Penal Substitution vs. Medical Substitution: A Historical Comparison An analysis of the atonement theology ("medical substitution") of early church theologians, including Ignatius of Antioch, Irenaeus of Lyons, the Odes of Solomon, Justin Martyr of Rome, Melito of Sardis, Tertullian of Carthage, Methodius of Olympus, Athanasius of Alexandria (paper in progress to include later theologians, bishops, and councils)

Clement of Rome, Epistle to the Corinthians, chapter 16 quotes the Greek LXX version of Isaiah 53.  The significance of the Greek LXX, in comparison with the Hebrew Masoretic and Dead Sea Scrolls, is that it more clearly understands Isaiah 53 as a medical substitutionary atonement text.  See Isaiah's Understanding of Sacrificial Animals on the Anastasis Center blog for more information. In chapter 49:6, Clement writes:

Because of the love that he had for us, Jesus Christ our Lord, in accordance with God’s will, gave his blood for us, and his flesh for our flesh, and his life for our lives.

Because of his prior use of LXX Isaiah 53, Clement should be understood as teaching medical substitution. Otherwise, Clement does not present us with much material from which to understand his teaching on atonement.