From the LCMS website under its FAQ section:
The LCMS does not teach, nor has it ever taught, that any individual Pope as a person, is to be identified with the Antichrist. The historic view of LCMS on the Antichrist is summarized as follows by the Synod's Theological Commission:
The New Testament predicts that the church throughout its history will witness many antichrists (Matt. 24:5, 23-24; Mark 13:6, 21-22; Luke 21:8; 1 John 2:18, 22, 4:3; 2 John 7). All false teachers who teach contrary to Christ's Word are opponents of Christ and, insofar as they do so, are anti-Christ.
However, the Scriptures also teach that there is one climactic "Anti-Christ" (Dan. 7:8, 11, 20-21, 24-25, 11:36-45; 2 Thess. 2; 1 John 2:18, 4:3; Rev. 17-18) ... Concerning the historical identity of the Antichrist, we affirm the Lutheran Confessions' identification of the Antichrist with the office of the papacy whose official claims continue to correspond to the Scriptural marks listed above.
It is important, however, that we observe the distinction which the Lutheran Confessors made between the office of the pope (papacy) and the individual men who fill that office. The latter could be Christians themselves. We do not presume to judge any person's heart.
Also, we acknowledge the possibility that the historical form of the Antichrist could change. Of course, in that case another identified by these marks would rise.
In a footnote, the Commission adds:
To the extent that the papacy continues to claim as official dogma the canons and decrees of the Council of Trent which expressly anathematizes, for instance, the doctrine "that justifying faith is nothing else than trust in divine mercy which remits sins for Christ's sake, or that it is that trust alone by which we are justified," the judgment of the Lutheran Confessional writings that the papacy is the Antichrist holds. At the same time, of course, we must recognize the possibility, under God's guidance, that contemporary discussions and statements (e.g., 1983 U.S. Lutheran-Roman Catholic dialogue statement on "Justification by Faith") could lead to a revision of the Roman Catholic position regarding Tridentine dogma.