Crystal Mallow

SEMA4D compromises blood-brain barrier, activates microglia, and inhibits remyelination in neurodegenerative disease

Multiple sclerosis (MS) is a chronic neuroinflammatory disease characterized by immune cell infiltration of CNS, blood-brain barrier (BBB) breakdown, localized myelin destruction, and progressive neuronal degeneration. There exists a significant need to identify novel therapeutic targets and strategies that effectively and safely disrupt and even reverse disease pathophysiology. Signaling cascades initiated by semaphorin 4D (SEMA4D) induce glial activation, neuronal process collapse, inhibit migration and differentiation of oligodendrocyte precursor cells (OPCs), and disrupt endothelial tight junctions forming the BBB. To target SEMA4D, we generated a monoclonal antibody that recognizes mouse, rat, monkey and human SEMA4D with high affinity and blocks interaction between SEMA4D and its cognate receptors. In vitro, anti-SEMA4D reverses the inhibitory effects of recombinant SEMA4D on OPC survival and differentiation. In vivo, anti-SEMA4D significantly attenuates experimental autoimmune encephalomyelitis in multiple rodent models by preserving BBB integrity and axonal myelination and can be shown to promote migration of OPC to the site of lesions and improve myelin status following chemically-induced demyelination. Our study underscores SEMA4D as a key factor in CNS disease and supports the further development of antibody-based inhibition of SEMA4D as a novel therapeutic strategy for MS and other neurologic diseases with evidence of demyelination and/or compromise to the neurovascular unit.

CXCL13 antibody for the treatment of autoimmune disorders

BackgroundHomeostatic B Cell-Attracting chemokine 1 (BCA-1) otherwise known as CXCL13 is constitutively expressed in secondary lymphoid organs by follicular dendritic cells (FDC) and macrophages. It is the only known ligand for the CXCR5 receptor, which is expressed on mature B cells, follicular helper T cells (Tfh), Th17 cells and regulatory T (Treg) cells. Aberrant expression of CXCL13 within ectopic germinal centers has been linked to the development of autoimmune disorders (e.g. Rheumatoid Arthritis, Multiple Sclerosis, Systemic Lupus Erythematosis). We, therefore, hypothesized that antibody-mediated disruption of the CXCL13 signaling pathway would interfere with the formation of ectopic lymphoid follicles in the target organs and inhibit autoimmune disease progression. This work describes pre-clinical development of human anti-CXCL13 antibody MAb 5261 and includes therapeutic efficacy data of its mouse counterpart in murine models of autoimmunity.ResultsWe developed a human IgG1 monoclonal antibody, MAb 5261 that specifically binds to human, rodent and primate CXCL13 with an affinity of approximately 5 nM and is capable of neutralizing the activity of CXCL13 from these various species in in vitro functional assays. For in vivo studies we have engineered a chimeric antibody to contain the same human heavy and light chain variable genes along with mouse constant regions. Treatment with this antibody led to a reduction in the number of germinal centers in mice immunized with 4-Hydroxy-3-nitrophenylacetyl hapten conjugated to Keyhole Limpet Hemocyanin (NP-KLH) and, in adoptive transfer studies, interfered with the trafficking of B cells to the B cell areas of mouse spleen. Furthermore, this mouse anti-CXCL13 antibody demonstrated efficacy in a mouse model of Rheumatoid arthritis (Collagen-Induced Arthritis (CIA)) and Th17-mediated murine model of Multiple Sclerosis (passively-induced Experimental Autoimmune Encephalomyelitis (EAE)).ConclusionsWe developed a novel therapeutic antibody targeting CXCL13-mediated signaling pathway for the treatment of autoimmune disorders.

Antibody Blockade of Semaphorin 4D Promotes Immune Infiltration into Tumor and Enhances Response to Other Immunomodulatory Therapies

Evans and colleagues describe a novel immunomodulatory function of semaphorin 4D (SEMA4D) and show that blocking SEMA4D enhances immune infiltration into tumor and increases antitumor activity in synergy with other immunomodulatory therapies. Semaphorin 4D (SEMA4D, CD100) and its receptor plexin-B1 (PLXNB1) are broadly expressed in murine and human tumors, and their expression has been shown to correlate with invasive disease in several human tumors. SEMA4D normally functions to regulate the motility and differentiation of multiple cell types, including those of the immune, vascular, and nervous systems. In the setting of cancer, SEMA4D–PLXNB1 interactions have been reported to affect vascular stabilization and transactivation of ERBB2, but effects on immune-cell trafficking in the tumor microenvironment (TME) have not been investigated. We describe a novel immunomodulatory function of SEMA4D, whereby strong expression of SEMA4D at the invasive margins of actively growing tumors influences the infiltration and distribution of leukocytes in the TME. Antibody neutralization of SEMA4D disrupts this gradient of expression, enhances recruitment of activated monocytes and lymphocytes into the tumor, and shifts the balance of cells and cytokines toward a proinflammatory and antitumor milieu within the TME. This orchestrated change in the tumor architecture was associated with durable tumor rejection in murine Colon26 and ERBB2+ mammary carcinoma models. The immunomodulatory activity of anti-SEMA4D antibody can be enhanced by combination with other immunotherapies, including immune checkpoint inhibition and chemotherapy. Strikingly, the combination of anti-SEMA4D antibody with antibody to CTLA-4 acts synergistically to promote complete tumor rejection and survival. Inhibition of SEMA4D represents a novel mechanism and therapeutic strategy to promote functional immune infiltration into the TME and inhibit tumor progression. Cancer Immunol Res; 3(6); 689–701. ©2015 AACR.

Antibody blockade of semaphorin 4D breaks down barriers to enhance tumoricidal immune infiltration and supports rational immunotherapy combinations

Semaphorin 4D (SEMA4D, CD100) and its receptor plexin-B1 are broadly expressed in cancer and expression correlates with invasive disease in several human tumors. SEMA4D normally functions to regulate the motility and differentiation of multiple cell types, including those of the immune, vascular, and nervous systems. In the setting of cancer, we describe a novel immunomodulatory function of SEMA4D in regulating immune cell infiltration and anti-tumor activity. Activity is enhanced in preclinical studies when combined with other immunotherapies, including immune checkpoint blockade inhibition.

Abstract 3661: Breaking down the barrier restricting infiltration and differentiation of APC in the tumor microenvironment with a first-in-class antibody targeting Semaphorin4D, and rational combination therapies

Purpose: We expand mechanistic findings in preclinical studies to demonstrate that antibody blockade of Semaphorin 4D (SEMA4D, CD100) reduces expansion of MDSC and shifts the balance of myeloid cells within the TME to facilitate tumor rejection. Efficacy is further enhanced when combined with various immunotherapies. Design of Phase 1b/2 combination trials of VX15/2503, a humanized IgG4 antibody targeting SEMA4D, with immune checkpoint inhibition will be presented. Methods: Anti-SEMA4D antibodies were evaluated alone and in combination with other immunotherapies in various preclinical models. Anti-tumor activity and immune response was characterized by immunohistochemistry, flow cytometry, functional assays, and cytokine, chemokine and gene expression analysis. A Phase I trial for single agent VX15/2503 was completed, and several 1b/2 combination immunotherapy trials are planned. Results: SEMA4D restricts migration of monocytes and promotes expansion of suppressive myeloid cells in vitro. Strong expression of SEMA4D at the invasive margins of actively growing tumors in vivo restricts the infiltration and modulates polarization of leukocytes in the TME. Antibody blockade of SEMA4D facilitated recruitment of activated DCs and T lymphocytes in preclinical models. M-MDSCs were significantly reduced in tumor and blood following treatment. A significant shift towards increased Th1 cytokines (IFNγ, TNFα) and CTL-recruiting chemokine CXCL9, with concurrent reduction in Treg-, MDSC- and M2-macrophage promoting chemokines (CCL2, CXCL1, CXCL5) was observed. Accordingly, Teff:Treg ratio (3x, p Conclusions: SEMA4D blockade represents a novel mechanism to promote functional immune infiltration into the tumor and enhance immunotherapy. VX15/2503 treatment was well tolerated in a Phase I multiple ascending dose trial in patients with advanced refractory solid tumors. Phase 1b/2 trials of combination therapy with avelumab in NSCLC patients who are immunotherapy naive, and combinations with anti- anti-PD-1 and/or anti-CTLA-4 in melanoma and HNSCC patients who are refractory to PD1 inhibitors are planned in 2017. Citation Format: Elizabeth E. Evans, Holm Bussler, Crystal Mallow, Christine Reilly, Sebold Torno, Maria Scrivens, Cathie Foster, Alan Howell, Stephen R. Comeau, Leslie Balch, Alyssa Knapp, John E. Leonard, Terrence L. Fisher, Siwen Hu-Lieskovan, Antoni Ribas, Ernest S. Smith, Maurice Zauderer. Breaking down the barrier restricting infiltration and differentiation of APC in the tumor microenvironment with a first-in-class antibody targeting Semaphorin4D, and rational combination therapies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3661. doi:10.1158/1538-7445.AM2017-3661

Abstract B023: Antibody blockade of Semaphorin 4D enhances infiltration of APC and CD8 T cells and reduces immune suppression to facilitate immune-mediated tumor rejection

Semaphorin 4D (SEMA4D, CD100) and its receptor plexin-B1 are broadly expressed in cancer and expression correlates with invasive disease in several human tumors. We have reported a novel role for SEMA4D in modulating the tumor microenvironment (TME) to exclude activated antigen presenting cells and cytotoxic T lymphocytes so as to promote tumor growth; this effect can be reversed by antibody blockade. Purpose: Characterize immune-related anti-tumor activity mediated by antibody neutralization of SEMA4D, as a single agent and in combination with other immunomodulatory therapies, including immune checkpoint inhibition. Methods: Blockade of SEMA4D with monoclonal murine antibody was evaluated in murine melanoma and colon cancer models. Immune response in pre-clinical models was characterized by immunohistochemistry, flow cytometry, functional assays, as well as cytokine, chemokine and gene expression analysis. Therapeutic activity was evaluated in various preclinical models. A Phase I trial in patients with advanced solid tumors was completed. Results: SEMA4D restricts migration of macrophage cell lines and promotes expansion of suppressive tumor associated macrophage (TAM) and myeloid derived suppressor cells (MDSC) in vitro. Strong expression of SEMA4D at the invasive margins of actively growing tumors in vivo modulates the infiltration and polarization of leukocytes in the TME. In preclinical models, antibody neutralization disrupted the SEMA4D gradient at the invasive margin, which correlated with recruitment of activated APCs and T lymphocytes into the TME. This was accompanied by a significant shift towards increased Th1 cytokines (IFNΓ, TNFA) and CTL-recruiting CXCL9 chemokine, with concurrent reduction in Treg-, MDSC- and M2-macrophage promoting chemokines (CCL2, CXCL1, CXCL5). Accordingly, an increase in Teff:Treg ratio (3x, p Conclusion: Inhibition of SEMA4D represents a novel mechanism and therapeutic strategy to promote functional immune infiltration into the tumor and inhibit tumor progression. Phase 1b/2a trials of combination therapy with immune checkpoint inhibition are planned. Citation Format: Elizabeth E. Evans, Holm Bussler, Crystal Mallow, Christine Reilly, Sebold Torno, Ekaterina Klimatcheva, Maria Scrivens, Cathie Foster, Alan Howell, Leslie Balch, Alyssa Knapp, John E. Leonard, Mark J. Paris, Terrence L. Fisher, Siwen Hu-Lieskovan, Antoni Ribas, Ernest S. Smith, Maurice Zauderer. Antibody blockade of Semaphorin 4D enhances infiltration of APC and CD8 T cells and reduces immune suppression to facilitate immune-mediated tumor rejection [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr B023.

Abstract A119: Antibody blockade of Semaphorin 4D neutralizes barrier to immune infiltration and facilitates immune-mediated tumor rejection

Semaphorin 4D (SEMA4D, CD100) and its receptor plexin-B1 are broadly expressed in cancer and expression correlates with invasive disease in several human tumors. SEMA4D normally functions to regulate the motility and differentiation of multiple cell types, including those of the immune, vascular, and nervous systems. In the setting of cancer, we describe a novel immunomodulatory function of SEMA4D in regulation of immune cell infiltration and activity in the tumor microenvironment (TME). Purpose: Characterize immune-related and anti-tumor activity mediated by antibody neutralization of SEMA4D, as a single agent and in combination with other immunomodulatory therapies. Methods: Blockade of SEMA4D with monoclonal murine antibody was evaluated in subcutaneous models, as well as an orthotopic ERBB2+ breast carcinoma syngeneic model. Anti-tumor immune response in pre-clinical models was characterized by selective in vivo immune cell depletions, as well as immunohistochemistry, flow cytometry, and functional assays. The safety and tolerability of a humanized anti-SEMA4D antibody VX15/2503 was assessed in Phase I clinical trials in oncology. Results: SEMA4D restricts migration of macrophage cell lines in vitro. Strong expression of SEMA4D at the invasive margins of actively growing in vivo tumors modulates the infiltration and spatial distribution of leukocytes in the TME. Antibody neutralization of SEMA4D disrupts this gradient and facilitates recruitment of potent antigen presenting cells and T lymphocytes into the TME, shifting the balance of cytokines toward increased Th1 and reduced immunosuppressive cytokines. This orchestrated change in the tumor architecture was associated with durable tumor rejection and immunologic memory in preclinical models. Immune-mediated tumor rejection may enhance the disruption of ERBB2 transactivation with SEMA4D receptors, which has been reported for ERBB2 and Met oncogenes. Importantly, the immunomodulatory activity of anti-SEMA4D antibody can also be further enhanced by combination with other immunotherapies, including immune checkpoint inhibition and chemotherapy. Strikingly, the combination of anti-SEMA4D antibody with antibody to CTLA-4 acts synergistically to promote complete tumor rejection and survival, with significant 58% increase in tumor regression and maximal increase in survival, as compared to monotherapy. Treatment with anti-SEMA4D antibodies was well tolerated in nonclinical and clinical studies, including completion of a Phase I prospective multiple ascending dose trial in patients with advanced refractory solid tumors. Weekly doses of between 0.3 and 20 mg/kg were administered; no MTD was determined. Patients with the longest duration of treatment, 48-55 weeks, included colorectal, breast, and a papillary thyroid patient, who had a partial response by RECIST. Progression free survival correlated with elevated baseline lymphocyte counts, supporting an immune mediated mechanism of action for VX15/2503. Conclusion: Inhibition of SEMA4D represents a novel mechanism and therapeutic strategy to promote functional immune infiltration into the tumor and inhibit tumor progression. A phase 1b/2a trial of combination therapy with immune checkpoint inhibition is planned. Citation Format: Elizabeth E. Evans, Holm Bussler, Sebold Torno, Crystal Mallow, Laurie A. Winters, Christine Reilly, Ekaterina Klimatcheva, Janaki Veeraraghavan, Alan S. Jonason, Maria Scrivens, Renee Kirk, Alan Howell, Leslie Balch, John E. Leonard, Mark Paris, Terrence L. Fisher, Ernest S. Smith, Maurice Zauderer. Antibody blockade of Semaphorin 4D neutralizes barrier to immune infiltration and facilitates immune-mediated tumor rejection. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr A119.

Abstract 4888: Antibody blockade of semaphorin 4D breaks down stromal barriers to enhance tumoricidal immune infiltration, supporting rational immunotherapy combinations

Semaphorin 4D (SEMA4D, CD100) and its receptor plexin-B1 are broadly expressed in cancer; increased expression correlates with poor prognosis. SEMA4D normally functions to regulate the motility and differentiation of multiple cell types, including those of the immune, vascular, and nervous systems. In the tumor microenvironment (TME), SEMA4D is expressed strongly at the invasive margin and modulates the infiltration and spatial distribution of leukocytes, suppressing anti-tumor activity. Neutralization of SEMA4D was evaluated for effects on immune activity and tumor growth in preclinical models, incorporating single agent and combination treatments with other immunotherapies, including immune checkpoint blockade inhibitors. The safety and tolerability of humanized anti-SEMA4D antibody VX15/2503 was assessed in a Phase I clinical trial. RESULTS: SEMA4D restricts migration of myeloid cells expressing cognate PLXNB1/2 receptors, determined using trans-well migration assays and IHC of in vivo tumors. Antibody neutralization disrupted the SEMA4D gradient at the invasive margin, which correlated with recruitment of activated APCs and T lymphocytes into the TME, and significant shift toward increased Th1 cytokines (IFNg, TNFa) and CTL-recruiting CXCL9 chemokine, with concurrent reduction in Treg- and M2-macrophage promoting chemokines (CCL2, CXCL1, CCL17). Accordingly, an increase in Teff:Treg ratio (3x, p SEMA4D antibody treatment was well tolerated in nonclinical and clinical studies; including a Phase I multiple ascending dose trial in patients with advanced refractory solid tumors. Patients with the longest duration of treatment, 48-55 weeks, included colorectal, breast, and a papillary thyroid patient, who had a partial response by RECIST. Progression free survival strongly correlated with elevated baseline lymphocyte counts (r = 0.6133), supporting an immune mediated mechanism of action for VX15/2503. CONCLUSION: Inhibition of SEMA4D represents a novel mechanism and therapeutic strategy to promote functional immune infiltration into the tumor and inhibit tumor progression. A phase 1b/2 trial of combination therapy with an immune checkpoint inhibitor is planned. Citation Format: Elizabeth E. Evans, Holm Bussler, Sebold Torno, Crystal Mallow, Christine Reilly, Maria Scrivens, Ekaterina Klimatcheva, Laurie A. Winter, Renee Kirk, Alan Howell, Leslie Balch, John E. Leonard, Mark Paris, Terrence L. Fisher, Siwen Hu-Lieskovan, Antoni Ribas, Ernest S. Smith, Maurice Zauderer. Antibody blockade of semaphorin 4D breaks down stromal barriers to enhance tumoricidal immune infiltration, supporting rational immunotherapy combinations. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4888.

Abstract A67: Phase 1 study of VX15/2503, an immunomodulatory antibody to Semaphorin 4D that reverses tumor growth in preclinical studies

Semaphorin 4D (SEMA4D, CD100) normally functions to regulate the motility and differentiation of multiple cell types, including those of the immune, vascular, and nervous systems. In the setting of cancer, SEMA4D promotes tumor progression and metastasis. SEMA4D and its receptor plexin B1 are broadly expressed in murine and human tumors; expression correlates with invasive disease in several human tumors. SEMA4D is highly expressed on T cells and is also released as a biologically active soluble molecule by activated inflammatory cells. Preclinical studies demonstrate a novel immunomodulatory function of SEMA4D, whereby SEMA4D influences the recruitment and distribution of leukocytes in the tumor microenvironment. Antibody blockade of SEMA4D with the murine progenitor of VX15/2503 regulates the balance and activity of inflammatory and tolerance-inducing cells and cytokines to effectively delay tumor growth and promote durable tumor rejection in syngeneic colon and breast cancer models. Combination of anti-SEMA4D antibody with immune checkpoint inhibitor anti-CTLA-4 enhances anti-tumor immune activity and synergistically increases tumor rejection. Combinations with anti-PD-1 or cyclophosphamide, an immunomodulatory chemotherapy reported to differentially affect regulatory T cells, also increases efficacy and frequency of tumor rejection. Inhibition of SEMA4D represents a novel mechanism and therapeutic strategy to promote immune infiltration and distribution in the tumor microenvironment and inhibit tumor progression. The humanized anti-SEMA4D antibody, VX15/2503, has successfully completed a Phase I multiple ascending dose trial in adult patients with advanced refractory solid tumors. Patients were administered weekly IV doses of VX15/2503 until progression. Dose levels were 0.3 to 20 mg/kg. Tumors were assessed by RECIST 1.1 after each 8 dose cycle. The study has concluded (n=42 Pts); sex 40%M/60%F. Mean age (yrs) 64.8; ECOG 0/1/2 are 28.6%/69%/2.4%. No MTD was found. One DLT (grade 3 GGT elevation; 15 mg/kg) was reported in a pancreatic cancer patient with disease progression. The most frequent treatment-related AE9s (n=42 pts) included grade 1/2 nausea (14.3%) and fatigue (11.9%) and 15 unrelated SAE9s were reported in 12 patients. Thirteen of 42 pts at all dose levels exhibited stable disease for at least 8 weeks. Patients with the longest duration of treatment, 48-55 weeks, included colorectal (9 mg/kg); breast (15 mg/kg); and papillary thyroid (20 mg/kg)—this patient had a partial response by RECIST and stable disease for at least 6 months following cessation of treatment at 48 weeks. VX15/2503 serum concentrations of ≥ 0.3 µg/mL produced complete saturation of membrane SEMA4D on circulating T cells. HAHA responses (titer > 100) with possible effects on PK were observed in 4 of 41 patients (10%); in only 1 patient (2%) was an effect of HAHA on PD observed. VX15/2503 was well tolerated at dose levels up to 20 mg/kg, with 459 doses administered to 42 patients. A phase 1b/2a trial of combination therapy with anti-CTLA-4 is planned. Citation Format: Elizabeth E. Evans, Terrence L. Fisher, Cynthia Edington, Holm Bussler, Sebold Torno, Alan S. Jonason, Jr., Janaki Veeraraghavan, Christine Reilly, Michael A. Doherty, Jennifer Seils, Laurie A. Winter, Tracy Pandina, Crystal Mallow, Renee Kirk, Alan Howell, Sue Giralico, Maria Scrivens, Katya Klimatcheva, William J. Bowers, Mark Paris, Drew Warren Rasco, Ramesh K. Ramanathan, Amita Patnaik, Glen J. Weiss, Danielle Mutz, Lisa Blaydorn, Anthony W. Tolcher, Valerie Iddison, Ernest S. Smith, John E. Leonard, Maurice Zauderer. Phase 1 study of VX15/2503, an immunomodulatory antibody to Semaphorin 4D that reverses tumor growth in preclinical studies. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy: A New Chapter; December 1-4, 2014; Orlando, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2015;3(10 Suppl):Abstract nr A67.

Abstract 5030: Antibody blockade of Semaphorin 4D promotes tumor rejection and improves response to immune checkpoint blockade and chemotherapy

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Semaphorin4D (SEMA4D) normally functions to regulate, adhesion, motility and activation state of multiple cell types including those of the nervous, vascular and immune systems. In the setting of cancer, SEMA4D has been shown to promote tumor progression and metastasis. SEMA4D and its high affinity receptor plexin B1 are broadly expressed in human and murine tumors, and expression levels correlate with invasive disease in several human tumors. The interaction of plexin B1 with MET and ERBB2 can lead to SEMA4D-mediated transactivation of these membrane receptor kinases with a direct effect on tumor cell migration and invasive growth. Moreover, SEMA4D is highly expressed by inflammatory cells that are recruited to the tumor microenvironment. Purpose: Determine the role(s) of SEMA4D in shaping the tumor microenvironment, and investigate the anti-tumor response mediated by antibody neutralization of SEMA4D as a single agent or in combination with other immunomodulatory therapies. Methods: Subcutaneous colon and orthotopic ERBB2+ breast carcinoma models were employed to investigate treatment with a monoclonal antibody to SEMA4D. Anti-tumor response and tumor infiltrating immune cell profiles were characterized by in vivo growth kinetics, immunohistochemistry, FACS, and functional assays. Results: We describe an immunomodulatory function of SEMA4D within the tumor microenvironment, whereby SEMA4D influences the recruitment and activity of cytotoxic CD8+ T cells, the density of B cells within the tumor, and regulates the balance and localization of inflammatory M1 and tolerance-inducing M2 macrophage in tumor stroma. Antibody blockade of SEMA4D modifies the balance of immune cells and production of pro-inflammatory cytokines within the tumor microenvironment, promotes tumor rejection, and induces ∼30% tumor growth delay (TGD) in Colon26 and >70% TGD in Tubo breast tumor models. Furthermore, combination of SEMA4D antibody with immune checkpoint blockade inhibitor antibodies to CTLA4 and PD1, significantly improves frequency of complete tumor rejection (58% and 37%) and increases survival (>295% and >55% TGD respectively) as compared to monotherapy with these targeted agents. Similar combinatorial effects were observed when anti-SEMA4D antibody is administered with immunomodulatory chemotherapy, such as cyclophosphamide, which increases efficacy (81% TGD) and frequency of complete rejection (40%) in tumor engrafted mice. Conclusion: SEMA4D represents a novel immunological target and antibody neutralization of SEMA4D may be a novel therapeutic option for cancer treatment. The humanized anti-SEMA4D antibody, VX15/2503, has successfully completed IND-enabling toxicology testing and the dose escalation phase of a Phase I trial, in which the highest doses were well tolerated in adult patients with advanced solid tumors. Citation Format: Elizabeth E. Evans, Holm Bussler, Sebold Torno, Janaki Veeraraghavan, Alan S. Jonason, Michael A. Doherty, Christine Reilly, Crystal Mallow, Jennifer Seils, Mark Paris, Terrence L. Fisher, William J. Bowers, Maria Scrivens, Leslie Balch, Renee Kirk, Alan Howell, Valerie Iddison, John E. Leonard, Ernest S. Smith, Maurice Zauderer. Antibody blockade of Semaphorin 4D promotes tumor rejection and improves response to immune checkpoint blockade and chemotherapy. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5030. doi:10.1158/1538-7445.AM2014-5030