Loss of cytomegalovirus-specific immunological memory in a patient with thymoma

Cytomegalovirus (CMV) retinitis is a re-activation infection associated with severely impaired T cell-mediated immunity. We describe a patient with long-standing Crohn's disease and thymoma who developed severe CMV retinitis. While thymoma can be associated with impaired humoral immunity and a quantitative CD4+ T helper cell deficiency, these were not evident in our patient. However, more detailed investigation of anti-CMV responses showed absence of specific T cell responses to CMV antigen. Normal CMV seropositive controls have detectable proliferation and interferon-gamma production by T cells in response to stimulation with CMV antigen, but this was absent in this patient both during the acute infection and in convalescence. Other measures of T cell function were normal. Since CMV retinitis is due to reactivation of latent CMV infection, it appears that selective loss of CMV-specific immunity had occurred, perhaps secondary to a thymoma. The causes of thymoma-associated immune impairment are not understood, but this case demonstrates that selective defects can occur in the absence of global T cell impairment. Opportunistic infections should therefore be suspected in patients with thymoma even in the absence of quantitative immune deficiencies.