Low prevalence of flower cells in U.S.A. blood donors infected with human T-lymphotrophic virus types I and II.

Large lymphocytes with basophilic cytoplasm and cleaved/cerebriform nuclei called flower cells have been described in human T-lymphotrophic virus type I (HTLV-I) seropositive individuals and may be precursors of adult T-cell leukaemia (ATL). A cohort of 546 HTLV-seropositive former blood donors, 32 HTLV-positive sexual partners of these donors and 799 HTLV-seronegative controls has been followed as part of the Retrovirus Epidemiology Donor Study. A novel methodology was developed to systematically review peripheral blood slides from these subjects for HTLV-related lymphocyte abnormalities, using an algorithm based on morphologic features to objectively identify flower cells. The algorithm included: absence of azurophil granules; nuclear chromatin condensation; cell size >1.5 small lymphocytes; nuclear to cytoplasmic ratio >80%; and presence of nuclear folding/lobulation. Peripheral slides from subjects were screened by a medical technologist blinded to HTLV status. 6.8% of HTLV-I subjects (P = 0.0001 versus seronegatives), 0.9% of HTLV-II subjects and 1.1% of seronegatives were confirmed to have cells classified as flower cells by two haematologists using objective criteria, and blinded to serostatus. Despite the higher prevalence of flower cells in HTLV-I positives, no clinical correlations were found. Longitudinal follow-up may yield higher rates of cellular abnormalities as the sequelae of HTLV infection develop.