Immune attacks are key issues for cell transplantation. To assess the safety and the immune reactions after iPS cells-derived retinal pigment epithelium (iPS-RPE) transplantation, we transplanted HLA homozygote iPS-RPE cells established at an iPS bank in HLA-matched patients with exudative age-related macular degeneration. In addition, local steroids without immunosuppressive medications were administered. We monitored immune rejections by routine ocular examinations as well as by lymphocytes-graft cells immune reaction (LGIR) tests using graft RPE and the patient’s blood cells. In all five of the cases that underwent iPS-RPE transplantation, the presence of graft cells was indicated by clumps or an area of increased pigmentation at 6 months, which became stable with no further abnormal growth in the graft during the 1-year observation period. Adverse events observed included corneal erosion, epiretinal membrane, retinal edema due to epiretinal membrane, elevated intraocular pressure, endophthalmitis, and mild immune rejection in the eye. In the one case exhibiting positive LGIR tests along with a slight fluid recurrence, we administrated local steroid therapy that subsequently resolved the suspected immune attacks. Although the cell delivery strategy must be further optimized, the present results suggest that it is possible to achieve stable survival and safety of iPS-RPE cell transplantation for a year.

Citation: Nakano S, Sugita S, Tomaru Y, et al. Establishment of multiplex solidphase strip PCR test for detection of 24 ocular infectious disease pathogens. Invest Ophthalmol Vis Sci.

PURPOSE. To report occurrence of acute severe inflammation after surgical implantation of mycoplasma-infected induced pluripotent stem cell-derived RPE (iPS-RPE) cells into the eyes of healthy primates, and determine the immunopathological mechanisms of the inflammation. METHODS.Ophthalmic allogeneic transplantation of iPS-RPE cells was performed in the subretina of major histocompatibility complex (MHC)-matched (two eyes) and MHCmismatched (one eye) healthy cynomolgus monkeys. The clinical course after transplantation was observed using color fundus photography, fluorescence angiography, and optical coherence tomography. After the animals were killed at 1 month after surgery, eyeballs were removed and pathologically examined. Microorganisms were analyzed by PCR methods and BLAST analysis using preserved graft iPS-RPE cells and the recipients' vitreous humor. Mixed lymphocyte-RPE assay was performed on the mycoplasma-infected and noninfected iPS-RPE cells in vitro. RESULTS.In tested eyes, abnormal findings were observed in the grafted retina 2 weeks after surgery. Here, we observed retinal vasculitis and hemorrhage, retinal detachment, and infiltration of inflammatory cells into the retina of the eyes. One month after surgery, animals were killed due to the severe immune responses observed. Using PCR methods, sequence analysis detected mycoplasma-DNA (Mycoplasma arginini species) in both the grafted RPE cells and the collected vitreous fluids of the monkeys. Mixed lymphocyte-RPE assay revealed that the infected iPS-RPE cells enhanced the proliferation of inflammatory cells in vitro. CONCLUSIONS.Transplantation of graft iPS-RPE cells contaminated with mycoplasma into the subretina caused severe ocular inflammation. Mycoplasma possesses the ability to cause immune responses in the host.

Contamination of cells/tissues by infectious pathogens (e.g., fungi, viruses, or bacteria, including mycoplasma) is a major problem in cell-based transplantation. In this study, we tested a polymerase chain reaction (PCR) method to provide rapid, simple, and sensitive detection of mycoplasma contamination in laboratory cultures for clinical use. This mycoplasma PCR system covers the Mycoplasma species (spp.) listed for testing in the 17th revision of the Japanese Pharmacopoeia, and we designed it for use in transplantable retinal cells. Here, we analyzed mycoplasma contamination in induced pluripotent stem cell (iPS cell)-derived transplantable retinal pigment epithelium (RPE) cells. In the spike tests to RPE cells with nine species of class Mollicutes bacteria, including seven Mycoplasma spp. and one of each Acholeplasma spp. and Ureaplasma spp., contamination at the concentration of 100 and 10 CFU/mL were detected with 100% probability in all cases, while 1 CFU/mL had a detection rate of 0–75%. DNA prepared from bacteria species other than class Mollicutes species was not detectable, indicating the specificity of this PCR. While iPS cells and iPS-RPE cells established in our laboratory were all negative by this PCR, some of the commercially available cell lines were positive. Cells for transplantation should never have infection, as once pathogens are implanted into the eyes, they can cause severe intraocular inflammation. Thus, it is imperative to monitor for infections in the transplants, although generally, mycoplasma infection is difficult to detect.