Perforin Expressing CD4+T Cells Respond to CMV Antigens in CMV Seropositive Patients with B Cell Chronic Lymphocytic Leukaemia (B-CLL).

Introduction: Perforin (PF) expressing CD4+ T cells are expanded in B-CLL patients [1] and are able to induce PF-mediated apoptosis of autologous leukaemic cells in the presence of bispecific anti-CD3/CD19 antibodies [2]. However, the role of the expanded PF+CD4+ T population in B-CLL remains unclear. In this study we have examined possible involvement of this cell subset in immune responses to cytomegalovirus (CMV).

Methods: Blood mononuclear cells from 11 CMV seropositive (SP) and 6 seronegative (SN) B-CLL patients were cultured for 4 and 18 hours in presence of Downe cell lysates containing CMV-antigen or cell lysates alone (control) and brefeldin and co-stimulated with anti-CD28 and anti-CD49 monoclonal antibodies. Anti-CMV response was assessed by flow cytometry as percentages of CD69+ and IFNγ+ cells in PF+ and PF- CD4+T cell populations.

Results: CD4+ T cells from 9 of 11 SP patients showed a strong increase in percentages of IFNγ+ cells after 18h, but not 4h, in culture with CMV antigens, compared to the control lysates and SN patients (Table) and healthy age-matched SP subjects (1.78±0.45, p=0.012). In contrast, none of the 6 SN patients as well as 2 out of 11 SP patients responded to CMV by increased IFNγ expression. In responders IFNγ+ cells were proportionally distributed between PF+ and PF- CD4+ T cells. High levels of cell activation measured by CD69 expression, especially in PF+ population, were mainly due to the Downe cell lysate since expression was significantly lower in lysate free cell cultures (8.3±11.5%, p=0.0018 for SP B-CLL patients). Anti-CMV response was accompanied by a decrease in percentages of CD4+PF+ cells suggesting antigen-induced degranulation.

Conclusion: PF+CD4+ T cells respond to CMV antigens suggesting an expansion of mature CMV specific cytotoxic CD4+ T cells in the majority of CMV seropositive B-CLL patients.

IFN-γ and CD69 expression by CD4+PF+ and PF- T cells after 18h exposure to CMV+ and CMV- lysates in CMV seropositive and seronegative B-CLL patients