Are you Holly M Horton?

Claim your profile

Publications (8)84.11 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The CTLA4-Ig fusion proteins abatacept and belatacept are clinically proven immunosuppressants used for rheumatoid arthritis and renal transplant, respectively. Given that both biologics are typically administered chronically by infusion, a need exists for a next-generation CTLA4-Ig with more convenient dosing. We used structure-based protein engineering to optimize the affinity of existing CTLA4-Ig therapeutics for the ligands CD80 and CD86, and for the neonatal Fc receptor, FcRn. From a rationally designed library, we identified four substitutions that enhanced binding to human CD80 and CD86. Coupled with two IgG1 Fc substitutions that enhanced binding to human FcRn, these changes comprise the novel CTLA4-Ig fusion protein, XPro9523. Compared with abatacept, XPro9523 demonstrated 5.9-fold, 23-fold, and 12-fold increased binding to CD80, CD86, and FcRn, respectively; compared with belatacept, CD80, CD86, and FcRn binding increased 1.5-fold, 7.7-fold, and 11-fold, respectively. XPro9523 and belatacept suppressed human T cell proliferation and IL-2 production more potently than abatacept. XPro9523 also suppressed inflammation in the mouse collagen-induced arthritis model. In cynomolgus monkeys, XPro9523 saturated CD80 and CD86 more effectively than abatacept and belatacept, potently inhibited IgM and IgG immunization responses, and demonstrated longer half-life. Pharmacokinetic modeling of its increased potency and persistence suggests that, in humans, XPro9523 may demonstrate superior efficacy and dosing convenience compared with abatacept and belatacept.
    mAbs 04/2013; 5(3). · 5.28 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: HM1.24, an immunologic target for multiple myeloma (MM) cells, has not been effectively targeted with therapeutic monoclonal antibodies (mAbs). In this study, we investigated in vitro and in vivo anti-MM activities of XmAb5592, a humanized anti-HM1.24 mAb with Fc-domain engineered to significantly enhance FcγR binding and associated immune effector functions. XmAb5592 increased antibody-dependent cellular cytotoxicity (ADCC) several fold relative to the anti-HM1.24 IgG1 analog against both MM cell lines and primary patient myeloma cells. XmAb5592 also augmented antibody dependent cellular phagocytosis (ADCP) by macrophages. Natural killer (NK) cells became more activated by XmAb5592 than the IgG1 analog, evidenced by increased cell surface expression of granzyme B-dependent CD107a and MM cell lysis, even in the presence of bone marrow stromal cells. XmAb5592 potently inhibited tumor growth in mice bearing human MM xenografts via FcγR-dependent mechanisms, and was significantly more effective than the IgG1 analog. Lenalidomide synergistically enhanced in vitro ADCC against MM cells and in vivo tumor inhibition induced by XmAb5592. A single dose of 20 mg/kg XmAb5592 effectively depleted both blood and bone marrow plasma cells in cynomolgus monkeys. These results support clinical development of XmAb5592, both as a monotherapy and in combination with lenalidomide, to improve patient outcome of MM.
    Blood 03/2012; 119(9):2074-82. · 9.78 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Sequestration of IgE to prevent its binding to high-affinity IgE receptor FcεRI on basophils and mast cells is an effective therapy for allergic asthma. IgE production requires differentiation of activated IgE(+) B cells into plasma cells upon allergen sensitization. B-cell receptor signaling is suppressed by the inhibitory IgG Fc receptor FcγRIIb; therefore, we reasoned that a therapeutic antibody that coengages FcγRIIb and IgE B-cell receptor would not only sequester IgE but also suppress its production by blocking IgE(+) B-cell activation and differentiation to IgE-secreting plasma cells. To explore the effects of IgE sequestration versus IgE suppression by comparing omalizumab to FcγRIIb-optimized anti-IgE antibodies in humanized mouse models of immunoglobulin production. By using a murine anti-IgE antibody as a template, we humanized, increased IgE binding, and modified its Fc domain to increase affinity for FcγRIIb. We next compared effects of this antibody (XmAb7195) versus omalizumab on the secretion of IgE and other isotypes in human PBMC cultures and in PBMC-engrafted severe combined immunodeficiency mice. Relative to omalizumab, XmAb7195 has a 5-fold higher affinity for human IgE and more than 400-fold higher affinity for FcγRIIb. In addition to sequestering soluble IgE, XmAb7195 inhibited plasma cell differentiation and consequent human IgE production through coengagement of IgE B-cell receptor with FcγRIIb. In PBMC-engrafted mice, XmAb7195 reduced total human IgE (but not IgG or IgM) levels by up to 40-fold relative to omalizumab. XmAb7195 acts by IgE sequestration coupled with an FcγRIIb-mediated inhibitory mechanism to suppress the formation of IgE-secreting plasma cells and reduce both free and total IgE levels.
    The Journal of allergy and clinical immunology 01/2012; 129(4):1102-15. · 12.05 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Engagement of the low-affinity Ab receptor FcγRIIb downregulates B cell activation, and its dysfunction is associated with autoimmunity in mice and humans. We engineered the Fc domain of an anti-human CD19 Ab to bind FcγRIIb with high affinity, promoting the coengagement of FcγRIIb with the BCR complex. This Ab (XmAb5871) stimulated phosphorylation of the ITIM of FcγRIIb and suppressed BCR-induced calcium mobilization, proliferation, and costimulatory molecule expression of human B cells from healthy volunteers and systemic lupus erythematosus (SLE) patients, as well as B cell proliferation induced by LPS, IL-4, or BAFF. XmAb5871 suppressed humoral immunity against tetanus toxoid and reduced serum IgM, IgG, and IgE levels in SCID mice engrafted with SLE or healthy human PBMC. XmAb5871 treatment also increased survival of mice engrafted with PBMC from a unique SLE patient. Unlike anti-CD20 Ab, coengagement of FcγRIIb and BCR complex did not promote B cell depletion in human PBMC cultures or in mice. Thus, amplification of the FcγRIIb inhibitory pathway in activated B cells may represent a novel B cell-targeted immunosuppressive therapeutic approach for SLE and other autoimmune diseases that should avoid the complications associated with B cell depletion.
    The Journal of Immunology 02/2011; 186(7):4223-33. · 5.52 Impact Factor
  • Journal of Allergy and Clinical Immunology - J ALLERG CLIN IMMUNOL. 01/2011; 127(2).
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: CD40 is highly expressed on various B-lineage malignancies and represents an attractive immunotherapy target for neoplastic disease. Previous work showed that engineering the Fc domain of an antibody for increased binding to Fcγ receptors (FcγRs) significantly enhanced Fc-mediated immune effector function and antitumor activity in vitro and in vivo. We developed a humanized anti-CD40 antibody similarly Fc-engineered for increased FcγR binding (XmAbCD40) and compared its efficacy with that of an anti-CD40 native IgG1 analog and the anti-CD20 antibody rituximab. XmAbCD40 increased antibody-dependent cell-mediated cytotoxicity (ADCC) up to 150-fold relative to anti-CD40 IgG1 against B-lymphoma, leukemia, and multiple myeloma cell lines, and significantly enhanced ADCC against primary tumors. XmAbCD40 was also superior to rituximab in enhancing ADCC (both in cell lines and primary tumors) and in augmenting antibody-dependent cellular phagocytosis. XmAbCD40 significantly inhibited lymphoma growth in disseminated and established mouse xenografts and was more effective than the IgG1 analog or rituximab. An anti-CD40 antibody constructed to abrogate FcγR binding showed no reduction of tumor growth, indicating that the in vivo antitumor activity of XmAbCD40 is primarily mediated via FcγR-dependent mechanisms. These data demonstrate that XmAbCD40 displays potent antitumor efficacy and merits further evaluation for the treatment of CD40(+) malignancies.
    Blood 10/2010; 116(16):3004-12. · 9.78 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Improved affinity for the neonatal Fc receptor (FcRn) is known to extend antibody half-life in vivo. However, this has never been linked with enhanced therapeutic efficacy. We tested whether antibodies with half-lives extended up to fivefold in human (h)FcRn transgenic mice and threefold in cynomolgus monkeys retain efficacy at longer dosing intervals. We observed that prolonged exposure due to FcRn-mediated enhancement of half-life improved antitumor activity of Fc-engineered antibodies in an hFcRn/Rag1(-/-) mouse model. This bridges the demand for dosing convenience with the clinical necessity of maintaining efficacy.
    Nature Biotechnology 02/2010; 28(2):157-9. · 32.44 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: CD19 is a pan B-cell surface receptor expressed from pro-B-cell development until its down-regulation during terminal differentiation into plasma cells. CD19 represents an attractive immunotherapy target for cancers of lymphoid origin due to its high expression levels on the vast majority of non-Hodgkin's lymphomas and some leukemias. A humanized anti-CD19 antibody with an engineered Fc domain (XmAb5574) was generated to increase binding to Fcgamma receptors on immune cells and thus increase Fc-mediated effector functions. In vitro, XmAb5574 enhanced antibody-dependent cell-mediated cytotoxicity 100-fold to 1,000-fold relative to an anti-CD19 IgG1 analogue against a broad range of B-lymphoma and leukemia cell lines. Furthermore, XmAb5574 conferred antibody-dependent cell-mediated cytotoxicity against patient-derived acute lymphoblastic leukemia and mantle cell lymphoma cells, whereas the IgG1 analogue was inactive. XmAb5574 also increased antibody-dependent cellular phagocytosis and apoptosis. In vivo, XmAb5574 significantly inhibited lymphoma growth in prophylactic and established mouse xenograft models, and showed more potent antitumor activity than its IgG1 analogue. Comparisons with a variant incapable of Fcgamma receptor binding showed that engagement of these receptors is critical for optimal antitumor efficacy. These results suggest that XmAb5574 exhibits potent tumor cytotoxicity via direct and indirect effector functions and thus warrants clinical evaluation as an immunotherapeutic for CD19(+) hematologic malignancies.
    Cancer Research 11/2008; 68(19):8049-57. · 9.28 Impact Factor