PROJECT SUMMARY HIV-infected individuals are at an increased risk of developing non-Hodgkin lymphoma (NHL). Virtually all AIDS- related lymphomas (ARL) are of B-cell origin. Two major mechanisms are thought to contribute to the genesis of ARL: 1) loss of immune-mediated control of EBV+ B-cells and their transformation as a result of impaired T- cell function late in the course of HIV disease, and 2) chronic B-cell activation leading to DNA-modifying events that contribute to oncogene mutations/translocations. Thus, both chronic B-cell activation and impaired T-cell function are important contributors to lymphomagenesis. We and others have shown that elevated levels of several cytokines (IL-6, IL-10, CXCL13, TNFα, and IP-10/CXCL10), molecules associated with B-cell activation (sCD23, sCD27, sCD30, κ and λ-immunoglobulin free-light-chains), and microbial translocation factors (e.g. lipopolyssacharide-binding protein (LPB), sCD14, EndoCab) precede the development of AIDS-related NHL (ARL). In addition, B-regulatory cells (Bregs) (CD19+CD24+CD38+), which also express programmed death- ligand 1 (PD-L1) and secrete IL-10, are significantly elevated in peripheral blood of HIV positive individuals who develop ARL. Therefore, inflammation and microbial translocation precede the development of ARL and play an important role in lymphomagenesis. Recently, a novel population of CD4+ helper T-cells has been described (CXCR5-CXCR3+PD-1hi CD4+), which have been named peripheral T-helper cells (TPH). TPH cells have been reported in blood and chronically inflamed peripheral tissues of rheumatoid arthritis and systemic lupus erythematosus patients. TPH cells have B-cell activating capacities and secrete IL-10. We hypothesize that TPH cells accumulate in peripheral tissues in response to inflammation and microbial translocation during HIV infection while inducing B-cell activation, and play a role in the development and maintenance of the tumor niche, thus, contributing to lymphomagenesis and tumor growth, as well as B-cell dysfunction. In this study, we will test this hypothesis by determining if: 1) TPH cells isolated from HIV-positive and negative individuals induce B-cell activation and/or differentiation, and/or induce the expression of Breg cell markers known to be associated with risk for ARL (Aim 1); if 2) immune activation-associated inflammation and/or microbial translocation contribute to the generation of TPH cells (Aim 2); and if 3) TPH cells form part of the tumor microenvironment in ARL cases and if so, define their function in that environment (Aim 3).