Adaptive immune cells protect the host by providing specific immune response against an invading pathogen. While we are surrounded by countless number of pathogens, we carry only a finite amount of adaptive immune cells with us. This cell number decreases further in aging individuals. So, here comes the question. How can a host with limited arsenal respond to these different set of pathogens specifically? What are the molecular mechanisms behind it? These are the fundamental questions we are trying to address using biochemistry, molecular biology, immunology and Next Generation Sequencing (NGS) Technology.