ASED represent a highly effective therapy for many modalities of severe dry eye syndrome of autoimmune, degenerative, or traumatic genesis [
17]. They promote wound healing via growth factors like EGF, vitamin A, TGF-beta, and fibronectin, lubricate the ocular surface, lower ocular surface inflammation levels, and are frequently being used to treat patients with severe chronic ocular graft versus host disease and have been shown to be both successful and safe in this entity [
17,
18]. However, there are multiple peculiarities regarding this group of patients that may have an impact on therapy with ASED, which have not been sufficiently examined. For one, most patients with ocular GVHD also present with systemic manifestations (e.g., liver, intestines, skin, lung) and need to be treated with systemic glucocorticoids and/or immunosuppressants. In our clinic, the standard regime for patients after hematopoietic stem cell transplantation consists of cyclosporine (in dosages of 150 to 750 mg daily) and mycophenolic acid (in dosages of 500 to 1000 mg daily). Depending on clinical response, this immunosuppressant therapy may be reduced, increased, or changed for tacrolimus or everolimus. Furthermore, antifungal agents are administered following allogeneic stem cell transplantation on a regular basis, since antifungal prophylaxis has been shown to decrease all-cause mortality after chemotherapy, popular substances being amphotericin b, fluconazole, itraconazole, and posaconazole [
19]. In CMV-seropositive patients, an additional preemptive therapy with ganciclovir or foscarnet can be necessary [
20]. Whether all these systemically applied agents are detectable in ASED was unclear, as well as the implications of the possible presence of pharmacologically active substances in serum eye drops. In this study, we were able to detect systemically applied cyclosporine and mycophenolic acid in ASED manufactured from the blood of patients with severe ocular GVHD for the first time. Since mycophenolic acid does not show relevant distribution between plasma and blood cells [
21], it could be detected in ASED at concentrations that are usually achieved with standard doses used for systemic immunosuppression (Fig.
1). In contrast, cyclosporine, tacrolimus, and everolimus are distributed in erythrocytes, and whole blood is the preferred matrix for drug monitoring of these agents [
22]. It is well known that cyclosporine levels in whole blood are comparatively higher than in plasma under treatment [
23]. In our study, mean cyclosporine ASED concentration was therefore below generally accepted therapeutic target ranges (100–400 ng/ml) [
26] which have been established in the whole blood matrix (Fig.
1). In addition, in vitro studies suggested sufficient inhibition of monocytes and lymphocytes by cyclosporine at concentrations ranging from 100 to 500 ng/ml [
27], while effective concentrations of mycophenolic acid in vitro were reported to be in the range of 160 ng/ml [
28], both well exceeding the concentrations we detected in ASED. Likewise, tacrolimus plasma concentrations can be very low (therapeutic range 5–15 ng/ml) [
26] and undetectable by enzyme immunoassay [
24], and more than 75% of everolimus is partitioned into red blood cells at therapeutic concentrations [
25], which could explain why both substances were not detected in ASED. Concluding from these findings, we are led to suspect that therapy-modifying agents can be found in serum eye drops manufactured from patients receiving systemic therapy in concentrations well below therapeutic ranges in vivo. Moreover, drug concentrations in ASED may likely vary in dependence on the timing of the drug intake relative to the time of blood donation for ASED manufacturing with possibly much higher concentrations of immunosuppressants in ASED when blood is drawn at peak serum concentration. This constitutes a limitation of this study as information was not documented.
Clinical follow-up of our patients did not appear to depict differences of ASED efficacy in regard to detected immunosuppressants at different concentrations, for which we see two possible explanations: either the patient collective was too small to infer the significant impact of systemically administered immunosuppressants on the efficacy of ASED or there is no impact that could be measured. To enhance explanatory power in this important aspect of ASED therapy, it is necessary to observe more patients over longer periods of time to elaborate possible effects of systemic therapy on the efficacy of ASED. Hereby, follow-up periods of up to 9 months are necessary, to be able to detect statistical significant improvements in contrast to clinical observed improvements on signs but most notably symptoms, that often improve only a few weeks after onset of treatment. Since cyclosporine and tacrolimus are being used by ophthalmologists as a topical therapy for GVHD, an additional beneficial effect of ASED containing those substances is possible. To further investigate this hypothesis and to address the second aspect mentioned above regarding possible influence of immunosuppressants on serum eye drops efficacy, we plan to analyze the effects of immunosuppressants on wound healing promotion by ASED in vitro for example using corneal epithelial scratch assays. In the long term, the now established LC-MS/MS method will be used in our clinic to assess drug levels in patients, who show limited or no response to ASED in order to identify possible contraindications for this therapy. This is of clinical relevance, since in recent history there are efforts to provide heterologous serum eye drops for those patients, who are not able to donate blood due to critical general health status. Should a specific systemically applied immunosuppressant be identified as impedimentary to ASED therapy, those patients could directly receive heterologous serum eye drops and fully benefit from this therapy modality. Should, however, a certain immunosuppressive substance show a beneficial effect on ASED therapy, these substances could be added to ASED during the manufacturing process to enhance efficacy, as long as safe and efficient concentrations were to be identified.