Generation and Functional Characterization of T Cells Against Candida albicans as Potential Immunotherapy after Allogeneic Stem Cell Transplantation.

Invasive fungal infections (IFI), in particular infections due to Aspergillus spp and Candida spp, still pose considerable problems in patients undergoing allogeneic stem cell transplantation (SCT). Despite the availability of new antifungal agents, morbidity and mortality of IFI are still unacceptable high. Although neutropenia is known as the single most important risk factor for IFI, there is a growing body of evidence that T cells play a major role in the defense against fungi. Therefore, adoptive immunotherapy with T cells against Candida spp. might be an interesting therapeutic option in patients undergoing allogeneic SCT. After overnight incubation of 1×10⁸ peripheral blood mononuclear cells from 4 healthy individuals with cellular extracts of C.albicans, activated T cells were selected using the IFN-γ secretion-assay (Miltenyi Biotec, Bergisch Gladbach, Germany). After 14 days of culture, T cell clones were generated by limiting dilution and incubated for another 14 days. The median number of cells obtained was 2.6×10⁷ (range, 0.85–5.75×10⁷). Flow cytometry revealed a highly homogenous population of CD3⁺CD4⁺ cells (97.2% ± 2.6; n=6), of which an average of 8.6% (range, 4.8–58.2%) produced IFN-gamma on re-stimulation with C.albicans antigens, as assessed by intracellular cytokine staining assay. 20.5% (range, 5.8–72.4%) of the generated cells produced TNF-alpha, whereas no significant number of cells produced T_H2 cytokines such as IL-4 and IL-10, indicating that the generated T cell clones were T_H1 cells. The percentage of IFN-gamma producing T cells was significant upon stimulation with C.albicans and C.tropicalis, whereas less than 1% of cells produced IFN-gamma upon stimulation with antigens of other yeasts such as C.glabrata, Debaryomyces hansenii and Kluyveromyces lactis and molds such as A.fumigatus, Penicillium chrysogenum and Alternaria alternata. Compared to CD4⁺ T cells of the original fraction, the isolated and expanded anti-Candida T cells showed reduced alloreactivity, as assessed by means of CSFE. In addition, a strong proliferation of the generated anti-Candida T cells was seen after re-stimulation with C.albicans antigens. The potency of the generated T-cells to damage C.albicans was evaluated using the XTT assay. Compared to polymorphonucelar cells (PMNs), APCs and T-cells alone or to the combination of PMNs with T cells or APCs, respectively, the combination of PMNs, APCs and T-cells showed highest fungal damage (n=4).

In conclusion, our data suggest that the isolation and expansion of anti-Candida T cells is possible and feasible. The generated T cells show low alloreactivity in vitro and increase the antimycotic potential of phagocytes. Thus, antimycotic T cells might become an important tool in the prophylaxis and therapy of IFI in patients after allogeneic SCT.