Borrelia burgdorferi may cause an acute infection of the central nervous system (CNS) that rarely leads to chronic disease. To characterize host immunity to B. burgdorferi in humans, we performed serial T cell receptor (TCR) variable beta (TCRBV) chain analyses in blood and cerebrospinal fluid (CSF) samples from 10 patients with acute neuroborreliosis. In most patients, we found significant differences in TCRBV expression between CSF and peripheral blood T cells, predominantly involving CD8(+) T cells. T cells that accumulated in the CSF had a memory phenotype and expressed high levels of C-C chemokine receptor 5 and CD69. Serial studies demonstrated that CD8(+) T cell accumulation decreased continuously after resolution of the infection. In 2 patients, serial analysis of the TCR-alpha and -beta chain sequences revealed that overexpression of TCRBV in CSF was caused by extensive clonal expansion of CD8(+) T cells. Our findings support the role of CD8(+) T cells during the early host defense against spirochete infection of the CNS.