Solo Christo means that salvation is "by Christ alone," there is no other mediator between God and man for salvation.

For He delivered us from the domain of darkness, and transferred us to the kingdom of His beloved Son, in whom we have redemption, the forgiveness of sins. And He is the image of the invisible God, the first-born of all creation. For by Him all things were created, both in the heavens and on earth, visible and invisible, whether thrones or dominions or rulers or authorities-- all things have been created by Him and for Him. And He is before all things, and in Him all things hold together. He is also head of the body, the church; and He is the beginning, the first-born from the dead; so that He Himself might come to have first place in everything. (1TI 2:5-6; COL 1:13-18)