Melba M. Tejera, PhD

Research Title: Regulation of Effector and Memory T Cell Differentiation by Transcription Factor FoxO1 and Iĸ Bα Nuclear Export of NF-ĸB

Research Summary: The generation of long-term immunity and the development of vaccines against many viral pathogens such as polio, smallpox, and the flu, are dependent on the number and quality of long-lived memory cells. Previous work from the Suresh laboratory showed that FoxO3 constrains the accumulation of effector CD8 T cells during the expansion phase of the T cell response and limits the magnitude of CD8 T cell memory. By using mice that are conditionally deficient for FoxO1 in T cells (FoxO1-/), Melba examined the role of FoxO1 in regulating T cell immunity to an acute infection with lymphocytic choriomeningitis virus (LCMV). Her studies show that FoxO1 is not required for the differentiation of effectors, but is necessary for enforcing the effector-to-memory transition of CD8 T cells. She also demonstrated that FoxO1 plays a non-redundant role in maintaining the functionality and protective capacity of memory CD8 T cells. Additionally, she found that FoxO1 regulates the function of effector and memory CD4 T cells. In studies using bone marrow chimeras Melba showed that T-cell intrinsic FoxO1 is not required for clonal expansion, but is necessary for the survival of memory CD8 T cells under competitive conditions. With microarrays she was able to elucidate that the deficiency of FoxO1 impaired protective immunity by dysregulating the transcriptome of memory CD8 T cells. These findings have implications for the development of novel strategies to modulate FoxO1 activity in T cells, hence enhancing vaccine-induced CD8 T cell memory. Previous work suggested that continuous FoxO1 activity might be necessary for the maintenance of the full spectrum of effector functions and differentiation of memory CD8 T cells. By deleting FoxO1 in T cells in an inducible fashion, Melba investigated the T-cell intrinsic and temporal requirement for FoxO1 in the differentiation of memory CD8 T cells. In mice infected with LCMV, she ablated FoxO1 gene (via Tamoxifen treatment) at various intervals spanning the different phases of the T cell response to an acute LCMV infection. She found that full expression of key surface molecules including CD44, CD62L and CD127 in memory CD8 T cells requires continuous expression of FoxO1. Nuclear factor κB (NF-κB) is known to play an important role in regulating a diverse array of genes involved in inflammatory and immune responses. In unactivated resting T cells, NF-κB is sequestered in the cytoplasm by inhibitor IκBs. A collaborator here in Madison, Dr. Shigeki Miyamoto and his colleagues created the NfkbiaNES/NES mice, in which the nuclear export sequence of IκBα is mutated, and thus NF-kB export from the cell nucleus to the cytoplasm does not occur. Using these mice, Melba investigated the physiological significance of IκBα nuclear export in CD8 T cell differentiation during an acute LCMV infection. Strikingly, she found that the NES mutation of IκBa greatly diminishes CD8 T cell activation, differentiation, and IFN-γ production among virus-specific effector CD8 T cells. She also found that it regulates CD8 T cell memory differentiation by the reduction of key transcription factors such as FoxO1 and TCF-1. Together, these findings have provided fundamental insights into the role of IκBα nuclear export of NF-κB and its regulation of the homeostasis of CD8 T cell memory to intracellular pathogens. CD4 T cells, otherwise known as “T helper cells” are mainly recognized for their ability to help B cell and CD8 T cell responses. Melba has also elucidated a novel role of IκBα nuclear export of NF-κB in CD4 T cell differentiation during an acute LCMV infection. She showed that nuclear export of IκBα plays an integral role in the differentiation of TH1 and TFH CD4 T cell memory subsets by regulating the balance of key transcription factors T-bet, Bcl-6 and Blimp-1. She also found that the NES mutation in IκBa dysregulates the antigen-induced production of IFN-γ by virus-specific CD4 T cell. Hence, she proposes that nuclear export of IκBα is a key regulator that steers TH1 and TFH CD4 T cell memory differentiation. These findings have provided fundamental insights into the mechanisms that regulate CD4 T cell differentiation and viral clearance. These studies have elucidated and advanced the understanding for the molecular requirements of both FoxO1 and IκBα in the differentiation and functionality of T cells during an acute viral infection and suggest that the modulation of FoxO1 and IκBα is a promising strategy to enhance T cell responses to vaccinations or acute viral infections.