Where does “antirejection” come from?

antirejection (English) comes from English anti-, from Ancient Greek ἀντι-, from Ancient Greek ᾰ̓ντῐ́ — opposite.

antirejection (English): Acting to prevent rejection of a transplanted...

Definitions

Step	Language	Word	Meaning
1	English	anti-	Against, hostile to; Contrasting with the norm;...
2	Ancient Greek	ἀντι-	anti-, against; like, reminiscent of
3	Ancient Greek	ᾰ̓ντῐ́	opposite