Natural Killer (NK) cells have a crucial role in immune surveillance against a variety of infectious microorganisms and tumors. NK cells are known to mediate direct cytotoxicity as well as antibody dependent cellular cytotoxicity (ADCC) against a variety of tumor cells. Also, they are known to regulate the functions of other cells by producing key cytokines and chemokines. In the tumor microenvironment, cytotoxic function of NK cells is suppressed by a number of distinct effectors and their secreted factors. It has been shown that many cancer patients have decreased peripheral blood NK cell function, so NK cell-based immunotherapy has been used as a treatment in order to enhance NK cell function. However, limited availability of NK cells and ability to expand has restricted development of NK cell immunotherapy. Overcoming NK cell tolerance against tumors by developing new ways of activating endogenous NK cells that increase the expression of ligands for activating NK cell receptors or that render them more sensitive to NK cell mediated killing is crucial.

In this study, we found the novel way to expand NK cells and the functionality of NK cells generated under this condition demonstrated enhanced expression of activating NK receptors. Also, significant cytotoxic killing potential after culture was discovered as well as augmented cytokine secretion. Therefore, these expanded NK cells are highly functional in comparison to primary NK cells. Through the help of cytokines, sAJ2 bacteria and osteoclast, NK cells can be expanded and activated in vitro and furthermore, these expanded NK cells can be used to target tumors in vivo. Expanded NK cells can be used in combination with other treatment modalities, potentially leading to synergistic antitumor activities.

In economics, players are assumed to be rational: they exhibit self interested behavior and play equilibrium strategies. However, in laboratory games or actual markets, players often manifest behavior that is rather consistent with bounded rationality. This thesis consists of two chapters, which relax the standard assumptions on rationality and allow for bounded rationality of players.

The first essay weakens the assumption that players are self interested. In this essay, a retail market is empirically investigated under the relaxed assumption that firms may not be purely self interested or profit maximizing. Standard models of price competition stipulate that firms are pure profit maximizers; this assumption can be sensible and empirically useful in inferring product markups in a market with no direct government intervention. However, in markets for essential goods such as food and healthcare, a government may wish to address its consumer surplus concerns by imposing regulatory constraints or actively participating as a player in the market. As a consequence, some firms may have objectives beyond profit maximization and standard models may induce systematic biases in empirical estimation. This essay develops the structural model of price competition where some firms have consumer surplus concerns. Our model is applied in order to understand demand and supply behaviors in a retail grocery market where the dominant retailer publicly declares its consumer surplus objective. Our estimation results show that the observed low prices of this retailer arise indeed as a consequence of its consumer surplus concerns instead of its low marginal costs. The estimated degree of consumer surplus concerns suggests that the dominant retailer weighs consumer surplus to profit in a 1 to 7 ratio. The counterfactual analysis reveals that if the dominant retailer were to be profit maximizing as in the standard model, its prices would increase by 6.09% on average. As a consequence, its profit would increase by 1.16% and total consumer surplus would decrease by 7.18%. To the contrary, competitors lower their prices in response to the dominant retailer's increased prices, i.e., become less aggressive as if they are strategic substitutes. Interestingly, even though profit of all firms increases, total social surplus would decrease by 3.21% suggesting that profit maximization by all firms induces an inefficient outcome for the market.

The second essay relaxes the rationality assumption that players exhibit equilibrium behavior, and develops a model that explains nonequilibrium behavior of players in laboratory games. In standard nonequilibrium models of iterative thinking, there is a fixed rule hierarchy and every player chooses a fixed rule level; nonequilibrium behavior emerges when some players do not perform enough thinking steps. Existing approaches however are inherently static. In this essay, we generalize models of iterative thinking to incorporate adaptive and sophisticated learning. Our model has three key features. First, the rule hierarchy is dynamic, i.e., the action that corresponds to each rule level can evolve over time depending on historical game plays. Second, players' rule levels are dynamic. Specifically, players update beliefs about opponents' rule levels in each round and change their rule level in order to maximize payoff. Third, our model accommodates a continuous rule hierarchy, so that every possible observed action can be directly interpreted as a real-numbered rule level r. The proposed model unifies and generalizes two seemingly distinct streams of nonequilibrium models (level-k and belief learning models) and as a consequence nests several well-known nonequilibrium models as special cases. When both the rule hierarchy and players' rule levels are fixed, we have a static level-r model (which generalizes the standard level-k model). When only players' rule levels are fixed, our model reduces to a static level-r model with dynamic rule hierarchy and captures adaptive learning. When only the rule hierarchy is fixed, our model reduces to a dynamic level-r model and captures sophisticated learning. Since our model always converges to the iterative dominance solution, it can serve as a model of the equilibration process. Using experimental data on p-beauty contests, we show that our model describes subjects' dynamic behavior better than all its special cases. In addition, we collect new experimental data on a generalized price matching game. The estimation results show that it is crucial to allow for both adaptive and sophisticated learning in predicting dynamic choice behaviors across games.

The purpose of this dissertation is to identify what motivates leaders to seek to possess nuclear weapons. I argue that individual leaders’ risk propensities are associated with their behaviors in regard to nuclear proliferation. To test my theory, I aim to create a new dataset of leaders’ risk propensities on approximately 1,700 leaders from 1945 to 2000. My risk propensity index draws on insights from psychology and business management, which suggest that leaders’ age, socioeconomic backgrounds, college major, military experience, and international experience contribute to his or her risk tolerance. I build on data from the Leader Experience and Attribute Descriptions (LEAD) dataset. I supplement this data with my own in-depth coding of the demographic backgrounds of leaders, including childhood wealth, college major, and international experience. I find that certain demographic characteristics of leaders that are used as proxies for examining their risk propensity significantly influence their risk-taking behaviors with respect to nuclear weapons pursuit. I conclude that leaders possessing relatively higher levels of risk propensity are more likely to pursue nuclear weapons than leaders with lower levels of risk propensity. These statistical results are further confirmed by more in-depth case studies on South Korea and India.