cell type lymphoblast SNOMEDCT:15433008 An immature lymphocyte that has enlarged in response to antigenic stimulation. James Malone Often referred to as a blast cell. Unlike other usages of the suffix -blast a lymphoblast is a further differentiation of a lymphocyte, T- or B-, occasioned by an antigenic stimulus. The lymphoblast usually develops by enlargement of a lymphocyte, active re-entry to the S phase of the cell cycle, mitogenesis and production of much m-RNA and ribosomes. NCIt:C13013