What is the ruling of transplanting swine organs to humans? Isn’t swine categorized as najis mughalllazah in Islam?
I have explained the rulings of organ and tissue transplants here. As for organ or tissue transplant from one species in another also known as xenotransplantation, it needs further detailed discussion. Xenotransplantation is (i) the transplantation of living cells, tissue, or animal organs that originates from humans or (ii) the transplantation of human fluid or body cells which has a connection with non-human cells or tissues. 
The basic principles for organ transplantation which involves human-animal are; it is haram to use najis for treatment if there are pure substances available. Najis is permissible to be used if there is an exigent need and there is no other pure substance available that can be used.
The basis of the prohibition of swine is clear according to syarak as stated by Allah SWT:
إِنَّمَا حَرَّمَ عَلَيْكُمُ الْمَيْتَةَ وَالدَّمَ وَلَحْمَ الْخِنزِيرِ وَمَا أُهِلَّ بِهِ لِغَيْرِ اللَّهِ ۖ فَمَنِ اضْطُرَّ غَيْرَ بَاغٍ وَلَا عَادٍ فَلَا إِثْمَ عَلَيْهِ ۚ إِنَّ اللَّهَ غَفُورٌ رَّحِيمٌ
“He has only forbidden to you dead animals, blood, the flesh of swine, and that which has been dedicated to other than Allah. But whoever is forced [by necessity], neither desiring [it] nor transgressing [its limit], there is no sin upon him. Indeed, Allah is Forgiving and Merciful.” 
Rasullullah PBUH said:
إِنَّ اللَّهَ حَرَّمَ الْخَمْرَ وَثَمَنَهَا، وَحَرَّمَ الْمَيْتَةَ وَثَمَنَهَا، وَحَرَّمَ الْخِنْزِيرَ وَثَمَنَهُ
“Allah forbade wine and the price paid for it, and forbade dead meat and the price paid for it, and forbade swine and the price paid for it.”
Scholars have agreed on the prohibition of the usage of najis as medicine however, it is different in its permissibility due to exigent situations. For madhhab Syafie, the usage of bones which is considered as najis isn’t permissible except in absolute exigent situations and there are no other alternative other pure substances except bones.
Imam al-Nawawi said: “If his bones broke, then it should be connected with pure bones. Syafi’iyyah scholars said ‘It is impermissible to connect it with najis as long as one is capable to find pure materials. If it is connected with najis due to a necessity and no other pure substances can be found, it is considered a debility (forgiven). If he doesn’t need it or other pure bones can be found [however, he still chose the najis bone], it is considered as sinful and it is obligatory to disconnect the bone [to be replaced with the pure bone] if there is no concern that it will harm himself.’” 
Majma’ al-Fiqh al-Islami Rabitah al-‘Alam al-Islami which convened on 28th Rabi’ al-Akhir until 7th Jamadil Awwal 1405H has decided that animal organ transplantation to humans must be from permissible animals to be eaten and that it has been slaughtered following the methods set by syarak. Other than this, it is only permissible if there is an exigent need. 
Likewise, this is also emphasized by Syeikh ‘Atiyyah Saqar, former Grand Mufti of the Arab Republic of Egypt in his fatwa dated May 1997 for the question “If the bones of a person broke and no other bones can be found to reconnect it except the bones of an animal that is considered najis, is it permissible to connect it?”  The same opinion is presented by Syeikh Jad al-Haq ‘Ali Jad al-Haq, former Egypt’s Grand Mufti on 5th December 1979 in his fatwa. 
When prohibition and harm collided, the Islamic legal maxim that should be considered is:
إذَا تَعَارَضَ مَفْسَدَتَانِ رُوعِيَ أَعْظَمُهُمَا ضَرَرًا بِارْتِكَابِ أَخَفِّهِمَا
“When two mafsadah meet, then protect (reject) the greater harm by doing the lesser harm.” 
Syeikh Mustafa Al-Zarqa said: “[What is meant by] celebrating the heavier from the two by leaving it. The reason is the harms that are celebrated by getting rejected the same way beneficial matters are celebrated by performing it.” 
Coming back to the above Surah al-Baqarah verse 173, Allah SWT concluded at the end saying,
فَمَنِ اضْطُرَّ غَيْرَ بَاغٍ وَلَا عَادٍ فَلَا إِثْمَ عَلَيْهِ ۚ إِنَّ اللَّهَ غَفُورٌ رَّحِيمٌ
But whoever is forced [by necessity], neither desiring [it] nor transgressing [its limit], there is no sin upon him. Indeed, Allah is Forgiving and Merciful.
Our teacher, Syeikh Dr Muhammad bin Muhammad al-Mukhtar al-Syinqiti set two conditions for najis animal organ transplant which are:
- The patient is in exigent need of the najis animal organ transplant and this is acknowledged by a medical expert of its necessity.
- There is no other pure organ alternative.
If these two conditions are fulfilled, then there is no issue for the organ transplant to be performed. It also doesn’t affect the patient’s prayer and worship where its condition is to be in a pure state due to the debility, he experienced for him that he has to use the najis. 
To conclude, in my opinion, swine organ transplant to humans is permissible on the condition that it is an exigent need as verified by medical experts and there are no other suitable alternatives. If other halal alternatives then become available, then the permissibility is abrogated. However, if the swine organ has been transplanted into the patient, it doesn’t have to be replaced if it would harm the patient. I also think that it is the right time for the National Muzakarah Committee for Religious Affairs Malaysia to issue its opinion on this matter. Indeed, such research is vital in resolving this critical issue in our current times which is related to treatment and medicine. Wallahu a’lam.