999 © Lippincott-Raven Publishers Introduction The occurrence of peripheral blood cytopenia (throm- bocytopenia, granulocytopenia, anaemia) and various dysplastic lesions of the bone marrow, which are often associated with HIV-1 infection, together with in vitro impaired survival/proliferation, with or without differentiation capacity of CD34+ haematopoietic progenitor cells (HPC) isolated from HIV-1-infected patients, indicates the presence of a virus-dependent Impaired telomerase activity in uninfected haematopoietic progenitors in HIV-1-infected patients Monica Vignoli, Barbara Stecca*, Giuliano Furlini, Maria Carla Re, Vilma Mantovani*, Giorgio Zauli † , Giuseppe Visani ‡ , Vincenzo Colangeli § and Michele La Placa Background: Haematopoietic progenitor cells (HPC) of HIV-1-infected patients are severely compromised in their replication and clonogenic capacities, and show an enhanced propensity to apoptosis, despite the lack of productive or latent HIV-1 infection. Objective: To investigate telomerase enzyme levels in CD34+ HPC isolated from HIV-1-infected patients, because the absence of telomerase activity has been found to be correlated with a diminished replication potential. Methods: Telomerase levels were measured by a PCR-based telomeric repeat amplification protocol. CD34+ HPC isolated from the peripheral blood of 11 HIV- 1-infected patients were compared with CD34+ HPC isolated from peripheral blood (nine subjects) or bone marrow (six subjects) from 15 healthy donors. Telomerase levels were also studied in normal HPC after exposure to either gp120 or transforming growth factor (TGF)-β1. Results: CD34+ HPC isolated from either peripheral blood or bone marrow from healthy donors expressed a high level of telomerase activity. On the contrary, CD34+ HPC isolated from HIV-1-seropositive patients did not express any detectable telomerase activity in nine patients, and a clearly reduced enzymatic activity in two patients. Furthermore, telomerase activity in normal CD34+ HPC exposed to recombinant gp120 was significantly reduced, and to a higher extent than in CD34+ HPC exposed to recombinant TGF-β1. Conclusions: This is the first study to demonstrate severely impaired telomerase activity in uninfected CD34+ HPC isolated from HIV-1-infected patients. The mechanism underlying this impairment probably involves the interaction of HIV-1 envelope glycoprotein gp120 with the cell membrane. These results may add to our understanding of the pathogenesis of the lesion of the HPC compartment. © 1998 Lippincott-Raven Publishers AIDS 1998, 12:999–1005 Keywords: Telomerase, haematopoietic progenitor cells, HIV-1 infection, transforming growth factor-β1, gp120 From the Department of Clinical and Experimental Medicine, Section of Microbiology, University of Bologna, the *Central Laboratory, St Orsola General Hospital, Bologna, the † Institute of Human Anatomy, University of Ferrara, Ferrara, the ‡ Institute of Haematology, and the § Section of Infectious Diseases, University of Bologna, Bologna, Italy. Sponsorship: Supported by the AIDS Project of Italian Ministry of Health, Fund for Selected Research Topics of the University of Bologna, MURST 60%, and CNR Strategic Project on Apoptosis. Requests for reprints to: Michele La Placa, Department of Clinical and Experimental Medicine of the University of Bologna, Section of Microbiology, St Orsola General Hospital, 9 Via Massarenti, 40138 Bologna, Italy. Date of receipt: 16 December 1997; revised: 26 March 1998; accepted: 7 April 1998.