The expression of interleukin-2 (IL-2) is a key event in T helper (Th) lymphocyte activation, controlling both, the expansion and differentiation of effector Th cells as well as the activation of regulatory T cells. We demonstrate that the strength of TCR stimulation is translated into the frequency of memory Th cells expressing IL-2 but not into the amount of IL-2 per cell. This molecular switch decision for IL-2 expression per cell is located downstream of the cytosolic Ca2+ level. Here we show that in a single activated Th cell, NFATc2 activation is digital but NF-κB activation is graded after graded T cell receptor (TCR) signaling. Subsequently, NFATc2 translocates into the nucleus in an all-or-none fashion per cell, transforming the strength of TCR-stimulation into the number of nuclei positive for NFATc2 and IL-2 transcription. Thus, the described NFATc2 switch regulates the number of Th cells actively participating in an immune response.

Infections with cytomegalovirus (CMV) can induce severe complications after transplantation, particularly in patients resistant to virostatic therapy. Adoptive transfer of CMV-specific T-cell lines has demonstrated promising results in patients after hematopoietic stem cell transplantation. However, the generation of specific T-cell lines ex vivo and their function in vivo is complicated in solid organ transplant (SOT) recipients. Here, we present the successful adoptive transfer of autologous CMV-specific T cells to a lung transplant recipient with ganciclovir-resistant CMV-pneumonia requiring mechanical ventilation. Infused T cells rapidly expanded in vivo and efficiently inhibited viral replication as confirmed by extensive longitudinal immunological monitoring. After full recovery, the patient was released from the clinic. After 4 weeks, the infection reappeared and persisted at a low level even after a second T-cell infusion. Our experimental data indicate that this could be the consequence of the late differentiated phenotype of the infused T cells and therefore their insufficient longevity in vivo. In summary, our report signifies the high therapeutic potential of adoptive immunotherapy in the treatment of SOT recipients when all other measures show no effect. Further studies have to elucidate the most potent strategies to generate antigen-specific T cells with high functional capacity and robust long-term persistence.

(Re)activation of quiescent viral diseases is a major problem in immunosuppressed transplant patients. Polyoma BK virus-associated nephropathy (PVAN) caused by active polyoma BK virus (BKV) infection became a main reason for graft loss in kidney transplantation. After diagnosis, most transplant centers react by reducing immunosuppression (IS) to allow the immune system to control the infection. However, the impact of reduced IS on BKV immunity is not well researched. Here we present an HLA type-independent method to monitor BKV-specific T-cell immunity. Applying our method, viral protein 1-specific CD4 + and CD8 + T-cell responses were detected in patients with serum BKV-DNA levels >250 000 copies/mL. In addition, specific T-cell responses were also found in allograft-infiltrating cells. The method can be used to assess the impact of decreased immunosuppresson on BKV immunity and to clarify the role of specific T cells in the pathogenesis of PVAN. We strongly recommend its implementation in future clinical studies.

Chronically immunosuppressed patients, like solid-organ-transplant (SOT) recipients, are at increased risk for severe human cytomegalovirus (HCMV) infection. Despite the availability of effective antiviral drugs, lasting control of remaining viruses is dependent on an effective T-cell immunity. So in some patients conventional antiviral therapy cannot control the infection and prolonged virostatic therapy is limited by its side effects and the development of viral resistance. Selective reconstitution of cellular immunity by adoptive transfer of HCMV-specific T cells derived from healthy donors is a safe and effective approach in hematopoietic stem cell transplant recipients. The aim of this study was to determine whether functional HCMV-specific T cells can also be generated from chronically immunosuppressed patients. Autologous CD4+/8+ T-cell lines directed against the HCMV protein IE-1 were generated from the peripheral blood of SOT patients using a recently developed modular protocol easily applicable to good-manufacturing-practice conditions. T-cell lines from SOT patients showed similar features as cells from healthy donors regarding phenotype, functionality (HCMV-specific killing, gene expression pattern, and cytokine secretion), IE-1 epitope recognition, and dominance of distinct T-cell receptor V beta families. Most importantly, this protocol also allowed the generation of T-cell lines from immunosuppressed patients with HCMV infection/chronic HCMV disease. Our data suggest the potential of this autologous approach for the treatment of SOT recipients suffering from HCMV infection/disease poorly responding to virostatic therapy.