The Role of CTLs in Persistent Viral Infection: Cytolytic Gene Expression in CD8 Lymphocytes Distinguishes between Individuals with a High or Low Proviral Load of Human T Cell Lymphotropic Virus Type 1

The proviral load in human T cell lymphotropic virus type 1 (HTLV-1) infection is typically constant in each infected host, but varies by >1000-fold between hosts and is strongly correlated with the risk of HTLV-1-associated inflammatory disease. However, the factors that determine an individual’s HTLV-1 proviral load remain uncertain. Experimental evidence from studies of host genetics, viral genetics, and lymphocyte function and theoretical considerations suggest that a major determinant of the equilibrium proviral load is the CD8 + T cell response to HTLV-1. In this study, we tested the hypothesis that the gene expression profile in circulating CD8 + and CD4 + lymphocytes distinguishes between individuals with a low proviral load of HTLV-1 and those with a high proviral load. We show that circulating CD8 + lymphocytes from individuals with a low HTLV-1 proviral load overexpressed a core group of nine genes with strong functional coherence: eight of the nine genes encode granzymes or other proteins involved in cell-mediated lysis or Ag recognition. We conclude that successful suppression of the HTLV-1 proviral load is associated with strong cytotoxic CD8 + lymphocyte activity in the peripheral blood.