Welcome to the website for Protul A. Shrikant, PhD and his team. For more information, please feel free to contact us at the Department of Immunology, Roswell Park Cancer Institute, Elm and Carlton Streets, Buffalo, NY 14263 or by phone at (716) 845-8969 or email at Protul.Shrikant@roswellpark.org.

Although the critical need for CD8 T cells in host tumor immunity is well documented, the precise contributions of effector and/or memory functions of CD8 T cells for tumor immunity remains unclear and mechanisms regulating their differentiation remain poorly understood. The goal of our laboratory investigations is to better understand CD8 T cell biology and use the information generated to devise new therapeutic approaches to eradicate tumor. The studies are based in murine models of ovarian, thymoma or melanoma, wherein the tumor cells are engineered to express a nominal antigen recognized by T cells derived from TCR transgenic mice; CD4+ (OT-2) and CD8+ (OT-1). By varying the 3 signals that program naïve T cells to undergo activation, proliferation, differentiation, we are actively delineating the molecular (second messenger and transcriptional) pathways that regulate effector and memory differentiation with the hope that this information when extrapolated will permit enhanced tumor immunity by immunization and/or adoptive cell transfer strategies.

We have three interrelated but distinct lines of investigations ongoing in the laboratory.

1. Understanding molecular mechanisms underpinning cytokine (innate; IL-12 and adaptive; IL-21) mediated regulation of antigen specific CD8 T cell responses.

The goal of this project is characterize the Jak/STAT pathways that regulate the transcriptional factors T-bet, Gata-3 and/or Hlx that govern effector and memory cell fate. We have established a novel in vitro model system, which permits isolation of IL-12 or IL-21 impact on antigen induced CD8 T cell responses. In this system, we have observed a non-essential role for STAT4 induced T-bet, but a critical requirement for Hlx in IL-12 programmed effector maturation. Moreover, we have demonstrated a requirement for T-bet to program effector CD8 T cells to undergo memory transition via IL-15. Ongoing studies are addressing the role of STAT1 and STAT4 activation in IL-12 and IL-21 induced effector and memory cell fates by studying TCR transgenic CD8 T cells with specific gene deletions and establishing the role of Jak1 and/or Jak3 in the signaling pathway.

2. The integrative potential of strength of antigen stimulation, co-stimulation and cytokines like IL-12 and IL-21 to program effector and memory CD8 T cell responses.

Recognition of antigen by the T cells in the context of co-stimulatory molecules like B7.1 and cytokines results in activation, proliferation and differentiation. In the absence of co-stimulation or cytokines the induced T cell response is rapidly anergized and rendered ineffective due to poor differentiation and/or activation-induced cell death (AICD). Recent evidence has implicated the mammalian target of rapamycin (mTOR) as a cellular integrator that senses the physiological health of the cell and tunes the cellular response to various signals generated by the TCR, cytokines and co-stimulatory molecules. In this project, we are actively characterizing the integrative potential of the strength of antigen and cytokines to imprint T cell responses and we hope to determine the role of extrinsic and intrinsic physiological parameters like glucose, amino-acid and calcium levels to affect outcomes of the TCR and cytokine signals via mTOR signaling. The data generated is being used to develop new algorithms for mathematical modeling of antigen specific T cell responses, which should facilitate development of new strategies to optimize T cell, mediated immunity.

3. Immunization strategies to augment effector and restrict regulatory (CD8+ and CD4+) T cell responses in tumor bearing hosts.

To test novel immunization strategies to prevent or intervene tumor growth, we have established several animal models that allow us to visualize tumor-antigen specific T cells (CD4+ and CD8+) and monitor the induction, progression and resolution of the adaptive response. In the ovarian tumor model, we have established that effector CD8 T cells are held in check by regulatory CD4 T cells (Fox3P+), however immunization with a novel second generation glycolipid; a-C-Galactosyl Ceramide, recruits NK/NKT cell to produce IFNg and thereby activates DC presentation of antigen in the context of IL_12 to tumor-antigen specific CD8 T cells enabling their effector maturation. Moreover, the glycolipid adjuvant induced myeloid maturation inhibits the tumor-induced T regulatory cell generation, thereby causing an imbalance in the ovarian tumor-bearing host to promote immunity. To better characterize the transient nature of the induced immunity, our studies are testing complementary strategies to sustain the induced responses by either direct cytokine administration and/or irradiation induced lymphopenia.