CLONALITY OF CD3 NEGATIVE LARGE GRANULAR LYMPHOCYTE PROLIFERATIONS DETERMINED BY PCR BASED X-INACTIVATION STUDIES

Aims-To examine persistent CD3- large granular lymphocytosis (L%L) cas es for clonality, both by lineage specific (T cell receptor) and Linea ge independent (X-inactivation) molecular methods; and to find out whe ther X-inactivation studies are more appropriate than gene rearrangeme nt studies for this subset of LGL disorders. Methods-Patients were sel ected who had LGL of more than six months' duration and identified as CD3- by immunophenotyping. T cell receptor studies and, where possible , X-inactivation studies of the phosphoglycerate kinase (PGK) gene wer e carried out. Analysis of subpopulations was carried out on cases het erozygous for PGK by the use of a polymerase chain reaction (PCR) meth od for X-inactivation. Results-Of 17 CD3- LGL cases studied, all were found to be germline for beta, gamma, and delta T cell receptor studie s, and immunoglobulin heavy chain genes. However, six of these were an alysed by X-inactivation of the PGK gene and two cases gave clonal ban d patterns but only within the CD3- subpopulation. Conclusions-Clonal analysis by the lineage independent method of X-inactivation allows cl onal expansion undetected by T and B cell specific markers to be ident ified. It is therefore a more appropriate method for the analysis of C D3- LGL. This has implications for diagnosis in CD3- LGL disorders.