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Dive into the research topics where Ramraj Velmurugan is active.

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Featured researches published by Ramraj Velmurugan.


Molecular Cancer Therapeutics | 2016

Macrophage-Mediated Trogocytosis Leads to Death of Antibody-Opsonized Tumor Cells

Ramraj Velmurugan; Dilip K. Challa; Sripad Ram; Raimund J. Ober; E. Sally Ward

Understanding the complex behavior of effector cells such as monocytes or macrophages in regulating cancerous growth is of central importance for cancer immunotherapy. Earlier studies using CD20-specific antibodies have demonstrated that the Fcγ receptor (FcγR)–mediated transfer of the targeted receptors from tumor cells to these effector cells through trogocytosis can enable escape from antibody therapy, leading to the viewpoint that this process is protumorigenic. In the current study, we demonstrate that persistent trogocytic attack results in the killing of HER2-overexpressing breast cancer cells. Further, antibody engineering to increase FcγR interactions enhances this tumoricidal activity. These studies extend the complex repertoire of activities of macrophages to trogocytic-mediated cell death of HER2-overexpressing target cells and have implications for the development of effective antibody-based therapies. Mol Cancer Ther; 15(8); 1879–89. ©2016 AACR.


Journal of Immunology | 2013

The Encephalitogenic, Human Myelin Oligodendrocyte Glycoprotein–Induced Antibody Repertoire Is Directed toward Multiple Epitopes in C57BL/6-Immunized Mice

Pankaj Bansal; Tarique Khan; Uta Bussmeyer; Dilip K. Challa; Rafal Swiercz; Ramraj Velmurugan; Raimund J. Ober; E. Sally Ward

Although Abs specific for myelin oligodendrocyte glycoprotein (MOG) have been detected in patients with multiple sclerosis (MS), their contribution to pathogenesis remains poorly understood. Immunization of C57BL/6 mice with recombinant human MOG (hMOG) results in experimental autoimmune encephalomyelitis involving MOG-specific, demyelinating Abs. This model is therefore informative for understanding anti-MOG humoral responses in MS. In the current study, we have characterized the hMOG-specific Ab repertoire in immunized C57BL/6 mice using both in vitro and in vivo approaches. We demonstrate that hMOG-specific mAbs are not focused on one specific region of MOG, but instead target multiple epitopes. Encephalitogenicity of the mAbs, assessed by the ability of the mAbs to exacerbate experimental autoimmune encephalomyelitis in mice, correlates with the activity of the mAbs in binding to CNS tissue sections, but not with other in vitro assays. The targeting of different MOG epitopes by encephalitogenic Abs has implications for disease pathogenesis, because it could result in MOG cross linking on oligodendrocytes and/or immune complex formation. These studies reveal several novel features concerning pathogenic, humoral responses that may have relevance to human MS.


Immunology Letters | 2014

Targeting FcRn for therapy: From live cell imaging to in vivo studies in mice

E. Sally Ward; Ramraj Velmurugan; Raimund J. Ober

The role of FcRn in regulating antibody levels and transport in the body is well documented. The use of fluorescence microscopy to investigate the subcellular trafficking behavior of FcRn and its IgG ligand has led to insight into the function of this receptor, including the identification of new intracellular pathways. The inhibition of FcRn using engineered antibodies that bind to this receptor with increased affinity through their Fc region can be exploited to treat antibody mediated autoimmunity. The efficacy of this approach in mouse models of arthritis and multiple sclerosis has been demonstrated. Finally, the cross-species difference between mouse and man for FcRn-IgG interactions needs to be considered when engineering antibodies for improved activities in FcRn-mediated functions.


Traffic | 2018

Phagocytosis of antibody-opsonized tumor cells leads to the formation of a discrete vacuolar compartment in macrophages

Ramraj Velmurugan; Sreevidhya Ramakrishnan; Mingin Kim; Raimund J. Ober; E. Sally Ward

Despite the rapidly expanding use of antibody‐based therapeutics to treat cancer, knowledge of the cellular processes following phagocytosis of antibody‐opsonized tumor cells is limited. Here we report the formation of a phagosome‐associated vacuole that is observed in macrophages as these degradative compartments mature following phagocytosis of HER2‐positive cancer cells in the presence of the HER2‐specific antibody, trastuzumab. We demonstrate that this vacuole is a distinct organelle that is closely apposed to the phagosome. Furthermore, the size of the phagosome‐associated vacuole is increased by inhibition of the mTOR pathway. Collectively, the identification of this vacuolar compartment has implications for understanding the subcellular trafficking processes leading to the destruction of phagocytosed, antibody‐opsonized cancer cells by macrophages.


Molecular Cancer Therapeutics | 2018

Targeting phosphatidylserine with calcium-dependent protein-drug conjugates for the treatment of cancer

Ran Li; Srinivas Chiguru; Li Li; Dongyoung Kim; Ramraj Velmurugan; David Kim; Siva Charan Devanaboyina; Hong Tian; Alan J. Schroit; Ralph P. Mason; Raimund J. Ober; E. Sally Ward

In response to cellular stress, phosphatidylserine is exposed on the outer membrane leaflet of tumor blood vessels and cancer cells, motivating the development of phosphatidylserine-specific therapies. The generation of drug-conjugated phosphatidylserine-targeting agents represents an unexplored therapeutic approach, for which antitumor effects are critically dependent on efficient internalization and lysosomal delivery of the cytotoxic drug. In the current study, we have generated phosphatidylserine-targeting agents by fusing phosphatidylserine-binding domains to a human IgG1-derived Fc fragment. The tumor localization and pharmacokinetics of several phosphatidylserine-specific Fc fusions have been analyzed in mice and demonstrate that Fc-Syt1, a fusion containing the synaptotagmin 1 C2A domain, effectively targets tumor tissue. Conjugation of Fc-Syt1 to the cytotoxic drug monomethyl auristatin E results in a protein–drug conjugate (PDC) that is internalized into target cells and, due to the Ca2+ dependence of phosphatidylserine binding, dissociates from phosphatidylserine in early endosomes. The released PDC is efficiently delivered to lysosomes and has potent antitumor effects in mouse xenograft tumor models. Interestingly, although an engineered, tetravalent Fc-Syt1 fusion shows increased binding to target cells, this higher avidity variant demonstrates reduced persistence and therapeutic effects compared with bivalent Fc-Syt1. Collectively, these studies show that finely tuned, Ca2+-switched phosphatidylserine-targeting agents can be therapeutically efficacious. Mol Cancer Ther; 17(1); 169–82. ©2017 AACR.


international symposium on circuits and systems | 2017

Automatic endosomal structure detection and localization in fluorescence microscopic images

Dongyun Lin; Zhiping Lin; Ramraj Velmurugan; Raimund J. Ober

This paper proposes a modified spatially-constrained similarity measure (mSCSM) method for endosomal structure detection and localization under the bag-of-words (BoW) framework. To our best knowledge, the proposed mSCSM is the first method for fully automatic detection and localization of complex subcellular compartments like endosomes. Essentially, a new similarity score and a novel two-stage output control scheme are proposed for localization by extracting discriminative information within a group of query images. Compared with the original SCSM which is formulated for instance localization, the proposed mSCSM can address category based localization problems. The preliminary experimental results show the proposed mSCSM can correctly detect and localize 79.17% of the existing endosomal structures in the microscopic images of human myeloid endothelial cells.


Proceedings of SPIE | 2017

Remote focusing multifocal plane microscopy for the imaging of 3D single molecule dynamics with cellular context

Jerry Chao; Ramraj Velmurugan; Sungyong You; Dongyoung Kim; E. Sally Ward; Raimund J. Ober

Three-dimensional (3D) single molecule fluorescence microscopy affords the ability to investigate subcellular trafficking at the level of individual molecules. An imaged single molecule trajectory, however, often reveals only limited information about the underlying biological process when insufficient information is available about the organelles and other cellular structures with which the molecule interacts. A new 3D fluorescence microscopy imaging modality is described here that enables the simultaneous imaging of the trajectories of fast-moving molecules and the associated cellular context. The new modality is called remote focusing multifocal plane microscopy (rMUM), as it extends multifocal plane microscopy (MUM) with a remote focusing module. MUM is a modality that uses multiple detectors to image distinct focal planes within the specimen at the same time, and it has been demonstrated to allow the determination of 3D single molecule trajectories with high accuracy. Remote focusing is a method that makes use of two additional objective lenses to enable the acquisition of a z-stack of the specimen without having to move the microscope’s objective lens or sample stage, components which are required by MUM to be fixed in place. rMUM’s remote focusing module thus allows the cellular context to be imaged in the form of z-stacks as the trajectories of molecules or other objects of interest are imaged by MUM. In addition to a description of the modality, a discussion of rMUM data analysis and an example of data acquired using an rMUM setup are provided in this paper.


Cancer Research | 2016

Abstract 597: Defining the role of macrophage mediated trogocytosis in the clearance of antibody-opsonized tumor cells

Ramraj Velmurugan; Dilip K. Challa; Sripad Ram; Raimund J. Ober; E. Sally Ward

Understanding the complex behavior of effector cells such as monocytes or macrophages in regulating cancerous growth is of central importance for cancer immunotherapy. Earlier studies using CD20-specific antibodies have demonstrated that the Fcγ receptor (FcγR)-mediated transfer of the targeted receptors from tumor cells to these effector cells through trogocytosis can enable escape from antibody therapy, leading to the viewpoint that this process is pro-tumorigenic. However, there is limited information concerning the role of trogocytosis in antibody-based treatment of solid tumors such as breast cancer. We have used advanced microscopy methods and quantitative flow cytometric assays to study the effect of antibody-mediated trogocytosis on breast cancer cells and whether they can lead to tumor cell death. Our results show that long-term coculture with macrophages can reduce cancer cell numbers in an antibody-dependent manner even at low effector:target ratios. Quantitation from simultaneous long-term imaging of macrophage:cancer cell interactions reveals that this cell death is caused by both macrophage-mediated phagocytosis and trogocytosis, with the contribution of each process differing by the phenotype of the effector macrophages. Together, our results add to our understanding of the numerous interactions macrophages can have with cancer cells, and how therapeutic antibodies modulate their effects. Our recent observations in this area will be presented. Citation Format: Ramraj Velmurugan, Dilip Challa, Sripad Ram, Raimund J. Ober, E. Sally Ward. Defining the role of macrophage mediated trogocytosis in the clearance of antibody-opsonized tumor cells. [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 597.


Cancer Research | 2016

Abstract PR08: Macrophage-mediated trogocytosis leads to death of antibody-opsonized tumor cells

Ramraj Velmurugan; Dilip K. Challa; Sripad Ram; Raimund J. Ober; E. Sally Ward

The interplay between innate immune cells and antibodies to control cancerous growth is of central importance for mediating direct anti-tumor effects and the induction of long-lived anti-tumor immunity. Phagocytosis of antibody-opsonized cells by macrophages through Fcgamma receptor interactions is well characterized and leads to cell death through target cell engulfment into phagosomes. By contrast, the contribution of the related process called trogocytosis, involving the ingestion of limited amounts of the target cell by phagocytic cells, to cell attrition is less certain. In the current study we have developed a high throughput, quantitative assay to distinguish whole cell phagocytosis (WCP) and trogocytosis for different macrophage:breast cancer cell combinations. These analyses, combined with long term microscopic imaging, demonstrate that trogocytosis leads to target cell death. The implementation of multifocal plane microscopy to investigate trogocytic events at high spatiotemporal resolution reveals that these processes involve tubular extensions of opsonized tumor cells that are subsequently pinched off by the recipient macrophage. Of relevance to the design of second generation antibodies with improved efficacy, antibody engineering to enhance Fcgamma receptor interactions results in increased trogocytic activity. Collectively, these studies have significance to the rapidly expanding use of antibodies to treat cancer. Citation Format: Ramraj Velmurugan, Dilip K. Challa, Sripad Ram, Raimund J. Ober, E. Sally Ward. Macrophage-mediated trogocytosis leads to death of antibody-opsonized tumor cells. [abstract]. In: Proceedings of the Fourth AACR International Conference on Frontiers in Basic Cancer Research; 2015 Oct 23-26; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2016;76(3 Suppl):Abstract nr PR08.


Current Topics in Microbiology and Immunology | 2014

FcRn: From molecular interactions to regulation of IgG pharmacokinetics and functions

Dilip K. Challa; Ramraj Velmurugan; Raimund J. Ober; E. Sally Ward

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Dilip K. Challa

University of Texas Southwestern Medical Center

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Sripad Ram

University of Texas Southwestern Medical Center

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Andrea Grosso

University of Texas at Dallas

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Anish V. Abraham

University of Texas at Dallas

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Sripad Ram

University of Texas Southwestern Medical Center

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