be understood that this invention is not limited to the particular molecules, compositions, methodologies, or protocols described, as these may vary. Any methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present invention. It is further to be understood that the disclosure of the invention in this specification includes all possible combinations of such particular features. For example, where a particular feature is disclosed in the context of a particular aspect or embodiment of the invention, or a particular claim, that feature can also be used, to the extent possible, in combination with and/or in the context of other particular aspects and embodiments of the invention, and in the invention generally. 
     Where reference is made herein to a method comprising two or more defined steps, the defined steps can be carried out in any order or simultaneously (except where the context excludes that possibility), and the method can include one or more other steps which are carried out before any of the defined steps, between two of the defined steps, or after all the defined steps (except where the context excludes those possibilities). 
     All references, patents and applications cited herein are incorporated herein by reference in their entireties. Furthermore, where a definition or use of a term in a reference, which is incorporated by reference herein is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply. 
     To facilitate a better understanding of the present invention, the following examples of specific embodiments are given. The following examples should not be read to limit or define the entire scope of the invention. 
     EXAMPLES 
     Example 1: Selection of Anti-TEM scFvs Using Phage Display 
     scFvs selectively binding to the extracellular domain (ECD) of tumor endothetial marker 1 (TEM1) were selected using phage display. 
     Phage Display Selections 
     All phage display selections were carried out using two large, fully human scFv libraries (CHV101_DMk and CHV101_DM1; SMD) constructed from the peripheral blood of 120 healthy volunteer donors. Briefly, IgD/IgM VH, and Vk/Vl domain repertoires were amplified from cDNA prepared from mRNA affinity-purified from enriched CD19 +  cells, using a newly designed primer panel. Amplicons were pooled, purified and cloned sequentially (Vk/Vl followed by VH) into the gIII display cassette of a newly designed phagemid vector (pCHV101; SMD). A bacterial library of ˜2×10 10  colonies was generated following electroporation into  E. coli  TG1 cells. Phage library rescue was performed according to standard published procedures and single-use phage aliquots were stored in a stabilization buffer at −80° C. 
     Two solid-phase targets were used for phage display selections: (1) streptavidin magnetic beads pre-coated with biotinylated SpyTag (bSpyT), which were further coated with a fusion protein comprising SpyCatcher (SpyC) and the ECD of TEM1 and (2) streptavidin magnetic beads coated directly with purified and biotinylated h/mTEM1 ECD. SpyT is a peptide that can quickly form an amide bond to its protein partner SpyC, allowing quick immobilization of SpyC fusion proteins. 
     The scFv phage libraries were first blocked with PBST containing 2% skimmed milk, 1% BSA for 30 min at RT, and then incubated for 30 min with streptavidin beads coated only with SpyC domain to subtract (‘de-select’) non-specific or SpyC-specific binders. Subsequently, blocked and deselected phage particles were transferred to tubes containing similarly blocked SpyC-antigen beads, and incubation was continued at RT for 1 h. Non-binding phage were removed by 5×1 ml washes with PBST followed by 1×1 ml PBS. Typically, the stringency of selection was increased at the second round by transferring the 5×1 ml PBST washed beads into a Falcon tube containing 50 ml PBST and allowing lower affinity phage to passively dissociate over 20 min prior to rapid magnetic capture and final washing with 1 ml 1×PBS. Bound phage were eluted from the beads with 200 μl of 20 μg/ml trypsin (Sigma Aldrich, #T1426) in PBS for 30 min at 37° C. (stationary). Eluted phage were allowed to infect minimal medium-grown  E. coli  TG1 cells grown to an OD600 of 0.4-0.5 in 10 ml of 2TY medium supplemented with 2% glucose (2TYG) for 1 h at 37° C. (stationary). The infected cells were collected by centrifugation at 4000 rpm (RT), resuspended in 3 ml 2TYG, and plated on 2TYA(ampicillin)G agar with incubation at 30° C. for 18-20 h. Colonies were scraped from plates and the cells stored frozen in 2TYG containing 15% glycerol pending further rounds of phage rescue and selection. Phage rescue between rounds was performed according to standard protocols using M13KO7 helper phage (Life Technologies, #18311019) added at a MOI of 5:1. Secreted phage were collected and purified by two rounds of PEG/NaCl precipitation according to standard protocols, and stored as frozen, single-use aliquots in a stabilization buffer. Clones were cultured for primary screening by picking individual colonies into 2TYAG liquid medium, growing until turbid and then inoculating cells into supplemented TB medium for the induction of protein expression as described above. Clones of interest were subjected to affinity maturation. 
     Example 2: Affinity Maturation of Anti-TEM1 Clone Candidates 
     Affinity maturation of selected scFvs was performed to identify high-affinity anti-TEM1 antibodies and antigen-binding portions thereof that are cross-reactive binders and bind to both human and murine TEM1 ECD. 
     Affinity Maturation and Selection of High-Affinity Binders 
     Selected scFv clones from Example 1 were subjected to random mutagenesis across the whole scFv, using error-prone PCR with the Diversify PCR random mutagenesis kit (Takara, #630703). The scFv was amplified in one, two or three subsequent rounds of PCR with 25 cycles in the presence of 640 μM MnSO4 and 40 μM dGTP in order to generate variants with low, intermediate and high mutational load. Mutated scFv library DNA was cloned into pCHV101 and electroporated into  E. coli  TG1 cells to generate libraries of −10 9  colonies. Phage particles displaying the mutagenized scFv libraries were rescued and PEG/NaCl-precipitated before being used in high-stringency affinity maturation selections using purified biotinylated TEM1 (bio-TEM1). In order to enrich for high-affinity, cross-reactive binders towards both human and murine TEM1 ECD, the first round of selection was performed against bead-immobilized bio-hTEM1 and the second round against bio-mTEM1. Both rounds included competition (‘off-rate selection’) with 200 nM free unlabelled antigen and an extended high-volume washing step of 50 ml PBST (30 min for R1 and overnight for R2). Random colonies were picked from the R2 selection output and sequenced to assess clone integrity and diversity prior to the initiation of screening. 
     Example 3: Analysis of scFv Binding to TEM1 ECD Using ELISA 
     The binding of the selected scFvs to SpyC-TEM1 ECD fusion proteins was assessed by enzyme-linked immunosorbent assay (ELISA). 
     ELISA Binding Assays 
     Wash steps were performed using 300 ml PBST dispensed from a BioTek 405 automatic plate washer. Nunc Maxisorp 96-well plates (Thermo Fisher Scientific, #442404) were coated with 100 ml of 10 mg/ml Neutravidin (Life Technologies, #31000) in PBS over-night at 4° C., washed 3× with PBST and incubated with 100 ml of 1 μM bSpyT peptide in PBS for 1 h at RT with gentle agitation. After blocking in 5% skimmed milk/PBST for 1 h, wells were washed 3× with PBST and 100 μl SpyC-TEM1 ECD expression supernatants (typically diluted 1:10 in PBST+1% BSA for mammalian expression, or blocking buffer for bacterial expression) were added to allow covalent capture by the bound bSpyT. Incubation was at RT for 1.5 h. Wells were washed 4× with PBST and 100 μl blocked scFv culture supernatants added. Wells were washed 4× with PBST and binders were detected using a primary recombinant anti-myc tag antibody (derived from parental mAb clone 9E10, in-house) and a horseradish peroxidase (HRP) conjugated goat anti-mouse IgG antibody (Sigma Aldrich, #A9917). The colorimetric read-out was developed with TMB substrate reagent (Biolegend, #34029) and stabilized with 2N sulfuric acid. Absorbance was measured at 450 nm and 620 nm on a BioTek Synergy plate reader. ELISAs were performed in parallel against both cognate SpyC-TEM1 ECD and non-fused SpyC in order to eliminate hits to the latter. 
     Results 
     scFv candidates 1C1, 1C1mut (an affinity matured variant of 1C1), 2B11, and 3B6 were identified has high-affinity binders using this screen. Their respective CDR, VH, and VL sequences are shown in Tables 1-3. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Light chain sequences of anti-TEM1 scFvs 1C1, 1C1mut, 2B11, and 3B6. 
               
               
                 SEQ ID NOs are indicated for amino acid sequences longer  
               
               
                 than three amino acids. 
               
            
           
           
               
               
               
               
               
            
               
                   
                 CDR1L 
                 CDR2L 
                 CDR3L 
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 IMGT 
                 Kabat 
                 IMGT 
                 Kabat 
                 IMGT 
                 Kabat 
                 VL 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 1C1 
                 11 
                 14 
                 SNN 
                 15 
                 13 
                 13 
                 3 
               
               
                 1C1mut 
                 11 
                 14 
                 SNN 
                 15 
                 13 
                 13 
                 5 
               
               
                 2B11 
                 23 
                 26 
                 DAS 
                 27 
                 25 
                 25 
                 7 
               
               
                 3B6 
                 34 
                 37 
                 STY 
                 38 
                 36 
                 36 
                 9 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Heavy chain sequences of anti-TEM1 scFvs  
               
               
                 1C1, 1C1mut, 2B11, and 3B6. 
               
               
                 SEQ ID NOs are indicated. 
               
            
           
           
               
               
               
               
               
            
               
                   
                 CDR1H 
                 CDR2H 
                 CDR3H 
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 IMGT 
                 Kabat 
                 IMGT 
                 Kabat 
                 IMGT 
                 Kabat 
                 VH 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 1C1 
                 16 
                 19 
                 17 
                 20 
                 18 
                 21 
                 4 
               
               
                 1C1mut 
                 16 
                 19 
                 17 
                 20 
                 22 
                 48 
                 6 
               
               
                 2B11 
                 28 
                 31 
                 29 
                 32 
                 30 
                 33 
                 8 
               
               
                 3B6 
                 39 
                 42 
                 40 
                 43 
                 41 
                 49 
                 10 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Variable chain sequences of anti-TEM1 scFvs 1C1, 1C1mut, 2B11, and 3B6. 
               
            
           
           
               
               
               
               
            
               
                   
                   
                   
                 Amino acid sequence 
               
               
                   
                   
                 VH/VL 
                 (IMGT designated CDR cores are underlined, 
               
               
                 SEQ ID NO: 
                 Antibody 
                 chain 
                 Kabat designated CDR cores are bolded) 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                  3 
                 1C1 
                 VL 
                 QPVLTQPPSASGTPGQRVTISC SGS     VN WYQQLPGTAPKLLIY 
               
               
                   
                   
                   
                     QRPS GVPDRFSGSKSGTSASLAISGLQSEDEADYYC   
               
               
                   
                   
                   
                 FGGGTKLTVL 
               
               
                   
               
               
                  4 
                 1C1 
                 VH 
                 QVQLVQSGAEVKKPGSSVKVSCKAS   IS WVRQAPGQGLEWMG G   
               
               
                   
                   
                   
                     NYAQKFQG RVTITADKSTSTAYMELSSLRSEDTAVYYC AS   LT   
               
               
                   
                   
                   
                   SYYGDPTGFDY WGQGTLVTVSS 
               
               
                   
               
               
                  5 
                 1C1 mut 
                 VL 
                 QPVLTQPPSASGTPGQRVTISCS GS     VN WYQQLPGTAPKLLIY 
               
               
                   
                   
                   
                     QRPS GVPDRFSGSKSGTSASLAISGLQSEDEADYYC   
               
               
                   
                   
                   
                 FGGGTKLTVL 
               
               
                   
               
               
                  6 
                 1C1 mut 
                 VH 
                 QVLQVQSGAEVKKPGSSVKVSCKAS   IS WVRQAPGQGLEWMGG 
               
               
                   
                   
                   
                    NYAQKFQGRVTITADKSTSTAYMELSSLRSEDTAVYYC 
               
               
                   
                   
                   
                      WGQGTLVTVSS 
               
               
                   
               
               
                  7 
                 2B11 
                 VL 
                 DIQMTQSPPTLSASVGDRVTITC RAS     LA WYQQKPGKAPNLLIY 
               
               
                   
                   
                   
                     NLQS GVPSRFSGSGSGTEFTLTISSLQPDDFGTYYC   
               
               
                   
                   
                   
                 FGQGTKLEIK 
               
               
                   
               
               
                  8 
                 2B11 
                 VH 
                 EVQLVETGGGLVKPGGSLRLSCAAS   MN WVRQAPGKGLEWVS S   
               
               
                   
                   
                   
                     YYADSVKG RFTISRDNAKNSLYLQMNSLRAEDTAVYYC 
               
               
                   
                   
                   
                      WGQGTMVTVSS 
               
               
                   
               
               
                  9 
                 3B6 
                 VL 
                 QAVLTQPPSASGTPGQRVTISCS GS     VN WYQQLPGTAPKLLIY 
               
               
                   
                   
                   
                     QRPS GVPGRFSGSKSATSASLAISGLQSEDEADYYC   
               
               
                   
                   
                   
                 FGGGTKLTVL 
               
               
                   
               
               
                 10 
                 3B6 
                 VH 
                 QVQLVQSGAEVKKPGASVKVSCKAS   MH WVRQAPGQGLEWMG W   
               
               
                   
                   
                   
                     NYAQKFQG RVTMTRDTSISTAYMELSRLRSDDTAVYYC 
               
               
                   
                   
                   
                      WGQGTLVTVSS 
               
               
                   
               
            
           
         
       
     
     Example 3: Reformatting of Selected scFvs into scFv-Fc Fusions or T-Cell Engagers 
     Selected scFv candidates (1C1, 2B11, and 3B6) were subcloned into a pTT-based vector containing a vector-encoded human IgG1 constant region to produce scFv-Fc fusion proteins (see  FIG. 1  A). Alternatively, the selected scFv candidates were fused to an scFv derived from an anti-CD3 antibody (clone UCHT1) to generate secreted T-cell engagers (BiTE). 
     Production of scFv-Fc Fusion Proteins and BiTE Molecules 
     Recombinant protein was produced using the mammalian HEK293-6E/pTT transient expression system (National Research Council of Canada; obtained under license). HEK293-6E cells were grown in Freestyle F17 medium (Thermo Fisher Scientific, #A13835) containing 4 mM GlutaMAX (Life Technologies, #35050061), 0.1% Pluronic® F-68 (Life Technologies, #24040032) and 25 μg/mL G418 (Life Technologies, #10131019) at 37° C., 5% CO 2  and 120 rpm. For transfection, the DNA was mixed with FectoPRO (Polyplus, #116-010) transfection reagent in F17 medium without supplements, according to the manufacturer&#39;s instructions. After five days of protein expression, cultures were subjected to low speed centrifugation and the media collected. Samples could be used immediately for direct capture and immobilization (dCI) selection/assay experiments or snap-frozen and stored at −80° C. until required. 
     Purification of scFv-Fc Fusion Proteins and BiTE Molecules 
     ScFv-Fc fusions were purified from clarified expression media using a HiTrap™ MabSelect column (GE Healthcare, #11003494), followed by extensive dialysis against phosphate-buffered saline (PBS). Also purified was sc78-Fc as a positive control. Sc78 is an anti-TEM1 antibody and was previously described in WO2011060233A1. 
     His-tagged T-cell engagers were purified by IMAC chromatography using a HisTrap™ Excel column (GE Healthcare, #17-3712-05). The peak monomer fractions were pooled and buffer-exchanged into PBS using a Superdex 200 Increase 10/300 GL preparatory grade column (GE Healthcare, #28-9909-44). 
     Expression of Recombinant Human and Mouse TEM1 for Soluble and Cell-Based Assays 
     Extracellular domain (ECD) fragments of human and mouse TEM1 membrane antigens were synthesized (GeneArt, Thermo Fisher Scientific) based on sequences and predicted topologies obtained from UniprotKB. Gene fragments were either fused N- or C-terminally to vector-encoded CnaB2-derived SpyCatcher (SpyC; Genbank accession: JQ478411.1; amino acids 28-136), or to a 6×his/AviTag motif housed in a pTT-based mammalian episomal expression vector. A semi-synthetic signal peptide was used to target expressed protein for secretion to the medium. The 6×his-tagged variants of human or murine TEM1 ECD containing a C-terminal biotinylation sequence were purified using a HisTrap™ excel column followed by site-directed enzymatic biotinylation using purified BirA.3 Following confirmation of biotinylation by avidin gel shift assay, the proteins were buffer exchanged into PBS supplemented with 0.1% BSA and stored at −80° C. Transient transfection of HEK293T cells with the full length (FL) hTEM1 cDNA ORF (extracted from Genbank RefSeq NM_020404.3) and an irrelevant membrane-localized control ORF (anti-hCD19 2nd generation CAR construct) utilized the pTagGFP2-N CMV promotor vector (Evrogen, #FP192). Briefly, HEK293T cells were detached and plated in 6-well plates at 10 6  cells/well in a volume of 4 ml. Recombinant plasmid DNA (4 μg) was combined with 400 μl serum-free DMEM and 6 μl Turbofect reagent (Life Technologies, #R0532), and incubated for 20 min at RT before being added dropwise to the plated cells. Transfected cells were maintained at 37° C., 5% CO 2  under a humidified atmosphere for 48 h. Transient transfection of HEK293-6E with FL-canine TEM1 cloned into pTagGFP2-N was performed using the NCBI Reference Sequence: XM_540833.6. ( FIG. 1B ). 
     Example 4: Analysis of scFv-Fc Fusion Binding to Human TEM1 Expressing Cells Using FACS 
     The ability of anti-TEM1 scFv-Fc fusions to bind to TEM1 expressed on cells was assessed using fluorescence-activated cell sorting (FACS). 
     Adherent cells were detached using 10 mM EDTA, counted and resuspended in fresh, complete culture medium. All subsequent steps were performed on ice. For each sample, 0.5×10 6  cells were first blocked in FACS buffer (5% FBS in PBS) and then incubated for 1 h with test antibody (typically 1-2 μg/ml) or expression supernatant diluted in FACS buffer. After washing three times with FACS buffer, the secondary antibody, Alexa Fluor 647 AffiniPure Goat Anti-Human IgG (Jackson Immunoresearch, #109-605-098, 1:200 dilution) was added. Following incubation for 30 min the cells were washed again three times. Immediately before data acquisition, dead cells were stained with 4′,6-Diamidino-2-phenylindole (DAPI, 1:2000 dilution). Data was acquired using an LSR-II flow cytometer equipped with FACSDIVA software (BD Biosciences). Data analysis and plotting were carried out using FlowJo v10 (FlowJo LLC). As shown in  FIG. 2 , anti-TEM1 scFv-Fc fusions 1C1, 2B11, and 3B6 bound to TEM1 expressing cell lines, but not to TEM1 −  control cell lines, demonstrating that the selected scFv-Fc fusions are selective for TEM1. sc78-Fc served as a (TEM1 binding) positive control and was previously described in WO2011060233A1. 
     Similarly,  FIG. 5  shows that scFv-Fc fusions 1C1, 1C1 mut (see Example 5), 2B11, and 3B6 bind to cells transiently transfected with native FL-hTEM1, but not to a control cell line. 
     Example 5: Analysis of scFv-Fc Fusion/T-Cell Engager Binding to Human TEM1 Using Surface Plasmon Resonance (SPR) 
     The binding of 1C1 and 1C1mut in scFv-Fc fusion and T-cell engager (BiTE) format were determined by surface plasmon resonance (SPR). Bi-specific T-cell engagers (BiTEs) are bispecific monoclonal antibodies that T-cells to cancer cells. BiTEs are fusion proteins comprising a scFv targeting a cancer antigen such as TEM1, and a scFv that binds to T-cells via the CD3 receptor. 
     SPR 
     SPR analysis was performed on a Biacore T200 instrument (GE Healthcare). Experiments involving TEM1-SpyC ligand immobilization used a Series S SA sensor chip (GE Healthcare, #BR-1005-31). Briefly, 1 ml of crude TEM1-SpyC expression media was incubated with 1 μM of bSpyT at RT for 2 h with gentle rotation. The resulting covalent TEM1-SpyC:bSpyT complex was separated from free bSpyT by buffer-exchange into 1× filtered Biacore running buffer (HBS-EP+; 0.01 M HEPES, 0.15 M NaCl, 0.05% Surfactant P20, 3 mM EDTA, pH 7.4; GE Healthcare, #BR-1006-69) using a spin column with a 10 KDa cut-off (Vivaspin 6; GE Healthcare, #28932296). The biotinylated TEM1-SpyC ligand complex was immobilized on the SA chip at a density of 150 RU. For kinetic analysis, analytes were diluted into running buffer and injections/dissociations carried out at 30 μl/min with data collected in Single Cycle Kinetics mode. For Fc-capture experiments, 10000 RU of AffiniPure Goat Anti-Human IgG (Jackson ImmunoResearch, #109-005-098) were immobilized on a CMS Series S sensor chip (GE Healthcare, #BR-1005-30) by amine coupling according to the manufacturer&#39;s instructions. Anti-TEM1 scFv-Fc molecules were captured at a target density of 100 RU and analytes were injected and dissociated at 30 μl/min with data acquired in Multiple Cycle Kinetics mode. Surfaces were regenerated between cycles/experiments by injecting 10 mM glycine-HCl, pH 1.5 for 30 s. Corrections for bulk shift and refractive index changes were performed by subtracting the signal of a reference flow cell from the active cell. 
     Results 
     As show in  FIG. 3 , 1C1mut shows a 70-80 fold increased affinity for human TEM1 in both BiTE as well as scFv-Fc format. 
     Example 6: Cross-Reactivity of Isolated scFv-Fc Fusions 
     As shown in  FIG. 4 , 1C1mut recognizes both human and murine TEM1, demonstrating that this antibody may be used in animal studies and can also serve as a therapeutic agent in humans. 
     As shown in  FIGS. 6 and 7 , 1C1 binds to cells transiently expressing canine TEM1, as well as to TEM1 +  canine tumor cells. 
     Example 7: Generation of TEM1-Binding Tri-Lobed Bi-Directional T-Cell Engager Molecules 
     Tri-lobed Bi-specific T cell engager (tB)molecules were generated by C-terminal fusion of an anti-TEM1 (1C1 and 1C1mut) scFv domain to the VH-CH1 (derived from human IgG1) and VL-CK domain of a humanized and chimeric anti-CD3 Fab (derived from clone UCHT1) via a flexible, glycine/serine-rich linker (see  FIG. 1C ). The resulting constructs are referred to as 1C1-tB (Tri-lobed Bi-specific T cell engager (tB) comprising 1C1 scFv) and 1C1m-tB (Tri-lobed Bi-specific T cell engager (tB) comprising 1C1mut scFv). 
     Generation of Tri-Lobed Bi-Specific T Cell Engager (tB) Constructs 
     To generate the Tri-lobed Bi-specific T cell engager (tB) constructs, nucleic sequences were synthesized encoding the heavy and light chains of the humanized and chimeric anti-CD3 clone UCHT1 were synthesized in Fab format (GeneArt, Thermo Fisher Scientific) (VH sequence of anti-CD3 antibody: SEQ ID NO:44; VL sequence of anti-CD3 antibody: SEQ ID NO:45). The following, stabilizing mutations were introduced at the CH1-CK interface: S64E and S66V (CH1 domain) and S69L and T71S (Cκ domain). The sequences encoding for the heavy and light chains of the resulting chimeric molecule were separately cloned into a pTT-based mammalian episomal expression vector. Both constructs contained modular cloning sites (NcoI/SalI) to accommodate insertion of the anti-TEM1 scFv encoding sequences. In the resulting Tri-lobed Bi-specific T cell engager (tB) molecules, the scFv fragments were C-terminally fused to the CH1 or CK domain of the anti-CD3 Fab via a flexible, glycine/serine-rich) linker (i.e., GGGGSGGGSGGGS (SEQ ID NO:46) for Cκ and DKTHTGGGGSGGGGS for CH1 (SEQ ID NO:47). 
     Protein Expression 
     Recombinant protein was produced using the mammalian HEK293-6E/pTT transient expression system (National Research Council of Canada). HEK293-6E cells were grown in Freestyle F17 medium (Thermo Fisher Scientific, #A13835) containing 4 mM GlutaMAX (Life Technologies, #35050061), 0.1% Pluronic® F-68 (Life Technologies, #24040032) and 25 μg/mL G418 (Life Technologies, #10131019) at 37° C., 5% CO 2  and 120 rpm. For transfection, the DNA was mixed with FectoPRO (Polyplus, #116-010) transfection reagent in F17 medium without supplements, according to the manufacturer&#39;s instructions. After five days of protein expression, cultures were subjected to low speed centrifugation and the media collected. 
     Protein Purification of Tri-Lobed Bi-Specific T Cell Engagers (tBs) 
     Tri-lobed Bi-specific T cell engagers (tBs) were purified from clarified expression media by immobilized metal ion affinity chromatography (IMAC) using a HisTrap excel column (GE Healthcase, #17371205) at a flow-rate of 1 ml/min. The column was equilibrated with 50 mM Tris, 0.5 M NaCl, 10 mM imidazole, pH 7.5 and protein was eluted with 50 mM Tris, 0.5 M NaCl, 300 mM imidazole, pH 7.4 in 1 ml fractions. Monomeric peak fractions were immediately separated by preparative size-exclusion chromatography using a Superdex 200 Increase 10/300 GL column (GE Healthcare, #28990944) at a flow-rate of 0.75 ml/min. PBS (0.01 M phosphate, 0.14 M NaCl, pH 7.4) was used as sample diluent and eluent. All chromatography experiments were run on an AKTApure chromatography system (GE Healthcare). 
     Biophysical Protein Characterization of Tri-Lobed Bi-Specific T Cell Engagers (tBs) 
     Purified protein samples were quality controlled by SDS-PAGE. 2 μg purified tB protein were resuspended in 1×LDS buffer (NuPAGE; Life Technologies, #NP0007) with or without 10% reducing agent (NuPAGE; Life Technologies, #NP0009) and heated at 70° C. for 10 min. Samples were separated on a Novex 4-12% Bis-Tris gel (Life Technologies, #NP0321) for 38 min at 200 V and separated protein bands visualized by Coomassie Blue staining (InstantBlue; Expedeon, #ISB1L). 
     The integrity and homogeneity of tB candidates was assessed by size-exclusion chromatography (SEC) using an ĀKTApure chromatography system (GE Healthcare). To this end, 100 μl concentrated (≈1 mg/ml) protein sample was injected and separated over a Superdex 200 Increase 5/150 GL analytical grade column (GE Healthcare, #28990945) at a flow rate of 0.45 ml/min. PBS (0.01 M phosphate, 0.14 M NaCl, pH 7.4) was used as sample diluent and eluent. 
     In order to compare the relative thermal stability of different scFv clones, a thermal shift assay was performed following the Protein Thermal Shift Assay protocol from Applied Biosystems (#4461146). Therefore, purified protein was diluted to 5 μM with PBS and mixed with 5 μl Protein Thermal Shift Buffer and 2.5 μl 8× Protein Thermal Shift Dye. Each reaction was prepared in triplicate in a MicroAmp Fast Optical Reaction Plate (Lifetechnologies, #4346907) and sealed with MicroAmp Optical Adhesive Film (Lifetechnologies, #4360954). Melting curves were generated with a 7500 Fast RT-PCR machine (Applied Biosystems), starting at 25° C. and gradually increasing the temperature by 0.05° C./s until reaching 99° C. To obtain relative melting temperatures based on the transition point of the melting curve, the derivative of the fluorescence signal was calculated as a function of temperature. Data analysis was carried out using Applied Biosystems 7500 Fast RT-PCR software. 
     Results 
     Recombinant expression in HEK293-6E cells followed by affinity chromatography yielded good protein quantities (≈20 mg/l) of the expected size (≈110 kDa). Analyses of protein homogeneity of the purified material by analytical SEC revealed &gt;95% monomeric species for both 1C1-tB and 1C1m-tB. Assessment of thermostability by Differential Scanning Fluorimetry (DSF) revealed melting transitional temperatures comparable to those obtained in the scFv-Fc fusion format: 71.4° C. for 1C1-tB and 64.9° C. for 1C1m-tB. 
     Example 8: Anti-TEM1 Tri-Lobed Bi-Specific T Cell Engager (tB) Molecules Engage and Activate Human T-Cells In Vitro 
     The ability of anti-TEM1 Tri-lobed Bi-specific T cell engager (tB) molecules to specifically engage and activate primary human T-cells, to induce T-cell cytokine secretion, and to induce T-cell cytotoxicity was assessed. 
     Purification of Primary Human T-Cells 
     For the isolation of primary T-cells, peripheral blood mono-nucleated cells (PBMCs) were isolated from fresh buffy coats obtained from healthy volunteer donors (Service de transfusion, Epalinges, Switzerland). PBMCs were separated by density centrifugation using Lymphoprep (Axonlab, #1114545). Pan-T-cells were subsequently extracted by magnetic separation using a human pan-T-cell isolation kit (Miltenyi Biotec, #130-096-535) and stimulated with human T-cell activator CD3/CD28 beads (Life Technologies, #11161D) and 50 RU IL-2 (Peprotech, #200-02-50 UG) for 5 days. After the removal of the beads, primary T-cells were further expanded with IL-7 and IL-15 (Miltenyi Biotec, #130-095-367 and #130-095-765) for a further 5-10 days. 
     Early T-Cell Activation Assay 
     For measuring early T-cell activation, 0.5×10 6  A673 (hTEM1 + ) or Raji (hTEM1 − ) target cells were seeded into 24-well plates. Subsequently, 0.5×10 6  purified and expanded primary human T-cells were added the wells. When used, purified tB protein was added to a final concentration of 5 nM. After 16-18 h of co-culture, the stimulated T-cells were recovered and washed once in FACS buffer. Cells were blocked with FACS buffer (5% FBS, PBS) for 20 min on ice and incubated with the following staining mix: APC anti-hCD8 (Biolegend #344722), BV785 anti-hCD4 (Biolegend #317441), Alexa Fluor 700 anti-hCD69 (Biolegend #310922), PE anti-hCD25 (Biolegend #302606). After 30 min of incubation on ice, the cells were washed again three times. Immediately before data acquisition, dead cells were stained with 4′,6-Diamidino-2-phenylindole (DAPI, 1:2000 dilution). Data was acquired using an LSR-II flow cytometer equipped with FACSDIVA software (BD Biosciences). Data analysis and plotting were carried out using FlowJo v10 (FlowJo LLC). 
     Quantification of IFN-γ effector cytokine 
     Supernatants of co-cultures set up as described above were tested for the presence of T-cell-secreted IFN-γ effector cytokine. Quantification was by performed using beads (MultiCyt QBeads, Bucher Biotec #90603). Assays were performed according to the manufacturer&#39;s instructions. Standard curves were prepared to quantify secreted cytokine. MultiCyt beads were analyzed on an Intellicyt iQue™ Screener PLUS instrument (10 s sampling; 1 ul/s). 
     Cytotoxicity Assay (LDH Release) 
     For T-cell activation assays, 2×10 4  adherent target cells were seeded in 96-well flat-bottom plates and allowed to attach for ˜20 h. When approximately 30% confluency was observed, soluble tBs were added as 3-fold serial dilutions, typically starting from 5 nM. Positive control wells were lysed using 1% Triton X-100. 1.25×10 6  purified and expanded primary human T-cells were added to the plate to reach an E:T ratio of around 5:1 and incubated for 24 h at 37° C. Specific target cell killing was assessed by measuring LDH release with the CytoTox 96 kit from Promega (#G1780), following the manufacturer&#39;s instructions. Control wells were lysed using 10% Triton X-100. Subsequently, 50 μl clarified culture supernatant was mixed with 50 μl CytoTox 96 Reagent and incubated at RT for 30 min (protected from light). The reaction was stopped by adding 50 μl stop solution and LDH activity was quantified colorimetrically, measuring absorbance at 490 nm on a BioTec H1MFG Synergy plate reader. Background signal was subtracted from all samples and corrected cell killing (spontaneous release by targets and effectors subtracted) were calculated as a percentage of maximum lysis. 
     Real-Time Kinetics of Cell Killing 
     For the assessment of specific target cell killing using real-time kinetic cell imaging, 2×10 4  adherent target cells were seeded in 96-well flat-bottom plates and allowed to attach for ˜20 h. When approximately 30% confluency was observed, soluble Tri-lobed Bi-specific T cell engagers (tBs) were added at a concentration of 0.6 nM or 0.06 nM, respectively. Positive control wells were lysed using 1% Triton X-100. 1.25×10 6  purified and expanded primary human T-cells were added to the plate to reach an E:T ratio of around 5:1. Cytotox Red reagent (Essen Bioscience, #4632) was added to a final dilution of 1:4000, and resultant cell death was monitored as an increase in fluorescence over time, acquiring images every hour. Image acquisition and data analysis were performed on an Incucyte Live Cell Analysis system (Essen Bioscience). 
     Results 
     Co-cultivation of TEM1-expressing A673 cells, human T-cells and either Tri-lobed Bi-specific T cell engager (tB) construct 1C1-tB or 1C1m-tB led to significant early T-cell activation as evidenced by increased T-cell expression of CD69 and CD25, early markers of T-cell activation ( FIG. 8 ). No T-cell activation was observed in presence of hTEM1 −  Raji cells ( FIG. 8 ). 
     Anti-TEM1 Tri-lobed Bi-specific T cell engagers (tBs) stimulated primary human T-cells to secrete IFN-γ effector cytokine and to lyse hTEM1 +  tumor cells (A673 or SK-N-AS) after 24 h of co-culture (A673 is a human sarcoma cell line, and SK-N-AS is a human neuroblastoma cell line) ( FIG. 9 ). The activation of T-cell effector functions was specific and did not occur in the presence of hTEM1 −  AsPC-1 cells (human adenocarcinoma cell line). At lower tB concentrations (0.1 nM), the higher-affinity variant 1C1m achieved the lysis of a higher proportion of target cells ( FIG. 9 ). 
     In a time-lapse microscopy-based killing assay, both 1C1m and the previously published anti-TEM1 scFv sc78 specifically and rapidly redirected primary human T-cells to lyse relevant target cells in the Tri-lobed Bi-specific T cell engager (tB) format. In both cases, complete lysis was reached after 12 h. 1C1m-tB was able to efficiently mediate complete lysis of TEM1-expressing target cells at a ten times lower molecular concentration than sc78-tB. Furthermore, neither of these molecules activated T-cells in the presence of control cells, thereby sparing them from T-cell mediated cytotoxicity ( FIG. 10 ). 
     To fine-tune Tri-lobed Bi-specific T cell engager (tB) specificity and T-cell engagement, mono- and bi-valent Tri-lobed Bi-specific T cell engagers (tBs) of both 1C1 (low-affinity variant) and 1C1mut (high affinity variant) were generated and their respective ability to achieve T-cell induced lysis of hTEM1 +  cells was examined. As expected, the bivalent Tri-lobed Bi-specific T cell engager (tB) comprising the high affinity scFv (1C1mut) led to the highest degree of target cell killing, whereas the mono-valent Tri-lobed Bi-specific T cell engager (tB) comprising the lower affinity scFv (1C1) resulted in the lowest degree of killing ( FIG. 11 ). 
     Example 9: Anti-TEM1 Tri-Lobed Bi-Specific T Cell Engager (tB) Molecules Engage and Activate Human T-Cells In Vivo 
     The ability of a Tri-lobed Bi-specific T cell engager (tB) comprising the 1C1mut-scFv (1C1m-tB) to redirect primary human T-cells to tumor cells in vivo was assessed using a mouse model. 
     Tumor Growth Assay 
     For the A673 xenograft study, 30 female NSG mice (10-week old) were implanted with 10 6  A673 cells s.c. on the right flank. 10 out of the 30 animals received only A673 cells and 20 mice received the tumor cells mixed with 10 7  primary human T-cells. Human pan-T-cells were isolated from a fresh buffy coat and expanded using CD3/CD28 beads as described previously. One hour after tumor implantation, 10 of the T-cell-implanted mice received 1 mg/kg 1C1m-tB in 100 μl PBS into the tail vein. Control groups (n=10) received 100 μl PBS. The i.v. dosing of 1C1m-tB or PBS vehicle control was repeated 24 h and 48 h after tumor implantation. Subsequently, mice were monitored three times a week and tumors were measured using calipers for a total of 45 days, or until the tumor volume approached 1000 mm 3 . NSG mice were bred and housed in a specific and opportunistic pathogen-free environment. All experiments were performed in accordance with the guidelines of the Swiss Federal Veterinary Office and approved by the Cantonal Veterinary Office under the license number 2797.1 
     Results 
     The A673 cells rapidly formed tumors in the untreated animals. The co-administration of human T-cells together with the tumor cells substantially delayed tumor outgrowth, but all animals eventually developed tumors. In contrast, following the IV administration of 1C1m-tB, tumor establishment was prevented, or significantly suppressed suggesting an effective delivery of the tB to the tumor site. ( FIG. 12 ). Five out of ten animals treated with 1C1m-tB never developed any tumor, indicating that all tumor cells were eradicated efficiently. Other animals treated with 1C1m-tB developed only flat, scar-like lesions, which never grew to a three-dimensional tumor mass. These results show that an anti-TEM1 Tri-lobed Bi-specific T cell engager (tB) can effectively redirect human T-cells to kill TEM1-expressing target cells in vivo. Further, the administration of 1C1m-tB had no impact on body weight and no apparent toxicities were observed over the course of the experiment. Finally, pharmacokinetic analyses conducted for anti-TEM1 Tri-lobed Bi-specific T cell engager (tB) suggests complete clearance of the molecule in ˜48 h. 
     Example 10: Generation of TEM1-Binding CAR 
     Instead of using soluble mediators to recruit T-cells to the tumor site, T-cells can also be engineered to express synthetic tumor targeting receptors, termed chimeric antigen receptors (CARs). Anti-TEM1 scFv domains were embedded in a modular second-generation CAR construct comprising a CD28 spacer, transmembrane (TM) domain and cytosolic domain fused to CD3 immunoreceptor tyrosine-based activation motif (ITAM) signaling elements (which mediate T-cell activation upon antigen recognition) and an in-frame monomeric GFP (as a reporter) ( FIG. 1D ). 
     Generation of CAR-T-Cells 
     For the manufacturing of CAR-T-cells, sequences encoding anti-TEM1 scFv or anti-CD19 (FMC63; sequence extracted from U.S. Pat. No. 7,446,179) were fused to a spacer/hinge transmembrane region and intracellular costimulatory domain derived from hCD28, followed by an intracellular hCD3ζ signaling domain. The resulting 2 nd  generation CAR cassettes were cloned in-frame to a monomeric green fluorescent protein ORF (TagGFP2, Evrogen) into a modified pRRL lentiviral vector (originally developed by Didier Trono, EPFL). Lentivirus was produced by transient transfection of HEK293T cells using pCMVR8.74 and pMD2.G plasmids for packaging (origin: Didier Trono lab, EPFL) and Turbofect transfection reagent (Life Technologies, #R0532). Virus-containing supernatant was harvested after 48 h, concentrated by ultracentrifugation and 100 μl were added directly to 5×10 6  Jurkat-NFAT reporter cells or primary human T-cells pre-plated in 48-well plates on the previous day. Primary T-cells were transduced the day after isolation. All transduced cells were expanded for 10-14 days before performing functional assays. 
     Jurkat NFAT Activation Reporter Cell Assays 
     For the assessment of CAR-induced ITAM-signaling, Jurkat-NFAT-mCherry reporter cells were transduced with CAR-GFP constructs as described above. 10-14 days after transduction, 10 6  transduced Jurkat reporters were seeded in 24-well plates together with 10 6  target cells. After 24 h of co-culture, Jurkat-NFAT-mCherry cells were harvested by pipetting, washed in FACS buffer (5% FBS, PBS) and analyzed for GFP and mCherry expression by flow cytometry. 
     Early T-Cell Activation Assay 
     For measuring early T-cell activation, 0.5×10 6  A673 (hTEM1 + ) or AsPC-1 (hTEM1 − ) target cells were seeded into 24-well plates. Subsequently, 0.5×10 6  purified and expanded primary human CAR-T-cells expressing anti-TEM1 or anti-CD19 scFv targeting moieties were added the wells. After 16-18 h of co-culture, the stimulated CAR-T-cells were recovered and washed once in FACS buffer. Cells were blocked with FACS buffer (5% FBS, PBS) for 20 min on ice and incubated with the following staining mix: APC anti-hCD8 (Biolegend #344722), BV785 anti-hCD4 (Biolegend #317441), Alexa Fluor 700 anti-hCD69 (Biolegend #310922), PE anti-hCD25 (Biolegend #302606). After 30 min of incubation on ice, the cells were washed again three times. Immediately before data acquisition, dead cells were stained with 4′,6-Diamidino-2-phenylindole (DAPI, 1:2000 dilution). Data was acquired using an LSR-II flow cytometer equipped with FACSDIVA software (BD Biosciences). Data analysis and plotting were carried out using FlowJo v10 (FlowJo LLC). 
     Real-Time Kinetics of Cell Killing 
     For the assessment of specific target cell killing using real-time kinetic cell imaging, 2×10 4  adherent target cells were seeded in 96-well flat-bottom plates and allowed to attach for ˜20 h. When approximately 30% confluency was observed, 1.25×10 6  purified and expanded anti-TEM1-CAR-T-cells were added to the plate to reach an E:T ratio of around 5:1. Cytotox Red reagent (Essen Bioscience, #4632) was added to a final dilution of 1:4000, and resultant cell death was monitored as an increase in fluorescence over time, acquiring images every 2 hours. Image acquisition and data analysis were performed on an Incucyte Live Cell Analysis system (Essen Bioscience). 
     Results 
     Anti-TEM1 CAR constructs were generated comprising anti-TEM1 scFv domains derived from antibodies 1C1, 1C1m, and sc78. An anti-CD19 CAR construct (scFv derived from clone FMC63) was used as a control. To demonstrate the activating potential of anti-TEM1 CARs, Jurkat NFAT-reporter cells were engineered to express the fluorescent protein mCherry under the control of an NFAT-driven promoter. The cells were virally transduced with a construct for the expression of the anti-TEM1 CAR. CAR T-cells comprising the high-affinity scFv 1C1m triggered a differential induction of CD3-driven NFAT signaling in response to TEM1-expressing target cells, compared to TEM1 −  control cells ( FIG. 13 ). 
     Further, 1C1m-CAR-T-cells unregulated the T-cell activation markers CD69 and CD25 upon stimulation with TEM1 +  A673 cells, with the magnitude of expression by 1C1m-CAR-T-cells reaching levels comparable with FMC63-CAR-T-cells co-cultured with CD19 +  Raji cells. Importantly, CD69/CD25 expression observed in the presence of TEM1 −  control cells remained low. Of note, sc78 did not seem to induce significant activation of CD3ζ-ITAM signaling in CAR format ( FIG. 14 ). 
     Finally, consistent with the observed up-regulation of CD69/CD25, 1C1m-CAR-T-cells specifically lysed TEM1-expressing A673 tumor cells, in a real-time cytotoxicity assay, while sparing TEM1-negative cells. Maximum lysis was completed after 24 h of co-culture. CAR-T-cells equipped with the previously described clone sc78 did not lyse TEM1 +  target cells ( FIG. 15 ).