Further characterization of memory T cells existing in a case of CD8 deficiency

CD8 deficiency is a rare primary immuno-deficiency caused by a defect of ZAP-70, which plays a pivotal role in T cell activation. We previously reported the existence of memory phenotype-CD4⁺ T cells in a case of CD8 deficiency, which demonstrates that activation signals through ZAP-70 are not essential to the phenotypic conversion of T cells from 'naive' to 'memory.' In this study, we further characterized CD45RO⁺ T cells in a CD8 deficient patient. We showed that the patient's CD45RO⁺ T cell population had a wide variety of T cell receptor Vβ-chain gene usage, and contained few clonally expanded T cells, while many clonally expanded T cells were present in the memory T cell population of age-matched healthy children. These results suggest that various kinds of antigens were involved in the differentiation of the patient's T cells, and that the differentiation into memory T cells was not accompanied by profound T cell proliferation. Moreover, our findings confirmed that the patient's CD45RO⁺CD4⁺ T cells had acquired effector- cytokine producing ability, indicating that there exists an alternative activation pathway which is independent of ZAP-70 for the acquisition of effector-cytokine producing ability.