Abstract 4888: Antibody blockade of semaphorin 4D breaks down stromal barriers to enhance tumoricidal immune infiltration, supporting rational immunotherapy combinations
Authors: Evans Elizabeth E. , Bussler Holm , Torno Sebold , Mallow Crystal , Reilly Christine , Scrivens Maria , Klimatcheva Ekaterina , Winter Laurie A. , Kirk Renee , Howell Alan , Balch Leslie , Leonard John E. , Paris Mark , Fisher Terrence L. , Hu-Lieskovan Siwen , Ribas Antoni , Smith Ernest S. , Zauderer Maurice 
Published: July 2016

Abstract
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&lt;0.005) and CTL activity (4x, p&lt;0.0001) was observed. This orchestrated change in the tumoral immune context was associated with durable tumor rejection and immunologic memory in preclinical colon, breast, and melanoma models. Importantly, the immunomodulatory activity of anti-SEMA4D antibody can be further enhanced by combination with other immunotherapies, including immune checkpoint inhibitors and chemotherapy. Strikingly, the combination with antibody to CTLA-4 acts synergistically, with maximal increase in survival (110% tumor growth delay, p&lt;0.01) and complete tumor regression in 100% of mice, as compared to 22% with monotherapy (p&lt;0.01).
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.