Emigration of mature naïve CD4 SP T cells from the human thymus to the periphery is a field that remains not fully understood, although elucidation of the mechanisms that govern egress of T cells is crucial to understanding both basic immunology and the immune response in disease states such as HIV infection. In this dissertation work, I have examined the expression and function of a novel requisite T cell egress receptor expressed within the human thymus, as well as characterized changes observed in the expression and function of this receptor during HIV infection, and finally examined additional markers of maturation stages of human thymocytes. In Chapter 2, ("S1P/ S1P-R1 signaling is required for migration of naïve human T cells from the thymus to the periphery") I investigated whether Sphingosine-1-phosphate receptors (S1P-Rs) are expressed on human thymocyte populations and whether they function in the egress of mature human thymocytes from the thymus to the periphery. In Chapter 3 ("HIV-1 infection results in upregulation of sphingosine-1-phosphate receptor 1 on mature human thymocytes and functional naïve T cell response to S1P"), I examined whether Human Immunodeficiency Virus 1 (HIV-1) infection affects the expression and function of S1P-R1 utilizing humanized (NSG thy/liv) mice as well as various ex vivo assays to investigate the function of S1P-R downstream signaling. Finally, in Chapter 4, ("Alternative markers for maturation stages of human thymocytes: Expression of CD31 (PECAM-1) during T cell differentiation in the human thymus"), work I performed in collaboration with others within the AIDS Institute at UCLA, I contributed to the characterization of additional markers of developing thymocytes within the human thymus. Interestingly, a novel marker characterized may play a role in modulation of TCR signaling during T cell development in the thymus and may moreover be coexpressed with S1P-R1 on mature human thymocytes. Taken together, this work should advance the fields of basic T cell Immunology as well as HIV Immunology and open new avenues for exploration into therapeutics for HIV infected individuals.