Survival of rabbit limbal stem cell allografts after administration of cyclosporin A

Evaluating the clinical translational relevance of animal models for limbal stem cell deficiency: A systematic review

PURPOSE

Animal models are pivotal for elucidating pathophysiological mechanisms and evaluating novel therapies. This systematic review identified studies that developed or adapted animal models of limbal stem cell deficiency (LSCD), assessed their reporting quality, summarized their key characteristics, and established their clinical translational relevance to human disease.

METHODS

The protocol was prospectively registered (PROSPERO CRD42020203937). Searches were conducted in PubMed, Ovid EMBASE and Web of Science in August 2020. Two authors screened citations, extracted data, assessed the reporting quality of eligible studies using the ARRIVE guidelines, and judged the clinical translational relevance of each model using a custom matrix.

RESULTS

105 studies were included. Rabbits were the most common animal species. Overall, 97% of studies recapitulated LSCD to a clinical etiology, however 62% did not provide sufficient methodological detail to enable independent reproduction of the model. Adverse events and/or exclusion of animals were infrequently (20%) reported. Approximately one-quarter of studies did not produce the intended severity of LSCD; 34% provided insufficient information to assess the fidelity of disease induction. Adjunctive diagnostic confirmation of LSCD induction was performed in 13% of studies.

CONCLUSIONS

This is the first systematic review to assess the reporting quality and clinical translational relevance of animal models of LSCD. Models of LSCD have evolved over time, resulting in variable reporting of the characteristics of animals, experimental procedures and adverse events. In most studies, validation of LSCD was made using clinical tests; newer adjunctive techniques would enhance diagnostic validation. As most studies sought to evaluate novel therapies for LSCD, animal models should ideally recapitulate all features of the condition that develop in patients.

Live Related versus Cadaveric Limbal Allograft in Limbal Stem Cell Deficiency

AIM

To compare outcomes of live related limbal allograft (Lr-CLAL) versus cadaveric keratolimbal allograft (KLAL) in limbal stem cell deficiency (LSCD) secondary to ocular burns.

METHODS

Twenty patients with stage IIb LSCD were randomized so that cases underwent either Lr-CLAL or KLAL. Fibrovascular pannus was removed and superficial keratectomy done on the recipient bed. Limbal lenticule of 2-3 clock hours' length was harvested from the donor, which was placed over the host bed and sutured followed by bandage contact lens application. Parameters assessed were uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), conjunctivalization, corneal neovascularization, epithelial defects, corneal clarity, Schirmer's test, tear film breakup time (tBUT), and ultrasonic pachymetry.

RESULTS

At 6 months follow-up, the Lr-CLAL group had a higher gain in vision (p = 0.029), decrease in conjunctivalization (p = 0.009), and increase in Schirmer's values (p = 0.009).

CONCLUSION

Lr-CLAL seems to have better result in terms of vision gain and ocular surface restoration.

A new model for limbal transplantation using E-GFP for follow-up of transplant survival

Limbal transplants in humans show a high rate of rejection even under local and systemic immunotherapy. In order to test immunomodulatory treatments a new limbal transplant model in the rat was developed using enhanced green fluorescent protein (E-GFP) as marker for follow-up. Sixty E-GFP-positive limbal transplants from Sprague-Dawley TgN(act-EGFP)Osb4 rats were transplanted onto 18 wild-type inbred Sprague-Dawley (isografts) rats, six wild-type litter mate Sprague-Dawley (sibling) rats, 18 Fischer 344 (allografts) rats, and 18 Fischer 344 rats depleted from monocytes and macrophages by subconjunctival treatment with clodronate liposomes. All rats were monitored three times a week with fluorescence microscopy, until fluorescence had disappeared. At postoperative days 6, 9, 12, and 15, three rats of all groups were killed for immunohistochemical analysis of infiltrating cells. Using a modified digital fluorescence microscope, we were able to monitor transplant behavior over time without disturbance of the ocular surface. The average days of rejection were 14 days in the isograft group, the sibling group, and the untreated allograft group. However, the average day of rejection in the allogeneic macrophage-depleted group was 27 days. Marked infiltration of macrophages and lymphocytes was seen in the untreated isografts and allografts. In the clodronate liposome-treated allografts infiltration was minor. A successful new limbal transplant model is described. The transplant can be accurately followed up in vivo by E-GFP labeling of the donor tissue without disturbing the corneal surface. Although E-GFP itself proved to be immunogenic, local clodronate liposome injections significantly increased graft survival. So the model seems to be useful for testing immunosuppressive or modulatory agents in limbal transplantation studies.

Efficacy of Systemic Cyclosporine A and Amniotic Membrane on Rabbit Conjunctival Limbal Allograft Rejection

PURPOSE

To evaluate the effect of intramuscular cyclosporine A (CsA) and amniotic membrane (AM) on conjunctival limbal allograft survival in a rabbit model.

METHODS

Eighty-two female rabbits (59 New Zealand white rabbits, 23 Dutch pigmented rabbits) were used. The New Zealand white rabbits were divided into 4 treatment groups: group 1 (n=13), conjunctival limbal autograft transplantation; group 2 (n=12), conjunctival limbal allograft transplantation without additional treatment; group 3 (n=18), conjunctival limbal allograft transplantation and human AM; and group 4 (n=16), conjunctival limbal allograft transplantation and systemic CsA (10 mg/kg/day intramuscularly). The 23 Dutch pigmented rabbits were used as limbal stem cell allograft donors. The rejection index, the mean survival time, and the rejection rates were calculated for each group.

RESULTS

After 28 days of follow-up, there were no episodes of limbal rejection in groups 1 and 4, whereas the rejection rate was 100% in groups 2 and 3. There was no significant difference in mean survival time of the rejected grafts between groups 2 and 3.

CONCLUSIONS

A model of rejection of conjunctival limbal transplantation was developed in the rabbit. Intramuscularly injected CsA effectively prevents limbal allograft rejection. Human AM is not useful for this purpose.

The long term outcome of limbal allografts: the search for surviving cells

BACKGROUND/AIMS

Limbal allotransplantation is increasingly being used for ocular surface repair in patients with limbal stem cell dysfunction. However, it is uncertain whether donor cells survive long term on the ocular surface and whether patients maintain the early benefits of the procedure. The aims of this study were to investigate the long term outcome of clinical limbal allografts and to correlate outcome with donor cell survival.

METHODS

Five patients who had undergone allotransplantation-four keratolimbal allografts and one tarsoconjunctival allograft-from 3-5 years previously, and for whom residual frozen donor ocular tissue was available, were reviewed. Survival of donor cells lifted from the recipient ocular surface by impression cytology was investigated by DNA fingerprinting using primers detecting variable nucleotide tandem repeat sequences. Recipient buccal cells and scleral samples from the remnant donor eye were used to genotype recipients and donors, respectively. Polymerase chain reaction products were sized by Genescan analysis.

RESULTS

An objective long term benefit from the procedure (improved Snellen acuity, reduced frequency of epithelial defects, reduced vascularisation, and scarring) was recorded for four patients. Some subjective benefit was also reported. However, in no instances were donor cells recovered from the ocular surface at 3-5 years post-graft. Initial experiments to examine sensitivity indicated that any surviving donor cells must have constituted less than 2.5% of cells sampled.

CONCLUSION

Limbal stem cell allotransplantation can provide long term benefits, as measured by objective criteria. However, such benefits do not necessarily correlate with survival of measurable numbers of donor cells on the ocular surface.

Reconstruction of ocular surface with heterologous limbal epithelium and amniotic membrane in a rabbit model

PURPOSE

To report in vivo reconstruction of the ocular surface using amniotic membrane and heterologous transplants of epithelial limbal cells in rabbits with chemical burns.

METHODS

After severe damage to the ocular surface with n-heptanol and keratectomy, 15 rabbits developed total limbal deficiency with conjunctival epithelialization, vascularization, and chronic inflammation. One month later, a complete keratectomy was performed in all eyes: 12 received additional transplantation of human amniotic membrane and heterologous limbal epithelial cells in a double amniotic membrane layer, 2 received amniotic membrane only, and 1 control eye received no procedure.

RESULTS

After 1 month of follow-up, corneas in eight of the operated eyes presented minimal vascularization, without signs of rejection. Corneal surface reconstruction was demonstrated with the growth of new corneal-like epithelial phenotype and integration of amniotic membrane to the basal corneal surface. A superficial amniotic membrane (with the amnion side up as a dressing) peeled off after 7 to 10 days. The epithelialization with heterologous limbal epithelial cells was evident underneath. The other four operated eyes were followed for 6 months; the ocular surface was also stable with a corneal-like epithelial phenotype.

CONCLUSION

Simultaneous transplantation of amniotic membrane and heterologous limbal epithelial cells in severe ocular surface disorders could restore ocular surface and may be useful in patients with severe bilateral limbal epithelial loss, giving new perspectives for the treatment of severe ocular surface disorders.

The evolution of lamellar keratoplasty

Recent advancements in lamellar keratoplasty have two aspects: the refinement in surgical technique, which has improved postoperative visual outcomes and the transplantation of specific tissues of the donor cornea, such as limbal stem cells. Stem cell transplantation has expanded dramatically as a method of ocular surface reconstruction. Long-term prognosis for limbal allograft transplantation has recently been reported, and postoperative treatments including epithelial management and immunosuppression are now major topics to be studied.