Title of Invention: HER2-TARGETING MOLECULES COMPRISING DE-IMMUNIZED, SHIGA TOXIN A SUBUNIT SCAFFOLDS Abstract: Provided herein are HER2-targeting molecules comprising Shiga toxin A Subunit derived polypeptides having 1) de-immunization and 2) reduced, protease-cleavage sensitivity while retaining Shiga toxin function(s), such as, e.g., potent cytotoxicity via ribosome inhibition. Certain HER2-targeting molecules of the present invention exhibit reduced immunogenic potential in mammals and are well-tolerated by mammals while retaining aforementioned features. The HER2-targeting molecules of the present invention have uses for selectively killing specific cells (e.g., HER positive tumor cells); for selectively delivering cargos to specific cells (e.g., HER positive tumor cells), and as therapeutic and/or diagnostic molecules for treating and diagnosing a variety of conditions, including cancers and tumors involving the expression or over-expression of cell-surface HER2. Detailed Description: CROSS-REFERENCE TO RELATED APPLICATIONS This application is a Continuation Application of International Application No. PCT/US2019/027627, filed Apr. 16, 2019, which claims benefit under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application No. 62/659,116, filed Apr. 17, 2018, the contents of each of which are incorporated herein by reference in their entirety. SEQUENCE LISTING The instant application contains a Sequence Listing which has been submitted electronically in ASCII format and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Apr. 16, 2019, is named PCT-Sequence-Listing-as-filed-P61033WO.txt and is 290485 bytes in size. TECHNICAL FIELD The present invention relates to HER2-targeting molecules comprising Shiga toxin effector polypeptides, derived from the A Subunits of naturally occurring Shiga toxins, that comprise a combination of mutations providing (1) de-immunization, (2) a reduction in protease sensitivity, and/or (3) an embedded, T-cell epitope(s); wherein the Shiga toxin effector polypeptides retain one or more Shiga toxin functions, such as, e.g., potent cytotoxicity. The HER2-targeting molecules of the present invention are useful for administration to multicellular organisms, such as, e.g., when it is desirable to (1) eliminate or reduce non-specific toxicities and/or (2) eliminate or reduce certain immune responses. The HER2-targeting molecules of the present invention are useful (1) for selectively killing specific HER2-positive cell type(s) amongst other cells and (2) as therapeutic molecules for treating a variety of diseases, disorders, and conditions involving HER2-expressing cells, including cancers and tumors. BACKGROUND HER2 is a particularly attractive molecular target for therapeutics because of its overexpression on the surfaces of tumor and/or cancer cells, its correlation with poor prognoses, and its functional roles in tumorigenesis and cancer development, such as invasiveness and metastasis, and anti-neoplastic drug resistance (Nielsen D et al., Breast 22: 1-12 (2013); Ocafia A, Pandiella A, Curr Pharm Des 19: 808-17 (2013)). HER2 (human epidermal growth factor receptor 2) is a type I transmembrane tyrosine kinase receptor of the ErbB family (Yamamoto T et al., Nature 319: 230-4 (1986); Slamon D et al., Science 235: 177-82 (1987)). Members of the ErbB family are integral glycoproteins which regulate cell growth, differentiation, and survival by binding to growth factor ligands as dimers (Chantry A, J Biol Chem 270: 3068-73 (1995)). HER2 is prominently associated with the pathogenesis, progression, and prognosis of certain breast cancers, among other cancers (Citri A, Yarden Y, Nat Rev Mol Cell Biol 7: 505-16 (2006)). The proto-oncogene HER2, which encodes HER2, was found to be amplified and overexpressed in breast cancer cells (King et al., Science 229: 974-6 (1985); Slamon et al. Science 235: 177-82 (1987)). Amplification and/or over-expression of HER2 occurs in approximately 15-30% of breast cancers, and the presence of HER2 in breast cancer is strongly associated with aggressive malignancy, increased disease recurrence, and poor prognosis (Slamon D et al., Science 244: 707-12 (1989)); Bernstein H, N Engl J Med 353: 1652-4 (2005); Pritchard I et al., N Engl J Med 354: 2103-11 (2006); Tan M, Yu D, Adv Exp Med Biol 608: 119-29 (2007); Mitri Z et al., Chemother Res Pract 2012: 743193 (2012)). HER2 is overexpressed in many other diverse cancers and may functionally contribute to tumorigenesis generally. HER2 overexpression has been observed in breast, colorectal, endometrial, esophageal, gastric, head and neck, lung, ovarian, prostate, pancreatic, and testicular germ cell tumor cells (Kern J et al., Cancer Res 50: 5184-7 (1990); Natali Petal., Int J Cancer 45: 457-61 (1990); Jaehne J et al., J Cancer Res Clin Oncol 118: 474-9 (1992); Signoretti S et al., J Natl Cancer Inst 92: 1918-25 (2000); Di Lorenzo G et al., Clin Cancer Res 8: 3438-44 (2002); Owens Metal., Clin Breast Cancer 5: 63-9 (2004); Roskoski R, Biochem Biophys Res Commun 319: 1-11 (2004); Cohen G et al., Cancer Res 66: 5656-64 (2006); Santin A et al., Int J Gynaecol Obstet 102: 128-31 (2008); Vermeij J et al., BMC Cancer 8: 3 (2008); Chen P et al., J Clin Pathol 66: 113-9 (2013); Chou et al., Genome Med 5: 78 (2013); Cros J et al., Ann Oncol 24: 2624-9 (2013); Konig A et al., Anticancer Res 33: 4975-82 (2013); Sugishita Y et al., Int J Oncol 42: 1589-96 (2013)). In addition, overexpression of HER2 in a tumor cell can confer drug resistance to anti-neoplastic agents (Koutras A et al., Crit Rev Oncol Hematol 74: 73-8 (2010)). There is an urgent need for new therapeutics to supplement present day therapies for HER2-bearing neoplasms. Thus, it would be desirable to have cytotoxic cell-targeting molecules which target HER2 for use as therapeutic molecules to treat a variety of diseases, such as, e.g., cancers and tumors, that can be treated by selective killing of, or selective delivery of a beneficial agent into, a HER2 positive cell. In particular, it would be desirable to have HER2-binding, cytotoxic, cell-targeting molecules exhibiting low antigenicity and/or immunogenicity, low off-target toxicity, and potent cytotoxicity. Furthermore, it would be desirable to have HER2-targeting therapeutic and/or diagnostic molecules exhibiting low antigenicity and/or immunogenicity, low off-target toxicity, high stability, and/or the ability to deliver peptide-epitope cargos for presentation by the MHC class I system of a target cell. For example, it would be desirable to have cytotoxic HER2-targeting molecules comprising Shiga toxin A Subunit derived components which maintain potent cytotoxicity to target cells while 1) reducing the potential for unwanted antigenicities and/or immunogenicities, 2) reducing the potential for non-specific toxicities, 3) allowing for drug tolerability over a wide range of dosages, 4) allowing for drug tolerance after repeated administration, and 5) retaining effectiveness in the presence of one or more additional HER2-targeted therapies. SUMMARY OF THE INVENTION The Shiga toxin A Subunit derived components of the HER2-targeting molecules of the present invention each comprise a combination of features (e.g., de-immunized sub-region(s) and a protease-cleavage resistant sub-region). Certain combination Shiga toxin effector polypeptides of the present invention are more useful because they provide several Shiga toxin effector functions in a single polypeptide, such as, e.g., promoting cellular internalization, directing sub-cellular routing to the cytosol, ribosome inactivation, and/or delivering cargos to subcellular compartments. Certain HER2-targeting molecules of the present invention are more useful because they provide a combination of several properties in a single molecule, such as, e.g., efficient cellular internalization, potent cell-targeted cytotoxicity, selective cytotoxicity, de-immunization, low non-specific toxicity at high dosages, high stability, CD8+ T-cell hyper-immunization, and/or 5) retention of effectiveness in the presence of one or more additional HER2-targeted therapies. Different embodiments of the HER2-targeting molecules of the present invention are described below with reference to sets of embodiments numbered #1-3. Embodiment Set #1—HER2-Targeting Molecule Comprising a De-Immunized Shiga Toxin Effector Polypeptide Comprising an Embedded or Inserted, Heterologous, T-Cell Epitope and a Non-Overlapping De-Immunized Sub-Region The present invention provides cell-targeting molecules, each comprising (i) a binding region capable of specifically binding an extracellular target biomolecule (HER2/neu/ErbB2) and (ii) a de-immunized, Shiga toxin A Subunit effector polypeptide. For example, certain embodiments of Set #1 is the cell-targeting molecule comprising (i) a binding region capable of specifically binding an extracellular target biomolecule and (ii) a de-immunized, Shiga toxin effector polypeptide comprising a Shiga toxin A1 fragment region and a carboxy-terminus, wherein the Shiga toxin A subunit effector polypeptide comprises: (a) at least one inserted or embedded, heterologous epitope; and (b) at least one disrupted, endogenous, B-cell and/or CD4+ T-cell epitope region which does not overlap with the embedded or inserted, heterologous, T-cell epitope. For certain further embodiments, the Shiga toxin effector polypeptide is capable of exhibiting at least one Shiga toxin effector function, such as, e.g., directing intracellular routing to the endoplasmic reticulum and/or cytosol of a cell in which the polypeptide is present, inhibiting a ribosome function, enzymatically inactivating a ribosome, causing cytostasis, and/or causing cytotoxicity. The Shiga toxin effector polypeptide of Embodiment Set #1 may be truncated at its carboxy-terminus, relative to a wild-type Shiga toxin A Subunit, resulting in the elimination of one or more endogenous, B-cell and/or CD4+ T-cell epitope regions. The Shiga toxin effector polypeptide of Embodiment Set #1 may comprise a disrupted furin-cleavage motif at the carboxy-terminus of the A1 fragment region. In certain embodiments, the furin-cleavage motif is disrupted by a carboxy-terminal truncation of the Shiga toxin effector polypeptide as compared to the carboxy-terminus of a wild-type Shiga toxin A Subunit. For example, the present invention provides a Shiga toxin effector polypeptide comprising a Shiga toxin A1 fragment region and a carboxy-terminus, wherein the Shiga toxin A subunit effector polypeptide comprises: (a) an embedded or inserted, heterologous, epitope; (b) a disruption of at least one, endogenous, B-cell and/or CD4+ T-cell epitope region; and (c) a disrupted furin-cleavage motif at the carboxy-terminus of the Shiga toxin A1 fragment region; wherein the Shiga toxin A subunit effector polypeptide is capable of exhibiting a Shiga toxin effector function. In a further example, the present invention provides a Shiga toxin A subunit effector polypeptide comprising a Shiga toxin A1 fragment region and a carboxy-terminus, wherein the Shiga toxin A subunit effector polypeptide comprises (a) an embedded or inserted, heterologous, CD8+ T-cell epitope which disrupts an endogenous, B-cell and/or CD4+ T-cell epitope region; (b) a disruption of at least four, endogenous, B-cell and/or CD4+ T-cell epitope regions which do not overlap with the embedded or inserted, heterologous, CD8+ T-cell epitope; and (c) a disrupted furin-cleavage motif at the carboxy-terminus of the Shiga toxin A1 fragment region; and wherein the Shiga toxin A subunit effector polypeptide is truncated at its carboxy-terminus, relative to a wild-type Shiga toxin A subunit, resulting in the elimination of one or more endogenous, B-cell and/or CD4+ T-cell epitope regions; wherein the Shiga toxin A subunit effector polypeptide is capable of exhibiting a Shiga toxin effector function. Accordingly, the present invention provides a HER2-targeting molecule that comprises: (i) an immunoglobulin binding region capable of specifically binding an extracellular part of HER2/neu/ErbB2, and comprising one or more of: an antibody variable fragment, a single-domain antibody fragment, a single-chain variable fragment, a Fd fragment, an antigen-binding fragment, an autonomous VH domain, a VHH fragment derived from a camelid antibody, a heavy-chain antibody domain derived from a cartilaginous fish antibody, a VNAR fragment, and an immunoglobulin new antigen receptor; and ii) a Shiga toxin A subunit effector polypeptide comprising a Shiga toxin A1 fragment region and a carboxy-terminus, wherein the Shiga toxin A subunit effector polypeptide comprises: (a) an embedded or inserted, heterologous, CD8+ T-cell epitope which disrupts an endogenous, B-cell and/or CD4+ T-cell epitope region; (b) a disruption of at least four, endogenous, B-cell and/or CD4+ T-cell epitope regions which do not overlap with the embedded or inserted, heterologous, CD8+ T-cell epitope; and (c) a disrupted furin-cleavage motif at the carboxy-terminus of the Shiga toxin A1 fragment region; and wherein the Shiga toxin A subunit effector polypeptide is truncated at its carboxy-terminus, relative to a wild-type Shiga toxin A subunit, resulting in the elimination of one or more endogenous, B-cell and/or CD4+ T-cell epitope regions; wherein the Shiga toxin A subunit effector polypeptide is capable of exhibiting a Shiga toxin effector function. For certain further embodiments, the cell-targeting molecule is capable when introduced to cells of exhibiting a cytotoxicity comparable or better than a reference molecule, such as, e.g., a second cell-targeting molecule consisting of the cell-targeting molecule except for all of its Shiga toxin effector polypeptide components comprise a wild-type Shiga toxin furin-cleavage site at the carboxy terminus of its A1 fragment region. For certain embodiments of Embodiment Set #1, the cell-targeting molecule exhibits reduced relative antigenicity and/or relative immunogenicity as compared to a reference molecule, such as, e.g., a wild-type Shiga toxin A Subunit or a third cell-targeting molecule consisting of the cell-targeting molecule except for all of its Shiga toxin effector polypeptide component(s) each comprise a wild-type Shiga toxin A1 fragment. In certain embodiments of Embodiment Set #1, the binding region and Shiga toxin effector polypeptide are linked together, either directly or indirectly. In certain embodiments of Embodiment Set #1, the binding region comprises a polypeptide comprising an immunoglobulin or immunoglobulin-type binding region. In certain further embodiments, the binding region comprising a polypeptide selected from the group consisting of: an autonomous VH domain, single-domain antibody fragment (sdAb), Nanobody®, heavy chain-antibody domain derived from a camelid antibody (VHH or VH domain fragment), heavy-chain antibody domain derived from a cartilaginous fish antibody (VHH or VH domain fragment), immunoglobulin new antigen receptor (IgNAR), VNAR fragment, single-chain variable fragment (scFv), antibody variable fragment (Fv), complementary determining region 3 fragment (CDR3), constrained FR3-CDR3-FR4 polypeptide (FR3-CDR3-FR4), Fd fragment, small modular immunopharmaceutical (SMIP) domain, antigen-binding fragment (Fab), Armadillo repeat polypeptide (ArmRP), fibronectin-derived 10th fibronectin type III domain (10Fn3), tenascin type III domain (TNfn3), ankyrin repeat motif domain, low-density-lipoprotein-receptor-derived A-domain (LDLR-A), lipocalin (anticalin), Kunitz domain, Protein-A-derived Z domain, gamma-B crystallin-derived domain, ubiquitin-derived domain, Sac7d-derived polypeptide (affitin), Fyn-derived SH2 domain, miniprotein, C-type lectin-like domain scaffold, engineered antibody mimic, and any genetically manipulated counterparts of any of the foregoing which retain binding functionality. In certain embodiments, the binding region comprises a polypeptide selected from the group consisting of: an autonomous VH domain, single-domain antibody fragment (sdAb), Nanobody®, heavy chain-antibody domain derived from a camelid antibody (VHH or VH domain fragment), heavy-chain antibody domain derived from a cartilaginous fish antibody (VHH or VH domain fragment), immunoglobulin new antigen receptor (IgNAR), VNAR fragment, single-chain variable fragment (scFv), antibody variable fragment (Fv), Fd fragment, and antigen-binding fragment (Fab). In certain embodiments, the cell-targeting molecule of the present invention comprises an immunoglobulin binding region capable of specifically binding an extracellular part of HER2/neu/ErbB2, and comprising one or more of: an antibody variable fragment, a single-domain antibody fragment, a single-chain variable fragment, a Fd fragment, an antigen-binding fragment, an autonomous VH domain, a VHH fragment derived from a camelid antibody, a heavy-chain antibody domain derived from a cartilaginous fish antibody, a VNAR fragment, and an immunoglobulin new antigen receptor. In certain embodiments, the binding region comprises, consists essentially of, or consists of a single-chain variable fragment (scFv). In certain embodiments, the binding region comprises a single-chain variable fragment (scFv). In certain embodiments, the binding region comprises, consists essentially of, or consists of a VHH fragment derived from a camelid antibody. In certain embodiments of Embodiment Set #1, the binding region and the Shiga toxin effector polypeptide are fused, either directly or indirectly, forming a continuous polypeptide such that the binding region is associated, either directly or indirectly, with the carboxy-terminus of the Shiga toxin effector polypeptide. For certain embodiments of Embodiment Set #1, the cell-targeting molecule of the present invention is capable of exhibiting (i) a catalytic activity level comparable to a wild-type Shiga toxin A1 fragment or wild-type Shiga toxin effector polypeptide, (ii) a ribosome inhibition activity with a half-maximal inhibitory concentration (IC50) value of 10,000 picomolar or less, and/or (iii) a significant level of Shiga toxin catalytic activity. For certain embodiments of Embodiment Set #1, the cell-targeting molecule of the present invention and/or its Shiga toxin effector polypeptide is (i) capable of exhibiting subcellular routing efficiency comparable to a reference cell-targeting molecule, such as, e.g., a third cell-targeting molecule consisting of the cell-targeting molecule except for all of its Shiga toxin effector polypeptide component(s) each comprise a wild-type Shiga toxin A1 fragment, and/or (ii) capable of exhibiting a significant level of intracellular routing activity to the endoplasmic reticulum and/or cytosol from an endosomal starting location of a cell. For certain embodiments of Embodiment Set #1, whereby administration of the cell-targeting molecule of the present invention to a cell physically coupled with the extracellular target biomolecule of the cell-targeting molecule's binding region, the cell-targeting molecule is capable of causing death of the cell. For certain further embodiments, administration of the cell-targeting molecule of the invention to two different populations of cell types which differ with respect to the presence or level of the extracellular target biomolecule, the cell-targeting molecule is capable of causing cell death to the cell-types physically coupled with an extracellular target biomolecule of the cytotoxic cell-targeting molecule's binding region at a CD50 at least three times or less than the CD50 to cell types which are not physically coupled with an extracellular target biomolecule of the cell-targeting molecule's binding region. For certain embodiments, whereby administration of the cell-targeting molecule of the present invention to a first populations of cells whose members are physically coupled to extracellular target biomolecules of the cell-targeting molecule's binding region, and a second population of cells whose members are not physically coupled to any extracellular target biomolecule of the binding region, the cytotoxic effect of the cell-targeting molecule to members of said first population of cells relative to members of said second population of cells is at least 3-fold greater. For certain embodiments, whereby administration of the cell-targeting molecule of the present invention to a first populations of cells whose members are physically coupled to a significant amount of the extracellular target biomolecule of the cell-targeting molecule's binding region, and a second population of cells whose members are not physically coupled to a significant amount of any extracellular target biomolecule of the binding region, the cytotoxic effect of the cell-targeting molecule to members of said first population of cells relative to members of said second population of cells is at least 3-fold greater. For certain embodiments, whereby administration of the cell-targeting molecule of the present invention to a first population of target biomolecule positive cells, and a second population of cells whose members do not express a significant amount of a target biomolecule of the cell-targeting molecule's binding region at a cellular surface, the cytotoxic effect of the cell-targeting molecule to members of the first population of cells relative to members of the second population of cells is at least 3-fold greater. For certain embodiments of Embodiment Set #1, the cell-targeting molecule of the present invention is capable when introduced to cells of exhibiting a cytotoxicity with a half-maximal inhibitory concentration (CD50) value of 300 nM or less and/or capable of exhibiting a significant level of Shiga toxin cytotoxicity. For certain further embodiments, the cell-targeting molecule exhibits reduced relative antigenicity and/or relative immunogenicity as compared to a reference molecule, such as, e.g., a wild-type Shiga toxin A Subunit or a third cell-targeting molecule consisting of the cell-targeting molecule except for all of its Shiga toxin effector polypeptide component(s) each comprise a wild-type Shiga toxin A1 fragment. In certain embodiments of Embodiment Set #1, the heterologous, T-cell epitope is a CD8+ T-cell epitope, such as, e.g., with regard to a human immune system. For certain further embodiments, the heterologous, T-cell epitope is capable of being presented by a MHC class I molecule of a cell. In certain further embodiments, the cell-targeting molecule of the present invention is capable of one or more the following: entering a cell, inhibiting a ribosome function, causing cytostasis, causing cell death, and/or delivering the embedded or inserted, heterologous, T-cell epitope to a MHC class I molecule for presentation on a cellular surface. For certain further embodiments, the cell-targeting molecule is capable when introduced to cells of exhibiting a cytotoxicity comparable or better than a reference molecule, such as, e.g., a third cell-targeting molecule consisting of the cell-targeting molecule except for all of its Shiga toxin effector polypeptide component(s) each comprise a wild-type Shiga toxin A1 fragment. For certain embodiments of Embodiment Set #1, the cell-targeting molecule of the present invention is capable of delivering an embedded or inserted, heterologous, CD8+ T-cell epitope to a MHC class I presentation pathway of a cell for cell-surface presentation of the epitope bound by a MHC class I molecule. In certain embodiments of Embodiment Set #1, the cell-targeting molecule comprises a molecular moiety located carboxy-terminal to the carboxy-terminus of the Shiga toxin A1 fragment region. For certain embodiments of Embodiment Set #1, the cell-targeting molecule of the present invention is capable when introduced to a chordate of exhibiting improved in vivo tolerability and/or stability compared to a reference molecule, such as, e.g., a fourth cell-targeting molecule consisting of the cell-targeting molecule except for all of its Shiga toxin effector polypeptide component(s) each comprise a wild-type Shiga toxin A1 fragment and/or wild-type Shiga toxin furin-cleavage site at the carboxy terminus of its A1 fragment region. In certain further embodiments, the Shiga toxin effector polypeptide is not cytotoxic and the molecular moiety is cytotoxic. In certain embodiments of Embodiment Set #1, the cell-targeting molecule comprises a molecular moiety associated with the carboxy-terminus of the Shiga toxin effector polypeptide. In certain embodiments, the molecular moiety comprises or consists of the binding region. In certain embodiments, the molecular moiety comprises at least one amino acid and the Shiga toxin effector polypeptide is linked to at least one amino acid residue of the molecular moiety. In certain further embodiments, the molecular moiety and the Shiga toxin effector polypeptide are fused forming a continuous polypeptide. In certain embodiments of Embodiment Set #1, the cell-targeting molecule further comprises a cytotoxic molecular moiety associated with the carboxy-terminus of the Shiga toxin effector polypeptide. For certain embodiments, the cytotoxic molecular moiety is a cytotoxic agent, such as, e.g., a small molecule chemotherapeutic agent, anti-neoplastic agent, cytotoxic antibiotic, alkylating agent, antimetabolite, topoisomerase inhibitor, and/or tubulin inhibitor known to the skilled worker and/or described herein. For certain further embodiments, the cytotoxic molecular moiety is cytotoxic at concentrations of less than 10,000, 5,000, 1,000, 500, or 200 pM. In certain embodiments of Embodiment Set #1, the binding region is linked, either directly or indirectly, to the Shiga toxin effector polypeptide by at least one covalent bond which is not a disulfide bond. In certain further embodiments, the binding region is fused, either directly or indirectly, to the carboxy-terminus of the Shiga toxin effector polypeptide to form a single, continuous polypeptide. In certain further embodiments, the binding region is an immunoglobulin or immunoglobulin-type binding region. In certain embodiments of Embodiment Set #1, the disrupted furin-cleavage motif comprises one or more mutations in the minimal, furin-cleavage site relative to a wild-type Shiga toxin A Subunit. In certain embodiments, the disrupted furin-cleavage motif is not an amino-terminal truncation of sequences that overlap with part or all of at least one amino acid residue of the minimal furin-cleavage site. In certain embodiments, the mutation in the minimal, furin-cleavage site is an amino acid deletion, insertion, and/or substitution of at least one amino acid residue in the R/Y-x-x-R furin cleavage motif. In certain further embodiments, the disrupted furin-cleavage motif comprises at least one mutation relative to a wild-type Shiga toxin A Subunit, the mutation altering at least one amino acid residue in the region natively positioned (1) at 248-251 of the A Subunit of Shiga-like toxin 1 (SEQ ID NO:1), Shiga toxin (SEQ ID NO:2), or another Shiga toxin 1 variant sequence (e.g. SEQ ID NOs: 4-6); or (2) at 247-250 of the A Subunit of Shiga-like toxin 2 (SEQ ID NO:3) or a Shiga-like toxin 2 variant sequence (e.g. SEQ ID NOs: 7-18), or the equivalent amino acid sequence position in any Shiga toxin A Subunit. In certain further embodiments, the mutation is an amino acid residue substitution of an arginine residue with a non-positively charged, amino acid residue. In certain embodiments of Embodiment Set #1, the Shiga toxin effector polypeptide comprises, consists essentially of, or consists of: (i) amino acids 75 to 251 of any one of SEQ ID NOs: 1-6 and 37; (ii) amino acids 1 to 241 of any one of SEQ ID NOs: 1-18 and 75-89; (iii) amino acids 1 to 251 of any one of SEQ ID NOs: 1-6, 37, and 75-89; or (iv) amino acids 1 to 261 of any one of SEQ ID NOs: 1-3; wherein the Shiga toxin effector polypeptide comprises at least one embedded or inserted, heterologous T-cell epitope and at least one (two, three, four or more) disrupted, endogenous, B-cell and/or CD4+ T-cell epitope region(s) which does not overlap with the embedded or inserted, heterologous, T-cell epitope. In certain embodiments of Embodiment Set #1, the cell-targeting molecule of the present invention is capable when introduced to cells of exhibiting cytotoxicity comparable to a cytotoxicity of a reference molecule, such as, e.g., a third cell-targeting molecule consisting of the cell-targeting molecule except for all of its Shiga toxin effector polypeptide component(s) each comprise a wild-type Shiga toxin A1 fragment. In certain embodiments of Embodiment Set #1, the binding region may comprise at least one heavy-chain variable domain polypeptide comprising (i) the HCDR1, HCDR2, and HCDR3 amino acid sequences shown in SEQ ID NOs: 51, SEQ ID NO:52, and SEQ ID NO:53, respectively; and at least one light-chain variable domain polypeptide comprising: (i) the LCDR1, LCDR2, and LCDR3 amino acid sequences shown in SEQ ID NO:54, SEQ ID NO:55, and SEQ ID NO:56, respectively. For example, the binding region may comprises at least one heavy-chain variable domain polypeptide comprising (i) the HCDR1, HCDR2, and HCDR3 amino acid sequences shown in SEQ ID NOs: 57, SEQ ID NO:58, and SEQ ID NO:59, respectively; and at least one light-chain variable domain polypeptide comprising (i) the LCDR1, LCDR2, and LCDR3 amino acid sequences shown in SEQ ID NO:60, SEQ ID NO:61, and SEQ ID NO:62, respectively. For example, the binding region may comprises at least one heavy-chain variable domain polypeptide comprising (i) the HCDR1, HCDR2, and HCDR3 amino acid sequences shown in SEQ ID NOs: 63, SEQ ID NO:64, and SEQ ID NO:65, respectively; and at least one light-chain variable domain polypeptide comprising (i) the LCDR1, LCDR2, and LCDR3 amino acid sequences shown in SEQ ID NO:66, SEQ ID NO:67, and SEQ ID NO:68, respectively. The binding region having these CDRs may be an immunoglobulin binding region comprising a single-chain variable fragment. In certain embodiments of Embodiment Set #1, the binding region may comprises the binding region comprises a polypeptide selected from the group consisting of: a) a heavy chain only variable (VHH) domain comprising (i) a HCDR1 comprising or consisting essentially of the amino acid sequences as shown in SEQ ID NO:69 or SEQ ID NO:72; (ii) a HCDR2 comprising or consisting essentially of the amino acid sequence as shown in SEQ ID NO:70 or SEQ ID NO:73; and (iii) a HCDR3 comprising or consisting essentially of the amino acid sequence as shown in SEQ ID NO:71 or SEQ ID NO:74. The binding region having these CDRs may be an immunoglobulin binding region comprising a heavy chain only variable (VHH) domain derived from a camelid antibody. In certain embodiments of Embodiment Set #1, the binding region may comprise: (a) at least one heavy chain variable (VH) domain comprising, consisting essentially of, or consisting of: amino acids 269 to 387 of SEQ ID NOs: 26, 29, 30, or 36; amino acids 269 to 397 of SEQ ID NO:25; amino acids 381 to 500 of SEQ ID NO: 24 or 27; amino acids 401 to 522 of SEQ ID NO:36, or amino acids 401 to 520 of SEQ ID NO:28; and (b) at least one light chain variable (VL) domain comprising, consisting essentially of, or consisting of: amino acids 269 to 375 of SEQ ID NO: 24, 27, or 28; amino acids 393 to 499 of SEQ ID NO:26; amino acids 403 to 513 of SEQ ID NO:25; amino acids 408 to 514 of SEQ ID NO:36; and amino acids 413 to 519 of SEQ ID NO: 29 or 30. For example, the binding region may comprise (a) at least one heavy chain variable (VH) domain comprising, consisting essentially of, or consisting of amino acids 269 to 387 of SEQ ID NO:29; and (b) at least one light chain variable (VL) domain comprising, consisting essentially of, or consisting of amino acids 413 to 519 of SEQ ID NO:29. For example, the binding region may comprise (a) at least one heavy chain variable (VH) domain comprising, consisting essentially of, or consisting of amino acids 269 to 387 of SEQ ID NO:36; and (b) at least one light chain variable (VL) domain comprising, consisting essentially of, or consisting of amino acids 408 to 514 of SEQ ID NO:36 In certain embodiments of Embodiment Set #1, the binding region comprises, consists essentially of, or consists of the polypeptide represented by any one of the following polypeptide sequences: amino acids 269 to 513 of SEQ ID NO:25; amino acids 269 to 499 of SEQ ID NO:26; amino acids 269 to 519 of SEQ ID NO:29 or SEQ ID NO:30; amino acids 268 to 386 of SEQ ID NO:31; amino acids 253 to 370 of SEQ ID NO:34; amino acids 253 to 367 of SEQ ID NO:35; or amino acids 269 to 514 of SEQ ID NO:36. For example, the binding region comprises, consists essentially of, or consists of the polypeptide represented by amino acids 269 to 519 of SEQ ID NO:29. For example, the binding region comprises, consists essentially of, or consists of the polypeptide represented by amino acids 268 to 518 of SEQ ID NO:102. For example, the binding region comprises, consists essentially of, or consists of the polypeptide represented by amino acids 268 to 386 of SEQ ID NO:31. For example, the binding region comprises, consists essentially of, or consists of the polypeptide represented by amino acids 253 to 370 of SEQ ID NO:34. For example, the binding region comprises, consists essentially of, or consists of the polypeptide represented by amino acids 253 to 367 of SEQ ID NO:35. For example, the binding region comprises, consists essentially of, or consists of the polypeptide represented by amino acids 269 to 514 of SEQ ID NO:36. In certain embodiments of Embodiment Set #1, the cell-targeting molecule of the present invention comprises, consists essentially of, or consists of the polypeptide shown in any one of SEQ ID NOs: 22-36 and 97-108. In certain embodiments of Embodiment Set #1, the cell-targeting molecule of the present invention comprises, consists essentially of, or consists of the polypeptide shown in any one of SEQ ID NOs: 29, 31, 34, 35, 36, 102, 104, and 106-108. In certain further embodiments, the cell-targeting molecule of the present invention further comprises an amino terminal methionine residue. In certain further embodiments, the cell-targeting molecule of the present invention comprises, consists essentially of, or consists of the polypeptide shown in SEQ ID NO: 29 or 102. In certain embodiments of Embodiment Set #1, the binding region sterically covers the carboxy-terminus of the A1 fragment region. In certain embodiments of Embodiment Set #1, the molecular moiety sterically covers the carboxy-terminus of the A1 fragment region. In certain further embodiments, the molecular moiety comprises the binding region. In certain embodiments of Embodiment Set #1, the cell-targeting molecule of the present invention comprises a binding region and/or molecular moiety located carboxy-terminal to the carboxy-terminus of the Shiga toxin A1 fragment region. In certain further embodiments, the mass of the binding region and/or molecular moiety is at least 4.5 kDa, 6, kDa, 9 kDa, 12 kDa, 15 kDa, 20 kDa, 25 kDa, 28 kDa, 30 kDa, 41 kDa, 50 kDa, 100 kDa, or greater. In certain embodiments of Embodiment Set #1, the cell-targeting molecule comprises a binding region with a mass of at least 4.5 kDa, 6, kDa, 9 kDa, 12 kDa, 15 kDa, 20 kDa, 25 kDa, 28 kDa, 30 kDa, 41 kDa, 50 kDa, 100 kDa, or greater, as long as the cell-targeting molecule retains the appropriate level of the Shiga toxin biological activity noted herein (e.g., cytotoxicity and/or intracellular routing). In certain embodiments of Embodiment Set #1, the binding region is comprised within a relatively large, molecular moiety comprising such as, e.g., a molecular moiety with a mass of at least 4.5 kDa, 6, kDa, 9 kDa, 12 kDa, 15 kDa, 20 kDa, 25 kDa, 28 kDa, 30 kDa, 41 kDa, 50 kDa, 100 kDa, or greater, as long as the cell-targeting molecule retains the appropriate level of the Shiga toxin biological activity noted herein. In certain embodiments of Embodiment Set #1, the amino-terminus of the Shiga toxin effector polypeptide is at and/or proximal to an amino-terminus of a polypeptide component of the cell-targeting molecule. In certain further embodiments, the binding region is not located proximally to the amino-terminus of the cell-targeting molecule relative to the Shiga toxin effector polypeptide. In certain further embodiments, the binding region and Shiga toxin effector polypeptide are physically arranged or oriented within the cell-targeting molecule such that the binding region is not located proximally to the amino-terminus of the Shiga toxin effector polypeptide. In certain further embodiments, the binding region is located within the cell-targeting molecule more proximal to the carboxy-terminus of the Shiga toxin effector polypeptide than to the amino-terminus of the Shiga toxin effector polypeptide. For certain further embodiments, the cell-targeting molecule of the present invention is capable when introduced to cells of exhibiting cytotoxicity that is greater than that of a third cell-targeting molecule having an amino-terminus and comprising the binding region and the Shiga toxin effector polypeptide which is not positioned at or proximal to the amino-terminus of the third cell-targeting molecule. For certain further embodiments, the cell-targeting molecule of the present invention exhibits cytotoxicity with better optimized, cytotoxic potency, such as, e.g., 4-fold, 5-fold, 6-fold, 9-fold, or greater cytotoxicity as compared to the cytotoxicity of the third cell-targeting molecule. For certain further embodiments, the cytotoxicity of the cell-targeting molecule of the present invention to a population of target positive cells is 3-fold, 4-fold, 5-fold, 6-fold, 7-fold, 8-fold, 9-fold, 10-fold or greater than the cytotoxicity of the third cell-targeting molecule to a second population of target positive cells as assayed by CD50 values. In certain further embodiments, the third cell-targeting molecule does not comprise any carboxy-terminal, endoplasmic reticulum retention/retrieval signal motif of the KDEL family (e.g. SEQ ID NO:109). In certain embodiments of Embodiment Set #1, the amino-terminus of the Shiga toxin effector polypeptide is at and/or proximal to an amino-terminus of a polypeptide component of the cell-targeting molecule. In certain further embodiments, the binding region is not located proximally to the amino-terminus of the cell-targeting molecule relative to the Shiga toxin effector polypeptide. In certain further embodiments, the binding region and Shiga toxin effector polypeptide are physically arranged or oriented within the cell-targeting molecule such that the binding region is not located proximally to the amino-terminus of the Shiga toxin effector polypeptide. In certain further embodiments, the binding region is located within the cell-targeting molecule more proximal to the carboxy-terminus of the Shiga toxin effector polypeptide than to the amino-terminus of the Shiga toxin effector polypeptide. For certain further embodiments, the cell-targeting molecule of the present invention is not cytotoxic and is capable when introduced to cells of exhibiting a greater subcellular routing efficiency from an extracellular space to a subcellular compartment of an endoplasmic reticulum and/or cytosol as compared to the cytotoxicity of a reference molecule, such as, e.g., a fifth cell-targeting molecule having an amino-terminus and comprising the binding region and the Shiga toxin effector polypeptide which is not positioned at or proximal to the amino-terminus of the fifth cell-targeting molecule. In certain further embodiments, the fifth cell-targeting molecule does not comprise any carboxy-terminal, endoplasmic reticulum retention/retrieval signal motif of the KDEL family. In certain embodiments of Embodiment Set #1, the amino-terminus of the Shiga toxin effector polypeptide is at and/or proximal to an amino-terminus of a polypeptide component of the cell-targeting molecule. In certain further embodiments, the binding region is not located proximally to the amino-terminus of the cell-targeting molecule relative to the Shiga toxin effector polypeptide. In certain further embodiments, the binding region and Shiga toxin effector polypeptide are physically arranged or oriented within the cell-targeting molecule such that the binding region is not located proximally to the amino-terminus of the Shiga toxin effector polypeptide. In certain further embodiments, the binding region is located within the cell-targeting molecule more proximal to the carboxy-terminus of the Shiga toxin effector polypeptide than to the amino-terminus of the Shiga toxin effector polypeptide. For certain further embodiments, the cell-targeting molecule of the present invention exhibits low cytotoxic potency (i.e. is not capable when introduced to certain positive target cell types of exhibiting a cytotoxicity greater than 1% cell death of a cell population at a cell-targeting molecule concentration of 1000 nM, 500 nM, 100 nM, 75 nM, or 50 nM) and is capable when introduced to cells of exhibiting a greater subcellular routing efficiency from an extracellular space to a subcellular compartment of an endoplasmic reticulum and/or cytosol as compared to the cytotoxicity of a reference cell-targeting molecule, such as, e.g., a fifth cell-targeting molecule having an amino-terminus and comprising the binding region and the Shiga toxin effector polypeptide which is not positioned at or proximal to the amino-terminus of the fifth cell-targeting molecule. In certain further embodiments, the fifth cell-targeting molecule does not comprise any carboxy-terminal, endoplasmic reticulum retention/retrieval signal motif of the KDEL family. In certain embodiments of Embodiment Set #1, the cell-targeting molecule of the present invention, or a polypeptide component thereof, comprises a carboxy-terminal, endoplasmic reticulum retention/retrieval signal motif of a member of the KDEL family. For certain further embodiments, the carboxy-terminal endoplasmic reticulum retention/retrieval signal motif is selected from the group consisting of: KDEL (SEQ ID NO:109), HDEF (SEQ ID NO:110), HDEL (SEQ ID NO:111), RDEF (SEQ ID NO:112), RDEL (SEQ ID NO:113), WDEL (SEQ ID NO:114), YDEL (SEQ ID NO:115), HEEF (SEQ ID NO:116), HEEL (SEQ ID NO:117), KEEL (SEQ ID NO:118), REEL (SEQ ID NO:119), KAEL (SEQ ID NO:120), KCEL (SEQ ID NO:121), KFEL (SEQ ID NO:122), KGEL (SEQ ID NO:123), KHEL (SEQ ID NO:124), KLEL (SEQ ID NO:125), KNEL (SEQ ID NO:126), KQEL (SEQ ID NO:127), KREL (SEQ ID NO:128), KSEL (SEQ ID NO:129), KVEL (SEQ ID NO:130), KWEL (SEQ ID NO:131), KYEL (SEQ ID NO:132), KEDL (SEQ ID NO:133), KIEL (SEQ ID NO:134), DKEL (SEQ ID NO:135), FDEL (SEQ ID NO:136), KDEF (SEQ ID NO:137), KKEL (SEQ ID NO:138), HADL (SEQ ID NO:139), HAEL (SEQ ID NO:140), HIEL (SEQ ID NO:141), HNEL (SEQ ID NO:142), HTEL (SEQ ID NO:143), KTEL (SEQ ID NO:144), HVEL (SEQ ID NO:145), NDEL (SEQ ID NO:146), QDEL (SEQ ID NO:147), REDL (SEQ ID NO:148), RNEL (SEQ ID NO:149), RTDL (SEQ ID NO:150), RTEL (SEQ ID NO:151), SDEL (SEQ ID NO:152), TDEL (SEQ ID NO:153), SKEL (SEQ ID NO:154), STEL (SEQ ID NO:155), and EDEL (SEQ ID NO:156). In certain further embodiments, the cell-targeting molecule of the present invention is capable when introduced to cells of exhibiting cytotoxicity that is greater than that of a reference molecule, such as, e.g., a sixth cell-targeting molecule consisting of the cell-targeting molecule except for it does not comprise any carboxy-terminal, endoplasmic reticulum retention/retrieval signal motif of the KDEL family. In certain further embodiments, the cell-targeting molecule of the present invention is capable of exhibiting a cytotoxicity with better optimized, cytotoxic potency, such as, e.g., 4-fold, 5-fold, 6-fold, 9-fold, or greater cytotoxicity as compared to the sixth cell-targeting molecule. In certain further embodiments, the cell-targeting molecule of the present invention is capable of exhibiting a cytotoxicity with better optimized, cytotoxic potency, such as, e.g., 4-fold, 5-fold, 6-fold, 9-fold, or greater cytotoxicity as compared to the sixth cell-targeting molecule. In certain further embodiments, the cytotoxicity of the cell-targeting molecule of the present invention to a population of target positive cells is 3-fold, 4-fold, 5-fold, 6-fold, 7-fold, 8-fold, 9-fold, 10-fold or greater than the cytotoxicity of the sixth cell-targeting molecule to a second population of target positive cells as assayed by CD50 values. Embodiment Set #2—HER2-Targeting Molecule Comprising a Shiga Toxin Effector Polypeptide Comprising (i) an Embedded or Inserted, Heterologous, T-Cell Epitope and (ii) a Disrupted, Furin-Cleavage Motif The present invention provides cell-targeting molecules, each comprising (i) a binding region capable of specifically binding an extracellular target biomolecule (HER2/neu/ErbB2) and (ii) a Shiga toxin A Subunit effector polypeptide comprising an inserted or embedded, heterologous, epitope; and (iii) a disrupted furin-cleavage motif. In certain embodiments, the cell-targeting molecule of the present invention comprises (i) a binding region capable of specifically binding an extracellular target biomolecule; (ii) a Shiga toxin effector polypeptide comprising a Shiga toxin A1 fragment derived region and a carboxy terminus, wherein the Shiga toxin effector polypeptide comprises: (a) an inserted or embedded, heterologous, epitope; and (b) a disrupted furin-cleavage motif at the carboxy-terminus of the A1 fragment region. For certain further embodiments, the Shiga toxin effector polypeptide is capable of exhibiting at least one Shiga toxin effector function, such as, e.g., directing intracellular routing to the endoplasmic reticulum and/or cytosol of a cell in which the polypeptide is present, inhibiting a ribosome function, enzymatically inactivating a ribosome, causing cytostasis, and/or causing cytotoxicity. In certain embodiments, the furin-cleavage motif is disrupted by a carboxy-terminal truncation of the Shiga toxin effector polypeptide as compared to the carboxy-terminus of a wild-type Shiga toxin A Subunit. The Shiga toxin effector polypeptide may be truncated at its carboxy-terminus, relative to a wild-type Shiga toxin A subunit, resulting in the elimination of one or more endogenous, B-cell and/or CD4+ T-cell epitope regions. The Shiga toxin effector polypeptide of Embodiment Set #2 may further comprise at least one disrupted, endogenous, B-cell and/or CD4+ T-cell epitope region. In certain embodiments, the at least one disrupted, endogenous, B-cell and/or CD4+ T-cell epitope region does not overlap with the embedded or inserted, heterologous, epitope. For example, the present invention provides a Shiga toxin effector polypeptide comprising a Shiga toxin A1 fragment region and a carboxy-terminus, wherein the Shiga toxin A subunit effector polypeptide comprises: (a) an embedded or inserted, heterologous, epitope; (b) a disruption of at least one, endogenous, B-cell and/or CD4+ T-cell epitope region; and (c) a disrupted furin-cleavage motif at the carboxy-terminus of the Shiga toxin A1 fragment region; wherein the Shiga toxin A subunit effector polypeptide is capable of exhibiting a Shiga toxin effector function. In a further example, the present invention provides a Shiga toxin A subunit effector polypeptide comprising a Shiga toxin A1 fragment region and a carboxy-terminus, wherein the Shiga toxin A subunit effector polypeptide comprises (a) an embedded or inserted, heterologous, CD8+ T-cell epitope which disrupts an endogenous, B-cell and/or CD4+ T-cell epitope region; (b) a disruption of at least four, endogenous, B-cell and/or CD4+ T-cell epitope regions which do not overlap with the embedded or inserted, heterologous, CD8+ T-cell epitope; and (c) a disrupted furin-cleavage motif at the carboxy-terminus of the Shiga toxin A1 fragment region; wherein the Shiga toxin A subunit effector polypeptide is truncated at its carboxy-terminus, relative to a wild-type Shiga toxin A subunit, resulting in the elimination of one or more endogenous, B-cell and/or CD4+ T-cell epitope regions; and wherein the Shiga toxin A subunit effector polypeptide is capable of exhibiting a Shiga toxin effector function. In certain further embodiments, the heterologous, T-cell epitope is a CD8+ T-cell epitope, such as, e.g., with regard to a human immune system. For certain further embodiments, the heterologous, T-cell epitope is capable of being presented by a MHC class I molecule of a cell. In certain further embodiments, the cell-targeting molecule of the present invention is capable of one or more the following: entering a cell, inhibiting a ribosome function, causing cytostasis, causing cell death, and/or delivering the embedded or inserted, heterologous, T-cell epitope to a MHC class I molecule for presentation on a cellular surface. For certain further embodiments, the cell-targeting molecule is capable when introduced to cells of exhibiting a cytotoxicity comparable or better than a reference molecule, such as, e.g., a second cell-targeting molecule consisting of the cell-targeting molecule except for all of its Shiga toxin effector polypeptide components comprise a wild-type Shiga toxin furin-cleavage site at the carboxy terminus of its A1 fragment region. In certain embodiments of Embodiment Set #2, the binding region and Shiga toxin effector polypeptide are linked together, either directly or indirectly. In certain embodiments of Embodiment Set #2, the binding region comprises a polypeptide comprising an immunoglobulin or immunoglobulin-type binding region. In certain further embodiments, the binding region comprising a polypeptide selected from the group consisting of: an autonomous VH domain, single-domain antibody fragment (sdAb), Nanobody®, heavy chain-antibody domain derived from a camelid antibody (VHH or VH domain fragment), heavy-chain antibody domain derived from a cartilaginous fish antibody (VHH or VH domain fragment), immunoglobulin new antigen receptor (IgNAR), VNAR fragment, single-chain variable fragment (scFv), antibody variable fragment (Fv), complementary determining region 3 fragment (CDR3), constrained FR3-CDR3-FR4 polypeptide (FR3-CDR3-FR4), Fd fragment, small modular immunopharmaceutical (SMIP) domain, antigen-binding fragment (Fab), Armadillo repeat polypeptide (ArmRP), fibronectin-derived 10th fibronectin type III domain (10Fn3), tenascin type III domain (TNfn3), ankyrin repeat motif domain, low-density-lipoprotein-receptor-derived A-domain (LDLR-A), lipocalin (anticalin), Kunitz domain, Protein-A-derived Z domain, gamma-B crystallin-derived domain, ubiquitin-derived domain, Sac7d-derived polypeptide (affitin), Fyn-derived SH2 domain, miniprotein, C-type lectin-like domain scaffold, engineered antibody mimic, and any genetically manipulated counterparts of any of the foregoing which retain binding functionality. In certain embodiments, the binding region comprises a polypeptide selected from the group consisting of: an autonomous VH domain, single-domain antibody fragment (sdAb), Nanobody®, heavy chain-antibody domain derived from a camelid antibody (VHH or VH domain fragment), heavy-chain antibody domain derived from a cartilaginous fish antibody (VHH or VH domain fragment), immunoglobulin new antigen receptor (IgNAR), VNAR fragment, single-chain variable fragment (scFv), antibody variable fragment (Fv), Fd fragment, and antigen-binding fragment (Fab). In certain embodiments, the cell-targeting molecule of the present invention comprises an immunoglobulin binding region capable of specifically binding an extracellular part of HER2/neu/ErbB2, and comprising one or more of: an antibody variable fragment, a single-domain antibody fragment, a single-chain variable fragment, a Fd fragment, an antigen-binding fragment, an autonomous VH domain, a VHH fragment derived from a camelid antibody, a heavy-chain antibody domain derived from a cartilaginous fish antibody, a VNAR fragment, and an immunoglobulin new antigen receptor. In certain embodiments, the binding region comprises, consists essentially of, or consists of a single-chain variable fragment (scFv). In certain embodiments, the binding region comprises a single-chain variable fragment (scFv). In certain embodiments, the binding region comprises, consists essentially of, or consists of a VHH fragment derived from a camelid antibody. In certain embodiments of Embodiment Set #2, the binding region and the Shiga toxin effector polypeptide are fused, either directly or indirectly, forming a continuous polypeptide such that the binding region is associated, either directly or indirectly, with the carboxy-terminus of the Shiga toxin effector polypeptide. In certain embodiments of Embodiment Set #2, the embedded or inserted, heterologous, T-cell epitope disrupts the endogenous, B-cell and/or CD4+ T-cell epitope region selected from the group of natively positioned Shiga toxin A Subunit regions consisting of: (i) 1-15 of SEQ ID NO:1 or SEQ ID NO:2; 3-14 of SEQ ID NO:3; 26-37 of SEQ ID NO:3; 27-37 of SEQ ID NO:1 or SEQ ID NO:2; 39-48 of SEQ ID NO:1 or SEQ ID NO:2; 42-48 of SEQ ID NO:3; and 53-66 of SEQ ID NO:1, SEQ ID NO:2, or SEQ ID NO:3, or the equivalent region in a Shiga toxin A Subunit or derivative thereof (ii) 94-115 of SEQ ID NO:1, SEQ ID NO:2, or SEQ ID NO:3; 141-153 of SEQ ID NO:1 or SEQ ID NO:2; 140-156 of SEQ ID NO:3; 179-190 of SEQ ID NO:1 or SEQ ID NO:2; 179-191 of SEQ ID NO:3; 204 of SEQ ID NO:3; 205 of SEQ ID NO:1 or SEQ ID NO:2; and 210-218 of SEQ ID NO:3; and (iii) 240-260 of SEQ ID NO:3; 243-257 of SEQ ID NO:1 or SEQ ID NO:2; 254-268 of SEQ ID NO:1 or SEQ ID NO:2; 262-278 of SEQ ID NO:3; 281-297 of SEQ ID NO:3; and 285-293 of SEQ ID NO:1 or SEQ ID NO:2, or the equivalent region in a Shiga toxin A Subunit or derivative thereof. In certain embodiments of Embodiment Set #2, the disrupted furin-cleavage motif comprises one or more mutations, relative to a wild-type Shiga toxin A Subunit, the mutation altering at least one amino acid residue in a region natively positioned at (1) at 248-251 of the A Subunit of Shiga-like toxin 1 (SEQ ID NO:1), Shiga toxin (SEQ ID NO:2), or another Shiga toxin 1 variant sequence (e.g. SEQ ID NOs: 4-6); or (2) at 247-250 of the A Subunit of Shiga-like toxin 2 (SEQ ID NO:3) or a Shiga-like toxin 2 variant sequence (e.g. SEQ ID NOs: 7-18); or the equivalent region in a Shiga toxin A Subunit or derivative thereof. In certain further embodiments, the disrupted furin-cleavage motif comprises one or more mutations, relative to a wild-type Shiga toxin A Subunit, in a minimal furin cleavage site of the furin-cleavage motif. In certain further embodiments the minimal furin cleavage site is represented by the consensus amino acid sequence R/Y-x-x-R and/or R-x-x-R. In certain embodiments of Embodiment Set #2, the Shiga toxin effector polypeptide comprises, consists essentially
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