Pittet, Mikael, PhD
Research
I. In vivostudies of anti-tumor T cell immunity. Extensive research over the past 15 years has established that tumor-specific cytotoxic T lymphocyte (CTL) immune responses frequently develop in cancer patients, yet in most cases the CTL fail to eradicate tumors. In vitro and ex vivo studies suggest that regulatory T (Treg) cells contribute to immune evasion in cancer by repressing endogenous tumor-specific CTL activity, and represent a major obstacle in cancer immunotherapy. Because the complexity of in vivo environments is not easy to faithfully reproduce in vitro, my goal is to objectively study tumor-specific CTL and Treg cell responses in vivo. Specifically, I aim to understand how Treg cells interfere with CTL immunity and how Treg-cell mediated suppression can be manipulated in the context of immunotherapy.
The laboratory employs a recently validated mouse model that recapitulates observations made in cancer patients, and that allows in vivo tracking of CTL and Treg cells with specificity for the same tumor cells. In vivo imaging technologies include fluorescent protein tomography, single photon emission computed tomography/computed tomography, intravital multiphoton microscopy, bioluminescence imaging and magnetic resonance imaging. Areas of emphasis include (i) the dynamics of CTL and Treg cell trafficking to tumors and (ii) the functional activity of CTL and Treg cells in priming and target sites.
It has also become clear that sensitive assays and imaging techniques are needed to monitor tumor-specific CTL responses in individual patients. The laboratory is developing and validating cell-tracking nanoparticles with high cell-membrane permeability, prolonged intracellular retention with eventual biodegradability, low toxicity, multimodal detectability (e.g., magnetic, nuclear and optical imaging), and that can be used in a clinical setting. In vitro-activated tumor-specific CTL labeled with cell-tracking nanoparticles are followed after adoptive transfer into tumor-bearing animals (adoptive transfer immunotherapy) simulating various clinical settings.
II. In vivo studies of monocytes in atherosclerosis. Atherosclerosis involves accumulation of cholesterol in the arterial wall, local inflammation, leukocyte recruitment, and development of fibrotic lesions. Monocyte recruitment to the intima is the hallmark of fatty streaks, the earliest grossly detectable lesion of human and experimental atherosclerosis. In the intima, monocytes differentiate into macrophages, ingest oxidized lipoproteins and modulate plaque development. Thrombosis, the chief complication and cause of myocardial infarction and stroke, often involves rupture of a vulnerable plaque, defined by its thin fibrous cap and large lipid core. Elucidating the biology and dynamics of leukocyte recruitment to atherosclerotic lesions, therefore, is of clinical and biological importance. We are utilizing various technologies for dynamic, quantitative and qualitative assessment of monocyte activity in hyper-cholesterolemic mice. These studies aim to better understand the role of leukocyte migration in disease progression and may form the basis of novel immunotherapeutic intervention strategies.