I. Howard Marshall writes that the Johannine Comma "appears in no reputable modern version of the Bible as the actual text; most editions adopt the same practice as in the NIV of relegating the extra words to a footnote, while some (such as the RSV and NEB) totally ignore them" (Marshall, The Epistles of John, 236).
Marshall continues: "The words in fact occur in none of the Greek manuscripts of 1 John, except for a few late and worthless ones, and are not quoted by any early church writers, not even by those who would have joyfully seized upon this clear biblical testimony to the Trinity in their attacks on heretics: they probably owe their origin to some scribe who wrote them in the margin of his copy of 1 John: later they were erroneously regarded as part of the text. Beyond any shadow of a doubt the wording of the NIV text represents what John actually wrote. We must, therefore, confine our attention to the three witnesses of whom John did write, the Spirit, the water, and the blood" (Ibid).
Lastly, Marshall writes in ftn. 19 (Ibid):
"None of the ancient versions of the New Testament contains the words, except the Latin versions."
True, Marshall does say that the three neuter nouns in 1 John 5:8 that are introduced by a clause expressed in the masculine plural is "striking." He consequently attempts to explain their presence not by saying that the Comma has been wrongfully taken out of the Bible, but Marshall insists that John regards the Spirit as personal, and this leads to his subsequent personification of the Spirit. However, Daniel B. Wallace disagrees with Marshall here and points out in essence that personification may be employed by the writer without necessarily personalizing the Spirit (Wallace, GGBB, 332).
οτι τρεις εισιν οι μαρτυρουντες (1 John 5:7 Tischendorf 8th Edition)