Radiation Therapy for Lymphoma (2013-present)

Solid tumor radiation studies suggests that radiation induced antitumor response is mediated by the immune system of the host. Although lymphomas are extremely sensitive to radiation, it is unclear if antitumor response to radiation therapy requires host immune response. My current research investigates the role of host adaptive and innate immune system in modulating anti-tumor response in radiation therapy for non-Hodgkin lymphoma in mouse models (Clinical Cancer Research. 2015, Radiation Research 2014).

 

Graft versus host disease versus graft versus leukemia effect of memory CD8 +T cells (2007- present)

 

Allogeneic hematopoietic stem cell transplantation (HSCT) is used for treatment of several hematological malignancies as well as immune disorders. However, donor T cells in that are infused in HSCT recognize the recipient’s cells as foreign and attack the epithelial cells in the skin, liver and gut causing acute graft versus host disease (GVHD) that accounts for significant morbidity and mortality.

It has been reported that T cells displaying a memory phenotype (CD44^hi) are incapable of inducing GVHD in allogeneic model of Bone Marrow Transplantation (BMT). However, graft versus leukemia (GVL) capacity of memory phenotype CD8⁺ T cells is not known. In collaboration with Dr. Robert Negrin’s laboratory (Division of Blood and Marrow Transplantation), I have identified that memory phenotype CD8⁺ T cells are able to mediate graft versus lymphoma (GVL) without causing acute GVHD. These cells can cure the relapse of lymphoma without inducing GVHD in a murine lymphoma model (Blood 2011).

 

Currently, I am investigating the GVL response of memory phenotype CD8⁺ T cells in a non-myeloablative model of BMT that involves conditioning of recipients with Total Lymphoid Irradiation and Antitymocyte Serum.

 

Tolerance to combined organ and bone marrow transplantation after total lymphoid irradiation is dependent on both regulatory NKT and CD4⁺CD25⁺ T_reg cells (2009- 2010)

 

Studies in mice showed that following heterotopic heart transplantation, hosts conditioned with total lymphoid irradiation (TLI) and anti-thymocyte globulin (ATG), combined with transplantation of allogeneic MHC-mismatched donor bone marrow cells, became partial T cell chimeras and were protected against Graft Versus Host Disease.  These hosts developed immune tolerance and accepted donor heart transplants. Recipient CD4⁺CD25⁺Foxp3⁺ T_reg cells in the chimeric animals were significantly increased after conditioning and bone marrow transplantation, which persisted at an elevated level even after 14 weeks of transplantation. In contrast, in NKT-deficient CD1d^-/- recipient mice, the percentage of these CD4⁺CD25⁺Foxp3⁺ T_reg cells initially increased after transplantation, however, decreased to preconditioning level by 6 weeks. With another lab member, I am participated in a study to further elucidate the mechanism of NKT and CD4⁺CD25⁺Foxp3⁺ T_reg cell interaction in the induction of allograft tolerance.(Blood 2012)

 

2005 - 2006: Natural killer T (NKT) cells and donor CD4+CD25+ Treg cells are required for protection against GVHD after TLI/ATS host conditioning and bone marrow transplantation

 

A non-myeloablative regimen of total lymphoid irradiation (TLI) and anti-thymocyte serum (ATS) prevents acute graft-versus-host disease (GVHD) in bone marrow transplant recipients. This regimen is being used in a clinical trial at Stanford. The mechanism by which TLI/ATS-conditioning prevent GVHD was not clearly known. A study in our laboratory demonstrated that NKT cells facilitate the expansion of donor Treg cells in TLI/ATS-conditioned mice. I contributed in the initial part of two studies to determine whether this conditioning affects the trafficking of donor T cells to GVHD target organs. We showed that in this regimen, donor T cells fail to induce GVHD due to their inability to migrate to mesenteric lymph nodes and GVHD target organs mainly liver and colon. However, in TLI/ATS conditioned NKT cell-deficient hosts, donor T cell traffic to host gut associated lymphoid tissue and GVHD target organs causing lethal GVHD. Injection sorted host NKT cells from wild-type mice into TLI/ATS conditioned NKT cell deficient hosts given transplants resulted in an in vivo expansion of donor Tregs and prevented conventional donor T cells from expanding and trafficking to GVHD target organs. (Journal of Immunology, 2007, Blood, 2009)

 

2004 - 2006: Induction of GVHD by alloantigen exposed effector memory T cells in Bone marrow Transplantation

 

CD4+ T cells with an effector memory phenotype are known to be incapable of inducing GVHD in an allogeneic model of bone marrow transplantation. My studies showed that effector memory CD4⁺ T cells exposed to host alloantigens induce GVHD. A part of this study performed by undergraduate student for the partial requirement of Stanford Biological Science honors thesis under my direct supervision. (Journal of Immunology, 2007)

 

May, 2002 - 2004: Role of L-Selectin and b7 integrin on donor T cells in induction of colitic phase of lethal acute graft versus host disease

 

Previous studies showed that in a MHC mismatched model of bone marrow transplantation, recipient mice mainly die from donor cell infiltration and injury of the colon. I have identified two candidate molecules, L-selectin and b7 integrin on donor CD4⁺ T cells that are necessary for homing to mesenteric lymph nodes. The trafficking of CD4⁺ T cells to mesenteric lymph nodes are necessary for migration to colon for subsequent induction of acute colitis of lethal acute GVHD. The lethal acute colitis induced by the CD4⁺ T cells was significantly delayed when cells lacking these two key molecules were used for transplantation. (Blood, 2005)

 

2002 - 2004: CD62L⁺ subpopulation of CD4⁺CD25⁺ regulatory T cells protects from lethal acute GVHD

 

In murine models of allogeneic bone marrow transplantation, adoptive transfer of donor CD4⁺CD25⁺ Treg cells protects recipient mice from lethal acute graft versus host disease induced by donor CD4⁺CD25^- T cells. In a collaborative study with Dr. Fathman’s laboratory, we found that only CD62L⁺ subset of the CD4⁺CD25⁺ Treg cells prevented severe tissue damage to the colon and protected recipients from lethal GVHD. Subsequently, CD4⁺CD25⁺CD62L⁺ Treg cells showed a significantly higher capacity than their CD62L^- counterpart to inhibit the expansion of donor CD4⁺CD25^- T cells. The ability of Treg cells to efficiently enter the priming sites of pathogenic alloreactive T cells appears to be a prerequisite for their protective function in acute GVHD. (Blood 2005)

 

August 2000 - April 2002: Studies on the quasispecies diversity of Hepatitis C virus in plasma and peripheral blood mononuclear cells of patients co-infected with HIV and Hepatitis C

 

During this period, I studied the quasispecies diversity of Hepatitis C virus (HCV) in plasma and peripheral blood mononuclear cells of patients co-infected with HIV and Hepatitis C, who are on highly active retroviral therapy for HIV infection. In this study, the effect of antiviral therapy (HAART) on the changes in quasispecies diversity in the hypervariable region of the E2 gene of the Hepatitis C, which encodes for a protein that harbors epitopes for recognition by host anti-HCV antibodies, was examined. This study has clinical implication for the progression of Hepatitis C disease and treatment response in HIV/HCV co-infected patients.

 

July 1999-November 1999: Expression of T cell activation markers in psoriatic skin I worked as a research fellow at the Psoriasis Research Institute, Palo Alto, CA.

 

Here, I studied the temporal expression of T cell activation markers in an effort to elucidate the etiology of psoriasis. Immunohistochemical techniques involving immunofluorescence and immunoperoxidase methods were used to detect T cell activation markers namely CD25 and HLADR in skin biopsies from psoriatic patients following the induction of psoriasis in lesion free skin. My studies showed that these activation markers were gradually expressed with progression of disease and highly abundant in chronic plaque suggesting a role of activated T cells in the pathogenesis of psoriasis.

 

April 1994-February 1999: Liposomal monensin and its application potential (Doctoral Thesis)

 

My doctoral thesis focused on designing an effective liposomal delivery system for the hydrophobic carboxylic ionophore monensin for in vivo use. I used different formulations of liposomally delivered monensin to study their efficacy as a potentiator of ricin toxicity, as an antimalarial agent and as an inhibitor of protein degradation for its potential applications. Initially, I prepared different formulations of monensin liposomes e.g. polyethyleneglycol coated, sugar conjugated, positively and negatively charged to study their effect on ricin toxicity in vivo and in vitro. The potentiation of ricin toxicity by liposomal monensin was found to be dependent on the composition of the liposomes. In another possible application, I used liposomally delivered monensin in malaria chemotherapy. The antimalarial activity of various formulations of monensin in positively and negatively charged and long circulating liposomes were studied in a murine model of malaria. The long circulating liposomal monensin was found to be most effective in the treatment of murine malaria. In a separate study, I looked at the effect of liposomal monensin on inhibition of degradation of endocytosed maleylated bovine serum albumin in a murine macrophage cell line. Negatively charged phosphatidyl serine liposome, which are endocytosed through scavenger receptors on macrophages, produced the maximum inhibition of protein degradation as compared to other formulations. In brief, all these studies on liposomal monensin indicate that the activity of monensin can be modulated by liposomal compositions and have several application potentials. (Antimicrob Agents Chemotherapy 2015