HIV patients on antiretroviral therapy have high frequencies of CD8 T cells specific for Immediate Early protein-1 of cytomegalovirus Shelley F. Stone a,b , Patricia Price a,b , Naeem Khan c , Paul A. Moss c and Martyn A. French a,b Objective: To assess the frequency and phenotype of cytomegalovirus (CMV)-specific CD8 T cells in previously immunocompromised HIV patients with stable undetectable HIV viremia due to highly active antiretroviral therapy (HAART). Methods: Twenty-one CMV-seropositive HIV patients with nadir CD4 T-cell counts < 50  10 6 cells/l, at least 4 years on HAART and 6 months of complete viral suppression (< 50 HIV RNA copies/ml) and 12 CMV-seropositive, HIV-seronegative age/sex-matched controls were studied. CD4 and CD8 T-cell responses to whole CMV and two HLA-A  02 restricted CMV peptides [NLV from pp65 and VLE from Immediate Early 1 (IE1)] were measured by interferon (IFN)g ELISpot. Phenotypes of peptide- specific CD8 T cells were determined by tetramer staining. Results: In the ELISpot assay, HIV patients had significantly more CD8 T cells produ- cing IFNg in response to VLE than controls, whereas numbers of NLV-specific and CMV- specific IFNg spots were similar. Four HIV patients and one control had large VLE and/or NLV-specific CD8 T-cell populations despite the absence of CMV-specific CD4 T cells. The majority of peptide-specific CD8 T cells from HIV patients and controls were CD28, CD45ROþ and CD45RA. However, a significantly higher proportion of VLE- specific CD8 T cells expressed perforin compared to NLV-specific CD8 T cells in HIV patients. Conclusions: HIV patients had elevated numbers of IE1-specific, IFNg-producing perforin-positive CD8 T cells compared to controls. As IE1 is expressed early during CMV reactivation, these cells may be important for preventing CMV replication to pathogenic levels. In addition, CMV-specific CD4 T cells are not essential for main- tenance of large populations of CMV-specific CD8 T cells in aviremic HIV patients on HAART. ß 2005 Lippincott Williams & Wilkins AIDS 2005, 19:555–562 Keywords: HAART, CMV, CD8 T-cells, IFNg ELISpot, perforin Introduction Most HIV-infected subjects are cytomegalovirus (CMV) seropositive. Prior to the availability of highly active antiretroviral therapy (HAART), the incidence of CMV end-organ disease (EOD; usually retinitis, colitis or neurological disease) was > 20% per year among HIV patients with CD4 T-cell counts < 100  10 6 cells/l [1,2]. Since the introduction of HAART, the incidence of CMV EOD among HIV-infected individuals has declined dramatically [3], probably due to the reconstitu- tion of CMV-specific T cells that control CMV From the a Department of Clinical Immunology and Biochemical Genetics, Royal Perth Hospital,Perth, Western Australia, the b School of Surgery and Pathology, University of Western Australia, Perth, Western Australia, and the c Cancer Research UK Institute for Cancer Studies, University of Birmingham, Edgbaston, UK. Correspondence to S. F. Stone, School of Surgery and Pathology, University of Western Australia, Level 2, MRF Building, Rear 50 Murray St, Perth WA 6001, Australia. E-mail: sfstone@graduate.uwa.edu.au ISSN 0269-9370 Q 2005 Lippincott Williams & Wilkins 555