Professional Education

  • Bachelor of Engineering, Mumbai University (2009)
  • Doctor of Philosophy, University of Maryland Baltimore (2014)

Stanford Advisors

Research & Scholarship

Current Research and Scholarly Interests

Cancer Immunology


All Publications

  • Distinct predictive biomarker candidates for response to anti-CTLA-4 and anti-PD-1 immunotherapy in melanoma patients. Journal for immunotherapy of cancer Subrahmanyam, P. B., Dong, Z., Gusenleitner, D., Giobbie-Hurder, A., Severgnini, M., Zhou, J., Manos, M., Eastman, L. M., Maecker, H. T., Hodi, F. S. 2018; 6 (1): 18


    While immune checkpoint blockade has greatly improved clinical outcomes in diseases such as melanoma, there remains a need for predictive biomarkers to determine who will likely benefit most from which therapy. To date, most biomarkers of response have been identified in the tumors themselves. Biomarkers that could be assessed from peripheral blood would be even more desirable, because of ease of access and reproducibility of sampling.We used mass cytometry (CyTOF) to comprehensively profile peripheral blood of melanoma patients, in order to find predictive biomarkers of response to anti-CTLA-4 or anti-PD-1 therapy. Using a panel of ~?40 surface and intracellular markers, we performed in-depth phenotypic and functional immune profiling to identify potential predictive biomarker candidates.Immune profiling of baseline peripheral blood samples using CyTOF revealed that anti-CTLA-4 and anti-PD-1 therapies have distinct sets of candidate biomarkers. The distribution of CD4+ and CD8+ memory/non-memory cells and other memory subsets was different between responders and non-responders to anti-CTLA-4 therapy. In anti-PD-1 (but not anti-CTLA-4) treated patients, we discovered differences in CD69 and MIP-1? expressing NK cells between responders and non-responders. Finally, multivariate analysis was used to develop a model for the prediction of response.Our results indicate that anti-CTLA-4 and anti-PD-1 have distinct predictive biomarker candidates. CD4+ and CD8+ memory T cell subsets play an important role in response to anti-CTLA-4, and are potential biomarker candidates. For anti-PD-1 therapy, NK cell subsets (but not memory T cell subsets) correlated with clinical response to therapy. These functionally active NK cell subsets likely play a critical role in the anti-tumor response triggered by anti-PD-1.

    View details for PubMedID 29510697

    View details for PubMedCentralID PMC5840795

  • CyTOF Measurement of Immunocompetence Across Major Immune Cell Types. Current protocols in cytometry Subrahmanyam, P. B., Maecker, H. T. 2017; 82: 9.54.1?9.54.12


    The central role of the immune system is becoming appreciated in a wide variety of diseases. Cancer immunotherapy is one area that has yielded much recent success, although not all patients benefit equally. At the same time, recent studies have highlighted the heterogeneity of the human immune system. Despite this heterogeneity, we do not routinely measure immune competence in clinical practice, and there are no consensus assays of healthy immune function. Using mass cytometry (CyTOF), we can simultaneously detect ?40 markers to identify various cell subsets and determine their function by the expression of cytokines, cytotoxicity, and activation markers. This can help assess 'immunocompetence' and facilitate better implementation of immunotherapies, both in specific disease settings and perhaps eventually as a prognostic tool in healthy subjects. Here we introduce the concepts behind this assay and provide a protocol that we have successfully implemented to identify possible predictive biomarkers of immunotherapy outcome. © 2017 by John Wiley & Sons, Inc.

    View details for PubMedID 28967988

    View details for PubMedCentralID PMC5678938

  • A Prospective Clinical Trial Combining Radiation Therapy With Systemic Immunotherapy in Metastatic Melanoma. International journal of radiation oncology, biology, physics Hiniker, S. M., Reddy, S. A., Maecker, H. T., Subrahmanyam, P. B., Rosenberg-Hasson, Y., Swetter, S. M., Saha, S., Shura, L., Knox, S. J. 2016; 96 (3): 578-588


    Local radiation therapy (RT) combined with systemic anti-cytotoxic T-lymphocyte-associated protein-4 immunotherapy may enhance induction of systemic antimelanoma immune responses. The primary objective of the present trial was to assess the safety and efficacy of combining ipilimumab with RT in patients with stage IV melanoma. The secondary objectives included laboratory assessment of induction of antimelanoma immune responses.In our prospective clinical trial, 22 patients with stage IV melanoma were treated with palliative RT and ipilimumab for 4 cycles. RT to 1 to 2 disease sites was initiated within 5 days after starting ipilimumab. Patients had ?1 nonirradiated metastasis measuring ?1.5 cm available for response assessment. Tumor imaging studies were obtained at baseline, 2 to 4 weeks after cycle 4 of ipilimumab, and every 3 months until progression. Laboratory immune response parameters were measured before and during treatment.Combination therapy was well-tolerated without unexpected toxicities. Eleven patients (50.0%) experienced clinical benefit from therapy, including complete and partial responses and stable disease at median follow-up of 55 weeks. Three patients (27.3%) achieved an ongoing systemic complete response at a median follow-up of 55 weeks (range 32-65), and 3 (27.3%) had an initial partial response for a median of 40 weeks. Analysis of immune response data suggested a relationship between elevated CD8-activated T-cells and response.This is the second prospective clinical trial of treatment of metastatic melanoma using the combination of RT and systemic immunotherapy and the first using this sequence of therapy. The results from the present trial demonstrate that a subset of patients may benefit from combination therapy, arguing for continued clinical investigation of the use of RT combined with immunotherapy, including programmed cell death 1 inhibitors, which might have the potential to be even more effective in combination with RT.

    View details for DOI 10.1016/j.ijrobp.2016.07.005

    View details for PubMedID 27681753

  • Sphingosine 1-phosphate signaling impacts lymphocyte migration, inflammation and infection. Pathogens and disease Tiper, I. V., East, J. E., Subrahmanyam, P. B., Webb, T. J. 2016; 74 (6)


    Sphingosine 1-phosphate (S1P) is a sphingosine containing lipid intermediate obtained from ceramide. S1P is known to be an important signaling molecule and plays multiple roles in the context of immunity. This lysophospholipid binds and activates G-protein-coupled receptors (GPCRs) known as S1P receptors 1-5 (S1P1-5). Once activated, these GPCRs mediate signaling that can lead to alterations in cell proliferation, survival or migration, and can also have other effects such as promoting angiogenesis. In this review, we will present evidence demonstrating a role for S1P in lymphocyte migration, inflammation and infection, as well as in cancer. The therapeutic potential of targeting S1P receptors, kinases and lyase will also be discussed.

    View details for DOI 10.1093/femspd/ftw063

    View details for PubMedID 27354294

  • Natural killer T (NKT) cells accelerate Shiga toxin type 2 (Stx2) pathology in mice FRONTIERS IN MICROBIOLOGY Obata, F., Subrahmanyam, P. B., Vozenilek, A. E., Hippler, L. M., Jeffers, T., Tongsuk, M., Tiper, I., Saha, P., Jandhyala, D. M., Kolling, G. L., Latinovic, O., Webb, T. J. 2015; 6


    Shiga toxin-producing Escherichia coli (STEC) is a leading cause of childhood renal disease Hemolytic Uremic Syndrome (HUS). The involvement of renal cytokines and chemokines is suspected to play a critical role in disease progression. In current article, we tested the hypothesis that NKT cells are involved in Stx2-induced pathology in vivo. To address this hypothesis we compared Stx2 toxicity in WT and CD1 knockout (KO) mice. In CD1KO mice, which lack natural killer T (NKT) cells, Stx2-induced pathologies such as weight loss, renal failure, and death were delayed. In WT mice, Stx2-specific selective increase in urinary albumin occurs in later time points, and this was also delayed in NKT cell deficient mice. NKT cell-associated cytokines such as IL-2, IL-4, IFN-?, and IL-17 were detected in kidney lysates of Stx2-injected WT mice with the peak around 36 h after Stx2 injection. In CD1KO, there was a delay in the kinetics, and increases in these cytokines were observed 60 h post Stx2 injection. These data suggest that NKT cells accelerate Stx2-induced pathology in mouse kidneys. To determine the mechanism by which NKT cells promote Stx2-associated disease, in vitro studies were performed using murine renal cells. We found that murine glomerular endothelial cells and podocytes express functional CD1d molecules and can present exogenous antigen to NKT cells. Moreover, we observed the direct interaction between Stx2 and the receptor Gb3 on the surface of mouse renal cells by 3D STORM-TIRF which provides single molecule imaging. Collectively, these data suggest that Stx2 binds to Gb3 on renal cells and leads to aberrant CD1d-mediated NKT cell activation. Therefore, strategies targeting NKT cells could have a significant impact on Stx2-associated renal pathology in STEC disease.

    View details for DOI 10.3389/fmicb.2015.00262

    View details for Web of Science ID 000352551400001

    View details for PubMedID 25904903

  • Bcl-xL Regulates CD1d-Mediated Antigen Presentation to NKT Cells by Altering CD1d Trafficking through the Endocytic Pathway JOURNAL OF IMMUNOLOGY Subrahmanyam, P. B., Carey, G. B., Webb, T. J. 2014; 193 (5): 2096-2105


    NKT cells are a unique subset of T cells that recognize glycolipid Ags presented in the context of CD1d molecules. NKT cells mount strong antitumor responses and are a major focus in developing effective cancer immunotherapy. It is known that CD1d molecules are constantly internalized from the cell surface, recycled through the endocytic compartments, and re-expressed on the cell surface. However, little is known about the regulation of CD1d-mediated Ag processing and presentation in B cell lymphoma. Prosurvival factors of the Bcl-2 family, such as Bcl-xL, are often upregulated in B cell lymphomas and are intimately linked to sphingolipid metabolism, as well as the endocytic compartments. We hypothesized that Bcl-xL can regulate CD1d-mediated Ag presentation to NKT cells. We found that overexpression or induction of Bcl-xL led to increased Ag presentation to NKT cells. Conversely, the inhibition or knockdown of Bcl-xL led to decreased NKT cell activation. Furthermore, knockdown of Bcl-xL resulted in the loss of CD1d trafficking to lysosome-associated membrane protein 1(+) compartments. Rab7, a late endosomal protein, was upregulated and CD1d molecules accumulated in the Rab7(+) late endosomal compartment. These results demonstrate that Bcl-xL regulates CD1d-mediated Ag processing and presentation to NKT cells by altering the late endosomal compartment and changing the intracellular localization of CD1d.

    View details for DOI 10.4049/jimmunol.1400155

    View details for Web of Science ID 000341140600012

    View details for PubMedID 25070854

  • NKT Cell Responses to B Cell Lymphoma. Medical sciences : open access journal Li, J., Sun, W., Subrahmanyam, P. B., Page, C., Younger, K. M., Tiper, I. V., Frieman, M., Kimball, A. S., Webb, T. J. 2014; 2 (2): 82?97


    Natural killer T (NKT) cells are a unique subset of CD1d-restricted T lymphocytes that express characteristics of both T cells and natural killer cells. NKT cells mediate tumor immune-surveillance; however, NKT cells are numerically reduced and functionally impaired in lymphoma patients. Many hematologic malignancies express CD1d molecules and co-stimulatory proteins needed to induce anti-tumor immunity by NKT cells, yet most tumors are poorly immunogenic. In this study, we sought to investigate NKT cell responses to B cell lymphoma. In the presence of exogenous antigen, both mouse and human NKT cell lines produce cytokines following stimulation by B cell lymphoma lines. NKT cell populations were examined ex vivo in mouse models of spontaneous B cell lymphoma, and it was found that during early stages, NKT cell responses were enhanced in lymphoma-bearing animals compared to disease-free animals. In contrast, in lymphoma-bearing animals with splenomegaly and lymphadenopathy, NKT cells were functionally impaired. In a mouse model of blastoid variant mantle cell lymphoma, treatment of tumor-bearing mice with a potent NKT cell agonist, ?-galactosylceramide (?-GalCer), resulted in a significant decrease in disease pathology. Ex vivo studies demonstrated that NKT cells from ?-GalCer treated mice produced IFN-? following ?-GalCer restimulation, unlike NKT cells from vehicle-control treated mice. These data demonstrate an important role for NKT cells in the immune response to an aggressive hematologic malignancy like mantle cell lymphoma.

    View details for DOI 10.3390/medsci2020082

    View details for PubMedID 24955247

    View details for PubMedCentralID PMC4063678

  • Connecting the Dots: Artificial Antigen Presenting Cell-Mediated Modulation of Natural Killer T Cells JOURNAL OF INTERFERON AND CYTOKINE RESEARCH Sun, W., Subrahmanyam, P. B., East, J. E., Webb, T. J. 2012; 32 (11): 505-516


    Natural killer T (NKT) cells constitute an important subset of T cells that can both directly and indirectly mediate antitumor immunity. However, we and others have reported that cancer patients have a reduction in both NKT cell number and function. NKT cells can be stimulated and expanded with ?-GalCer and cytokines and these expanded NKT cells retain their phenotype, remain responsive to antigenic stimulation, and display cytotoxic function against tumor cell lines. These data strongly favor the use of ex vivo expanded NKT cells in adoptive immunotherapy. NKT cell based-immunotherapy has been limited by the use of autologous antigen-presenting cells, which can vary substantially in their quantity and quality. A standardized system that relies on artificial antigen-presenting cells (aAPCs) could produce the stimulating effects of dendritic cell (DC) without the pitfalls of allo- or xenogeneic cells. In this review, we discuss the progress that has been made using CD1d-based aAPC and how this acellular antigen presenting system can be used in the future to enhance our understanding of NKT cell biology and to develop NKT cell-specific adoptive immunotherapeutic strategies.

    View details for DOI 10.1089/jir.2012.0045

    View details for Web of Science ID 000310842800001

    View details for PubMedID 23050947

  • Natural killer T cell based Immunotherapy. Journal of vaccines & vaccination Subrahmanyam, P. B., Sun, W., East, J. E., Li, J., Webb, T. J. 2012; 3: 144


    Natural killer T (NKT) cells play an important immunoregulatory role and are thought to bridge the innate and adaptive immune responses. Following activation through cognate interactions with lipid antigen presented in the context of CD1d molecules, NKT cells rapidly produce a plethora of cytokines and can also mediate cytotoxicity. Due to their potent effector functions, extensive research has been performed to increase our understanding on how to effectively modulate these cells. In fact, NKT cell agonists have been used as vaccine adjuvants to enhance antigen specific T and B cell responses to infections and malignancy. In this review, we will focus on recent advances in NKT cell-based vaccination strategies. Given the role that NKT cells play in autoimmune disease, infectious diseases, cancer, transplant immunology and dermatology, it is important to understand how to effectively guide their effector functions in order to develop novel immunotherapeutic strategies.

    View details for DOI 10.4172/2157-7560.1000144

    View details for PubMedID 24089657

    View details for PubMedCentralID PMC3786600

  • Boosting the Immune Response: The Use of iNKT cell ligands as vaccine adjuvants. Frontiers in biology Subrahmanyam, P., Webb, T. J. 2012; 7 (5): 436?44


    Natural killer T (NKT) cells comprise a small, but important T cell subset and are thought to bridge the innate and adaptive immune responses. The discovery of NKT cells and extensive research on their activating ligands have paved the way for modulation of these potent immunoregulatory cells in order to improve the outcome of various clinical conditions. Efforts to modulate NKT cell effector functions have ranged from therapy for influenza to anti-tumor immunotherapy. These approaches have also led to the use of NKT cell agonists such as ?-Galactosylceramide (?-GalCer) and its analogs as vaccine adjuvants, an approach that is aimed at boosting specific B and T cell responses to a vaccine candidate by concomitant activation of NKT cells. In this review we will provide a comprehensive overview of the efforts made in using ?-GalCer and its analogs as vaccine adjuvants. The diverse array of vaccination strategies used, as well as the role of NKT cell activating adjuvants will be discussed, with focus on vaccines against malaria, HIV, influenza and tumor vaccines. Collectively, these studies demonstrate the efficacy of NKT cell-specific agonists as adjuvants and further suggest that these compounds warrant serious consideration during the development of vaccination strategies.

    View details for DOI 10.1007/s11515-012-1194-2

    View details for PubMedID 23264781

    View details for PubMedCentralID PMC3524977

Footer Links:

Stanford Medicine Resources: