As much as 20-30% of human corneas taken from cadavers and transplanted into patients get rejected. Unlike in the case of other tissues, the conventional tissue engineering technique that uses polymer scaffolds to seed cells and culture tissues in the lab do not succeed in the case of cornea as transparency, which is vital for cornea, gets compromised. Against this backdrop, a team of researchers led by Prof. Sourabh Ghosh from Indian Institute of Technology (IIT) Delhi have found corneas taken from goats and transplanted into rabbits are not rejected and transparency is not compromised. The work was done in collaboration with clinicians from All India Institute of Medical Sciences, Delhi.
Dr Radhika Tandon, Professor of Ophthalmology at AIIMS and one of the authors of a paper published in the journal ACS Biomaterials Science & Engineering is optimistic of study’s translation potential. “These findings open up maximal utilisation of donor corneas. Human donor corneas, which for various reasons are categorised as unsuitable for keratoplasty [where abnormal corneal tissue is replaced by a healthy cornea], can be processed in this manner and be useful for successful transplants for patch grafts and anterior lamellar keratoplasties,” she says.
Though there is no blood supply to corneas (avascular), lymphatic system is absent, and the blood-eye barrier greatly minimises the chances of rejection, cornea from one species to another gets rejected. Removing all traces of protein, cellular and nuclear material from the cornea without destroying the anatomical microstructure and extracellular matrix of the cornea is therefore essential to minimise the chances of rejection.
Corneal transparency
“Corneal transparency is determined by the orderly alignment of collagen fibres in a particular direction and regular spacing between the fibres so light does not get diffracted and instead passes through the cornea,” explains Prof. Ghosh, corresponding author of the paper.
By directly passing a detergent at very precise flow rate and direction through the cornea, the researchers had already demonstrated the ability to remove all cellular and nuclear material without affecting the integrity of corneas. However, the secondary collagen alignment or confirmation still gets distorted leading to certain hidden antigenic sites getting exposed.
Thus there are chances of immune response getting evoked leading to rejection when the decellularised cornea is transplanted.
To overcome this problem, the team used a chemical (chondroitin sulphate) naturally found in a cornea to combine with the decellularised cornea. “The chemical combines with the decellularised cornea and restores collagen alignment thereby increasing the chances of integration of the cornea, and reducing the chances of evoking immune response and a possible rejection,” says Juhi Chakraborty from IIT Delhi and first author of the paper.
Enhanced integration
The researchers hypothesised that combining the chemical with the decellularised cornea will result in enhanced graft integration, reduced immune response and less inflammation. To test this they used cornea without removing any cellular or nuclear material, corneas with cellular and nuclear material removed and finally decellularised corneas with the chemical combined to them. “During in vitro studies we found some immune response in the case of decellularised corneas but decellularised corneas was conjugated [combined] with the chemical showed no immune response,” says Prof. Ghosh.
The researchers implanted the three types of goat corneas in rabbits and tested the immune response. Three rabbits were used for each group. “Decellularised cornea showed the most inflammation and blood vessel formation [vascularisation]. Interestingly, the decellularised cornea combined with the chemical had less inflammation and vascularisation,” says Chakraborty.
